RF performance of GaAs pHEMT switches with various upper/lower δ-doped ratio designs

AlGaAs/InGaAs pseudomorphic high-electron-mobility transistor (pHEMT) single-pole-single-throw (SPST) switches with various upper/lower δ-doped ratio designs were fabricated and investigated for the first time. Both off-state capacitance and the specific on-resistance (R_on) of pHEMT are dominated factors and showed characteristics of sensitive to upper/lower δ-doped ratio for RF switch applications. By adopting the series-shunt architecture, upper/lower ratio of 3:1 switch achieved the lowest insertion loss compared to 4:1 design owing to the device shunt to ground (M2) of 4:1 design exhibited a worse fundamental signal isolation especially at high power level. As to the isolation under same architecture, however, due to the lowest R_on can be obtained, the 4:1 design provided better isolation performance. In addition, the M2 also dominated the second and third harmonics suppression and meanwhile, the lowest R_on of 4:1 design was found to be beneficial to the reduction of the harmonics power transmitted to the output terminal.