Periodic Monitoring of BTI Induced Aging in SRAM Sense Amplifiers

Transistor bias-temperature instability (BTI) effects are a serious reliability concern in nanometer technology static random access memories (SRAMs). In this paper, a methodology and a circuit for the periodic monitoring of BTI induced aging in SRAM sense amplifiers is presented. It is reported in the literature that under realistic memory workloads the input offset voltage of a sense amplifier is increased due to asymmetric BTI-related transistor degradation. Increased sense amplifier input offset voltage may lead to failures generation in the field of operation. According to the proposed technique, periodic monitoring provides the ability to avoid SRAM failures by early detecting over-aged sense amplifiers (near failure) and then properly react in order to maintain the memory reliable operation. The aging monitoring scheme is based on a differential ring oscillator, which can be easily embedded in an SRAM array without affecting the normal mode of operation, at a very low performance, power consumption, and silicon area cost. Moreover, the proposed solution can be further exploited for the characterization and testing of SRAM sense amplifiers at the fabrication phase.