PBTI/NBTI monitoring ring oscillator circuits with on-chip Vt characterization and high frequency AC stress capability

We propose a new ring oscillator (RO) structure to monitor NBTI and PBTI effects separately. In addition, the unique circuit topology makes it possible to directly correlate the RO frequency degradation to transistor threshold voltage (Vt) degradation without relying on compact modeling with device parameters extracted from transistor-level measurements. It also enables high-speed (> GHz) AC BTI stress experiment with accompanying on-chip AC stress circuitry. The validity of the circuit concept is confirmed by measurements from a test chip in a high-k/metal gate SOI CMOS technology.