Yasuhisa Oana

Technical developments and trends in a-Si TFT-LCDs

Abstract Prototype a-Si TFT-LCDs with a 14.3-inch diagonal screen size or with a high resolution of 212-lines/inch have been demonstrated for developing new markets. The major trends in a-Si TFT-LCD technology are : (1) improvement of a-Si TFT and LCD performance, (2) increases in yield and throughput, and (3) construction of a total simulator using a CAD system.

Low resistivity quasi-epitaxial Mo−Ta alloy and high-quality anodic oxide for a-Si thin-film transistor liquid-crystal display

Sputtered Mo‐Ta alloy and its anodic oxide have been studied in a Mo composition range from 0 to 30 at. %. Resistivity abruptly changed as Mo composition increased above 10 at. % from 185 μΩ cm to about 35 μΩ cm. The crystal structure transformed from tetragonal to cubic at this Mo composition. For higher Ta compositions, the crystal structure varied according to the under‐layer polycrystalline film crystal structure, which may be denoted as quasi‐epitaxial deposition, and the resistivity decreased to as low as 22 μΩ cm. Anodic oxide films of Mo‐Ta alloy were superior to conventional Ta anodic oxide films in regard to resistivity and breakdown field, and the best insulator was obtained at Ta 95 at. %. This quasi‐epitaxial Mo‐Ta alloy and anodic oxide were applied for thin‐film transistor matrix substrates.

Barrier metal against Ga and Zn out‐diffusion in p‐GaP/Au:Zn contact system

Molybdenum, tungsten, titanium, 10 wt% titanium: tungsten, and tantalum are evaluated as barrier metals for preventing gallium and zinc out‐diffusion from alloyed p‐GaP/Au:Zn contact system. Secondary‐ion mass spectrometry is employed to assess qualitatively the extent of out‐diffusion. SIMS analysis indicates that effectiveness of barrier metals decreases in the order of 10 wt% Ti:W≳Ta≫W≳Mo≫Ti. Furthermore, specific contact resistances are determined by accounting for both spreading resistance and series resistance. Among the present metallization systems, 10 wt% Ti:W is proved to be the most suitable barrier metal.