Adaptive Techniques for Overcoming Performance Degradation Due to Aging in CMOS Circuits

Negative bias temperature instability (NBTI) in pMOS transistors has become a major reliability concern in present-day digital circuit design. Further, with the recent introduction of Hf-based high-k dielectrics for gate leakage reduction, positive bias temperature instability (PBTI), the dual effect in nMOS transistors, has also reached significant levels. Consequently, designs are required to build in substantial guardbands in order to guarantee reliable operation over the lifetime of a chip, and these involve large area and power overheads. In this paper, we begin by proposing the use of adaptive body bias (ABB) and adaptive supply voltage (ASV) to maintain optimal performance of an aged circuit, and demonstrate its advantages over a guard banding technique such as synthesis. We then present a hybrid approach, utilizing the merits of both ABB and synthesis, to ensure that the resultant circuit meets the performance constraints over its lifetime, and has a minimal area and power overhead, as compared with a nominally designed circuit.