SiC Strained nMOSFETs With Enhanced High- Frequency Performance and Impact on Flicker Noise and Random Telegraph Noise

Abstract

Silicon–carbon (SiC) strained nMOSFETs with sub-35-nm gate length in a 40-nm CMOS technology can realize superior cutoff frequency ( $f_{T}$ ) up to 405 GHz, attributed to more than 20% enhancement of the mobility and transconductance. This super-400-GHz $f_{T}$ makes SiC strained nMOS an attractive high mobility device aimed at millimeter-wave (mm-wave) CMOS circuits design. However, the SiC nMOSFETs reveal a dramatic increase in flicker noise and random telegraph noise (RTN), which may cause worse phase noise and detrimental impact on CMOS oscillator stability. The complex RTN features abnormally long capture and emission time constants ( $\tau _{c}$ and $\tau _{e}$ ) and suggests electron-phonon coupling responsible for the anomalously slow trapping and detrapping, due to a significant increase of relaxation energy from SiC strain. This critical tradeoff between high-frequency performance and low-frequency noise becomes a key factor to be considered for the most appropriate adoption of high mobility devices and design optimization adapted to various circuits.