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EP0265903A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

A light-activated light valve with a silicon control element

Assignee: International Business Machines Corp
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Filing: 1987-10-27
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Granted: —
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Expires: 2007-10-27
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Abstract

Abstract In contrast to existing light addressed light valves for projection displays which use a homogene­ous CdS or Se photoconductive layer as the control element for a liquid crystal cell, a silicon photo-diode array is disclosed which makes an effective control element capable of applying a spatially varying AC voltage across a liquid crystal light valve. Writing may be done with a mini­ature CRT in an optical or electron excitation mode. It is shown that for a video mode the ratio of diode capacitance to liquid crystal cell capacitance with the diode, and the frequency of the applied square wave voltage, define the buildup or decay time of the liquid crystal cell voltage. thus, the frequency of the applied AC voltage can be used to control sensitivity and transient response and there is no lag. The dynamic range of the cell voltage is shown to depend on the ratio of diode capacitance to liquid crystal cell capacitance. The display can be used in a storage mode by erasing with an AC voltage and writing with a constant voltage. The silicon photodiode array is compatible with a CCD frame store using direct minority carrier injection for writing. This light addressed version thus represents a desirable milestone in achieving an all solid-state projection display.

Inventors

  • 👤 Ifay Fay Chang
  • 👤 Eugene Irving Gordon

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-06 00:35
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/01; G02F1/13; G02F1/133; G02F1/1333; G02F1/133348; G02F1/135; G02F1/1354; Y; Y10; Y10S; Y10S359/00; Y10S359/90

Claims Analysis

Total Claims: 9
Claim 1
Independent Claim 95 words
Light-activated light valve (LALV) having a liquid crystal layer and means for applying a locally varying voltage across said liquid crystal layer, characterized in that the means for applying the voltage comprises: a silicon single crystal substrate (14) having one side in engagement with said liquid crystal layer; a plurality of junction photodiodes formed in a high resistivity layer (11) on the opposite side of said silicon substrate form, and in electrical contact with, said liquid crystal layer; and means (20) for applying an AC voltage to said photodiodes and across said liquid crystal layer.
Claim 2
Dependent Claim 95 words
Light-activated light valve (LALV) having a liquid crystal layer and means for applying a locally varying voltage across said liquid crystal layer, characterized in that the means for applying the voltage comprises: a silicon single crystal substrate (14) having one side in engagement with said liquid crystal layer; a plurality of junction photodiodes formed in a high resistivity layer (11) on the opposite side of said silicon substrate form, and in electrical contact with, said liquid crystal layer; and means (20) for applying an AC voltage to said photodiodes and across said liquid crystal layer.
Claim 3
Dependent Claim 34 words
A LALV as in claim 1 further comprising glass plate means (50) for sealing said liquid crystal layer against said substrate, said glass plate means carrying transparent electrode means (40) for defining pel electrodes.
Claim 4
Dependent Claim 29 words
A LALV as in one of the claims 1 or 2 further comprising means for applying light patterns to said photodiodes, such as micro CRT or a fiberoptic faceplate.
Claim 5
Dependent Claim 24 words
A LALV as in claim 1 or 2 further comprising means for applying radiation to said photodiodes, such as a GaAs CCD frame store.
Claim 6
Dependent Claim 22 words
A LALV as in claim 1 or 2 wherein said photodiodes are directly activated by an electron beam of a micro CRT.
Claim 7
Dependent Claim 46 words
A LALV as in one of the claims 1-5 further comprising means for operating said LALV in a storage mode, whereby erasure is performed with several cycles of a high frequency square wave applied in the absence of input light, followed by a steady DC voltage.
Claim 8
Dependent Claim 38 words
A LALV as in one of the claims 1-5 further comprising means for operating said LALV in a video mode, whereby a square wave voltage is applied at a constant frequency which is half the video frame rate.
Claim 9
Independent Claim 127 words
A method for constructing a light-activated light valve (LALV) in accordance with one of the claims 1-7, comprising the steps of: providing a silicon single crystal wafer as a substrate (14); forming a pair of p-n junction diodes in a high resistivity layer (11) on one side of said substrate; etching away said substrate using a self-limiting etching process to stop the etch at the boundary of two different conducting types; mounting said etched substrate on a glass plate (50) having transparent electrodes (40) formed thereon with a space between said electrodes and said substrate; filling the space with liquid crystal and sealing it therein; and connecting electrical leads to said diodes and said transparent electrodes for the application of an AC voltage across said liquid crystal.

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