Introduction

Abstract

Static random access memory (SRAM) has been widely used as the representative memory for logic LSIs. This is because SRAM array operates fast as logic circuits operate, and consumes a little power at standby mode. Another advantage of SRAM cell is that it is fabricated by same process as logic, so that it does not need extra process cost. These features of SRAM cannot be attained by the other memories such as DRAM and Flash memories. SRAM memory cell array normally occupies around 40% of logic LSI nowadays, so that the nature of logic LSI such as operating speed, power, supply voltage, and chip size is limited by the characteristics of SRAM memory array. Therefore, the good design of SRAM cell and SRAM cell array is inevitable to obtain high performance, low power, low cost, and reliable logic LSI.