Phase Transition Material-Assisted Low-Power SRAM Design

The threshold switching properties of the phase transition material (PTM) can be exploited to realize a heterogeneous static random access memory (SRAM) bitcell, which can obviate the need for assist techniques. This unique PTM-SRAM bitcell is designed by placing the PTM in series with the gate of pull-down nMOS transistors. The large insulating state resistance of the PTM device blocks the propagation of read voltage rise during a read operation and noise during retention operation, thereby enhancing read/retention stability. On the flip side, the write-time and write-ability are impacted, which can be improved by tuning the access transistor strength. Overall, the PTM-SRAM bitcell achieves active- V
_MIN
equivalent to baseline SRAM V
_MIN
aided by both read- and write-assist techniques. Furthermore, the read access time of the PTM-SRAM bitcell does not degrade with reducing read V
_MIN
in contrast to other read-assist techniques. For an isoactive- V
_MIN
of 0.52 V, the PTM-SRAM has 20% lower read access time, 35% lower read power, 16% higher write time, and 55% lower write power compared to the baseline SRAM aided by assist techniques. Also, the dynamic retention stability of the PTM-SRAM improves by 11.36× compared to baseline SRAM. Detailed analysis highlighting the sensitivity of PTM parameters on PTM-SRAM performance metrics is also presented.