Simple ring-oscillator circuit has been used to estimate the degradation in circuit performance due to negative bias temperature instability (NBTI) effect but it fails to isolate the degradation from the NBTI for PMOS and the positive bias temperature instability (PBTI) for NMOS in high-k dielectric/metal gate CMOS technology. In this paper, we propose new circuit structures which monitor the NBTI and the PBTI effects separately while conserving the simplicity and efficiency of a ring oscillator based circuit. We also show that the proposed circuits have better sensitivity to the NBTI effect than conventional ring-oscillator circuit when they are used in technologies that experience negligible PBTI effect.
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