Radio Frequency Microelectromechanical System Switch Research Articles

Ultrabroadband (DC–80 GHz) RF MEMS DC/capacitive load shunt switch

AbstractThis study presents the design and fabrication of a novel direct current (DC)/capacitive radio frequency (RF) Micro‐Electro‐Mechanical Systems (MEMS) switch in the ultrabroadband range from DC to 80 GHz. This proposed RF MEMS switch consists of two arms, with one arm providing a DC loading state (), whereas the second arm provides a capacitive loading state () to the ground when pull‐in voltage is applied. Insertion loss less than 1.85 dB and return loss better than 10 dB are achieved in the OFF state () from DC to 80 GHz (no pull‐in voltage is applied). Due to the novel design topology, this switch can act as a DC‐only switch (0–17 GHz) that provides isolation better than 25 dB during the state. A capacitive‐only switch (48–80 GHz) provides isolation better than 17 dB. This proposed structure can act as either DC(S1) or a capacitive () switch (17–48 GHz) and provides isolation better than 10 dB in either state. This proposed switch finds its best application in reconfigurable circuits like phase shifters due to switching between DC and capacitive loading during the On state from 17 to 48 GHz. The proposed switch's measured pull‐in and lift‐off voltages are 3.5 and 2.85 V, respectively.

Revolutionizing wireless communication: A review perspective on design and optimization of RF MEMS switches

Micro Electro Mechanical System (MEMS) technology revolutionized electronics by enabling miniaturization and integration of components like sensors, actuators, & switches. MEMS switches offer advantages over conventional switches, with Radio Frequency (RF) MEMS switches gaining attention in wireless communication systems. Designing and optimizing RF MEMS switches necessitate a profound comprehension of their electromagnetic and mechanical behavior, achieved using simulation and optimization techniques. This review provides an overview of different optimization techniques, including Finite Difference Time Domain (FDTD), Finite Element Method (FEM), Method of moments (MoM), Taguchi method, Response Surface Method (RSM), Artificial Neural Network (ANN) model and Evolutionary Algorithm (EA) based model, with the ANN and EA model being the most efficient due to its capability to handle complex designs and provide accurate predictions. This review aims to provide insights into the current state-of-the-art in RF MEMS switch design and optimization, stimulating further research to address existing challenges and limitations.

Low-Voltage and High-Reliability RF MEMS Switch with Combined Electrothermal and Electrostatic Actuation.

In this paper, we report a novel laterally actuated Radio Frequency (RF) Microelectromechanical Systems (MEMS) switch, which is based on a combination of electrothermal actuation and electrostatic latching hold. The switch takes the advantages of both actuation mechanisms: large actuation force, low actuation voltage, and high reliability of the thermal actuation for initial movement; and low power consumption of the electrostatic actuation for holding the switch in position in ON state. The switch with an initial switch gap of 7 µm has an electrothermal actuation voltage of 7 V and an electrostatic holding voltage of 21 V. The switch achieves superior RF performances: the measured insertion loss is −0.73 dB at 6 GHz, whereas the isolation is −46 dB at 6 GHz. In addition, the switch shows high reliability and power handling capability: the switch can operate up to 10 million cycles without failure with 1 W power applied to its signal line.

Design of RF-MEMS Switch Integration with Circular Microstrip Patch Antenna

This paper presents the design and analysis of a microstrip circular patch antenna, integrated with the RF-MEMS capacitive type switch. Here, two different types of RF-MEMS (Radio frequency Micro-electromechanical systems) switches are proposed, one is a bridge-type and the other is a single-beam type switch. These two switches are designed and simulated by using FEM (Finite Element Model) tool, the pull-in voltages of the two switches are obtained as 1.9 V, 4.9 V. Both switches are integrated with the circular patch antenna and measure the device characteristics and analysed in HFSS (High Frequency Structure Simulator) tool. The work is focused on analysing the performance of circular micro strip patch antenna such as return loss, radiation pattern, gain, VSWR (voltage standing wave ratio) and bandwidth and compared the performances of both switches are in ON and OFF condition. The circular microstrip patch antenna with RF-MEMS switches are designed to achieve antenna re-configurability at low frequencies up to 15 GHz.

Manufacturing and Testing of Radio Frequency MEMS Switches Using the Complementary Metal Oxide Semiconductor Process.

A radio frequency microelectromechanical system switch (MSS) manufactured by the complementary metal oxide semiconductor (CMOS) process is presented. The MSS is a capacitive shunt type. Structure for the MSS consists of coplanar waveguide (CPW) lines, a membrane, and springs. The membrane locates over the CPW lines. The surface of signal line for the CPW has a silicon dioxide dielectric layer. The fabrication of the MSS contains a CMOS process and a post-process. The MSS has a sacrificial oxide layer after the CMOS process. In the post-processing, a wet etching of buffer oxide etch (BOE) etchant is employed to etch the sacrificial oxide layer, so that the membrane is released. Actuation voltage for the MSS is simulated using the CoventorWare software. The springs have a low stiffness, so that the actuation voltage reduces. The measured results reveal that actuation voltage for the MSS is 10 V. Insertion loss for the MSS is 0.9 dB at 41 GHz and isolation for the MSS is 30 dB at 41 GHz.

AZ4620 Photoresist as an Alternative Sacrificial Layer for Surface Micromachining

The mechanical actuation of suspended structures in microelectromechanical system (MEMS) switches plays an important role in obtaining an open or short circuit in radio-frequency (RF) transmission lines. These micromachined switches have moving parts which are realized by a sacrificial layer. Several sacrificial materials have been utilized in the fabrication of MEMS structures. The traditional method of using metal such as copper or nickel as a sacrificial layer is difficult due to metal etchant compatibility issues. A photoresist is the best choice for this process. Generally, the HiPR photoresist has been found to be suitable␣for the role of sacrificial layer. However, the HiPR is no longer available in the commercial market. As an alternative to the HiPR, the AZ4620 photoresist can be used. In this paper, a unit process optimization technique is described featuring an AZ4620 photoresist as a sacrificial layer for the microfabrication of a suspended structure. The AZ4620 meets all the requirements for the development of RF MEMS switches. Hence, the recipe and fabrication technique are optimized according to the required thickness. Preliminary measurements of the fabricated switch beam indicate that the required gap has been achieved. This optimized process is compatible with standard MEMS technology.

Design and fabrication of a 4-bit RF MEMS attenuator with a high attenuation accuracy

This paper presents a 4-bit micro-electromechanical system (MEMS) digital attenuator with improved attenuation accuracy by surface micromachining. The attenuator is consisted of monoblack type radio frequency MEMS switches and TaN film resistors fabricated on a glass substrate to control the reconfigurable power within DC ~ 18 GHz. The simulation results revealed that the device had favorable terminal matches ranging from 0 to 70 dB with a 10 dB step. The attenuation accuracy was better than 1.2 dB, the insertion loss was less than 1.32 dB, and the voltage standing wave rations were better than 1.56 under these eight attenuation steps. Additionally, the package size of this device was designed as 8.28 mm × 2.37 mm × 0.85 mm, such that it could be applied to miniaturized microwave instruments.

Surface roughness effects on electromechanical performance of RF-MEMS capacitive switches

The effect of surface roughness on the electromechanical performance of radio frequency micro-electromechanical system (RF-MEMS) based capacitive switches is an important reliability concern. This paper presents a finite element method (FEM) based simulation methodology for the estimation of surface roughness effects on the electromechanical characteristics of parallel plate capacitive RF-MEMS switch. The important electromechanical characteristics considered for the analysis of surface roughness effect include up-state capacitance, down-state capacitance, pull-in voltage, pull-in gap and switching time of RF-MEMS switch. A simple roughness model is employed consisting of semi-circles of constant radius along the surface of an RF-MEMS switch. It is shown that there are significant, but predictable shifts in electromechanical characteristics of RF-MEMS switch due to surface roughness. The results illustrate that the normalized value of up-state capacitance and pull-in gap increases, whereas the values of downstate capacitance, pull-in voltage and switching time decreases with an increase in surface roughness. The change in pull in voltage for an initial air gap of 0.4μm and roughness of 50nm is around 28.5% which is about quarter the value of voltage required for the actuation of smooth surface RF-MEMS switch. The results obtained through FEM based analysis in this work are in good agreement with the adopted analytical model and experimental results presented in literature.

Linearity and RF Power Handling on Capacitive RF MEMS Switches

Linearity characteristics of capacitive tuners under large radio frequency (RF) power have become an important issue for today’s cellphone industry. The use of these devices as antenna tuners has become critically important due to the RF spectrum opening in the low-frequency range. Capacitive tuners connected directly to the antenna to change the RF voltage/current pattern and tune lower frequencies are subjected to suffer large voltage swings, especially in the isolation state or minimum capacitance. In this article, we analyze the effects of the large RF power or equivalent rms voltage to capacitive micro-electromechanical systems (MEMS) switches. The theoretical analysis combined with Coventor MEMS+ simulations will allow us to study the capacitance change and MEMS mechanical frequency response. This article evaluates two types of measurement setups to investigate the RF power effects on nominal capacitance and mechanical frequency response. Measurements up to 6 W were completed with two capacitive MEMS tuner products, confirming the modeling predictions and demonstrating the robustness of this technology under large RF power or voltage swings.

Novel design and analysis of RF MEMS shunt capacitive switch for radar and satellite communications

<span>In this paper, a new type of Radio Frequency Micro-Electro-Mechanical System (RF-MEMS) shunt capacitive switch is designed and studied. RF MEMS switch has a number of advantages in a modern telecommunication system such as low power consumption, easy to fabricate and power handling capacity at radio frequency. At high frequency applications, this switch shows very superior performance due to which it now became one of the key elements for RF application. In this proposed design, an innovative type of MEMS switch is designed. The MEMS switch structure consists of substrate, co-planar waveguide (CPW), dielectric material and a metallic bridge. The proposed MEMS switch has a dimension of 508 µm × 620 µm with a height of 500 µm. The substrate used is GaAs material. The relative permittivity of the substrate is 12.9. This proposed MEMS switch is designed and simulated in both UP (ON) state and DOWN (OFF) state. The proposed RF-MEMS switch is designed and simulated using Ansoft High frequency structure simulator (HFSS) electromagnetic simulator. The simulated result shows better performance parameters such as return loss ( <-10 dB) and insertion loss ( > -0.5 dB) in UP state, whereas return loss ( > -0.5 dB) and isolation (<-10 dB) in DOWN state. This switch has good isolation characteristics of – 43 dB at 27 GHz frequency.</span>

Laterally Movable Triple Electrodes Actuator toward Low Voltage and Fast Response RF-MEMS Switches.

A novel actuator toward a low voltage actuation and fast response in RF-MEMS (radio frequency micro-electro-mechanical systems) switches is reported in this paper. The switch is comprised of laterally movable triple electrodes, which are bistable by electrostatic forces applied for not only the on-state, but also the off-state. The bistable triple electrodes enable the implementation of capacitive series and shunt type switches on a single switch, which leads to high isolation in spite of the small gap between the electrodes on the series switch. These features of the actuator are effective for a low voltage and fast response actuation in both the on- and off-state. The structure was designed in RF from a mechanical point of view. The laterally movable electrodes were achieved using a simple, low-cost two-mask process with 2.0 µm thick sputtered aluminum. The characteristics of switching response time and actuation voltage were 5.0 µs and 9.0 V, respectively.

Comprehensive Study on RF-MEMS Switches Used for 5G Scenario

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 Compact Single-Cantilever Multicontact RF-MEMS Switch With Enhanced Reliability

This letter presents a novel cantilever and electrode biasing design of a metal-contact radio frequency microelectromechanical systems (RF-MEMS) switch to integrate multiple contact points in a single cantilever to improve the reliability of the switch. In the design presented in this letter, multiple contact points are integrated in a single cantilever. The contact points are used to conduct RF current one by one until one point fails. To switch between the contact points, two actuator electrodes are placed under the cantilever and biased with different voltages and the touching point between the cantilever and bottom RF electrode are changed. The parasitic capacitance of the switch is kept to be the same with that of a single contact point RF-MEMS switch. The OFF-state isolation will not be worsen, while accumulation of the lifetime of each contact point can improve the overall lifetime of the switch. Without the need of shrinking the actuator to maintain small parasitics capacitance, the contact force is also not sacrificed when comparing to the case of putting several miniature switches together. The performance and reliability improvement of the switch are experimentally demonstrated. The insertion losses of the switch of different contact points are <1 dB, and the isolation is better than 10 dB up to 20 GHz.

RF-MEMS-Based Bandpass-to-Bandstop Switchable Single- and Dual-Band Filters With Variable FBW and Reconfigurable Selectivity

Bandpass (BP)-to-bandstop (BS) switchable filters using radio frequency microelectromechanical system switch are presented here. The filters are implemented in both single- and dual-band versions with variable fractional bandwidth (FBW). Tuning of transmission zeros (TZs) and transmission poles (TPs) for BP filter (BPF) and BS filter (BSF), respectively, is achieved in both single- and dual-band cases leading to reconfigurable selectivity. The first odd-mode frequency of the filter is suppressed using a fixed capacitor and the second odd mode is brought closer to the first even-mode with another variable capacitor to form the passband(s). The second capacitor tunes both the second odd mode and TZs (for BPF) or TPs (for BSF) minimizing the requirement of any extra tuning element. In a single-band fabricated BPF, tuning second odd mode gives the FBW variation of 9.3%–72.7% with TZ on the lower side and 5.6%–55.6% with TZ on the higher side of the passband. The 15-dB FBW of a single-band BSF having TP on both sides of the stopband varies over 5.2%–20.7%. The two passbands of a dual-band BPF independently vary over 4.5%–24% and 4.5%–13%. Also, the 15-dB FBW of the first and second stopbands of BSF independently varies over 6.5%–13.2% and 1.5%–3.6%, respectively.

High-Power High-Isolation RF-MEMS Switches With Enhanced Hot-Switching Reliability Using a Shunt Protection Technique

This paper presents a shunt protection technique to improve the hot-switching reliability of metal-contact radio-frequency microelectromechanical systems (RF-MEMS) switches. The proposed technique places shunt protection contacts in front of the main contact of an RF-MEMS metal contact switch to block RF signal while the main contact is switching ON or OFF. The shunt protection contact creates a local cold-switching condition for the main contact to increase the lifetime of the switch under hot-switching condition. The shunt protection technique can also increase the overall isolation of the switch. To demonstrate the technique, RF-MEMS switches with and without shunt protection were fabricated using all metal process. Compared with the unprotected switch, the protected switch has longer lifetime under hot-switching condition. The protected switch has >100-million cycles and up to 500-million cycles lifetime under the 1-W hot-switching condition, measured in open-air laboratory environment. Besides, the isolation of the shunt-protected switch is 70 dB at 1.0 GHz and 36 dB at 40 GHz, and the insertion loss is 0.30 dB at 1.0 GHz and 0.43 dB at 40 GHz.

Modeling, design, and simulation of a radio frequency microelectromechanical system capacitive shunt switch

AbstractThis tutorial paper presents an empirical model of a capacitive radio frequency microelectromechanical system switch in the microwave domain. The simulation results of the mechanical and electrical aspects of the proposed model were computed with Matlab. The mechanical modeling is validated by COMSOL software through the finite element method to determine the spring constant and the necessary applied voltage. The electromagnetic simulation results are validated by 3 different software: the High‐Frequency Structure Simulator based on the finite element method, the Computer Simulation Technology based on finite integration technique method, and the Advanced Design System based on the method of moments. The obtained results are performed in both down (OFF) and up (ON) states in the frequency range of 1 to 40 GHz, and the considered performance benchmarks are the insertion loss, return loss, isolation, and phase.

Analysis of a novel double driving signal line and driving electrodes separated RF MEMS switch

A novel double driving signal line and driving electrodes separated radio frequency (RF) micro-electromechanical system (MEMS) switch was proposed in this paper to overcome the problems of the high actuation voltage, small displacement, and long pull-down time of the RF MEMS switches. Dynamic equations of the micro beam were built based on the small deflection theory. Dynamic behaviors of the proposed RF MEMS switch were analyzed and calculated by the variable separation method. The effects of different driving voltages, structure parameters and materials on the RF MEMS switch performance were discussed in detail. The simulation results presented that the proposed RF MEMS switch had an actuation voltage of 26 V, a pull-down time of 31.5 [Formula: see text] and an actuation displacement of 3 [Formula: see text]. The results also showed that the pull-down time of micro beam increased as the dielectric layer thickness increased. When the beam thickness was higher than 1.1 [Formula: see text], the switch could not pull down anymore. Additionally, the switch had a lowest pull down time when Al was used as micro beam material, compared to Au, Si, and SiC. The COMSOL Multiphysics finite element analysis was carried out to validate the MATLAB simulation results, and the comparison results were basically consistent with the MATLAB simulation results. Besides, the proposed switch had an insertion loss of −0.2 dB on up-state and isolation of more than −20 dB on down-state at 60 GHz derived from the electromagnetic simulation results. The actuation voltage, pull-down time, actuation displacement, and electromagnetic performances of the proposed RF MEMS switch were compared to some other switches, which were better than some existing switches.

Effect of surface asperities on the capacitances of capacitive RF MEMS switches

The effects of surface asperities on the up- and down-state capacitances of the capacitive radio frequency (RF) micro electromechanical system (MEMS) switches were studied in this paper based on the single asperity model and statics. The research results demonstrated that surface asperities effects on the up-state capacitance could be neglected, whereas surface asperities must be taken into consideration at the down-state position in the RF MEMS switches because the surface asperities significantly affected the down-state capacitance. The down-state capacitance typically decreased as the root mean square (RMS) roughness and asperity radius increased. The down-state capacitance was approximately 26% of the theoretical value when the RMS roughness was 20 nm, and 32% of the theoretical value when the asperity radius was 100 nm. The experimental results were in good agreement with the simulation results.

Electromagnetic and small-signal modeling of an encapsulated RF-MEMS switch for D-band applications

In this work, an electromagnetic (EM) model and a small-signal (lumped-element) model of a wafer-level encapsulated (WLE) radio frequency microelectromechanical systems (RF-MEMS) switch is presented. The EM model of the WLE RF-MEMS switch is developed to estimate its RF performance. After the fabrication of the switch, the EM model is used to get accurate S-parameter simulation results. Alternative to the EM model, a small-signal model of the fabricated WLE RF-MEMS switch is developed. The developed model is integrated into a 0.13 µm SiGe BiCMOS process technology design kit for fast simulations and to predict the RF performance of the switch from a pure electrical point of view. The 0.13 µm SiGe BiCMOS embedded WLE RF-MEMS shows beyond state-of-the-art measured RF performances in D-band (110–170 GHz) and provides a high capacitance Con/Coffratio of 11.1. The results of the both EM model and small-signal model of the switch are in very good agreement with the S-parameter measurements in D-band. The measured maximum isolation of the WLE RF-MEMS switch is 51.6 dB at 142.8 GHz with an insertion loss of 0.65 dB.

Design and experimental validation of a restoring force enhanced RF MEMS capacitive switch with stiction-recovery electrodes

This paper presents an approach for restoring force enhancement to radio frequency (RF) micro-electro-mechanical systems (MEMS) switch with stiction-recovery actuation mechanism. It is based on additional anti-stiction electrodes which are inserted to the coplanar waveguide (CPW) between the signal line and ground planes of a RF MEMS switch. If the movable membrane sticks to the substrate, electrostatic force, as extra restoring force, generated by the bias voltage between the anti-stiction electrodes can promise restoring action. The designed device with the proposed approach is fabricated. The restoring force of the fabricated device had reached 75, 177 and 520 μN by the bias voltages of 0, 10 and 20 V, respectively.