U.S. patent number 3,644,741 [Application Number 04/825,289] was granted by the patent office on 1972-02-22 for display screen using variable resistance memory semiconductor.
This patent grant is currently assigned to Energy Conversion Devices, Inc.. Invention is credited to Stanford R. Ovshinsky.
United States Patent |
3,644,741 |
Ovshinsky |
February 22, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
DISPLAY SCREEN USING VARIABLE RESISTANCE MEMORY SEMICONDUCTOR
Abstract
An electrically operated display screen including a support
surface on which active layers, preferably of electroluminescent
phosphor having a nonlinear voltage-brightness characteristic and
variable resistance memory semiconductor materials, are deposited
one adjacent the other with transparent conductive layers disposed
on either side thereof to provide electrode surfaces for connection
to an alternating current voltage source which substantially
excites the electroluminescent layer to generate relatively
high-intensity visible light in those areas thereof where the
variable resistance memory semiconductor material is in the
low-resistance condition. The layer of memory semiconductor
material has discrete portions which are individually alterable
between stable high- and low-resistance conditions by application
of predetermined amounts of energy to form the desired visible
light patterns on the display screen.
Inventors: |
Ovshinsky; Stanford R.
(Bloomfield Hills, MI) |
Assignee: |
Energy Conversion Devices, Inc.
(Troy, MI)
|
Family
ID: |
25243619 |
Appl.
No.: |
04/825,289 |
Filed: |
May 16, 1969 |
Current U.S.
Class: |
250/214LA;
365/111; 313/507; 365/113 |
Current CPC
Class: |
H05B
33/12 (20130101) |
Current International
Class: |
H05B
33/12 (20060101); H01l 017/00 () |
Field of
Search: |
;250/213,83.3IR
;340/173LS ;313/18A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stolwein; Walter
Claims
I claim:
1. An electrically operated display screen for displaying a lighted
pattern at a front side thereof and for receiving energy from a
side thereof to form or change the display pattern, said display
screen comprising: a first layer of conductive material; first and
second active layers in electrical connection along their
confronting surface areas, one of said first and second active
layers being disposed on said first layer of conductive material,
said one of said first and second active layers being an
electroluminescent material having means to emit light of at least
a given amount of intensity at selected portions thereof as a
result of a given exciting current and voltage across said selected
portions thereof, and the other of said first and second active
layers being a variable resistance memory semiconductor material
including means capable of having discrete portions thereof
selectively reversibly stably structurally changed in configuration
or conformation by only momentary application of said energy
thereto, selectively to one stable condition of high resistance or
a different stable structural condition of low resistance, said
different conditions of high and low resistance persisting
indefinitely after all sources of energy have been removed
therefrom, a second layer of conductive material disposed on one of
said first and second active layers in electrical connection along
the confronting surface areas thereof at the side remote from said
first layer of conductive material, the layer of conductive
material nearest said layer of variable resistance memory material
being transparent to said energy which alters the same between said
high- and low-resistance conditions, the one of said first and
second layers of conductive material on the viewing side of the
display screen being transparent to light emitted by the layer of
electroluminescent material, and said first and second layers of
conductive material forming electrodes for connection to a voltage
source such that said exciting current and voltage are present
between said first and second layers of conductive material only in
the regions of said selected discrete portions where said variable
resistance memory material is in said condition of low resistance
to energize said selected portion of said electroluminescent
material to provide a light-emitting display pattern on the viewing
side of the display screen.
2. The electrically operated display screen according to claim 1
wherein said layer of conductive material nearest said layer of
variable resistance memory material is transparent to a narrow beam
of energy capable of altering discrete portions of said layer of
variable resistance memory material from said low-resistance to
said high-resistance conditions and also transparent to a wide beam
of energy capable of altering simultaneously all the portions of
said variable resistance memory material from said low resistance
to said high-resistance structural condition.
3. The electrically operated display screen according to claim 1
wherein the voltage source to be connected to said first and second
layers of conductive material is an alternating current voltage
source and said first and second active layers are selected to have
relative capacitive reactances wherein the impedance of discrete
portion of said electroluminescent material is substantially
greater than the impedance of the corresponding discrete portion of
said variable resistance memory semiconductor material when in the
high-resistance condition and in such condition the impedance of
said variable resistance memory semiconductor material being
sufficient to reduce the voltage across said electroluminescent
material below the significant light-emitting value thereof.
4. The electrically operated display screen according to claim 1
wherein said layer of conductive material nearest said layer of
variable resistance memory material is at the rear of the screen
and the layer of conductive material in the viewing side of the
screen is the other layer of conductive material.
5. The electrically operated display screen according to claim 4 in
combination with means mounted behind said layer of conductive
material nearest said layer of variable resistance memory material
for altering discrete selected portions of the same between said
high- and low-resistance conditions thereof.
6. The electrically operated display screen according to claim 1
wherein said first and second layers of conductive material and
said first and second active layers are deposited on a
substrate.
7. The electrically operated display screen according to claim 6
wherein said substrate is adjacent said layer of conductive
material nearest said layer of variable resistance memory material
and together therewith form the rear portion of said display
screen, said substrate and the last-mentioned layer of conductive
material are transparent to said energy capable of altering
discrete portions of said layer of variable resistance memory
material between said high- and low-resistance conditions.
8. The electrically operated display screen according to claim 1 in
combination with a closure for receiving said display screen; a
first energy source in said closure for directing a narrow beam of
energy toward said layer of conductive material nearest said layer
of variable resistance memory material to alter the resistance
condition of said variable resistance memory material between said
high- and low-resistance conditions; deflection means in said
closure for deflecting said narrow beam of energy to a desired
point on the display screen; a second energy source in said closure
for directing a wide beam of energy toward the rear of the display
screen to reset the portions of said variable resistance memory
material from said low-resistance condition back to said
high-resistance condition; and control means mounted outside of the
closure and connected to said first and second energy sources and
said deflection means to control the operation thereof for changing
the display pattern on the display screen.
9. The electrically operated display screen according to claim 8
forms an exterior wall of said closure from which display patterns
can be viewed.
10. The electrically operated display screen according to claim 3
wherein said layer of electroluminescent material has a nonlinear
voltage-brightness characteristic to provide a region where
relatively small changes of voltage produce relatively large
changes of brightness in said electroluminescent material
11. The display screen according to claim 1 in combination with: a
source of exciting current and voltage for said electroluminescent
material which source is coupled across said layers of conductive
material to provide said given exciting current and voltage at
those points of said electroluminescent material which are adjacent
said discrete portions of said variable resistance memory material
in said stable low-resistance condition, the portions of said
electroluminescent material adjacent discrete portions of said
variable resistance memory material in said high-resistance
condition being devoid of said exciting current and voltage, and
energy source means for selectively altering any of said discrete
portions of said variable resistance memory material through said
energy transparent layer of conductive material nearest said layer
of variable resistance memory material from said high-resistance to
said low-resistance condition or from said low-resistance to said
high-resistance condition in the absence of any other source of
current or voltage.
12. In combination: a display screen for displaying a lighted
pattern, said display screen including light-emitting material
distributed over various portions of the display screen, each of
the various portions of said light-emitting material distributed
over said screen being capable of emitting light of at least a
given minimum amount of intensity when sufficient exciting voltage
is applied to the same, variable resistance memory material
distributed over said screen and having portions thereof
electrically coupled in series with said respective portions of
said light-emitting material, said variable resistance memory
material having at least two stable conditions respectively where
the material has one structural condition where the resistance
thereof is relatively high and a different structural condition
where the resistance thereof is relatively low, the impedance of
each portion of light-emitting material being appreciably larger
than that of the high-resistance condition of the associated
portion of said variable resistance memory material, so the voltage
changes across each portion of the light-emitting material is
relatively small as the associated portion of the variable
resistance memory material varies between said relatively high- and
low-resistance conditions, said portions of variable resistance
memory material including means capable of being reversibly stably
structurally changed in configuration or conformation, by only
momentary application of energy thereto, selectively to said stable
condition of high resistance or to said stable condition of low
resistance, said different structural conditions of high and low
resistance persisting indefinitely after all sources of energy has
been removed therefrom, a source of exciting voltage coupled across
said series connected portions of said light-emitting and variable
resistance memory materials, each of said portions of said
light-emitting material receiving said sufficient exciting voltage
from said voltage source when such portion of light-emitting
material is connected in series with a portion of said variable
resistance memory material in said condition of low resistance and
receiving insufficient exciting voltage when said associated
portion of variable resistance memory material is in said condition
of low resistance, said respective portions of light-emitting
material having a nonlinear brightness-voltage characteristic
wherein with the application of two similar relatively high levels
of voltage thereto the amount of light generated varies from a
point where little or no light emission occurs to a point of
substantial light emission, the relative values of the impedances
of said series connected portions of said light-emitting material
and variable resistance memory materials being such that the
voltage applied to any of said portions of light-emitting material
as the associated portion of variable resistance memory material is
structurally changed to said conditions of high and low resistance
varies between said two similar relatively high levels; and a
source of energy to be applied to said portions of variable
resistance memory material selectively structurally to change the
same selectively to said condition of high resistance or to said
condition of low resistance.
13. The combination of claim 12 wherein said means of said portions
of variable resistance memory material are capable of being altered
by application of said energy thereto to different relative
conditions of low resistance, so appreciably varying light
intensities can be produced by said various portions of
light-emitting material.
14. In combination: a display screen for displaying a lighted
pattern at a front side thereof, said display screen including
light-emitting material distributed over various portions of said
display screen, each of the various portions of said light-emitting
material distributed over said screen being capable of emitting
light of at least a given minimum amount of intensity when
sufficient exciting voltage is applied to the same, variable
resistance memory material distributed over said screen and having
portions thereof electrically coupled with said respective portions
of said light-emitting material, said variable resistance memory
material having at least two stable conditions respectively where
the material has one structural condition where the resistance
thereof is relatively high and a different structural condition
where the resistance thereof is relatively low, said portions of
variable resistance memory material including means capable of
being reversibly stably structurally changed in configuration or
conformation, by only momentary application of energy thereto,
selectively to said stable condition of high resistance or to said
stable condition of low resistance, said different structural
condition of high and low resistance persisting indefinitely after
all sources of energy has been removed therefrom; a source of
exciting voltage coupled to said portions of said light-emitting
material; each of said portions of said light-emitting material
being related to the associated portion of variable resistance
memory material to receive said sufficient exciting voltage from
said voltage source when said associated portion of variable
resistance memory material is in said stable condition of low
resistance and not to receive said sufficient exciting voltage when
said associated portion of variable resistance memory material is
in said stable condition of low resistance, and said portions of
said variable resistance memory material being capable of being
altered by application of said energy thereto to different relative
states of low resistance, so appreciably varying light intensities
can be produced by said various portions of light-emitting
material; and a source of energy for selective application to said
portions of variable resistance memory material to alter the same
selectively to said various conditions of high and low
resistance.
15. The combination of claim 14 wherein said portions of variable
resistance memory material are positioned to receive said energy
directed upon one side thereof in varying degrees at different
positions.
16. A display screen for displaying a lighted pattern, said display
screen including light-emitting material distributed over various
portions of the display screen, each of the various portions of
said light-emitting material distributed over said screen being
capable of emitting light of at least a given minimum amount of
intensity when a sufficient exciting voltage is applied to the
same, variable resistance memory material distributed over said
screen and having portions thereof electrically coupled with said
respective portions of said light-emitting material, said variable
resistance memory material having at least two stable conditions
respectively where the material has one structural condition where
the resistance thereof is relatively high and a different
structural condition where the resistance thereof is relatively
low, said portions of variable resistance memory material including
means capable of being reversibly stably structurally changed in
configuration or conformation, by only momentary application of
energy thereto, selectively to said stable condition of high
resistance or to said stable condition of low resistance, said
different stable conditions of high and low resistance persisting
indefinitely after all sources of energy have been removed
therefrom, means for applying a voltage source to said portions of
said light-emitting material, each of said portions of
light-emitting material being related to the associated portion of
variable resistance memory material to receive said sufficient
exciting voltage from said voltage source when said associated
portion of variable resistance memory material is in one of said
stable conditions and not to receive said sufficient exciting
voltage when said associated portion of variable resistance memory
material is in the other stable condition, and said portions of
variable resistance memory material being adapted to receive a
source of energy selectively structurally to change the same to
said stable condition of high resistance or to said stable
condition of low resistance.
17. The display screen of claim 16 wherein said portions of
light-emitting material distributed over said screen are formed as
a single integral layer of material, and said portions of variable
resistance memory material forming a single integral layer, and the
layer of variable resistance memory material being exposed to a
source of energy to be applied from one side thereof.
18. The display screen of claim 16 wherein each of said portions of
light-emitting material is connected in series circuit relation
with said associated portion of variable resistance memory
material, and each said associated portion of variable resistance
memory material being in its low-resistance condition to provide
said sufficient exciting voltage to the associated portion of
light-emitting material.
Description
This invention relates generally to display screens, and more
particularly to electrically operated luminescent display screens
for displaying a picture of information to a viewer.
An object of this invention is to provide a luminescent display
screen which, at any given time, has a fixed pattern of
light-emitting portions forming a given display pattern and wherein
the display pattern can be readily altered.
The luminescent display screen of this invention may be flat or
arcuately shaped viewed in cross section and have any desired
length and width. The screen is a relatively thin laminate body of
adjacent layers of conductive, variable resistance memory
semiconductor, and luminescent materials. The luminescent layer is
most desirably an electroluminescent material having a nonlinear
voltage-brightness characteristic such that there is provided a
region where small changes of AC voltage applied thereto will cause
relatively large changes in brightness of visible light output. A
light transparent conductive electrode-forming layer, such as tin
oxide (SnO.sub.2) is formed on the outer side of the layer of
luminescent material. The luminescent layer is most desirably a
continuous layer of luminescent material, but it can be divided
into separated, closely spaced areas or spots of such luminescent
material. There is provided immediately behind the luminescent
layer a layer of variable resistance memory semiconductor material
also most advantageously formed as a continuous layer of such
material. A layer of light transparent conductive electrode-forming
material, which also may be of tin oxide, is placed on the outside
of the memory material. The layer of variable resistance memory
semiconductor material is such that discrete portions thereof can
be readily alterable between stable high- and low-resistance
conditions by application of suitable amounts of energy through the
light transparent layer in contact therewith, such energy may be in
the form of a laser beam and/or a photoflash lamp. These discrete
portions of the layer of variable resistance memory semiconductor
material act as switches between the last-mentioned conductive
layer and the luminescent layer. A source of voltage, preferably an
alternating current voltage source where an electroluminescent
material is used, is applied across the light transparent
electrode-forming conductive layers so that increased voltage is
applied only to the discrete portion of the layer of luminescent
material opposite discrete portions of the layer of variable
resistance memory semiconductor material that are in the
low-resistance condition, so that a light pattern is emitted by the
layer of luminescent material which corresponds to the pattern of
high- and low-resistance portions of the layer of variable
resistance memory semiconductor material. The amplitude and/or
frequency of the output of said source of voltage must be
sufficiently low as not to affect the high- or low-resistance
condition of the layer of variable resistance memory semiconductor
material. The layers of the display screen between the luminescent
material and what is to be the front visible side of the screen
must be transparent to the light emitted in the latter layer. The
display pattern can be formed on the display screen by selectively
impinging a modulated beam of energy, such as, a laser beam, on the
memory semiconductor layer for changing desired discrete portions
thereof from a high-resistance condition to a low-resistance
condition, and the display pattern may be erased by applying
energy, such as, for example, energy from an electron beam, laser
beam, spark discharge or high-intensity photoflash lamp light, to
the memory semiconductor layer. The display pattern formed on the
display screen can be changed to a new display pattern by modifying
the existing pattern of high- and low-resistance portions on the
variable resistance memory semiconductor layer by a modulated beam
of energy, such as a laser beam, modulated in accordance with the
new display pattern. It is most advantageous to provide a display
screen with the energy generating means mounted behind the screen,
with the memory semiconductor layer thereof rearwardly of the
luminescent layer. In such case, the electrode-forming layer on the
rear side of the memory semiconductor layer is transparent to said
energy and the electrode-forming conductive layer on the front side
of the luminescent layer is transparent to the light emitted by the
luminescent layer.
The memory semiconductor material, which is capable of having
desired discrete portions thereof reversibly altered or changed
between a stable high-resistance condition and a stable
low-resistance condition, is preferably a polymeric material which,
in a stable manner, may be normally in either of these conditions
and a large number of different compositions may be utilized. As
for example, the memory semiconductor material may comprise
tellurium and germanium at about 85 percent tellurium and 15
percent germanium in atomic percent with inclusions of some oxygen
and/or sulphur. Another composition may comprise Ge.sub.15
As.sub.15 Se.sub.70. Still other compositions may comprise
Ge.sub.15 Te.sub.81 S.sub.2 and P.sub.2 or Sb.sub.2 and Se.sub.15
Se.sub.81 S.sub.2 and P.sub.2 or Sb.sub.2. Further compositions
which are also effective in accordance with this invention may
consist of the memory materials disclosed in Stanford R.
Ovshinsky's U.S. Pat. No. 3,271,591, granted on Sept. 6, 1966,
(such materials being sometimes referred to therein as Hi-Lo and
circuit breaker device materials). By appropriate reduction of
compositions and thicknesses of layers, desired resistances and
capacitances in the low- and high-resistance conditions may be
obtained.
Assuming the layer of memory semiconductor material to be in its
stable high-resistance condition, desired discrete portions thereof
may be altered to a stable low-resistance condition by energy
applied thereto which can be in the form of energy pulses of
sufficient duration (e.g., 1- 100 milliseconds or more) to cause
the alteration to the low-resistance condition to take place and be
frozen in. Such desired discrete portions may be realtered to the
stable high-resistance condition by energy applied thereto which
can be in the form of energy pulses of short duration (e.g., 10
microseconds or less) to cause the realteration to the
high-resistance condition to take place and be frozen in.
Conversely, assuming the layer of memory semiconductor material to
be in its stable low-resistance condition, desired discrete
portions thereof may be altered to a stable high-resistance
condition by energy applied thereto which can be in the form of
energy pulses of short duration (e.g., 10 microseconds or less) to
cause the alteration to the high-resistance condition to take place
and be frozen in. Such desired discrete portions may be realtered
to the stable low-resistance condition by energy applied thereto
which can be in the form of energy pulses of sufficient duration
(e.g., 1-100 milliseconds or more) to cause the realteration to the
low resistance condition to take place and be frozen in.
The reversible alteration of desired discrete portions of the layer
of the memory semiconductor material between the high resistance or
insulating condition and the low resistance or conducting condition
can involve configurational and conformational changes in atomic
structure of the semiconductor material which is preferably a
polymeric-type structure. These structural changes, which can be of
a subtle nature, may be readily effected by applications of various
forms of energy at the desired discrete portions of the layer. It
has been found, particularly where changes in atomic structure are
involved, that the high-resistance and low-resistance conditions
are substantially permanent and remain until reversibly changed to
the other condition by the appropriate application of energy to
make such change.
In its stable high resistance or insulating condition, the memory
semiconductor material (which is preferably a polymeric material)
is a substantially disordered and generally amorphous structure
having local order and/or localized bonding of the atoms. Changes
in the local order and/or localized bonding which constitute
changes in atomic structure, i.e., structural changes, which can be
of a subtle nature, provide drastic changes in the electrical
characteristics of the semiconductor material, as for example,
resistance, capacitance, dielectric constant, and the like. These
changes in these various characteristics may be used in determining
the structure of the desired discrete portions with respect to that
of the remaining portions of the layer of semiconductor
material.
The changes in local order and/or localized bonding, providing the
structural change in the semiconductor material, can be from a
disordered condition to a more ordered condition, such as, for
example, toward a more ordered crystallinelike condition. The
changes can be substantially within a short range order itself
still involving a substantially disordered and generally amorphous
condition, or can be from a short-range order to a long-range order
which could provide a crystallinelike or pseudocrystalline
condition, all of these structural changes involving at least a
change in local order and/or localized bonding and being reversible
as desired. Desired amounts of such changes can be effected by
applications of selected levels of energy.
The aforementioned alterations can be effected in various ways, as
by energy in the form of electric fields, radiation of heat, or
combinations thereof, the simplest being the use of heat. For
example, where energy in the form of electromagnetic energy, such
as, laser beams, photoflash lamp light, or the like, is used both
radiation and heat can be involved. Where energy in the form of
particle beam energy, such as electron or proton beams, is used, in
addition to heat, there also can be involved a charging and
flooding of the semiconductor material with current carriers. Since
heat energy is the simplest to use and explain, this invention will
be considered by way of explanation in connection with the use of
such heat energy, it being understood that other forms of energy
may be used in lieu thereof or in combination therewith within the
scope of this invention.
When energy in the form of energy pulses of relatively long
duration is applied to desired discrete portions of a layer of
memory semiconductor material in its stable high resistance or
insulating condition, such portions are heated over a prolonged
period and changes in the local order and/or localized bonding
occur during this period to alter the desired discrete portions of
the semiconductor material to the stable low-resistance condition
which is frozen in. Such changes in the local order and/or
localized bonding to form the stable low-resistance condition can
provide a more ordered condition, such as, for example, a condition
toward a more ordered crystallinelike condition, which produces low
resistance, as mentioned hereinabove.
When realtering the desired discrete portions of the memory
semiconductor material from the low-resistance condition to the
high-resistance condition by energy in the form of energy pulses of
relatively short duration, sufficient energy is provided to heat
the desired discrete portions of the semiconductor material
sufficiently to realter the local order and/or localized bonding of
the semiconductor material back to a less-ordered condition, such
as back to its substantially disordered and generally amorphous
condition of high resistance which is frozen in. These same
explanations apply where the normal condition of the memory
semiconductor material is the low resistance or conducting
condition and where the desired discrete portions thereof are
altered to the high resistance or insulating condition. In the
memory semiconductor materials used in this invention, it is found
that the changes in local order and/or localized bonding as
discussed above, in addition to providing changes in electrical
resistance, they also provide changes in capacitance, dielectric
constant and the like.
The energy applied to the memory semiconductor material for
altering and realtering the desired discrete portions thereof may
take various forms, as for example, electrical energy in the form
of voltage and current, beam energy, such as electromagnetic energy
in the form of radiated heat, photoflash lamp light, laser beam
energy or the like, particle beam energy, such as electron or
proton beam energy, energy from a high-voltage spark discharge or
the like, or energy from a heated wire or a hot airstream or the
like. These various forms of energy may be readily modulated to
produce narrow discrete energy pulsations of desired duration and
of desired intensity to effect the desired alteration and
realteration of the desired discrete portions of the memory
semiconductor material, they producing desired amounts of localized
heat for desired durations for providing the desired pattern of
information in the layer of the memory semiconductor material.
The pattern of information so produced in the layer of memory
semiconductor material described remains permanently until
positively erased, so that it is at all times available for display
purposes. Also, by varying the energy content of the various
aforesaid forms of energy used to set and reset desired discrete
areas of the memory semiconductor material, the magnitude of the
resistance and the other properties referred to can be accordingly
varied with some memory materials.
Therefore, when the memory semiconductor material described above
is used to form a part of a display screen as contemplated by this
invention many advantages are obtained. For example, a particular
display pattern is quickly and easily modified or completely
eliminated and a new display pattern put in its place on the same
screen. Also, different light intensities may be obtained at
different discrete points of the screen which may vary between
complete absence or substantially complete absence of emitted light
and the maximum amount of emitted light possible to achieve with
the particular luminescent material being used. This variation of
light intensity is made possible by the different relative states
of conductivity of the memory semiconductor material used or by
controlling the number of dots or discrete points which are
permitted to be conductive. Also, when using luminescent materials
such as AC-operated electroluminescent materials, desirable amounts
of light variation between the minimum and maximum values is most
advantageously obtained by selecting such materials having a
nonlinear voltage-brightness characteristic. Such
electroluminescent materials are well known, and, in addition,
there is known several methods of making electroluminescent
material nonlinear or more nonlinear.
The display screen of this invention may take various forms, as for
example, the screen may be an integral part of the scanning and
resetting apparatus located behind the screen with the screen
forming one wall of an enclosure. Another form would include only
the screen which had a display pattern formed thereon so that when
operating voltage is applied to the electrode layers, the pattern
will appear as distinctive light emitting portions, the display
screen of the latter form being relatively thin and capable of wall
mounting similar to that of a picture.
Many objects, features and advantages of this invention will be
more fully realized and understood from the following detailed
description when taken in conjunction with the accompanying
drawings wherein like reference numerals throughout the various
views of the drawings are intended to designate similar elements or
components.
FIG. 1 is a diagrammatic enlarged view of the display screen of the
invention in fragmentary section and the associated means for
operating the same;
FIG. 2 is a perspective view of the entire display screen device of
FIG. 1 illustrating one form of the invention;
FIG. 3 is a front view of the display screen without the scanning
apparatus and illustrates another form of the invention;
FIG. 4 is an equivalent electric circuit of a discrete portion of
the display screen when the variable resistance memory
semiconductor material thereof is in its high-resistance
condition;
FIG. 5 is an equivalent electric circuit of a discrete portion of
the display screen when the variable resistance memory
semiconductor material is in a low-resistance condition;
FIG. 6 shows the current-voltage characteristics of the various
component layers of the display screen under the various conditions
of operation thereof; and
FIG. 7 shows a voltage-brightness characteristic of a suitable
AC-operated electroluminescent material which can be used with this
invention.
Referring now to FIG. 1 there is shown a rectangular display screen
designated generally by reference numeral 9 illustrated as being of
a flat or straight configuration, viewed in cross section, it being
understood that the screen may be curved viewed in cross section
and have other than a rectangular shape. In the most advantageous
form of this invention the screen is a laminate body comprising
various layers deposited on a substrate or support base 11 which is
preferably made of material transparent to energy beams 10 and 10a
shown here as one method used to set and reset a display pattern on
the display screen 9. In the example of the invention being
described the energy beams 10 and 10a are laser and photoflash lamp
beams respectively and so the substrate 11 is made of relatively
thin visible light transparent glass or plastic material. A thin
layer 12 of conductive material, also transparent to visible light,
such as, tin oxide (SnO.sub.2), is deposited on the substrate 11 to
form an electrode for connection to a source of voltage.
Deposited over the transparent conductive layer 12 is a layer 13 of
variable resistance memory semiconductor material of the type
described hereinabove which is capable of having discrete portions
of the material being reversibly altered by the beams 10 and 10a
between a high-resistance blocking condition and a low-resistance
conducting condition. Deposited over the variable resistance memory
layer 13 is a layer 14 of electroluminescent material, such as,
zinc sulphide (ZnS.sub.2), which emits light from selected portions
of the material as a result of alternating current voltage applied
to these selected portions, and overlying the layer 14 of
electroluminescent material is a layer 16 of transparent conductive
material, such as, tin oxide (SnO.sub.2), which serves as the other
sheetlike electrode layer for the display screen. If desired, a
layer 15 of transparent insulating material, such as, glass or the
like, may be positioned over the layer 16 to insulate the outer
surface of the display screen 9. Operating voltage is applied to
the display screen 9 by electrical connection of a voltage source,
such as, an AC-voltage source, to the layers 12 and 16 to cause
small amounts of current to flow between these layers in the
regions of low resistance of the layer 13 to energize the adjacent
areas of the luminescent material of layer 14. Extremely small
amounts of leakage current may flow between the electrode layers 12
and 16 in the regions of the memory semiconductor material in the
high-resistance condition, but, due to the proper selection of
luminescent material having a nonlinear voltage-brightness
characteristic the small amounts of leakage current will have
little or no noticable affect on the light output in these
regions.
The layers 12, 13, 14, 15 and 16 may be deposited films which can
be deposited by vacuum deposition of by sputtering or the like.
After the layer 13 of variable resistance memory material is
applied to the screen 9, as well as the other layers 12, 14 and 16,
the display screen is positioned in proximity to an energy source
17 which may be located within a closure 18, seen in FIG. 2, the
screen being the front wall thereof, and the energy beam 10 is
directed toward the display screen to penetrate the support base 11
and electrode layer 12 to impinge upon the surface of the layer 13
to alter selected portions of the layer from its stable
high-resistance condition to its stable low-resistance condition.
The energy source 17 may be a laser diode which directs a very
small beam upon the memory layer 13. The beam 10 is deflected by a
deflection device 20 to effect movement of the beam through the
desired predetermined pattern corresponding to the pattern to be
displayed from the surface of the display screen 10. Impingement of
the energy beam 10 on the variable resistance memory material of
layer 13 will cause the material to alter from its substantially
high-resistance blocking condition to its low-resistance conducting
condition only in the regions receiving the beam energy. Therefore,
as the energy beam 10 is deflected from side to side or through a
desired pattern by the influence of the deflection device 20,
discrete elemental lengths of the variable resistance memory
material 13 will form conductive paths through the material. These
discrete conductive paths will allow an increased voltage to be
applied to the immediately adjacent portions of the layer 14 of
luminescent material and this increased voltage will cause a
corresponding increase in current to energize the material to emit
light therefrom at these regions while other portions of the
material will emit little or no light.
The preferred form of beam energy is that of modulated beam pulses,
as indicated by the square wave pulses 21 and 22, it being
understood that other forms of beam energy may be used. When the
layer 13 of memory-type material is deposited, the entire surface
area and thickness of the layer is in a substantially disordered
generally amorphous condition of high resistance. To selectively
alter desired portions of the semiconductor material from this
high-resistance blocking condition to a low-resistance conducting
condition, the beam 10 is modulated to form beam pulses of
relatively long duration, as indicated by pulses 21 to change the
local order and/or localized bonding of the molecular structure of
the memory material to create the desired discrete low-resistance
conductive paths through the material. On the other hand, if it is
desired to realter the memory material from its low-resistance
conducting condition to the original high-resistance blocking
condition only at selected regions thereof, the beam energy 10 is
modulated with short duration beam pulses, as indicated by the
pulses 22, which tend to rearrange or reform the local order and/or
localized bonding of the molecular structure to substantially its
original condition of high resistance. When the beam 10 is
modulated by pulses 21, the pulses of beam energy are applied for a
sufficient period of time to allow the change of conductivity to
take place, for example, a millisecond or so and the movement of
the energy beam is sufficiently slow to ensure overlap of beam
pulses applied to the surface of the semiconductor material thereby
ensuring a continuous conductive path through the thickness of the
material as well as along the desired length of the material.
On the other hand, if the entire area of the memory material of
layer 13 is to be realtered to its original condition of high
resistance, this may be accomplished by a single flash of light
from a high-intensity photoflash lamp 23 (a Xenon photoflash lamp
being a particularly useful and effective photoflash lamp) which
directs the wide angle light beam 10a to impinge upon the entire
area of the layer 13, and thereafter a completely new display
pattern can be formed on the screen 9. A suitable control means 24
is provided to control the energy source 17, deflection device 20
and the photoflash lamp 23. The control means 24 may be in a
console attached to or separate from an enclosure 18. Operating
voltage is applied to the control means 24 and screen 9 by one or
more cables 25. However, the flat display screen can be a separate
wall mounted unit 9a as shown in FIG. 3 where it has its display
pattern modified or changed at a location remote from its normal
location. Also, the screen 9 in FIG. 2 may be made removable from
the enclosure 18 so it can be replaced by another screen like 92
which can be remotely set to a desired display pattern. The control
means 24 may include a scanning photodensitometer, a device well
known in the art, which scans printed matter and develops pulses
responding to the light or dark areas of the information being
scanned. The scan control of the photodensitometer may be operated
in synchronism with the control means 17 and the deflection device
20.
A source 28, preferably of alternating current voltage where
AC-operated electroluminescent materials are used, is connected to
the electrode layers 12 and 16, so energizing current will flow
between the electrode layers through the low-resistance portions
26, 27, etc., (FIG. 1) of the memory layer 13 and the immediately
adjacent portions 26a and 27a of the electroluminescent layer 14.
The voltage amplitude of the voltage source 28 is preferably
maintained at all times below the threshold voltage value of the
memory material such that the applied voltage will not cause
changes in the resistance condition of the memory material. The
portions of the luminescent layer 14 through which the voltage is
sufficiently increased become energized to emit light thereby
forming the desired display pattern on the display screen 9.
The variable resistance memory semiconductor material of the layer
13 is symmetrical in electrical operation in that it conducts
current substantially equally in both directions in its
low-resistance condition, and blocks current substantially equally
in both directions in its high-resistance condition. Therefore,
when voltage is applied to electrodes 12 and 16, the entire screen
surface appears electrically to be a plurality of parallel
connected circuits with the majority of the current flow passing
through the low-resistance parallel circuits and each of these
parallel circuits providing a different voltage to be applied at
different selected areas of the luminescent layer 14, more voltage
causing substantial light to be emitted and less voltage causing
little or no light emission.
Although the broad aspects of this invention can be utilized with
luminescent materials or devices of various kinds it is herein
disclosed in conjunction with AC-operated electroluminescent
materials the use of which provides several advantages in
constructing display screens in accordance with this invention.
Such advantages are ease of manufacture, low-cost, low-power
consumption and reliability. Electroluminescent phosphor materials
can be deposited on large areas such as by vapor deposition,
painting or other equally simple methods. Also, electroluminescent
phosphor materials have, for the most part, very high dielectric
constants thereby being substantially voltage responsive rather
than current responsive, there being small amounts of current
passing through such materials while in the energized
light-emitting state. Typical orders of magnitude of dielectric
constant of electroluminescent phosphor materials are 10.sup. 14
-10.sup. 18 ohms/cm. although other orders of magnitude may be
obtained. However, when using electroluminescent phosphor materials
of this type in conjunction with the memory semiconductor material
disclosed herein it becomes necessary, for best results, to use
such phosphor materials having a nonlinear voltage-brightness
characteristic. This is because of the dielectric constant of the
memory semiconductor material is many orders of magnitude less than
the dielectric constant of the phosphor material. As for example,
the dielectric constant of present memory semiconductor materials
may be between 10.sup. 5 -10.sup. 7 ohms/cm. Therefore, with the
deposited layer construction of a display screen as disclosed
herein, a majority of the applied voltage will be impressed across
the electroluminescent material even with the memory semiconductor
material in its high-resistance blocking condition. To compensate
for the disparity of the dielectric constants between the two
active materials it is contemplated in accordance with one aspect
of this invention to use in combination with such memory
semiconductor materials an electroluminescent material having a
nonlinear voltage-brightness characteristic similar to that shown
in FIG. 7. Here, changes of voltage applied across the
electroluminescent material cause changes of brightness as
indicated by the nonlinear curve 29, there being a region 29a where
relatively small changes of voltage cause relatively large changes
of brightness. By way of example, a point 29b on the curve 29
indicates the amount of brightness obtained with approximately 80
volts applied across the electroluminescent material while a point
29c indicates the amount of brightness with approximately 120 volts
applied across the electroluminescent material, there being a
substantial spread between these two brightness conditions to
provide the necessary contrast for a display panel. Therefore, and
by way of example, when 120 volts AC is applied the electrode
layers 12 and 14 by the voltage source 28, with the memory
semiconductor material in its high-resistance blocking condition,
and with layers of memory and electroluminescent materials of
approximately equal thickness, approximately 80 volts will be
impressed across the electroluminescent layer thus providing little
or no light output and 40 volts will be impressed across the memory
semiconductor material, this 40-volt value being less than the
voltage threshold level of the memory semiconductor material.
However, when the desired discrete portions 26 and 27 of the layer
13 of memory semiconductor material are altered from the
high-resistance blocking conditions to the low-resistance
conducting condition substantially the entire value of the applied
voltage, i.e., 120 volts, will be impressed across the
electroluminescent material 26a and 27a adjacent the portions 26
and 27, and relatively large amounts of light will be emitted
therefrom.
For a better understanding of the electrical properties of the
display screen of this invention, reference is now made to FIG. 4
which illustrates the equivalent electric circuit of a portion of
the display screen which has the memory semiconductor material in a
high-resistance blocking condition. A capacitor 30 is shown
representing the capacitive reactance of a discrete portion of the
memory material in its high-resistance condition and resistor 31
represents the high-leakage resistance thereof. A capacitor 32 is
shown representing the capacitive reactance of the discrete portion
of the electroluminescent layer 14 in front of the discrete portion
of the memory semiconductor material represented by capacitor 30
and resistor 31. The relative capacitances of the layer 13 of
memory semiconductor material and the electroluminescent layer 14
are a function of the relative thicknesses and dielectric constants
of the materials involved and are selected so enough capacitive
reactance is in series with the electroluminescent material to
reduce the voltage thereon to a value where little or no light
output is obtained when the memory semiconductor material is in the
high-resistance condition. Therefore, application of alternating
current voltage across discrete portions of the layers of memory
and electroluminescent materials represented by the capacitors 30
and 32, respectively, will result in sufficient voltage being
dropped across the memory material with the remainder of the
voltage dropped across the electroluminescent material, so little
or no light will be emitted by the electroluminescent material
involved. The reactive impedance characteristics of the serially
connected components is shown in the FIG. 6 which illustrates the
capacitive reactive impedance of capacitor 32 by the slope of curve
34, and the capacitive reactance of the capacitor 30 by the slope
of curve 35.
However, when a discrete portion of the memory material is altered
from its high-resistance blocking condition to its low-resistance
conducting condition, it acts as a low-value resistor represented
by the resistor 36 of FIG. 5 which has a resistance significantly
low in value, so substantially all of the voltage from the source
28 is applied across the capacitor 32. The resistance or impedance
characteristic of the semiconductor material represented by the
resistor 36 is illustrated by the curve 37 of FIG. 6.
Accordingly, this invention provides a display screen of unitary
construction wherein selected portions of the screen are energized
to display light therefrom while unselected portions remain
deenergized, and wherein the display pattern formed on the screen
can be easily altered or modified by resetting the low-resistance
conductive condition of the semiconductor material to its original
high-resistance blocking condition and then selectively setting
another pattern of low-resistance conditions on the semiconductor
material.
It will be understood that variations and modifications may be
effected of the forms of the invention described above without
departing from the spirit and scope of the novel concepts of this
invention.
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