A Broadband and Scalable Lossy Substrate Model for RF Noise Simulation and Analysis in Nanoscale MOSFETs With Various Pad Structures

Abstract

An enhanced lossy substrate model is developed with important features of broadband accuracy and scalability. The broadband accuracy is justified by a good match with open pad S-parameters measured up to 110 GHz and MOSFETs' S- and Y-parameters over 40 GHz. The proven model can accurately simulate four noise parameters (NF(min), R(n), Re(Y(opt)), and Im(Y(opt))) and power spectral density of current noises (S(id) and S(ig)). The scalability has been validated over nanoscale MOSFETs with different finger numbers and adopting various pad structures (lossy, normal, and small pads). This scalable lossy substrate model attributed to two substrate RLC networks under the pads and transmission lines (TMLs) can consistently predict the abnormally strong finger number dependence and nonlinear frequency dependence of noise figure (NF(min)) revealed in devices with lossy pads. The enhanced model is useful in guiding pad and TML layouts for effective reduction of extrinsic noises and low noise design. Using a normal pad structure, the NF(min) can be effectively suppressed to approach the intrinsic performance, which is nearly independent of finger numbers.