RF Microelectromechanical Systems 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.

Bending characteristics of radio frequency microelectromechanical system low‐pass filter based on flexible substrate

The aim of this paper is to investigate the bending characteristics of a low-pass RF MEMS (radio frequency microelectromechanical system) filter based on a flexible substrate. The proposed filter is achieved by complementary split ring resonator and MEMS bridge which are fabricated on a flexible LCP (liquid crystal polymer) substrate. The bending characteristics of the filter are revealed by theory, simulation and measurement. The experimental results demonstrate that the return loss of the filter deteriorates and the cut-off frequency of the filter decreases with the curvature of the flexible substrate increasing. The cut-off frequency is 38.5 GHz and the return loss is −22.7 dB at 10 GHz with the flat substrate. When the curvature of the substrate increases to 28.57 m–1, the cut-off frequency decreases to 14.8 GHz, and the return loss deteriorates to −5.7 dB at 10 GHz.

A novel multifunctional electronic calibration kit integrated by MEMS SPDT switches* *Project supported by the National Defense Technology Industry Strong Foundation Project, China (Grant No. JCKY2018408B006), the Information System New Items Project, China (Grant Nos. 2018XW0026 and 2019XW0010), and the Information System Pre-research Project, China (Grant No. 31513060101).

Design and simulation results of a novel multifunctional electronic calibration kit based on microelectromechanical system (MEMS) single-pole double-throw (SPDT) switches are presented in this paper. The short-open-load-through (SOLT) calibration states can be completed simultaneously by using the MEMS electronic calibration, and the electronic calibrator can be reused 106 times. The simulation results show that this novel electronic calibration can be used in a frequency range of 0.1 GHz–20 GHz, the return loss is less than 0.18 dB and 0.035 dB in short-circuit and open-circuit states, respectively, and the insertion loss in through (thru) state is less than 0.27 dB. On the other hand, the size of this novel calibration kit is only 6 mm × 2.8 mm × 0.8 mm. Our results demonstrate that the calibrator with integrated radio-frequency microelectromechanical system (RF MEMS) switches can not only provide reduced size, loss, and calibration cost compared with traditional calibration kit but also improves the calibration accuracy and efficiency. It has great potential applications in millimeter-wave measurement and testing technologies, such as device testing, vector network analyzers, and RF probe stations.

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 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.

Balanced-Bridge Method for the Characterization of Dielectric Charging in RF MEMS Cantilever Switches

This paper presents a balanced-bridge method for the characterization of dielectric charging effect in RF MEMS (radio frequency micro-electromechanical system) cantilever switches. The method measures the relative change of up-state capacitance caused by dielectric charging. Compared with previous methods, this approach employs simple and inexpensive test equipment. The test system consists of two symmetric capacitive switches, two adjustable resistors, a function generator, and a voltmeter. Measurement results indicate that it can achieve a resolution of 0.1 fF/ $\Omega $ . By this test system, the slight variation of up-state capacitance can be converted to the significant change of the resistance. Analysis of the experimental data shows that dielectric charging under the DC-voltage stress mainly occurs in the first 1200 seconds. The mechanisms resulting in capacitance variation can be divided into two groups: dielectric polarization and charge injection. Moreover, in contrast to the DC voltage, the RF signal does not have a significant influence on the charging process.

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.

SyLMAND: a microfabrication beamline with wide spectral and beam power tuning range at the Canadian Light Source.

SyLMAND, the Synchrotron Laboratory for Micro and Nano Devices, is a recently commissioned microfabrication bend magnet beamline with ancillary cleanroom facilities at the Canadian Light Source. The synchrotron radiation is applied to pattern high-aspect-ratio polymer microstructures used in the area of micro-electro-mechanical systems (MEMS). SyLMAND particularly focuses on spectral and beam power adjustability and large exposable area formats in an inert gas atmosphere; a rotating-disk intensity chopper allows for independent beam-power reduction, while continuous spectral tuning between 1-2 keV and >15 keV photon energies is achieved using a double-mirror system and low-atomic-number filters. Homogeneous exposure of samples up to six inches in diameter is performed in the experimental endstation, a vertically scanning precision stage (scanner) with tilt and rotation capabilities under 100 mbar helium. Commissioning was completed in late 2017, and SyLMAND is currently ramping up its user program, mostly in the areas of RF MEMS, micro-fluidics/life sciences and micro-optics.

Exploitation of RF-MEMS Switches for the Design of Broadband Modulated Scattering Technique Wireless Sensors

The use of RF microelectromechanical systems (RF-MEMS) switches for the design of broadband modulated scattering techniques (MSTs) wireless sensors has been investigated in this letter. In an MST sensor, the antenna is loaded with different resistive loads to produce a modulation in the backscattered field by means of an electronic switch. At microwave frequency bands, the RF switches are quite expensive, moreover, they are quite narrowband. The narrowband behavior of MST sensors is one of their major drawbacks. The adoption of RF-MEMS microwave switches could be a good opportunity to overcome this problem. In particular, MEMS switches are able to perform good up to 110 GHz with a reduced dimension and complexity. In this letter, an MST sensor prototype based on MEMS switches and able to work in the whole X -band from 8 to 12 GHz has been designed, fabricated, and experimentally assessed. The obtained results are quite good and they demonstrate the feasibility of such kind of sensors. In particular, the MEMS switches demonstrate that they could play a key role for the design of millimetric and submillimetric frequencies bands MST sensors, where the standard microwave switches technologies cannot operate.

New Analytical Capacitance Modeling of the Perforated Switch Considering the Fringing Effect

Movable suspended microstructures are common features of sensors and devices in the field of micro electro mechanical systems (MEMS). This paper addresses the study of approach to model the capacitance for the crab-type meander-based RF MEMS shunt switch with etching holes on the beam. The presented paper evaluates the parallel-plate capacitance and fringing-field capacitance caused by the etching holes on the beam and introduces empirical formulae. From the literature study, an accurate empirical formula is presented. The capacitance involves a parallel plate and a fringing field. The parallel-plate capacitance term is proposed by the authors of this work; the fringing-field capacitance term is adopted from previous work. The proposed accurate empirical capacitance formulae are derived by curve fitting the simulated values through the commercially available FEM solver. The two existing benchmark models of fringing-field capacitance are used to modify the perforated MEMS switch to obtain the proposed formula. With the existing models and presented formula, the capacitances are computed for a wide range of dimensions; the simulated results of the presented formula are validated with the calculated results. The deviation of the presented formula has an error estimation of ±0.1%. The variation of the capacitance with different deictic thicknesses and errors is estimated and analyzed for the presented formula. The Mejis model is found to be satisfactory for a lower air gap and a 1-μm-thick beam. The Yang's model is sufficient for a higher air gap and a large number of etching holes. The proposed formulae are good for the ligament efficiency μ ≤ 0.5, with thickness >1 μm, and the deviation of error estimation is within ±5%.

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.