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From the perspectives of characterized data, calibrated TCAD simulations and compact modeling, we present a deeper investigation of the very high frequency behavior of state-of-the-art sub-THz silicon germanium heterojunction bipolar transistors (SiGe HBTs) fabricated with 55-nm BiCMOS process technology from STMicroelectronics. The TCAD simulation platform is appropriately calibrated with the measurements in order to aid the extraction of a few selected high-frequency (HF) parameters of the state-of-the-art compact model HICUM, which are otherwise difficult to extract from traditionally prepared test-structures. Physics-based strategies of extracting the HF parameters are elaborately presented followed by a sensitivity study to see the effects of the variations of HF parameters on certain frequency-dependent characteristics until 500 GHz. Finally, the deployed HICUM model is evaluated against the measured s-parameters of the investigated SiGe HBT until 500 GHz.

Maximum oscillation frequency (fMAX ) of mmwave transistors is one of the key figures of merit (FOMs) for evaluating the HF-performance of a given technology. However, accurate measurements of fMAX are very difficult. Determination of fMAX is significantly affected by the measurement uncertainties in the admittance (y) parameters. In order to get rid of the random measurement error and to obtain a reliable and stable fMAX value, the frequency dependent y-parameters are described by rational functions formulated from the smallsignal hybrid π-model of the transistor under investigation. The parameters of these functions are determined following a least square error technique that minimizes the functional error with the measured data. The approach is especially useful for a fast and reliable evaluation of fMAX value. Devices from two different SiGe and an FDSOI (Fully Depleted Silicon On Insulator) MOS technology are measured and stable fMAX values are estimated following this approach.Index Terms-SiGe HBTs; MOS; y-parameters; maximum oscillation frequency; analytical modeling; small-signal model. I. INTRODUCTIONT HE demand for increased functionality and speed of modern communication system drives the evaluation of various transistor technologies [1]. These unique technologies differ from one another in terms of doping profiles, geometries and structures. In this rapid development, heterojunction bipolar transistors (HBTs) or advanced CMOS technologies find applications in millimeter and sub-millimeter wave frequency range [2], [3], [4], [5]. In this region of applications, realizations of power amplifiers and low noise amplifiers are limited by transit frequency (f T ) and maximum oscillation frequency (f M AX ). Also to achieve the required functionality, f T and Manuscript received October 02, 2020; revised November 20, 2020. This work is partly funded by the French nouvelle Aquitaine Authorities through the FAST project. The research leading to these results has received funding from the European Commission's ECSEL Joint Undertaking under grant agreement n • 737454 -project TARANTO -and the respective Public Authorities of France,