RF MEMS Capacitive Switches Research Articles

A novel capacitive RF-MEMS switch for multi-frequency operation

Abstract This paper reports a novel capacitive RF-MEMS switch. The presented device has frequency reconfigurable characteristics and thus can be used in multi-band wireless systems. The switch is realized through two non-uniform cantilevers with dissimilar shape. The structure of the cantilevers is kept dissimilar to achieve the different value of inductance in the down-state of the device and hence the different electrical resonant frequency. Further, the proposed device has also overcome issue of shift in the isolation response caused by residual stress in switching structure and micro-roughness in the deposited SiO2 layer. The device forms a M-I-M capacitor at the central conductor of the transmission line to resolve the above cited problem and also allows the use of cantilever structures for the implementation of capacitive switches in place of conventional bridge type structures. The measured isolation response shows three optimum values of 25.40 dB, 20.44 dB, and 30.80 dB at 9.4 GHz, 11.6 GHz, and 25.2 GHz respectively. The measured insertion loss is also better than 0.41 dB up to 30 GHz. Under, mechanical characterization, cantilever with two narrow beams shows resonant frequency of 3.90 kHz and cantilever with single narrow beam shows resonant frequency of 4.66 kHz. Furthermore, the device has measured pull-in voltage which is less than 16 V.

Design and performance analysis of double cantilever type capacitive shunt RF MEMS switch

This paper presents a novel structure of capacitance shunt type RF switch for 5G applications. The proposed RF MEMS switch is having Cantilever type designed with optimized dimensions to operate in V-band applications. The electromechanical analysis is done by using the COMSOL tool. The actuation voltage of the proposed switch is 10.5 V with the air gap of 1 µm and gold as a beam material. The proposed switch with the meanders and perforations show the scattering parameters in HFSS software such as insertion loss (S12) of − 0.033 dB and return loss (S11) less than − 48 dB and the isolation (S21) calculated in off-state as − 62 dB at 50 GHz.

Optimization of shunt capacitive RF MEMS switch by using NSGA-II algorithm and uti-liti algorithm

The present paper aimed at designing, optimizing, and simulating the RF MEMS Switch which is stimulated electrostatically. The design of the switch is located on the CoplanarWaveguide (CPW) transmission line. The pull-in voltage of the switch was 2V and the axial residual stress of the proposed design was obtained at 23MPa. In order to design and optimize the geometric structure of the switch, the desired model was extracted based on the objective functions of the actuation voltage and the return loss up-state and also the isolation down-state using the mathematical programming. Moreover, the model was solved by the NSGA-II meta-heuristic algorithm in MATLAB software. In addition, the design requirements and the appropriate levels for designing the switch were obtained by presenting the Pareto front from the beam actuation voltage and also the return loss up-state and isolation down-state. Finally, the RF parameters of the switch were calculated as S11=-2.54dB and S21=-33.18dB at the working frequency of 40GHz by extracting the appropriate parameters of the switch design through simulating a switch designed by the COMSOL Multiphysics software 4.4a and the advanced design system (ADS).

Beam and dielectric materials impact on improvement of the performance of a novel capacitive shunt RF MEMS switch

AbstractThis paper presents a novel radiofrequency micro‐electro‐mechanical systems (RF MEMS) shunt capacitive switch having high isolation and low insertion loss for microphone applications. The device optimization and various electromechanical analysis are performed using a finite element modeler (FEM) solver. The proposed switch results in a pull‐in voltage of 36.88 V to displace movable beam 2/3rd of its initial gap. By varying beam material, dielectric material, beam‐dielectric thickness, and air gap between movable beam and dielectric layer, various electromechanical and electromagnetic analyses are carried out. For better isolation, silicon nitride (Si3N4) is used for the dielectric layer than hafnium oxide (HfO2) and silicon carbide (SiC). To achieve maximum displacement of the beam, various materials such as aluminum, gold, nickel, and copper are chosen; among all, this gold shows high displacement because of its good conductivity. By implementing various meandering techniques along with perforations, pull‐in voltage and stiction problems are reduced. The switch exhibits good return loss of −28 dB and insertion loss of −0.017 dB during on‐state at 5 GHz and high isolation of −41.26 dB at 10.5 GHz during off‐state. The proposed switch is used at the subsystem/device level in the future microphone, aircraft navigation, and satellite applications.

Compact high isolation and improved bandwidth hybrid RF MEMS SPDT switch for 5G applications

Fifth generation (5G) communication system enables the pathway for a higher data transfer rate. The frequency bands used for 5G communication system are distributed from lower frequency range (600 MHz) to a higher frequency range (60 GHz). So it is necessary that a single switch should be able to cover the complete range of 5G frequency bands. The ohmic radio frequency-micro electromechanical system (RF-MEMS) switch has offered high isolation at lower frequencies (> 40 dB up to 2.5 GHz). However, 5G requires a higher frequency range which is covered by capacitive switch. The capacitive switch has limitations of limited bandwidth and large size. In this paper, a hybrid technique is used for the designing of a compact, high isolation and the enhanced bandwidth SPDT RF MEMS switch for 5G applications. The size of the proposed switch is half from the conventional capacitive RF MEMS switch and offer greater than 40 dB isolation over a wide frequency range (> 40 dB over 22.10 GHz bandwidth) with less than 0.30 dB insertion loss over the entire band.

Investigation on Switching Structure Material Selection for RF-MEMS Shunt Capacitive Switches Using Ashby, TOPSIS and VIKOR

This paper utilizes three material selection methodologies to select the most promising material for switching structure of RF-MEMS shunt capacitive switches. The material should be selected such that RF-MEMS capacitive switches should have low pull-in voltage, low RF loss, high thermal conductivity and maximum displacement of the beam. For this purpose, the concerned material indices are as follows: low value of Young’s modulus, low electrical resistivity, high thermal conductivity and high fracture strength. Following Ashby, TOPSIS and VIKOR method were used to select the best material. The results obtained from these methods show good correlation. The end results suggest that gold and copper are the most suitable materials for RF-MEMS switches.

Effect of Parasitic Capacitance on RF MEMS Switch OFF/ON Ratio

Radio frequency micro-electro-mechanical system (RF MEMS) switch is basic component for transponders used in communication system. Switch “OFF/ON” capacitance ratio plays major role in controlling signal to noise ratio. Theoretically, with high dielectric constant material or floating metal concept, capacitance ratio can be improved up to 2000 or even more. Whereas, in most of the practical cases, measured ratio is less than 200. In present paper, RF MEMS capacitive switch LCR parameters are extracted considering parasitic capacitance to explain the mismatch of measured results. Parasitic capacitance is independent from device overlap area. Parasitic capacitance is function of switch geometry and directly proportional to dielectric constant of the substrate material.

Design and Performance Analysis of Low Pull-In Voltage of Dimple Type Capacitive RF MEMS Shunt Switch for Ka-Band

This paper deals with the study of dimple type RF MEMS capacitive shunt switch using different meandering techniques for high isolation and low actuation voltage. The novelty of the proposed RF MEMS switch is it incorporates the meanders and dimples, which help to reduce the actuation voltage. The proposed switch structure is optimized, designed, and simulated with FEM analysis such as electromechanical and electromagnetic by using COMSOL and HFSS tools respectively. The best performance of the switch is observed by varying different parameters such as beam material, beam thickness, dielectric thickness, and airgap. The proposed switch with different meandering techniques attains the pull-in voltage in the range of 10.3-46 V, particularly the three uniform meander technique has low actuation voltage of 10.3 V. The RF performance of the device is particularly tuned in the range of 26.5-40 GHz frequency range and it is analyzed for all types of meanders. Among them, the non-uniform single meander has attained the best isolation of -54.13 dB at 40 GHz in the off state. The insertion and return losses of the device are -0.514 dB and -17.35 dB over 1-40 GHz frequency in on state.

Design, Modeling and Analysis of Perforated RF MEMS Capacitive Shunt Switch

This paper illustrates the design, modeling, and analysis of bridge type structure based capacitive RF MEMS switch with different beam thickness and materials. We have used Ashby’s approach to select the best materials in each and every level which helped to improve the overall performance of the switch in terms of mechanical, electrical, and RF properties. Silicon Nitride thin film ( $\varepsilon _{\mathrm {r}}= 7.8$ ) is used as a dielectric material. The beam structure stiffness is analyzed with different materials, such as gold, titanium, and platinum, within these materials gold with high thermal conductivity and Euler–Young’s modulus of 77 GPa is offering the best performance. Incorporation of meanders and perforations to the membrane helped to reduce the pull-in voltage. The proposed switch is offering very low pull-in voltage of 1.9 V. The deflection of beam thickness is tabulated for the three materials among them the 2 $\mu \text{m}$ thickness is best beam thickness for the switch for X-band applications. The switch offers best return loss (S11) of −21.36 dB, insertion loss (S12) of −0.147 dB, and isolation (S21) of −52.04 dB at 8GHz. The switch presented in this paper is preferable in X-band applications.

Reduced dielectric charging RF MEMS capacitive switch

The presence of dielectric charging in a switch causes stiction and drift in pull-in voltage. A design to alleviate charging issues for RF MEMS switches is proposed. An RF MEMS capacitive switch has been fabricated and characterized. Measured pull-in of the switch is <20 V and pull-up voltage is 17 V with a switching time of 78 μs. Insertion loss and isolation of the switch are measured by varying RF power from 0 to 15 dBm at room temperature. Insertion loss and isolation of the switch are better than 0.1 and 17 dB, respectively. Resonant frequency of the device is 8.4 kHz. The switch has completed 600 million cycles.

High Performance Capacitive RF-MEMS Switch Based on HfO2 Dielectric

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, HfO2 a high-k dielectric material has been used in place of SiO2. The switch based on HfO2 has 8 times less central overlap area, leading to the overall reduction of about 15% in the switch size as compared to the SiO2 based switch. The compactness has been achieved further through the interdigitation of signal lines with actuation electrodes. Further, a floating metal layer has been incorporated in the design to eliminate the capacitance reduction problem in the down-state due to surface roughness. The floating metal layer also makes the down-state behavior predictable in terms of resonant frequency. The switch based on HfO2 shows 52.70 dB isolation and 0.06 dB insertion loss at 9 GHz as compared to the 50.60 dB isolation, 0.25 dB insertion loss for the switch with SiO2. Pull-in voltage has been reduced around 65% at a gap of 1 µm between bridge and transmission line without much affecting the RF performance due to the reduced overlap area. In addition, improvement of around 2 times in the bandwidth has also been achieved. The designed switch can be used at device and sub-system level in the future telecommunication applications.

Low temperature epoxy bonding for RF MEMS capacitive switch

Packaging is one of the most critical tasks for MEMS devices. Unlike solid state devices, MEMS structures involves moving structures which needs to be protected from outer environment ensuring free movement of the structure. In the present paper, inverted silicon cavity is used for capping the MEMS devices. However, in case of RF MEMS, silicon cavity would add parasitics and affects its electrical performance. Enclosing the MEMS structure, its mechanical response will also alter. The electrical as well as mechanical characteristics of the RF MEMS switch are analyzed using finite element method simulations. The electrical response of the fabricated switch after packaging is compared with unpackaged device.

Probabilistic Physics of Failure (PPOF) Reliability Analysis of RF-MEMS Switches under Uncertainty

MEMS reliability analysis is a challenging area of research which comprises various physics of failure and diverse failure mechanisms. Reliability issues are critical in both design and fabrication phases of MEMS devices as their commercialization is still delayed by these problems. In this research, a hybrid methodology is developed for the reliability evaluation of MEMS devices. Its first step is the identification of dominant failure modes by FMEA, evaluation of failure mechanisms and an updated lifetime estimation by the Bayesian method. The reliability of MEMS devices is studied using probabilistic physics of failure (PPoF) by determining the dominant failure mechanism. Accordingly, a deterministic model is selected for the analysis of the life and reliability of the dominant failure mechanisms. To convert the deterministic model to a probabilistic model, the uncertainty sources affecting the dielectric lifetime are determined. This model is simulated by the utilization of the Monte Carlo method. In the final stage, the results of life estimation are updated using the Bayesian method. Considering wide application and advantages of RF MEMS capacitive switches, it has been selected as a case study. A framework is developed for reliability evaluation of these switches failures due to stiction mechanism. The results contain FMEA table, lifetime estimation in different voltages, number of duty cycles and at the end, updated results of life estimation using the Bayesian method.

Role of dielectric layer and beam membrane in improving the performance of capacitive RF MEMS switches for Ka-band applications

In this paper, we have analyzed the role of dielectric layer and different beam membranes on the performance parameters of shunt capacitive RF MEMS switch. The investigation mainly focused on the major challenges of performance parameters are reducing actuating voltage and improving the isolation. The actuation voltage is reduced by incorporation of non-uniform meanders to the serpentine membrane structure and also improved the isolation using 50 nm AlN dielectric thin film. Here, we have incorporated the holes to the top membrane which help the switch to improve the insertion property. The actuation voltage required to move the switch downwards is 5.4 V and the switch operates at transition time of 12 μs. The isolation − 72.4 dB is observed at the frequency of 27 GHz and insertion − 0.34 dB is observed at the frequency of 27 GHz. The characteristics of switch have been observed by simulating the switch design in FEM tool and results have been compared with theoretical calculations. Finally, the switch is optimized based on the switch performance parameters and it is suitable for Ka-band applications.

On characterization of symmetric type capacitive RF MEMS switches

This paper presents the design, fabrication and characterization of capacitive type MEMS switch for space and terrestrial communication applications. The deviation in measured actuation voltage and RF response of the switches are discussed in terms of the process variation which occurred unintentionally during the fabrication of devices. For example the measured actuation voltage is 15 V, about 20% higher than the designed voltage of 12.25 V. The deviation corresponds to the increase in thickness of the membrane while electroplating. The impact of process parameters on mechanical resonance frequency of the switches, and on/off time is also discussed. Measured S-parameters shows isolation of > − 20 dB for 7–16 GHz and an insertion loss better than − 0.6 dB up to 20 GHz. The capacitance ratio of the fabricated switch is 77, which is 15% lower than the designed capacitance ratio. The switch has been tested for 1 million 65 thousand cycles without switching failure. The deviation of simulated and measured results is discussed in the following sections.

Study and analysis of novel RF MEMS switched capacitor

In this paper we have designed and analyzed shunt capacitive fixed-fixed RF MEMS switch to maintain low actuation voltage. The pull - in voltage of the proposed switch is 7.7V for 2 um air gap. The electromagnetic analysis for the designed structure is, return loss is -23dB in the range of 1-40 GHz, insertion loss is -0.04dB at a frequency range of 1-40 GHz and isolation is - 38.5dB obtained at a frequency of 23.5 GHz. Mechanical analysis for the designed structure is also performed using FEM tool.

Rotated Serpentine Spring Structure for Low Actuation Voltage CPW RF MEMS Switch

Background: RF MEMS switches can be used in radars, wireless systems, communication systems, phase shifters and switch matrices in order to achieve low power consumption, high isolation, small size and weight. Objective: This paper reports a low actuation voltage Capacitive Shunt RF MEMS Switch with two flexures, based on rotated serpentine spring concept. Method: The switch is designed on a CPW line with an impedance of 50 Ω. The dielectric is used is silicon nitrate with the thickness of 0.1 µm. Also, a cantilever beam switch and a switch with the serpentine spring structure based on meanders are simulated with the Comsol software and compared with the proposed switch. Conclusion: The results show actuation voltages of 15.89 V, 10 V and 7.755 V for the cantilever beam structure, serpentine spring structure and the proposed switch, respectively. RF scattering parameters are simulated by HFSS. Result: The results show that the return loss is -0.18 at 9.3GHz and the isolation is -37 dB at 9.3 GHz. Keywords: RF MEMS switch, low actuation voltage, spring structure, RF signal, microstrip, radio frequency.

Neural Based Lumped Element Model of Capacitive RF MEMS Switches

Abstract In this paper a lumped element model of RF MEMS capacitive switches which is scalable with the lateral dimensions of the bridge is proposed. The dependence of the elements of the model on the bridge dimensions is introduced by using one or more artificial neural networks to model the relationship between the bridge dimensions and the inductive and resistive elements of the lumped element model. The achieved results show that the developed models have a good accuracy over the whole considered range of the bridge dimension values.

Fabrication and Characterization of Capacitive RF MEMS Perforated Switch

In this paper, we have designed, simulated, fabricated, and characterized a clamped-clamped micro mechanical structure-based shunt capacitive RF MEMS switch. The clamped–clamped micromechanical structure is micromachined using a gold metal thickness of 500 nm. AlN is used as a dielectric material, and it is deposited using the dc sputtering PVD process. In the MEMS technology, particularly in devices fabrication, releasing the membrane is a difficult task, and here, we have presented a novel wet process to release the membrane. Primarily, the S1813 sacrificial layer is etched by using the piranha solution and cleaned with the IPA solution. Critical point drying is done after fabrication to reduce the stiction effect on the switch. Overall, the switch requires the pull-in voltage of 5.5 V for 1.8- $\mu \text{m}$ displacement. In the process of optimization, primarily, the switch is designed and simulated using finite-element method tools. The reliability of the capacitive RF MEMS switches depends on the stiction problem caused by dielectric charging, and the proposed capacitive switch dielectric charging behavior is characterized using the CV curve method.

Multiport RF MEMS switch for satellite payload applications

Design, fabrication and characterization of a novel RF switch is proposed in this paper. The multiport RF MEMS switch provides a single input multiple output novel topology suitable for satellite payload applications. A single ETA is used to switch the device from one mode to another. When a voltage difference is applied across the electrode pads of ETA, and depending on the configuration, the actuator actuates forward or backward in plane producing either a quad or dual output respectively. The reflection loss and insertion loss are improved effectively. Measurement results show that in `dual mode’ position, the input reflection coefficient (S 11) is less than − 50 dB with the forward transmission coefficient (S 21) better than − 2 dB at 0–15 GHz. At ‘quad mode’, position, the input reflection coefficient (S 11) is less than − 55 dB with the forward transmission coefficient (S 21) better than − 4 dB at 0–15 GHz. The larger than 50 dB over 0–15 GHz isolation realized in both modes of operation ensures dual and quad mode outputs without information loss. The actuation voltage is reduced to 4.5 V. The measured power handling capability can reach up to 35 dBm while the power consumption of the switch is 50 mW. This compact RF MEMS capacitive switch possesses excellent performances in terms of low insertion loss, high isolation, low power and high power handling capability.