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Working liquid-crystal displays were first shown in 1968 by George Heilmeier's team at the American company RCA, but they used too much power for a small battery. Around 1970 Wolfgang Helfrich and Martin Schadt in Switzerland and James Fergason in the US separately found a low-power design that made LCD watches and calculators practical.

George Heilmeier and RCA (1968); Wolfgang Helfrich, Martin Schadt and James Fergason (around 1970)

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The story behind the card

Liquid crystals flow like a liquid, but their rod-shaped molecules line up in order, like a crystal, and turn when a voltage is applied. RCA's 1968 displays used 'dynamic scattering': a current stirred the crystal until it turned cloudy, which needed a constant flow of power. The newer 'twisted nematic' display (nematic is the name for liquid crystals whose molecules lie side by side) holds the crystal between two polarising filters, with its molecules twisted in a spiral. A small voltage untwists them and that part of the screen goes dark, using almost no current. Helfrich and Schadt, at the Swiss company Hoffmann-La Roche, filed their patent on 4 December 1970, and Fergason filed in the US in 1971. The dispute was settled out of court, with all sides sharing the royalties.

Türkçe oku
Çalışan ilk sıvı kristal ekranları 1968'de Amerikan RCA şirketinde George Heilmeier'in ekibi tanıttı, ama bunlar küçük bir pil için fazla güç harcıyordu. 1970 dolaylarında İsviçre'de Wolfgang Helfrich ile Martin Schadt, ABD'de de James Fergason, ayrı ayrı çok az güçle çalışan bir tasarım buldu; LCD'li saatler ve hesap makineleri bu sayede yaygınlaştı.

Sıvı kristaller sıvı gibi akar, ama çubuk biçimli molekülleri bir kristaldeki gibi düzenli sıralanır ve elektrik gerilimi uygulanınca döner. RCA'nın 1968'deki ekranları “dinamik saçılma” denen yöntemle çalışıyordu: akım kristali karıştırıp bulanıklaştırıyordu ve bunun için sürekli güç gerekiyordu. Daha yeni “bükülmüş nematik” ekranda (nematik, molekülleri yan yana dizilen sıvı kristallere verilen addır) kristal iki polarize filtrenin arasına yerleştirilir ve molekülleri sarmal biçiminde bükülür. Küçük bir gerilim bu bükülmeyi açar ve ekranın o bölümü kararır; bunun için neredeyse hiç akım harcanmaz. İsviçre'deki Hoffmann-La Roche şirketinde çalışan Helfrich ile Schadt, 4 Aralık 1970'te patent başvurusu yaptı; Fergason ise 1971'de ABD'de başvurdu. Anlaşmazlık mahkeme dışında çözüldü ve telif gelirleri taraflar arasında paylaşıldı.

Sources and further reading

Background reading: Twisted nematic field effect
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