RF Microelectromechanical Systems Research Articles

A Novel Transmitting Module Self-Monitoring Protection System Based On MEMS Sensors and Actuators

Design, fabrication, and measurements of a novel transmitting module self-monitoring protection system are presented in this letter. Such a system is based on microelectromechanical systems (MEMS) sensors and actuators for monitoring and protecting the microwave amplifier circuit. The transmitting module self-monitoring protection system consists of the RF MEMS switches, the directional coupler, and the MEMS power sensors. When the microwave amplifier circuit is at an abnormal state (“open,” “short,” or “overload”), the transmitting module self-monitoring protection system can isolate the microwave amplifier circuit out of order and reconfigure the transmitting module into impedance matching within 36 ms. When the microwave amplifier circuit is at the overload state, the error between the set switching power and the actual switching power is less than 9%. The measured results agree well with the theory.

Pull-in-voltage and RF analysis of MEMS based high performance capacitive shunt switch

This paper presents design of a RF MEMS (Radio Frequency Micro Electro Mechanical system) capacitive shunt switch to study the switch performance which depends on various indices. To achieve high performance in the MEMS switch, the different component materials of the switch were chosen very carefully. Modeling equations were also derived for designed fixed-fixed beam of the switch considering formed capacitances in both upstate and downstate positions. The FEM simulation and accurate analytical results were obtained to study the effect of capacitance on the RF performance of the switch. The optimum dimensions were chosen for achieving a low pull in voltage as approximately 19 V for the designed switch. Static analysis confirms the optimum dimensions of the switch that provide several advantages such as high isolation, low insertion loss and low pull in voltage in the switch circuit. RF analysis study concludes that for the optimized switch provide return loss, insertion loss and isolation as −43 dB, −0.05 dB, −12 dB respectively.

Double-Sided Process for MEMS SOI Sensors With Deep Vertical Thru-Wafer Interconnects

This paper reports an approach for co-fabrication of silicon-on-insulator (SOI) sensors with low-resistance vertical electrical interconnects in thick (up to $600~\mu \text{m}$ ) wafers. The thru-wafer interconnects double-sided (TWIDS) process is based on bottom-up seedless copper electroplating, and allows for voids-free features and high aspect ratio (wafer thickness to copper diameter ratio of 10:1). This work describes the design trade-offs, process flow, and characterization of interconnects. TWIDS technology is compatible with a standard SOI micro-electro-mechanical systems (MEMS) fabrication process and is applicable for micro sensors, such as accelerometers, gyroscopes, resonators, and RF MEMS devices, as well as for the 3-D MEMS assemblies. As a demonstration of potential applications, miniature toroidal ring gyroscopes were fabricated using the TWIDS process. The experimental characterization showed that the low-resistance interconnects with low parasitic losses are suitable for integration with capacitive-detection sensors. In addition, the mechanical stability of the interconnects is discussed in this paper, and a method to enhance structural rigidity by means of filling the insulating gaps with Parylene C is demonstrated. [2017-0179]

Design and development of miniaturized low voltage triangular RF MEMS switch for phased array application

Nowadays, Micro-Electro-Mechanical System (MEMS) is widely used for various applications ranging from switches to sensors. The central idea of this work is to design and analyze metal to metal contact based miniaturized low voltage triangular MEMS switch. The prioritized aim of this work is to develop the MEMS switch with improved characteristics such as low actuation voltage, high isolation, low insertion loss, low-stress factor, and good return loss. The MEMS switch is designed in a series configuration with coplanar waveguide (CPW) implementation. In this current design, the triangular beam based switch is developed and analysed with an electrode material of gold. The electromagnetic analysis of the current design was performed using Intellisuite, whereas the finite element method based mechanical analysis is performed on Ansoft HFSS. The software analysis revealed that the triangular switch showed an insertion loss of about 0.2 dB with 20 dB as a return loss, under the ON state, whereas under the OFF state, isolation is around 26 dB at Dc–20 GHz. Further, pull-in voltage of the current design is optimized to 5.6 V with the maximum induced stress of about 5 MPa.With all these improved characteristics, the current MEMS-based switch can be potentially used for real-time application with the calculated switching time of approximately 3.9 μs.

Fabrication and characterisation of RF MEMS capacitive switches tuned for X and Ku bands

Microelectromechanical systems (MEMS) capacitive switches discussed in this paper employ electrostatic actuation to perform switching. Capacitive switches employ inductive tuning for excellent switching characteristics in X and Ku bands. Employing inductive tuning is found to increase the switch beam inductance by a few tens of pico-henry. This enhances the Q factor and enables tuning of isolation over a narrow band of frequencies. Beam inductance can be extracted from the simulated isolation characteristics of the switch by curve fitting. This paper presents design, fabrication and characterisation of inductive tuned MEMS capacitive switches tuned for X and Ku bands. The devices are fabricated on high resistive (10 KΩ) silicon substrate by a five mask process. The characterisation of the fabricated devices are conducted using Cascade probe station and high frequency Power network analyser. Characterisation results show an actuation voltage of 18.5 volts. The insertion - loss and isolation are better than 0.5 dB and -40 dB respectively in the 8-18 GHz band.

Fabrication and characterisation of RF MEMS capacitive switches tuned for X and Ku bands

Microelectromechanical systems (MEMS) capacitive switches discussed in this paper employ electrostatic actuation to perform switching. Capacitive switches employ inductive tuning for excellent switching characteristics in X and Ku bands. Employing inductive tuning is found to increase the switch beam inductance by a few tens of pico-henry. This enhances the Q factor and enables tuning of isolation over a narrow band of frequencies. Beam inductance can be extracted from the simulated isolation characteristics of the switch by curve fitting. This paper presents design, fabrication and characterisation of inductive tuned MEMS capacitive switches tuned for X and Ku bands. The devices are fabricated on high resistive (10 KΩ) silicon substrate by a five mask process. The characterisation of the fabricated devices are conducted using Cascade probe station and high frequency Power network analyser. Characterisation results show an actuation voltage of 18.5 volts. The insertion - loss and isolation are better than 0.5 dB and -40 dB respectively in the 8-18 GHz band.

MEMS based monolithic Phased array using 3-bit Switched-line Phase Shifter

This article details the design of an electronically scanning phased array antenna with proposed fabrication process steps. Structure is based upon RF micro-electromechanical system (MEMS) technology. Capacitive type shunt switches have been implemented here to cater high frequency operation. The architecture, which is deigned at 30 GHz, consists of 3-bit (11.25º, 22.5º and 45º) integrated Switched-line phase shifter and a linearly polarized microstrip patch antenna. Detailed design tricks of the Ka-band phase shifter is outlined here. The whole design is targeted for future monolithic integration. So, the substrate of choice is High Resistive Silicon (ρ > 8kΩ-cm, tan δ =0.01 and ϵr =11.8). The overall circuit occupies an cross-sectional area of 20 × 5 mm2. The simulated results show that the phase shifter can provide nearly 11.25º/22.5º/45º phase shifts and their combinations at the expense of 1dB average insertion loss at 30 GHz for eight combinations. Practical fabrication process flow using surface micromachining is proposed here. Critical dimensions of the phased array structure is governed by the deign rules of the standard CMOS/MEMS foundry.

A Switchable Bandpass Filter Employing RF MEMS Switches and Open-Ring Resonators

A switchable bandpass filter is presented in this paper, which is able to operate at two different frequencies. The “open-ring” resonators and cantilever microelectromechanical systems (MEMSs) switches are employed to form the switchable filter with a high rejection at out-of passband and a controlled dc bias of 26 V. A hybrid resonance circuit with both series circuit and parallel circuit are used as the equivalent circuit, which is used to accurately analyze the structure parameters. The MEMS switch capacitance, used for equivalent circuit and driving voltage estimation, is analyzed to achieve an exact predicted value by equivalent microstrip line model. The isolation of designed MEMS switch is greater than 40 dB with awideband from4 to 9GHz, the filter is switched on and off to achieve the center frequency at ~7.81 and ~8.35 GHz separately. The filter is fabricatedon high-resistance silicon, and the measured results showed a good agreement with the simulated results. The filter performance shows a sharp rejection greater than 40dB at the frequency of ( ${\textsf {f}}_{ { {{\textsf {0}}}}} \pm 0.5$ GHz), and the insertion loss is >−3.4 dB in the passband.

Low insertion loss and high isolation capacitive RF MEMS switch with low pull-in voltage

Micro electromechanical system (MEMS) shunt capacitive switches behave chiefly as a capacitor at both up and down states. Therefore, input-output matching for these switches is affected by varying the frequency. Although increasing the amount of capacitance at the up state reduces the actuation voltage, it deteriorates the RF parameters. This paper proposes a remedy for this problem in the form of two short high-impedance transmission lines (SHITLs) which are included at both ends of the MEMS switch. The SHITLs are implemented through adoption of a discontinued CPW transmission line. With this implementation, the switch can be modelled as a T circuit, neutralizing a capacitance behavior of MEMS switch at the up state. The paper also proposes an optimised fabrication process to realize a flat and planar bridge for the suggested RF MEMS switch. The measurement recorded by SEM and AFM shows that the proposed method significantly improves the planarity of the membrane. The RF and mechanical parameters of the fabricated switch are evaluated by Vector Network Analyser and Laser Doppler Vibrometer. At the up state, the switch has a return loss less than -20 dB in the entire frequency band (C-K). The isolation at the down state is better than 10 dB for the lower frequencies and increases to values better than 18 dB for the higher frequencies. The measured pull-in voltage is almost 20 V and the mechanical resonance frequency is 164 kHz.

A Conceptual Study of Microelectromechanical Disk Resonators

Microelectromechanical systems (MEMS) resonators serve as frequency-selective components in applications ranging from biology to communications. In this paper, the dynamic behavior of an RF MEMS disk resonator is formulated using an analytical method. The resonator is simultaneously subjected to a DC-bias voltage superimposed with an ac harmonic voltage applied across the electrode-to-resonator gap. The governing equation of motion is derived by minimization of the Hamiltonian and generalized to include the viscous damping effect. Periodic solutions are determined by means of a shooting method and their stability is investigated by determining the well-known Floquet exponents of the perturbed motions. The influence of intermolecular forces such as van der Waals and Casimir on the dynamics of each mode of the disk resonator are investigated and the influence of design parameters are discussed. The results indicate that a high quality factor at ultrahigh frequency (UHF), a weak nonlinearity, and a low actuation voltage make polydiamond disk resonators excellent contenders for the next generation of micromechanical RF filters and channelizers. Furthermore, the resonant frequencies observed in the second (1.3 GHz) and third (2.1 GHz) modes allow for power-efficient operation of the disk resonator in the UHF range.

The Sky's the Limit: A Switchable RF-MEMS Filter Design for Wireless Avionics Intracommunication

The switchable RF-microelectromechanical systems (MEMS) filter described in this article was presented as part of the student design competitions at the 2016 IEEE Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium held in San Francisco in May 2016. The goal of this competition, sponsored by Technical Committee MTT-21, was to design a switchable filter to separate the industrial, scientific, and medical (i.e., ISM) band (2.4-2.5 GHz) from the wireless avionics intracommunication (WAIC) band (4.2-4.4 GHz). The upcoming availability of the 4.2-4.4 GHz band for WAIC to implement wireless connectivity inside passenger aircraft cabins provided the main motivation for this design, and the filter footprint was the most important requirement.

Tunable RF MEMS-Based Frequency-Dependent Power Limiter

A novel approach to frequency-dependent power limiters (FDPLs) is proposed. RF microelectromechanical systems (MEMS) switches are integrated with bandpass filters to form a power limiter, where the output RF power is limited to specific levels, based on the frequency bands. Both the nonplanar and planar versions of FDPLs are presented using circulators and hybrids, and RF MEMS-based power limiters are analyzed theoretically and experimentally for one frequency band. The limiter attenuates the high-power signal only within the bandwidth of the integrated filter. The design of the proposed power limiter is expanded to achieve power limiting for various frequency bands. The flatness of the threshold level can be set to the desired value by controlling the return loss of the filters used in the FDPL circuit. Measured results for an FDPL circuit are presented, demonstrating that the limiting power level can be controlled by adjusting the dc bias of the MEMS switches. The commercially available electrostatically actuated switches OMRON and Radant are employed for the realization of the FDPL. Additionally, a varactor-based tunable filter is designed and implemented in FDPL circuits. The tunable FDPL circuits are fabricated and measured, demonstrating the feasibility of realizing adaptive FDPLs.

Radio Frequency-micro Electromechanical System Switch with High Speed and Low Actuated Voltage

This paper presents a novel RF MEMS (Micro Electromechanical System) fixed-fixed switch for very fast switching. Using the obtained equations, the switching time depends on the stiffness and effective mass of the switch beam so that the switching time will be decreased by higher stiffness (spring constant) and lower effective mass. In new design, the suspension bridge is a three-layer beam so that the middle layer is aluminum and outer layers are alumina. The reduced dimensions and three layers of beam cause to increase stiffness and reduce the mass of the beam. This led to increase the resonance frequency and as result, the switching time is reduced. The results show that, the switching time is 127 ns for the applied voltage of 27v and also the pull-in voltage is 18V. The return loss is 12 dB at frequency of 60 GHz that is desirable and the achieved results is better than the previous works. Thus, this switch is suitable for high frequency applications.

Design, Analysis, and Verification of Ka-Band Pattern Reconfigurable Patch Antenna Using RF MEMS Switches.

This paper proposes a radiating pattern reconfigurable antenna by employing RF Micro-electromechanical Systems (RF MEMS) switches. The antenna has a low profile and small size of 4 mm × 5 mm × 0.4 mm, and mainly consists of one main patch, two assistant patches, and two RF MEMS switches. By changing the RF MEMS switches operating modes, the proposed antenna can switch among three radiating patterns (with main lobe directions of approximately −17.0°, 0° and +17.0°) at 35 GHz. The far-field vector addition model is applied to analyse the pattern. Comparing the measured results with analytical and simulated results, good agreements are obtained.

A Reconfigurable Microwave Equalizer With Different Maximum Attenuations Based on RF MEMS Switches

The design, fabrication, and measurements of a novel reconfigurable microwave equalizer based on RF micro-electro-mechanical system (MEMS) switches for adjusting the maximum attenuations of microwave signals are presented in this letter. The reconfigurable equalizer is driven by four lateral dc-contact RF MEMS switches, which can select the different attenuation resistances and obtain various maximum attenuations compared with the traditional microwave equalizer with fixed maximum attenuation. The proposed reconfigurable equalizer is fabricated by MetalMUMPs process. The experimental results show that the reconfigurable equalizer can realize four maximum attenuations of 7, 6.6, 5.9, and 5.6 dB by the actuation of RF MEMS switches, the reflection losses are all below -16 dB at the frequency range from 17 to 19 GHz, the experimental results agree well with the theory.

Submillimeter-Wave 3.3-bit RF MEMS Phase Shifter Integrated in Micromachined Waveguide

This paper presents a submillimeter-wave 500–550-GHz MEMS-reconfigurable phase shifter, which is based on loading a micromachined rectangular waveguide with 9 E-plane stubs. The phase shifter uses MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide. Each MEMS-reconfigurable surface is designed so that in the nonblocking state, it allows the electromagnetic wave to pass freely through it into the stub, while in the blocking state, it serves as the roof of the main waveguide and blocks the wave propagation into the stub. The phase-shifter design comprises three micromachined chips that are mounted in the H-plane cuts of the rectangular waveguide. Experimental results of the first device prototypes show that the microelectromechanical system (MEMS)-reconfigurable phase shifter has a linear phase shift of 20 $\mathbf {^{\circ }}$ in ten discrete steps (3.3 bits). The measured insertion loss is better than 3 dB, of which only 0.5–1.5 dB is attributed to the MEMS surfaces and switched stubs, and the measured return loss is better than 15 dB in the design frequency band of 500–550 GHz. It is also shown that the major part of the insertion loss is attributed to misalignment and assembly uncertainties of the micromachined chips and the waveguide flanges, shown by simulations and reproducibility measurements. The MEMS-reconfigurable phase shifter is also operated in an analog tuning mode for high phase resolution. Furthermore, a detailed study has been carried out identifying the reason for the discrepancy between the simulated (90 $\mathbf {^{\circ }}$ ) and the measured (20 $\mathbf {^{\circ }}$ ) phase shift. Comb-drive actuators with spring constant variations between 2.13 and 8.71 N/m are used in the phase shifter design. An actuation voltage of 21.94 V with a reproducibility better than $\mathbf {\sigma }=$ 0.0503 V is measured for the actuator design with a spring constant of 2.13 N/m. Reliability measurement on this actuator was performed in an uncontrolled laboratory environment and showed no deterioration in the functioning of the actuator observed over one hundred million cycles.

Preface for the special issue on “MEMS and Sensors”

This special issue on MicroElectroMechanical Systems (MEMS) and Sensors has a few selected papers from the presentations at the International Conference on MEMS and Sensors (ICMEMSS 2014) held during 18–20 December 2014 at IIT Madras and contains two reviews and four contributed papers. The first review by Psychogiou and Peroulis, in the area of radio frequency micro-electro-mechanical systems (RF MEMS), reports on recent advances in reconfigurable waveguide-resonator based filter architectures which will contribute greatly to the area of multi-frequency and multistandard communication services. The second review by Packirisamy et al. uses conventional and lab-on-a-chip technologies for the detection of bovine growth hormone, an unfortunate practice in the dairy industry frowned upon but prevalent in many countries. The two reviews are followed by four contributed papers. The first two papers are on MEMS followed by two papers on Sensors. The paper by Mohanty et al. discusses a bulk micromachining technique that restricts the device area. Angira et al. report on RF MEMS switches for multiband wireless applications. The paper by Das et al. discusses improved binding capability of antibody on graphene coated nanoporous silicon as compared to standard functionalisation methods. And the last paper by Trivedi and Nemade reports on the simulation of a Love wave resonator using coupled resonance with ZnO nanorods for biosensing applications. The area of MEMS and Sensors is vast and it would be impossible to contain that in one issue. Our emphasis for the conference was on processes, technology and devices and we hope this small and eclectic collection of papers for the special issue will be useful for our community.

Ka-Band Tunable Filter Using Metamaterials and RF MEMS Varactors

The design of a metamaterial-based tunable band elimination filter is described on silicon coplanar wave- guide (CPW) using complementary split ring resonators (CSRRs) and radio frequency microelectromechanical systems (MEMS) varactors to ensure compatibility with integrated circuit fabrication technology. CSRRs are patterned on both the active signal line and ground on both sides. A cantilever bridge is suspended on the signal line to realize variable capacitance. The rejection band of the filter is tuned by moving the MEMS bridge up or down using electrostatic actuation. A stopband around the center frequency of 35.32 GHz with a rejection ratio of $\sim 20.19$ dB is obtained when the bridge is pulled down. Another stopband around the center frequency 38.80 GHz is observed with a rejection ratio of $\sim 18.29$ dB when the bridge is allowed to remain in its up state without electrostatic actuation. Simulation for RF behavior is performed using ANSOFT High Frequency Structural Simulator v13. Numerical extraction of the filter parameters has been done using Agilent ADS (2009) and COVENTORWARE (2010) for mechanical and electromechanical characterization. This is the first reported tunable CPW filter having CSRR on the signal line and ground plane on silicon substrate using MEMS technology. [2014-0365]

Novel high capacitance ratio compact float metal based RF MEMS switch for multi band and variable bandwidth: design and RF performance analysis

Modern complex systems, as they are multi functional, they require many small unit cells for multi functionality. These are certain applications, where the change in operational frequency band is required and switches designed for specific band is usually incorporated depending on requirement. The most complex task in radio-frequency RF microelectromechanical system (RF MEMS) switches is the designing of switches that are tuned for particular frequency band. To overcome these problems, we have proposed the design and modeling of multi band RF MEMS switch. The switch designed shows high capacitance ratio that is usually hard to achieve by conventional designs. This design also offers variable bandwidth. Reliability concerns of RF MEMS like stiction has been taken care of by using float metal based approach in this design. The proposed compact MEMS switch incorporates four cantilever beams to be used in various configurations. We have simulated the RF performance by actuating these beams in different configurations. The switch shows very promising results including isolation of >30 dB in X band, >45 dB in C band, >44 dB in F band with bandwidth ranging from narrow 5 GHz to wide 48 GHz with high isolation and till 100 GHz bandwidth with moderate RF performance.

RF MEMS and CSRRs-based tunable filter designed for Ku and K bands application

AbstractThis paper presents the design and simulation of a reconfigurable stop-band filter on a silicon substrate based on the combination of RF microelectromechanical system and metamaterial-based technologies. The device is implemented on coplanar waveguide structure by embedding complementary split-ring resonators on the central line and an RF MEMS varactor bridge supporting the neighboring ground planes. The response characteristics of this metamaterial-based filter can be dynamically tuned, thus enhancing its usefulness. The device operates within a frequency range of 16.5–19.5 GHz, giving a tuning range of 15%, and can be tuned from Ku-frequency band to K-frequency band. It works with a comparative low pull-in voltage of 17.42 V and a faster switching time of 0.138 µs. A thorough electromechanical analysis has been done by varying various structural and material parameters. Moreover, a comparative electrical performance of silicon and glass has been shown to overcome the cons of silicon by high-resi...