Traveling-wave microwave switch using III-N gateless devices with capacitively-coupled contacts
Radio-frequency (RF) switches using Field-Effect Transistors (FETs) have low loss, high switching speed. The fabrication process allows for monolithic integration with such as power amplifiers, phase shifters, arrays, and other components. Recent advancements in III-nitride heterostructure field-effect transistors (HFET) have led to RF switches with remarkably low-loss and high power handling capability, ideal for numerous applications [1, 2]. However, relatively large OFF-state capacitance of HFETs limits their application to frequencies below 4–6 GHz. In the past, traveling-wave (TW) RF switches using GaAs-based HFETs have been reported with operating frequencies up to 40–80 GHz [3]. The achieved insertion loss and isolation were below 3 dB and above 24 dB, correspondingly. The problem with GaAs-based TW switches is that for broadband performance, the switch should contain significant number (at least 10) of unit cells, each comprising multi-finger FETs. To make this technology feasible, either relatively small number of cell is used, or the unit cell periphery is decreased, or the source — drain distance is increased. All these measures deteriorate the performance. In addition, GaAs-based RF switches have relatively low power handling capability, high insertion loss and low maximum operating temperatures limited by fundamental material properties.