How RCA Lost the LCD

The Road to Twisted Liquid Crystals

Wolfgang Helfrich
Photo: Freie Universität Berlin

The dynamic scattering displays developed at RCA were used in the first liquid crystal wristwatches and calculators. The devices’ bright white readouts were well suited for indoor use, but their reflective backplate made them hard to read in sunlight. RCA physicist Wolfgang Helfrich [left] devised a new LCD configuration to solve this problem.

Scientists already knew that you could align the molecules in a nematic liquid crystal by placing them on a glass plate that had been rubbed in one direction with a piece of paper. If you placed the liquid crystal between two such plates and rotated one plate by 90 degrees, the molecules nearest to each plate retained their original orientation, while those in the middle formed a helical structure. This helix, it turned out, could rotate the plane of polarized light.

Helfrich’s plan was to sandwich this “twisted” liquid crystal between two pieces of conductive glass and then bookend the glass plates with a pair of crossed polarizers. Normally any light passing through the first polarizer would be blocked by the second, but in this case the helix rotated the light so it could proceed through the cell. If you then applied a voltage, the liquid crystal molecules would align themselves with the field, demolishing the helix and preventing light transmission.

Twisted nematic displays used less power than their dynamic ­scattering counterparts and had higher ­contrast in direct sunlight. According to Helfrich, Heilmeier rejected the idea due to its reliance on ­polarizers. Helfrich left RCA to develop the concept elsewhere. At Hoffmann–La Roche, he and Martin Schadt constructed a functional twisted ­nematic display in November 1970. A few months later, James Fergason of the International Liquid Xtal Co. filed a patent on a similar device, which he said he had developed in December 1969. Between them, Helfrich, Schadt, and Fergason confirmed the ­viability of the twisted nematic display and set the stage for the emergence of the modern LCD industry.

—B.G.

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