Low-frequency noise and radiation response of buried oxides in SOI nMOS transistors

The back channel low-frequency noise of 1.2 μm×2.3 μm SOI nMOS transistors with a buried oxide thickness of 170 nm was measured as a function of frequency, back gate bias V_bg and temperature T. For a temperature range of 85≤T≤320 K, noise measurements were performed at frequencies of 0.3≤f≤1 kHz with top gate bias V_bg=0 V and V_bg-V_bg-th=4 V, where V_bg-th is the back gate threshold voltage. The temperature and frequency dependences of the 1/f noise of back channel SOI nMOS transistors show thermally activated charge exchange between the Si channel and defects in the buried oxide. Comparison is made with the Dutta and Horn model of 1/f noise. Devices on one particular wafer appear to show a mixture of 1/f noise and noise with a higher frequency exponent at low temperatures. Little change is observed in back gate noise with irradiation for the devices and irradiation conditions studied. This is probably due to large preirradiation defect densities in the buried oxides.