Self-Aligned Top-Gate Coplanar a-Si:H Thin-Film Transistors With a $\hbox {SiO}_{2}$ –Silicone Hybrid Gate Dielectric

We have made self-aligned top-gate coplanar hydrogenated amorphous-silicon (a-Si:H) thin-film transistors using a SiO₂-silicone hybrid material as the gate dielectric. The hybrid dielectric layer is 150 nm thick and separates a chromium gate electrode from nickel silicide source and drain. The nickel silicide is formed by rapid thermal reaction of a deposited nickel film with the underlying a-Si:H. The electron field-effect mobility is ~1.0 cm²/V · s, the subthreshold slope is ~380 mV/decade, and the ON/OFF current ratio is ~10⁵. The gate leakage current of ~10 pA across the 150-nm-thick hybrid dielectric is ~1/10 of that observed across the typical 300-nm-thick SiN_x dielectric. The whole process needs only two masks.