W-Band True-Time Delay Phase Shifters Using Paraffin Microactuators

We report a distributed loaded line phase shifter based on a new class of electro-thermally actuated RF MEMS devices using paraffin phase-change material (PCM). Paraffin is a low loss (tan δ = 6.6×10−4) mechanical phase-change material that exhibits a 15% volumetric change through its solid-liquid transition. Due to its unique electrical and mechanical properties, paraffin PCM variable capacitors exhibit a very low loss which is critical in designing reconfigurable structures. Here, a low-loss paraffin PCM based true-time delay, continuously-tunable phase shifter is designed and optimized. A figure-of merit of 71.8◦/dB is achieved while maintaining a return loss more than 12 dB. Designed phase shifter has a maximum insertion loss of 5 dB for a 360◦ phase shift. Electro-thermo-mechanical performance of the paraffin PCM device is studied by carrying out a fully coupled multiphysics simulation. Maximum displacement of 0.8 μm is achieved with a 2.6 μm-thick paraffin film. A new fabrication method for the deposition of the thin paraffin film is developed and a fabrication process for the device is presented.