NBTI-aware flip-flop characterization and design

Abstract

With the scaling down of the CMOS technologies, Negative Bias Temperature Instability (NBTI) has become a major concern due to its impact on PMOS transistor aging process and the corresponding reduction in the long-term reliability of CMOS circuits. This paper investigates the effect of NBTI phenomenon on the setup and hold times of flip-flops. First, it is shown that NBTI tightens the setup and hold timing constraints imposed on the flip-flops in the design. Second, different types of flip-flops exhibit different levels of susceptibility to NBTI-induced change in their setup/hold time values. Finally, an NBTI-aware transistor sizing technique can minimize the NBTI effect on timing characteristics of the flip-flops.

Effect of NBTI/PBTI aging and process variations on write failures in MOSFET and FinFET flip-flops

“…The raising electric field through the oxide thickness generates interface traps in P-type devices and results in unwanted increase in threshold voltage (Vth) [23] which ultimately affects propagation delay and noise margins. In [5] and [18], investigations have been done on propagation delay for various flip-flops subject to NBTI aging.…”

Multi-corner, energy-delay optimized, NBTI-aware flip-flop design

“…These points are the critical points which can be defined by the designer. There can be two or three points as mentioned in [8]; for example, the points with minimum setup or hold times.…”

“…In [7], the effect of NBTI on different low power and high performance flip-flops was studied; however, no solution was offered to alleviate the problem. The authors of [8] introduced an ad-hoc selective transistor-level sizing to combat the NBTI effect without considering energy consumption as part of the objective.…”

Guest Editorial

“…Different types of flipflops exhibit different levels of susceptibility to NBTI-induced change in their setup/hold time values. An elaborated NBTI-aware transistor sizing technique can minimize the NBTI effect on timing characteristics of the flip-flops [Abrishami et al 2008]. Furthermore, memory-like structures have a special characteristic in NBTI degradation.…”