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Selective Thermal Erasure for Cathodochromic Storage Display Device using Transition Metal Oxide Films

IP.com Disclosure Number: IPCOM000079986D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR [+4]

Abstract

The thermal-erase mode in a cathodochromic storage display tube is more useful than the optical-erase mode because of the higher contrast ratio obtainable, and because reading does not deteriorate the stored image. Both of the most commonly used methods of erasing a thermal-mode image, i.e., heating with tungsten filaments placed near the cathodochromic material and heating a thin film conductor in contact with the material, erase the entire image. While the erasure time is reasonably rapid (about 1 second), the time needed for the screen to return to thermal equilibrium (about 30 seconds) before it is possible to begin to write again, is long.

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Selective Thermal Erasure for Cathodochromic Storage Display Device using Transition Metal Oxide Films

The thermal-erase mode in a cathodochromic storage display tube is more useful than the optical-erase mode because of the higher contrast ratio obtainable, and because reading does not deteriorate the stored image. Both of the most commonly used methods of erasing a thermal-mode image, i.e., heating with tungsten filaments placed near the cathodochromic material and heating a thin film conductor in contact with the material, erase the entire image. While the erasure time is reasonably rapid (about 1 second), the time needed for the screen to return to thermal equilibrium (about 30 seconds) before it is possible to begin to write again, is long.

Since it has been reported that metal to semiconductor transition occurs in certain oxides, there has been considerable interest in the preparation and properties of vanadium oxide films. This interest has been stimulated by the sharp transition in electrical resistivity (up to four orders of magnitude) over a temperature interval of 2 degrees C at about 68 degrees C. This transition lends itself to rapid switching based on thermal effect. Accordingly, a thermal erasure scheme utilizing the switching phenomenon between the two states of resistivity in transition metal oxide for selectively erasing single line, or a specific region in a stored display, is illustrated.

In the above schematic, L1 and L2 are sets of transparent conducting interdigital lines (tin or indium oxide films having resistivity of about 50 ohms per sq) etched or deposited on a suitable substrate S with alternating lines connected together. Vanadium oxide films F of 15-20 mu thickness are deposited across the ends of lines L1 and L2 by reactive evaporation, chemical vapors deposition or reactive sputtering. Cathodochromic material C is deposited between the two strips F of the transition metal-oxide films. Vanadium oxide is semiconducting below 68 degrees C and metallic at higher temperature. In the nonerasing state (at ambient temperature) resistivity of the vanadium oxide films is sufficiently high (1-10 omega cm), so that there is no appreciable heating current flowing in the selected interdigital lines. This thick-film material switches between two states of resistivity from semiconducting (1-10 omega cm) to metallic (10/-3/ omega cm) at the transition temperature. The switch may be triggered either electronicall...