PERFORMANCE AND PHYSICAL-MECHANISMS IN SIMOX MOS-TRANSISTORS OPERATED AT VERY LOW-TEMPERATURE

The performance and the physical properties of SIMOX MOS transistors are studied from room to liquid helium temperatures with particular emphasis on the behavior of carrier mobility, threshold voltage, subthreshold swing, leakage current, and kink effect. Various SIMOX substrates, such as partially depleted films annealed at low or high temperature, and ultrathin films (100 nm) are analyzed and compared. Enhancement- and depletion-mode devices with different doping levels, channel lengths, and geometries are considered. The front and back channels are activated independently in order to assess the electrical quality of both interfaces. The comparison with bulk Si transistors points out a number of interesting features of SIMOX devices, which are explained by using comprehensive models. The advantages of low-temperature operation of SIMOX transistors are related to the decrease in subthreshold swing and leakage, increase in mobility, and reasonable shift of the threshold voltage. The capability of ultrathin film devices is excellent in the whole range of temperatures, while partially depleted transistors exhibit optimum performance at 77 K. © 1990 IEEE