BCB-bridged Ka-band MMICs using In0.5Al0.5As/In0.5Ga0.5As metamorphic HEMTs

The InAlAs/InGaAs metamorphic HEMT (mHEMT) two-stage Ka-band amplifier and DC-30 GHz distributed SPST switch were designed and fabricated using low-k benzocyclobutene (BCB) bridged technology. This fabrication technology takes the advantages of its low dielectric permittivity (2.7), low loss tangent (0.008), low curing temperature, low water up-take, and simple manufacturing process. The MMIC fabrication process involves wet etching for isolation, alloyed ohmic contacts, NiCr resistor, Si3N4 metal–insulator–metal (MIM) capacitors, and the BCB via holes and bridges. The two-stage Ka-band amplifier can achieve a linear gain of 14 dB, and an input return loss of 15 dB at 34 GHz. The DC-30 GHz distributed SPST switch exhibits an insertion loss less than 5 dB and an isolation larger than 30 dB. As to the switch power performance, this switch can operate up to 12 dBm at 2.4 GHz without significant signal distortion. To further investigate the robustness of the DC-30GHz distributed SPST distributed switch, the reliability test of the insertion loss and isolation were carried out. After 250 hrs of 85–85 (temperature= 85C, humidity= 85%) environmental evaluation, this BCB passivated and bridged MMIC switch demonstrates reliable RF characteristics without any performance change, which proves that this process using the low-k BCB layer is attractive for millimeter wave circuit applications.