Toward Industrial Exploitation of THz Frequencies: Integration of SiGe MMICs in Silicon-Micromachined Waveguide Systems

A new integration concept for THz systems is presented, wherein patterned silicon-on-insulator wafers form all DC, IF and RF networks in a homogeneous medium, in contrast to existing solutions. Using this concept, silicon-micromachined waveguides are combined with silicon germanium (SiGe) microwave monolithic integrated circuits (MMICs) for the first time. All features of the integration platform lie in the waveguide's H-plane. Heterogeneous integration of SiGe chips is achieved using a novel in-line H-plane transition. As an initial step towards complete systems, we outline the design, fabrication and assembly of back-to-back transition structures, for use at D-band frequencies (110 – 170 GHz). Special focus is given to the industrial compatibility of all components, fabrication and assembly processes, with an eye on the future commercialisation of THz systems. Prototype devices are assembled via two distinct processes, one of which utilises semi-automated die-bonding tools. Positional and orientation tolerances for each process are quantified. An accuracy of ±3.5 μm, ±1.5 ° is achieved. Measured S-parameters for each device are presented. The insertion loss of a single-ended transition, largely due to MMIC substrate losses, is 4.2 – 5.5 dB, with a bandwidth of 25 GHz (135 – 160 GHz). Return loss is in excess of 5 dB. Measurements confirm the excellent repeatability of the fabrication and assembly processes and thus their suitability for use in high-volume applications. The proposed integration concept is highly scalable, permitting its usage far into the THz frequency spectrum. This work represents the first stage in the shift to highly-compact, low-cost, volume-manufacturable THz waveguide systems.