Impact of Sensing Gate Bias on NBTI of Hf-based Dielectric Stacks

Abstract

The negative bias temperature instability (NBTI) is limiting the lifetime of pMOSFETs with SiON gate dielectric and it is generally believed that Hf-based dielectric stack has higher instability than SiON. As Hf-based dielectric stacks are replacing SiON, there is a pressing need for characterizing their NBTI. Traditionally, the threshold voltage instability, ΔVth, is evaluated with a sensing gate bias, Vgsense, close to Vth. Vth is lower than the digital circuit operation bias and the implicit assumption is that ΔVth is independent of Vgsense. This work will show that ΔVth for Hf-based stacks increases substantially when Vgsense rises from Vth to the operation level. This Vgsense effect should be taken into account when modeling the impact of NBTI on circuit operation in the future.