RF MEMS Research Articles

Design and simulation of RF MEMS shunt capacitive switch with non-uniform meanders for C-band applications

This paper presents, the design and simulation of RF MEMS shunt capacitive switch. The electromechanical and electromagnetic analysis of the switch has been done using COMSOL(FEM) and HFSS tools. The proposed switch has the design with non-uniform meanders and dielectric material Silicon Nitrate (Si3N4). Different beam materials such as Gold, Aluminum, and Platinum are used to design the switch and analyze it. In the electro mechanical analysis of the switch, the pull-in voltage obtained for the beam material Platinum is 10.56 V for a gap (between the beam and signal-line dielectric) of 2.5 µm which is effective in comparison to the other materials like Gold and Aluminum. As far as the RF performance analysis is concerned, the isolation, insertion loss and return loss have been calculated. The isolation, return loss and insertion loss are − 25 dB, − 14.3 dB and − 0.33 dB respectively. On performing the stress analysis of the switch, a stress value of 0.05 N/m2 has been obtained for the applied pull-in voltage. The proposed switch is used for C band applications.

Design and simulation of capacitive SPDT RF MEMS switch to improve its isolation

This paper presents the simulation and analysis of capacitive shunt SPDT RF MEMS switch for high radio frequency applications. The design is based on the shunt configuration consisting of 2 capacitive type switches. To reduce pull in voltage, the high-frequency capacitive SPDT switch is proposed. The beam is designed with non-uniform meanders with perforations. By using the COMSOL Multiphysics tool, we found the pull-in voltage as 1.5 V at a beam thickness of 0.5 μm. The corresponding capacitance ratio is 44 for the dielectric of Silicon Nitrate. The up sate and downstate capacitance of the switch is calculated and simulated. The performance analysis is done by using HFSS tool and is found to RF-perform excellently at 28 GHz with isolation of − 68 dB, the return and insertion losses are − 61 dB and − 0.1 dB respectively.

Design and of analysis of SPDT Ohmic RF MEMS switch

This paper reports on the simulation and analysis of Ohmic SPDT (single pole double throw) switch for telecommunication application. A comparative study is performed by varying the gaps from 3 to 2 μm for three different types of beam materials, namely gold, aluminum, and platinum. The design is based on the series configuration consisting of two cantilever type switches. In order to improve isolation, low-frequency Ohmic SPDT switch is proposed. The main objective of the paper is to achieve low frequency to fit into C-band. By using COMSOL Multiphysics tool, we found pull-in-voltage as 2.8 V at a beam with 0.5 μm. The performance analysis is done by using HFSS tool and is found to perform at 7.3 GHz with isolation of − 43 dB, the return loss and insertion losses are − 21 and − 1.3 dB, respectively.

Design and analysis of serpentine meander asymmetric cantilever RF-MEMS shunt capacitive switch

In this paper, the design of asymmetric cantilever radio frequency micro electromechanical system (RF-MEMS) capacitive shunt switch is presented. The analysis and design have considered for single meander, uniform serpentine and non-uniform serpentine asymmetric cantilever RF-MEMS capacitive shunt switches were proposed. The non-uniform serpentine meander cantilever structure shows better performance compared to other structures. The actuation voltage attained for the serpentine meander cantilever is 1.1 V, 3.2 V with the spring constants 0.03 N m, 0.32 N m for the left and right cantilevers respectively. The proposed model isolations observed in-off states at left, right and both side cantilevers are − 52 dB, − 61 dB, − 45 dB at frequency of 7 GHz, 11.1 GHz, 12 GHz respectively. The proposed device insertion loss is − 0.2 dB and return loss is − 44 dB over 12 GHz is observed at on-state of the proposed model. The performance parameters are also observed for spring constant, pull in voltage, quality factor, stress analysis, switching time, resistance, inductance, capacitance, stiction loss and variation of gap with respect to spring constants and actuation voltages are calculated and analysed.

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.

Investigation of on-chip integrated inductors fabricated in SOI-MUMPs for RF MEMS ICs

This paper presents for the first time implementation of zig–zag and solenoidal on-chip inductors in standard and cost effective SOI-MUMPs fabrication process. The solenoidal inductor offers high Q-factor and inductance as compared to planar zig–zag inductor. Bonding wires are used to construct the top conductor loop of the solenoidal inductor. The inductors are also characterized at elevated temperature for performance investigation in harsh environment. The mechanical resonance frequency of the inductors are characterized using the Finite element software COMSOL. The inductors are characterized using a vector network analyzer from 60 MHz to 3 GHz, and the results of both inductors are compared. The total size of the device is 2 × 0.7 mm2.

Design and optimisation of a novel structure capacitive RF MEMS switch to integrate with an antenna to improve its performance parameters

In this study, a step-down structured switch is designed and compared with and without optimised dimensions to increase the isolation and to lower the pull-in-voltage with respective electromechanical and electromagnetic characteristics. The optimised switch is designed to operate only in K-band frequencies with the high isolation of -54.17 dB at the centre frequency of 22 GHz. The antenna using MEMS switch exhibits a frequency shift of 1.5 GHz from the first case to the second case and 7.4 GHz in the third case due to change in radiating length of patch antenna operating at different ON/OFF combinations of switches whereas the antenna with PIN diode shifts the frequency approximately same, but the low isolation of PIN diode makes it less immune to noise.

Design and characterization of compact digital RF MEMS capacitors and phase shifters in CMOS 0.35 µm technology

This work reports on the design, fabrication and characterization of compact digital RF MEMS capacitors and phase shifters that are built in the back end of line (BEOL) of CMOS 0.35 µm technology. The devices are micromachined using a maskless post-processing sequence with cryogenic cooling on to control the out-of-plane warping of the metal-oxide structural layers. The implemented vertical electrostatic actuation in the developed post process allows the realization of highly compact designs of both devices, and an operating voltage of the devices is stay below 70 V. The 4-bit capacitors provide a measured tuning ratio close to 10:1 which corresponds to 0.15 pF to 1.2 pF over the frequency range 3–10 GHz. The overall footprint of the digital capacitor is 0.6 mm × 0.9 mm. The measured quality factor after de-embedding the losses due to the RF probing pads is up to 120. The measurement of the 4-bit phase shifters reveals low insertion loss <3 dB at 20 GHz along with low variation of the insertion loss <1 dB up to the same frequency. The measured phase shift is 150 at 20 GHz. The overall footprint of the 4-bit phase shifter is around 1 mm × 1 mm.

Inductively tuned bulk micromachined RF MEMS switch with high isolation and improved reliability

In this paper, a reliable K-band RF MEMS shunt switch with high isolation is presented. The switch is fabricated on a high-resistivity silicon substrate (ρ = 10,000 Ω cm, er = 11.7, h = 675 µm) using bulk micro-machined techniques. A novel symmetrical tri-layer sandwich (insulator–metal–insulator) concept is implemented in membrane design which results in stress-free membrane and thus results in lower actuation voltage of 15V. The inductive effect created in the CPW ground not only brings down the resonant frequency which eliminates the need to increase the membrane length but also improves the isolation (> 40 dB). This electrostatically actuated switch has measured insertion loss and isolation of 1.51 dB and 46.42 dB at 20.25 GHz, respectively. The switch shows consistent performance in terms of RF as well as mechanical after 8 h of continuous operation without stiction. The switch can have applications in telecommunication, defense and space-based phased array system, etc.

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.

A 77‐GHz polarization‐agile microelectromechanical system antenna

AbstractA 77 GHz polarization‐agile radio frequency microelectromechanical system (RF MEMS) patch antenna integrated with single‐pole single throw switches is presented. The polarization of the proposed antenna can be switched among linear polarization, right‐hand circular polarization, and left‐hand circular polarization. The RF MEMS antenna is fabricated on 25 mil alumina with permittivity of 9.8. The reflection and radiation parameters of antenna including return loss, radiation patterns, gain, and axial ratio are measured and are found to be in correlation with simulated results. The proposed work is useful for automotive radar applications.

Perforated serpentine membrane with AlN as dielectric material shunt capacitive RF MEMS switch fabrication and characterization

In this communication, we have designed, simulated, performance improved, fabricated and characterized a shunt capacitive RF MEMS switch with perforated serpentine membrane (Au). Fabrication is done using surface micromachining with four masks. AlN dielectric material of 50 nm thickness is offering high isolation of − 58.5 dB at 31.5 GHz, and incorporation of perforation to the membrane the switch insertion loss is very low i.e., − 0.4 dB. The perforated serpentine membrane with non-uniform meanders of 500 nm thickness using Au material is helped to reduce the actuation voltage, the fabricated switch is requiring 4.5 V actuation voltage. DC sputtering PVD is used to deposit metal (Au) and dielectric (AlN) thin Films. S1813 photoresist is used as a sacrificial layer and the membrane structure is released using piranha, IPA and critical point drying (Pressure 1260 Psi, Temperature 31 °C).

Thermally activated discharging mechanisms in SiNx films with embedded CNTs for RF MEMS capacitive switches

In the present work, we investigate thermally activated processes in nanostructured SiNx films with embedded CNTs, which can be used in RF MEMS capacitive switches. Nanostructured films have been fabricated with a simple process, in order to incorporate CNTs on the lower SiNx layer and a reference SiNx material has been also fabricated with the same method (without CNTs), in order to compare the properties of the nanostructured films with the pristine material. Thermally stimulated depolarization currents (TSDC) assessment and a single-point Kelvin Probe (KP) system have been used in MIM capacitors, in order to investigate the electrical properties of the utilized films.The nanostructured material is found to exhibit lower charging and smaller discharging time, which makes it a promising candidate for RF MEMS capacitive switches. Thermally activated discharging mechanisms have been identified and the presence of CNTs is found to diminish a discharging mechanism with a characteristic time larger than five days at room temperature. Different discharging mechanisms are identified and distinguished for the first time, to the best of our knowledge, between a reference and a nanostructured SiNx dielectric film. Charge displacement in the bulk material during discharge takes place through hopping processes and larger mean hopping distance and zero field conductivity has been found in the nanostructured films. The reduction of the discharge characteristic time and the simultaneous suppression of trapping centers in the films with embedded CNTs indicate a direct relation between the macroscopic electrical properties and the microscopic defects in the dielectric material.

The Mechanical Effects Influencing on the Design of RF MEMS Switches

Radio-frequency switches manufactured by microelectromechanical systems technology are now widely used in aerospace systems and other mobile installations for various purposes. In these operating conditions, these devices are often exposed to intense mechanical environmental influences that have a strong impact on their operation. These negative effects can lead to unwanted short-circuit or open-circuit in the radio-frequency transmission line or to irreversible damage to structural elements. Such a violation in the operation of radio-frequency microelectromechanical switches leads to errors and improper functioning of the electronic equipment in which they are integrated. Thus, this review is devoted to the analysis of the origin of these negative intense mechanical effects of the environment, their classification, and analysis, as well as a review of methods to reduce or prevent their negative impact on the design of radio-frequency microelectromechanical switches.

A tunable ferroelectric based unreleased RF resonator

This paper introduces the first tunable ferroelectric capacitor (FeCAP)-based unreleased RF MEMS resonator, integrated seamlessly in Texas Instruments’ 130 nm Ferroelectric RAM (FeRAM) technology. The designs presented here are monolithically integrated in solid-state CMOS technology, with no post-processing or release step typical of other MEMS devices. An array of FeCAPs in this complementary metal-oxide-semiconductor (CMOS) technology’s back-end-of-line (BEOL) process were used to define the acoustic resonance cavity as well as the electromechanical transducers. To achieve high quality factor (Q) of the resonator, acoustic waveguiding for vertical confinement within the CMOS stack is studied and optimized. Additional design considerations are discussed to obtain lateral confinement and suppression of spurious modes. An FeCAP resonator is demonstrated with fundamental resonance at 703 MHz and Q of 1012. This gives a frequency-quality factor product f cdot Q = 7.11 times 10^{11} which is 1.6× higher than the most state-of-the-art Pb(Zr,Ti)O3 (PZT) resonators. Due to the ferroelectric characteristics of the FeCAPs, transduction of the resonator can be switched on and off by adjusting the electric polarization. In this case, the resonance can be turned off completely at ±0.3 V corresponding to the coercive voltage of the constituent FeCAP transducers. These novel switchable resonators may have promising applications in on-chip timing, ad-hoc radio front ends, and chip-scale sensors.

ELECTROMECHANICAL AND RF PERFORMANCE ANALYSIS OF SERIES CONFIGURATION BASED MEMS SWITCH

The paper presents a RF MEMS (Radio-Frequency-Micro-Electro-Mechanical-System) of cantilever series switch which is developed with low actuation voltage which depends upon the beam characteristics and the gap between the plane and metal beam. The MEMS series switch that designed is operating with a frequency range (0-60GHz) and it provides control of the other devices. The RF MEMS switching component consists of a electrode with tuning fork shaped which is fixed using anchor points on coplanar waveguide lines to decrease the actuation voltage and the insertion loss of the switch. The Air gap in between the tuning fork shaped electrode and actuation electrode of RF MEMS series switch is designed to boost the isolation attributes of the switch with less actuation voltage. The switching voltage for designing the switch is 18 V. The designed RF MEMS series switch can be used for sub-system level for broadband applications and communication devices.

Miniaturized Folded Ridged Quarter-Mode Substrate Integrated Waveguide RF MEMS Tunable Bandpass Filter

This paper presents a miniaturized RF MEMS tunable bandpass filter design developed by application of folded ridged quarter-mode substrate integrated waveguide cavity. Using packaged RF MEMS SP4T chips, a switchable reactive loading is applied to the folded ridged quarter-mode substrate integrated waveguide cavity, tuning the resonance frequency. Overall miniaturizations of 70.3% and 78.8% are achieved for inductively- and capacitively-loaded filters compared to an RF MEMS tunable filter using half-mode substrate integrated waveguide. Here, an analysis of inductive or capacitive loading along with their advantages and disadvantages are discussed. Two different two-pole folded ridged quarter-mode substrate integrated RF MEMS tunable bandpass filters are designed and measured. The first prototype employing inductive loading achieves 4.4% tuning range at a center frequency of 1.713 GHz, insertion loss of 3.10-3.92 dB, and return loss greater than 15 dB for all tuning modes. The second prototype employing capacitive loading is measured with a 35.2% tuning range at a center frequency of 865 MHz, insertion loss of 1.6-4.3 dB, and return loss greater than 10 dB for all tuning modes. The reported performance and extreme miniaturization of folded ridged quarter-mode substrate integrated waveguide cavities shows great promise for their application in tunable filter design.

Hybrid neural lumped element approach in inverse modeling of RF MEMS switches

RF MEMS switches have been efficiently exploited in various applications in communication systems. As the dimensions of the switch bridge influence the switch behaviour, during the design of a switch it is necessary to perform inverse modeling, i.e. to determine the bridge dimensions to ensure the desired switch characteristics, such as the resonant frequency. In this paper a novel inverse modeling approach based on combination of artificial neural networks and a lumped element circuit model has been considered. This approach allows determination of the bridge fingered part length for the given resonant frequency and the bridge solid part length, generating at the same time values of the elements of the switch lumped element model. Validity of the model is demonstrated by appropriate numerical examples.

ELECTROMECHANICAL AND RF INVESTIGATIONS OF FIXED-FIXED CONFIGURATION-BASED RF MEMS SWITCH

ELECTROMECHANICAL AND RF INVESTIGATIONS OF FIXED-FIXED CONFIGURATION-BASED RF MEMS SWITCH

Reconfigurable Antenna using Micromechanical Actuation Switches for K and Ku-Band Applications

In this paper, we have proposed a reconfigurable antenna using micro mechanical actuation switches for K and Ku-band applications. Overall two identical cantilever micro mechanical switches (S1 &amp; S2 ) are used to design reconfigurable patch antenna. The switches are working by electrostatic actuation mechanism. With the switches, overall the antenna is offering four resonant frequencies based on the switches ON/OFF condition. The Micro mechanical switches are offering an isolation loss of -18.5dB and an insertion loss of -1dB. The switch requires a DC actuation voltages of 6V. The Proposed reconfigurable antenna is resonating at four different frequencies based on the different switching conditions of RF MEMS switches. If S1 &amp; S2 both are ON the antenna is resonating at 16.9GHZ, if S1 -ON &amp; S2 -OFF the antenna is resonating at 47.3GHZ &amp; 59.1GHZ, if S1 -OFF &amp; S2 -ON the antenna is resonating at 28.4GHZ, if S1 -OFF &amp; S2 -OFF the antenna is resonating at 27.9GHZ