RF Microelectromechanical Systems Switches Research Articles

Implementation of Highly Reliable Contacts for RF MEMS Switches.

A contact is the key structure of RF MEMS (Radio Frequency Microelectromechanical System) switches, which has a direct impact on the switch's electrical and mechanical properties. In this paper, the implementation of highly reliable contacts for direct-contact RF MEMS switches is provided. As a soft metal material, gold has the advantages of low contact resistance, high chemical stability, and mature process preparation, so it is chosen as the metal material for the beam structure as well as the contacts of the switch. However, a Pt film is used in the bottom contact area to enhance the reliability of the contact. Three kinds of contacts with various shapes are fabricated using different processes. Particularly, a circular-shaped contact is obtained by dry/wet combined processes. The detailed fabrication process of the contacts as well as the Pt film on the bottom contact area are given. The experimental test shows that the contact shape has little effect on the RF performance of the switches. However, the circular contact shows better reliability than other contacts and can work well even after 1.2 × 109 cycles.

Design of a Ka-Band Five-Bit MEMS Delay with a Coplanar Waveguide Loaded U-Shaped Slit.

This paper designs a five-bit microelectromechanical system (MEMS) time delay consisting of a single-pole six-throw (SP6T) RF switch and a coplanar waveguide (CPW) microstrip line. The focus is on the switch upper electrode design, power divider design, transmission line corner compensation structure design, CPW loading U-shaped slit structure design, and system simulation. The switch adopts a triangular upper electrode structure to reduce the cantilever beam equivalent elastic coefficient and the closed contact area to achieve low drive voltage and high isolation. The SP6T RF MEMS switch uses a disc-type power divider to achieve consistent RF performance across the output ports. When designed by loading U-shaped slit on transmission lines and step-compensated tangents at corners, the system loss is reduced, and the delay amount is improved. In addition, the overall size of the device is 2.1 mm × 2.4 mm × 0.5 mm, simulation results show that the device has a delay amount of 0-60 ps in the frequency range of 26.5-40 GHz, the delay accuracy at the center frequency is better than 0.63 ps, the delay error in the whole frequency band is less than 22.2%, the maximum insertion loss is 3.69 dB, and the input-output return rejection is better than 21.54 dB.

Design and Analysis of a Fluid-Filled RF MEMS Switch

In the present study, a fluid-filled RF MEMS (Radio Frequency Micro-Electro-Mechanical Systems) switch is proposed and designed. In the analysis of the operating principle of the proposed switch, air, water, glycerol and silicone oil were adopted as filling dielectric to simulate and research the influence of the insulating liquid on the drive voltage, impact velocity, response time, and switching capacity of the RF MEMS switch. The results show that by filling the switch with insulating liquid, the driving voltage can be effectively reduced, while the impact velocity of the upper plate to the lower plate is also reduced. The high dielectric constant of the filling medium leads to a lower switching capacitance ratio, which affects the performance of the switch to some extent. By comparing the threshold voltage, impact velocity, capacitance ratio, and insertion loss of the switch filled with different media with the filling media of air, water, glycerol, and silicone oil, silicone oil was finally selected as the liquid filling medium for the switch. The results show that the threshold voltage is 26.55 V after filling with silicone oil, which is 43% lower under the same air-encapsulated switching conditions. When the trigger voltage is 30.02 V, the response time is 10.12 μs and the impact speed is only 0.35 m/s. The frequency 0-20 GHz switch works well, and the insertion loss is 0.84 dB. To a certain extent, it provides a reference value for the fabrication of RF MEMS switches.

Design and Fabrication of a MEMS Bandpass Filter with Different Center Frequency of 8.5-12 GHz.

The design simulation and fabrication results of a bandpass filter based on micro-electro-mechanical system (MEMS) switches are presented in this paper. The MEMS filter element consists of a MEMS capacitance switch and two resonant rings that are fixed onto coplanar waveguide lines through anchor points. The micromachine characteristics of the filter could be optimized to change the center frequency from 8.5 to 12 GHz by improving the geometrical parameters; other electrical parameters of the filter, such as stopband rejection, insertion loss, and return loss at each center frequency, were simulated and calculated. In order to evaluate the MEMS filter design methodology, a filter working at 10.5 GHz fabricated with an aluminum top electrode was used, and it displayed a low insertion loss of 1.12 dB and a high stopband rejection of 28.3 dB. Compared with the simulation results, these proposed filter showed better electrical performance. Our results demonstrated that the filter with the integrated RF MEMS switch not only provides the benefit of reduced size compared with a traditional filter, but also improves stopband rejection, insertion loss, and return loss.

The Design and Fabrication of a MEMS Electronic Calibration Chip.

During the test of microelectromechanical system (MEMS) devices, calibration of test cables, loads and test instruments is an indispensable step. Calibration kits with high accuracy, great operability and small loss can reduce the systematic errors in the test process to the greatest extent and improve the measurement accuracy. Aiming at the issues of the conventional discrete calibration piece unit, which presents cumbersome calibration steps and large system loss, an integrated electronic calibration chip based on frequency microelectromechanical system (RF MEMS) switches is designed and fabricated. The short-open-load-through (SOLT) calibration states can be completed on a single chip, step by step, by adjusting the on-off state of the RF MEMS switches. The simulation results show that the operating frequency of the electronic calibration piece covers the range of DC~26.5 GHz, the insertion loss in through (thru) state is less than 0.2 dB, the return loss is less than 1.0 dB in short-circuit and open-circuit states, the return loss under load-circuit state is less than 20 dB and its size is only 2.748 mm × 2.2 mm × 0.5 mm. This novel calibration chip design has certain esteem for advancing calibration exactness and effectiveness.

A Packaged THz Shunt RF MEMS Switch With Low Insertion Loss

This paper demonstrates a packaged THz shunt capacitor micro-electromechanical systems (MEMS) switch with low insertion loss. In-line shunt switch is used to achieve a low loss in THz band, which is realized by reducing the equivalent parallel inductance of switch. The equivalent circuit of the switch is analyzed systematically, the equivalent resistance is obtained based on the skin effect of high frequency current on the conductor and the current density distribution characteristics of the conductor cross-section. The equivalent capacitance is obtained by using &#x201C;double microstrip&#x201D; characteristic impedance calculation method, and the correction factor (<inline-formula> <tex-math notation="LaTeX">$\Delta$ </tex-math></inline-formula>) is introduced to calculate the equivalent inductance accurately. By optimizing equivalent circuit parameters and switch sizes, the structure of MEMS switch with low loss and high isolation characteristics are achieved. The switch is packaged by rectangular waveguide and achieved a low insertion loss. The comparison between the switch simulation results and the equivalent circuit simulation results verify that the parameter extraction method and circuit analysis are correct. The packaged MEMS switch is measured, and the results are in an acceptable agreement with simulation, the switch is actuated under voltage of &#x007E;30V. The measured result has achieved a low insertion loss with less than &#x003C; 2dB from 220 to 280GHz, and isolation with &#x007E;16 dB from 240GHz to 320GHz in the &#x201C;down&#x201D; state.

A novel low-loss four-bit bandpass filter using RF MEMS switches

This paper details the design and simulation of a novel low-loss four-bit reconfigurable bandpass filter that integrates microelectromechanical system (MEMS) switches and comb resonators. A T-shaped reconfigurable resonator is reconfigured in a ‘one resonator, multiple MEMS switches’ configuration and used to gate the load capacitances of comb resonators so that a multiple-frequency filtering function is realized within the 7–16 GHz frequency range. In addition, the insertion loss of the filter is less than 1.99 dB, the out-of-band rejection is more than 18.30 dB, and the group delay is less than 0.25 ns. On the other hand, the size of this novel filter is only 4.4 mm × 2.5 mm × 0.4 mm. Our results indicate that this MEMS reconfigurable filter, which can switch 16 central frequency bands through eight switches, achieves a low insertion loss compared to those of traditional MEMS filters. In addition, the advantages of small size are obtained while achieving high integration.

Serial and Parallel Active Decoupling Characterization Using RF MEMS Switches for Receiver Endoluminal Coils at 1.5 T

MEMS (Micro Electro Mechanical System) switches were assessed and compared to PIN diode in fulfilling the task of active decoupling of Receiver Endoluminal Coils (RECs). Three prototype RECs with the PIN diode in parallel ( ${p}$ PIN), MEMS in parallel ( ${p}$ MEMS) and MEMS in series ( ${s}$ MEMS) with the REC loop were built. Quality factors (Q-values), decoupling efficiency and switching delays were characterized on bench and Signal-to-Noise Ratios (SNRs) established on images at 1.5 T. Q-values were equal to 62.5, 41.2 and 65.1 for ${p}$ PIN, ${s}$ MEMS and ${p}$ MEMS, respectively. In the decoupled state, reflection coefficients S11 and S21 at resonance frequency both indicated proper decoupling. Switching delays were less than $0.7~\mu \text{s}$ and $10~\mu \text{s}$ for ${p}$ PIN and MEMS RECs, respectively. Decoupling/coupling delays of MEMS remained compatible with most Magnetic Resonance (MR) clinical applications. For all prototypes, MR images displayed no signal saturation and similar elliptical image sensitivity patterns. No artifacts due to active decoupling failure were observed. Mean SNR values obtained with ${p}$ MEMS REC were higher than those obtained with ${s}$ MEMS REC but lower than with ${p}$ PIN REC because of the use of additional instrumentation to render the scanner compatible with the MEMS utilization. MEMS in parallel are an interesting alternative to PIN diode for decoupling and could lead to better SNR with a compatible MR system (dedicated control signal). The MEMS in series can be used for both decoupling and reconfiguration of the REC loop geometry for colon wall examination.

Sacrificial layer optimization for RF MEMS switches

This paper introduces the characterization of AZ-P4620 photoresist as a sacrificial layer for Radio Frequency MEMS (Micro-Electro-Mechanical System) switches. The surface micromachining process is opted for the fabrication of RF MEMS switches, which includes a suspended structure. Initially, a thick photoresist is coated and patterned, to be utilized as a sacrificial layer and then the structural layer is deposited on it. For proper connectivity of the structural layer, edge coverage is required. This photoresist is optimized at different post-baking temperatures. We investigated that slope angles decrease with an increase in post bake temperature. Using the optimized recipe, the RF MEMS switch is fabricated and characterized successfully. The measured isolation, pull-in voltage, and insertion loss, are − 30 dB, 23 V, and − 0.2 dB, respectively at 18 GHz frequency.

Ni–P electroless on nonconductive substrates as metal deposition process for MEMS fabrication

During past decades Micro Electro Mechanical Systems (MEMS) have been developed and presented in the market. It is important to find new processes and methods to facilitate MEMS production regarding to growing demand of MEMS devices in IoT, smart and intelligent systems, consumer electronics and medical applications. In this paper, Ni–P layer deposition on insulator substrates is presented. The layer is deposited based on chemical reactions in electroless process. There is a similar method, electroplating, for metal deposition but the substrate must be conductor to transfer electrons and provide essential conditions for electroplating. Electroplating process is not applicable for insulator substrates, while the proposed electroless process can be useful. Different steps, materials, conditions and experimental results for Ni–P electroless are presented. A fabrication process for DC contact RF MEMS switch based on Ni–P electroless is introduced, too. As one advantage of this process, Ni and Ni–P are ferromagnetic material and any suspended structure can be actuated by magnetic fields. It will be beneficial when applying other actuation mechanisms like electrostatic, thermal or piezoelectric are difficult or impossible to be applied.

Design of a novel structure capacitive RF MEMS switch to improve performance parameters

This study reports the design and analysis of novel step structure RF micro-electromechanical system (MEMS) switch for low pull-in voltage, low insertion loss and high isolation by using uniform single meander. The central beam of the membrane is designed with 0.5 µm lower than the side beams to form a step-down structure which reduces the pull-in voltage. Stress analysis, electromechancial, switching time, quality factor and RF analysis have done to understand the behavioural characteristics of the proposed step-down switch. The analysis has been carried out for different beam and dielectric materials among them switch with gold material exhibits low pull-in voltage of 4.7 V, low insertion loss <1 dB and high isolation of −38.3 dB at 28.2 GHz for silicon nitride. The switch also shows good quality factor of 0.95 for gold material along with high capacitance ratio of 132. The upstate capacitance of 56.8 pF contributes low return loss and made the switch to transmit the signal up to 26.2 GHz and provides 7.2 pF of downstate capacitance to produce high isolation at 26.2 GHz which is efficiently used for K-band satellite applications.

Design and Simulation of RF MEMS Switch for X-band Applications

This article presents the design and simulation of RF microelectromechanical systems (MEMS) switch which works at X-band frequency(8-12 GHz). The design consists of a thin micromechanical bridge suspended over a silicon nitride which is used as the dielectric material with 0.1 µm thickness and air gap of switch is 0.9 µm. The design, modelling and simulation are done using the COMSOL Multiphysics 5.1. The designed switch has low actuation voltage, low pull-in voltage, optimum capacitance ratio, low switching time which makes it a perfect switch to work at X-band frequency. The switch has actuation voltage of 5 V, pull-in voltage of 1.58 V, capacitance ratio 66 and switching timing of 35 µs.

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.

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.

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 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.

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.

Miniatured Phase Shifter

Objective: RF MEMS has emerged as a technology with immense potential for wireless communication and defence applications. In this work, a 5 bit RF MEMS switched line phase shifter is presented using cantilever switch achieving low actuation voltage. Methodology: In this work 5 different phase shifters are designed to get 5 bit phase shift at a particular frequency 10 GHz. The phase shifters consist of stubs like structure designed in the ground of CPW and MEMS capacitive series switches. Solid-state phase shifters based on p-i-n diodes or Field-Effect Transistor (FET) switches are used because they provide a good planar solution at a variety of microwave frequency ranges. Micro Electro Mechanical Systems (MEMS) phase shifters are progress today are mainly have established designs because of which the solid-state switch is replaced by a MEMS switch. Findings: By analysing theoretically and practically the results showed that a novel RF MEMS switch was capable of liberating less than 0.1dB insertion loss and more than 19 dB isolation between input and output ports at 20 GHz .This RF MEMS switch shows a 5V actuation voltage. Switching time of RF MEMS switches is measured using a theoretical approach. The switches demonstrated maximum switching time of 0.1μs. By using this switch a 5-bit miniaturized phase shifter is designed i.e. 180° bit, 90°, 45°, 22.25° and 11.5° bits were achieved using the switched line type phase shifters at 10 GHz. A novel switched line type phase shifter loaded with multiple switch pairs was developed and was capable of liberating a multiple phase shift angles within single design

Integration of Niobium Low-Temperature-Superconducting RF Circuits With Gold-Based RF MEMS Switches

A novel eight-mask fabrication process for the integration of low-temperature-superconducting niobium (Nb) RF circuits with gold-based RF microelectromechanical system (MEMS) switches is proposed. DC-contact and capacitive-contact RF MEMS switches integrated with Nb-based transmission lines are presented for the first time. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate that the proposed gold-based MEMS fabrication process did have a major impact on the superconducting characteristics of Nb. A switched capacitor bank is also designed, implementing a dc-contact RF MEMS switch. The measured results of the capacitor bank show the variation of the capacitance value from 0.22 to 5.25 pF at 4 K. A thermal analysis of the devices under test (DUTs) is also performed, and an investigation is carried out to minimize the thermal loss between the chuck and the DUT.