Method of screening static random access memory cells for positive bias temperature instability

Abstract

A method of screening complementary metal-oxide-semiconductor CMOS integrated circuits, such as integrated circuits including CMOS static random access memory (SRAM) cells, for n-channel transistors susceptible to transistor characteristic shifts over operating time. For the example of SRAM cells formed of cross-coupled CMOS inverters, static noise margin and writeability (V) screens are provided. Each of the n-channel transistors in the CMOS SRAM cells are formed within p-wells that are isolated from p-type semiconductor material in peripheral circuitry of the memory and other functions in the integrated circuit. Forward and reverse body node bias voltages are applied to the isolated p-wells of the SRAM cells under test to determine whether such operations as read disturb, or write cycles, disrupt the cells under such bias. Cells that are vulnerable to threshold voltage shift over time can thus be identified.