THE CRYOGENIC BEHAVIOR OF METAL-OXIDE-SEMICONDUCTOR TRANSISTORS FABRICATED IN HIGH-RESISTIVITY SILICON SUBSTRATES

This paper discusses the static device operation of pmosts fabricated in high-resistivity (HR) Si substrates at cryogenic temperatures. It i s shown that the anomalies observed at room temperature, i.e. the subt hreshold leakage and the parasitic bulk conduction in saturation, are still present at 77 K and at 4.2 K, although considerable improvement of the subthreshold behaviour is observed. Furthermore, unlike mosts f abricated in standard substrates, little hysteresis is observed in the I-V characteristics down to liquid-helium temperatures. The observati ons are discussed in view of an analytical model adapted for HR-Si dev ices, which is extended for low-temperature operation. Finally, the ef fect of a reverse substrate bias, which is important for nuclear-radia tion detection applications, and of the substrate contact on the devic e characteristics is demonstrated and discussed.