Multilayer, low‐parasitic, interconnection scheme for advanced submillimetre‐wave GaN circuits

A multilayer, low-parasitic interconnection scheme for highly scaled GaN high electron mobility transistors is reported. The fabrication process offers three Au interconnects embedded in benzocyclobutene (BCB) dielectric, with an integrated air-box in the active area in order to minimise the gate parasitic capacitances. With the addition of the air-box, it is demonstrated that the performance of the BCB encapsulated device is similar to that of a non-encapsulated device. Furthermore, by utilising the multilayer interconnection scheme a low-loss (0.75 dB) 3 dB tandem coupler operating from 140 to 220 GHz is demonstrated.