1/F NOISE AND RADIATION EFFECTS IN MOS DEVICES

An extensive comparison of the 1/f noise and radiation response of MOS devices is presented. Variations in the room-temperature 1/f noise of unirradiated transistors in the linear regime of device operation correlate strongly with variations in postirradiation threshold-voltage shifts due to oxide-trap charge. A simple number fluctuation model has been developed to semi-quantitatively account for this correlation. The 1/f noise of irradiated n-channel MOS transistors increases during irradiation with increasing oxide-trap charge and decreases during postirradiation positive-bias annealing with decreasing oxide-trap charge. No such correlation is found between low-frequency 1/f noise and interface-trap charge. The noise of irradiated p-channel MOS transistors also increases during irradiation, but in contrast to the n-channel response, the p-channel transistor noise magnitude increases during positive-bias annealing with decreasing oxide-trap charge. A qualitative model involving the electrostatic charging and discharging of border traps, as well as accompanying changes in trap energy, is developed to account for this difference in n- and p-channel postirradiation annealing response. The correlation between the low-frequency 1/f noise of unirradiated devices and their postirradiation oxide-trap charge suggests noise measurements can be used as a nondestructive screen of oxide-trap charge related failures in discrete MOS devices and for small scale circuits in which critical transistors can be isolated. It also suggests that process techniques developed to reduce radiation-induced-hole trapping in MOS devices can be applied to reduce the low-frequency 1/f noise of MOS circuits and devices. In particular, reducing the number of oxygen vacancies and vacancy complexes in the SiO2 can significantly reduce the 1/f noise of MOS devices both in and outside a radiation environment. Optimized radiation-hardened MOSFET's can show preirradiation noise magnitudes approaching the low levels of bulk silicon and JEET's and postirradiation noise levels significantly below those of commercial nonradiation-hardened devices.