Considerations for Through-Substrate-Via Placement in InGaAs mHEMT THz Circuits Using Thin-Film Wiring

This paper discusses the necessity of through-substrate vias for compact integrated circuits (ICs) at frequencies around 300GHz, which are implemented using backside-process-free thin-film microstrip line (TFMSL) matching networks. The technology used is a 35-nm InGaAs mHEMT technology, which is processed on a GaAs substrate. The measured S-parameters of 300-GHz common-source (CS) and cascode power amplifier ICs with different via-placement scenarios are presented, which indicate a topology-dependent necessity of through-substrate-via implementation in order to suppress the excitation of substrate resonances and inter-device coupling. Different scenarios for via placement are investigated experimentally and evaluated in simulation, in order to define requirements for via-placement considerations in compact TFMSL circuits in this InGaAs mHEMT technology.