A 35 fJ/bit-access sub-VT memory using a dual-bit area-optimized standard-cell in 65 nm CMOS

A 128×32 bit ultra-low power (ULP) memory with one read and one write port is presented. A full-custom standard-cell compliant dual-bit latch with two integrated NAND-gates was designed. The NAND-gate realizes the first stage of a read multiplexer. A dense layout reduces the physical cell area by 56 %, compared to a pure commercial standard-cell equivalent. Effectively, an overall memory area reduction of 32%is achieved. The gates are integrated into a digital standard-cell based memory (SCM) flow. Silicon measurements show correct read and write operation deep in the subthreshold domain (sub-V_T), down to 370mV, and data is retained down to 320mV. At the energy minimum voltage (450 mV) the memory dissipates 35 fJ/operation.