RF MEMS Capacitive Switches Research Articles

Design and Simulation of Radio Frequency Micro Electro Mechanical Capacitive Shunt Switches

Radio Frequency Micro ElectroMechanical (RFMEM) switches play an important role in microwave switching. The demand for low voltage, low insertion loss, high Isolation RF MEMS capacitive switches for high frequency (10-40GHz) applications has led to the development of MEMS based switching devices in the RF domain. This work reports the design and simulation of RF MEMS capacitive shunt switches for K and Ka bands. The switching element consists of a thin gold membrane which gets actuated over a transmission line under an applied bias. The dc simulation is carried out in CoventorWare and the designed switch is found to actuate at 18.75 volts. HFSS simulation results demonstrate an acceptable RF performance with an insertion loss of 0.25 dB in the range 20-35GHz and an isolation better than 20dB beyond 20GHz.

Performance improvement of a reconfigurable series-shunt switch via asymmetric structure based RF-MEMS capacitive switch

This paper presents a series combination of metal to metal contact and capacitive RF-MEMS switches for multi-band wireless applications. For performance improvement a novel capacitive shunt switch is used and the response has been compared with a conventional shunt device. The proposed design shows the insertion loss better than 0.35 dB and return loss below 13.96 dB up to 30 GHz as compared to 1.64 dB insertion loss and 6.14 dB of return loss with conventional device. Isolation peaks of 75.33, 71.58 and 72.98 dB has been observed at 8.2, 7.3 and 15.5 GHz when left, right or both cantilevers are electro-statically actuated in the down-state respectively, whereas conventional device has peak only at 7.3 GHz. Further, a reduction of about 60 % in the pull-in voltage of capacitive switch and 17.5 % in device area has also been observed. The proposed design can be used as a building block for multiple throw switches and switch matrices for the future reconfigurable RF front end applications.

A novel design for low insertion loss, multi-band RF-MEMS switch with low pull-in voltage

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, float metal concept is utilized to reduce the RF overlap area between the movable structure and central conductor of CPW for improving the insertion loss of the device. This has been achieved without affecting the down-state response. Further, float metal also makes the down-state behavior predictable in terms of resonant frequency. For reducing the pull-in voltage, the switch is implemented with cantilever type of structure on either side of the transmission line. This structure also has the capability to inductively tune the isolation optimum value to the different bands and thus can be used in the reconfigurable RF systems. The device shows an insertion loss less than 0.10 dB, a return loss below 36.80 dB up to 25 GHz as compared to 1.00 dB insertion, 7.67 dB return loss for the conventional switch. In the OFF state, proposed device shows two isolation peaks i.e. 48.80 dB at 4.5 GHz and 54.56 dB at 9.7 GHz, when either or both cantilevers are electro-statically actuated to the down-state position respectively. The conventional device has a single isolation peak in the X-band. In addition, improvement of around 3 times in the bandwidth has also been achieved. The designed switch can be used at device and sub-system level for the future multi-band communication applications.

Dielectric charging effects in floating electrode MEMS capacitive switches

The paper presents a study oriented to the understanding of the floating electrode role on the charging characteristics of floating electrode RF MEMS capacitive switches. Identical devices with and without floating electrode have been stressed under induced charging mode. Biases of different levels and polarities were applied to the transmission line. Reduced and asymmetric, with respect to the bias polarity, charging effects were obtained on devices with floating electrode compared to the conventional ones. The results contribute towards the conclusion that the use of floating electrode in conjunction with the appropriate actuation polarity may reduce the charging effects and thus improving the device lifetime.

Induced charging phenomena on SiNx dielectric films used in RF MEMS capacitive switches

Contact-less charging process has been found to constitute a compensation mechanism to dielectric charging of MEMS capacitive switches. The present paper aims to provide a better knowledge of induced charging mechanisms that appear in HF PECVD silicon nitride films. The characteristics of this process as well as the degree of compensation are investigated for different stressing field intensities of both polarities in MEMS capacitive switches. The experimental results indicate that the degree of compensation in HF PECVD SiNx films seems to increase with the intensity of the applied electric field and it is also affected by the polarity of the stressing bias. A new theoretical model that describes the build-up of induced charging is also proposed. Taking into account that the electric field during contact-less charging is quite low, the model assumes that induced charging arises from charge displacement inside the film through hopping conduction processes.

Design, optimization and simulation of a low-voltage shunt capacitive RF-MEMS switch

This paper presents the design, optimization and simulation of a radio frequency (RF) micro-electromechanical system (MEMS) switch. The capacitive RF-MEMS switch is electrostatically actuated. The structure contains a coplanar waveguide, a big suspended membrane, four folded beams to support the membrane and four straight beams to provide the bias voltage. The switch is designed in standard 0.35 µm complementary metal oxide semiconductor process and has a very low pull-in voltage of 3.04 V. Taguchi method and weighted principal component analysis is employed to optimize the geometric parameters of the beams, in order to obtain a low spring constant, low pull-in voltage, and a robust design. The optimized parameters were obtained as w = 2.5 µm, L1 = 30 µm, L2 = 30 µm and L3 = 65 µm. The mechanical and electrical behaviours of the RF-MEMS switch were simulated by the finite element modeling in software of COMSOL Multiphysics 4.3® and IntelliSuite v8.7®. RF performance of the switch was obtained by simulation results, which are insertion loss of ?5.65 dB and isolation of ?24.38 dB at 40 GHz.

Performance analysis of RF MEMS capacitive switch with non uniform meandering technique

This Paper reports on investigation of High Con Coff ratio Capacitive Shunt RF MEMS Switch and detailed comparison between uniform three meander beam with non-uniform single meander beam RF MEMS switch. RF MEMS Switches are designed for operation in the range 5---40 GHz. Pull in analysis is performed with gold as a beam material. Simulation reveals that use of high K dielectric material can drastically improve the capacitance ratio of switch. For the same geometry, pull in voltage is 2.45 V for HfO2, 2.7 V for Si3N4 and Capacitive Ratio of the switch with Si3N4 is 83.75 and Capacitive Ratio with HfO2 is 223 at 2g0 (air gap) and 0.8 μm thickness of beam. The Radio Frequency performance of RF MEMS switch is obtained by scattering parameters (insertion loss, Return loss and isolation) which are mainly dominated by down to up capacitance ratio and MEMS bridge geometries. RF analysis shows that insertion loss as low as ź0.4 dB at 20 GHz and isolation as high as 80 dB at 20 GHz can be achieved. Investigation of three uniform meander Design and non-uniform single meander design reveals that use of non-uniform design reduces the design complexity and saves substrate area still maintaining almost same device performance. S-parameter analysis is carried out to compare device performance for both structures. DC analysis of the proposed switch is carried out using Coventorware and RF analysis is performed in MATLAB.

A Novel Approach for Low Insertion Loss, Multi-band, Capacitive Shunt RF–MEMS Switch

This paper presents a novel capacitive shunt RF-MEMS switch. In the proposed design, broadside bridge structure joined with two cantilevers on either side has been used to implement the switch. The transmission line and actuation electrodes under the bridge are designed in the interdigitated form to reduce the area. Switch shows an insertion loss better than 0.11 dB, a return loss below 23.67 dB up to 25 GHz. In down-state, three resonant peaks of 34.71, 34.33 and 40.7 dB at 10.4, 11.0 and 21.4 GHz have been achieved as compared to a single peak in the case of the conventional switch. The proposed device has a bandwidth of 2.2 GHz in X-band and 5.2 GHz in K-band. Bridge structure shows a pull-in voltage of 12.25 V, actuation time of 34.40 µs while cantilevers have 7.5 V and 57 µs. Further, the electrical equivalent model has been presented to represent the switch. The model has been implemented in commercially available software. A good agreement with the 3-D electromagnetic simulated results validates the presented model.

A MIM capacitor study of dielectric charging for RF MEMS capacitive switches

MIM capacitors are considered equally important devices for the assessment of dielectric charging in RF MEMS capacitive switches. Beside the obvious similarities between the down state condition of RF MEMS and MIM capacitors there are also some important differences. The paper aims to introduce a novel approach to the study of dielectric charging in MEMS with the aid of MIM capacitors by combining experimental results obtained by the application of DC, Charging Transient and Kelvin Probe techniques. The strengths and weaknesses are discussed in conjunction with experimental results obtained on SiNx based MIM capacitors and MEMS capacitive switches fabricated under the same conditions.

Analysis of RF MEMS capacitive switches by using switch EM ANN models

Artificial neural networks (ANNs) have appeared to be an alternative to the conventional models of RF MEMS switches. In this paper, neural models of an RF MEMS capacitive switch are developed and used for the electrical design of the switch. Namely, an ANN model relating the switch resonant frequency and the bridge dimensions is used to analyze efficiently the switch behavior with changes of bridge dimensions. Furthermore, it is illustrated how the developed model can be used for the determination of bridge dimensions in order to achieve the desired switch resonant frequency. In addition, application of a switch inverse ANN model for the determination of bridge dimensions is analyzed as well.

电容式RF MEMS开关膜片上边缘电场的表征

电容式RF MEMS开关膜片上边缘电场的表征

Application of RF MEMS Switch for Reconfiguring Micromachined Antennas

For mobile and wireless applications where the size of the system has to be minimized, antenna and RF components are to be integrated on to the same substrate. The contradicting requirements of the substrate with respect to the antenna and the RF circuit can be resolved by using micromachined antennas. If the principle of reconfigurability is applied to the micromachined antenna, it increases the versatality of the system. This paper proposes reconfigurability of micromachined antennas using RF MEMS switches. In the case of micromachined antennas, which involve low voltage signals, RF MEMS switches with low actuation voltage are required for achieving reconfigurability. In this paper an RF MEMS capacitive switch operating at a low actuation voltage of 1 Volt is presented

A low insertion loss, multi-band, fixed central capacitor based RF-MEMS switch

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, switch consists of a beam in the form of two symmetric cantilevers anchored at the central conductor of CPW, where they generate a fixed capacitance, whereas the free ends of the cantilevers are hanging over the ground plane of the CPW. The net up-state capacitance thus can be approximately determined from the area of overlap between the ground plane and free ends of cantilevers rather than the central overlap area as in the case of conventional movable bridge based approach. Further, the switch is used to inductively tune the isolation peaks in C and X bands i.e. 44.53 dB at 4.5 GHz and 51.08 dB at 9.8 GHz, when either or both cantilevers are electro-statically actuated to the down-state position. The device with movable bridge has isolation peak only at a single frequency in X band. Device shows an insertion loss less than 0.15 dB, a return loss below 21.38 dB up to 25 GHz as compared to 1.00 dB insertion, 7.67 dB return loss for the equivalent conventional switch with movable bridge. In addition, improvement of around 3.5 times in the bandwidth and 50 % reduction in the pull-in voltage has also been achieved. The designed switch can be useful at device and sub-system level for the future multi-band communication applications.

Electrical assessment of diamond MIM capacitors and modeling of MEMS capacitive switch discharging

This paper presents the electrical assessment and modeling of the discharge process in RF MEMS capacitive switches with nanocrystalline diamond dielectric film. The assessment is performed by taking into account the detailed dc electrical characterization of the dielectric film at different temperatures with the aid of metal–insulator–metal (MIM) capacitors fabricated on the same die. The model assumes screening of trapped charges through carriers that are injected from the bottom electrode, transported through grain boundaries and redistributed across the diamond film surface through the sp2 state of non-diamond carbon. Simulated data and experimental results are found to be in excellent agreement, clearly indicating that nanocrystalline diamond can be considered as a MEMS dielectric with predictable discharging process.

A fabrication process based on structural layer formation using Au–Au thermocompression bonding for RF MEMS capacitive switches and their performance

This paper presents a radio frequency micro-electro-mechanical-systems (RF MEMS) fabrication process based on a stacked structural layer and Au–Au thermocompression bonding, and reports on the performance of a sample RF MEMS switch design implemented with this process. The structural layer consists of 0.1 µm SiO2/0.2 µm SixNy/1 µm Cr–Au layers with a tensile stress less than 50 MPa deposited on a silicon handle wafer. The stacked layer is bonded to a base wafer where the transmission lines and the isolation dielectric of the capacitive switch are patterned. The process flow does not include a sacrificial layer; a recess etched in the base wafer provides the air gap instead. The switches are released by thinning and complete etching of the silicon handle wafer by deep reactive ion etching (DRIE) and tetramethylammonium hydroxide (TMAH) solution, respectively. Millimeter-wave measurements of the fabricated RF MEMS switches demonstrate satisfactory up-state performance with the worst-case return and insertion losses of 13.7 and 0.38 dB, respectively; but the limited isolation at the down-state indicates a systematic problem with these first-generation devices. Optical profile inspections and retrospective electromechanical analyses not only confirm those measurement results; but also identify the problem as the curling of the MEMS bridges along their width, which can be alleviated in the later fabrication runs through proper mechanical design.

Microwave Performance Simulation of RF-MEMS Switch

This paper presents the calculation model of capacitive RF-MEMS switch for the isolation and insertion loss, and then adopts CST software to simulate microwave performances. The simulation results show that return loss can reach-21.5dB and isolation can reach-0.26dB when the distance between contacting metal and dielectric layer adopts 2ڌ̏̽, 6×?103ڌ̏̽2 of contacting area and 20ڌ̏̽ of groove depth.

Impact Velocity Analysis of Capacitive RF-MEMS Switch

Impact velocity is an important performance parameter for capacitive RF-MEMS switch. This paper establishes a differential equation, in order to analyse the influencing factors of impact velocity. The simulation results show that impact velocity can reach 1.5m/s when bias voltage equals to 0.7V, frequency equals to 3×105Hz, voltage type adopts rectangular wave.

Design and investigation of a low insertion loss, broadband, enhanced self and hold down power RF-MEMS switch

This paper presents a low insertion loss capacitive shunt RF-MEMS switch. In the presented design, float metal concept is utilized to reduce the capacitance in up-state of the device. Float metal switch shows an insertion loss <0.11 dB, a return loss below 26.27 dB up to 25 GHz as compared to 0.81 dB insertion, 8.67 dB return loss for the conventional switch without float metal. OFF state response is same for the both devices. Further pull-in voltage of 12.75 V and switching time of 69.62 µs have been observed in case of the conventional switch whereas device with float metal have 11.75 V and 56.41 µs. Improvement of around 2.5 times in bandwidth and 4 times in input power has been observed without self actuation, hold down problem. The designed switch can be useful at device and sub-system level for multi-band applications.

Performance improvement of RF-MEMS capacitive switch via asymmetric structure design

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, float metal concept has been utilized to make the asymmetric structure on either side of the transmission line to implement the switch. This novel structure is used to inductively tune the isolation in C, X and Ku bands. Isolation peaks of 42.63, 44.22 and 47.75 dB has been observed at 7.2, 8.8 and 16.5 GHz when left, right or both cantilevers are electro-statically actuated in the down-state respectively, whereas conventional switch has peak only in X-band. Switch shows an insertion loss better than 0.10 dB, a return loss below 23.93 dB up to 25 GHz as compared to 0.90 dB insertion loss and 8.02 dB of return loss in case of conventional device. Further, improvement of around 5 times in bandwidth, 50 % in the pull-in voltage and 16.7 % in device area have also been observed. The designed switch can be useful at device and sub-system level for the future multi-band communication applications.

Probing contactless injection dielectric charging in RF MEMS capacitive switches

Dielectric charging is a major reliability issue preventing commercialisation of RF MEMS capacitive switches. To date two major modes have been considered as responsible for the charging of the dielectric films in RF MEMS. The one takes place during the pull-down state and therefore it is called contacted or injection charging, whereas the second occurs when the bridge is still in the up state and is referred to as contactless or induced charging. Experimental results supporting contactless charge injection as an additional charging mechanism in RF MEMS capacitive switches are presented.