Analysis of the relationship between random telegraph signal and negative bias temperature instability

Abstract

Random telegraph signal (RTS) is shown to be an intrinsic component of the shift in MOSFET threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> ) due to bias temperature instability (BTI). This is done by starting from a well-known model for negative BTI (NBTI), to derive the formula for RTS-induced V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> shift. Based on this analysis, RTS simply contributes an offset in NBTI degradation, with an acceleration factor that is dependent on the gate voltage and temperature. This is verified by 3-dimensional (3-D) device simulations and measurements of 45nm-node bulk-Si PMOS transistors. It has an important implication for design of robust SRAM arrays in the future: design margin for RTS should not be simply added, because it is already partially accounted for within the design margin for NBTI degradation.