Electro-optical display device

• US 4,413,885 A
• Filed: 02/11/1980
• Issued: 11/08/1983
• Est. Priority Date: 02/13/1979
• Status: Expired due to Term

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson-CSF
• Inventors: Huignard, Jean-Pierre, Hareng, Michel, Le Berre, Serge
• Primary Examiner(s): Punter, William H.
• Application Number:
  US06/120,319
• Time in Patent Office: 1,366 Days
• Field of Search: 350/342, 350/352, 350/388, 350/337, 350/393, 350/3.63, 350/356, 350/334, 350/332, 350/162 S, 350/339 F, 350/345, 365/108-109, 365/110, 365/112, 358/236, 340/783, 250/213 R, 250/484
• US Class Current: 349/25
• CPC Class Codes: G02F 1/133509 Filters, e.g. light shielding masks
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence
• CPC Class Codes: G02F 1/1357 Electrode structure

Abstract

An electro-optical display device which comprises a twisted nematic liquid crystal layer and a photo-conducting layer. Two crossed electrode assemblies allow the liquid crystal to be made transparent at the points to be displayed. The light which passes at these points makes the photo-conductor conducting which applies the whole of the voltage to the liquid crystal and gives greater rapidity of inscription and a memory effect.

Claims

1. An electro-optical display device which comprises:

a layer of electro-optical material having a first and a second face;

at least a first electrode on the first face of said layer of electro-optical material;

a layer of photo-conducting material having a first face facing the second face of said electro-optical material layer and a second face;

at least a second electrode on the second face of said layer of photo-conducting material, defining with said first electrode at least one point of inscription and

means for causing to emerge through said second face of said layer of electro-optical material and at said point of inscription an incident light applied to said first face of said layer of electro-optical material when an electrical voltage greater than a given value is applied between said electrode;

said light thus emerging at said point of inscription causing the resistivity of said photo-conducting material to drop at said point and thus increasing the effect of said electrical voltage on said layer of electro-optical material, wherein said electro-optical material presents a threshold of sensitivity of the electrical voltage, and the thickness of said layer of photo-conducting material allows an electrical voltage to be permanently applied between said two electrodes which is divided into a first fraction applied to said layer of photo-conducting material;

said first fraction being less than said threshold of sensitivity, wherein there is further provided a first plurality of electrodes comprising said first electrode and a second plurality of electrodes comprising said second electrode;

said two pluralities of electrodes defining a set of inscription points addressable in a matrix, wherein said electro-optical material is a liquid crystal presenting a twisted nematic structure;

said means for causing the light to emerge comprising two polarizing films oriented in the said direction and situated respectively on each side of said liquid crystal layer, wherein a filter is further deposited on said second face of said layer of photo-conducting material to eliminate an external light capable of energizing said photo-conducting material through its second face, and a layer of fluorescent material deposited on said filter to emit under the action of said external light a light inactinic for said photo-conducting material and which passes through said filter to allow visualization by transmission of this inactinic light through the apparatus.

2. An electro-optical display device which comprises:

a layer of electro-optical material having a first and second face;

an array of first electrodes on the first face of said layer of electro-optical material;

a layer of photo-conducting material having a first face facing the second face of said electro-optical material layer and a second face;

an array of second electrodes on the second face of said layer of photo-conducting material, defining with said array of first electrodes a set of inscription points addressable in matrix;

said layers forming a sandwich arrangement between said first and second arrays;

means for causing to emerge through said second face of said layer of electro-optical material and at any one of said points of inscription an incident light applied to said first face of said layer of electro-optical material when an external control voltage greater than a given value is applied between those of said first and second electrode crossing each other at said one point;

said light thus emerging at said point of inscription causing the resistivity of said photoconducting material to drop at said point and thereby increasing the voltage drop portion of said electrical control voltage across said layer of electro-optical material as a result of the lowering of the voltage drop portion of said external control voltage across said layer of photo-conducting material wherein said electro-optical material presents a threshold of sensitivity to the electrical voltage, and the thickness of said layer of photo-conducting material allows an electrical voltage to be permanently applied between said two electrodes which is divided into a first fraction applied to said layer of electro-optical material and a second fraction applied to said layer of photoconducting material;

said first fraction being less than said threshold of sensitivity;

wherein said electro-optical material is a liquid crystal presenting a twisted nematic structure;

said means for causing the light to emerge comprising two polarizing films orientated in the same direction and situated respectively on each side of said liquid crystal layer;

wherein a filter is further deposited on said second face of said layer of photo-conducting material to eliminate an external light capable of energizing said photo-conducting material through its second face, and a layer of fluorescent material deposited on said filter to emit under the action of said external light a light inactinic for said photo-conducting material and which passes through said filter to allow visualization by transmission of this inactinic light through the apparatus.

3. An electro-optical display device which comprises:

a layer of electro-optical material having a first and second face;

an array of first electrodes on the first face of said layer of electro-optical material;

a layer of photo-conducting material having a first face facing the second face of said electro-optical material layer and a second face;

an array of second electrodes on the second face of said layer of photo-conducting material, defining with said array of first electrodes a set of inscription points addressable in matrix;

said layers forming a sandwich arrangement between said first and second arrays;

means for causing to emerge through said second face of said layer of electro-optical material and at any one of said points of inscription an incident light applied to said first face of said layer of electro-optical material when an external control voltage greater than a given value is applied between those of said first and second electrode crossing each other at said one point;

said light thus emerging at said point of inscription causing the resistivity of said photo-conducting material to drop at said point and thereby increasing the voltage drop portion of said electrical control voltage across said layer of electro-optical material as a result of the lowering of the voltage drop portion of said external control voltage across said layer of photo-conducting material wherein said electro-optical material presents a threshold of sensitivity to the electrical voltage, and the thickness of said layer of photo-conducting material allows an electrical voltage to be permanently applied between said two electrodes which is divided into a first fraction applied to said layer of electro-optical material and a second fraction applied to said layer of photoconducting material;

said first fraction being less than said threshold of sensitivity;

wherein said electro-optical material is a liquid crystal presenting a twisted nematic structure;

said means for causing the light to emerge comprising two polarizing films orientated in the same direction and situated respectively on each side of said liquid crystal layer;

wherein said electro-optical material is a liquid crystal being able to be rendered diffusing under the action of said electrical voltage;

said means for causing the light to emerge comprising two opaque masks situated respectively on the first and the second face of said liquid crystal layer and comprising complementary orifices at the position of said inscription points so as to let pass to said photo-conducting material only the incident light diffused by said liquid crystal.

4. A electro-optical display device which comprises:

a layer of electro-optical material having a first and a second face;

at least a first electrode on the first face of said layer of electro-optical material;

a layer of photo-conducting material having a first face facing the second face of said electro-optical material layer and a second face;

at least a second electrode on the second face of said layer of photo-conducting material, defining with said first electrode at least one point of inscription and

means for causing to emerge through said second face of said layer of electro-optical material and at said point of inscription an incident light applied to said first face of said layer of electro-optical material when an electrical voltage greater than a given value is applied between said electrode;

said light thus emerging at said point of inscription causing the resistivity of said photo-conducting material to drop at said point and thus increasing the effect of said electrical voltage on said layer of electro-optical material, wherein said electro-optical material presents a threshold of sensitivity to the electrical voltage, and the thickness of said layer of photo-conducting material allows an electrical voltage to be permanently applied between said two electrodes which is divided into a first fraction applied to said layer of photo-conducting material;

said first fraction being less than said threshold of sensitivity, wherein there is further provided a first plurality of electrodes comprising said first electrode and a second plurality of electrodes comprising said second electrode;

said two pluralities of electrodes defining a set of inscription points addressable in a matrix, wherein said electro-optical material is a liquid crystal being able to be rendered diffusing under the action of said electrical voltage;

said means for causing the light to emerge comprising two opaque masks situated respectively on the first and the second face of said liquid crystal layer and comprising complementary orifices at the position of said inscription points so as to let pass to said photo-conducting material only the incident light diffused by said liquid crystal.