Fundamental Issues in Space Electronics Reliability. Negative Bias Temperature Instability

摘要

Negative Bias Temperature Instability (NBTI) in silicon based metal-oxide-semiconductor- field-effect-transistors (MOSFETs) has been recognized as a critical reliability issue for advanced space qualified electronics. The phenomenon manifests itself as a modification of threshold voltage (Vth) resulting in degraded signal timing paths, and ultimately circuit failure. Despite the obvious importance of the issue, a standard measurement protocol has yet to be determined. This is a consequence of a large amount of complexity introduced by the strong dependencies of NBTI on temperature, electric field, frequency, duty cycle, and gate dielectric composition. Indeed, researchers are nowhere near a dependable circuit reliability lifetime predictor formula that would be accurate among a wide variety of technology specifications. We have improved upon the traditional measurement techniques which suffered from an underestimation of the magnitude of Vth shifts because they failed to account for trapped charge relaxation. Specifically, we have developed a means for measuring the maximum effect of NBTI by virtue of a method that can continuously monitor the Vth(t) without having to remove the stressing voltage. The interpretation methodology for this technique is explained in detail and the relevant approximations are justified. Using this method, we have examined the time and magnitude dependencies of change in Vth as a function of time (change in Vth(t)) on temperature, vertical electric field, inversion channel carrier density, and source-drain voltage (Vds). In the work presented here, we have evidenced temperature and vertical electric field dependent Vth shifts in SiO2 and HfSiON devices. Furthermore, we have collected substantial evidence that the traditional change in Vth=At(alpha) analysis fails to explain the experimental data in the early time domain.