U.S. patent application number 11/563914 was filed with the patent office on 2007-04-19 for image display apparatus and control method thereof.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Akira Fujii, Mitsutoshi Kuno, Osamu Sagano.
Application Number | 20070085777 11/563914 |
Document ID | / |
Family ID | 27519120 |
Filed Date | 2007-04-19 |
United States Patent
Application |
20070085777 |
Kind Code |
A1 |
Kuno; Mitsutoshi ; et
al. |
April 19, 2007 |
IMAGE DISPLAY APPARATUS AND CONTROL METHOD THEREOF
Abstract
An image display apparatus includes a display panel having an
electron source, an acceleration electrode for accelerating
electrons emitted from the electron source and phosphors for
emitting light by collision of electrons accelerated by the
acceleration electrode, and a detector for detecting a current
flowing through the acceleration electrode during a non-display
period. In addition, a controller is provided to decrease the
luminance level, stop display driving or transmit warning
information when the current detected becomes more than a
predetermined value.
Inventors: |
Kuno; Mitsutoshi;
(Kanagawa-ken, JP) ; Sagano; Osamu; (Kanagawa-ken,
JP) ; Fujii; Akira; (Kanagawa-ken, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
27519120 |
Appl. No.: |
11/563914 |
Filed: |
November 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10662416 |
Sep 16, 2003 |
7180514 |
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11563914 |
Nov 28, 2006 |
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09299878 |
Apr 27, 1999 |
6707437 |
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10662416 |
Sep 16, 2003 |
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Current U.S.
Class: |
345/74.1 |
Current CPC
Class: |
G09G 2300/06 20130101;
G09G 2330/045 20130101; G09G 2310/0275 20130101; G09G 2300/0452
20130101; G09G 3/22 20130101; G09G 2330/02 20130101; G09G 2300/0443
20130101; G09G 2310/027 20130101; G09G 2320/0285 20130101; G09G
2320/029 20130101; H01J 2201/3165 20130101; G09G 2310/0267
20130101; G09G 2310/0218 20130101; G09G 2300/043 20130101; G09G
2330/028 20130101; H01J 31/127 20130101; G06F 3/147 20130101; G09G
3/2014 20130101; G09G 2320/043 20130101; G09G 2330/04 20130101;
G09G 3/006 20130101; G09G 2330/021 20130101 |
Class at
Publication: |
345/074.1 |
International
Class: |
G09G 3/22 20060101
G09G003/22 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 1998 |
JP |
10-122525 |
Jan 18, 1999 |
JP |
11-009916 |
Jan 29, 1999 |
JP |
11-022622 |
Feb 26, 1999 |
JP |
11-049921 |
Apr 23, 1999 |
JP |
11-116337 |
Claims
1. An image display apparatus comprising: a display panel; and
detection means for detecting a state of said display panel,
wherein said image display apparatus is controlled in accordance
with the state of said display panel.
2-44. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image display apparatus
which displays an image by the emitted electrons, and control
method of the apparatuses.
[0003] 2. Description of the Related Art
[0004] Conventionally, two types of devices, namely hot and cold
cathode devices, are known as electron-emitting devices. Known
examples of the cold cathode devices are surface-conduction type
emission devices, field emission type electron-emitting devices (to
be referred to as FE type electron-emitting devices hereinafter),
and metal/insulator/metal type electron-emitting devices (to be
referred to as MIM type electron-emitting devices hereinafter).
[0005] Known examples of the FE type electron-emitting devices are
described in W. P. Dyke and W. W. Dolan, "Field emission", Advance
in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical
properties of thin-film field emission cathodes with molybdenium
cones", J. Appl. Phys., 47, 5248 (1976).
[0006] A known example of the surface-conduction type emission
devices is described in, e.g., M. I. Elinson, "Radio Eng. Electron
Phys., 10, 1290 (1965) and other examples will be described
later.
[0007] The surface-conduction type emission device utilizes the
phenomenon that electrons are emitted by a small-area thin film
formed on a substrate by flowing a current parallel through the
film surface. The surface-conduction type emission device includes
electron-emitting devices using an Au thin film [G. Dittmer, "Thin
Solid Films", 9,317 (1972)], an In.sub.2O.sub.3/SnO.sub.2 thin film
[M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519
(1975)], a carbon thin film [Hisashi Araki et al., "Vacuum", Vol.
26, No. 1, p. 22 (1983)], and the like, in addition to an SnO.sub.2
thin film according to Elinson mentioned above.
[0008] FIG. 27 is a plan view showing the device by M. Hartwell et
al. described above as a typical example of the device structures
of these surface-conduction type emission devices. Referring to
FIG. 27, reference numeral 3001 denotes a substrate; and 3004, a
conductive thin film made of a metal oxide formed by sputtering.
This conductive thin film 3004 has an H-shaped pattern, as shown in
FIG. 27. An electron-emitting portion 3005 is formed by performing
electrification processing (referred to as forming processing to be
described later) with respect to the conductive thin film 3004. An
interval L in FIG. 27 is set to 0.5 to 1 mm, and a width W is set
to 0.1 mm.
[0009] In the conventional electron-emitting devices, the
electron-emitting portion 3005 is generally formed by performing
electrification processing called forming processing for the
conductive thin film 3004. In the forming processing, for example,
a DC voltage or a voltage which increases at a very low rate of,
e.g., 1 V/min is applied across the conductive thin film 3004 to
partially destroy or deform the conductive thin film 3004, thereby
forming the electron-emitting portion 3005 with an electrically
high resistance. Note that the electron-emitting portion 3005 is a
fissure formed in part of the conductive thin film 3004. Electrons
are emitted near the fissure by applying a predetermined voltage
across the electron-emitting portion 3005.
[0010] FIG. 28 is a sectional view showing the device by C. A.
Spindt et al. described above as a typical example of the FE type
device structure. In FIG. 28, reference numeral 3010 denotes a
substrate; 3011, emitter wiring made of a conductive material;
3012, an emitter cone; 3013, an insulating layer; and 3014, a gate
electrode. In this device, a voltage is applied between the emitter
cone 3012 and gate electrode 3014 to emit electrons from the distal
end portion of the emitter cone 3012.
[0011] As another FE type device structure, there is an example in
which an emitter and gate electrode are arranged on a substrate to
be almost parallel to the surface of the substrate, in addition to
the multilayered structure of FIG. 28.
[0012] A known example of the MIM type electron-emitting devices is
described in C. A. Mead, "Operation of Tunnel-Emission Devices", J.
Appl. Phys., 32,646 (1961). FIG. 29 shows a typical example of the
MIM type device structure. FIG. 29 is a sectional view of the MIM
type electron-emitting device. In FIG. 29, reference numeral 3020
denotes a substrate; 3021, a lower electrode made of a metal; 3022,
a thin insulating layer having a thickness of about 100 .ANG.; and
3023, an upper electrode made of a metal and having a thickness of
about 80 to 300 .ANG.. In the MIM type electron-emitting device, an
appropriate voltage is applied between the upper and lower
electrodes 3023 and 3021 to emit electrons from the surface of the
upper electrode 3023.
[0013] Since the above-described cold cathode devices can emit
electrons at a temperature lower than that for hot cathode devices,
they do not require any heater. The cold cathode device has a
structure simpler than that of the hot cathode device and can
shrink in feature size. Even if a large number of devices are
arranged on a substrate at a high density, problems such as heat
fusion of the substrate hardly arise. In addition, the response
speed of the cold cathode device is high, while the response speed
of the hot cathode device is low because it operates upon heating
by a heater. For this reason, applications of the cold cathode
devices have enthusiastically been studied.
[0014] Of cold cathode devices, the above surface-conduction type
emission devices have a simple structure and can be easily
manufactured, and thus many devices can be formed on a wide area.
As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the
present applicant, a method of arranging and driving a lot of
devices has been studied.
[0015] Regarding applications of the surface-conduction type
emission devices to, e.g., image forming apparatuses such as an
image display apparatus and an image recording apparatus, charge
beam sources, and the like have been studied.
[0016] Particularly as an application to image display apparatuses,
as disclosed in the U.S. Pat. No. 5,066,833 and Japanese Patent
Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant,
an image display apparatus using the combination of an
surface-conduction type emission device and a fluorescent substance
which emits light upon reception of an electron beam has been
studied. This type of image display apparatus using the combination
of the surface-conduction type emission device and the fluorescent
substance is expected to exhibit more excellent characteristics
than other conventional image display apparatuses. For example,
compared with recent popular liquid crystal display apparatuses,
the above display apparatus is superior in that it does not require
any backlight because it is of a self-emission type and that it has
a wide view angle.
[0017] A method of driving a plurality of FE type electron-emitting
devices arranged side by side is disclosed in, e.g., U.S. Pat. No.
4,904,895 filed by the present applicant. As a known example of an
application of FE type electron-emitting devices to an image
display apparatus is a flat display apparatus reported by R. Meyer
et al. [R. Meyer: "Recent Development on Microtips Display at
LETI", Tech. Digest of 4th Int. Vacuum Microelectronics Conf.,
Nagahama, pp. 6-9 (1991)].
[0018] An example of an application of a larger number of MIM type
electron-emitting devices arranged side by side to an image display
apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738
filed by the present applicant.
SUMMARY OF THE INVENTION
[0019] The present inventors have examined cold cathode devices of
various materials, various manufacturing methods, and various
structures, in addition to the above-mentioned conventional cold
cathode devices. Further, the present inventors have made extensive
studies on a multi electron source having a large number of cold
cathode devices, and an image display apparatus using this multi
electron source. The present inventors have examined a multi
electron source having an electrical wiring method shown in, e.g.,
FIG. 30. That is, a large number of cold cathode devices are
two-dimensionally arranged in a matrix to obtain a multi electron
source, as shown in FIG. 30.
[0020] Referring to FIG. 30, reference numeral 4001 denotes a cold
cathode device; 4002, a row wiring; and 4003, a column wiring. The
row and column wirings 4002 and 4003 actually have finite
electrical resistances, which are represented as wiring resistances
4004 and 4005 in FIG. 30. This wiring method is called a simple
matrix wiring method. For the illustrative convenience, the multi
electron source is illustrated in a 6.times.6 matrix, but the size
of the matrix is not limited to this. For example, in a multi
electron source for an image display apparatus, a number of devices
enough to perform desired image display are arranged and wired.
[0021] In a multi electron source constituted by arranging cold
cathode devices in a simple matrix, appropriate electrical signals
are applied to the row and column wirings 4002 and 4003 to output a
desired electron beam. For example, to drive the cold cathode
devices on an arbitrary row in the matrix, a selection voltage Vs
is applied to the column wiring 4002 on the row to be selected, and
at the same time a non-selection voltage Vns is applied to the row
wirings 4002 on an unselected row. In synchronism with this, a
driving voltage Ve for outputting an electron beam is applied to
the column wiring 4003. According to this method, when voltage
drops across the wiring resistances 4004 and 4005 are neglected, a
voltage (Ve-Vs) is applied to the cold cathode devices on the
selected row, while a voltage (Ve-Vns) is applied to the cold
cathode devices on the unselected row. When the voltages Ve, Vs,
and Vns are set to appropriate magnitudes, an electron beam having
a desired intensity must be output from only the cold cathode
device on the selected row. When different driving voltages Ve are
applied to respective column wirings, electron beams having
different intensities must be output from the respective devices of
the selected row. A change in length of time for which the driving
voltage Ve is applied necessarily causes a change in length of time
for which an electron beam is output.
[0022] The multi electron source constituted by arranging cold
cathode devices in a simple matrix has a variety of applications.
For example, when an electrical signal corresponding to image
information is appropriately applied, the multi electron source can
be suitably used as an electron source for an image display
apparatus.
[0023] FIG. 31 is a perspective view of an example of a display
panel for a flat image display apparatus using the multi electron
source where part of the panel is removed for showing the internal
structure of the panel.
[0024] In FIG. 31, reference numeral 3115 denotes a rear plate;
3116, a side wall; and 3117, a face plate. The rear plate 3115,
side wall 3116, and face plate 3117 form an envelope (airtight
container) for keeping the interior of the display panel
vacuum.
[0025] The rear plate 3115 is fixed to a substrate 3111. N.times.M
cold cathode devices 3112 are formed on the substrate 3111. Note
that N and M are positive integers equal to 2 or more, and properly
set in accordance with a target number of display pixels. The
N.times.M cold cathode devices 3112 are wired by M row wirings 3113
and N column wirings 3114, as shown in FIG. 31. The portion
constituted by the substrate 3111, cold cathode devices 3112, and
row and column wirings 3113 and 3114 will be referred to as a multi
electron source. At an intersection of the row and column wirings
3113 and 3114, an insulating layer (not shown) is formed between
them to maintain electrical insulation.
[0026] A fluorescent film 3118 is formed from a fluorescent
substance under the face plate 3117, and colored in three, red (R),
green (G), and blue (B) primary colors (see FIGS. 18A and 18B). A
black conductive material (1010 in FIGS. 18A and 18B) is provided
between fluorescent substances of respective colors forming the
fluorescent film 3118. A metal back 3119 is formed from made of Al
(aluminum) or the like on the surface of the fluorescent film 3118
on the rear plate 3115 side.
[0027] Terminals D.sub.x1 to D.sub.xM, D.sub.y1 to D.sub.yN, and Hv
are connection terminals for the airtight structure provided to
electrically connect the display panel to a driving circuit (to be
described later). The terminals D.sub.x1 to D.sub.xM are
electrically connected to the row wirings 3113 of the multi
electron source; D.sub.y1 to D.sub.yN, to the column wirings 3114
of the multi electron source; and Hv, to the metal back 3119.
[0028] The interior of the airtight container is kept at a vacuum
of about 10.sup.-6 Torr. As the display area of the image display
apparatus increases, demand is arising for any means for preventing
deformation or destruction of the rear and face plates 3115 and
3117 caused by the difference between inner and outer pressures of
the airtight container. If destruction is prevented by making the
rear and facing plates 3115 and 3117 thick, this increases the
weight of the image display apparatus, and generates distortion and
parallax of an image when viewed diagonally. For this reason, the
display panel in FIG. 31 adopts a structure support (to be referred
to as a spacer or rib) 3120 which is made of a relatively thin
glass plate and supports the airtight container against the
atmospheric pressure. This spacer generally keeps the interval
between the substrate 3111 having the multi electron source and the
face plate 3117 having the fluorescent film 3118 at sub-mm to
several mm, thereby keeping the interior of the airtight container
in a high-vacuum state, as described above.
[0029] When a voltage is applied to respective cold cathode devices
3112 via the external terminals D.sub.x1 to D.sub.xM and D.sub.y1
to D.sub.yN, the image display apparatus using the above display
panel emits electrons from the cold cathode devices 3112. At the
same time, a high voltage of several hundred V to several kV is
applied to the metal back 3119 via the external terminal Hv to
accelerate the emitted electrons and collide them against the face
plate 3117. Then, fluorescent substances of respective colors in
the fluorescent film 3118 are excited to emit light, thereby
displaying a color image.
[0030] One side (upper surface) of the structure support (spacer)
3120 is joined to the metal back 3119 for applying a high voltage,
and the lower surface is mounted on the row wiring. In driving the
display panel, the upper surface of the spacer 3120 receives a high
voltage, and its lower surface receives a scanning voltage.
[0031] In FIG. 31, a conductive film material (e.g., NiO) or the
like is deposited on the entire surface of the spacer 3120. This
conductive film is formed to make the electric field inside the
display panel uniform upon application of a high voltage. The film
resistance is set to a resistance value of about 1.times.10.sup.8
to 1.times.10.sup.9.
[0032] Accordingly, a current (to be referred to as a spacer
current) from the high-voltage source flows from the metal back
3119 to the row wiring via the spacer 3120.
[0033] FIG. 32 is a sectional view showing a display panel for an
image display apparatus using a multi electron source manufactured
by the present inventors.
[0034] For the illustrative convenience, FIG. 32 does not show any
row and column wirings and the like on the substrate 3111 and shows
only one cold cathode device 3112 (surface-conduction emission type
device in FIG. 32) in a matrix layout. The metal back 3119 having
an anode electrode, fluorescent substance, and the like is formed
at a position where the metal back 3119 faces the substrate 3111.
The substrate 311, face plate, and support frame (not shown) form a
vacuum container. The cold cathode device 3112 is incorporated in
the high-vacuum container. Reference numeral 4104 denotes a signal
source for driving the cold cathode device 3112; and 4105, a
high-voltage source for applying a high voltage between the
substrate 3111 and metal back 3119. As shown in FIG. 32, electrons
emitted by the cold cathode device 3112 are attracted upward by the
metal back 3119 receiving a high voltage from the high-voltage
source 4105, and collide against the fluorescent substance facing
the cold cathode device 3112.
[0035] In some cases, unexpected discharge occurs in the container
in which electron-emitting devices are arranged. The unexpected
discharge may damage electron-emitting devices and wirings such as
row and column wirings to a non-negligible degree. If unexpected
discharge frequently occurs, problems arise.
[0036] When the above image display apparatus is used in a very
severe environment or used abnormally, faults abruptly occur in the
image display apparatus. For example, static electricity influences
the driving circuit in a very dry environment, or heat, which is
difficult to dissipate at a very high ambient temperature,
influences operation of the driving circuit system.
[0037] One aspect according to the present invention has the
following arrangement.
[0038] An image display apparatus comprises a display panel, and
detection means for detecting a state of the display panel, wherein
the image display apparatus is controlled in accordance with the
state of the display panel.
[0039] Since the arrangement of this aspect adopts the detection
means, the state of the display panel can be detected to control
the image display apparatus at good timing. In particular, the
present invention can preferably prolong the service life of the
display panel under this control and suppress deterioration of
characteristics to allow using the display panel for a long time.
From this viewpoint, a desirable detection device is performed in a
non-destructive condition in order to detect the state of the
display panel.
[0040] The state of the display panel is preferably electrically
detected.
[0041] For example, the state of the display panel can be detected
by detecting a current flowing through the display panel, and
especially a current flowing through an electrode arranged on the
display panel.
[0042] When the display panel comprises an electron source and an
acceleration electrode for accelerating an electron output from the
electron source, the detection means detects a current flowing
through the acceleration electrode.
[0043] The state of the display panel is preferably detected at a
plurality of portions on the display panel, e.g., by measuring
currents flowing through a plurality of portions on the display
panel. Detection at the plurality of portions enables detecting the
state of the display panel in units of the plurality of
portions.
[0044] For example, when the display panel comprises an electron
source and a plurality of acceleration electrodes for accelerating
electrons output from the electron source, the detection means
individually detects currents flowing through the plurality of
acceleration electrodes.
[0045] The display panel may comprise an electron source and an
acceleration electrode for accelerating an electron output from the
electron source, and the detection means may detect a current
flowing through a current path between the electron source and the
acceleration electrode. The current path is set by a structure
arranged between the electron source and the acceleration
electrode. For example, the structure is a spacer for maintaining
the interval between the electron source and the front plate on
which the acceleration electrode, fluorescent substance, or the
like is arranged. If a current flowing through the current path is
not directly detected, this current can be indirectly detected by
detecting a current flowing through the acceleration electrode or
the potential of the acceleration electrode. This current path is
preferably arranged outside the image formation area within the
display panel.
[0046] The display panel may comprise an electron source, and the
electron source may comprise an electron-emitting device for
emitting an electron for displaying an image, and an
electron-emitting device arranged to detect the state of the
display panel. In this case, the electron-emitting device arranged
to detect the state of the display panel is preferably set outside
the image display area.
[0047] The display panel may comprise an electron source, an
acceleration electrode for accelerating an electron output from the
electron source, and an electron capture electrode arranged to
detect the state of the display panel. In particular, a potential
applied to the electron capture electrode is preferably closer to
the potential of the electron source than the potential of the
acceleration electrode for accelerating an electron for displaying
an image. An electron-emitting device for outputting an electron to
the electron capture electrode may be arranged separately from the
electron-emitting device for emitting an electron for forming an
image.
[0048] The detection means may detect the state of the display
panel by detecting a potential of the display panel.
[0049] The detection means detects the state of the display panel
by detecting a potential of an electrode arranged in the display
panel.
[0050] The display panel may comprise an electron-emitting device,
and the detection means may detect the state of the display panel
by detecting a potential of an electrode electrically isolated from
the electron-emitting device.
[0051] The display panel may comprise an electron source for
outputting electrons, and the detection means may detect the state
of the display panel by detecting a potential of an electrode
arranged on the electron source.
[0052] When the display panel may comprise an electron source for
outputting electrons, the state of the display panel may be
detected while no electron is emitted by the electron source.
Consequently, the state of the display panel can be detected while
reducing the influence of output of electrons from the electron
source. For example, when the display panel comprises an electron
source having a plurality of electron-emitting devices and the
electron source outputs electrons from respective electron-emitting
devices while sequentially switching electron-emitting devices
selected from the plurality of electron-emitting devices, the state
of the display panel is detected when electron-emitting devices to
be selected are switched.
[0053] The detection means detects discharge in the display panel,
or even if discharge is not directly detected, detects a state
about discharge. The detection means may detect a state about power
consumption in the display panel such that the detection means
detects a current flowing through the spacer.
[0054] The detection means may detect a change in state of the
display panel.
[0055] If the image display apparatus comprises memory means for
storing information detected by the detection means, the state of
the panel can be preferably recorded.
[0056] The memory means stores information about the number of
abnormalities in the display panel, information about a generation
location of an abnormality in the display panel, or information
about either one or both of a generation time and/or date and an
end time and/or date of an abnormality in the display panel.
[0057] Control of the image display apparatus in accordance with
the state of the display panel is transfer of information by
information transfer means. As the information transfer means,
means using visual display or means for generating voice can be
preferably used.
[0058] Control of the image display apparatus in accordance with
the state of the display panel is control of transferring
information for prompting an information receiving person to
control the image display apparatus. The information receiving
person, e.g., the user of the image display apparatus or the
maintenance personnel of the image display apparatus can control to
suppress the progress of the abnormality in accordance with the
transferred information.
[0059] Control of the image display apparatus in accordance with
the state of the display panel may be control of a driving voltage
of the display panel. If the state of the display panel becomes
abnormal, the progress of the abnormality can be suppressed by
decreasing the driving voltage of the display panel. More
specifically, when the display panel comprises an electron source
and an acceleration electrode for accelerating an electron output
from the electron source, the voltage to be controlled is a voltage
between the electron source and the acceleration electrode. When
the display panel comprises an electron source for emitting an
electron upon application of a voltage, the voltage to be
controlled is the voltage for emitting an electron.
[0060] When the display panel comprises an airtight container for
keeping an internal pressure lower than an ambient pressure,
control of the image display apparatus in accordance with the state
of the display panel may be control of increasing a vacuum degree
in the airtight container. For example, the vacuum degree can be
increased by containing a getter set in the airtight container in
an atmosphere substance by heating or the like.
[0061] Control of the image display apparatus in accordance with
the state of the display panel is selected preferably from a
plurality of control operations, and more preferably from a
plurality of control operations in accordance with the state of the
display panel.
[0062] The display panel may comprise an electron source, and the
electron source may have a plurality of electron-emitting devices
connected in a matrix by a plurality of first wirings and a
plurality of second wirings extending in a direction intersecting
to the first wirings.
[0063] The display panel may comprise an electron source, and the
electron source may comprise a cold cathode device.
[0064] The above aspects are particularly effective when the
display panel is kept at a vacuum degree higher than an internal
pressure of 10.sup.-4 Torr when no abnormality occurs.
[0065] The present invention includes a television and computer
display to which the above aspects are applied.
[0066] A method of controlling an image display apparatus according
to the present invention has the following steps.
[0067] A method of controlling an image display apparatus having a
display panel comprises steps of detecting a state of the display
panel, and controlling the image display apparatus in accordance
with the detected state.
[0068] The electron source can be one having a ladder-like layout
in which a plurality of rows (to be referred to as a row direction
hereinafter) of a plurality of cold cathode devices arranged
parallel and each having two electrodes connected are arranged, and
electrons emitted by the cold cathode devices are controlled by a
control electrode (to be referred to as a grid hereinafter)
arranged above the cold cathode devices along the direction (to be
referred to as a column direction hereinafter) intersecting to this
wiring.
[0069] According to the concepts of the present invention, the
image display apparatus is not limited to an image forming
apparatus suitable for display, and can also be used as a
light-emitting source instead of a light-emitting diode for an
optical printer made up of a photosensitive drum, light-emitting
diode, and the like. At this time, by properly selecting M row
wirings and N column wirings, the image display apparatus can be
applied as not only a linear light-emitting source but also a
two-dimensional light-emitting source. In this case, the image
forming member is not limited to a substance which directly emits
light, such as a fluorescent substance used in the following
embodiments, but may be a member on which a latent image is formed
by charging of electrons.
[0070] According to the concept of the present invention, the
present invention can be applied to an electron-beam apparatus such
as an electron microscope in which the target member to be
irradiated with electrons emitted by the electron source is not an
image forming member such as a fluorescent substance. Hence, the
present invention can be adopted as a general electron-beam
apparatus which does not specify any target member to be
irradiated.
[0071] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] The accompanying drawings, which are incorporated in and
constitute part of the specification, illustrate embodiments of the
invention and, together with the descriptions, serve to explain the
principle of the invention.
[0073] FIG. 1 is a block diagram showing the arrangement of a
driving circuit for driving the display panel of an image display
apparatus according to the first embodiment of the present
invention;
[0074] FIG. 2 is a timing chart for explaining a measurement timing
according to the first embodiment;
[0075] FIG. 3 is a partially cutaway perspective view showing the
display panel of an image display apparatus according to the second
embodiment of the present invention;
[0076] FIG. 4 is a block diagram showing the arrangement of a
driving circuit for driving the display panel of the image display
apparatus according to the second embodiment;
[0077] FIG. 5 is a partially cutaway perspective view showing the
display panel of an image display apparatus according to the third
embodiment of the present invention;
[0078] FIG. 6 is a block diagram showing the arrangement of a
driving circuit for driving the display panel of the image display
apparatus according to the third embodiment;
[0079] FIG. 7 is a block diagram showing the arrangement of an
image display apparatus according to the fourth embodiment of the
present invention;
[0080] FIG. 8 is a timing chart showing the driving timing of the
image display apparatus according to the fourth embodiment;
[0081] FIG. 9 is a partially cutaway perspective view showing the
outer appearance of the image display unit of the image display
apparatus according to the fourth embodiment of the present
invention;
[0082] FIG. 10 is a circuit diagram showing the circuit arrangement
of the anode current detection unit of the image display apparatus
according to the fourth embodiment;
[0083] FIG. 11 is a partially cutaway perspective view showing the
outer appearance of the image display unit of an image display
apparatus according to the fifth embodiment;
[0084] FIG. 12 is a block diagram showing the arrangement of the
image display apparatus according to the fifth embodiment;
[0085] FIG. 13 is a block diagram for explaining connection between
the display panel and peripheral circuit of an image display
apparatus according to the sixth embodiment of the present
invention;
[0086] FIG. 14 is a flow chart showing processing of detecting
destruction of the airtight container by the control unit according
to the sixth embodiment;
[0087] FIG. 15 is a partially cutaway perspective view showing the
display panel of an image display apparatus according to the sixth
embodiment of the present invention;
[0088] FIG. 16 is a plan view showing the substrate of a multi
electron source used in the embodiment;
[0089] FIG. 17 is a sectional view showing part of the substrate of
the multi electron source used in the embodiment;
[0090] FIGS. 18A and 18B are plan views showing examples of the
alignment of fluorescent substances on the face plate of the
display panel;
[0091] FIG. 19A is a plan view showing a flat surface-conduction
type emission device used in the embodiment;
[0092] FIG. 19B is a sectional view showing the flat
surface-conduction type emission device used in the embodiment;
[0093] FIGS. 20A to 20E are sectional views showing the steps in
manufacturing the flat surface-conduction type emission device;
[0094] FIG. 21 is a graph showing an application voltage waveform
in forming processing;
[0095] FIG. 22A is a graph showing an application voltage waveform
in the activation processing;
[0096] FIG. 22B is a graph showing a change in emission current
Ie;
[0097] FIG. 23 is a sectional view showing a step type of
surface-conduction type emission device used in the embodiment;
[0098] FIGS. 24A to 24F are sectional views showing the steps in
manufacturing the step type of surface-conduction type emission
device;
[0099] FIG. 25 is a graph showing the typical characteristics of
the surface-conduction type emission device used in the
embodiment;
[0100] FIG. 26 is a block diagram showing a multi-functional image
display apparatus using the image display apparatus according to
the embodiment of the present invention;
[0101] FIG. 27 is a plan view showing an example of a
conventionally known surface-conduction type emission device;
[0102] FIG. 28 is a sectional view showing an example of a
conventionally known FE type device;
[0103] FIG. 29 is a sectional view showing an example of a
conventionally known MIM type device;
[0104] FIG. 30 is a diagram for explaining an electron-emitting
device wiring method examined by the present inventors;
[0105] FIG. 31 is a perspective view for explaining the structure
of the display panel of a conventional image display apparatus;
[0106] FIG. 32 is a sectional view for explaining the structure of
an image display apparatus posing problems which has been examined
by the present inventors;
[0107] FIG. 33 is a partially cutaway perspective view showing the
display panel of an image display apparatus according to the
seventh embodiment of the present invention;
[0108] FIG. 34 is a perspective view for explaining the structure
of the image display apparatus according to the seventh embodiment
of the present invention;
[0109] FIG. 35 is a block diagram showing the arrangement of the
image display apparatus according to the seventh embodiment of the
present invention;
[0110] FIG. 36 is a timing chart showing the potential state of a
surface potential electrode and a failsafe timing signal in the
seventh and eighth embodiments of the present invention;
[0111] FIG. 37 is a flow chart in the seventh embodiment of the
present invention;
[0112] FIG. 38 is a perspective view showing an image display
apparatus which displays a notice in the seventh and eighth
embodiments; and
[0113] FIG. 39 is a flow chart in the eighth embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0114] Preferred embodiments of the present invention will be
described in detail below with reference to the accompanying
drawings.
First Embodiment
[0115] As the first embodiment of the present invention, a display
panel using an electron-emitting device and a driving circuit for
the display panel will be described in detail. The display panel of
the first embodiment has the same structure as shown in FIG. 31,
and a detailed description thereof will be omitted.
[0116] FIG. 1 is a block diagram showing the arrangement of a
driving circuit for the display panel of an image display apparatus
according to the first embodiment.
[0117] In FIG. 1, reference numeral 1 denotes a display panel using
a cold cathode device (electron-emitting device: to be described in
detail later). An external video signal (e.g., an NTSC signal) is
input to a video signal detection circuit 2 for detecting a video
signal, and an output from the video signal detection circuit 2 is
input to a sync separation circuit 3 for separating and outputting
a video signal and horizontal and vertical sync signals.
[0118] The video signal separated by the sync separation circuit 3
is input to an A/D converter 4. The sync separation circuit 3
outputs the vertical and horizontal sync signals to vertical and
horizontal scanning timing circuits 5 and 6, respectively.
[0119] Outputs from the A/D converter 4 are digital data
corresponding to the luminances of R, G, and B color components,
which are output in accordance with the layout of color pixels of
the display panel 1 and sequentially input to a serial/parallel
conversion circuit 7. The horizontal scanning timing circuit 6
outputs a signal T.sub.sp for shifting and inputting serial digital
signals to the serial/parallel conversion circuit 7. The signal
T.sub.sp is a serial clock in synchronism with the video signal,
and N signals I.sub.1 to I.sub.N are stored in the serial/parallel
conversion circuit 7 in synchronism with the signal T.sub.sp. Note
that the serial/parallel conversion circuit 7 can be formed from,
e.g., a shift register.
[0120] The horizontal scanning timing circuit 6 outputs a signal
T.sub.m when I-line data of an input image is
serial/parallel-converted. Then, outputs from the serial/parallel
conversion circuit 7 are latched by a line memory 8. The line
memory 8 latches the N signals I.sub.1 to I.sub.N until a next
signal T.sub.m is input.
[0121] A modulation circuit 9 outputs a signal to the bases of
transistors G.sub.1 to G.sub.N respectively connected to wiring
electrodes D.sub.y1 to D.sub.yN of the display panel 1 on the basis
of the luminance values of the I-line image data input to the line
memory 8. The modulation circuit 9 outputs a phase-modulated signal
in accordance with a signal T.sub.mo synchronized with a scanning
signal applied to the row wiring. While the signal T.sub.mo is
output, the modulation circuit 9 outputs a modulated signal
corresponding to the luminance value of image data. The first
embodiment employs a phase-modulated signal of a pulse width
modulation scheme of changing the width of a voltage pulse in
accordance with a luminance value. Therefore, a voltage +Vf/2 is
applied to the column wiring of the display panel 1 with a pulse
width corresponding to the luminance value of image data.
[0122] A scanning signal switching circuit 10 sequentially selects
M row wirings of the display panel 1 in synchronism with an output
from the modulation circuit 9 to apply the voltage to the selected
row wiring. The switching timing is determined in synchronism with
a horizontal sync signal T.sub.H output from the horizontal
scanning timing circuit 6. A predetermined voltage (-Vf/2) is
applied to a selected one of the wiring electrodes D.sub.x1 to
D.sub.xM, and unselected electrodes are connected to GND.
[0123] The face plate (3117) side of the display panel 1 comprises
a high-voltage terminal Hv which receives a high voltage for
accelerating electrons emitted upon driving an electron-emitting
device 3112 formed on a substrate 3111 in FIG. 31 and colliding the
electrons against a fluorescent substance 3118. The high voltage is
applied from an anode voltage control circuit 11 via a current
detection circuit 12. The current detection circuit 12 detects a
current value flowing from the anode voltage control circuit 11 to
the high-voltage terminal Hv. The current detection circuit 12
realizes detection of a spacer current in the first embodiment.
[0124] A method of detecting the spacer current will be explained
with reference to FIG. 2.
[0125] FIG. 2 is a timing chart for explaining a method of
detecting the spacer current within the blanking period of the
scanning signal. In the display panel 1 of the first embodiment, a
high DC voltage is applied to a face plate 3117 upon driving. At
this time, the high voltage is also applied to a spacer 3120
interposed between the face plate 3117 and substrate 3111, and thus
(spacer current+electron emission current (I.sub.1+I.sub.2)) flows
as an anode current. For this reason, the period during which no
electron emission current is generated, i.e., the blanking period
between field signals as a non-display period during which no
electron-emitting device 3112 is driven is suitable for detecting
the spacer current with high precision.
[0126] During the blanking period, only the spacer current I1
flows. The current detection circuit 12 receives a signal Tv
representing a vertical blanking period from the vertical scanning
timing circuit 5, and detects the spacer current during the
vertical blanking period.
[0127] The current detection circuit 12 detects the spacer current
using an I/V conversion circuit or the like. The spacer 3120 used
in the first embodiment has a resistance value of about
1.times.10.sup.8 to 10.sup.9.OMEGA.. Spacers 3120 are uniformly
arranged on the display panel 1 on the order of several ten to
several hundred spacers depending on the size of the display panel
1.
[0128] For example, when the spacer resistance is
1.times.10.sup.9.OMEGA. and the number of spacers 3120 in use is
100, the spacer resistance when viewed from the anode (face plate
3117) side is (1.times.10.sup.9/100), i.e., about 10 .OMEGA.. If an
anode voltage of 10 kV is applied, a current value flowing through
the spacer 3120 owing to an anode current is about 1 mA, which can
be detected by the current detection circuit 12.
[0129] As described above, according to the first embodiment, the
spacer current can be detected on the anode-voltage application
side to suppress the power consumption of the display panel 1 with
respect to variations in spacer current.
[0130] For example, when a spacer current measured during the
blanking period exceeds a predetermined value, the current
detection circuit 12 can instruct the anode voltage control circuit
11 to decrease the anode voltage or can temporarily decrease the
luminance level of a video signal output from the sync separation
circuit 3, thereby decreasing the anode current of the whole
display panel 1.
[0131] If any problem arises from heat generated from the display
panel 1 by variations in spacer current, it can be solved by
temporarily stopping display driving itself (e.g., increasing the
voltage -Vf/2 applied to the row wiring or stopping driving
itself).
[0132] The above control can suppress actual heat generation and
power consumption of the display panel 1.
Second Embodiment
[0133] FIG. 3 is a perspective view of a display panel 1a according
to the second embodiment of the present invention where part of the
display panel 1a is removed for showing the internal structure of
the panel.
[0134] The display panel of the second embodiment has almost the
same structure as the display panel shown in FIG. 31 except that a
fluorescent substance 3118 and a metal back 3119 are uniformly
divided on a face plate 3117, as represented by fluorescent plates
13 in FIG. 3. In addition, the second embodiment uses a substrate
3111 as a rear plate without using any rear plate 3115. The same
reference numerals as in FIG. 31 denote the same parts, and a
description thereof will be omitted.
[0135] The fluorescent plates 13 are used to individually detect
local variations in spacer current inside the display panel 1a, and
enable detection of a partial anode current or the like, compared
to the first embodiment. The second embodiment employs 10 divided
fluorescent plates 13, and the respective fluorescent plates 13
comprise electrodes for applying anode voltages H.sub.v1 to
H.sub.v10. Note that the division number of fluorescent plates 13
is not limited to the second embodiment and can be arbitrarily
set.
[0136] FIG. 4 is a block diagram showing the arrangement of a
driving circuit for the display panel in FIG. 3. This circuit is
different from the circuit in FIG. 1 in that a current detection
circuit 14 is commonly connected to the high-voltage terminals
H.sub.v1 to H.sub.v10 of the fluorescent plates 13 divided on the
face plate 3117 side and that a voltage distribution control
circuit 15 for applying high voltages to the respective
high-voltage terminals is arranged. Since an anode voltage circuit
16 connected to the voltage distribution control circuit 15 and the
remaining arrangement are the same as in FIG. 1, the same reference
numerals as in FIG. 1 denote the same parts, and a description
thereof will be omitted.
[0137] The second embodiment can detect the anode current of the
display panel 1a along the row wiring direction because the
fluorescent substance and metal back on the face plate 3117 are
divided and provided with high-voltage extraction portions.
[0138] The current detection circuit 14 can detect a vertical
blanking period from a signal Tv from a vertical scanning timing
circuit 5 to individually detect anode currents flowing into the
respective divided fluorescent plates 13, similarly to the first
embodiment. The current values detected in this way can be fed back
to the voltage distribution control circuit 15 to individually
control voltage values applied to the terminals H.sub.v1 to
H.sub.v10.
[0139] The current detection circuit 14 may use an I/V conversion
circuit used in the first embodiment. I/V-converted outputs are
individually output as analog voltage values to the voltage
distribution control circuit 15.
[0140] When a detected anode current value is larger than a current
value set for a predetermined high voltage, the voltage
distribution control circuit 15 controls a high voltage
corresponding to the area.
[0141] An output signal from the current detection circuit 14 is
also output to the sync separation circuit 3. With this operation,
when an anode current value is larger than a predetermined value,
the luminance of a video signal output from the sync separation
circuit 3 is decreased to reduce the anode current of the whole
display panel, similarly to the first embodiment.
[0142] Further, the second embodiment adopts 10 fluorescent plates
13 for applying the anode voltage which are divided along the row
direction, and thus can decrease only the display luminance of a
desired area in synchronism with a row-direction scanning signal.
This control performs both detection of the spacer current and
current control in units of divided areas, so the display luminance
of the display panel 1a may vary depending on the degree of
control. If the luminance greatly varies and the anode current must
be controlled, display driving may be stopped. In this case,
application of all high voltages is stopped, or a voltage Vf for
driving the device is decreased.
[0143] As described above, according to the second embodiment, the
anode electrode on the face plate side is divided into a plurality
of electrodes which are respectively provided with terminals for
applying high voltages. This arrangement allows locally detecting
variations in spacer current and individually controlling
application of a high voltage with respect to each current. As a
result, the display panel can be driven while suppressing heat
generation and power consumption.
Third Embodiment
[0144] FIG. 5 is a perspective view of a display panel 1b according
to the third embodiment of the present invention. In FIG. 5, part
of the panel is removed for showing the internal structure of the
panel.
[0145] In the third embodiment, dummy spacers 16 are formed from
the same material by the same manufacturing method as spacers 3120
on a dummy wiring 17 formed along the column wiring in the display
panel of the second embodiment shown in FIG. 3. Similar to the
second embodiment, the dummy spacers 16 respectively correspond to
a plurality of fluorescent plates 13 each including a fluorescent
substance and metal back. The dummy spacers 16 are equal in number
to 10 divided fluorescent plates 13.
[0146] The dummy wiring 17 is formed at a position independently of
row and column wirings connecting electron-emitting devices 3112
laid out in a matrix.
[0147] The first and second embodiments detect a current value
flowing through the spacer itself in the display panel, whereas the
third embodiment detects a current value flowing through the dummy
spacer 16.
[0148] As described above, the dummy spacer 16 is formed from the
same material by the same method as the spacer 3120, but is
manufactured with a resistance value lower by about one or two
orders of magnitudes, which can widen the dynamic range of a
current value to be actually detected.
[0149] FIG. 6 is a block diagram showing the arrangement of a
driving circuit for the display panel 1b of the third embodiment.
This arrangement is almost the same as the circuit of the second
embodiment shown in FIG. 4 except that a current detection circuit
14 measures a current value flowing through the dummy spacer 16.
Similar to the second embodiment, this driving circuit comprises a
voltage distribution control circuit 15 and an anode voltage
circuit 16. The 10 divided fluorescent plates 13 are respectively
provided with high-voltage application electrodes H.sub.v1 to
H.sub.v10, and high voltages are also applied to the dummy spacers
16.
[0150] A current flowing through each dummy spacer 16 outputs to a
terminal H.sub.vg through the dummy wiring 17 (FIG. 5) formed along
the column direction. The terminal H.sub.vg is connected to the
current detection circuit 14 where a current value flowing through
the terminal H.sub.vg is measured to measure a current value
flowing through each dummy spacer 16. The current may be detected
by I/V conversion as in the second embodiment.
[0151] As an advantage of the third embodiment, the spacer current
can always be detected regardless of the video signal because the
dummy spacers 16 which receive high voltages are commonly connected
to the dummy wiring 17 to monitor currents flowing into the
terminal H.sub.vg.
[0152] Note that the third embodiment adopts the divided
fluorescent plates 13. However, the above detection method detects
the total of currents flowing through the dummy spacers 16, so the
anode electrode on the face plate side may not be divided.
[0153] As described above, the current value of each dummy spacer
16 formed on the display panel can be detected and used for
application control of a high voltage and control of the luminance
signal level, thereby suppressing heat generation and power
consumption of the display panel, similar to the first and second
embodiments.
Fourth Embodiment
[0154] The driving circuit of an image display apparatus according
to the fourth embodiment of the present invention will be explained
in detail with reference to the accompanying drawings. In the
following description, similar to the above-described embodiments,
the display scanning method in the display panel is non-interlace
line-sequential scanning. To display an image with gradation, the
electron-emitting period within one horizontal scanning period (1H)
is controlled by the time width of a modulated signal to control
the total light-emitting quantity of the fluorescent substance and
realize gradation expression.
[0155] FIG. 7 is a block diagram showing the arrangement of the
driving circuit and connection between respective units in the
image display apparatus according to the fourth embodiment of the
present invention.
[0156] In FIG. 7, reference numeral 6001 denotes a signal
processing circuit which receives a video signal such as an NTSC
signal to generate a horizontal sync signal, vertical sync signal,
digital video signal, and the like. The signal processing circuit
6001 includes a video intermediate frequency circuit, video signal
detection circuit, sync separation circuit, low-pass filter, A/D
conversion circuit, timing control circuit, and the like. Reference
numeral 6004 denotes an image display unit which has the same
arrangement as the display panel 1a (FIG. 3) of the second
embodiment except that no spacer 3120 is arranged, as will be
described below with reference to FIG. 9. Reference numeral 6002
denotes a scanning signal driver for sequentially selecting and
driving the row wirings of the image display unit 6004. That is,
the scanning signal driver 6002 outputs a scanning signal (to be
described later) for line-sequential scanning on the basis of a
horizontal sync signal separated by the signal processing circuit
6001. Reference numeral 6003 denotes a modulated signal driver for
driving the column wirings of the image display unit 6004 in
accordance with a video signal and outputting a modulated signal
(to be described later) based on a horizontal sync signal, vertical
sync signal, digital video signal, and the like separated by the
signal processing circuit 6001.
[0157] Reference numeral 6006 denotes a discharge detection unit
which has a plurality of anode current detection units 6005 for
detecting discharge generated in the image display unit 6004.
Discharge detected by the discharge detection unit 6006 is sent to
a discharge recording control unit 6008 of a discharge recording
unit 6012 and stored in a memory 6009. Information stored in the
memory 6009 may be sent to and processed by an external computer
device or the like via an interface 6010 and a connector 6011. The
discharge detection unit 6006 and discharge recording unit 6012
will be described in detail later.
[0158] FIG. 8 is a timing chart showing an example of the voltage
applied to the terminals of the row wiring (i.e., wiring to which
the scanning signal is supplied) and the column wiring (i.e.,
wiring to which the modulated signal is supplied) in driving the
image display unit 6004 of the image display apparatus according to
the fourth embodiment of the present invention.
[0159] The timing chart in FIG. 8 shows voltages applied to row
wirings on rows I, I+1, and I+2 and column wirings on columns J,
J+1, and J+2 on the modulated signal side while sequentially
driving the row wirings I, I+1, and I+2 of the image display unit
6004. In FIG. 8, 1<I<M-2 and 1<J<N-2 inevitably hold. M
and N represent the total numbers row and column wirings,
respectively.
[0160] In FIG. 8, an image of the I.sub.th row is displayed during
one horizontal scanning period K, an image of the (I+1).sub.th row
is displayed during the period (K+1), and an image of the
(I+2).sub.th row is displayed during the period (K+2).
[0161] Row wirings serving as the scanning side in non-interlace
line-sequential scanning are sequentially selected every horizontal
scanning period (to be referred to as 1H hereinafter). Row wirings
on selected rows sequentially receive scanning signal having a
pulse width corresponding to 1H and a peak value -Vf/2 (Vf is a
driving voltage; Vf=about 2V.sub.th (V.sub.th=threshold voltage)).
After the non-interlace line-sequential scanning is done for all
row wirings, it is repeated from the first row.
[0162] At this time, a modulated signal having a peak value Vf/2 is
applied to all column wirings in synchronism with the scanning
signal applied to the row wiring for a time (pulse width)
corresponding to a video signal (luminance) displayed on a selected
row.
[0163] This modulated signal rises in synchronism with the trailing
edge of the scanning signal, and falls after maintaining the peak
value Vf/2 for a time width corresponding to the value (luminance)
of the video signal. (The period between the leading and trailing
edges of the modulated signal will be simply referred to as the
pulse width of the modulated signal). The pulse width of the
modulated signal corresponds to the luminance of each of three, R,
G, and B colors obtained when a video signal displayed on a
selected row is color-separated. In practice, the pulse width is
not simply proportional to the luminance because various
corrections are done to display a high-quality image.
[0164] By applying a voltage having a pulse width corresponding to
an input video signal to each scanning row, the driving voltage Vf
is applied to cold cathode devices on a selected row for a time
corresponding to the pulse width of the modulated signal. Since the
emission current Ie of the cold cathode device has definite
threshold characteristics (to be described later) with respect to
the driving voltage Vf, an image corresponding to a desired video
signal is displayed on a selected row. Furthermore, an image is
displayed by all cold cathode devices in the image display unit
6004 by sequentially scanning all row wirings.
(Structure of Anode Electrode of Display Panel)
[0165] The image display unit (display panel) 6004 of the fourth
embodiment will be explained in detail with reference to FIG.
9.
[0166] FIG. 9 is a perspective view for explaining an anode
electrode 7001 and its terminal in the display panel used in the
fourth embodiment where part of the panel side wall (frame) and
face plate, fluorescent substance, and like are not illustrated for
showing the internal structure of the display panel.
[0167] In FIG. 9, reference numeral 1001 denotes a device
substrate; 1005, a rear plate; 1006, a side wall; 1007, a face
plate; 1002, a cold cathode device; 1003, a row wiring; and 1004, a
column wiring. Reference symbols D.sub.x1 to D.sub.xM denote row
terminals respectively connected to the row wirings 1003; and
D.sub.y1 to D.sub.yN, column terminals respectively connected to
the column wirings 1004. The remaining structure is the same as the
structure of the above-mentioned display panel 1a, and a detailed
description thereof will be omitted.
[0168] Reference numerals 7001 denote anode electrodes. As
described above, the anode electrodes 7001 are electrodes for
applying a high voltage on the anode side including the fluorescent
substance, black conductive material, and metal back. In the fourth
embodiment, as shown in FIG. 9, the anode electrodes 7001 are
divided into a plurality of areas, and anode electrode terminals
H.sub.v1 to H.sub.v10 respectively connected to the anode
electrodes 7001 are arranged outside the vacuum container. For
illustrative convenience, FIG. 9 does not illustrate the anode
electrode terminals H.sub.v4 to H.sub.v9 and corresponding anode
electrodes 7001 in order to explain the internal structure.
(Connection of Discharge Detection Unit and Discharge Recording
Unit)
[0169] The arrangement and operation of these anode electrodes 7001
will be explained in detail with reference to FIG. 7. In the fourth
embodiment, the discharge detection unit 6006 comprises the anode
current detection units 6005 for detecting currents flowing through
respective anode electrodes.
[0170] As shown in FIG. 9, a plurality of electrodes 7001 are
arranged on the anode side of the multi electron source, and the
terminals H.sub.v1 to H.sub.v10 connected to the anode electrodes
are connected to a high-voltage source 6007 via the anode current
detection units 6005. The fourth embodiment employs a plurality of
anode current detection units 6005 in order to independently
monitor changes in anode current in a plurality of divided areas,
thereby detecting the presence/absence and size of discharge in the
vacuum container and accurately detecting the area where the
discharge has occurred.
[0171] FIG. 10 is a circuit diagram showing the circuit arrangement
of the anode current detection unit 6005 according to the fourth
embodiment.
[0172] In FIG. 10, H.sub.vi represents an anode electrode terminal
connected to the anode electrode 7001 of the display panel 6004. A
resistor 6101 is a current monitoring resistor for generating a
voltage corresponding to an anode current flowing from the
high-voltage source 6007 to the anode electrode 7001. Reference
numeral 6102 denotes a differential amplifier for amplifying the
potential difference generated across the current monitoring
resistor 6101; 6103, an A/D converter for converting a voltage
value amplified by the differential amplifier 6102 into a digital
signal; and 6104, a photocoupler for isolating the differential
amplifier 6102 and A/D converter 6103 as high-voltage-side circuits
from the discharge recording control unit 6008 in order to stand
the breakdown voltage. The sampling period of the A/D converter
6103 is preferably short in terms of detecting very-high-frequency
discharge, and is set to 5 .mu.sec for practical use in the fourth
embodiment.
[0173] With this arrangement, a voltage value corresponding to a
current flowing from the high-voltage source 6007 to the anode
electrode 7001 due to discharge is amplified by the differential
amplifier 6102 and converted into a digital signal, and the digital
signal is set to and recorded on the discharge recording control
unit 6008 via the photocoupler 6104.
[0174] If a mechanism for switching the gain of the differential
amplifier 6102 to several values is adopted to widen the
measurement range of the anode current, the anode current can be
detected with higher precision.
[0175] The discharge recording unit 6012 of the fourth embodiment
will be described. The discharge recording unit 6012 comprises the
discharge recording control unit 6008 and a memory 6009. The
discharge recording control unit 6008 writes information (voltage
value) sent from the anode current detection unit 6005 in the
memory 6009, and when discharge information is to be read out in
maintenance of the image display apparatus by the serviceman, can
read out and output information stored in the memory 6009.
[0176] If an anode current equal to or larger than a predetermined
value is determined to flow on the basis of a voltage value (anode
current value) detected by the anode current detection unit 6005,
the discharge recording control unit 6008 stores in the memory 6009
the generation time and date (times and dates at the start and end
of discharge; the information can be obtained from an internal
timer (not shown)), the magnitude of the anode current (voltage
value/monitoring resistance value), and the area where discharge
occurred (any one of areas 1 to 10 corresponding to the terminals
H.sub.v1 to H.sub.v10). In this case, information is additionally
stored as history information in the memory 6009 without any
overwrite so long as the memory 6009 does not overflow.
[0177] In the fourth embodiment, the maximum value of an emission
current from one cold cathode device is estimated as about 10
.mu.A, and the predetermined value of the anode current is set to
30 mA. The predetermined value is determined in consideration of an
emission current when all cold cathode devices (M=3,072) in the
column direction simultaneously emit electrons owing to
line-sequential driving. This predetermined value must be changed
depending on the structures of the cold cathode device and image
display unit and the magnitudes of the driving voltage, anode
voltage Va, and the like.
[0178] If the memory 6009 has a sufficiently large capacity, it may
be formed from a nonvolatile memory, battery-driven RAM, or the
like. The fourth embodiment adopts a hard disk as the memory 6009.
In reading out information from the memory 6009, the information is
output from the external device connector 6011 via the interface
6010 in consideration of data consistency with an external device.
The external device connected via the connector 6011 may be, e.g.,
a personal computer, display device for simply displaying data, or
printer.
[0179] If discharge occurs in the display panel 6004, information
about the discharge generation time and date, the size of the
discharge (e.g., the change amount of the anode current), and a
rough location (area) where the discharge occurred can be recorded
as a history using the discharge detection unit 6006 and discharge
recording unit 6012 with this arrangement.
[0180] To specify the location where discharge occurred is very
effective for estimating the cause of the discharge. If the cause
of the discharge can be estimated, a recovery operation can be
appropriately performed.
[0181] For example, when discharge has concentratedly occurred in a
given area and does not occur in the remaining areas, the cause can
be estimated as the presence of an abnormal projection by a
manufacturing error or abnormal characteristics of a cold cathode
device at that position rather than a decrease in vacuum
degree.
[0182] As another example, when discharge has randomly occurred in
various areas, an abnormal operation can be confirmed on the whole
image display unit 6004, and the cause can be estimated as a
decrease in vacuum degree inside the vacuum container forming the
image display unit 6004 under any influence.
[0183] Many image display apparatuses each having the discharge
detection unit 6006, discharge recording unit 6012, memory 6009,
and the like were manufactured to display an image. After a
long-time durability test was conducted, some of these image
display apparatuses suffered discharge upon long-time driving even
with a very low probability, and the history of discharge was
stored in the memory 6009.
[0184] One image display apparatus in which discharge occurred will
be exemplified. The history information of discharge stored in the
memory 6009 reveals that discharge occurred not in a DC manner but
instantaneously, the generation frequency increased upon the lapse
of long time after the long-time durability test was conducted, the
magnitude of the anode current and the discharge generation
location (area) changed, and discharge randomly occurred. From
this, the cause of the discharge was estimated as a decrease in
vacuum degree by any influence with the lapse of time.
[0185] As a measure against this, a getter material was
additionally heated in order to increase the vacuum degree, and the
vacuum degree was increased by the absorption operation of the
getter film. As a result of this measure, generation of discharge
in the image display apparatus was suppressed for a predetermined
period, and a normal operation identical to that before the
long-time durability test was confirmed.
[0186] The interior of the container including the cold cathode
device 1002 is a low-pressure atmosphere at high vacuum degree, and
a high voltage is applied to the container. For this reason,
discharge readily occurs, and an unexpected discharge current
rarely flows between the anode side and substrate 1001 side of the
container. If a current by discharge is often generated, it may
damage the cold cathode device or electrode such as row or column
wiring.
[0187] The cause of discharge, which has not been cleared up yet,
includes a decrease in vacuum degree, charge-up of the insulating
layer of the substrate 1001, and projections and flashes
erroneously formed in manufacturing the substrate 1001 and metal
back 1009. However, the rare abnormal state such as discharge can
be adjusted based on criterion for adjustment by recording the
history of discharge and storing information for confirming whether
the operation state of the image display apparatus has always been
normal and information about the number of abnormal operations such
as discharge. Adjustment for recovering a normal operation can
therefore be done at good timing.
[0188] As described above, since history information about
generation of discharge is stored in the memory in the image
display apparatus of the fourth embodiment, whether the image
display apparatus normally operates can be checked. As for an
abnormal operation by discharge generated at a very low
probability, the cause of the discharge can be estimated. Even if
an abnormal operation occurs, the cause can be estimated.
Accordingly, an appropriate measure for recovering a normal
operation can be performed at a good timing.
[0189] Although the division number of areas is set to 10 for
descriptive convenience in the fourth embodiment, it is preferably
large in terms of detecting the discharge generation location.
However, if the division number of anode electrodes on the face
plate side actually increases, the manufacturing cost and the
number of discharge detection units 6006 increase. Hence, the
division number is set to a preferable value for practical use.
[0190] In the fourth embodiment, the anode electrode is divided in
a direction parallel to the scanning line. The manner of division
is not limited to this, and the anode electrode may be divided
perpendicularly to the scanning line.
Fifth Embodiment
[0191] In the fifth embodiment, discharge is detected by monitoring
the surface potential of a device substrate 1001 on which a
plurality of cold cathode devices 1002 are arranged, using a
plurality of surface potential measurement units (surface potential
measurement systems) for the device substrate 1001, and the history
of discharge is recorded using a discharge recording unit 6012 as a
feature of the fifth embodiment.
(Structure of Surface Potential Measurement Electrode)
[0192] FIG. 11 is a partially cutaway perspective view of an image
display unit 6004 for an image display apparatus according to the
fifth embodiment. In FIG. 11, the face plate and part of the side
wall (frame) are not illustrated in order to explain surface
potential measurement electrodes 7002 as part of a discharge
detection unit in the fifth embodiment. FIG. 12 is a block diagram
showing the arrangement of a driving circuit for the image display
apparatus of the fifth embodiment. In FIGS. 11 and 12, the same
reference numerals as in the fourth embodiment denote the same
parts, and a description thereof will be omitted.
[0193] In FIG. 11, reference numeral 7002 denote surface potential
measurement electrodes.
[0194] The discharge detection unit of the fifth embodiment
comprises the surface potential measurement electrodes 7002 and a
surface potential measurement unit (to be described later). That
is, the fifth embodiment newly employs the plurality of surface
potential measurement electrodes 7002 on the device substrate 1001.
Although the surface potential measurement electrodes 7002 can have
various shapes, they have a pattern shown in FIG. 11 in the fifth
embodiment.
[0195] The surface potential measurement electrodes 7002 are
arranged on the device substrate 1001 while being electrically
isolated from row and column wirings 1003 and 1004, cold cathode
devices 1002, and the like. The surface potential measurement
electrodes 7002 are connected to an external circuit via external
terminals D.sub.s1 to D.sub.s14 of the vacuum container.
[0196] A plurality of surface potential measurement electrodes 7002
are arranged on the device substrate 1001 in order to independently
monitor rises in surface potential of the device substrate 1001 in
units of several areas, and when discharge occurs on the substrate
1001, to record area information where the discharge has occurred,
thereby easily estimating the cause of the discharge. If the cause
of discharge can be estimated, an appropriate recovery operation
for recovering the image display apparatus to a normal operation
can be performed. Note that the surface potential measurement
electrodes 7002 suffice to be made of a conductive material, can be
formed from the same material as the row and column wirings 1003
and 1004 or device electrodes, and can be manufactured at the same
time as the wirings or device electrodes are manufactured on the
substrate. In the fifth embodiment, the surface potential
measurement electrodes 7002 are manufactured by the same method as
the device electrodes (1102 and 1103 in FIG. 19A).
(Connection of Surface Potential Measurement Electrode 7002 to
Surface Potential Measurement System, Discharge Recording Unit, and
the Like)
[0197] FIG. 12 is a block diagram for explaining connection of the
image display unit 6004 of the image display apparatus according to
the fifth embodiment to drivers 6002 and 6003 for driving the image
display unit 6004, surface potential measurement units 6016, a
discharge recording control unit 6008a, and the like. The same
reference numerals as in the above arrangement denote the same
parts.
[0198] As shown in FIG. 12, the terminals D.sub.s1 to D.sub.s14 of
the surface potential measurement electrodes 7002 of the image
display unit 6004 are respectively connected to the surface
potential measurement units 6016 having a high input impedance
(10.sup.13.OMEGA. or more) to independently monitor changes in
potential. If discharge occurs on the substrate 1001, the potential
at the location on the device substrate 1001 rises. The phenomenon
such as surface discharge raises not only the potential at the
discharge generation location but also the potential of a
peripheral conductive member. When discharge occurs around a
surface potential measurement electrode 7002, its potential rises.
Thus, a surface potential measurement unit 6016 connected to this
surface potential measurement electrode 7002 can detect generation
of the discharge.
[0199] A discharge recording unit 6012a of the fifth embodiment
comprises the discharge recording control unit 6008 and a memory
6009 which have almost the same arrangement as in FIG. 10. The
discharge recording control unit 6008a is different from the
above-described discharge recording control unit 6008 in that
potentials generated at the external terminals D.sub.s1 to
D.sub.s14 are input from the respective surface potential
measurement units 6016, the voltage values are amplified by a
differential amplifier 6102, and the amplified voltage values are
converted into digital signals by an A/D converter 6103. In this
fashion, changes in surface potential of each surface potential
measurement electrode 7002 are monitored. If a change in surface
potential exceeds a predetermined value, the discharge recording
control unit 6008a determines that discharge occurred, and stores
in the memory 6009 the discharge generation time and date (times
and dates at the start and end of the discharge), the change amount
of the surface potential, and the number of the electrode at which
the change in surface potential exceeds the predetermined
value.
[0200] Further, the discharge recording control unit 6008a is
constituted to allow reading out discharge information stored in
the memory 6009 in, e.g., maintenance of the image display
apparatus by the serviceman. The information read out from the
memory 6009 can be output to an external device via an interface
6010 and an external device connector 6011.
[0201] If discharge occurs, information about the discharge
generation time and date, the size of the discharge (e.g., the
change amount of the anode current), and a rough location (area)
where the discharge occurred can be recorded as a history using the
discharge detection unit and discharge recording unit with this
arrangement.
[0202] The present inventors have confirmed that to specify the
location where discharge occurred is very effective for estimating
the cause of the discharge. If the cause of the discharge can be
estimated, a recovery operation can be appropriately performed. For
example, when discharge has randomly occurred in various areas, an
abnormal operation can be confirmed on the whole image display
unit. In this case, the cause can be estimated as a decrease in
vacuum degree inside the vacuum container forming the image display
unit under any influence.
[0203] Many image display apparatuses each having the discharge
detection unit, discharge recording unit, memory, and the like were
actually manufactured to display an image. After a long-time
durability test was conducted, some of these image display
apparatuses suffered discharge upon even with a very low
probability, and the history of discharge was stored in the memory
6009.
[0204] One image display apparatus in which discharge occurred will
be exemplified. The history information of discharge stored in the
memory 6009 reveals that discharge occurred not in a DC manner but
instantaneously, the generation frequency increased upon the lapse
of long time after the long-time durability test was conducted, the
generation location changed, and discharge randomly occurred. From
this, the cause of the discharge was estimated as a decrease in
vacuum degree with the lapse of time.
[0205] As a measure against this, a getter material was
additionally heated in order to increase the vacuum degree, and the
vacuum degree was increased by the absorption operation of the
getter film. Consequently, generation of discharge in the image
display apparatus was suppressed for a predetermined period, and a
normal operation identical to that before the long-time durability
test was confirmed.
[0206] As described above, since history information about
discharge is stored in the image display apparatus of the fifth
embodiment, whether the image display apparatus normally operates
can be checked. As for an abnormal operation by discharge generated
at a very low probability, the cause of the discharge can be
estimated. Even if an abnormal operation occurs, the cause of the
discharge can be estimated. Therefore, an appropriate measure for
recovering a normal operation can be performed.
[0207] In the fifth embodiment, the surface potential measurement
electrodes 7002 are arranged at 14 portions outside the image
display area within the vacuum container, as shown in FIG. 11.
However, the number and layout of surface potential measurement
electrodes 7002, the size of the electrode, and the like are not
limited. The surface potential measurement electrodes 7002 are
preferably arranged on the device substrate 1001 within the vacuum
container over an area as large as possible in order to detect
discharge in an area as large as possible. However, the surface
potential measurement electrodes 7002 are arranged outside the
display area in order to avoid overlapping the image display area
and manufacturing errors.
[0208] Although a larger number of surface potential measurement
electrodes 7002 can detect discharge at higher resolution, the
number of surface potential measurement electrodes 7002 is
determined in consideration of the fact that the number of surface
potential measurement circuits connected to them also increases,
and the size of an area where discharge can be detected.
[0209] As described above, the image display apparatus of the fifth
embodiment can provide information for estimating the cause of
discharge for an abnormal operation such as generation of
discharge.
[0210] Even if an abnormal operation occurs, the cause can be
estimated whether the abnormal operation is based on generation of
discharge, and information for performing proper adjustment can be
provided to recover the image display apparatus to a normal
operation.
Sixth Embodiment
[0211] FIG. 13 is a block diagram for explaining connection between
the display panel and peripheral circuit of an image display
apparatus according to the sixth embodiment of the present
invention.
[0212] In FIG. 13, reference numeral 101 denotes a display panel
having almost the same arrangement as in FIG. 31 except that the
display panel 101 comprises a destruction detection high-voltage
electrode 103 and detection device 102 (to be described later) and
their terminals. A driving circuit for the display panel 101
includes a scanning signal generation circuit 109 for sequentially
driving row wirings in accordance with an externally input video
signal, a modulated signal generation circuit 110 for applying a
modulated signal corresponding to the video signal to column
wirings on a row selected by the video signal, and a high-voltage
source 106 for inputting an acceleration voltage Hv. The scanning
signal generation circuit 109 sequentially selects row terminals
Dx1 to DxM of the display panel 101 and applies a predetermined
voltage. The modulated signal generation circuit 110 applies a
pulse width modulated signal corresponding to a video signal to
column terminals D.sub.y1 to D.sub.yn.
[0213] In the sixth embodiment, at least one destruction detection
cold cathode device 102 is formed at a location other than the
image display area on the device substrate of the display panel
101. The destruction detection high-voltage electrode 103 is
arranged above the destruction detection cold cathode device 102
(on the face plate side) to capture electrons emitted by the
destruction detection cold cathode device 102. To prevent light
emission unrelated to an image to be displayed, no fluorescent
substance which emits light upon collision against electrons is
desirably formed on the destruction detection high-voltage
electrode 103. The destruction detection high-voltage electrode 103
receives, via a terminal 121, a voltage {Va.times.R2/(R1+R2)}
obtained by dividing an output Va from the high-voltage source 106
by a resistor 111 (resistance value R1) and a resistor 112
(resistance value R2).
[0214] The sixth embodiment sets the resistance values R1 and R2
such that the voltage applied to the destruction detection
high-voltage electrode 103 can capture an emission current and is
set to a voltage (about 80 V) as low as possible. The voltage
applied to the destruction detection high-voltage electrode 103 is
set low in order to reduce the cost by omitting any high-voltage
resistant measure (isolation) with respect to an ammeter 104
series-connected to the destruction detection high-voltage
electrode 103.
[0215] A method of detecting destruction of the airtight container
by the airtight container destruction detection means (destruction
detection cold cathode device 102, destruction detection
high-voltage electrode 103, and the like) will be explained
below.
[0216] When power is supplied from a main power source (not shown)
to the image display apparatus of the sixth embodiment, a pulse
generator 107 applies a voltage pulse (voltage Vf) for emitting
electrons to the destruction detection cold cathode device 102 via
terminals 120. Note that the pulse generator 107 may start
operating in response to a signal from a control unit 105 (to be
described below). At the same time, the ammeter 104
series-connected between the destruction detection high-voltage
electrode 103 and high-voltage source 106 detects the emission
current Ie from the destruction detection cold cathode device 102.
If the airtight container of the display panel 101 is destroyed,
the interior of the airtight container is exposed to the
atmospheric pressure, so electron emission from the destruction
detection cold cathode device 102 is stopped not to detect any
emission current Ie. Therefore, when no emission current Ie is
detected even upon application of the driving voltage pulse for
emitting electrons to the cold cathode device 102, the airtight
container can be determined to be destroyed. Note that this control
is done by the control unit 105. More specifically, when no current
is detected by the ammeter 104 while applying the pulse signal from
the pulse generator 107 to the cold cathode device 102 and the high
voltage Va from the high-voltage source 106 to the high-voltage
electrode 103, the control unit 105 determines that any abnormality
occurs in the airtight container of the display panel 101, and
stops applying the high voltage from the high-voltage source 106.
At this time, the control unit 105 may stop operating the pulse
generator 107.
[0217] Processing by the control unit 105 is shown in the flow
chart of FIG. 14. According to the abnormality detection and
control of the electron source in the sixth embodiment, processing
of detecting destruction of the airtight container is always
executed while the main power source of the image display apparatus
is turned on, as shown in the flow chart of FIG. 14.
[0218] The processing shown in FIG. 14 starts when the power source
of the apparatus is turned on. In step S1, the control unit 105
measures the emission current Ie from the destruction detection
cold cathode device 102 based on a current value measured by the
ammeter 104. The control unit 105 advances to step S2 to check
whether the current value is detected. If NO in step S2, the
control unit 105 shifts to step S3 to stop driving the high-voltage
source 106.
[0219] If YES in step S2, the control unit 105 advances to step S4
to check whether the main power source is turned off. If NO in step
S4, the control unit 105 returns to step S1 to execute the above
processing; if YES in step S4, completes the processing.
[0220] If the control unit 105 detects a state in which no emission
current is detected owing to destruction of the airtight container,
it stops applying the driving voltage to the image display unit
(including a high voltage applied to the high-voltage electrode
103). In this case, the control unit 105 may stop outputting the
pulse from the pulse generator 107 in step S3.
[0221] The control method of the sixth embodiment can eliminate any
danger such as an electric leakage or electric shock generated when
the airtight container of the electron source is destroyed. In the
sixth embodiment, the voltage pulse Vf applied to the destruction
detection cold cathode device 102 is a rectangular wave having a
peak value of 16.0 V, a pulse period of 1 ms, and a pulse width of
0.1 ms.
<General Description of Image Display Apparatus>
[0222] The structure and manufacturing method of the display panel
101 according to the sixth embodiment of the present invention will
be described in detail.
[0223] FIG. 15 is a perspective view of the display panel 101
according to the sixth embodiment where part of the display panel
101 is removed for showing its internal structure. In FIG. 15, the
same reference numerals as in FIG. 31 denote the same parts, and a
description thereof will be omitted.
[0224] In FIG. 15, reference numeral 120 denotes a terminal for
applying a pulse voltage from the pulse generator 107 (FIG. 13) to
the destruction detection cold cathode device 102; and 121, a
terminal for applying a high voltage to the destruction detection
high-voltage electrode 103. For illustrative convenience, no
destruction detection high-voltage electrode 103 is illustrated in
FIG. 15.
[0225] In the multi electron source used in the image display
apparatus according to the sixth embodiment of the present
invention, any material, shape, and manufacturing method for cold
cathode device devices may be employed as long as an electron
source is constituted by arranging cold cathode devices in a simple
matrix. Therefore, cold cathode devices such as surface-conduction
type emission devices, FE type devices, or MIM type devices can be
used.
[0226] The following description concerns the structure of a multi
electron source in which surface-conduction type emission devices
(to be described below) are arranged as cold cathode devices in a
simple matrix on the substrate.
[0227] FIG. 16 is a plan view of the substrate 3111 (1001) of the
multi electron source used in the display panel described
above.
[0228] Surface-conduction type emission devices like the one shown
in FIGS. 19A and 19B are arranged on the substrate 3111. These
devices are arranged in a simple matrix with the row and column
wirings 3113 and 3114. At an intersection of the row and column
wirings 3113 and 3114, an insulating layer (not shown) is formed
between electrodes to maintain electrical insulation.
[0229] FIG. 17 shows a cross-section cut out along the line B-B' in
FIG. 16.
[0230] Note that a multi electron source having this structure is
manufactured by forming the row and column wirings 3113 and 3114,
the inter-electrode insulating layers (not shown), and the device
electrodes and conductive thin films of the surface-conduction type
emission devices 3112 on the substrate 3111, then supplying
electricity to the respective devices via the row and column
wirings 3113 and 3114, thus performing forming processing (to be
described later) and activation processing (to be described
later).
[0231] In the sixth embodiment, the substrate 3111 of the multi
electron source is fixed to the rear plate 3115 of the airtight
container. If, however, the substrate 3111 of the multi electron
source has sufficient strength, the substrate 3111 of the multi
electron source may be used as the rear plate of the airtight
container.
[0232] A fluorescent film 3118 is formed on the lower surface of
the face plate 3117. As the display panel 101 (1) of the sixth
embodiment is a color display apparatus, the fluorescent film 3118
is colored with fluorescent substances of three, red, green, and
blue primary colors used in the CRT field. As shown in FIG. 18A,
the fluorescent substances of the respective colors are applied
into stripes, and black conductive members 1010 are applied between
the stripes of the fluorescent substances. The purpose of applying
the black conductive members 1010 is to prevent misregistration of
the display color even if the irradiation position of the electron
beam is shifted to some extent, to prevent degradation of display
contrast by shutting off reflection of external light, to prevent
charge-up of the fluorescent film by the electron beam, and the
like. As a material for the black conductive members 1010, graphite
is used as a main component, but other materials may be used so
long as the above purpose is attained.
[0233] The layout of the fluorescent substances of the three
primary colors is not limited to the stripe shown in FIG. 18A. For
example, a delta layout as shown in FIG. 18B or any other layout
may be employed. When a monochrome display panel is formed, a
single-color fluorescent substance may be applied to the
fluorescent film 3118, and the black conductive member may be
omitted.
[0234] A metal back 3119, which is well-known in the CRT field, is
formed on the fluorescent film 3118 on the rear plate side. The
purpose of forming the metal back 3119 is to improve the
light-utilization ratio by mirror-reflecting part of the light
emitted by the fluorescent film 3118, to protect the fluorescent
film 3118 from collision against negative ions, to use the metal
back 3119 as an electrode for applying the electron-beam
acceleration voltage, to use the metal back 3119 as a conductive
path for electrons which excited the fluorescent film 3118, and the
like. The metal back 3119 is formed by forming the fluorescent film
3118 on the face plate 3117, smoothing the upper surface of the
fluorescent film, and depositing Al on the smooth surface by vacuum
evaporation. When the fluorescent film 3118 is made of a
low-voltage fluorescent substance, no metal back 3119 is used.
[0235] A transparent electrode made of, e.g., ITO may be provided
between the face plate 3117 and fluorescent film 3118 in order to
apply the acceleration voltage or improve the conductivity of the
fluorescent film, though such electrode is not used in the sixth
embodiment.
[0236] The application voltage to the surface-conduction type
emission device of the sixth embodiment as a cold cathode device is
generally about 12 to 16 V, a distance d between the metal back
3119 and cold cathode device 3112 is about 0.1 mm to 8 mm, and the
voltage between the metal back 3119 and cold cathode device 3112 is
about 0.1 kV to 10 kV.
Seventh Embodiment
[0237] FIG. 33 is a perspective view of a display panel used in the
seventh embodiment where part of the panel is removed for showing
the internal structure of the panel.
[0238] In FIG. 33, reference numeral 1005 denotes a rear plate;
1006, a side wall; and 1007, a face plate. These parts 1005 to 1007
form an airtight container for maintaining the interior of the
display panel vacuum. To construct the airtight container, it is
necessary to seal-connect the respective parts to obtain sufficient
strength and maintain airtight condition. For example, frit glass
is applied to junction portions, and sintered at 400 to 500.degree.
C. in air or nitrogen atmosphere, thus the parts are
seal-connected. A method for evacuating the container will be
described later.
[0239] The rear plate 1005 is fixed to a substrate 1001. N.times.M
cold cathode devices 1002 are formed on the substrate. (N and M are
positive integers equal to 2 or more, and properly set in
accordance with a target number of display pixels. For example, in
a display apparatus for high-quality television display, N=3,000 or
more, M=1,000 or more are desirable. In the seventh embodiment,
N=3,072 and M=1,024.). The N.times.M cold cathode devices are
arranged in a simple matrix by M row wirings 1003 and N column
wirings 1004. The portion constituted by the parts 1001 to 1004
will be referred to as a multi electron source.
[0240] In the seventh embodiment, the substrate 1001 of the multi
electron source is fixed to the rear plate 1005 of the airtight
container. If, however, the substrate 1001 of the multi electron
source has sufficient strength, the substrate 1001 of the multi
electron-beam source may be used as the rear plate of the airtight
container.
[0241] A fluorescent film 1008 is formed on the lower surface of
the face plate 1007. As the seventh embodiment is directed to a
color display apparatus, the fluorescent film 1008 is colored with
fluorescent substances of three, red, green, and blue primary
colors used in the CRT field. As shown in FIG. 18A, the fluorescent
substances of the respective colors are applied into stripes, and
black conductive members 1010 are applied between the stripes of
the fluorescent substances. The purpose of applying the black
conductive members 1010 is to prevent misregistration of display
color even if the irradiation position of the electron beam is
shifted to some extent, to prevent degradation of display contrast
by shutting off reflection of external light, to prevent charge-up
of the fluorescent film by the electron beam, and the like. As a
material for the black conductive members 1010, graphite is used as
a main component, but other materials may be used so long as the
above purpose is attained.
[0242] The layout of the fluorescent substances of the three
primary colors is not limited to the stripe shown in FIG. 18A. For
example, a delta layout as shown in FIG. 18B or any other layout
may be employed.
[0243] When a monochrome display panel is formed, a single-color
fluorescent substance may be applied to the fluorescent film 1008,
and the black conductive member may be omitted.
[0244] A metal back 1009, which is well-known in the CRT field, is
formed on the fluorescent film 1008 on the rear plate side. The
purpose of forming the metal back 1009 is to improve the
light-utilization ratio by mirror-reflecting part of the light
emitted by the fluorescent film 1008, to protect the fluorescent
film 1008 from collision against negative ions, to use the metal
back 1009 as an electrode for applying the electron-beam
acceleration voltage, to use the metal back 1009 as a conductive
path for electrons which excited the fluorescent film 1008, and the
like. The metal back 1009 is formed by forming the fluorescent film
1008 on the face plate substrate 1007, smoothing the upper surface
of the fluorescent film, and depositing Al on the smooth surface by
vacuum evaporation. When the fluorescent film 1008 is made of a
low-voltage fluorescent substance, no metal back 1009 is used.
[0245] In the seventh embodiment, the electrode for applying the
acceleration voltage (high voltage) on the face plate side will be
referred to as an anode electrode, which includes the fluorescent
substance, black conductive member, and metal back.
[0246] A transparent electrode made of, e.g., ITO may be provided
as an auxiliary anode electrode between the face plate substrate
1007 and fluorescent film 1008 in order to apply the acceleration
voltage or improve the conductivity of the fluorescent film, though
such electrode is not used in the seventh embodiment.
[0247] Reference symbols D.sub.x1 to D.sub.xM, D.sub.y1 to
D.sub.yN, and Hv denote electric connection terminals for the
airtight structure provided to electrically connect the display
panel to an electric circuit (not shown). The terminals D.sub.x1 to
D.sub.xM are electrically connected to the row-direction wirings
1003 of the multi electron-beam source; D.sub.y1 to D.sub.yN, to
the column-direction wirings 1004 of the multi electron-beam
source; and Hv, to the metal back 1009 of the face plate.
[0248] To evacuate the airtight container, the airtight container
is connected to an exhaust pipe and vacuum pump (both not shown)
after assembling, and evacuated to a vacuum degree of about
10.sup.-7 Torr. Then, the exhaust pipe is sealed. To maintain the
vacuum degree in the airtight container, a getter film (not shown)
is formed at a predetermined position immediately before/after
sealing. The getter film is formed by heating and depositing a
getter material mainly containing, e.g., Ba, by a heater or RF
heating. The absorption operation of the getter film keeps the
airtight container at a vacuum degree of 1.times.10.sup.-5 or
1.times.10.sup.-7 Torr.
[0249] The basis structure and manufacturing method of the display
panel according to the seventh embodiment have been described.
(Driving Circuit for Driving Multi Electron-Beam Source)
[0250] A display method in the driving circuit of the seventh
embodiment will be explained in detail with reference to the
accompanying drawings.
[0251] In the following description, the scanning method in the
seventh embodiment is non-interlace line-sequential scanning. To
display an image with gradation, the electron-emitting period
within one horizontal scanning period (1H) is controlled by the
time width of a modulated signal to control the total
light-emitting quantity of the fluorescent substance and realize
gradation expression.
[0252] FIG. 35 is a block diagram showing the arrangement of the
electric circuit and connection between respective units in the
image display apparatus according to the present embodiment. In
FIG. 35, reference numeral 3521 denotes a circuit for generating a
horizontal sync signal, vertical sync signal, digital video signal,
and the like from a video signal such as an NTSC signal. This
circuit 3521 includes a video intermediate frequency circuit, video
signal detection circuit, sync separation circuit, low-pass filter,
A/D conversion circuit, timing control circuit, and the like.
[0253] Reference numeral 3522 denotes an image display unit of the
image display apparatus of the present invention.
[0254] Reference numeral 3523 denotes a scanning signal driver for
driving the row-direction wirings of the image display unit. The
scanning signal driver 3523 outputs a scanning signal (to be
described later with reference to a timing chart) on the basis of a
horizontal sync signal separated/generated by the circuit 3521.
[0255] Reference numeral 3524 denotes a modulated signal driver for
driving the column-direction wirings of the image display unit. The
modulated signal driver 3524 outputs a modulated signal (to be
described later with reference to a timing chart) based on a
horizontal sync signal, vertical sync signal, digital video signal,
and the like separated/generated by the circuit 3521.
[0256] FIG. 8 is a timing chart showing an example of the voltage
applied to the terminals of the row-direction wiring (i.e., wiring
to which the scanning signal is supplied) and the column-direction
wiring (i.e., wiring to which the modulated signal is supplied) in
driving the image display unit of the image display apparatus
according to the seventh embodiment. The timing chart in FIG. 8
shows voltages applied to row-direction wirings on rows I, I+1, and
I+2 and column-direction wirings on columns J, J+1, and J+2 on the
modulated signal side while sequentially driving the rows I, I+1,
and I+2 of the image display apparatus. (1<I<M-2 and
1<J<N-2 inevitably hold. M and N represent the total numbers
row and column wirings, respectively).
[0257] In FIG. 8, an image of the I.sub.th row is displayed during
one horizontal scanning period K, an image of the (I+1).sub.th row
is displayed during the period (K+1), and an image of the
(I+2).sub.th row is displayed during the period (K+2).
[0258] Row-direction wirings serving as the scanning side in
line-sequential scanning are sequentially selected every horizontal
scanning period (to be referred to as 1H hereinafter).
Row-direction wirings on selected rows sequentially receive a
scanning signal having a pulse width corresponding to 1H and a peak
value -Vf/2 (Vf is a driving voltage; Vf=about 2V.sub.th). After
the scanning is done for all row-direction wirings, it is repeated
from the first row.
[0259] A modulated signal having a peak value 1/2Vf is applied to
all column-direction wirings in synchronism with the scanning
signal applied to the row-direction wiring for a period
corresponding to a video signal displayed on a selected row.
[0260] This modulated signal rises in synchronism with the trailing
edge of the scanning signal, and falls after maintaining the peak
value Vf/2 for a time corresponding to the video signal. (The
period between the leading and trailing edges of the modulated
signal will be simply referred to as the pulse width of the
modulated signal)
[0261] The pulse width of the modulated signal corresponds to the
luminance of each of three, R, G, and B colors obtained by
color-separating a video signal displayed on a selected row. In
practice, the pulse width is not simply proportional to the
luminance because various corrections are done to display a
high-quality image.
[0262] By applying the voltage in this way, the driving voltage Vf
is applied to cold cathode devices on a selected row for the pulse
width of the modulated signal.
[0263] Since the emission current Ie of the cold cathode device has
the above-described definite threshold characteristics with respect
to Vf, an image corresponding to a desired video signal is
displayed on a selected row.
[0264] Furthermore, an image is displayed over all cold cathode
devices in the image display unit by line-sequential scanning.
[0265] In the seventh embodiment, the surface potential of the
device substrate on which cold cathode devices are arranged is
monitored to detect discharge using a plurality of surface
potential measurement units (surface potential measurement system)
for the device substrate. Upon generation of discharge, failsafe
control for the display apparatus (to be referred to as a panel) is
done. The history of potentials of the surface potential electrode
is stored in the memory to determine a failsafe method with respect
to discharge.
[0266] The internal structure of the panel and the surface
potential measurement electrode will be described. FIG. 34 is a
partially cutaway perspective view of the panel in the seventh
embodiment. In FIG. 34, the face plate and part of the side wall
(frame) are not illustrated in order to explain the surface
potential measurement electrode as part of the discharge detection
unit in the seventh embodiment. In FIG. 34, reference numeral 3411
denotes a device substrate; 3412, a cold cathode device; 3413, a
row-direction wiring; 3414, a column-direction wiring; 3415, a rear
plate; 3416, a side wall (frame); 3417, a surface potential
measurement electrode; and 3418, a guard electrode arranged around
the surface potential measurement electrode to guard it. In the
seventh embodiment, a plurality of surface potential measurement
electrodes are arranged at the periphery of the device substrate
3411, and each surface potential measurement electrode 3417 has a
rectangular shape. The surface potential measurement electrode 3417
is covered with the guard electrode 3418 to avoid any potential
influence on the display unit in the panel and measure the
potential value of the surface potential electrode with high
precision. Note that the surface potential measurement electrode
3417 may have any shape other than a rectangular shape so long as
the potential value can be measured. The number of electrodes is
not particularly limited. In the seventh embodiment, a plurality of
electrodes are arranged at the peripheral portion within the panel,
and thus the potential state on the surface can be independently
monitored in units of areas within the panel to specify the
location where discharge has occurred.
[0267] The surface potential measurement electrodes 3417 are
arranged on the device substrate so as to be electrically isolated
from the row-direction wiring 3413, column-direction wiring 3414,
cold cathode device 3412, and the like, and are extracted via outer
extraction lines D.sub.s1 to D.sub.s14 of the vacuum container.
Since the surface potential measurement electrodes 3417 are made of
the same material as the material for the row- and column-direction
wirings, they can also be formed at the same time as the wirings
and the like.
[0268] The material for the surface potential measurement electrode
3417 need only be conductive, and may be different from the wiring
material.
[0269] The circuit arrangement for realizing the failsafe function
will be described with reference to FIG. 35. Reference numeral 3525
denotes a potential measurement unit for outputting a potential
signal from the extraction line of the surface potential
measurement electrode, as described above. The surface potential
measurement electrode 3417 and surface potential measurement unit
3525 constitute a potential measurement means. A discharge
recording unit for recording a potential output on the memory or
the like is arranged on the output stage of the surface potential
measurement unit 3525, and constituted by a discharge recording
control unit 3529 and a memory 35210. A surface potential detection
unit for detecting the surface potential value is constituted by a
comparator 35211 for comparing the potential value with the
threshold and a detection unit 35212. An output from the surface
potential measurement unit 3525 is added with a potential signal by
a measurement unit having a higher input impedance than the surface
measurement electrode, and then output as a potential with a proper
gain. These signals are input as analog values. In this case, the
surface potential output may be output as a digital value and can
take an optimum form for the circuit arrangement. A discharge
detection means comprises the surface potential detection unit
having the comparator 35211 and detection unit 35212, and an
abnormality count means comprises the discharge recording unit
having the discharge recording control unit 3529 and memory
35210.
[0270] Failsafe control is performed by a failsafe control unit
which is made up of a determination circuit 35214 and a processing
control unit 35213. The processing control unit 35213 outputs
signals for actually performing failsafe control, and these signals
are input to a warning output means 35216 for outputting warning
information to the user (operator) or the like, control units 3526,
3527, and 3528 for power sources Vf and Va for applying power to
the matrix device in the panel, and a driving circuit power source
unit 35215 for controlling the power source voltage of the display
circuit system.
[0271] The warning output means 35216 serves as a control means for
displaying optimum information on the output unit 35217 made up of
a display indicator, speaker, or the like, and drives a speaker
3563 or an indicator unit 3562 in accordance with a control signal.
The +Vf control unit 3526, -Vf control unit 3527, and Va control
unit 3528 control application voltages to the device in accordance
with signals from the processing control unit 35213. They function
to reduce the power source voltages Vf and Va or change the voltage
values depending on signals from the processing control unit 35213.
With these functions, supply of the device voltage via the
modulation and scanning signal drivers 3524 and 3523 and
application of the anode voltage to the face plate side of the
panel can be limited to set the device at an operating voltage or
less and suppress the device current If and emission current
Ie.
[0272] The driving circuit power source unit 35215 supplies power
to the whole display circuit system, and in addition controls the
power source voltage of the driving circuit systems (mainly digital
and analog circuit systems) of the modulation and scanning signal
drivers 3524 and 3523. Depending on control from the processing
control unit 35213, the driving circuit power source unit 35215 can
limit supply of the power source voltage to the display circuit
system to stop the pulse width modulation driving by
line-sequential scanning performed in the seventh embodiment.
[0273] A detailed control method of each control unit for realizing
failsafe control upon discharge in the seventh embodiment will be
explained.
[0274] The discharge recording control unit 3529 serves as a
control means for recording a potential signal output from the
surface potential measurement unit 3525 on the memory 35210. More
specifically, the discharge recording control unit 3529
A/D-converts potential outputs Ds1 to Ds14 input as analog signals
at predetermined timings and writes the digital signals in the
memory 35210. Information written in the memory 35210 includes
surface potential amounts corresponding to the locations of Ds1 to
Ds14 and measurement time (time & date) data. For example,
surface potential amounts divided in units of locations may be
written in the memory 35210, and information may be written in the
memory 35210 in correspondence with a measurement time or the like.
These memory arrangements are desirably set optimally for
information in reading out the potential amount by the
determination circuit 35214 or externally accessing memory
information.
[0275] As for the write timing of discharge information in the
memory 35210, A/D conversion may be done using an external input
signal based on a signal from the detection unit 35212, or A/D
conversion and a write in the memory 35210 may be done using an
internal signal. The seventh embodiment adopts a method using both
the functions.
[0276] The comparator 35211 of the surface potential detection unit
compares an analog potential signal from the surface potential
measurement unit 3525 with a set threshold V.sub.th, converts a
potential equal to or lower than the threshold into a logic signal
(e.g., TTL level), and inputs the logic signal to the detection
unit 35212. The threshold V.sub.th of the comparator 35211 can be
externally set and can be changed in accordance with the panel
state. The comparator 35211 may be a buffer amplifier for directly
inputting the absolute value of the surface potential amount to the
detection unit 35212.
[0277] The detection unit 35212 comprises a means for detecting,
based on a signal from the comparator 35211, the location of an
electrode which exceeds V.sub.th out of a plurality of surface
potential measurement electrodes 3417, and detecting discharge
after a signal equal to or higher than V.sub.th is detected. The
timings of these signals will be explained with reference to FIG.
36.
[0278] FIG. 36 is a timing chart showing a change in time vs.
change in state of an output potential a from an arbitrary surface
potential measurement electrode 3417 causing discharge. Further,
FIG. 36 shows timings of signals S1 and S2 for detecting the
comparator signal and discharge when the surface potential output
exceeds V.sub.th set by the comparator 35211.
[0279] Before discharge occurs in the panel, the potential on the
matrix in the panel tends to rise over time. This is caused by
accumulation of charges on the device or device wiring electrode
along with deterioration of the atmosphere in the panel, and is
also influenced by panel driving conditions.
[0280] When the surface potential output exceeds the set V.sub.th
due to the above reason, like the potential a, the comparator
signal changes from L to H. At time T1, the comparator signal is
input as a latch clock by arranging a latch circuit in, e.g., the
detection unit 35212. The latch circuit outputs a latch enable
signal S1 by the input comparator signal. When discharge occurs at
time T4 near the surface potential electrode which exceeds
V.sub.th, the potential of the surface potential electrode 3417
instantaneously drops to V.sub.th or less owing to the discharge,
and the comparator signal changes from H to L.
[0281] Detection of discharge is done by determining as discharge
only a signal when the comparator signal changes from H to L while
the latch enable signal S1 is kept in an enable state.
[0282] When the surface potential is equal to or lower than
V.sub.th, i.e., no discharge occurs in FIG. 36, the latch enable
signal S1 is in a disable state, and even a change in signal S2 is
not regarded as discharge.
[0283] Hence, when generation of discharge is detected, the
potential of the surface potential electrode 3417 near the
discharge generation location always exceeds V.sub.th and can be
estimated to a certain degree. As another method, when generation
of discharge is detected by inputting the absolute value of the
surface potential, the surface potential amount is converted into a
digital value using an arithmetic processing system including an
A/D conversion circuit and CPU, and discharge is detected by
arithmetic processing.
[0284] In this manner, the surface potential detection unit
realizes detection of discharge on the basis of the comparator
signal with respect to output values from a plurality of surface
potential electrodes. The detection unit 35212 outputs a detection
signal upon discharge to the discharge recording control unit 3529
and the determination circuit 35214 in the failsafe control
unit.
[0285] To realize failsafe control for the panel, the failsafe
control unit is constituted by the determination circuit 35214 for
receiving signals from the detection unit 35212 and memory 35210,
and the processing control unit 35213. The determination circuit
35214 determines how to perform failsafe control for the panel on
the basis of a discharge detection signal input from the detection
unit 35212 and information in the memory 35210 in the panel. In the
present invention, the failsafe sequence is divided into three
modes and executed in accordance with a sequencer in the
determination circuit 35214. The determination circuit 35214
corresponds to a sequence determination means, and the
determination circuit 35214 and processing control unit 35213
constitute a protection control means.
[0286] FIG. 37 shows a failsafe sequence used in the seventh
embodiment. In a step S101, the determination circuit 35214
recognizes that the panel is in an abnormal state on the basis of
signals from the detection unit 35212 and memory 35210. In step
S102, the determination circuit 35214 determines which failsafe
sequence is the most optimum for the abnormal state.
[0287] In the seventh embodiment, the processing level is divided
into three modes, and a sequence corresponding to the abnormal
state is executed. "MODE 1" has a sequence of notifying the user
(operator) by a warning display indicator or voice. "MODE 2" has a
sequence of controlling the power source of the driving power
source system after the notice. "MODE 3" has a sequence of directly
turning off the whole driving system without any notice. Which
sequence is actually executed is determined by the abnormality
level in the panel. Of the sequences of "MODE 1" to "MODE 3", "MODE
1" and "MODE 2" are for a relatively low abnormal state level and
allow automatic return in the panel. To the contrary, "MODE 3" is
for a high abnormal state level and inhibits automatic return.
[0288] A flow corresponding to the set sequence will be explained.
In step S103, the processing sequence is selected. If "MODE 3" is
to be executed, the flow shifts to step S109; if "MODE 1" or "MODE
2" is to be executed, to step S104. In the step S104, a warning
display is determined as the sequences of "MODE 1" and "MODE
2".
[0289] In a step S105, the contents of the warning display
correspond to the level of the abnormal state. The indicator unit
3562 may be mounted on the front surface of an image display
apparatus 3861 shown in FIG. 38, or the voice output speaker 3563
may be mounted to output a message. For example, if no discharge is
detected and the potential state is stable, like "MODE 1", the
message indicator 3562 or speaker 3563 may instruct periodic
maintenance of the display apparatus. If discharge occurs like
"MODE 2", the state is determined as an emergency, and the message
indicator 3562 or speaker 3563 may notify the operator of turning
off the TV power source. The message indicator 3562 and speaker
3563 constitute an information transfer means. In step S106,
whether the sequence in progress is "MODE 2" is checked. If NO in
the step S106, the failsafe control ends.
[0290] If YES in the step S106, control of the driving power source
is instructed. This control instruction determines which system is
to be controlled in control of the power source executed in step
S108. For example, the power sources Va and Vf are subjected to
control of the power source. This control or operation is divided
into control of stopping the driving voltage itself to the cold
cathode device in the panel, and control of stopping the power
source voltage unit of the display circuit system itself, as
described above. When discharge is generated by any thermal factor
in the circuit system, both the display circuit system and device
driving voltage must be stopped. To the contrary, when the circuit
system is normal, discharge is determined to be generated by the
device itself in the panel, and only the device driving voltage is
stopped. This determination is enabled by monitoring by the
processing control unit 35213 whether an output current value from
the driving circuit power source unit 35215 is in an
excessive-current state when discharge occurs.
[0291] If NO in the step S103, the flow shifts from the step S103
to the step S109 to turn off the whole driving system. In this
case, the control system unconditionally turns off the driving
circuit power source unit 35215 and the +Vf, -Vf, and Va output
control units 3526, 3527, and 3528.
[0292] By these control units, the seventh embodiment realizes
detection of discharge, suppression of discharge upon generation of
discharge occurs, and failsafe control to the panel. Discharge is
detected using the detection means shown in FIG. 36. As mode
determination processing in the failsafe sequence, for example,
when discharge occurs a plurality of the number of times or
continuously, or the panel itself is destroyed by an external
operation, the vacuum degree (atmosphere or pressure) in the panel
is determined to be very low, and "MODE 3" is executed. When
discharge rarely occurs and the panel itself is almost free from
the influence of discharge, "MODE 2" is set. When the potential
state of the surface potential electrode 3417 is equal to or lower
than V.sub.th, or no discharge occurs and the potential is stable
even if the potential state exceeds V.sub.th, "MODE 1" is set.
Eighth Embodiment
[0293] The eighth embodiment of the present invention will be
described. The eighth embodiment uses a plurality of surface
potential measurement units (surface potential measurement system)
for the device substrate. A temporal change of the potential of the
surface potential electrode is measured based on information from
the memory storing the history of the surface potential of the
device substrate on which cold cathode devices are arranged. In
accordance with the change amount, generation of discharge is
estimated to notify the user. At the same time, the failsafe mode
is set to protect the panel from discharge.
[0294] The eighth embodiment has the same arrangement as described
in the seventh embodiment with reference to FIGS. 34, 35, and 8,
and a detailed description thereof will be omitted. FIG. 36 shows a
change in potential of a surface potential electrode 3417. The
potential of each electrode in the panel is written in a memory
35210 by a discharge recording control unit 3529 via a surface
potential measurement unit 3525. The write method in the memory
35210 is the same as in the seventh embodiment. As for a change in
arbitrary potential amount shown inn FIG. 36, the potential a which
may cause discharge increases in potential amount over time. In
contrast, the potential b on the electrode which does not cause
discharge is stable almost free from any change.
[0295] For this reason, to estimate discharge in the panel, a
determination circuit 35214 in FIG. 35 accesses the memory 35210 to
read out a plurality of surface potential amounts written in the
memory (the eighth embodiment exemplifies the potentials a and b on
two electrodes for descriptive convenience). The determination
circuit 35214 and memory 35210 constitute a potential change rate
calculation means.
[0296] For example, the potential amounts of the potentials a and b
correspond to Vt1 and Vt1' at time T1. After the lapse of a
predetermined time, the potential amounts Vt2 and Vt2' at time T2
are read. Similarly, the potential amounts Vt3 and Vt3' at time T3
are read. Then, changes in read potential amount are calculated as
changes .DELTA.V1, .DELTA.V1', .DELTA.V2, and .DELTA.V2' in
potential amount at .DELTA.T1 and .DELTA.T2. By this method,
changes in potential amount for a predetermined time can be
obtained. The changes .DELTA.V1 and .DELTA.V2 in potential amount
of the potential a which may cause discharge in FIG. 36 are
determined to be larger than the changes .DELTA.V1' and .DELTA.V2'
in potential amount of the potential b when no discharge
occurs.
[0297] The determination circuit 35214 compares the calculated
change in potential amount with a set value to check whether the
change in potential amount causes discharge. The discharge
prediction means is constituted by a potential measurement means
made up of the surface potential electrode 3417 and surface
potential measurement unit 3525 and a potential change rate
calculation means made up of the determination circuit 35214 and
memory 35210.
[0298] The set value is a normalized value of the gradient of a
potential change as a function of time, and is compared with the
calculated change amount.
[0299] In the example of FIG. 36, the gradients of the potential
changes .DELTA.V1 and .DELTA.V2 are determined to be larger than
the set value, and the gradients of the potential changes
.DELTA.V1' and .DELTA.V2' are determined to be smaller than the set
value. In other words, when surface potential amounts in the panel
exhibit different changes and the determination of comparison with
the set value becomes different, priority is given to failsafe
control for the potential changes .DELTA.V1 and .DELTA.V2 in order
to perform failsafe control against discharge.
[0300] The determination circuit 35214 may steadily access the
memory 35210 to read the potential amounts of a plurality of
surface potential electrodes in order to grasp the internal state
of the panel, or may access the memory 35210 as needed.
[0301] As another method, the absolute value of the surface
potential from the surface potential measurement unit 3525 can be
used.
[0302] In this case, discharge is determined by a comparator 35211
and detection unit 35212 of the surface potential detection unit
without any read from the memory 35210. To input the absolute
value, the comparator 35211 is used as a buffer amplifier. To
estimate discharge, the detection unit 35212 compares a temporal
change in potential amount with a set value, and outputs, e.g.,
abnormal value .DELTA.V1 and .DELTA.V2 to the determination circuit
35214. The temporal change in potential amount can be calculated by
the same method as mentioned above by performing the processing
function in the determination circuit 35214 by the detection unit
35212. The internal arrangement of the determination circuit 35214
may include an arithmetic processing system having an A/D
conversion circuit, CPU, and the like, as described in the seventh
embodiment. In this case, a potential change rate calculation means
comprises the comparator 35211 and detection unit 35212, and a
discharge prediction means comprises the potential change rate
calculation means and determination circuit 35214.
[0303] FIG. 39 shows a failsafe sequence used in the eighth
embodiment.
[0304] As processing corresponding to failsafe control, the
determination circuit 35214 determines whether the changes
.DELTA.V1 and .DELTA.V2 of the potential a may cause discharge
(step S111), and notifies the user (operator) of the abnormal state
via a processing control unit 35213 and a warning means 35216 (step
S113). A protection control means comprises the processing control
unit 35213 and determination circuit 35214.
[0305] The contents of the notice properly correspond to the
abnormal state, similar to the seventh embodiment (step S112). In
the above example, a message of turning off the TV switch SW is
displayed or output by voice from the speaker.
[0306] The determination circuit 35214 sets the failsafe mode
against discharge in the panel (step S114). The mode is set to
either "MODE 2" or "MODE 3" because discharge will occur at high
probability in this example. As for failsafe control when discharge
actually occurs, the discharge is detected by the comparator 35211
and detection unit 35212 in the surface potential detection unit,
and the detection signal is input to the determination circuit
35214 to execute failsafe control, similar to the seventh
embodiment. In this case, the notice in the step S105 of the
failsafe sequence in the seventh embodiment shown in FIG. 37 has
already been executed in step S113 and thus can be omitted.
[0307] When the value of the surface potential electrode 3417 in
the panel is very stable like .DELTA.V1' and .DELTA.V2' of the
potential b, the change amounts are equal to or smaller than the
set value, the probability of generation of discharge is determined
to be low, and the failsafe mode is set to "MODE 1" (step S119). In
this case, the user is notified in accordance with a normal
failsafe sequence (steps S120 and S121).
[0308] The eighth embodiment is different from the seventh
embodiment in that the user is notified of the abnormal state of
the panel and the failsafe mode is selected before discharge
occurs. As a failsafe setting criterion for "MODE 2" or "MODE 3" in
estimating discharge, when changes in potential amounts of a
plurality of surface potential electrodes 3417 exceed the set value
of the change amount, or when the potential amount steeply changes,
"MODE 3" is set. When the number of electrodes which exhibit
potentials exceeding the set value is small, the influence on the
panel is determined to be small, and "MODE 2" is selected.
Processing (steps S116, S117, and S118) after selecting "MODE 21"
or "MODE 3" is the same as in the seventh embodiment, and a
description thereof will be omitted.
[0309] Similar to the seventh embodiment, the notice to the user
may be output to an indicator 3562 or a speaker 3563 mounted on the
front surface of the display, as shown in FIG. 38.
[0310] As described above, the eighth embodiment realizes
estimation of the internal state of the panel and failsafe control
by detecting the gradients of temporal changes in potentials of a
plurality of surface potential electrodes.
[0311] In the eighth embodiment, generation of discharge is
estimated from the change amount of the surface potential.
Generation of discharge can also be predicted by comparing the
absolute value of a surface potential measured by the comparator
35211 and detection unit 35212 with the set value, and if the
measured value exceeds the set value, outputting a signal from the
detection unit 35212 to the determination circuit 35214. In this
case, the comparator 35211 and detection unit 35212 constitute a
comparison means, and the comparison means and determination
circuit 35214 constitute a discharge prediction means.
[0312] In both the seventh and eighth embodiments, the message
indicator 3562 is of a scheme of displaying a message to the user,
but may be of another scheme of notifying an abnormal state by
turning on, e.g., a lamp or LED. In addition, the speaker 3563 may
output warning sound other than voice as long as the user can
recognize an abnormal state.
[0313] The surface potential measurement electrode 3417 is arranged
outside the device area within the panel. However, the number of
electrodes, the arrangement position, and the electrode shape are
not particularly limited. To accurately detect discharge, the
number of electrodes may be increased. The electrode may be
arranged near the device as close as possible.
[0314] According to the image display apparatus of the present
invention, face-safe control can be executed for the display
apparatus by predicting generation of discharge or the state in
which discharge readily occurs. Moreover, the atmosphere in the
display apparatus can be estimated by providing a means for
detecting generated discharge and recording the history of the
generation time and date of the discharge.
[0315] By this means, the user (operator) can be notified of an
abnormality (state) by a warning output (display or voice).
[0316] As a result, the panel or user can be protected, and a
high-reliability display apparatus can be provided.
<Manufacturing Method of Multi Electron Source>
[0317] A method of manufacturing the multi electron source used in
the display panel of this embodiment will be described below. In
the multi electron source used in the image display apparatus of
this embodiment, any type of electron emission devices, and any
material, shape, and manufacturing method for cold cathode device
devices may be employed, especially an electron source arranging
cold cathode devices in a simple matrix is preferable. Therefore,
cold cathode devices such as surface-conduction type emission
devices, FE type devices, or MIM type devices can be used.
[0318] Under circumstances where inexpensive display apparatuses
having large display areas are required, a surface-conduction type
emission device, of these cold cathode devices, is especially
preferable. More specifically, the electron-emitting characteristic
of an FE type device is greatly influenced by the relative
positions and shapes of the emitter cone and the gate electrode,
and hence a high-precision manufacturing technique is required to
manufacture this device. This poses a disadvantageous factor in
attaining a large display area and a low manufacturing cost.
According to an MIM type device, the thicknesses of the insulating
layer and the upper electrode must be decreased and made uniform.
This also poses a disadvantageous factor in attaining a large
display area and a low manufacturing cost. In contrast to this, a
surface-conduction type emission device can be manufactured by a
relatively simple manufacturing method, and hence an increase in
display area and a decrease in manufacturing cost can be attained.
The present inventors have also found that among the
surface-conduction type emission devices, an electron source having
an electron-emitting portion or its peripheral portion consisting
of a fine particle film is excellent in electron-emitting
characteristic and can be easily manufactured. Such a device can
therefore be most suitably used for the multi electron source of a
high-brightness, large-screen image display apparatus. For this
reason, in the display panel 101 of this embodiment,
surface-conduction type emission devices each having an
electron-emitting portion or its peripheral portion made of a fine
particle film are used. The basic structure and manufacturing
method of the preferred surface-conduction type emission device
will be described.
(Preferred Structure of Surface-Conduction Type Emission Device and
Preferred Manufacturing Method)
[0319] Typical examples of surface-conduction type emission devices
each having an electron-emitting portion or its peripheral portion
made of a fine particle film include two types of devices, namely
flat and step type devices.
(Flat Surface-Conduction Type Emission Device)
[0320] First, the structure and manufacturing method of a flat
surface-conduction type emission device will be described.
[0321] FIGS. 19A and 19B are a plan view and a sectional view,
respectively, for explaining the structure of the flat
surface-conduction type emission device.
[0322] Referring to FIGS. 19A and 19B, reference numeral 1011
denotes a substrate; 1102 and 1103, device electrodes; 1104, a
conductive thin film; 1105, an electron-emitting portion formed by
the forming processing; and 1113, a thin film formed by the
activation processing. As the substrate 1011, various glass
substrates of, e.g., quartz glass and soda-lime glass, various
ceramic substrates of, e.g., alumina, or any of those substrates
with an insulating layer formed thereon can be employed.
[0323] The device electrodes 1102 and 1103, provided in parallel to
the substrate 1011 and opposing to each other, comprise conductive
material. Examples of the material are metals such as Ni, Cr, Au,
Mo, W, Pt, Ti, Cu, Pd, and Ag, alloys of these metals, metal oxides
such as In.sub.2O.sub.3--SnO.sub.2, and semiconductors such as
polysilicon. These electrodes 1102 and 1103 can be easily formed by
the combination of a film-forming technique such as
vacuum-evaporation and a patterning technique such as
photolithography or etching, however, any other method (e.g.,
printing technique) may be employed.
[0324] The shape of the electrodes 1102 and 1103 is appropriately
designed in accordance with an application object of the
electron-emitting device. Generally, an interval L between
electrodes is designed by selecting an appropriate value in a range
from several hundred .ANG. to several hundred .mu.m. Most
preferable range for a display apparatus is from several .mu.m to
several ten .mu.m. As for electrode thickness d, an appropriate
value is selected in a range from several hundred .ANG. to several
.mu.m.
[0325] The conductive thin film 1104 comprises a fine particle
film. The "fine particle film" is a film which contains a lot of
fine particles (including masses of particles) as film-constituting
members. In microscopic view, normally individual particles exist
in the film at predetermined intervals, or in adjacent to each
other, or overlapped with each other.
[0326] One particle has a diameter within a range from several
.ANG. to thousand .ANG.. Preferably, the diameter is within a range
from 10 .ANG. to 200 .ANG.. The thickness of the fine particle film
is appropriately set in consideration of conditions as follows.
That is, condition necessary for electrical connection to the
device electrode 1102 or 1103, condition for the forming processing
to be described later, condition for setting electrical resistance
of the fine particle film itself to an appropriate value to be
described later etc. Specifically, the thickness of the film is set
in a range from several .ANG. to thousand .ANG., more preferably,
10 .ANG. to 500 .ANG..
[0327] Examples of the material used for forming the fine particle
film are metals such as Pd, Pt, Ru, Ag, Au, Ti, In, Cu, Cr, Fe, Zn,
Sn, Ta, W and Pb, oxides such as PdO, SnO.sub.2, In.sub.2O.sub.3,
PbO and Sb.sub.2O.sub.3, borides such as HfB.sub.2, ZrB.sub.2,
LaB.sub.6, CeB.sub.6, YB.sub.4, and GdB.sub.4, carbides such as
TiC, ZrC, HfC, TaC, SiC, and WC, nitrides such as TiN, ZrN, and
HfN, semiconductors such as Si and Ge, and carbons. Any material is
appropriately selected.
[0328] As described above, the conductive thin film 1104 is formed
with a fine particle film, and sheet resistance of the film is set
to reside within a range from 10.sup.3 to 10.sup.7
(.OMEGA./.quadrature.)
[0329] As it is preferable that the conductive thin film 1104 is
electrically connected to the device electrodes 1102 and 1103, they
are arranged so as to overlap with each other at one portion. In
FIG. 19A, the respective parts overlap in the order of the
substrate, device electrodes, and conductive thin film from the
bottom. However, they may overlap in the order of the substrate,
conductive thin film, and device electrodes from the bottom.
[0330] The electron-emitting portion 1105 is a fissured portion
formed at part of the conductive thin film 1104. The
electron-emitting portion 1105 has a resistance characteristic
higher than peripheral conductive thin film. The fissure is formed
by the forming processing to be described later on the conductive
thin film 1104. In some cases, particles, having a diameter of
several .ANG. to several hundred .ANG., are arranged within the
fissured portion. As it is difficult to exactly illustrate actual
position and shape of the electron-emitting portion, therefore,
FIGS. 19A and 19B show the fissured portion schematically.
[0331] The thin film 1113 made of carbon or a carbon compound
covers the electron-emitting portion 1115 and its peripheral
portion. The thin film 1113 is formed by the activation processing
to be described later after the forming processing.
[0332] The thin film 1113 is preferably made of graphite
monocrystalline, graphite polycrystalline, amorphous carbon, or
mixture thereof, and the thickness is 500 .ANG. or less and more
preferably, 300 .ANG. or less. As it is difficult to exactly
illustrate actual position or shape of the thin film 1113, FIGS.
19A and 19B show the film schematically. FIG. 19A shows the device
where part of the thin film 1113 is removed.
[0333] The preferred basic structure of the surface-conduction type
emission device is as described above. In the embodiment, the
device has the following constituents.
[0334] That is, the substrate 1011 comprises a soda-lime glass, and
the device electrodes 1102 and 1103, an Ni thin film. The electrode
thickness d is 1,000 .ANG. and the electrode interval L is 2
.mu.m.
[0335] The main material of the fine particle film is Pd or PdO.
The thickness of the fine particle film is about 100 .ANG., and its
width W is 100 .mu.m.
[0336] Next, a method of manufacturing a preferred flat
surface-conduction type emission device will be described with
reference to FIGS. 20A to 20D which are sectional views showing the
manufacturing processes of the surface-conduction type emission
device. Note that reference numerals are the same as those in FIGS.
19B and 19A.
[0337] (1) First, as shown in FIG. 20A, the device electrodes 1102
and 1103 are formed on the substrate 1011.
[0338] In forming the device electrodes 1102 and 1103, the
substrate 1011 is fully washed with a detergent, pure water and an
organic solvent, then, material of the device electrodes is
deposited there. (As a depositing method, a vacuum film-forming
technique such as evaporation and sputtering may be used.)
Thereafter, patterning using a photolithography etching technique
is performed on the deposited electrode material. Thus, the pair of
device electrodes (1102 and 1103) shown in FIG. 19A are formed.
[0339] (2) Next, as shown in FIG. 20B, the conductive thin film
1104 is formed. In forming the conductive thin film 1104, first, an
organic metal solvent is applied to the substrate 1011 in FIG. 20A,
and then the applied solvent is dried and sintered, thus forming a
fine particle film. Thereafter, the fine particle film is patterned
into a predetermined shape by the photolithography etching method.
The organic metal solvent means a solvent of organic metal compound
containing material of minute particles, used for forming the
conductive thin film, as main component. (More specifically, Pd is
used in this embodiment. In the embodiment, application of organic
metal solvent is made by dipping, however, any other method such as
a spinner method and spraying method may be employed.)
[0340] As a film-forming method of the conductive thin film made
with the minute particles, the application of organic metal solvent
used in the embodiment can be replaced with any other method such
as a vacuum evaporation method, a sputtering method or a chemical
vapor-phase accumulation method.
[0341] (3) Then, as shown in FIG. 20C, appropriate voltage is
applied between the device electrodes 1102 and 1103, from a power
source 1110 for the forming processing, then the forming processing
is performed, thus forming the electron-emitting portion 1105.
[0342] The forming processing here is electric energization of a
conductive thin film 1104, for example, made of a fine particle
film to appropriately destroy, deform, or deteriorate part of the
conductive thin film, thus changing the film to have a structure
suitable for electron emission. In the conductive thin film made of
the fine particle film, the portion changed for electron emission
(i.e., electron-emitting portion 1105) has an appropriate fissure
in the thin film. Comparing the thin film 1104 having the
electron-emitting portion 1105 with the thin film before the
forming processing, the electrical resistance measured between the
device electrodes 1102 and 1103 has greatly increased.
[0343] The electrification method will be explained in more detail
with reference to FIG. 21 showing an example of the waveform of
appropriate voltage applied from the forming power source 1110.
Preferably, in case of forming a conductive thin film of a fine
particle film, a pulse-like voltage is employed. In this
embodiment, as shown in FIG. 21, a triangular-wave pulse having a
pulse width T1 is continuously applied at pulse interval of T2.
Upon application, a wave peak value Vpf of the triangular-wave
pulse is sequentially increased. Further, a monitor pulse Pm to
monitor status of forming the electron-emitting portion 1105 is
inserted between the triangular-wave pulses at appropriate
intervals, and current that flows at the insertion is measured by a
galvanometer 1111.
[0344] In this embodiment, in 10.sup.-5 Torr vacuum atmosphere, the
pulse width T1 is set to 1 msec; and the pulse interval T2, to 10
msec. The wave peak value Vpf is increased by 0.1 V, at each pulse.
Each time the triangular-wave has been applied for five pulses, the
monitor pulse Pm is inserted. To avoid ill-effecting the forming
processing, a voltage Vpm of the monitor pulse is set to 0.1 V.
When the electrical resistance between the device electrodes 1102
and 1103 becomes 1.times.10.sup.6, i.e., the current measured by
the galvanometer 1111 upon application of monitor pulse becomes
1.times.10.sup.-7 A or less, the electrification of the forming
processing is terminated.
[0345] Note that the above processing method is preferable for the
surface-conduction type emission device of this embodiment. In case
of changing the design of the surface-conduction type emission
device concerning, e.g., the material or thickness of the fine
particle film, or the device electrode interval L, the conditions
for electrification are preferably changed in accordance with the
change of device design.
[0346] (4) Next, as shown in FIG. 20D, appropriate voltage is
applied, from an activation power source 1112, between the device
electrodes 1102 and 1103, and the activation processing is
performed to improve electron-emitting characteristic.
[0347] The activation processing here is electrification of the
electron-emitting portion 1105 formed by the forming processing, on
appropriate conditions, for depositing carbon or carbon compound
around the electron-emitting portion 1105. (In FIG. 20D, the
deposited material of carbon or carbon compound is shown as
material 1113.) Comparing the electron-emitting portion 1105 with
that before the activation processing, the emission current at the
same application voltage has become typically 100 times or
more.
[0348] The activation is made by periodically applying a voltage
pulse in 10.sup.-4 or 10.sup.-5 Torr vacuum atmosphere, to
accumulate carbon or carbon compound mainly derived from an organic
compound existing in the vacuum atmosphere. The accumulated
material 1113 is any of graphite monocrystalline, graphite
polycrystalline, amorphous carbon or mixture thereof. The thickness
of the accumulated material 1113 is 500 .ANG. or less, more
preferably, 300 .ANG. or less.
[0349] The electrification method will be described in more detail
with reference to FIG. 22A showing an example of the waveform of
appropriate voltage applied from the activation power source 1112.
In this embodiment, the activation processing is performed by
periodically applying a rectangular wave at a predetermined
voltage. A rectangular-wave voltage Vac is set to 14 V; a pulse
width T3, to 1 msec; and a pulse interval T4, to 10 msec. Note that
the above electrification conditions are preferable for the
surface-conduction type emission device of the embodiment. In the
case in which the design of the surface-conduction type emission
device is changed, the electrification conditions are preferably
changed in accordance with the change of device design.
[0350] In FIG. 20D, reference numeral 1114 denotes an anode
electrode, connected to a direct-current (DC) high-voltage power
source 1115 and a galvanometer 1116, for capturing emission current
Ie emitted by the surface-conduction type emission device. (In the
case in which the substrate 1011 is incorporated into the display
panel before the activation processing, the Al layer on the
fluorescent surface of the display panel is used as the anode
electrode 1114). While applying voltage from the activation power
source 1112, the galvanometer 1116 measures the emission current
Ie, thus monitors the progress of activation processing, to control
operation of the activation power source 1112. FIG. 22B shows an
example of the emission current Ie measured by the galvanometer
1116. As application of pulse voltage from the activation power
source 1112 is started in this manner, the emission current Ie
increases with elapse of time, gradually comes into saturation, and
almost never increases then. At the substantial saturation point,
the voltage application from the activation power source 1112 is
stopped, then the activation processing is terminated.
[0351] Note that the above electrification conditions are
preferable for the surface-conduction type emission device of the
embodiment. In case of changing the design of the
surface-conduction type emission device, the conditions are
preferably changed in accordance with the change of device
design.
[0352] As described above, the surface-conduction type emission
device as shown in FIG. 20E is manufactured.
(Step Type of Surface-Conduction Type Emission Device)
[0353] Next, another typical structure of the surface-conduction
type emission device where an electron-emitting portion or its
peripheral portion is formed of a fine particle film, i.e., a step
type of surface-conduction type emission device will be
described.
[0354] FIG. 23 is a sectional view schematically showing the basic
construction of the step surface-conduction type emission device.
Referring to FIG. 23, reference numeral 1201 denotes a substrate;
1202 and 1203, device electrodes; 1206, a step-forming member for
making height difference between the electrodes 1202 and 1203;
1204, a conductive thin film using a fine particle film; 1205, an
electron-emitting portion formed by the forming processing; and
1213, a thin film formed by the activation processing.
[0355] The difference between the step and flat devices is that one
of the device electrodes (1202 in this example) is formed on the
step-forming member 1206 and the conductive thin film 1204 covers
the side surface of the step-forming member 1206. The device
interval L in FIG. 19A is set in this structure as a height
difference Ls corresponding to the height of the step-forming
member 1206. Note that the substrate 1201, device electrodes 1202
and 1203, and conductive thin film 1204 using the fine particle
film can comprise the materials given in the explanation of the
flat surface-conduction type emission device. Further, the
step-forming member 1206 contains an electrically isolating
material such as SiO.sub.2.
[0356] Next, a method of manufacturing the step surface-conduction
type emission device will be described.
[0357] FIGS. 24A to 24F which are sectional views showing the
manufacturing processes. In these figures, reference numerals of
the respective parts are the same as those in FIG. 23.
[0358] (1) First, as shown in FIG. 24A, the device electrode 1203
is formed on the substrate 1201.
[0359] (2) Next, as shown in FIG. 24B, an insulating layer for
forming the step-forming member is deposited. The insulating layer
may be formed by accumulating, e.g., SiO.sub.2 by a sputtering
method, however, the insulating layer may be formed by a
film-forming method such as a vacuum evaporation method or a
printing method.
[0360] (3) As shown in FIG. 24C, the device electrode 1202 is
formed on the insulating layer.
[0361] (4) As shown in FIG. 24D, part of the insulating layer is
removed by using, e.g., an etching method, to expose the device
electrode 1203.
[0362] (5) As shown in FIG. 24E, the conductive thin film 1204
using the fine particle film is formed. Upon formation, similar to
the above-described flat device structure, a film-forming technique
such as an applying method is used.
[0363] (6) Similar to the flat device structure, the forming
processing is performed to form an electron-emitting portion. (The
forming processing similar to that explained using FIG. 20C may be
performed).
[0364] (7) Similar to the flat device structure, the activation
processing is performed to deposit carbon or carbon compound around
the electron-emitting portion. (Activation processing similar to
that explained using FIG. 20D may be performed).
[0365] As described above, the step surface-conduction type
emission device shown in FIG. 24F is manufactured.
(Characteristic of Surface-Conduction Type Emission Device Used in
Display Apparatus)
[0366] The structure and manufacturing method of the flat
surface-conduction type emission device and those of the step
surface-conduction type emission device are as described above.
Next, the characteristic of the electron-emitting device used in
the display apparatus will be described below.
[0367] FIG. 25 shows a typical example of (emission current Ie) to
(device voltage (i.e., voltage to be applied to the device) Vf)
characteristic and (device current If) to (device application
voltage Vf) characteristic of the device used in the display
apparatus. Note that compared with the device current If, the
emission current Ie is very small, therefore it is difficult to
illustrate the emission current Ie by the same measure of that for
the device current If. In addition, these characteristics change
due to change of designing parameters such as the size or shape of
the device. For these reasons, two lines in the graph of FIG. 25
are respectively given in arbitrary units.
[0368] Regarding the emission current Ie, the device used in the
display apparatus has three characteristics as follows:
[0369] First, when voltage of a predetermined level (referred to as
"threshold voltage V.sub.th") or more is applied to the device, the
emission current Ie drastically increases, however, with voltage
lower than the threshold voltage V.sub.th, almost no emission
current Ie is detected. That is, regarding the emission current Ie,
the device has a nonlinear characteristic based on the clear
threshold voltage V.sub.th.
[0370] Second, the emission current Ie changes in dependence upon
the device application voltage Vf. Accordingly, the emission
current Ie can be controlled by changing the device voltage Vf.
[0371] Third, the emission current Ie is output quickly in response
to application of the device voltage Vf to the device. Accordingly,
an electrical charge amount of electrons to be emitted by the
device can be controlled by changing period of application of the
device voltage Vf.
[0372] The surface-conduction type emission device with the above
three characteristics is preferably applied to the display
apparatus. For example, in a display apparatus having a large
number of devices provided corresponding to the number of pixels of
a display screen, if the first characteristic is utilized, display
by sequential scanning of display screen is possible. This means
that the threshold voltage V.sub.th or more is appropriately
applied to a driven device in accordance with a desired emission
luminance, while voltage lower than the threshold voltage V.sub.th
is applied to an unselected device. In this manner, sequentially
changing the driven devices enables display by sequential scanning
of display screen.
[0373] Further, emission luminance can be controlled by utilizing
the second or third characteristic, which enables gradation
display.
[0374] FIG. 26 is a block diagram showing an example of a display
apparatus capable of displaying image information provided from
various image information sources such as television broadcasting
on a display panel using the surface-conduction type emission
device of this embodiment as an electron source. Referring to FIG.
26, reference numeral 2100 denotes a display panel; 2101, a driving
circuit for the display panel; 2102, a display controller; 2103, a
multiplexer; 2104, a decoder; 2105, an I/O interface circuit; 2106,
a CPU; 2107, an image generation circuit; 2108, 2109, and 2110,
image memory interface circuits; 2111, an image input interface
circuit; 2112 and 2113, TV signal reception circuits; and 2114, an
input portion.
[0375] In the display apparatus of this embodiment, upon reception
of a signal containing both video information and audio information
such as a TV signal, the video information is displayed while the
audio information is reproduced. A description of a circuit or a
speaker for reception, division, reproduction, processing, storage,
or the like of the audio information, which is not directly related
to the features of the present invention, will be omitted. The
functions of the respective parts will be explained in accordance
with the flow of an image signal.
[0376] The TV signal reception circuit 2113 receives a TV image
signal transmitted using a radio transmission system such as radio
waves or spatial optical communication. The scheme of the TV signal
to be received is not particularly limited, and is the NTSC scheme,
the PAL scheme, the SECAM scheme, or the like. A more preferable
signal source to take the advantages of the display panel realizing
a large area and a large number of pixels is a TV signal (e.g., a
so-called high-quality TV of the MUSE scheme or the like) made up
of a larger number of scanning lines than that of the TV signal of
the above scheme. The TV signal received by the TV signal reception
circuit 2113 is output to the decoder 2104.
[0377] The TV signal reception circuit 2112 receives a TV image
signal transmitted using a wire transmission system such as a
coaxial cable or optical fiber. The scheme of the TV signal to be
received is not particularly limited, as in the TV signal reception
circuit 2113. The TV signal received by the circuit 2112 is also
output to the decoder 2104.
[0378] The image input interface circuit 2111 receives an image
signal supplied from an image input device such as a TV camera or
image read scanner, and outputs it to the decoder 2104. The image
memory interface circuit 2110 receives an image signal stored in a
video tape recorder (to be briefly referred to as a VTR
hereinafter), and outputs it to the decoder 2104. The image memory
interface circuit 2109 receives an image signal stored in a video
disk, and outputs it to the decoder 2104. The image memory
interface circuit 2108 receives an image signal from a device
storing still image data such as a so-called still image disk, and
outputs the received still image data to the decoder 2104.
[0379] The I/O interface circuit 2105 connects the display
apparatus to an external computer, computer network, or output
device such as a printer. The I/O interface circuit 2105 allows
inputting/outputting image data, character data, and graphic
information, and in some cases inputting/outputting a control
signal and numerical data between the CPU 2106 of the display
apparatus and an external device.
[0380] The image generation circuit 2107 generates display image
data on the basis of image data or character/graphic information
externally input via the I/O interface circuit 2105, or image data
or character/graphic information output from the CPU 2106. This
circuit 2107 incorporates circuits necessary to generate images
such as a programmable memory for storing image data and
character/graphic information, a read-only memory storing image
patterns corresponding to character codes, and a processor for
performing image processing. Display image data generated by the
circuit 2107 is output to the decoder 2104. In some cases, display
image data can also be input/output from/to an external computer
network or printer via the I/O interface circuit 2105.
[0381] The CPU 2106 mainly performs control of operation of this
display apparatus, and operations about generation, selection, and
editing of display images. For example, the CPU 2106 outputs a
control signal to the multiplexer 2103 to properly select or
combine image signals to be displayed on the display panel. At this
time, the CPU 2106 generates a control signal to the display panel
controller 2102 in accordance with the image signals to be
displayed, and appropriately controls operation of the display
apparatus in terms of the screen display frequency, the scanning
method (e.g., interlaced or non-interlaced scanning), the number of
scanning lines for one frame, and the like. The CPU 2106 directly
outputs image data or character/graphic information to the image
generation circuit 2107. In addition, the CPU 2106 accesses an
external computer or memory via the I/O interface circuit 2105 to
input image data or character/graphic information. The CPU 2106 may
also be concerned with operations for other purposes. For example,
the CPU 2106 can be directly concerned with the function of
generating and processing information, like a personal computer or
word processor. Alternatively, the CPU 2106 may be connected to an
external computer network via the I/O interface circuit 2105 to
perform operations such as numerical calculation in cooperation
with the external device.
[0382] The input portion 2114 allows the user to input an
instruction, program, or data to the CPU 2106. As the input portion
2114, various input devices such as a joystick, bar code reader,
and speech recognition device are available in addition to a
keyboard and mouse.
[0383] The decoder 2104 inversely converts various image signals
input from the circuits 2107 to 2113 into three primary color
signals, or a luminance signal and I and Q signals. As is indicated
by the dotted line in FIG. 26, the decoder 2104 desirably
incorporates an image memory in order to process a TV signal of the
MUSE scheme or the like which requires an image memory in inverse
conversion. This image memory advantageously facilitates display of
a still image, or image processing and editing such as thinning,
interpolation, enlargement, reduction, and synthesis of images in
cooperation with the image generation circuit 2107 and CPU
2106.
[0384] The multiplexer 2103 appropriately selects a display image
on the basis of a control signal input from the CPU 2106. More
specifically, the multiplexer 2103 selects a desired one of the
inversely converted image signals input from the decoder 2104, and
outputs the selected image signal to the driving circuit 2101. In
this case, the image signals can be selectively switched within a
1-frame display time to display different images in a plurality of
areas of one frame, like a so-called multiwindow television.
[0385] The display panel controller 2102 controls operation of the
driving circuit 2101 on the basis of a control signal input from
the CPU 2106.
[0386] As for the basic operation of the display panel, the display
panel controller 2102 outputs, e.g., a signal for controlling the
operation sequence of a driving power source (not shown) of the
display panel to the driving circuit 2101. As for the method of
driving the display panel, the display panel controller 2102
outputs, e.g., a signal for controlling the screen display
frequency or scanning method (e.g., interlaced or non-interlaced
scanning) to the driving circuit 2101. In some cases, the display
panel controller 2102 outputs to the driving circuit 2101 a control
signal about adjustment of the image quality such as the
brightness, contrast, color tone, or sharpness of a display
image.
[0387] The driving circuit 2101 generates a driving signal to be
applied to the display panel 2100, and operates based on an image
signal input from the multiplexer 2103 and a control signal input
from the display panel controller 2102.
[0388] The functions of the respective parts have been described.
The arrangement of the display apparatus shown in FIG. 26 makes it
possible to display image information input from various image
information sources on the display panel 2100. More specifically,
various image signals such as television broadcasting image signals
are inversely converted by the decoder 2104, appropriately selected
by the multiplexer 2103, and supplied to the driving circuit 2101.
On the other hand, the display controller 2102 generates a control
signal for controlling operation of the driving circuit 2101 in
accordance with an image signal to be displayed. The driving
circuit 2101 applies a driving signal to the display panel 2100 on
the basis of the image signal and control signal. As a result, the
image is displayed on the display panel 2100. A series of
operations are systematically controlled by the CPU 2106.
[0389] In the display apparatus of this embodiment, the image
memory incorporated in the decoder 2104, the image generation
circuit 2107, and the CPU 2106 can cooperate with each other to
simply display selected ones of a plurality of pieces of image
information and to perform, for the image information to be
displayed, image processing such as enlargement, reduction,
rotation, movement, edge emphasis, thinning, interpolation, color
conversion, and conversion of the aspect ratio of an image, and
image editing such as synthesis, erasure, connection, exchange, and
pasting. Although not described in this embodiment, an audio
circuit for processing and editing audio information may be
arranged, similar to the image processing and the image
editing.
[0390] The display apparatus of this embodiment can therefore
function as a display device for television broadcasting, a
terminal device for video conferences, an image editing device
processing still and dynamic images, a terminal device for a
computer, an office terminal device such as a word processor, a
game device, and the like. This display apparatus are useful for
industrial and business purposes and can be variously applied.
[0391] FIG. 26 merely shows an example of the arrangement of the
display apparatus using the display panel having the
surface-conduction type emission device as an electron source. The
present invention is not limited to this, as a matter of course.
For example, among the constituents in FIG. 26, a circuit
associated with a function unnecessary for the application purpose
can be eliminated from the display apparatus. To the contrary,
another constituent can be added to the display apparatus in
accordance with the application purpose. For example, when the
display apparatus of this embodiment is used as a television
telephone set, transmission and reception circuits including a
television camera, audio microphone, lighting, and modem are
preferably added as constituents.
[0392] In the display apparatus of this embodiment, since
particularly the display panel using the surface-conduction type
emission device as an electron source can be easily made thin, the
width of the whole display apparatus can be decreased. In addition
to this, the display panel using the surface-conduction type
emission device as an electron source is easily increased in screen
size and has a high brightness and a wide view angle. This display
apparatus can therefore display an impressive image with reality
and high visibility.
[0393] The present invention is not limited to the above
embodiments and various changes and modifications can be made
within the spirit and scope of the present invention. Therefore, to
apprise the public of the scope of the present invention, the
following claims are made.
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