Binary-Coded 4.25-bit $W$-Band Monocrystalline–Silicon MEMS Multistage Dielectric-Block Phase Shifters

摘要

This paper presents a novel concept of a microwave microelectromechanical systems (MEMS) reconfigurable dielectric-block phase shifter with best loss/bit at the nominal frequency and best maximum return and insertion loss ever reported over the whole $W$ -band. A seven-stage phase shifter is constructed by $lambda/2$-long high-resistivity silicon dielectric blocks, which can be moved vertically by MEMS electrostatic actuators based on highly reliable monocrystalline silicon flexures on-top of a 3-D micromachined coplanar transmission line. The dielectric constant of each block is artificially tailor made by etching a periodic pattern into the structure. Stages of 15$^{circ}$ , 30$^{circ}$ , and 45$^{circ}$ are optimized for 75 GHz and put into a binary-coded ${hbox{15}}^{circ}+{hbox{30}}^{circ}+{hbox{5}}times {hbox{45}}^{circ}$ configuration with a total phase shift of 270$^{circ}$ in 19$,times ,$15$^{circ}$ steps (4.25 bits). Return and insertion losses are better than $- {hbox{17}}$ and $-{hbox{3.5 dB}}$ at 75 GHz, corresponding to a loss of $-{hbox{0.82 dB}}/{hbox{bit}}$, and a phase shift efficiency of 71.1$^{circ}/{hbox{dB}}$ and 490.02$^{circ}/{hbox{cm}}$ . Return and insertion losses are better than $-{hbox{12}}$ and $-{hbox{4 dB}}$ for any phase combination up to 110 GHz (98.3$^{circ}/{hbox{dB}}$ ; 715.6$^{circ}/{hbox{cm}}$ ). The intercept point of third order, determined by nonlinearity measurements and intermodulation analysis, is 49.15 dBm for input power modulation from 10 to 40 dBm. The power handling is only limited by the transmission line itself since no current-limiting thin air-suspended metallic bridges as in conventional MEMS phase shifters are utilized. This is confirmed by temperature measurements at 40 dBm at 3 GHz with skin effect adjusted extrapolation to 75 GHz by electrothermal finite-element method simulations.