Embedded SRAM ring oscillator for in-situ measurement of NBTI and PBTI degradation in CMOS 6T SRAM array

One of the major reliability concerns in nano-scale CMOS VLSI design is the time-dependent Bias Temperature Instability (BTI) degradation. Negative Bias Temperature Instability and Positive Bias Temperature Instability (NBTI and PBTI) weaken MOSFETs over usage/stress time. We present an embedded 6T SRAM ring oscillator structure which provides in-situ measurement/characterization capability of cell transistor degradation induced by bias temperature instability. The viability of the embedded ring oscillator odometer and the impact of bias temperature instability are demonstrated in 55nm standard performance CMOS technology.