![]() ![]() With the a-Si:H TFT active-matrix panels, the AM Ch-LCDs were fabricated and operated with the frame rate of 60 Hz and the maximum contrast ratio of ∼30. The fabricated a-Si:H TFT active-matrix panels can be operated at the voltage of 50 and 60V, applied to the data and gate lines, respectively. Thin-film transistors (TFTs) are critical elements used for thin film electronics, and their most important application includes the pixel switching. Based on our a-Si:H TFTs studies, we designed an a-Si:H TFT active-matrix panel and fabricated the AM Ch-LCDs either by optimizing a-Si:H TFT processing or adopting the GP a-Si:H TFT technology. This type of display features a TFT for each individual pixel. For this BFP a-Si:H TFT, a low OFF-current (1.04 pA) and a high ON/OFF-current ratio (5.68 x 106) up to VGS = VDS = ∼30 V were obtained. A thin-film transistor (TFT) is a type of field-effect transistor that is usually used in a liquid crystal display (LCD). Secondly, in the BFP a-Si:H TFT, an offset region and a buried field plate were introduced between the drain/source and gate electrodes to reduce the electric field in the pinch-off region. ![]() In a flat-panel display, light must be able to pass through the substrate material to reach the viewer. But TFT ON-current of GP a-Si:H TFT was reduced due to the introduction of the thick low dielectric BCB layer. Thin-Film Transistor (TFT): A transistor whose active, current-carrying layer is a thin film (usually a film of silicon), in contrast to MOSFETs, which are made on Si wafers and use the bulk-silicon as the active layer. The GP a-Si:H TFT showed normal TFT characteristic up to VGS = VDS = ∼100 V without any device failure. Firstly, in the GP a-Si:H TFTs, we used a thick spin-coated benzocyclobutene (BCB) layer beneath a thin hydrogenated amorphous silicon nitride (a-SiNx:H) layer for gate insulator. In order to improve the TFT characteristics under high bias conditions, we propose two new a-Si:H TFT structures called gate planarized (GP) and buried field plate (BFP) high voltage a-Si:H TFTs. And it was concluded that high OFF-current of conventional a-Si:H TFTs and low ON-current of gate offset high voltage a-Si:H TFTs were main problems for reflective AM Ch-LCD applications. In order to investigate the applicability of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) for the switching devices of active-matrix (AM) Ch-LCDs, the characteristics of conventional and gate offset high voltage a-Si:H TTFs were examined under high bias conditions. However, because the threshold voltage of cholesteric, liquid crystal is high (>20V), the switching devices for active-matrix addressing should satisfy required characteristics even under high bias conditions. Active-matrix addressing should allow fast image updating or video-rate operation. But conventional passive-matrix addressing of Ch-LCDs allows only a slow image updating speed. Furthermore, due to their bistability Ch-LCDs can retain their images virtually forever without additional power consumption. Reflective cholesteric liquid crystal displays (Ch-LCDs) have advantages, such as, high brightness, low power consumption, and wide viewing angle, since they do not need any polarizer, color filter, and backlight. ![]()
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