Deep-Reactive-Ion-Etched Wafer-Scale-Transferred All-Silicon Dielectric-Block Millimeter-Wave MEMS Phase Shifters

Abstract

This paper reports on design, fabrication, and characterization of a novel multistage all-silicon microwave MEMS phase-shifter concept, based on multiple-step deep-reactive-ion-etched monocrystalline-silicon dielectric blocks which are transfer bonded to an RF substrate containing a 3-D micromachined coplanar waveguide. The relative phase shift of 45° of a single stage is achieved by vertically moving the ?/2-long blocks by MEMS electrostatic actuation. The measurement results of the first prototypes show that the return and insertion loss of a 7 × 45° of a single stage is achieved by vertically moving the ?/2-long blocks by MEMSage phase shifter over the whole frequency spectrum from 1 to 110 GHz are better than -12 and -5.1 dB, respectively. The monocrystalline high-resistivity silicon blocks are acting as a dielectric material from an RF point of view, and at the same time as actuation electrodes for dc electrostatic actuation. The mechanical reliability was investigated by measuring life-time cycles. All tested phase shifters with three-meander 36.67-N/m mechanical spring and a pull-in voltage of 29.9 V survived 1 billion cycles after which the tests were discontinued, no indication of dielectric charging could be found, neither caused by the dielectric block nor by the Si3 N4 distance keepers to the bottom electrodes. Finally, it is investigated that, by varying the fill factor of the etch hole pattern, the effective dielectric constant of the block can be tailor made, resulting in 45°, 30°, and 15° phase-shifter stages fabricated out of the same dielectric material by the same fabrication process flow.