A Scalable Lossy Substrate Model for Nanoscale RF MOSFET Noise Extraction and Simulation Adapted to Various Pad Structures

A broadband and scalable lossy substrate model is developed and validated for nanoscale RF MOSFETs of different finger numbers and adopting various pad structures such as lossy, normal, and small pads. The broadband accuracy is justified by good match with S-and Y-parameters up to 40 GHz. The measured noise characteristics in terms of four noise parameters can be accurately simulated up to 18 GHz. The scalable lossy substrate model can consistently predict the abnormally strong finger number dependence and nonlinear frequency response of noise figure (NF_min) revealed by the devices with lossy pads. Furthermore, the scalable model can precisely distribute the substrate loss between the transmission line (TML) and pads of various metal topologies and the resulted excess noises. The enhanced model provides useful guideline for appropriate layout of pads and TML to effectively reduce the excess noises. The remarkably suppressed noise figure to ideally intrinsic performance can be approached by the small pad in this paper.