GaN RF switch with low off-state capacitance and harmonic distortion enabled by an AlGaN back barrier structure

Against the bottlenecks of off-state capacitance and isolation (ISO) performance in GaN radio frequency (RF) switches, this paper proposes an epitaxial regulation strategy based on a back barrier (BB) layer. By reshaping the distribution of two-dimensional electron gas and optimizing the electric-field coupling mechanism, a significant reduction in off-state capacitance (Coff) and synergistic improvement of RF performance are achieved. By utilizing this AlGaN BB structure, the optimal device demonstrated a low Coff of 136 fF/mm, a superior ISO performance higher than 13 dB at 8.5 GHz, and a high power-handling capability of 36 dBm. Notably, it also delivers significantly improved second- (H2) and third- (H3) order harmonic distortions, reaching −82.5 and −102.5 dBm, respectively, at an input power of 15 dBm. Furthermore, the underlying mechanism for the influence of the BB structure on Coff performance was systematically investigated. Technology computer-aided design simulations revealed the modulation effect of the BB layer on individual capacitive components, demonstrating that the BB layer effectively reduces the vertical electron concentration near the gate edges in the off state, thereby lowering Coff. These findings demonstrated the potential of the proposed BB structure for high-performance RF-switch applications.