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 SiO/sub 2/ can significantly reduce the 1/f noise of MOS devices both in and outside a radiation environment.<
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