We have studied the 1/f noise and the radiation response of transistors with silicon-on-insulator (SOI) buried oxides, and with Al2O3/SiOxNy/Si(100) gate dielectrics. The former is significant for understanding the response of advanced SOI transistor structures (e.g., double gate devices), and the latter is important for the incorporation of high-K gate dielectrics into advanced MOS processes. The 1/f noise of MOSFETs fabricated on silicon-implanted SOI buried oxides shows little change after 1 Mrad(SiO2) irradiation. Silicon implantation creates shallow electron traps in the buried oxide of the SOI devices, leading to improved radiation tolerance, but also additional noise and bias instabilities. Whether the traps that lead to these instabilities are filled or empty does not significantly affect the 1/f noise of the back-channel transistor. Low frequency noise in the strongly coupled front-to-back (quasi double-gate) mode of device operation is also investigated, and found to help mitigate the 1/f noise in fully depleted SOI MOSFETs. The decrease in noise is associated primarily with an increase in the number of carriers in the channel for this quasi double-gate mode of operation. In transistors with high-K dielectrics, the low-frequency noise is significantly larger than typically observed for high-quality thermal SiO2 thin films.
We have measured the back channel low frequency noise of 0.6um*2.3um SOI nMOS transistors with a buried oxide thickness of 170 nm as a function of frequency (f), back gate bias (Vbg ), and temperature (T). For a temperature range of, noise measurements were performed at frequencies of, with top gate grounded and Vbg-Vbgth=4V, where Vbgth is the back gate threshold voltage. After zero-bias X-ray irradiation, the noise power increases, in agreement with previous work on the noise response of bulk MOSFETs. The temperature and frequency dependences of the 1/f noise of back channel SOI nMOS transistors shows 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 due to diffusion of a hydrogen-related species.