OFF-state induced threshold voltage relaxation after PBTI stress

The influence of different relaxation biases on positive bias temperature instability (PBTI) recovery is investigated. The threshold voltage (V_th) relaxation after stress is found to be accelerated by OFF-state bias in comparison to zero volt recovery. 2D device simulations evidence an increase in the drain side channel potential as well as an increase in the minimum potential for short channel devices. The relaxation effect is attributed to an enhanced detrapping of charge carriers by the drain-gate electrical field and becomes significant for short channel device below 0.1 μm length.

I. Introduction

The continuous scaling of MOSFETs and introduction of high-k metal gate technology result in a high variability of device parameters and altered degradation behaviour. In this context, the threshold voltage (V_th) shift caused by positive bias temperature instability (PBTI) has become a key reliability issue [1], [2]. PBTI and is accelerated by temperature and characterized by electron trapping into the Hafnium based high-k layer [3], [4].