RF MEMS Inductors and Their Applications—A Review

Inductors are primary elements in many radio frequency circuitries and devices. This review gives a comprehensive survey on the developments and performances of fixed and variable RF MEMS inductors. MEMS inductors are the core of this review due to their high-yield performances and the wide choices of possible tuning techniques. First, the factors that constrain high-performance micro coils and the conventional solutions to overcome them are highlighted. Next, this paper systematically reviews varieties of MEMS inductors starting with the fixed inductors and according to inductors' topologies and performance enhancement techniques. In addition, the variable types of inductors are subsequently discussed, mainly from the point of view of their tuning techniques. Many quantitative comparisons are given in terms of the values of quality factor, inductance, self-resonance frequency, and tuning range. This will provide readers with an overall evaluation of different studies and assist them in choosing the inductors' topologies and layouts that best suit their applications. This review also sheds light on different and most common RF MEMS inductors applications, including RF communication devices and wireless sensors and actuators applications. Finally, this paper summarizes the best fabrication and tuning approaches inferred from the reviewed works and discusses some design guidelines to achieve better inductor performance.