An analysis of the dynamic characteristics of pull-in for parallel-plate and torsional electrostatic actuators is presented. Traditionally, the analysis for pull-in has been done using quasi-static assumptions. However, it was recently shown experimentally that a step input can cause a decrease in the voltage required for pull-in to occur. We propose an energy-based solution for the step voltage required for pull-in that predicts the experimentally observed decrease in the pull-in voltage. We then use similar energy techniques to explore pull-in due to an actuation signal that is modulated depending on the sign of the velocity of the plate (i.e., modulated at the instantaneous mechanical resonant frequency). For this type of actuation signal, significant reductions in the pull-in voltage can theoretically be achieved without changing the stiffness of the structure. This analysis is significant to both parallel-plate and torsional electrostatic microelectromechanical systems (MEMS) switching structures where a reduced operating voltage without sacrificing stiffness is desired, as well as electrostatic MEMS oscillators where pull-in due to dynamic effects needs to be avoided.

Dynamic pull-in of parallel plate and torsional electrostatic MEMS actuators.

MEMS switch is a movable device manufactured by means of semiconductor technology, possessing many incomparable advantages such as a small volume, low power consumption, high integration, etc. This paper reviews recent research of MEMS switches, pointing out the important performance indexes and systematically summarizing the classification according to driving principles. Then, a comparative study of current MEMS switches stressing their strengths and drawbacks is presented, based on performance requirements such as driven voltage, power consumption, and reliability. The efforts of teams to optimize MEMS switches are introduced and the applications of switches with different driving principles are also briefly reviewed. Furthermore, the development trend of MEMS switch and the research gaps are discussed. Finally, a summary and forecast about MEMS switches is given with the aim of providing a reference for future research in this domain.

Research Status and Development Trend of MEMS Switches: A Review.

This paper is designed to review the MEMS switch by considering key aspects on the basis of mechanical structure, actuation methods, and types of contact and circuit configurations. The cantilevered and clamped–clamped switch structures are explored and discussed. Actuation methods and switch configurations have also been covered to give more insights about their placements and performances in RF systems. The electrostatic and piezoelectric actuation mechanisms can result in fast RF MEMS switches and better reliability but at the cost of increased pull-in voltage. The electrostatic method is mostly employed in MEMS switches due to its distinctive advantages. The resistive switch uses less actuation voltage compare to a capacitive switch but suffers from reliability issue. Nevertheless, the capacitive MEMS switches are prominent in use over ohmic contact switches due to better RF performance and reliabilities by offering lifetime of 3–10 million cycles. The RF MEMS switches can be placed in series, shunt and mixed configurations as per application requirements. Capacitive switches are mostly utilized in RF systems and placed in shunt with coplanar waveguide signal lines. These RF MEMS switches find applications in sensors, resonators, amplifiers, phase shifters, and MEMS satellite vehicles for space applications.

A review on RF micro-electro-mechanical-systems (MEMS) switch for radio frequency applications

Nanomechanical cantilever (NMC) active probes have recently received increased attention in a variety of nanoscale sensing and measurement applications Current modeling practices call for a uniform cantilever beam without considering the intentional jump discontinuities associated with the piezoelectric layer attachment and the NMC cross-sectional step This paper presents a comprehensive modeling framework for modal characterization and dynamic response analysis of NMC active probes with geometrical discontinuities The entire length of the NMC is divided into three segments of uniform beams followed by applying appropriate continuity conditions The characteristics matrix equation is then used to solve for system natural frequencies and mode shapes Using an equivalent electromechanical moment of a piezoelectric layer, forced motion analysis of the system is carried out An experimental setup consisting of a commercial NMC active probe from Veeco and a state-of-the-art microsystem analyzer, the MSA-400 from Polytec, is developed to verify the theoretical developments proposed here Using a parameter estimation technique based on minimizing the modeling error, optimal values of system parameters are identified Mode shapes and the modal frequency response of the system for the first three modes determined from the proposed model are compared with those obtained from the experiment and commonly used theory for uniform beams Results indicate that the uniform beam model fails to accurately predict the actual system response, especially in multiple-mode operation, while the proposed discontinuous beam model demonstrates good agreement with the experimental data Such detailed and accurate modeling framework can lead to significant enhancement in the sensitivity of piezoelectric-based NMC sensors for use in variety of sensing and imaging applications

Modeling and experimental vibration analysis of nanomechanical cantilever active probes

This paper describes and demonstrates a terahertz (THz) frequency tunable fishnet metamaterial (TFMM) using an electrically controlled polymer dispersed liquid crystal (PDLC) matrix. In contrast to other PDLC-based devices, the TFMM employs a novel method for encapsulating PDLC using a thin (1.5 μm) polyimide “skin layer” to form a uniform surface for metal electrodes while minimizing the Fabry-Perot effect of the skin layer on the TFMM measurements. The tunability was verified by measuring the frequency shift in the reflection coefficient (0.01 THz), with an observed minimum negative refractive index of −15 at 0.55 THz.

Tunable terahertz fishnet metamaterial

This paper presents the design, fabrication and characterization of an RF MEMS switch. Low actuation voltage and high isolation of the switch were achieved by exploiting buckling and bending effects induced by well-controlled residual stress. The effects of residual stress on improving the switch performance have been investigated using both analytical and numerical methods. The proposed RF switch has been fabricated by surface micromachining. The minimum actuation voltage of the fabricated switch was measured to be 10.2 V. At a 5 GHz signal frequency, the measured insertion loss and isolation are 0.21 dB and −44 dB, respectively. These results demonstrate that low voltage and high isolation of RF MEMS switches can be achieved with proper utilization of residual stresses.

https://iopscience.iop.org/article/10.1088/0960-1317/17/8/031/pdf

A low actuation voltage electrostatic actuator for RF MEMS switch applications

A tunable capacitor based on polymer-dispersed liquid-crystal (PDLC) technology is presented in this paper. Its application for robust power harvesting microsystems was investigated. The power harvesting device utilized a piezoelectric microcantilever excited by ambient random vibrations to convert mechanical energy into electric power. For improving the power harvesting efficiency, the PDLC tunable capacitor was used to adjust the resonance frequency of the piezoelectric microcantilever beam to match the frequency of the ambient vibrations in real time. The fabrication process and measurement results of the PDLC tunable capacitor are detailed. The measured tuning ratio of the PDLC tunable capacitor was 63% at 300-Hz excitation frequency when a 25-V driving voltage was applied. The dielectric and optical properties of the fabricated PDLC tunable capacitor have been examined thoroughly. Based on the results of the experiment, an equivalent lumped-element model of the PDLC tunable capacitor has been developed. The simulation results showed that the impedance of the developed model agreed well with that of the fabricated tunable capacitor. This model can be incorporated into the equivalent circuit of the integrated power harvesting system for efficiency optimization.

Tunable Capacitor Based on Polymer-Dispersed Liquid Crystal for Power Harvesting Microsystems

This paper presents the design methodology, fabrication and characterization of flip-chip bonded MEMS capacitor for tuning high temperature superconductive resonator. Because the main issue of MEMS capacitor integrated with high temperature superconductor (HTS) is high driving voltage due to accumulated thermal stress, a methodology to decrease the thermal stress is discussed. In this work, the thermal stress can be reduced to several MPa, and driving voltage is about 40 V. To avoid degradation of HTS thin film during MEMS process, MEMS capacitor is fabricated separately and then flip-chip bonded on the HTS resonator. The tuning effects of this MEMS capacitor applied on HTS resonator of 3 GHz resonant frequency are presented.

Flip-chip bonded MEMS capacitor Applied on tuning superconductive resonator

This paper presents a tunable power harvesting device and explains how a tunable capacitor based on polymer-dispersed liquid crystal (PDLC) can be used to optimize the power harvesting efficiency. For improving the power harvesting efficiency, we have developed a PDLC tunable capacitor to adjust the resonance frequency of the piezoelectric micro-cantilever beam to match the frequency of environmental random vibration in real time. Fabrication process and measurement results of the PDLC tunable capacitor are detailed. Large tuning ratio up to 117.5% of the PDLC tunable capacitor is measured at 75 kHz signal frequency. At 12 V driving voltage, tuning ratio as 55% can be achieved.

Tunable Capacitor Based on Polymer-Dispersed Liquid Crystal for Optimum Micro-Power Harvesting

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Papers

A low actuation voltage electrostatic actuator for RF MEMS switch applications

Tunable Capacitor Based on Polymer-Dispersed Liquid Crystal for Power Harvesting Microsystems

Flip-chip bonded MEMS capacitor Applied on tuning superconductive resonator

Tunable Capacitor Based on Polymer-Dispersed Liquid Crystal for Optimum Micro-Power Harvesting