Novel C-band and K-band 3-D InGaP/InGaAs MMICs using low-k BCB interlayer

A C-band and a K-band In_0.49Ga_0.51P/ In_0.15Ga_0.85As doped-channel HFET (DCFET) monolithic amplifier were developed and fabricated by using a low-k benzocyclobutene (BCB) interlayer technology. With the photo-sensitive low-k BCB interlayer (ε = 2.7), not only the passivation layer, but the capacitor insulator, via holes, and bridge process of the C-band circuit can be realized simultaneously, where the process complexity and cost can be reduced. Besides, the K-band MMIC utilizes a high impedance BCB CPW microstrip line (Z₀ = 70 Ω) for the biasing circuit, and a BCB CPW line (Z₀ = 50 Ω) for the RF signal transmission path. The low dielectric constant characteristic of the BCB interlayer is beneficial for common-ground bridge process.