The statistics of NBTI-induced VT and β mismatch shifts in pMOSFETs

Negative bias temperature instability (NBTI) is a pFET degradation mechanism that can result in threshold voltage shifts up to 100 mV or more, even in very thin oxide devices. Since analog circuits that utilize matched pairs of devices, such as current mirrors and differential pairs, generally depend on V_T matching considerably better than this, NBTI-induced V_T mismatch shift may represent a serious reliability concern for CMOS analog applications. Furthermore, induced β mismatch shift (affecting drain current level at a fixed gate overdrive voltage) may also impact drain current and transconductance mismatch. In this paper, experimental results of the statistics and scaling properties of NBTI-induced V_T and β mismatch shifts in saturation, and models describing these results, are presented.