Application of Amorphous-Silicon Field-Effect Transistors in Three-Dimensional Integrated Circuits

Amorphous-silicon field-effect transistors have been integrated into three-dimensional form for the first time, and the static as well as dynamic characteristics were evaluated. Inverters and nine-stage ring-oscillators fabricated on a fused silica substrate have two layers of FETs isolated by CVD SiO 2 . The inverters had step-like transfer characteristics and a small-signal gain of about 10 was obtained. The ring-oscillator experiment showed that the minimum proparation delay time per gate was about 60 µsec.