DETERMINATION OF FLAT-BAND VOLTAGES FOR FULLY DEPLETED SILICON-ON-INSULATOR (SOI) METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS (MOSFETS)

Abstract

A method to determine the flat-band voltage, V(FB), in silicon-on-insulator (SOI) metal-oxide semiconductor (MOS) structures has been proposed. It is based on the measurement of the back channel threshold voltages of SOI MOS field-effect transistors (MOSFET's) as a function of the front gate bias. This method is very useful for fully depleted SOI MOSFET's with a low channel dopant concentration. Mean values of V(FB)'S obtained from this method were -0.79 V for n+ polysilicon gate SOI n-MOSFET's with a gate oxide of 205 angstrom and an acceptor concentration of 4 x 10(15) cm-3, and -0.12 V for n+ polysilicon gate SOI p-MOSFET's with a gate oxide of 205 angstrom and a donor concentration of 5 x 10(15) cm-3 . The accuracy in the determination of V(FB) is mainly dependent on precise evaluations of the front gate oxide thickness, the surface silicon thickness, and the channel dopant concentration.