Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Simple Matrix Addressing Structure for Large Area Liquid Crystal Display Devices

IP.com Disclosure Number: IPCOM000081047D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Kuhn, L: AUTHOR [+2]

Abstract

In addressing liquid crystal display devices by X-Y matrix scan methods it is necessary to provide nonlinear current-voltage characteristics for each display element. In particular, in using an AC drive, a minimum or two diodes are necessary, as shown in Fig. 1, which illustrates the most simple electrical circuit for a unit cell, or element.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 3

Simple Matrix Addressing Structure for Large Area Liquid Crystal Display Devices

In addressing liquid crystal display devices by X-Y matrix scan methods it is necessary to provide nonlinear current-voltage characteristics for each display element. In particular, in using an AC drive, a minimum or two diodes are necessary, as shown in Fig. 1, which illustrates the most simple electrical circuit for a unit cell, or element.

The element is driven alternately through diodes connected to positive (+) and negative (-) lines traversing the surface in the Y direction, with the return path through X-directed lines on a second substrate, which forms the other surface of a liquid crystal display.

In order to function most efficiently, each pair of diodes must:
(a) be well isolated from every other pair; (b) have Low leakage in the reverse-current direction of each diode; (c) have moderate junction capacitance, small compared to that of a display element; and (d) have moderate forward resistance, very much smaller than the cell resistance of the display element.

In order to satisfy all these requirements on large areas, the use of insulating substrates as carriers for active devices, as well as cell electrodes and addressing lines, appears to provide an attractive manner for very inexpensive fabrication. What is here described is an implementation for such arrays, and several alternatives usable to obtain the required arrays using a minimal number of fabrication operations.

The final Y array which forms one plate of the liquid crystal display device is schematically illustrated in Fig. 2, which shows the smallest repeatable elementary area. This basic unit is replicated by translation through distance S in the Y direction and by distance (2 x S) in the X direction. Each basic unit consists of two display elements, each in turn addressed by a pair of diodes fabricated in thin-film semiconductor material as described below. This grouping is in itself not unique, but has been chosen so as to minimize complexity as well as to provide the same voltage polarity to the (closely-spaced) parallel drive lines in each track between elements.

The steps of fabrication are:
1. Small islands of P-type semiconductor (e.g., silicon) are

delineated on an insulating substrate (e.g., fused quartz).

This semiconductor film may consist of polycrystalline

material, and is of thickness approx. 1 micrometer. It may

be formed into islands by one of several procedures:

a) Subtractive etching of a previously deposited thin film,

using photolithographic techniques.

b) Deposition through a physical mask, e.g., by chemical vapor

deposition.

c) "Selective chemical vapor deposition method", whereby the

semiconductor film is caused to nucleate only within

previously delineated areas, and not upon the surrounding

surface.

1

Page 2 of 3

II. The diodes may be fabricated by one of two methods:

a) Regions of photoresist are delineated over part of th...