Browse Prior Art Database

Dynamic Scattering Display

IP.com Disclosure Number: IPCOM000082221D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Freiser, MJ: AUTHOR [+2]

Abstract

There is described herein a dynamic scattering display device capable of two-frequency addressing with homeotropic alignment. This device combines the response time advantages of two-frequency addressing with the cosmetic advantages of homeotropic alignment.

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Dynamic Scattering Display

There is described herein a dynamic scattering display device capable of two-frequency addressing with homeotropic alignment. This device combines the response time advantages of two-frequency addressing with the cosmetic advantages of homeotropic alignment.

Two-frequency addressing arrangements for dynamic scattering display devices are based on the existence of a high-frequency cutoff, i.e., on the existence of a frequency, f(c), above which an applied field suppresses dynamic scattering. In Figs. 1a and 1b there are shown cross-sectional and plan views, respectively, of a device suitable for use in a two frequency addressing arrangement. In this device, structures 10 and 12 are quartz substrate members. On the inner surface of substrate member 12, there are disposed horizontal electrodes 14 and on the inner surface of substrate member 10, there are disposed vertical electrodes 16. Filling the space between substrate members 10 and 12 and electrodes 14 and 16 is a thin film of a nematic liquid crystal material 18.

The device as shown in Figs. 1a and 1b enables the construction of a forty- character alphabet, using a nematic liquid crystal film 18 driven by 12 orthogonal electrodes (5 vertical electrodes 16 and 7 vertical electrodes 14). Such variety of alphabetic character arrangements is not attainable from nematic liquid crystal films, driven by purely sinuosoidal voltages with a 5x7 electrode matrix.

Briefly, the basic technique for generating the dynamic scattering mode in nematic liquid crystals consists of the application of a sufficiently large voltage (AC or DC) to a nematic liquid crystal layer, whereby there occurs significant turbidity in the layer. The result of this turbidity is a brightening (due to diffuse scattering) over the area to which the voltage is applied. The existence of a "cutoff" frequency, Omega , such that voltages applied at frequencies greater than Omega (c) suppress the dynamic scattering effect, makes possible a greater flexibility in matrix addressing than is attainable with a single frequency.

Schemes which have been proposed employ a scanning mode. A scheme is described here which treats the phases of the voltages, as well as their amplitudes, as subject to choice depending upon the information to be displayed. By this means, a multiplicity of characters can be displayed in a continuing wave, rather than scanning mode.

Let it be assumed that at a given point in the matrix, the voltage across the liquid crystal 18 is: V(t) = V(1) cos Omega(1) t + V(2) cos Omega (2)t , where Omega (1) << Omega (c) << Omega (2) , Omega (c) being the cutoff frequency. Then the dynamic scattering effect will occur only if V/2/(1) > V/2/(c) + V/...