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This paper presents a comprehensive study on radio frequency-microelectromechanical systems (RF-MEMS) switches, which are expected to be extensively integrated into 5G infrastructures. The specifications of the RF-MEMS switch in use case and scenario for 5G have been summarized in part 2 and followed by the study of the state-of-the-art RF-MEMS switches in part 3. Both metal-contact and capacitive RF-MEMS switches, which have been developed and fabricated within the last two decades, are studied and tabled. In order to meet with the specification requirements of 5G scenario, the performance and characteristics of the RF-MEMS switches should be enhanced, such as acceptable RF performance, low actuation voltage, good reliability, short switching time, multiband topology, and on-chip integration and packaging. Different techniques for the improvement of the RF-MEMS switches' properties, for instance low spring constant, large actuation area, diverse actuation methods, push-pull mechanism, modified driving voltage waveform, inductive compensation, and so on, have been thoroughly investigated, classified, and summarized in part 4, which serves as the main contribution of the review. The findings from this review can be beneficial for further RF-MEMS switches' design and improvement. The upgraded RF-MEMS switches are capable of satisfying the growing need of cutting edge performance for 5G or high-performance applications.

A low-voltage low-loss K-band 3-bit MEMS switched-line phase shifter is presented in this work. The phase shifter is constructed by novel shunt capacitive RF-MEMS switches and coplanar waveguide lines on a high-resistivity silicon substrate. A low-voltage RF-MEMS switch (pull-in voltage = 3.04V) is employed and exhibits good RF characteristics by using T-match technique where its insertion loss and isolation is −0.1291dB and −28.75dB, respectively at frequency of 20GHz. The 3-bit MEMS phase shifter is assembled by three single-bit units (namely, 45°-bit, 90°-bit and 180°-bit) of switched-line structures; the average phase error and average insertion loss is 0.2445° and −2.447dB, respectively, at 20GHz; its return loss is better than 10dB at a wideband frequency range of up to 20GHz. The whole design area is 6mm∗4mm.

This paper presents a novel design and analysis of capacitive radio frequency (RF) micro-electromechanical system (MEMS) switch. The RF-MEMS switch is actuated by electrostatic force with low-actuation voltage of 2.9V while it can be operated in a robust condition with maximum von Mises stress of 13.208 MPa which is less than aluminum's yield stress. By finite-element-modeling (FEM) simulations, at switch-on state, insertion loss and reflection loss of the proposed RF-MEMS switch is obtained as −0.8023dB and −7.983dB, respectively; and at switch-off state, isolation and return loss is −22.45dB and − 0.8666dB, respectively. In order to improve the switch-on reflection loss to meet design specifications, two short high-impedance sections of transmission line have been calculated and added to the RF-MEMS switch. Then the reflection coefficient at switch-on state has been increased by 78.13% to −14.22dB which is less than −10dB while the insertion loss, isolation and return loss are all improved by 66.54%, 13.36% and 11.65%, respectively, with 65ohm high-impedance lines. The RF-MEMS switch's actuation time of 27µs is obtained. A detail comparison among the proposed RF-MEMS switch and other state-of-the-art designs has been summarized in the end.