Laser annealing yields high-resolution liquid-crystal display

Researchers at Asahi Glass Co. (Yokohama, Japan) used argon-ion laser annealing to improve the relatively poor resolution of liquid-crystal-display (LCD) panels intended for small- to mid-sized applications, such as lapto¥computers, automobile navigation systems, and digital camera systems. The researchers fabricated a low-temperature, polycrystalline silicon (p-Si) thin-film transistor (TFT) reflective extended graphics array. The 2-in.-diagonal 768 ¥ 1024 array had 40-µm pixels and an 81% aperture ratio. A high-resolution image was produced by applying the array to a liquid-crystal/polymer-composite scattering mode light valve.

The argon-ion laser output was focused to an 80-µm-diameter beam and scanned across an amorphous silicon (a-Si) layer on a glass substrate at about 10 m/s to produce p-Si TFT pixel and driver-circuit elements in parallel 40-µm-wide p-Si stripes across the a-Si layer. The 80-µm beam width was chosen to avoid interference between adjacent stripes and to increase crystallization speed. Because carrier mobility along the beam scan direction is higher than in the perpendicular direction, TFTs were oriented in the array to yield current flow parallel to the beam-scanning direction.