Browse Prior Art Database

Thermal-Switching of Optical Light Valves of Smectic Liquid Crystal for Printhead Applications

IP.com Disclosure Number: IPCOM000044454D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 3 page(s) / 80K

Publishing Venue

IBM

Related People

Lean, EG: AUTHOR [+2]

Abstract

In reference [*] a smectic liquid crystal light valve is described wherein the basic structure is shown schematically in Fig. 1 above. A long horizontal strip of high resistivity indium tin oxide (ITO) is deposited on one transparent substrate to form a row electrode and contacted along edges with two metal electrodes (electrodes A and B). On the opposing transparent substrate, an array of separate column electrodes (low resistivity ITO fingers with contacting metal electrodes, is fabricated. In operation, a short voltage pulse is applied across electrodes A and B so that a current flows through the high resistivity ITO and heats the adjacent smectic liquid crystal to its isotropic (or nematic) phase.

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Thermal-Switching of Optical Light Valves of Smectic Liquid Crystal for Printhead Applications

In reference [*] a smectic liquid crystal light valve is described wherein the basic structure is shown schematically in Fig. 1 above. A long horizontal strip of high resistivity indium tin oxide (ITO) is deposited on one transparent substrate to form a row electrode and contacted along edges with two metal electrodes (electrodes A and B). On the opposing transparent substrate, an array of separate column electrodes (low resistivity ITO fingers with contacting metal electrodes, is fabricated. In operation, a short voltage pulse is applied across electrodes A and B so that a current flows through the high resistivity ITO and heats the adjacent smectic liquid crystal to its isotropic (or nematic) phase. As the heated strip of liquid crystal cools back down to the smectic phase after the pulse, it will adopt a scattering texture unless there is a voltage on any of the opposing electrodes (electrodes 1,2,3...). The presence of an electric field during cooling will cause the liquid crystal (LC) opposite those electrodes with voltage to align into a clear rather than a scattering state. The light-valve printhead can be operated either in a transmissive or a reflective mode. Reference [*] has the shortcoming of applying the regular thermal pulses along the row electrode all the time independent of either a dark or a light pel (picture element). The light pel (or dark pel) is decided by the presence (or the absence) of the column electric pulse during the cooling period of the LC medium. Since the liquid crystal becomes instantaneously clear (isotropic) during the heating pulse, the light source should not be on during this portion of the writing cycle; otherwise, the printout of any two consecutive dark spots on a pel location will have a bright window in between them. Therefore, a light source, such as a strobe, synchronized to be off during the heating pulse would be appropriate for the printhead application. This article will describe a scheme for printhead application which requires only thermal pulses applied along the column electrodes at each pel location. It eliminates the need for row electrodes and row drivers. The problems of synchronization between the row and column drivers and the projection lamp are completely avoided. In the present invention, the printing speed is improved and the package of the light valve column electrodes with the associated column drivers is also simplified. On a piece of glass substrate, electrode patterns are fabricated, as shown in Fig. 2, where the shaded area represents the highly electrical-conductive strips, such as Al films, ITO, or thin tungsten film, and the crossed area denotes lightly resistive transparent film, such as ITO. The parallel column electrodes 1,3,5,... and 2,4,6,... are connected to column drivers. When voltage pulses are applied across the column electrodes and the common electrode...