RF MEMS Research Articles

Design and performance analysis of uniform meander structured RF MEMS capacitive shunt switch along with perforations

This paper presents design and simulation of uniform structured RF MEMS capacitive shunt switch using FEM tool and HFSS software. The switches with different shaped meanders and perforations which result in less spring constant, less pull-in voltage, high isolation loss, high switching speed and low insertion loss have been designed. From the simulated results it is observed that the rectangular perforations gives the better results, when compared with square and cylindrical shaped perforations. Comparative study is done for zigzag, plus and three square shaped meander along with rectangular perforations on each structure. When the gap between the dielectric and the movable beam is 0.8 µm, the up state capacitance for HfO2 is 4.06fF and for Si3N4 is 3.80fF. The downstate capacitance for HfO2, Si3N4 is 49fF, 26.9fF respectively. The capacitance ratio is 120.6. Poly-tetra-fluoro-ethylene material is given for the movable beam whose young’s modulus is 0.4 GPa and the spring constant is calculated theoretically for each structure; by using this the pull in voltage and the settling time are calculated. Step switch with three square Meander has switching time 10.25 µs, pull in voltage as 2.45 V. By using HFSS 3-D electromagnetic model we observed the return loss (S11) is less than −60 dB, the insertion loss is less than −0.07 dB in the range of 1–40 GHz frequency and switch isolation (S21) is −61 dB at 28 GHz frequency.

Fabrication and test of RF MEMS in LTCC technology

RF MEMS in low-temperature co-fired ceramics (LTCC) technology have been designed, manufactured and tested for potential utilization in reconfigurable space sub-systems. Specifically, single-pole-single-throw (SPST) and single-pole-double-throw (SPDT) ohmic switch configurations have been studied for wide-band applications. Advantages coming from the measured RF performances and from the integration of RF MEMS by means of the LTCC technology only, to be used also for packaging, are discussed. Furthermore, preliminary on-wafer DC test on a double-pole-double-throw (DPDT) ohmic switch has been done in order to check both the mechanical response and the quality of the ohmic contact (contact resistance).

Ka‐band RF MEMS capacitive switch with low loss, high isolation, long‐term reliability and high power handling based on GaAs MMIC technology

This study presents a Ka-band radio frequency (RF) micro electro mechanical systems (MEMS) capacitive switch with low loss, high isolation, long-term reliability and high power handling based on GaAs microwave monolithic integrated circuit (MMIC) technology. In this design, a T-matching structure is employed to realise impendence matching at ‘up-state’ by modifying the dimensions of centre signal line. Thus, the reflection loss and insertion loss are improved effectively. Measurement results show that in ‘up-state’ position, the input reflection coefficient (S11) is less than −20.4 dB with the forward transmission coefficient (S21) of better than −0.27 dB at Ka-band (27–40 GHz). At ‘down-state’, the switch is designed in a state of self-resonance to obtain high isolation. The measured isolation is better than 20 dB over Ka-band and can reach 35 dB at its self-resonant frequency of 35 GHz. The measured actuation voltage is about 36 V. The measured lifetime is at least 5.76 × 107 cycles. The measured power handling capability can reach up to 39 dBm. The proposed compact RF MEMS capacitive switch possesses excellent performances in terms of low insertion loss, high isolation, long lifetime and high power handling capability.

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.

Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator**Project supported by the National Natural Science Foundation of China (Grant Nos. 61234007, 61404136, and 61504130), the Fund from the Ministry of Science and Technology of China (Grant No. 2013YQ16055103), the Key Research & Development Program of Jiangsu Province, China (Grant No. BE2016007-2), and the

In this paper, we present a three-dimensional (3D) vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system (RF MEMS) resonator, in which low-loss silicon vias is used to transmit RF signals. Au–Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio (SBR) of 24 dB is achieved, as well as the quality factor (Q-factor) of the resonator increases from 8000 to 10400 after packaging. The packaged resonator has a linear frequency–temperature (f–T) characteristic in a temperature range between 0 °C and 100 °C. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.

High on/off capacitance ratio RF MEMS capacitive switches

In this paper, high on/off capacitance ratio radio frequency micro-electro-mechanical-systems (RF MEMS) switches are designed, fabricated, measured and analyzed. Two types of RF MEMS switches, a shunt switch with a contact point and an inline switch without a contact point, are presented. Metal–insulator–metal (MIM) fixed capacitors are used in the MEMS switches. The electrode topologies of RF MEMS switches are analyzed. The parameter λ is defined to describe the relationship between the capacitance ratio, the height of the beam and the actuation voltage. The measured results indicate that, for MEMS switch #1 with a contact point and gap of 1 µm, the insertion loss is better than 0.64 dB up to 40 GHz, and the isolation is more than 20 dB from 11.28 to 30.38 GHz with an actuation voltage of 42 V. For the inline MEMS with a displacement of 1.5 µm, the insertion loss is better than 0.56 dB up to 40 GHz, and the isolation is more than 20 dB from 4.45 to 30.48 GHz with an actuation voltage of 36 V. Circuit models and measured results of the proposed MEMS switches show good agreement. From the fitted results, the on/off capacitance ratio is ~227 for the MEMS switch #1 and ~313 for the MEMS switch #2, respectively. Compared with traditional MEMS capacitive switches with dielectric material Si3N4 and a relatively lower gap (1.5 µm), the proposed MEMS switches exhibit high on/off capacitance ratios.

Design, simulation and analysis of a digital RF MEMS varactor using thick SU-8 polymer

This paper presents the design, simulation and analysis of a 5-bit RF MEMS digital variable capacitor using thick SU-8 polymer to achieve both high capacitance ratio (varvec{C}_{varvec{r}}) and Q-factor. The proposed varactor design consists of five capacitive shunt switches loaded over a co-planar waveguide (CPW) line. This results 32 capacitance steps ranging from 102.23 fF to 3.57 pF (varvec{C}_{varvec{r}} = 35). The high capacitance ratio of the varactor is achieved by implementing SU-8 polymer as the base structure of the capacitor due to its low dielectric constant (varvec{varepsilon}_{varvec{r}} = 4) hence reducing the overall minimum capacitance (varvec{C}_{{varvec{min}}}). The optimization of the SU-8 thickness has been carried out to get the optimum capacitance ratio and Q-factor. Moreover, the inclusion of semi-elliptical slot at the ground of CPW and variable sizes of CPW line further reduce the parasitic capacitance. To improve the reliability of the variable capacitor design, a new aluminium (Al) stopper design is used to prevent contact between the beams and the pull-down electrodes. Mechanical simulations and analysis have been carried out to investigate the effects of in-plane residual stress and stress gradient on the spring constant and the initial displacement of the proposed horizontal truss fixed–fixed beam structure. Compared to the conventional doubly clamped solid beam design, the proposed beam has less sensitivity to in-plane residual stress. This makes the pull in voltage to be less affected by the stress due to the fabrication. The simulated pull-in and lift-off voltages are 30 and 25 V respectively while the estimated switching time for the beam is 4.64 μs. The overall size of the varactor is 740 μm × 653 μm. The proposed RF MEMS varactor could be integrated in reconfigurable filters, phase shifters and matching networks targeting future multi-standard wireless communication systems.

Utility of RF MEMS miniature switched capacitors in phase shifting applications

This paper demonstrates research carried out towards the development of switched capacitors having miniature dimensions. Such devices are based on the Radio Frequency Micro Electro Mechanical Systems (RF MEMS) technique which has gained prominence in implementing a wide variety of microwave and millimetre devices till date. Switched capacitors having standard or conventional dimensions are prone to several limitations which are addressed by scaling down the standard dimensions by 150× times (in terms of area requirement). Such switched capacitors are employed to develop phase shifters working in K-band (22GHz) frequency range to yield appreciable performance both in terms of electromechanical and RF characterizations. Such switched capacitors are utilized to develop phase shifters which find immense applications in the design of Phased Array RADARs. Switched capacitors fabricated on 500µm thick quartz substrates, result in 30° phase shift (0.66mm×1mm in dimension) with associated minimum −0.18dB insertion loss and better than −21dB reflection coefficient at 22GHz frequency. Electromechanical characterization reports an actuation voltage of 14.6V, mechanical vibration frequency of 2.5MHz and a switching time of 620ns respectively. Demonstrations showing complete realization of 180° phase shifter (4mm×1mm) employing a cascaded arrangement of six similar 30° unit cells are also included in this paper.

Dielectric Charging Asymmetry in SiN Films Used in RF MEMS Capacitive Switches

This paper presents a systematic investigation of the effect of stressing bias polarity to the discharge process of plasma enhanced chemical vapor deposition SiN films that have been fabricated under different deposition conditions. Dielectric charging asymmetry has been observed on the utilized films of metal-insulator-metal capacitors and microelectromechanical systems capacitive switches, since charging is enhanced when negative polarization bias is applied to the top electrode. In addition, it is shown that deposition conditions play a key issue role on the degree of this asymmetry. Finally, a physical model which assumes that hopping dominates the discharging process is used in order to gain a better understanding of the processes that are responsible for the appearance of asymmetric dielectric charging and the results correlate with the material’s electrical properties.

RF-MEMS-Based DPDT Switch on Silicon Substrate for Ku-Band Space-Borne Applications

A RF-MEMS (radio-frequency microelectromechanical-system) based DPDT (double pole double throw) switch for the Ku band has been designed and analyzed for this article. The switch topology is based on the FG-CPW (finite ground-coplanar waveguide) configuration of a microstrip-transmission line. An FEM-based multiphysics solver is used for the evaluation of the spring constant, stress distribution, and pull-in voltage regarding the requirements of the switch-beam unit. The electromagnetic performance of the switch is investigated for a <TEX>$675{\mu}m$</TEX> thick silicon substrate. For the operational frequency of 14.5 GHz, an insertion loss better than -0.3 dB, a return loss better than -40 dB, and input/output- and output-port isolations better than -35 dB are achieved for the switching unit.

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.

Fabrication process induced changes in scattering parameters of meander type RFMEMS shunt switch

This paper reports about the effect of fabrication process induced changes on scattering parameters of RF MEMS switch structure with meander geometry for 18–40 GHz (Ka-band) application. The designed structure showed a return loss better than 15 dB with a maximum isolation of 43 dB at 35 GHz. From the parametric analysis, both the return loss and isolation parameters are found to be more dependent on the meander width and dielectric thickness compared to the other dimensions. The switch structure is fabricated by surface micromachining technique. The effect of variation of fabricated device dimensions, due to the various processing steps, on the isolation characteristic is also studied. The fabricated structure exhibited an on–off capacitance ratio of ~200:1. The pull-down voltage is found to be 12.5 V. The return loss of the fabricated switch structure is found to be better than 13.5 dB; whereas, the maximum isolation (32 dB) is observed at 33 GHz. The shift in the resonance is due to the reduction of silicon nitride layer thickness during sacrificial layer removal (to release the switch structure) in diluted HF solution. The measured scattering parameters are found to be matching well with the corresponding simulation data of the fabricated switch dimensions.

A high-force and high isolation metal-contact RF MEMS switch

A simple structure, high-force and high isolation metal contact RF MEMS switch was fabricated based on micro electroplating technology, and the mechanical and RF performance of the switch were measured. After release and annealing, the switch’s cantilever beam showed a tip-up of less than 1 µm over the beam length of 485 µm, indicating a good stress control and thermal stability of the electroplated gold. The pull-in voltage and the switching characteristics at different temperatures, ranging from 25 to 90 °C, were investigated. A fast, stable and temperature independent switching process was observed as the actuation voltage was 10% larger than the pull-in voltage. Based on the classical cantilever beam model, both the electrostatic actuation force and the return force of the switch were larger than 1000 μN, and the extracted effective spring constant of the free-standing beam was 718 N/m. Cold RF tests were carried out at various temperatures by a network analyzer, and we found that temperature showed very less influence on the insertion and isolation of the switch in the present case. At 25 °C, the insertion loss was −0.13 dB at 10 GHz, and was lower than −0.3 dB over the 0.05−20 GHz frequency range. The isolation was −36 dB at 10 GHz, and was higher than −27 dB over the entire scanning frequency range. The high isolation performance is consistent with a lumped-element equivalent circuit analysis of the switch.

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.

Design and Analysis of a Silicon-Based Pattern Reconfigurable Antenna Employing an Active Element Pattern Method

In this paper, a silicon-based radio frequency micro-electromechanical systems (RF MEMS) pattern reconfigurable antenna for a Ka-band application was designed, analyzed, fabricated, and measured. The proposed antenna can steer the beam among three radiating patterns (with main lobe directions of −20°, 0°, and +20° approximately) at 35 GHz by switching RF MEMS operating modes. The antenna has a low profile with a small size of 3.7 mm × 4.4 mm × 0.4 mm, and consists of one driven patch, four parasitic patches, two assistant patches, and two RF MEMS switches. The active element pattern method integrated with signal flow diagram was employed to analyze the performances of the proposed antenna. Comparing the measured results with analytical and simulated ones, good agreements are obtained.

RF-MEMS Tuned GaN HEMT based Cavity Oscillator for X-band

This letter presents a radio frequency micro-electromechanical systems (RF-MEMS) tuned cavity oscillator for X-band. The active part of the oscillator is implemented in GaN-HEMT MMIC technology. The RF-MEMS-switches are realized on a quartz substrate that is surface mounted on a low loss PCB. The PCB is intruded in an aluminum cavity acting as an electrically moveable wall. For a three-row RF-MEMS setup, a tuning range of 5 % around an oscillation frequency of 10 GHz is demonstrated in measurements. The phase noise is as low as −140 dBc/Hz to −129 dBc/Hz at 100 kHz from the carrier, depending on the configuration of the RF-MEMS.

Novel Conception of a Tunable RF MEMS Resonator

This paper presents a new monolithic microwave integrated circuit (MMIC) based on coplanar waveguide (CPW) design for a tunable resonator based on RF MEMS. This RF structure, which can be used for system on chip (SOC), is constituted with MEMS Bridge placed between two meander inductors and the tenability is controlled by a variable applied DC voltage. Moreover, this device presents a compactness characteristic and the possibility to operate at high frequencies. The resonant frequency and the bandwidth can be changed easily by changing the bridge gap of the RF MEMS. The numerical simulations of this novel structure of a tunable RF MEMS resonator were performed with the electromagnetic solvers CST MWS (Computer simulation Technology Microwave Studio) and validated by the more accurate electromagnetic solver HFSS (High Frequency Structural Simulator). The simulation results, for three different spacing of the bridge gap, show that the tunable frequency band are between 10 and 40 GHz with the two electromagnetic solvers and exhibiting three resonant frequencies (21, 23.1 and 24.6 GHz).The simulation results of the return loss using CST achieves 29 dB with an insertion loss less than 1 dB; However, the HFSS simulation shows similar performance in the resonant frequencies and in the bandwidth giving better results in terms of the return loss (about 35dB instead of 29 dB) and showing a good adaptation.

High-Linearity 3-Bit Frequency-Tunable Planar Inverted-F Antenna for RF Applications

A compact planar inverted-F antenna (PIFA) has been designed, fabricated, and characterized to work either for receiving or transmitting applications. The antenna center frequency can be tuned from 1.52 up to 2.25 GHz, using switched auxiliary strips. Ohmic contact radio frequency microelectromechanical system (RF-MEMS) switches are used to connect and disconnect the auxiliary strips, maintaining both efficiency and antenna linearity (power handling capability). The measured PIFA efficiency for all states in an anechoic chamber is between 52% and 95%. The antenna linearity has also been measured using an adjacent channel power ratio test bench, showing 42-dB dynamic range up to 28-dBm input power.

Design and analysis of CPW based shunt capacitive RF MEMS switch

This paper is about, the design and analysis of shunt capacitive RF MEMS switch with less actuation voltage, low insertion losses and high isolation losses. The switch design is incorporated the El...