A Simple Circuit to Investigate Threshold Voltage Variation and Its Application in Monitoring Negative Bias Temperature Instability Degradation

Abstract

This paper presents a test circuit which can be used to analyze the p-MOSFET threshold voltage (VT) shift and fluctuation. The proposed circuit includes two p-MOSFETs, series connection. Using the circuit, we can directly measure threshold voltage shift on the output side and gather fluctuation statistics of p-MOSFET devices. The principle and the sensitivity of this method are demonstrated, followed by simulation and experimental results. A predictive model of negative bias temperature instability (NBTI) is introduced to analyze the PMOS degradation under constant stress. The NBTI stress experimental results have shown that this circuit can monitor NBTI degradation accurately, and offer a significant improvement in efficiency over existing Id–Vg methods.