Ka-band flip-chip assembled power amplifier

In this paper, we present a Ka-band two-stage power amplifier with flip-chip assembled 0.15 mum-gate pHEMTs. With characterized 0.15 mum- gate GaAs pHEMT and consideration of the Au-Sn pillar bump transition, the GaAs pHEMTs were flip-chip assembled on Al₂O₃ substrate where the passive components and coplanar waveguide (CPW) connection were designed and fabricated. The measured maximum S₂₁ at 38.56 GHz is 20.7 dB with bias conditions of V_D = 3 V, V_G1 = -0.2 V, V_G2 = -0.15 V, I_D1 = 52 mA, and I_D2 = 110 mA. The output power at 38 GHz is larger than 15 dBm with linear gain of 15 dB. The load-pull measurement was also carried out on the amplifier to demonstrate the difference from 50Omega load measurement. The difference shows the capability of pHEMT model used at Ka-band for delivering the maximum power.