SNM analytical approach to robust subthreshold SRAM operation based on the 55nm DDC technology

Subthreshold operational characteristics of Ultra-Low Leakage (ULL) 6T-SRAM bit-cell and circuit based on the 55nm deeply depleted channel (DDC) technology was evaluated. The maximum operation frequency was 5 to 20 MHz (TT @RT) under 0 to 0.34V range of forward back bias (VBB) condition and leakage current in the retention mode reduced down to 285fA/cell by reverse VBB. It was confirmed that the ULL SRAM has sufficient static noise margin (SNM) to operate in the subthreshold region by optimizing NMOS and PMOS VBB separately.