A Benchmark of Cryo-CMOS Embedded SRAM/DRAMs in 40-nm CMOS

The interface electronics needed for quantum processors require cryogenic CMOS (cryo-CMOS) embedded digital memories covering a wide range of specifications. To identify the optimum architecture for each specific application, this article presents a benchmark from room temperature (RT) down to 4.2 K of custom SRAMs/DRAMs in the same 40-nm CMOS process. To deal with the significant variations in device parameters at cryogenic temperatures, such as the increased threshold voltage, lower subthreshold leakage, and increased variability, the feasibility of different memories at cryogenic temperature is assessed and specific guidelines for cryogenic memory design are drafted. Unlike at RT, the 2T low-threshold-voltage (LVT) DRAM at 4.2 K is up to <inline-formula> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> more power efficient than both SRAMs for any access rate above 75 kHz since the lower leakage increases the retention time by <inline-formula> <tex-math notation="LaTeX">$40\,000\times $ </tex-math></inline-formula>, thus sharply cutting on the refresh power and showing the potential of cryo-CMOS DRAMs in cryogenic applications.