U.S. patent application number 10/465878 was filed with the patent office on 2003-12-18 for current-driven light-emitting display apparatus and method of producing the same.
This patent application is currently assigned to Seiko Epson Corporation. Invention is credited to Itoh, Tomoyuki, Kimura, Mutsumi.
Application Number | 20030231273 10/465878 |
Document ID | / |
Family ID | 26371058 |
Filed Date | 2003-12-18 |
United States Patent
Application |
20030231273 |
Kind Code |
A1 |
Kimura, Mutsumi ; et
al. |
December 18, 2003 |
Current-driven light-emitting display apparatus and method of
producing the same
Abstract
A method for producing an organic EL display device is
disclosed. The display device comprises a substrate, a transistor
disposed on the substrate, a flattened inter-layer insulation film
covering the transistor, a pixel electrode, and an organic EL
layer.
Inventors: |
Kimura, Mutsumi; (Suwa-shi,
JP) ; Itoh, Tomoyuki; (Okaya-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Seiko Epson Corporation
Tokyo
JP
|
Family ID: |
26371058 |
Appl. No.: |
10/465878 |
Filed: |
June 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10465878 |
Jun 20, 2003 |
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10224412 |
Aug 21, 2002 |
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10224412 |
Aug 21, 2002 |
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09155644 |
Oct 2, 1998 |
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6462722 |
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09155644 |
Oct 2, 1998 |
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PCT/JP98/00655 |
Feb 17, 1998 |
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Current U.S.
Class: |
349/139 ;
438/30 |
Current CPC
Class: |
H01L 27/1255 20130101;
H01L 51/5206 20130101; G09G 2300/0439 20130101; G09G 3/3266
20130101; G09G 3/3233 20130101; G09G 2300/0842 20130101; G09G
2300/0876 20130101; H05B 44/00 20220101; G09G 2300/0819 20130101;
G09G 2320/043 20130101; G09G 2300/0417 20130101; G09G 3/3291
20130101; G09G 3/3225 20130101; H01L 27/3248 20130101; H01L 27/3244
20130101; G09G 2310/06 20130101; H01L 51/5234 20130101; G09G
2300/0866 20130101; H01L 2251/5315 20130101; Y02B 20/30
20130101 |
Class at
Publication: |
349/139 ;
438/30 |
International
Class: |
H01L 021/00; G02F
001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 1997 |
JP |
9-32474 |
Mar 19, 1997 |
JP |
9-66046 |
Claims
What is claimed is:
1. A method for producing a display, the steps comprising: forming
a transistor on a substrate; forming and flattening an inter-layer
insulation film over the transistor, forming a contact hole in the
inter-layer insulation film; forming a pixel electrode on the
inter-layer insulation film; and forming an organic EL layer in a
pixel region corresponding to the pixel electrode, the transistor
being connected to the pixel electrode through the contact
hole.
2. A method for producing a display, the steps comprising: forming
a transistor on a substrate; forming a first inter-layer insulation
film over the transistor; forming and flattening a second
inter-layer insulation film over the first inter-layer insulation
film; forming a pixel electrode on the flattened second inter-layer
insulation film; forming an organic EL layer in a pixel region
corresponding to the pixel electrode; and forming a contact hole in
the first inter-layer insulation film and the second inter-layer
insulation film, the transistor being connected to the pixel
electrode through the contact hole.
3. A method for producing a display, the steps comprising: forming
a transistor on a substrate; forming a first inter-layer insulation
film over the transistor; forming a first contact hole in the first
inter-layer insulation film, the transistor being connected to an
electrode layer through the first contact hole; forming and
flattening a second inter-layer insulation film over the first
inter-layer insulation film and the electrode layer; forming a
pixel electrode on the second inter-layer insulation film after the
flattening process of the second inter-layer insulation film;
forming an organic EL layer in a pixel region corresponding to the
pixel electrode; and forming a second contact hole in the second
inter-layer insulation film, the transistor being connected to the
pixel electrode through the second contact hole.
4. The method according to claim 1, further comprising forming a
bank layer for defining the pixel region.
5. The method according to claim 1, the forming of the organic EL
layer being performed by an ink-jet method.
6. A display, comprising: a substrate; a transistor disposed on the
substrate; a flattened inter-layer insulation film covering the
transistor; a pixel electrode formed on the flattened inter-layer
insulation film; and an organic EL layer disposed between the pixel
electrode and a counter electrode.
7. The display according to claim 6, further comprising a contact
hole, the transistor being connected to the pixel electrode through
the contact hole.
8. The display according to claim 6, the organic EL layer being
surrounded by a bank layer.
9. The display according to claim 8, the bank layer being formed on
the inter-layer insulation film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The invention relates to a display apparatus in which a
current-driven light-emitting device such as an organic electro
luminescence (hereinafter referred to a "EL") display device, are
driven by using thin-film transistors. More particularly, the
invention relates to a current-driven light-emitting display
apparatus driven by thin-film-transistors, which realizes the
suppression of deterioration with time, and to a method of
producing the same.
[0003] 2. Description of Related Art
[0004] The inventor of this invention carefully examined organic EL
display devices driven by thin-film transistors, and ascertained
the following facts.
[0005] (1) In an organic EL display device driven by thin-film
transistors, since the organic EL display device is a
direct-current device, direct current also runs through thin-film
transistors, which are connected in series to the EL device, for
the purpose of controlling it.
[0006] (2) Thin-film transistors are classified into an n-channel
type and a p-channel type. These types differ extremely in the
manner in which deterioration with time occurs.
[0007] Accordingly, an object of the present invention is to
suppress the deterioration with time of thin-film transistors in a
current luminescent device driven by the thin-film transistors.
SUMMARY OF THE INVENTION
[0008] (1) In the present invention, there is provided a
current-driven light-emitting display apparatus comprising a
plurality of scanning lines and a plurality of data lines,
thin-film transistors and current luminescent devices being formed
in positions corresponding to each of the intersections of the
scanning lines and the data lines, wherein at least one of the
thin-film transistors is a p-channel type thin-film transistor.
[0009] It is possible to suppress the deterioration with time of a
thin-film transistor with this apparatus.
[0010] (2) In the present invention, there is provided a
current-driven light-emitting display apparatus in which a
plurality of scanning lines a plurality of data lines, common
electrodes, and opposite electrodes are formed, with first
thin-film transistors being formed in positions corresponding to
the intersections of the scanning lines and the data lines, second
thin-film transistors, holding capacitors, pixel electrodes, and
current luminescent elements, the first thin-film transistors
controlling conductivity between the data lines and the holding
capacitors by the potentials of the scanning lines, the second
thin-film transistors controlling conductivity between the common
electrodes and the pixel electrodes by the potentials of the
holding capacitors, to thereby control the current which flows
through the current luminescent elements provided between the pixel
electrodes and the opposite electrodes wherein the second thin-film
transistors are p-channel type thin-film transistors.
[0011] (3) In the present invention, there is provided a
current-driven light-emitting display apparatus according to (1) or
(2), further comprising a driving circuit for driving the current
luminescent element, the driving circuit is comprised of the
plurality of scanning lines, the plurality of data lines, the
thin-film transistors, and the current luminescent elements, which
are disposed on the substrate, wherein the p-channel type thin-film
transistors are formed in the same step as the thin-film
transistors in the driving circuits.
[0012] (4) In the current-driven light-emitting display apparatus
according to any of (1) or (3), the thin-film transistors are
polysilicon thin-film transistors.
[0013] (5) The invention provides a current-driven light-emitting
display apparatus according to (3), wherein the drive circuits
comprise complementary type thin-film transistors, the first
thin-film transistors are formed in the same step as n-channel type
thin-film transistors in the driving circuits, and the second
thin-film transistors are formed in the same step as the p-channel
type thin-film transistors in the driving circuits.
[0014] According to (5), it is possible to provide a current-driven
light-emitting display apparatus, which exhibits high performance
with no deterioration with time, without increasing the number of
steps for producing the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a block diagram of the basic structure of a
display to which the present invention is applied;
[0016] FIG. 2 is an equivalent circuit diagram of a display device
equipped with thin-film transistors according to a first embodiment
of the present invention;
[0017] FIG. 3 is a drive voltage diagram of the display device
equipped with thin-film transistors according to the first
embodiment of the present invention;
[0018] FIG. 4 is a current-voltage characteristic chart of a
current-thin-film transistor according to the first embodiment of
the present invention;
[0019] FIG. 5 is a current-voltage characteristic chart of an
organic EL display device according to the first embodiment of the
present invention;
[0020] FIG. 6(a) is a sectional view of an organic display EL
device equipped with thin-film transistors according to the first
embodiment of the invention, and FIG. 6(b) is a plan view of an
organic display EL device according to the first embodiment of the
present invention;
[0021] FIG. 7 is an equivalent circuit diagram of an organic EL
display device equipped with thin-film transistors used in a second
embodiment of the present invention;
[0022] FIG. 8 is a drive-voltage diagram of an organic EL display
device equipped with thin-film transistors according to the second
embodiment of the present invention;
[0023] FIG. 9 is a current-voltage characteristic chart of a
current-thin-film transistor according to the second embodiment of
the present invention;
[0024] FIG. 10 is a current-voltage characteristic chart of an
organic EL display device according to the second embodiment of the
present invention;
[0025] FIG. 11(a) is a sectional view of an organic EL display
device equipped with thin-film transistors according to the second
embodiment of the present invention, and FIG. 11(b) is a plan view
of an organic EL display device equipped with thin-film transistors
according to the second embodiment of the present invention;
[0026] FIG. 12 is a chart showing the deterioration with time of an
n-channel type thin-film transistor;
[0027] FIG. 13 is a chart showing the deterioration with time of a
p-channel type thin-film transistor; and
[0028] FIGS. 14(a)-(d) are flow diagrams of the process for
producing a thin-film-transistor-drive organic EL display device
according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] (The General Structure of an Organic El Display Device)
[0030] Referring to the drawings, the preferred embodiments of the
present invention will be described.
[0031] As shown in FIG. 1, the center region of a substrate 1
constitutes a display part. In the outer periphery of the
transparent substrate 1, at the top side of the drawing, a
data-side drive circuit 3, which outputs image signals to data
lines 112, is arranged, and at the left side of the drawing, a
scanning-side drive circuit 4, which outputs scanning signals to
scanning lines 111, is arranged. In these drive circuits 3 and 4,
n-type thin-film transistors and p-type thin-film transistors form
complementary type TFTs. These complementary type thin-film
transistors are included in shift register circuits, level shift
circuits, analog switch circuits, etc.
[0032] Arranged on the transparent substrate 1 are a plurality of
scanning lines 111, and a plurality of data lines 112 extending in
a direction perpendicular to the direction in which the scanning
lines extend. The intersections of these data lines 112 and
scanning lines 111 constitute pixels 7 in the form of a matrix.
[0033] Formed in each of these pixels 7 is a first thin-film
transistor (hereinafter referred to as "a switching thin-film
transistor") 121, in which scanning signals are supplied to a gate
electrode 21 (a first gate electrode) through the scanning line
111. One end of the source/drain region of the switching thin-film
transistor 121 is electrically connected to a data line 112, while
the other end of the source/drain region is electrically connected
to a potential holding electrode 113. In addition, a common line
114 is disposed in parallel to the scanning line 111. Holding
capacitor 123 is formed between the common line 114 and the
potential holding electrode 113. The common line is maintained at a
controlled potential. Accordingly, when the switching thin-film
transistor 121 is turned ON through the selection by a scanning
signal, the image signal from the data line 112 is written to the
holding capacitor 123 through the switching thin-film
transistor.
[0034] The potential holding electrode 113 is electrically
connected to the gate electrode of second thin-film transistor 122
(hereinafter referred to as "a current-thin-film transistor"). The
one end of the source/drain region of the current-thin-film
transistor 122 is electrically connected to a common line 114,
while, the other end of the source/drain region is electrically
connected to one electrode 115 of a luminescent element 131. When
the current-thin-film transistor 122 is turned ON, the current of
the common line 114 flows to the luminescent element 131 of such as
an organic EL display device through the current-thin-film
transistor 122, so that the luminescent element 131 emits light.
Further, although one electrode of the holding capacitor is
connected to a common line 114 in this arrangement, it is also
possible for it to be connected to a capacitance line being
provided separately, instead of being connected to the common line
114. Alternatively, one electrode of the holding capacitor may be
connected to an adjacent gate line.
[0035] (First Embodiment)
[0036] FIG. 2 is a block diagram of an organic EL display device
equipped with thin-film transistors, according to a first
embodiment of the present invention. FIG. 3 is a drive voltage
diagram of an organic EL display device with thin-film transistors,
according to the first embodiment of the present invention. FIG. 4
is a current-voltage characteristic diagram of a current-thin-film
transistor according to the first embodiment of the present
invention. FIG. 5 is a current-voltage characteristic chart of an
organic EL display device, according to the first embodiment of the
present invention.
[0037] In FIG. 2, there are shown a scanning line 111, a data line
112, a holding electrode 113, a common line 114, a pixel electrode
formed of Al 115, an opposite electrode formed of ITO 116, a
switching thin-film transistor 121, an n-channel type
current-thin-film transistor 122, a holding capacitor 123, an
organic EL display element 131 (hereinafter referred to as "a
forward oriented organic EL display device") which is caused to
emit light by the current flowing to the pixel electrode 115 from
the opposite electrode 116, and the current directions of the
organic EL display device 131 and 141.
[0038] In FIG. 3, there are shown a scanning potential 211, a
signal potential 212, a holding potential 213, a common potential
214, a pixel potential 215, and a counter potential 216. FIG. 3,
only a part of each potential is shown to illustrate the respective
potential relationships. The potential of the scanning line 111
corresponds to the scanning potential 211; the potential of the
data line 112 corresponds to the signal potential 212; the
potential of the holding electrode 113 corresponds to the holding
potential 213; the potential of the common line 114 corresponds to
the common potential 214; the potential of the pixel electrode 115
formed of Al corresponds to the pixel potential 215; and the
potential of the opposite electrode 116 formed of ITO (Indium Tin
oxide) corresponds to the counter potential 216. FIG. 3 shows each
signal potential schematically and partially.
[0039] Numeral 221 indicates a period in which a pixel is in the
display-state, wherein current flows into the forward oriented
organic EL display element 131, so that it emits light, and numeral
222 indicates a period in which the pixel is in the non-display
state, wherein current does not flow into the forward oriented
organic EL display element 131, so that it does not emit light.
[0040] Referring to FIG. 4, a curve 31 indicates the
current-voltage characteristic of the n-channel type
current-thin-film transistor 122 as observed when the drain voltage
is 4V, and a curve 32 indicates the current-voltage characteristic
of the n-channel type current-thin-film transistor 122 as observed
when the drain voltage is 8V. Regarding either drain voltage, the
following facts can been seen. When the gate voltage is low, the
n-channel type current-thin-film transistor 122 is turned OFF and a
small amount of drain current flows demonstrating a high
source/drain resistance. When the gate voltage is high, the
n-channel type current-thin-film transistor 122 is turned ON and a
large amount of drain current flows demonstrating a low
source/drain resistance.
[0041] In FIG. 5, numeral 4 indicates the current-voltage
characteristic of the forward oriented organic EL display element
131. Here, the voltage represents the counter potential 216 against
the pixel potential 215, and the current represents the current
which flows to the pixel electrode 115 from the opposite electrode
116. The forward oriented organic EL display element 131 is OFF
when the voltage is not higher than a certain threshold voltage;
the resistance is high and allows no current to flow, so that the
device does not emit light. The device is ON when the voltage is
over a certain threshold voltage, and the resistance is low and
allows current to flow, so that the device emits light. In this
case, the threshold voltage is approximately 2V.
[0042] The operation of an organic EL display device equipped with
the thin-film transistors of this embodiment will be described with
reference to FIG. 2, FIG. 3, FIG. 4, and FIG. 5.
[0043] The switching thin-film transistor 121 controls the
conductivity between the data line 112 and the holding electrode
113 by means of the potential of the scanning line 111. In other
words, the scanning potential 211 controls the conductivity between
the signal potential 212 and the holding potential 213. While in
this example, the switching thin-film transistor 121 is an
n-channel type thin-film transistor, a p-channel type thin-film
transistor is also applicable.
[0044] For the period 221 in which the pixel is in the
display-state, the signal potential 212 is high, and the holding
potential 213 is retained at a high level. For the period 222 in
which the pixel is in the non-display state, the signal potential
212 is low, and the holding potential 213 is retained at a low
level.
[0045] The n-channel type current-thin-film transistor 122 has the
characteristic as shown in FIG. 3 and controls the conductivity
between the common line 114 and the pixel electrode 115 by means of
the potential of the holding electrode 113. In other words, the
holding potential 213 controls the conductivity between the common
potential 214 and the pixel potential 222. For the period 221 in
which the pixel is in the display-state, the holding potential 213
is high, so that the common line 114 is electrically connected to
the pixel electrode 115. For the period 222 in which the pixel is
in the non-display state, the holding potential 213 is low, so that
the common line 114 is disconnected from the pixel electrode
115.
[0046] The organic EL display element 131 has the characteristic as
shown in FIG. 5. For the period 221 in which the pixel is in the
display-state, the current flows between the pixel electrode 115
and the opposite electrode 116, so that the organic EL display
element 131 emits light. For the period 222 in which the pixel is
in the non-display state, no current flows, so that the device does
not emit light.
[0047] FIG. 6(a) is a sectional view of a thin-film transistor
organic EL display device (1 pixel) according to an embodiment of
the present invention. FIG. 6(b) is a plan view of a thin-film
transistor organic EL display device (1 pixel) according to an
embodiment of the present invention. The section taken along the
line A-A' of FIG. 6(a) corresponds to the section taken along the
line A-A' of FIG. 6(b).
[0048] In FIG. 6(a), numeral 132 indicates a hole injection layer,
numeral 133 indicates an organic EL layer, and numeral 151
indicates a resist.
[0049] In this example, the switching thin-film transistor 121 and
the n-channel type current-thin-film transistor 122 adopt the
structure and the process ordinarily used for a low-temperature
polysilicon thin-film transistor, which are used for thin-film
transistor liquid crystal display devices, i.e., a top-gate
structure and a process conducted in the condition that the maximum
temperature is 600.degree. C. or less. However, other structures
and processes are also applicable.
[0050] The forward oriented organic EL display element 131 is
formed by the pixel electrode 115 formed of Al, the opposite
electrode 116 formed of ITO, the hole injection layer 132, and the
organic EL layer 133. In the forward oriented organic EL display
element 131, the direction of current of the organic EL display
device, indicated at 141, can be set from the opposite electrode
116 formed of ITO to the pixel electrode 115 formed of Al. Further,
the structure of the organic EL display device is not restricted to
the one used here. Other structures are also applicable, as long as
the direction of current of the organic EL display device,
indicated at 141, can be set to the direction from the opposite
electrode to pixel electrode.
[0051] Here, the hole injection layer 132 and the organic EL layer
133 are formed by an ink-jet printing method, employing the resist
151 as a separating structure between the pixels, and the opposite
electrode 116 formed of ITO is formed by a sputtering method, yet
other methods are also applicable.
[0052] In this embodiment, the common potential 214 is lower than
the counter potential 216, and the current-thin-film transistor is
the n-channel type current-thin-film transistor 122.
[0053] In the period 221 in which the pixel is in the
display-state, the n-channel type current-thin-film transistor 122
is ON. The current which flows through the forward oriented organic
EL display element 131, i.e., the ON-current of the n-channel type
current-thin-film transistor 122 depends on the gate voltage, as
shown in FIG. 4. Here, the term "gate voltage" means the potential
difference between the holding potential 213 and the lower one of
the common potential 214 and the pixel potential 215. In this
embodiment, the common potential 214 is lower than the pixel
potential 215, so that the gate voltage indicates the potential
difference between the holding potential 213 and the common
potential 214. The potential difference can be sufficiently large,
so that a sufficiently large amount of ON-current is obtainable.
The ON-current of the n-channel type current-thin-film transistor
122 also depends on the drain voltage. However, this does not
affect the above situation.
[0054] Conversely, in order to obtain a necessary amount of
ON-current, the holding potential 213 can be made lower, and the
amplitude of the signal potential 212 and therefore the amplitude
of the scanning potential 211 can be decreased. In other words, in
the switching thin-film transistor 121 and the n-channel type
current-thin-film transistor 122, a decrease in drive voltage can
be achieved without entailing any loss in image quality, abnormal
operations, or a decrease in the frequency enabling them to
operate.
[0055] Further, in the embodiment of the present invention, the
signal potential 212 for the pixel to be in the display-state is
lower than the counter potential 216.
[0056] As stated above, in the period 221 in which the pixel is in
the display-state, the ON-current of the n-channel type
current-thin-film transistor 122 depends on the potential
difference between the holding potential 213 and the common
potential 214, but not directly on the potential difference between
the holding potential 213 and the counter potential 216. Thus, the
holding potential 213, i.e., the signal potential 212 for the pixel
to be in the display-state, can be made lower than the counter
potential 216, and therefore, the amplitude of the signal potential
212 and the amplitude of the scanning potential 211 can be
decreased, while retaining a sufficiently large ON-current in the
n-channel type current-thin-film transistor 122. That is, in the
switching thin-film transistor 121 and the n-channel type
current-thin-film transistor 122, a decrease in drive voltage can
be accomplished without entailing any loss in image quality,
abnormal operations, and a decrease in the frequency enabling them
to operate.
[0057] Moreover, in this embodiment, the signal potential 212 for
the pixel to be in the non-display-state is higher than the common
potential 214.
[0058] In the period 222 in which the pixel is in the
non-display-state, when the signal potential 212 becomes slightly
higher than the common potential 214, the n-channel type
current-thin-film transistor 122 is not completely turned OFF.
However, the source/drain resistance of the n-channel type
current-thin-film transistor 122 becomes considerably higher, as
shown in FIG. 4. Thus, the pixel potential 215, which is determined
by dividing the common potential 214 and the counter potential 216
by the values of the resistance of the n-channel type
current-thin-film transistor 122 and the resistance of the forward
oriented organic EL display element 131, becomes a potential close
to the counter potential 216.
[0059] The voltage which is applied to the forward oriented organic
EL display element 131 is the potential difference between the
pixel potential 215 and the counter potential 216. As shown in FIG.
5, the forward oriented organic EL display element 131 is turned
OFF when the voltage is not higher than a certain threshold
voltage, when no current flows, so that the display device does not
emit light. Namely, the utilization of a threshold potential of the
forward oriented organic EL display element 131 makes it possible
for the forward oriented organic EL display element 131 not to emit
light, even if the signal potential 212 is slightly higher than the
common potential 214, and the n-channel type current-thin-film
transistor 122 is not completely turned OFF.
[0060] Here, the amplitude of the signal potential 212, and
therefore the amplitude of the scanning potential 211 can be
decreased by making the signal potential 212 for the pixel to be in
the non-display state to be higher than the common potential 214.
In other words, with regard to the switching thin-film transistor
121 and the n-channel type current-thin-film transistor 122, a
decrease in drive potential can be accomplished without entailing
any loss of image quality, abnormal operations, or a decrease in
the frequency enabling them to operate.
[0061] The operation of an organic EL display device equipped with
the thin-film transistors of this embodiment is not as simple as
described above; it operates under a more complicated relationship
between voltage and current. However, the description above holds
true approximately and qualitatively.
[0062] (Second Embodiment)
[0063] FIG. 7 is an equivalent circuit diagram of an organic EL
display device equipped with thin-film transistors, according to
the second embodiment of the present invention. FIG. 8 is a drive
voltage diagram of the organic EL display device with thin-film
transistors, according to the second embodiment of the present
invention. FIG. 9 is a current-voltage characteristic chart of the
organic EL display device according to the second embodiment of the
present invention.
[0064] In FIG. 7, there are shown a pixel electrode formed of ITO
615, an opposite electrode formed of Al 616, a p-channel type
current-thin-film transistor 622, and an organic EL display device
631 (hereinafter referred to as "a reverse oriented organic EL
display device"), which is caused to emit light by the current
flowing to the opposite electrode 616 from the pixel electrode 615.
Numeral 641 indicates the direction of the current of the organic
EL display device. This direction is the reverse of that shown in
FIG. 2. Except for this, this embodiment is the same as the above
first embodiment shown in FIG. 2.
[0065] FIG. 8 is the same as FIG. 3 except that the level of each
potential is different from that of FIG. 3.
[0066] In FIG. 9, a curve 81 indicates a current-voltage
characteristic of a p-channel type current-thin-film transistor 622
as observed when the drain voltage is 4V. A curve 82 indicates a
current-voltage characteristic of the p-channel type
current-thin-film transistor 622 as observed when the drain voltage
is 8V.
[0067] In FIG. 10, a curve 9 indicates a current-voltage
characteristic of a reverse oriented organic EL display device
631.
[0068] The organic EL display device equipped with the thin-film
transistors of this embodiment operates in the same way as that of
the first embodiment, except that the potential relationship
regarding the current-thin-film transistor is reversed due to the
fact that the current-thin-film transistor is the p-channel type
thin-film transistor 622.
[0069] FIG. 11(a) is a sectional view of an organic EL display
device (1 pixel) equipped with the thin-film transistors, according
to the second embodiment of the present invention. FIG. 11(b) is a
plan view of a thin-film transistor organic EL display device (1
pixel), according to the second embodiment of the present
invention. The section taken along the line A-A' of FIG. 11(a)
corresponds to the section taken along the line A-A' of FIG.
11(b).
[0070] FIG. 11(a) is the same as FIG. 6(a), except that it shows a
hole injection layer 632 and an organic EL layer 633.
[0071] The reverse oriented organic EL display device 631 is formed
by means of the pixel electrode 615 formed of ITO, the opposite
electrode 616 formed of Al, the hole injection layer 632, and the
organic EL layer 633. In the reverse oriented organic EL display
device 631, the direction of current of the organic EL display
device, indicated at 641, can be set to the direction from the
pixel electrode 615 formed of ITO to the opposite electrode 616
formed of Al.
[0072] In this embodiment, a common potential 714 is higher than a
counter potential 716. Further, the current-thin-film transistor is
the p-channel type current-thin-film transistor 622.
[0073] In this embodiment, a signal potential 712 for the pixel to
be in the display-state is higher than the counter potential
716.
[0074] Furthermore, in this embodiment, the signal potential 712
for the pixel to be in the non-display-state is lower than the
common potential 714.
[0075] All of the effects of the thin-film transistor organic EL
display device of this embodiment are also the same as those of the
first embodiment, except that the potential relationship regarding
the current-thin-film transistor is reversed due to the fact that
the current-thin-film transistor is the p-channel type thin-film
transistor 622.
[0076] In this embodiment, the current-thin-film transistor 122 is
a p-channel type thin-film transistor. This arrangement enables the
deterioration with time of the current-thin-film transistor 122 to
significantly decrease. Furthermore, the arrangement adopting a
p-channel type polysilicon thin-film transistor enables the
deterioration with time of the current-thin-film transistor 122 to
decrease even further.
[0077] FIG. 14 is a diagram of a process of producing the
current-driven light-emitting display apparatus equipped with the
thin-film transistors, according to the embodiment of the present
invention described above.
[0078] As shown in FIG. 14(a), an amorphous silicon layer with a
thickness of 200 to 600 angstroms is deposited all over a substrate
1, and the amorphous silicon layer is poly-crystallized by laser
annealing etc., to form a polycrystalline silicon layer. After
this, patterning is performed on the polycrystalline silicon layer
to form a silicon thin-film 421, which serves as a source/drain
channel region of the switching thin-film transistor 121, a first
electrode 423 of the storage capacitor 123, and a silicon thin-film
422, which serves as a source/drain channel region of the
current-thin-film transistor 122. Next, an insulation film 424,
which serves as a gate insulation film, is formed over the silicon
thin-films 421, 422, and the first electrode 423. Then,
implantation of phosphorous (P) ions is selectively effected on the
first electrode 423 to lower the resistance thereof. Next, as shown
in FIG. 14(b), gate electrodes 111 and 111', which consist of TaN
layers, are formed on the silicon thin-films 421 and 422 through
the intermediation of the gate insulation film. Next, a resist mask
42 is formed on the silicon layer 422 serving as a
current-thin-film transistor, and phosphorous (P) ions are
implanted through self-alignment using the gate electrode as a mask
to form an n-type source/drain region in the silicon layer 421.
Subsequently, as shown in FIG. 14(c), a resist mask 412' is formed
on the first silicon layer 421 and the first electrode, and boron
(B) is ion-implanted in the silicon layer 422 through
self-alignment using the gate electrode 111' as a mask to form a
p-type source/drain region in the silicon layer 422. In this way,
an n-channel type impurity doping 411 allows the switching
thin-film transistor 121 to be formed. At this time, the
current-thin-film transistor 122 is protected by the resist mask
42, so that the n-channel type impurity doping 411 is not
performed. Then, a p-channel type impurity doping 412 allows the
current-thin-film transistor 122 to be formed.
[0079] Further, though not illustrated, in a case in which a shift
register of a drive circuit section which drives the switching
transistor 121, and a thin-film transistor constituting a sample
hold circuit etc., are to be formed on the same substrate, it is
possible to form them simultaneously in the same step of process as
has been described above.
[0080] A second electrode 425 of the storage capacitor may be
formed together with the gate electrodes 111 and 111'
simultaneously, either of the same or different materials.
[0081] As shown in FIG. 14(d), after the formation of an
inter-layer insulation film 43 and, then, contact holes, electrode
layers 426, 427, 428 and 429 formed of aluminum, ITO or the like
are formed.
[0082] Next, after an inter-layer insulation film 44 is formed and
flattened, contact holes are formed; then, ITO 45 is formed with a
thickness of 1000 to 2000 angstroms, preferably about 1600
angstroms, in such a manner that one electrode of the
current-thin-film transistor is connected thereto. For each pixel
region, bank layers 46 and 47, which are not less than 2.0 .mu.m in
width, are defined. Next, an organic EL layer 48 is formed by an
ink-jet method etc., in the region surrounded by the bank layers 46
and 47. After the organic EL layer 48 is formed, an
aluminum-lithium layer with a thickness of 6000 to 8000 angstroms
is deposited as an opposite electrode 49 on the organic EL layer
48. Between the organic EL layer 48 and the opposite electrode 49,
a hole injection layer may be disposed, as shown in FIG. 6(a).
[0083] The process mentioned above enables an organic EL display
device driven by means of a high-performance thin-film transistor
to be formed. Since polysilicon is much higher in the mobility of
carriers than amorphous-silicon, a rapid operation is possible.
[0084] In particular, in this embodiment, when the p-type
current-thin-film transistor 122 and the n-type switching thin-film
transistor 121 are formed, it is possible to form both of n-type
and p-type thin-film transistors, which are complementary type
thin-film transistors constituting a shift register of a drive
circuit, a sample hold circuit and the like, being simultaneously
formed in the above mentioned embodiment. The arrangement makes it
possible to realize a construction capable of decreasing the
deterioration with time of the current-thin-film transistor 122,
without increasing the number of production steps.
[0085] As described above, in the first embodiment, an n-channel
type current-thin-film transistor is used, and, in the second
embodiment, a p-channel type current-thin-film transistor is used.
Here, the deterioration with time of p-channel and n-channel type
thin-film transistors will be examined.
[0086] FIG. 12 and FIG. 13 are charts showing respectively the
deterioration with time of n-channel type and p-channel type
thin-film transistors, especially of polysilicon thin-film
transistors, under equivalent voltage application conditions.
Numerals 511 and 512 of FIG. 12 indicate the conductivity
characteristics of an n-channel type thin-film transistor, in the
cases in which Vd=4V and in which Vd=8V, respectively, before
voltage application. Numerals 521 and 522 indicate the conductivity
characteristics of an n-channel type thin-film transistor, in the
cases in which Vg=0V and Vd=15V and in which Vd=4V and Vd=8V,
respectively, after voltage application of approximately 1000
seconds. Numerals 811 and 812 of FIG. 13 indicate the conductivity
characteristics of a p-channel type thin-film transistor in the
cases in which Vd=4V, and in which Vd=8V, respectively, before
voltage application. Numerals 821 and 822 indicate the conductivity
characteristics of a p-channel type thin-film transistor in the
cases in which Vg=0V and Vd=15V, and in which Vd=4V and Vd=8V,
respectively, after voltage application for approximately 1000
seconds. It can be seen that in the p-channel type thin-film
transistor, the decrease of ON-current and the increase of
OFF-current are smaller than in the n-channel type.
[0087] Taking into consideration the difference in the
deterioration-with-time characteristic between the p-type and the
n-type thin-film transistors as shown in FIG. 12 and FIG. 13
respectively, at least either a switching thin-film transistor or a
current-thin-film transistor is formed of a p-channel type
thin-film transistor, especially a p-type polysilicon thin-film
transistor, whereby the deterioration with time can be suppressed.
Further, by forming the switching thin-film transistor as well as
the current-thin-film transistor of a p-type thin-film transistor,
it is possible to maintain the characteristics of the display
device.
[0088] While an organic EL display device is used as the
luminescent device in the embodiment described above, this should
not be construed restrictively, yet, it is needless to say that an
inorganic EL display device or other current-driven luminescent
devices are also applicable.
[0089] Industrial Applicability
[0090] The display apparatus according to the present invention can
be used as a display apparatus equipped with a current-driven
luminescent device such as an organic EL display device or an
inorganic EL display device, and a switching device to drive the
luminescent device, such as a thin-film transistor.
* * * * *