New insights into AC RTN in scaled high-к / metal-gate MOSFETs under digital circuit operations

Abstract

Since devices actually operate under AC signals in digital circuits, it is more informative to study random telegraph noise (RTN) at dynamic AC biases than at constant DC voltages. We found that the AC RTN statistics largely deviates from traditional DC RTN, in terms of different distribution functions and the strong dependence on AC signal frequency, which directly impacts on the accurate prediction of circuit stability and variability. The AC RTN characteristics in high-к/metal-gate FETs are different from that in SiON FETs, and both of which cannot be described by classical RTN theory. A physical model based on quantum mechanics is proposed, which successfully explains the new observations of AC RTN. It is also demonstrated that, if using DC RTN statistics instead of AC RTN, a large error of 30% overestimation on the read failure probability in ultra-scaled SRAM cells will occur. These new understandings are critical for the robust circuit design against RTN in practical digital circuits.