On Distinguishing Process Corners for Yield Enhancement in Memory Compiler Generated SRAM

As the technology scales down to nanometer, the yield degradation caused by inter-die variations is getting worse. Using adaptive body bias is an effective method to mitigate the yield degradation (especially for memory compiler generated SRAMs), however we need to know a die having high threshold voltage or low threshold voltage (also called process corner) in order to use this technique. Unfortunately, it is hard to detect the process corners when PMOS and NMOS variations are uncorrelated. In this paper, we propose some improved circuits of delay monitor and leakage monitor for both PMOS and NMOS process corner detection, which are uncorrelated in inter-die variations. The experimental results show that our circuits can clearly distinguish each process corner of PMOS and NMOS, thus improve the yield by adopting correct body bias.