This work describes accurate methods for the characterization of sub-terahertz (sub-THz) devices and pad de-embedding procedures. The extraction of the intrinsic DUT is enabled by generating a precise pad model using two-tier calibration approaches. Moreover, the proposed approaches offer a solution to the designers to preserve precious silicon area by presenting a simplified and potentially parameterizable pad model. Employing two different thru-reflect-line (TRL) calibration kits (calKits) together with the DUT on the same die, this research validates the proposed calibration strategies. This paper uses as DUT at J-band, i.e. a Marchand balun, fabricated using IHP SiGe BiCMOS technology with an aluminum back-end-of-line (BEOL), alongside the mentioned calKits. The goal of the paper is to assess the performance of the DUT and validate two de-embedding methods. Moreover, the pad model offers a way for accurate DUT characterization saving silicon area for future optimized designs.