CA1178700A - Liquid crystal visual display unit and telephone terminal incorporating such a unit - Google Patents
Liquid crystal visual display unit and telephone terminal incorporating such a unitInfo
- Publication number
- CA1178700A CA1178700A CA000357016A CA357016A CA1178700A CA 1178700 A CA1178700 A CA 1178700A CA 000357016 A CA000357016 A CA 000357016A CA 357016 A CA357016 A CA 357016A CA 1178700 A CA1178700 A CA 1178700A
- Authority
- CA
- Canada
- Prior art keywords
- liquid crystal
- unit according
- unit
- lines
- visual display
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/132—Thermal activation of liquid crystals exhibiting a thermo-optic effect
Abstract
ABSTRACT OF THE DISCLOSURE
The invention relates to liquid crystal visual display units permitting a direct visual observation. In a known unit it consists of selecting the material supporting a system of heating electrodes so as to permit an adequately low thermal dissipation to limit the supply power of the unit, whilst still retaining an adequate inscription speed. The shape of the electrodes is adapted to the dimensions of the unit and to the resistance necessary for this supply power. It makes it possible to produce visual display units integrated into a telephone terminal.
The invention relates to liquid crystal visual display units permitting a direct visual observation. In a known unit it consists of selecting the material supporting a system of heating electrodes so as to permit an adequately low thermal dissipation to limit the supply power of the unit, whilst still retaining an adequate inscription speed. The shape of the electrodes is adapted to the dimensions of the unit and to the resistance necessary for this supply power. It makes it possible to produce visual display units integrated into a telephone terminal.
Description
117~ V
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal visual display units making it possible to display visual information represented by an electrical signal applied to said units. It also relates to telephone terminals incorporating such a unit and which make it possible, for example, to remotely consult a telephone directory.
It is known to construct liquid crystal visual display units using different electro-optical effects.
French Patent Application 2,389,955 published on December 1~ 1978 by the Applicant company and entitled "Picture display unit and television system using such a unit" describes a visual display unit in which inscription takes place by the process of electrical heating and biasing.
For this purpose the unit comprises a system of heating lines which are successively excited by a heating voltage. The liquid crystal passes into a liquid phase along the line which is heated and then becomes diffusive on cooling. The unit also comprises a system of columns which intersect with the system of lines. A group of voltages representing the line to be inscribed is applied to these columns during the cooling of the line. As a function of the value of the electrical field resulting from the voltages applied the liquid crystal becomes more or less diffusive at each 'q~
11787(~V
intersection between the colu~s and the cooling line~ It is thus p~ssible to inscribe or enter in the unit a picture or image analysed in accordance, for example, with a television field. This inscription takes place on a line by line basis. ~he thus inscribed picture remains stored until an erasure takes place. ~he latter occurs, for example, on inscribing the follo~/ing picture where each line is erased during heating and then inscribed with the new signal during cooling.
~ he dimensions of this unit are essentially limited for thermal dissipation reasons~ ~hus, if it was desired ~o obtain a unit which could be observed with the naked eye and at a reasonable dist~nce a very high power would have to be dissi ated in each .eating line. It would not be possible to control this power and it could lead to the destruction of the system. In order to observe the thus inscribed picture it is possible in cer+ain cases to use a magni ~ing glass, but most often it is projected on to a screen. ~or the use of such a unit in a television receiver the overall dimensions, cost and maintainance requirements of the ancillary devices necessary for carrying out such a projection are of little importance.
However, when using such a unit in a telephone terminal, particularly for consulting a directory, it is absolutely necessary to be able to see it directly without effecting a projection. ~he dimensions which are then necess-ary, approximately 10 centimeters, do not make it
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal visual display units making it possible to display visual information represented by an electrical signal applied to said units. It also relates to telephone terminals incorporating such a unit and which make it possible, for example, to remotely consult a telephone directory.
It is known to construct liquid crystal visual display units using different electro-optical effects.
French Patent Application 2,389,955 published on December 1~ 1978 by the Applicant company and entitled "Picture display unit and television system using such a unit" describes a visual display unit in which inscription takes place by the process of electrical heating and biasing.
For this purpose the unit comprises a system of heating lines which are successively excited by a heating voltage. The liquid crystal passes into a liquid phase along the line which is heated and then becomes diffusive on cooling. The unit also comprises a system of columns which intersect with the system of lines. A group of voltages representing the line to be inscribed is applied to these columns during the cooling of the line. As a function of the value of the electrical field resulting from the voltages applied the liquid crystal becomes more or less diffusive at each 'q~
11787(~V
intersection between the colu~s and the cooling line~ It is thus p~ssible to inscribe or enter in the unit a picture or image analysed in accordance, for example, with a television field. This inscription takes place on a line by line basis. ~he thus inscribed picture remains stored until an erasure takes place. ~he latter occurs, for example, on inscribing the follo~/ing picture where each line is erased during heating and then inscribed with the new signal during cooling.
~ he dimensions of this unit are essentially limited for thermal dissipation reasons~ ~hus, if it was desired ~o obtain a unit which could be observed with the naked eye and at a reasonable dist~nce a very high power would have to be dissi ated in each .eating line. It would not be possible to control this power and it could lead to the destruction of the system. In order to observe the thus inscribed picture it is possible in cer+ain cases to use a magni ~ing glass, but most often it is projected on to a screen. ~or the use of such a unit in a television receiver the overall dimensions, cost and maintainance requirements of the ancillary devices necessary for carrying out such a projection are of little importance.
However, when using such a unit in a telephone terminal, particularly for consulting a directory, it is absolutely necessary to be able to see it directly without effecting a projection. ~he dimensions which are then necess-ary, approximately 10 centimeters, do not make it
- 2 -V
possible to construct the unit without adaptation.
BRIEF SUMMARY OF THE INVENTION
The present invention therefore relates to a liquid crystal visual display unit of the type incor-porating a liquid crystal layer which can be inscribedby electrical heating and biasing and incorporated between two plates, whereof at least one is transparent, a system of resistive lines located between one of the plates and the liquid crystal layer and making it possible to heat the liquid crystal at least up to its erasure temperature successively in accordance with each of the lines and a system of columns located between the other plate and the liquid crystal layer intersecting with the lines and making it possible to apply to the whole of this layer during the cooling of a line an electric field representing the information to be inscribed along the cooling line, wherein the thermal diffusivity of the plate supporting the resistive lines is below a value making it possible to obtain a unit which can be observed with the naked eye~
DESCRIPTION OF THE DRAWINGS
Fi.gure 1 is a perspective view of the visual display unit;
Figure 2 is a sectional view thereof; and Figures 3, 4 and 5 are sectional views of a three embodiments a transparent heating line used in the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The view of Figure 1 is limited, for reasons of clarity, to a portion of the unit incorporating a single 11787(~) electrode in each direction and definin~ a single visual display point.
A liquid crystal layer 10~ is inserted between two plates 101 and 1C5. ~ system of resistive lines such as 102 is deposited on plate 101 in contact with the liquid crystal.
By means of electrodes such as ~ these lines are supplied by a heating voltage ~Jhich heate them by the Joule effect to a temperature bringing the liquid crystal into the isotropic phase. On removing the heating volta~e the liquid crystal cools and during cooling assumes a so-called focal conic structure which is diffusive.
On contact with the liquid crystal plate 105 carries a system of col~ns such as 104 provided with connections H. 3y applying a voltage of appropriate value between connections and H during the cooling o~ ~he liquid crystal an electric field is produced within said liquid crystal at the intersection points of lines 102 and columns 104. This electrical field then prevents the focal conic str~cture from ~eing established during cooling and the liquid crystal retains its transparent appearance.
~his electrical field only acts on the crystal which is being cooled and is unable to reorient the crystal which is being cooled and diffused ~efore the application of the electrical field.
~he system of lines 102 and columns 104 ma~es it possible to inscribe the desired information on each of the lines whilst proceeding with a line b~ line addressing by successively heatin~
each of the lines 102 and by applying the 5 desired voltages to columns 104.
~17~7~1 It is possible to produce a unit for providing a television-typ~ dislay, i.e.
with a maxim~m time for inscri`oing one line less than 64 microseconds. ~or this purpose it is neccessary to rapidly heat and cool the liquid crystal and consequently the entire zone surrounding the heating line used. The constraint on the cooling time leads to the use for plate 101 of a silicon substrate covered with a fine layer of silicon monoxide permitting the electrical insulation of the heating lines 102 from the said substrate.
The thus fixed heat diflusion rate to substrate 101 imposes a minimum value to the heat dissipation by the Joule effect and surface unit in line 102. lhus, the minimum power per heating line length unit is obtained, bearing in mind that it is necessary to respect a certaln for~.at of the picture to be displayed. Since it is necessary to be able to control the voltages applied tG connections ~ which in practice - impose the use of an integrated circuit in substrate 101, it is impossible to exceed a certain total supply power of the heating lines, which would in fact be destroyed by the heat given off if this po~er level was exceeded. Bearing in mind all these points the dimensions of the units produced are approximately 1 centimeter.
~ o use a visual display unit of this type in a telephone terminal for e.g.
remotely consulting a telephone directory it is desirable for the purpose of carrying out a direct observation under comfortable ~17B7(~0 conditions for the subscriber to produce a unit having dimensions of a proxim~tely 10 centimeters. If produced in the manner described hereinbefore such a unit would require an extravagant supply power of a few kilowatts.
However, i~ is not then necessary to use a television-type scanning and the usu81 specifications require the inscription of 120 alphanumeric characters/second in the form of 25 ~f lines 40 characters for a 10 x 10 cm screen. lhen assuming the analysis of an alphanumeric character prcduced according to a 7 x 5 matrix and counting 2 run-up times between the characters and 3 run-up times between the lines this corresponds to 200 lines and 200 columns or 2 lines and 2 columns /mm, their width being equal to a little less than 50 hundredths of a millimeter to take account of a certain gap betreen them. Thus, the lines are addressed to obtain 120 characters/second at a rate of 24 heating lines/second, i.e. a time available for the inscription of at the most equal to 40 milliseconds.
Thus, a much longer time is available than in the presently known unit for cooling the liquid crystal after it has been heated.
The thermal diffusivity of the silicon substrate covered with a thin layer (approxim-ately 5~ ) of silicon monoxide which is 1 cm2/s and which permitted the speed necessary for a television-type displa~ is no longer of any use here and can even be prejudicial due to the large dimensions of the unit and the 7Ul3 heatinO power which it requires. .~owever, a relatively large ~ount of heat mus~ be removed by plate 101 and not by liquid crystal 103 in order that a cu~ulative phenomenon does not bring the complete liquid crystal into the isotropic state without being able to return to the diffusive state, except by cutting ofi the power supply to the apparatus for a relatively long periQd. As the diffusivity of the liquid crystal is used is generally approximately 2.10 3 cm2/s it is possible, for example, to use glass, whose thermal diffusivity is substantially 5.5.10 3 cm2/s. ~his material is inexpensive and can be obtained with the desired dimensions with a surface state which is completely suitable for the envisaged application. ~owever, its diffusivity is a little too low compared with that of the ! li~uid crystal and, if necessary, it is possible to use silica (8.3.10 3 cm/s) or sapphire (8.4.10 2cm2/s~ or synthetic materials such as ethylene glycol polyterephthalate (2.10 4 cm2/s3 or polyimide (4.10 3cm2/s).
As these materials are flexible in the usually available thicknesses they are generally employed by doubling a plate forming a substrate and which can be of glass in the case of a unit used in transmission.
~here are two possible construction modes, depending on whether visual display takes place by re~lection of ambient light or by transmission of light coming from a source located behind the screen.
ln the case of operation by reflection, l~hich is already kno~Jn for the cell for the 11~787(~0 television visual display described hereinbefore, displa~- tal~es place by reflection of the reflecting surface of the heating lines. These lines can then be produced, for example, by evaporating under vacuum aluminium with a thickness of 2 to 3000 ~. A resistive line of this thickness, with a length of ~0 cm and a width of 40 hundredths of a millimeter will have a resistance substantially equal to 50 ohms.
In order to be able to carry out an inscription in less than 40 milliseconds the power neceesary for an ethylene glycol polyterephthalate substrate is 100 watts and for a polyimide substrate 50 watts. ~he supply voltage is then approximately 50 volts, which is quite compatible with the semiconductor switching devices liable to be used for control purposes.
'~he columns making it possible to apply the electrical fields to the liquid crystal are transparent and are made, for example, from a mixed oxide of indium and tin. As they do not dissipate power their construction is of an entirely conventional nat-~e.
To obtain a visual display by transmission it is necessary that the heating lines are transparent and are made, for exa~ple from a mixed oxide of indium and tin and in a limited thickness. Under these conditions the resistivity of the transparent oxide layer is necessarily higher. A standard value is 1250 ohms per square. In order to then obtain the necessary heating power by supplying such an electrode between its terminals it would be necessary to use a much too high voltage, ii78'7(~(~
~hich could not be s~ritched by semiconductor control devices. To obviate this disadvantage a special const~uction of the hea~in~ line is necessary.
i5 In a first embodiment of such a transparent heating line sho~m in Fig. 3 a transparent conductive layer of high resistivity 301 is placed between two conductors 302 and 303 extending along the line ard having a very low resistivity. ~hese conductors are, for example, obtained by aluminium evaporation with a relatively large~
thic~ness of e.g. 1 micron and their resistance is negligible compared ~rith that of layer 301.
The latter is consequently supplied Detween the positive and negative terminals on the heating voltage source perpendicular to its largest dimension and the overall resistance is thus brought to a correct value of approximately 50 ohms.
In a constructional variant sho~Jn in ~'ig.
4 layer 301 is divided into a series of blocks separated by slots 304 perpendicular to electrodes 302 and 303. These blocks exactly correspond to the intersection ~ith columns 104 permitting the application of the electrical field. ~his arrangement serves to regularize the current lines within layer 301.
In another constructional variant sho~m in Fig. 5 the transparent conductive layer of lower resistivity than that of Figs. 3 and 4 is used and in order to retain an adequate total resistance the heating line is divided into four equally long portions respectively 511 to 514, which are electrically arranged in _ g _ 1~787(~(~
series by flve electrodes 501 ~o 505 connected to portions 511 to 514 by their lrges-t sides.
~hus, the electrical current traverses each of these portions perpendicular to its greatest length. This leads to a relatively low resistance of each portion. However, these portions are then arranged in series, thereby multiplying by four, as compared with the resistance of one portion, the total resist~nce of the heating line. Thus, in the case of the drawing, the electrical current s~arts from electrode 501 to pass to electrode 502 across portion 511, then to electrode 503 across portion 512 and so on up to electrode 505.
The variant of Fig. 4 can oe used i-n this case by subdividing each portion such as 511 into pa~ts corresponding to the intersection with the columns 504. ~he slots used for t separating these parts are parellel to the current lines, so that the total resistance remains substantially unchanged.
By using the variant of ~ig. 5 with a different number of line por~ions it is possible to adapt the total resistance of the line to the resistivity of the l~yer used, this being within a wide range of resistivity.
~ Yhereas in television-type application it is conventional practice to use a liquid crystal of the cyano-alkyl-biphenyl type and particularly 4,4'-cyano-octyl-biphenyl, known as ~OB, which has between the liquid phase and the isotropic phase in succession a smectic phase A and then a nematic phase.
In the case of units according to the inven~ion where the inscription speed is not ~787~0 of vital import~lce to use 2 liquid crystal having a c-olesteric phase insvead of a nematic ~hase.
~or this purpose it is possible, for example, to use the same liquid crystal C03, hilst adding to it a small proportion of a chiral product such as turpentine oil. ~he thus doped C0~ then successively has the crystalline phases smectic l~ cholesteric and finally isotropic ~hen the vemperature rises.
During cooling the focal conic structure has a pitch which varies i-n si~e rith the percentage of chiral product used. As this percentage increases the dimension of the diffusing domains increases a-nd simultaneously the elec~rical field necessary for obtaining an ordinate phase decreases. ~ihen this pitch assumes too high a volume it exceeds the pitch o-r the screen and inscri tion becomes impossible. However, when there is little dopa;qt the field to be applied is too great, all the more so because the thickness of the liquid crystal to be used to obtain a continuous plate with a cell having such large dimensions is relatively great. For the construction used a correc~ value for the dopant quantity is a few percent.
Adjustment takes place in order to obtain a pitch for the focal conic structure between 1 and 100 microns.
possible to construct the unit without adaptation.
BRIEF SUMMARY OF THE INVENTION
The present invention therefore relates to a liquid crystal visual display unit of the type incor-porating a liquid crystal layer which can be inscribedby electrical heating and biasing and incorporated between two plates, whereof at least one is transparent, a system of resistive lines located between one of the plates and the liquid crystal layer and making it possible to heat the liquid crystal at least up to its erasure temperature successively in accordance with each of the lines and a system of columns located between the other plate and the liquid crystal layer intersecting with the lines and making it possible to apply to the whole of this layer during the cooling of a line an electric field representing the information to be inscribed along the cooling line, wherein the thermal diffusivity of the plate supporting the resistive lines is below a value making it possible to obtain a unit which can be observed with the naked eye~
DESCRIPTION OF THE DRAWINGS
Fi.gure 1 is a perspective view of the visual display unit;
Figure 2 is a sectional view thereof; and Figures 3, 4 and 5 are sectional views of a three embodiments a transparent heating line used in the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The view of Figure 1 is limited, for reasons of clarity, to a portion of the unit incorporating a single 11787(~) electrode in each direction and definin~ a single visual display point.
A liquid crystal layer 10~ is inserted between two plates 101 and 1C5. ~ system of resistive lines such as 102 is deposited on plate 101 in contact with the liquid crystal.
By means of electrodes such as ~ these lines are supplied by a heating voltage ~Jhich heate them by the Joule effect to a temperature bringing the liquid crystal into the isotropic phase. On removing the heating volta~e the liquid crystal cools and during cooling assumes a so-called focal conic structure which is diffusive.
On contact with the liquid crystal plate 105 carries a system of col~ns such as 104 provided with connections H. 3y applying a voltage of appropriate value between connections and H during the cooling o~ ~he liquid crystal an electric field is produced within said liquid crystal at the intersection points of lines 102 and columns 104. This electrical field then prevents the focal conic str~cture from ~eing established during cooling and the liquid crystal retains its transparent appearance.
~his electrical field only acts on the crystal which is being cooled and is unable to reorient the crystal which is being cooled and diffused ~efore the application of the electrical field.
~he system of lines 102 and columns 104 ma~es it possible to inscribe the desired information on each of the lines whilst proceeding with a line b~ line addressing by successively heatin~
each of the lines 102 and by applying the 5 desired voltages to columns 104.
~17~7~1 It is possible to produce a unit for providing a television-typ~ dislay, i.e.
with a maxim~m time for inscri`oing one line less than 64 microseconds. ~or this purpose it is neccessary to rapidly heat and cool the liquid crystal and consequently the entire zone surrounding the heating line used. The constraint on the cooling time leads to the use for plate 101 of a silicon substrate covered with a fine layer of silicon monoxide permitting the electrical insulation of the heating lines 102 from the said substrate.
The thus fixed heat diflusion rate to substrate 101 imposes a minimum value to the heat dissipation by the Joule effect and surface unit in line 102. lhus, the minimum power per heating line length unit is obtained, bearing in mind that it is necessary to respect a certaln for~.at of the picture to be displayed. Since it is necessary to be able to control the voltages applied tG connections ~ which in practice - impose the use of an integrated circuit in substrate 101, it is impossible to exceed a certain total supply power of the heating lines, which would in fact be destroyed by the heat given off if this po~er level was exceeded. Bearing in mind all these points the dimensions of the units produced are approximately 1 centimeter.
~ o use a visual display unit of this type in a telephone terminal for e.g.
remotely consulting a telephone directory it is desirable for the purpose of carrying out a direct observation under comfortable ~17B7(~0 conditions for the subscriber to produce a unit having dimensions of a proxim~tely 10 centimeters. If produced in the manner described hereinbefore such a unit would require an extravagant supply power of a few kilowatts.
However, i~ is not then necessary to use a television-type scanning and the usu81 specifications require the inscription of 120 alphanumeric characters/second in the form of 25 ~f lines 40 characters for a 10 x 10 cm screen. lhen assuming the analysis of an alphanumeric character prcduced according to a 7 x 5 matrix and counting 2 run-up times between the characters and 3 run-up times between the lines this corresponds to 200 lines and 200 columns or 2 lines and 2 columns /mm, their width being equal to a little less than 50 hundredths of a millimeter to take account of a certain gap betreen them. Thus, the lines are addressed to obtain 120 characters/second at a rate of 24 heating lines/second, i.e. a time available for the inscription of at the most equal to 40 milliseconds.
Thus, a much longer time is available than in the presently known unit for cooling the liquid crystal after it has been heated.
The thermal diffusivity of the silicon substrate covered with a thin layer (approxim-ately 5~ ) of silicon monoxide which is 1 cm2/s and which permitted the speed necessary for a television-type displa~ is no longer of any use here and can even be prejudicial due to the large dimensions of the unit and the 7Ul3 heatinO power which it requires. .~owever, a relatively large ~ount of heat mus~ be removed by plate 101 and not by liquid crystal 103 in order that a cu~ulative phenomenon does not bring the complete liquid crystal into the isotropic state without being able to return to the diffusive state, except by cutting ofi the power supply to the apparatus for a relatively long periQd. As the diffusivity of the liquid crystal is used is generally approximately 2.10 3 cm2/s it is possible, for example, to use glass, whose thermal diffusivity is substantially 5.5.10 3 cm2/s. ~his material is inexpensive and can be obtained with the desired dimensions with a surface state which is completely suitable for the envisaged application. ~owever, its diffusivity is a little too low compared with that of the ! li~uid crystal and, if necessary, it is possible to use silica (8.3.10 3 cm/s) or sapphire (8.4.10 2cm2/s~ or synthetic materials such as ethylene glycol polyterephthalate (2.10 4 cm2/s3 or polyimide (4.10 3cm2/s).
As these materials are flexible in the usually available thicknesses they are generally employed by doubling a plate forming a substrate and which can be of glass in the case of a unit used in transmission.
~here are two possible construction modes, depending on whether visual display takes place by re~lection of ambient light or by transmission of light coming from a source located behind the screen.
ln the case of operation by reflection, l~hich is already kno~Jn for the cell for the 11~787(~0 television visual display described hereinbefore, displa~- tal~es place by reflection of the reflecting surface of the heating lines. These lines can then be produced, for example, by evaporating under vacuum aluminium with a thickness of 2 to 3000 ~. A resistive line of this thickness, with a length of ~0 cm and a width of 40 hundredths of a millimeter will have a resistance substantially equal to 50 ohms.
In order to be able to carry out an inscription in less than 40 milliseconds the power neceesary for an ethylene glycol polyterephthalate substrate is 100 watts and for a polyimide substrate 50 watts. ~he supply voltage is then approximately 50 volts, which is quite compatible with the semiconductor switching devices liable to be used for control purposes.
'~he columns making it possible to apply the electrical fields to the liquid crystal are transparent and are made, for example, from a mixed oxide of indium and tin. As they do not dissipate power their construction is of an entirely conventional nat-~e.
To obtain a visual display by transmission it is necessary that the heating lines are transparent and are made, for exa~ple from a mixed oxide of indium and tin and in a limited thickness. Under these conditions the resistivity of the transparent oxide layer is necessarily higher. A standard value is 1250 ohms per square. In order to then obtain the necessary heating power by supplying such an electrode between its terminals it would be necessary to use a much too high voltage, ii78'7(~(~
~hich could not be s~ritched by semiconductor control devices. To obviate this disadvantage a special const~uction of the hea~in~ line is necessary.
i5 In a first embodiment of such a transparent heating line sho~m in Fig. 3 a transparent conductive layer of high resistivity 301 is placed between two conductors 302 and 303 extending along the line ard having a very low resistivity. ~hese conductors are, for example, obtained by aluminium evaporation with a relatively large~
thic~ness of e.g. 1 micron and their resistance is negligible compared ~rith that of layer 301.
The latter is consequently supplied Detween the positive and negative terminals on the heating voltage source perpendicular to its largest dimension and the overall resistance is thus brought to a correct value of approximately 50 ohms.
In a constructional variant sho~Jn in ~'ig.
4 layer 301 is divided into a series of blocks separated by slots 304 perpendicular to electrodes 302 and 303. These blocks exactly correspond to the intersection ~ith columns 104 permitting the application of the electrical field. ~his arrangement serves to regularize the current lines within layer 301.
In another constructional variant sho~m in Fig. 5 the transparent conductive layer of lower resistivity than that of Figs. 3 and 4 is used and in order to retain an adequate total resistance the heating line is divided into four equally long portions respectively 511 to 514, which are electrically arranged in _ g _ 1~787(~(~
series by flve electrodes 501 ~o 505 connected to portions 511 to 514 by their lrges-t sides.
~hus, the electrical current traverses each of these portions perpendicular to its greatest length. This leads to a relatively low resistance of each portion. However, these portions are then arranged in series, thereby multiplying by four, as compared with the resistance of one portion, the total resist~nce of the heating line. Thus, in the case of the drawing, the electrical current s~arts from electrode 501 to pass to electrode 502 across portion 511, then to electrode 503 across portion 512 and so on up to electrode 505.
The variant of Fig. 4 can oe used i-n this case by subdividing each portion such as 511 into pa~ts corresponding to the intersection with the columns 504. ~he slots used for t separating these parts are parellel to the current lines, so that the total resistance remains substantially unchanged.
By using the variant of ~ig. 5 with a different number of line por~ions it is possible to adapt the total resistance of the line to the resistivity of the l~yer used, this being within a wide range of resistivity.
~ Yhereas in television-type application it is conventional practice to use a liquid crystal of the cyano-alkyl-biphenyl type and particularly 4,4'-cyano-octyl-biphenyl, known as ~OB, which has between the liquid phase and the isotropic phase in succession a smectic phase A and then a nematic phase.
In the case of units according to the inven~ion where the inscription speed is not ~787~0 of vital import~lce to use 2 liquid crystal having a c-olesteric phase insvead of a nematic ~hase.
~or this purpose it is possible, for example, to use the same liquid crystal C03, hilst adding to it a small proportion of a chiral product such as turpentine oil. ~he thus doped C0~ then successively has the crystalline phases smectic l~ cholesteric and finally isotropic ~hen the vemperature rises.
During cooling the focal conic structure has a pitch which varies i-n si~e rith the percentage of chiral product used. As this percentage increases the dimension of the diffusing domains increases a-nd simultaneously the elec~rical field necessary for obtaining an ordinate phase decreases. ~ihen this pitch assumes too high a volume it exceeds the pitch o-r the screen and inscri tion becomes impossible. However, when there is little dopa;qt the field to be applied is too great, all the more so because the thickness of the liquid crystal to be used to obtain a continuous plate with a cell having such large dimensions is relatively great. For the construction used a correc~ value for the dopant quantity is a few percent.
Adjustment takes place in order to obtain a pitch for the focal conic structure between 1 and 100 microns.
Claims (11)
1. A liquid crystal visual display unit of the type incorporating a liquid crystal layer which can be inscribed by electrical heating and biasing and incor-porated between two plates, whereof at least one is transparent, a system of resistive lines located between one of the plates and the liquid crystal layer and making it possible to heat the liquid crystal at least up to its erasure temperature successively in accordance with each of the lines and a system of columns located between the other plate and the liquid crystal layer intersecting with the lines and making it possible to apply to the whole of this layer during the cooling of a line an electric field repre-senting the information to be inscribed along the cooling line, wherein the thermal diffusivity of the plate supporting the resistive lines is below a value making it possible to obtain a unit which can be observed with the naked eye.
2. A unit according to Claim 1, wherein the diffusivity of the plate supporting the resistive lines is below 2.10 2 cm2/s.
3. A unit according to Claim 2, wherein the liquid crystal can have a smectic A-cholesteric transition.
4. A unit according to Claim 3, wherein the liquid crystal is a chiral product-doped cyano-alkyl-biphenyl.
5. A unit according to Claim 1, wherein the plate supporting the resistive lines is made from glass.
6. A unit according to Claim l, wherein the plate supporting the resistive lines incorporates a substrate and a doubling material; said doubling material being a ethylene glycol polyterephthalate.
7. A unit according to Claim l, wherein the plate supporting the resistive lines incorporates a substrate and a doubling material; said doubling material being a polyimide material.
8. A unit according to Claim l, wherein the two pla-tes enclosing the liquid crystal are transparent and the resistive lines are formed by a transparent conductive strip of high resistivity inserted between two opaque conductive strips of low resistivity.
9. A unit according to Claim 8, wherein the transpa-rent conductive strip is divided into a number of por-tions corresponding to the intersections of the resistive lines with the columns.
10. A unit according to Claim l, wherein the two pla-tes enclosing the liquid crystal are transparent and each line comprises a system of aligned portions formed from a high resistivity, transparent conductive material, said portions being bordered by opaque, low resistivity conduc-tive strips making it possible to connect these portions in series in such a way that the electrical current traverses them in accordance with their width.
11. A telephone terminal of the type incorporating a telephone set and a visual display screen making it possible to display the information transmitted on the telephone line connected to the telephone set, wherein the display screen is a unit according to any one of the Claims 1 to 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7919426A FR2462755A1 (en) | 1979-07-27 | 1979-07-27 | LIQUID CRYSTAL VISUALIZATION DEVICE, AND TELEPHONE TERMINAL COMPRISING SUCH A DEVICE |
| FR7919426 | 1979-07-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178700A true CA1178700A (en) | 1984-11-27 |
Family
ID=9228374
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000357016A Expired CA1178700A (en) | 1979-07-27 | 1980-07-25 | Liquid crystal visual display unit and telephone terminal incorporating such a unit |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4390244A (en) |
| EP (1) | EP0023447B1 (en) |
| JP (1) | JPS5621184A (en) |
| CA (1) | CA1178700A (en) |
| DE (1) | DE3062622D1 (en) |
| FR (1) | FR2462755A1 (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4514045A (en) * | 1981-06-22 | 1985-04-30 | Minnesota Mining And Manufacturing Company | Helichromic-smectic liquid crystal compositions and display cells |
| FR2512243A1 (en) * | 1981-08-25 | 1983-03-04 | Thomson Csf | VISUALIZATION DEVICE WITH THERMO-ELECTRIC EFFECT |
| FR2523343A1 (en) * | 1982-03-09 | 1983-09-16 | Thomson Csf | SCREEN OF A VISUALIZATION DEVICE USING A THERMAL AND ELECTRICAL MIXED EFFECT |
| US4595260A (en) * | 1982-05-28 | 1986-06-17 | Nec Corporation | Liquid crystal projection display with even temperature elevation |
| JPS59127090A (en) * | 1983-01-10 | 1984-07-21 | インタ−ナショナル ビジネス マシ−ンズ コ−ポレ−ション | Matrix address smectic type liquid crystal display |
| JPS62119521A (en) * | 1985-11-19 | 1987-05-30 | Canon Inc | Optical modulating element and its driving method |
| US4818078A (en) * | 1985-11-26 | 1989-04-04 | Canon Kabushiki Kaisha | Ferroelectric liquid crystal optical modulation device and driving method therefor for gray scale display |
| US4824218A (en) * | 1986-04-09 | 1989-04-25 | Canon Kabushiki Kaisha | Optical modulation apparatus using ferroelectric liquid crystal and low-resistance portions of column electrodes |
| JP2505757B2 (en) * | 1986-07-23 | 1996-06-12 | キヤノン株式会社 | Driving method of optical modulator |
| US4859036A (en) * | 1987-05-15 | 1989-08-22 | Canon Kabushiki Kaisha | Device plate having conductive films selected to prevent pin-holes |
| FR2621728B1 (en) * | 1987-10-09 | 1990-01-05 | Thomson Csf | SYSTEM FOR VIEWING HALF-TONE IMAGES ON A MATRIX SCREEN |
| JPH0360438U (en) * | 1989-10-12 | 1991-06-13 | ||
| DE69223183T2 (en) * | 1991-06-10 | 1998-07-23 | Sharp Kk | Non-volatile memory device |
| FR2682798B1 (en) * | 1991-10-22 | 1994-01-21 | Sextant Avionique | METHOD AND DEVICE FOR OPTIMIZING THE PERFORMANCE OF A LIQUID CRYSTAL MATRIX SCREEN AS A FUNCTION OF THE ANGLE OF OBSERVATION. |
| US5444651A (en) * | 1991-10-30 | 1995-08-22 | Sharp Kabushiki Kaisha | Non-volatile memory device |
| FR2696258B1 (en) * | 1992-09-25 | 1994-10-28 | Sextant Avionique | Device for managing a human-machine interaction system. |
| GB2313226A (en) * | 1996-05-17 | 1997-11-19 | Sharp Kk | Addressable matrix arrays |
| JP3950327B2 (en) * | 2001-11-30 | 2007-08-01 | 株式会社日立製作所 | Manufacturing method of liquid crystal display element |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3401262A (en) * | 1965-06-29 | 1968-09-10 | Westinghouse Electric Corp | Radiation sensitive display system utilizing a cholesteric liquid crystalline phase material |
| US3912366A (en) * | 1973-12-06 | 1975-10-14 | Ibm | Liquid crystal display assembly having polyimide layers |
| FR2292253A1 (en) * | 1974-11-21 | 1976-06-18 | Thomson Csf | METHOD AND DEVICE USING A THERMO-OPTICAL EFFECT IN A LIQUID CRYSTAL FOR THE REPRODUCTION OF IMAGES IN REAL TIME AND WITHOUT MEMORY |
| FR2389955B1 (en) * | 1977-05-05 | 1981-12-04 | Thomson Csf | |
| DE2827471C2 (en) * | 1978-06-22 | 1982-09-02 | Siemens AG, 1000 Berlin und 8000 München | Liquid crystal cell with an induced cholesteric phase |
-
1979
- 1979-07-27 FR FR7919426A patent/FR2462755A1/en active Granted
-
1980
- 1980-07-18 EP EP80401076A patent/EP0023447B1/en not_active Expired
- 1980-07-18 DE DE8080401076T patent/DE3062622D1/en not_active Expired
- 1980-07-23 US US06/171,408 patent/US4390244A/en not_active Expired - Lifetime
- 1980-07-25 JP JP10232880A patent/JPS5621184A/en active Pending
- 1980-07-25 CA CA000357016A patent/CA1178700A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3062622D1 (en) | 1983-05-11 |
| JPS5621184A (en) | 1981-02-27 |
| EP0023447B1 (en) | 1983-04-06 |
| FR2462755B1 (en) | 1982-09-03 |
| EP0023447A1 (en) | 1981-02-04 |
| US4390244A (en) | 1983-06-28 |
| FR2462755A1 (en) | 1981-02-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |