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Polysilicon thin-film transistors (TFT's) with island thickness of 20 and 70 nm were fabricated with self-aligned cobalt and nickel silicide contacts to the source and drain. The silicide contacts are shown to reduce the series resistance, which limits the on-current of the device, thus significantly increasing the effective mobility in the 20-nm island devices. The mobilities of 20-nm cobalt and nickel silicided devices are similar to those with 70-nm islands, 31 versus 33 cm 2 /V-s, whereas the nonsilicided 20-nm devices have a mobility of only 13 cm 2 /V-s. The island thickness is shown to influence other device parameters affecting active matrix display driver circuit design, such as threshold voltage, leakage current, and subthreshold swing; all these parameters are improved when the island thickness is decreased.

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Thin films of cobalt, nickel, and tungsten were sputtered on three types of silicon materials to explore their potential for use as silicides in thin film transistor technologies for active matrix liquid crystal displays. The metals were sputtered onto single-crystal, polycrystalline, and amorphous silicon. The metals were annealed in vacuum after deposition over temperatures ranging from 250'C to 750'C. The sheet resistance of the resulting silicide films was measured using a four point probe apparatus. Cobalt silicides with sheet resistance of less than 4 f2l/ were formed at 600'C. Nickel produced films with sheet resistance below 10 f2/0 at 350'C, though the surface was required to be vacuum-clean. In this study, tungsten did not produce silicides. Surface preparation has been found to be an important factor in tungsten and nickel silicidation.

The crystallization of amorphous silicon by rapid thermal processing has some important advantages over other techniques such as laser annealing. This work investigates the characteristics of low temperature polysilicon flat panel display driver circuits fabricated in RTP crystallized polysilicon. Both digital (shift register) and analog (operational amplifier) circuits are presented.