Microfabricated Thick-Cu PZT-MEMS Millimeter-Wave Topologies and Devices

This letter reports the design, fabrication, and performance of millimeter-wave transmission lines and devices in a tri-layer thick-copper (Cu) process. Beneath the Cu layers is a low-voltage lead zirconium titanate (PZT) MEMS stackup atop a nitride membrane, on high-resistivity silicon. The 10 μm thick Cu layers enable several transmission-line topologies, and the PZT-MEMS functionality enables tunability. We designed transmission lines and un-optimized noncontact distributed MEMS transmission line (DMTL) phase shifters for 75-110 GHz, and present static measurements here. Simulation and measurements are in close agreement, with measured CPW line loss 0.15 dB greater than simulated (0.27 dB/mm at 95 GHz). Excess loss is attributed to Cu roughness, conductivity, and membrane/strap supports. Measured noncontact DMTL phase shifters exhibit a mean of 40 ^°/dB when intrinsic line loss is subtracted.