I. Introduction
The last decade has seen tremendous advances in transistor technology both in CMOS as well as in compound semiconductors (GaAs and InP) [1] [2]. These technologies have been used to implement a wide variety of applications including sensing, communications, and imaging [3] [4]. These advances in integrated-circuit technology have been enabled by significant advances in THz metrology. The development of 4- port vector network analyzers (VNAs) with substantially improved source stability, and the continued advances in GaAs-based Schottky diode multipliers and mixers has enabled the realization of THz frequency extension modules covering the waveguide bands from 100 GHz to over 1 THz. In addition, these advances in VNA frequency range have been accompanied by the development of THz frequency on-wafer probes that allow accurate and rapid measurements of transistors and integrated circuits.