United States Patent
`
`[19]
`
`Fergasoii
`
`[54] DISPLAY DEVICES UTILIZING LIQUID
`CRYSTAL LIGHT MODULATION
`
`[75]
`
`Inventor:
`
`James_L. Fergason, Kent, Ohio
`
`[73] Assignee:
`
`International Liquid Xtal Company,
`Cleveland, Ohio
`2
`
`l [22] Filed:
`
`Apr. 22, 1971
`
`[21] Appl.No.: 136,441
`
`Related US. Application Data
`
`[63] Continuation-in-part of Ser. No. 113,948, Feb. 9,
`1971, abandoned.
`
`'
`
`[52] U.S. Cl.............. ..350/150, 252/408, 340/324 R,
`.
`350/160 LC
`Int. Cl ............................................... ..G02f 1/18
`Field of Search ...... ..— ............ ..350/150,157, 160;
`252/408; 340/324 R
`
`[51]
`[58]
`
`[5 6]
`
`References Cited
`
`UNITED STATES PATENTS
`
`3,597,044
`3,499,702
`3,581,002
`3,597,043
`3,625,591
`3,576,364
`3,612,654
`
`8/1971
`3/1970
`5/1971
`8/1971
`12/1971
`4/1971
`10/1971
`
`Castellano .......................... ..350/160
`Goldmacher et al..
`.....350/150
`Dodds ................................ ..350/160
`Dreyer ............................... ..350/150
`Freiser
`.....350/150
`Zanoni.
`.....350/160
`Klein .................................. ..350/160
`
`Primary Examiner——-Edward S. Bauer
`Attorney——Brown, Murray, Flick & Peckham
`
`[ 5 7 ]
`
`ABSTRACT
`
`Optical display devices for converting electrical intel-
`
`[11]
`
`3,731,986
`
`[451 May 8, 1973
`
`ligence into optical images with the use of a shutter
`device comprising a layer of liquid crystal material
`sandwiched between opposing parallel plates coated
`with transparent conducting films. These plates, with
`the liquid crystal material therebetween, are disposed
`between and parallel to a pair of polarizers such that
`when an electrical potential is established across the
`conducting films and the liquid crystal
`layer,
`the
`device will change from a light transmitting to opaque
`medium, or vice versa, depending upon the orienta-
`tion of the two polarizers. By forming the two con-
`ducting films in the shape of a desired optical image,
`that image can be made to appear or disappear, de-
`pending _upon whether a potential
`is established
`between the conducting films. Furthermore, by, creat-
`ing separate conducting areas, as by etching the con-
`ducting films, any given number of conductive regions
`can be switched ON while other regions are not af-
`fected to produce any one of a number of different
`images with the same liquid crystal sandwich as-
`sembly. Finally, by etching a pattern of strips of trans-
`parent conducting material on the two opposing
`plates, by orienting the strips on the respective plates
`at right angles to each other, and by selectively apply-
`ing pulsed voltages to the strips on the respective
`plates, the area of liquid crystal layer can be scanned
`point by point to produce with the same display any
`one of a number of optical images such as numerals,
`letters or the like. The invention has particular utility
`in computer and calculator re_ad-outs, for example
`since the display can be energized at a voltage leve
`compatible with that used to drive the integrated cir-
`cuitry used in such devices without the necessity for
`relatively high voltage driving circuitry.
`
`11 Claims, 8 Drawing Figures
`
`Page 1 of 8
`
`Tianma Exhibit 1015
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`Page 1 of 8
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`Tianma Exhibit 1015
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`
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`
`Page 2 of8 '
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`Page 2 of 8
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`Page 3 of8-
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`Page 3 of 8
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`

`
`1
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`3,731,986
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`2
`
`DISPLAY DEVICES UTILIZKNG HJQIUIID CRYSTAL
`LIGHT MODULATION
`
`CROSS—REFERENC ES TO RELATED
`APPLICATIONS
`
`This application is a continuation—in-part of copend-
`ing application Ser. No. 113,948, filed Feb. 9, 1971 and
`now abandoned in the name of James L. Fergason as
`inventor and entitled “Liquid-Crystal Non-Linear
`Light Modulators Using Electric and Magnetic Fields.”
`
`BACKGROUND OF THE INVENTION -
`
`As is known, there are a large number. of organic
`chemical compounds that will, within a particular tem-
`perature range, exhibit nematic-phase liquid crystals.
`These compounds are liquid in the sense that their
`molecules are not dissociated as in a gas nor so tightly
`bound within a structure as to constitute a solid. At the
`
`same time, they are said to be crystalline, in that there
`is a particular ordering to the orientation of the
`molecules, as is sometimes evidenced by peculiar opti-
`cal effects.
`
`It is also known that when a nematic-phase liquid
`crystal material
`is sandwiched_ between transparent
`plates
`that
`have
`been rubbed,
`each of
`them
`unidirectionally and on the surface in contact with the
`nematic-phase liquid crystal material, there is obtained
`a liquid-crystal unit whose optic axis
`lies in the
`direction of unidirectional
`rubbing.
`If two rubbed
`plates with the rubbed directions at right angles to each
`other are used to contain a nematic liquid, then the
`resulting effect will be an optical media which rotates
`the plane of polarization by 90°. Similarly, if the two
`rubbed directions are aligned 45° with respect to each
`other, the resulting nematic liquid will rotate the plane
`of polarized light by 45°. Any amount of rotation
`between 0° and 90° can be obtained by using such
`rubbed surfaces.
`
`* By using nematic materials which align parallel with
`an applied electric or magnetic field, the nematic align-
`ment is disrupted at a low field level. The mechanism
`involved resides in the fact that the liquid crystal is
`elastically deformed by surface constraints such that
`the long axis of the nematic material is oriented in a
`helical manner. If the direction of the molecules at the
`
`center of the sample is changed such that they are
`parallel with an applied field which is also parallel with
`the twist direction, no torque is exerted on opposite
`sides of the liquid crystal and it no longer remains
`twisted. This will occur just as the molecules at the
`center of the nematic cell become parallel to the ap-
`plied electric field. Therefore, it will occur at a very
`sharp field level resulting in bistable operation. The
`voltage required is determined by the relationship:
`
`V=-zr(klAt)"’
`
`where k is an elastic constant and A t is the difference in
`electrical polarizability parallel and perpendicular to
`the long axis. When such a device with a 90° twist is
`placed between parallel polarizers, no light will be
`transmitted at zero voltage and it will be the equivalent
`of two crossed polarizers. When an electric field is ap-
`plied to the device, the structure will untwist at a well
`defined voltage and allow light transmission. If, how-
`ever,
`the same device is placed between crossed
`
`Page 4 of 8
`
`polarizers, then at zero voltage light is transmitted and
`the polarizers will effectively act as though they are
`parallel. However, with the application-of a critical
`voltage, the plane of polarization will no longer be
`rotated 90° and no light will be transmitted. Thus, the
`device acts as a shutter for transmitted light. The liquid
`crystal material used must be nematic and must have a
`positive dielectric anisotropy. At the same time, the
`material must be nematic over a substantial tempera-
`ture range, including the room temperature range. A
`suitable material
`for
`this purpose is described in
`copending application Ser_. No. 113,948, filed Feb. 9,
`1971, of which this application is a continuation—in-
`part. it comprises a mixture of 40 percent bis—(4’-n-oc-
`tyloxybenzal)-2-chlorophenylenediamine, 50 percent
`p-methylbenzal-p'—n-butylaniline and 10 percent p-
`cyanobenzal-p’-n-butylaniline.
`
`SUMMARY OF THE INVENTION
`
`liquid
`invention,
`In accordance with the present
`crystal material sandwiched between rubbed trans-
`parent plates and disposed between polarizers is util-
`ized to construct devices which display information
`spatially. Specifically, there is provided a device for
`converting electrical intelligence into an opticalimage
`comprising a layer of liquidcrystal material disposed
`between transparent parallel plates which are coated
`on only selected areas thereof with films of transparent
`conducting material, polarizers on opposite sides of the
`plates and essentially parallel thereto to provide a sand-
`wich structure through which light can pass, and means
`for establishing a potential difference between con-
`ducting transparent films on the respective plates such
`that areas of the sandwich structure will transmit light
`while others will not to form an optical image.
`In one embodiment of the invention, an optical
`image is formed by etching conductive glass in a pat-
`tern which represents a number or symbol. In another
`embodiment, separate conducting areas are created
`such that any number of conductive regions can be
`switched ON while other regions are not affected to
`produce any one of a number of different images.
`In accordance with still other embodiments of the in-
`
`vention, a pattern of strips of transparent conducting
`material is etched on the two transparent plates on op-
`posite sides of a film of nematic liquid crystal material.
`The strips are then rubbed in such a manner that the
`rubbed direction is parallel to the strips. The two trans-
`parent plates are placed together with the strips per-
`pendicular. By applying pulsed voltages to a pair of
`crossed strips on the respective glass plates, only that
`region where the strips cross will be transparent, for ex-
`ample, while the remainder of the liquid crystal
`is
`opaque. Thus, it is possible to scan a region point by
`point. If the strips on one plate are called rows while
`those on the other columns, each row can be scanned
`by applying a field pattern to the columns. With proper
`adjustment of voltages, it is then possible to scan such a
`system. The output of such a system is binary, being
`either ON or OFF.
`
`The above and other objects and features of the in-
`vention will become apparent
`from the following
`detailed description" taken in connection with the ac-
`companying drawings which form a part of this specifi-
`cation, and in which:
`
`Page 4 of 8
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`

`
`3
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`3,731,986
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`4»
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`FIG. 1 is a schematic view of a liquid crystal unit
`made in accordance with the present invention;
`FIG. 2 is a view illustrating the manner in which the
`transparent plates of the liquid crystal unit of FIG. 1 are
`rubbed at right angles with respect to each other;
`FIG. 3 is a schematic illustration showing the manner
`in which polarized light passes through the liquid
`crystal unit of the invention;
`FIG. 4 illustrates one manner in which an optical
`image may be produced with the liquid crystal unit of
`the invention;
`FIG. 5 illustrates the manner in which rows and
`
`columns of transparent conducting material may be
`etched on opposing transparent plates which bound a
`layer of liquid crystal material to effect an array which
`can be scanned;
`FIG. 6 is a schematic circuit diagram illustrating one
`manner in which an array, such as that shown in FIG. 5,
`can be scanned;
`FIG. 7 comprises waveforms illustrating the opera-
`tion of the circuitry of FIG. 6; and
`FIG. 8 illustrates still another manner in which con-
`
`ductive films on opposing transparent plates can be
`etched to provide different optical images.
`With reference now to the drawings, and particularly
`to FIG. 1, there is shown a liquid crystal unit 10 com-
`prising a first transparent plate 12, preferably of glass,
`and a second transparent plate 14, also of glass, and ex-
`tending parallel to the plate 12. The plates 12 and 14
`are spaced apart by suitable spacers, not shown, by ap-
`proximately 0.25 to 2 mils; although the spacing may in
`some instances be as little as 0.1 to 0.05 mil. This space
`is filled with a nematic-phase liquid crystal material
`with a positive dielectric anisotropy preferably of the
`kind hereinabove indicated, namely one comprising
`major portions such as 20 percent to 80 percent each of
`bis-(4'-n-octyloxybenzal-2-chlorophenylenediamine
`and p-methylbenzal-p’-n-butylaniline, these making up
`about 60 percent to 97 percent of the total composition
`and p-cyanobenzal—p’-n-butylaniline comprising the
`remaining 3 percent to 40 percent. This material, as
`mentioned above,
`is described in copending applica-
`tion Ser. No. 113,948, filed Feb. 9, 1971.
`Disposed on the interior surfaces of the transparent
`plates 12 and 14 and in contact with the liquid crystal
`layer 16 are coatings 18 and 20 of thin transparent
`electroconductive material, such as the known tin
`oxide or indium oxide coatings. These coatings are
`quite thin and highly resistive, for example, on the
`order of 150 ohms per unit square or above, and
`possibly as high as 5,000 to 10,000 ohms per unit
`square. It is desirable that the transparent electrocon-
`ductive coating be of the kind that is applied at relative-
`ly low temperatures such as about 500°F, by the
`process of cathode-sputtering in a vacuum, so that dan-
`gers of warpage may be safely avoided.
`In FIG. 2, there is shown a view of the plates 12 and
`I4 which may comprise flat glass on the order of about
`one—eighth inch thick having layers 18 and 20 of trans-
`parent conducting material deposited on the facing sur-
`faces thereof. In the preparation of a liquid crystal unit,
`the layers of transparent conducting material that are
`in contact with the nematic-phase liquid crystal materi-
`al must be prepared by being stroked or rubbed
`unidirectionally with, for example, a cotton cloth. The
`
`Page 5 of 8
`
`direction of rubbing on the respective plates 12 and 14
`is indicated by the lines 22 and 24 in FIG. 2; and it will
`be appreciated that the directions of rubbing on the
`respective plates are at right angles to each other. The
`effect of this is to produce a twisted nematic structure
`as explained above. In this respect, the molecules in a
`nematic-phase liquid crystal material are each long and
`straight, and they tend to lie parallel, like logs in a river
`or straws in a broom. Their parallelism is statistical,
`rather than perfect and exact. They are free to move
`with respect to one another, and there are some that
`are at a small acute angle with respect to the “main
`stream,” and a few others that are at any given moment
`in a position even less consonant with the bulk of the
`others. A property of the nematic-phase liquid crystal
`materials is that
`the molecules in the vicinity of a
`rubbed surface tend to align themselves with it. Thus,
`the molecules nearest the surface of the plate 12, for
`example, are inclined to orient themselves parallel with
`the lines 22, nd those nearest the surface of plate 14 are
`inclined to orient themselves parallel to the lines 24.
`The structure is fluid and active; and under conditions
`of no applied voltage, the molecules in the various
`layers that are parallel to the surfaces of plates 12 and
`14 arrange themselves in what may be considered a
`number of layers of suitable intermediate “main-
`stream” directions, ranging from one close to parallel
`to the lines 22 (a short distance from the surface of
`plate 12) through one at about a 45° angle with respect
`to both the lines 22 and 24 (at about the midpoint of
`the distance between the plates 12 and 14); and on to
`one close to parallel with the lines 24 (a short distance
`from the surface of plate 14).
`The effect of the liquid crystal unit on polarized light
`directed through the plates 12 and 14 and polarized
`parallel to the lines 22, for example, is that the unit ef-
`fects a rotation of the plane of polarization of the light
`as it passes through the unit, so that the light emanating
`from the surface of the plate 14 is plane polarized
`parallel to the lines 24. However, it would not matter if
`the plane polarized light impinging upon the plate 12,
`for example, were polarized in parallel planes that were
`at some angle with respect to the lines 22. The same ef-
`fect of rotation of the plane of polarization is obtained.
`The extent of rotation does not need to be 90°. Any
`desired extent of rotation may be obtained, merely by
`properly orienting the unidirectionally rubbed surfaces
`on the plates 12 and 14. However, when the directions
`of rubbing are at right angles to each other, the extent
`of rotation is 90°.
`
`The effect of the crystal unit 10 on polarized light is
`schematically illustrated in FIG. 3. Thus, a source of
`unpolarized or natural light at 26 impinges upon a con-
`ventional polarizer 28 which polarizes the light
`in-
`dicated by the broken lines 30. This polarized light, as
`it passes through a liquid crystal unit such as unit 10
`shown in FIG. 1, will be rotated through 90° so that the
`polarized light is then polarized in a plane indicated by
`the broken lines 32. This polarized light will then pass
`through a second polarizer 34 adapted to pass
`polarized light in a plane which is rotated at 90° with
`respect to the plane of polarization of polarizer 28, as
`indicated by the broken lines 36. Hence, under the con-
`ditions described, the polarized light passing through
`polarizer 28 will be rotated through 90° in unit 10 and
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`Page 5 of 8
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`3,731,986
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`will then pass through the polarizer 34. On the other
`hand, if the polarizer 34 should be rotated such that the
`plane of polarization indicated by broken lines 36 is
`parallel to the plane of polarization of polarizer 28,
`then no light will pass through polarizer 34.
`Now, if an electrical potential, on the order of 5 volts
`or greater, is applied between the conducting films I8
`and 20, the liquid crystal unit It) will no longer rotate
`the plane of polarization through 90°. In the arrange-
`ment shown in FIG. 3, for example, application of a
`suitable potential to the conducting films 18 and 20 will
`cause the polarizer 34 to block the transmission of
`light. It can thus be seen that the device acts as an opti-
`cal shutter. On the other hand, if the polarizer 34 is
`oriented 90° with respect to that shown in FIG. 3, no
`light will be transmitted in the absence of a potential
`applied between the films 118 and 20; whereas light will
`be transmitted when a potential is applied thereacross.
`Referring again to FIG. l, the polarizers 28 and 34
`are in the form of flat sheets, preferably dichroic
`polarizing sheets of the type manufactured by Polaroid
`Corporation. However, other types of polarizers may
`be used to suit requirements. For that matter, instead of
`using separate polarizing sheets or separate polarizers,
`the polarizers can be directly incorporated into the
`device 10. In this regard, the surfaces of the conductive
`coatings 18 and 20, for example, can be rubbed and
`treated with a solution of a dye which forms a dichroic
`film as described in Dreyer U.S. Pat. Nos. 2,544,659,
`2,524,286 and 2,400,877. Such a solution can com-
`prise a 4 percent aqueous solution of methylene blue.
`By coating the rubbed surface of the conductive film 18
`or 20 with this dye solution and allowing it to dry, a
`dichroic film will be deposited on the surface with a
`thickness on the order of about 1 micron. By placing
`the liquid crystal material as described above between
`the two rubbed plates treated with polarizing material,
`a single layer material will result which will have the
`complete system incorporated. Thus, the liquid crystal
`will align up parallel to the rubbed direction. When
`these are placed together, the polarizers will be crossed
`but with the liquid crystals between there will be a max-
`imum of transmission. When an electric field is applied
`to the conducting layers, the liquid crystal layer will
`become opaque. This will occur at approximately 5
`volts field since the dye represents but a small fraction
`of the insulating layers between the electrodes.
`In FIG. 1, the means for applying an electric field
`between the conducting films I8 and 20 is shown as a
`conventional battery 38 adapted to be connected into
`the conducting films I8 and 24) through switch 441). Al-
`ternatively, however, the same effect can be achieved
`(i.e., changing the plane of the polarized light passing
`through the device 10) with the use of a magnetic field
`in which the lines of flux extend perpendicular to the
`surfaces of the plates 12 and I4 as indicated by the
`north and south pole indications of FIG. 1. However, as
`will become apparent hereinafter, the use ofa magnetic
`field in most displays is impractical because of the dif-
`ficulties in localizing such a field.
`With reference now to FIG. 4, one type of optical
`display which can be provided with the liquid crystal
`device 10 of FIG. 1 is shown. It again comprises a pair
`of transparent plates 42 and 44 having their opposing
`surfaces rubbed in directions at right angles to each
`
`other and between which a layer of nematic liquid
`crystal material of positive dielectric anisotropy is
`disposed. The resulting sandwich is
`then placed
`between polarizers as in FIG. I, or the facing surfaces
`of the plates 42 and 44 are treated to form a dichroic
`film as described above. In this case, however, the con-
`ducting films 46 and 48 are in the form of the numeral
`4. Assuming that the plates 42 and 44 are assembled
`with polarizers in the arrangement of FIG. 3 and that
`switch 52 is closed to apply a potential from battery 50
`across the films 46 and 48, the area covered by the
`films will be opaque while the area around the conduct-
`ing films 46 and 48 will transmit light. Assuming that a
`white background is behind the assembled plates 42
`and 44 with liquid crystal material and that the plate is
`viewed from the side opposite the white background,
`the effect-will be to produce the numeral 4 in black-on-
`white. Of course, when the switch 52 is again opened,
`the device will be totally light transmitting and no nu-
`meral or other optical image will appear to the eye of
`the observer.
`
`The device of FIG. 4, while workable, can produce
`only a single optical image such as a numeral or letter
`within the area encompassed by plates 42 and 44. A
`system for producing any desired numeral, letter or
`other image within the same area is shown in FIGS.
`5-7. The system again includes two plates 54 and 56
`(FIG. 5) having facing surfaces which are rubbed at
`right angles with respect
`to each other,
`the space
`between the two surfaces being filled with a layer of ne-
`matic liquid crystal material of positive dielectric
`anisotropy. The mating surfaces of the plates 54 and 56
`are again coated with a conducting film; but in this
`case, the plate 54, for example, is etched, utilizing con-
`ventional photoresist masking techniques, to provide
`five vertical columns 58 each having seven enlarged
`areas 60 spaced along its length. In a somewhat similar
`manner, the plate 56 is coated and then etched to pro-
`vide seven horizontal rows 62 each provided with five
`enlarged area sections 64 of conducting film material
`between its ends. The plates 54 and 56, when facing
`each other with a layer of liquid crystal material
`therebetween, are positioned such that the enlarged
`area portions 60 on the plate 54 are aligned with or
`overlie the enlarged" area portions 64 on the plate 56.
`The ends of the strips or columns 58 on the plate 54 are
`connected to five electrical
`leads 66. Similarly, the
`ends of the strips or horizontal rows 62 on plate 56 are
`connected to a second set of seven electrical leads 68.
`The manner in which an assembly formed of the
`plates of FIG. 5 can be used to produce various images
`is shown in FIGS. 6 and 7. The assembled device com-
`
`prising plates 54 and 56 with a layer of nematic liquid
`crystal material
`therebetween of positive dielectric
`anisotropy and suitable cross polarizers is indicated in
`FIG. 6 by the reference numeral 7G. The circles on
`device '70 represent overlapping enlarged area portions
`6th and 64 formed in the columns 58 and rows 62,
`respectively.
`Clock pulses for the display are supplied from an
`oscillator 7 2 typically having a frequency of about 960
`hertz. These pulses are applied to a flip-flop circuit 73,
`the output of the flip-flop circuit being fed to a conven-
`tional three—bit ring counter '74 which produces pulses
`on leads '76, 78 and 80, those on lead '76 being divided
`
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`by two, those on lead 78 being divided by four and
`those on lead 80 being divided by eight. The pulses on
`leads 76-80 are applied to a decoding matrix 82 in ac-
`cordance with well-known techniques to produce pul-
`ses on output leads 84 which are displaced in phase 5
`with respect to each other. These are applied through
`inverters 86 and leads 68 to the respective horizontal
`rows 62 which are identified by the letters A-G.
`The outputs of the inverts 86 appearing on leads 68
`are identified as waveforms A through G in FIG. 7. 10
`During one frame period, a pulse appears on each of
`the rows in succession. Thus, the pulse in waveform A
`is applied to the top row first, followed by a pulse ap-
`plied to the second row, followed by a pulse applied to
`the third row, and so on. The time required for pulses in
`waveforms A-G to be applied in succession to each of
`the rows is referred to as one frame period and may
`typically be 16 microseconds; however
`the frame
`period may be any desired time interval, depending
`upon the size of the display and the number of horizon-
`tal rows employed. Note that the pulses in waveforms
`A-G are of negative polarity. These pulses are applied
`to the rows in succession continuously regardless of the
`optical image, such as a numeral or letter, which it is
`desired to produce.
`The pulses on leads 76—80 are also applied to a read-
`only memory unit 88 connected, for example, to com-
`puter circuitry 90 or the like. The pulses on leads
`76-80 activate the read-only memory unit 88 to apply
`to leads 92 a succession of pulses representative of a
`particular numeral, letter or other image to be dis-
`played. These are applied through inverters 94 and
`capacitors 96 to the vertical
`rows 58 which are
`identified by the letters H—M. It will be assumed that
`the background behind the unit 70 is white and that the
`liquid crystal sandwich including polarizers on opposite
`sides of the liquid crystal
`layer normally transmits
`polarized light in the absence of the application of an
`electrical potential applied across the liquid crystal
`layer. That is, the arrangement of FIG. 3 is employed.
`In order to produce the numeral 2, for example, only
`those areas colored black in FIG. 6 between the strips
`58 and 62 should have electrical potentials applied
`therebetween, whereby these areas will be opaque and
`appear black when viewed by an observer. In order to
`accomplish this effect, the waveforms H-M of FIG. 7
`are applied to the leads 66. Note that in order to
`produce the numeral 2, the second, sixth and seventh
`areas 60, 64 between the strips 58 and 62 in column I-I
`must have
`potentials
`applied
`thereacross. Con-
`sequently, the waveform I-I comprises a first positive
`pulse in the frame period coinciding with the negative
`pulse in waveform B, a second positive pulse coinciding
`with the negative pulse in waveform F, and a third posi-
`tive pulse coinciding with the negative pulse in
`waveform G. As the pulses on leads 63 sweep through
`one frame period, those which coincide with positive
`pulses in waveform I-I will cause the second, sixth and
`seventh areas to become opaque. Similarly, in column
`J, it is necessary to render the first, fifth and seventh
`areas opaque. This is caused by having a positive pulse
`in waveform J coincide with a negative pulse in
`waveform A, a positive pulse in waveform J to coincide
`with a negative pulse in waveform E and a positive
`pulse in waveform J to coincide with a negative pulse in
`
`waveform G. The various areas forming the numeral 2
`of FIG. 7 will not be continually opaque; however the
`sweeping action will occur sufficiently rapidly so that a
`continual image will appear to the naked eye. Any
`flicker effect appearing to the observer can be reduced
`by shortening the frame period and increasing the
`scanning frequency.
`In FIG. 8, still another embodiment of the invention
`is shown wherein one of two transparent plates 96 is
`provided with a continuous layer of transparent con-
`ducting material 98; while the other transparent plate
`99 is provided with a series of mutually insulated strips
`of transparent conducting material 100. The total con-
`figuration, when opaque, represents the numeral 8.
`Beneath the configuration 100 is a line or bar 102 and
`to the right of the configuration is a dot 104 which
`forms a decimal point when a plurality of the arrays of
`FIG. 8 are placed side-by-side. The dot 104 is aligned
`with area 98A of layer 98; while area 983 is aligned
`with the bar 102. The various mutually insulated con-
`ductive strips forming the configuration 100, in turn,
`are connected through a plurality of mutually insulated
`strips of transparent conducting material 106 to exter-
`nal leads, not shown. Assuming, for example, that it is
`desired to form the numeral 3, the plate 98 on one side
`of the layer of liquid crystal material will be connected
`to a source of positive potential while the transparent
`strips on the other side forming a 3 will be connected
`through leads 108 to a source of negative potential. If it
`is desired to place a decimal point beside the numeral,
`the lead connected to the spot 104 will be connected to
`the same source of negative potential; and if it
`is
`desired to provide a line beneath the numeral, the lead
`connected to strip 102 will be connected to the source
`of negative potential. In any case, only those portions
`on the plate 99 will appear opaque on a white
`background (or vice versa) which are connected to a
`source of potential of polarity opposite to that applied
`to the plate 98. As will be appreciated, a series of the
`displays shown in FIG. 8 can be assembled in side-by-
`side relationship to provide any desired number of
`digits.
`Although the invention has been shown in connec-
`tion with certain specific embodiments, it will be readi-
`ly apparent to those skilled in the art that various
`changes in form and arrangement of parts may be made
`to suit requirements without departing from the spirit
`and scope of the invention.
`I claim as my invention:
`
`intelligence
`1. A device for converting electrical
`into an optical
`image comprising a layer of liquid
`crystal material nematic at room temperature and
`disposed between transparent parallel plates, both of
`said plates being coated with films of transparent con-
`ducting material. at
`least one of said plates being
`coated on only selected areas thereof with films of
`transparent conducting material, means for effecting
`a twisted nematic structure in said layer of liquid
`crystal material, polarizers on opposite sides of
`said layer of liquid crystal material and extending
`essentially parallel to said plates to provide a sandwich
`structure through which light can pass, and means for
`establishing a potential difference between films on
`the respective plates such that some areas ofthe sand-
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`9
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`3,731,986
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`10
`
`light while others will
`transmit
`wich structure will
`not to thereby form an optical image.
`2. The device of claim 1 wherein said liquid crystal
`material comprises a mixture of 40 percent bis-(4'-n-
`octyloxybenzal)-2-chlorophenylenediamine, 50 per? 5
`cent plmethylbenzal-p'-n-butylaniline and 10 percent
`p-cyanobenzal-p’-n-butylaniline.
`3. The device of claim 1 wherein said polarizers com-
`prise polarizing sheets on the sides of said plates op-
`posite said liquid crystal material.
`4. The device of claim 1 wherein the crystal material
`is nematic and of positive dielectric anisotropy.
`5. The device of claim 1 wherein one of said
`polarizers polarizes light at right‘ angles to the other,
`whereby light will pass through the entirety of said
`sandwich
`structure with
`no
`electrical potential
`established between said films, said films acting to
`block the passage of light through selected areas of said
`sandwich structure upon application of a potential dif-
`ference between said films.
`6. The device of claim 1 wherein said films on the
`respective plates are in the form of a desired image.
`7.'The device of claim 1 wherein said films on the
`respective plates are in the form of mutually insulated
`strips which cross each other.
`8. The device of claim 9 including means for apply-
`
`ing pulses to the mutually insulated strips on the
`respective plates.
`9. The device of claim 10 including means for ap-
`plying pulses of one polarity in succession to the strips
`on one of said plates, and means for simultaneously and
`selectively applying pulses of the opposite polarity to
`the strips on the other of said plates, each of said pulses
`of the opposite polarity being in phase with at least one
`of the pulses of said one polarity, whereby light trans-
`mitting characteristics of said sandwich structure will
`be vari