Hybrid Integration of Microwave Circuit Solenoid Inductors and AlGaN/GaN HEMTs Using an SU-8 Photosensitive Epoxy Interposer Layer

Integration of active and passive microwave circuit components onto an inexpensive silicon substrate can be accomplished using photosensitive SU-8 epoxy as the interposer layer. This paper addresses the 3-dimensional integration of AlGaN/GaN high electron mobility transistor's (HEMT's) embedded into deep reactive ion etched (DRIE) pockets on a silicon substrate with gold-plated vias and transmission lines formed in a follow-on layer of SU-8 epoxy over the HEMT's. In addition, modeling, simulation, fabrication and testing of gold-plated, solenoid inductors embedded in SU-8 over the silicon substrate is covered. This integration process may replace variable inductance wire bond connections; with reproducible interconnects to enhance circuit design flexibility and accuracy. The solenoid inductors, whose inductance L and quality factor Q can be further optimized through the addition of ferrite or ferromagnetic cores, will help reduce the overall circuit footprint. This paper is organized into two parts: the solenoid model development and the HEMT integration process and test results.