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Thomas P. Brody, Co-Inventor of the Active Matrix LCD

September 27, 2011

The majority of larger display screens are active-matrix liquid crystal displays (AMLCDs). This was true also for smaller displays, as on cellular telephones , until recently when organic light emitting diode (OLED) and electronic paper displays have become popular. AMLCDs were invented by Thomas P. Brody in the early 1970s while he was at the Westinghouse Research and Development Center , near Pittsburgh . Thomas P. Brody died on September 18, 2011, at age 91.[1]

Until about ten years ago, cathode ray tubes were used almost exclusively as television and desktop computer displays, since they combined the useful properties of high definition, excellent color rendition , high contrast ratio , and low cost.

Over the span of the last twenty-five years, my family owned as many as twelve cathode ray tube displays that progressed in screen size from twelve inch to a behemoth twenty-one inch that took two men to carry. I can hold the nineteen inch LCD displays we now use two at a time, one in each hand. That's progress that you can feel!

An active-matrix LCD computer display

An active-matrix liquid crystal computer display.

(LCD photo by Briho, via Wikimedia Commons).

Liquid crystals have the useful property that their optical rotation can be modulated by an electric field . A thin film of liquid crystal sandwiched between transparent electrodes and polarizing filters forms a light modulator that can be used as a display pixel . Color filters added to the sandwich allow color display.

The simplest form of LCD display is a passive matrix in which the pixels are defined by a crosshatch of row and column electrodes. Application of a voltage to an appropriate row and column address will activate a pixel. The problem with the passive matrix approach is the one thing that plagues all high speed circuitry; namely, parasitic capacitance . Long row and column electrodes have large capacitance that limits display refresh rate.

Starting in 1968, Brody was doing research at Westinghouse on thin film transistors made from cadmium telluride . The immediate applications were for flexible versions of conventional circuitry, but the Westinghouse team made the first active-matrix LCD in 1972, followed by an active-matrix electroluminescent display in 1973.[2] In 1974, they demonstrated real-time video using the active-matrix approach. The basic AMLCD circuitry, as shown in a figure from the active-matrix patent, is essentially unchanged today.[3]

Figure three from US Patent No. 4,042,854.

Figure three from US Patent No. 4,042,854 by Fang-Chen Luo and Thomas P. Brody, "Flat panel display device with integral thin film transistor control system," August 16, 1977.

(Via Google Patents).[3]

In a decision understandable only to MBAs who are skilled at the divination of entrails in their arcane temples, Westinghouse canceled the active-matrix program in 1979. It was not as if the research program had been running smoothly until then. Research groups at Westinghouse and other large corporations were required to beg for money from operating units that were overly concerned with near-term profits. Scientists needed to paint an optimistic picture of the immediate profit potential of their research to get funding; and when the inevitable road blocks appeared in the research road map, research funding was cut.[4]

Brody was committed to his technology, so he quit Westinghouse to form Panelvision Corporation to manufacture AMLCD displays.[4] Panelvision marketed its first AMLCD display in 1983. In 1985, it was acquired by Litton Systems , and Brody went on to form Magnascreen Corporation, which, as its name implies, produced large-area displays. Brody left Magnascreen almost immediately, but he remained active in AMLCDs via his consulting group, Active Matrix Associates.[1] Brody ended his career as chief scientist for Advantech US , a manufacturer of low cost active-matrix backplanes for various display technologies, and he was active there until his death.[1]

According to the Pittsburgh Post-Gazette , Brody was born in Budapest, Hungary , where he qualified to enter the 1936 Olympics in the 100-meter freestyle , but never competed. In 1938, he went to London to train as a printer in order to take over the family business. He remained in England and served in the British Army during World War II . After the war, Brody received his Ph.D. in theoretical physics at the University of London in 1953, and he taught physics there through 1959, when he received a job offer from Westinghouse.[1]

Brody received two major awards from the Society for Information Display . These were a 1976 Special Recognition Award , and the first Karl Ferdinand Braun Prize in 1987.

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