Korean Journal of Optics and Photonics (한국광학회지)

Optical Society of Korea (한국광학회)
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Electro-optical Characteristics of the Dual-frequency Bistable Nematic Liquid Crystal Cell with Pixel-isolating Polymer Wall

폴리머 격벽에 의해 화소고립된 구조의 이중주파수 쌍안정 네마틱 액정셀의 전기광학 특성

  • Lee, Seong-Ryong (School of Electrical Engineering, Pusan National University) ;
  • Lee, Joong-Ha (School of Electrical Engineering, Pusan National University) ;
  • Shin, Jae-Hoon (School of Electrical Engineering, Pusan National University) ;
  • Song, Dong-Han (School of Electrical Engineering, Pusan National University) ;
  • Yoon, Tae-Hoon (School of Electrical Engineering, Pusan National University) ;
  • Kim, Jae-Chang (School of Electrical Engineering, Pusan National University)
  • Published : 2008.06.30
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Abstract

We propose a novel bistable nematic liquid crystal cell, which has a dual-frequency liquid crystal material and pixel-isolating polymer wall formed by an anisotropic phase separation of a mixture of liquid crystals and UV-curable pre-polymers. The proposed cell has two stable states of left- and right-handed ${\pi}$-twist. The switching between the two states is achieved by using a sequential waveform of low and high frequencies. A transmissive bistable liquid crystal display is designed, which achieves high contrast ratio by using the proposed cell and optical films.

본 논문에서는 왼손(left-handed)과 오른손(right-handed) 방향으로 각각 $180^{\circ}$ 트위스트(${\pi}$-twist)된 액정상을 두 개의 안정상태로 가지는 쌍안정(bistable) 액정 디스플레이(liquid crystal display)를 제안한다. 제안된 소자는 액정과 자외선경화 폴리머 물질의 혼합물의 비등방성 상분리 방법으로 형성된 격벽에 의해 화소고립된(pixel-isolation) 구조를 가지며, 인가전압의 주파수에 따라 유전율 이방성의 부호가 바뀌는 이중주파수(dual-frequency) 특성의 네마틱(Nematic) 액정을 사용한다. 두 안정된 액정상 사이의 스위칭은 인가전압의 주파수를 연속적으로 변화시킴으로써 이루어지며, 주파수 변화에 따른 액정의 유체 효과에 의해 발생하므로 응답특성이 매우 빠르다. 두 액정상은 카이랄 도펀트(chiral dopant)가 아니라 격벽이 가지는 앵커링(anchoring)의 영향으로 안정화됐기 때문에 거의 동일한 탄성에너지(elastic free energy)를 가지게 되어 우수한 메모리 특성을 나타낸다. 또한, 위상지연필름을 이용한 투과형 광학보상을 통해 높은 정면 명암비(contrast ratio)를 가질 수 있다.

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References

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