Investigation of Gate Field-Plate Effects on f max Improvement in GaN HEMTs for RF Applications

This work presents a comprehensive study on the impact of gate field-plate extension on the RF performance of AlGaN/GaN high-electron mobility transistors (HEMTs). Building on our previous demonstration of a 0.6 mu m gate-length micro field-plate T-gate GaN-on-SiC HEMT, achieving a high f(max )& times; L-g product of 48.2 GHz & centerdot; mu m, we investigate two additional devices with gate-to-drain field-plate lengths (L-gpd) of 0.5 and 0.8 mu m. Detailed DC and RF small-signal modeling analyses are conducted to identify the operational mechanisms contributing to the observed RF performance trends. Our findings reveal that the device with L-gpd = 0.5 mu m achieves a record-high peak f(max )& times; L-g product of 57.3 GHz & sdot;mu m along with fmax of 95.5GHz at V-ds=15 V, ascribed to a reduced gate resistance and improved channel-buffer isolation (increased R-ds), and an enhanced capacitance ratio of C-gs/C-gd at high drain bias. The extended field plate geometry enables more effective electric field redistribution, leading to suppressed buffer leakage and improved RF gain characteristics without compromising the DC performance. A detailed analysis using extracted small-signal parameters and f(max) formulation confirms that the gate field-plate extension in the investigated device structure improves f(max) as a result of optimized operational performance characteristics.