Glass Substrates for Liquid Crystal Displays

TLDR

AMLCD substrates must be thermally and mechanically stable, precisely dimensioned, ultra‑smooth, free of inclusions, and alkali‑free to avoid chemical or electronic interaction with TFTs, a requirement that drove the evolution from slot‑draw to fusion‑draw glass manufacturing and the development of alkali‑free compositions compatible with high‑viscosity fusion‑draw processes. The paper reviews Corning’s development of substrate glasses for AMLCD displays. The authors discuss technical challenges such as arsenic removal from substrate glass and minimizing dimensional change during high‑temperature polysilicon TFT processing.

Abstract

We present a brief history of substrate glasses developed by Corning Incorporated (Corning) for use in Active matrix liquid crystal display (AMLCD) displays. The most basic attributes required of AMLCD substrates include thermal and mechanical stability, precise geometry control, a surface that is basically perfectly smooth, and no inclusions large enough to block a pixel in the final display. In addition, the glasses used as substrate materials must be essentially alkali‐free so that they do not interact chemically or electronically with thin‐film transistors (TFT). Thin, precision sheet was first made at Corning via the slot‐draw process, but was eventually moved to the fusion‐draw process; neither process was originally intended for this application. Alkali‐free glasses were originally developed for electronic applications and lamp envelopes, and considerable research was required to invent compositions that were compatible with the high‐viscosity fusion‐draw process. Examples of the technical challenges presented by the evolving industry requirements are provided, including eliminating arsenic from the substrate glass and reducing the dimensional change during high‐temperature processing of polysilicon‐based TFT.