Performance analysis and insights into Schottky-gate and insulated-gate GaN-on-Si RF switch devices: A comparative study on RF isolation

Radio-frequency (RF) switches play a pivotal role in reconfigurable front-ends, antenna tuning, and transmit/receive modules; however, fundamental studies on their device-level physics and switching mechanisms remain relatively limited. This work presents a comparative investigation of Schottky-gate and insulated-gate RF switch devices fabricated on GaN-on-Si substrates, and provides the first systematic evidence of a correlation between drain-induced barrier lowering (DIBL) and isolation in insulated-gate structures. Small-signal characterization further reveals that the insertion loss shows only a small difference between the two devices, whereas the isolation performance differs considerably. To gain further insight into this phenomenon, we conducted an in-depth investigation. Experimental results demonstrate that although the incorporation of a SiN gate dielectric effectively reduces the peak electric field in the AlGaN barrier, this compromise in turn weakens gate controllability and aggravates the DIBL effect. As a result, although the electric field is mitigated, the addition of the gate insulator counterintuitively reduces the breakdown voltage, primarily due to buffer leakage. Benefiting from stronger gate control, the Schottky-gate switch consistently exhibits superior isolation compared with its insulated-gate counterpart, although the disparity diminishes with increasing frequency. At higher frequencies, particularly in millimeter-wave regimes, parasitic effects and fringing capacitance dominate, rendering the isolation difference nearly negligible. These findings not only provide new insights into the device physics of GaN-on-Si RF switches but also offer practical design guidelines for achieving high-performance operation.