Electrostatic micro-actuator with a pre-charged series capacitor: modeling, design, and demonstration

This paper presents the design, analysis, modeling and simulation of a novel RF MEMS series switches with low actuation voltage. A mechanical modeling is presented to describe the behavior of the series switch. The switch is designed with special mechanical structures. The novel mechanical and mathematical modeling of the switch leads to calculation of the accurate actuation voltage. The spring constant has been calculated in relation to the presence of the residual stress in the beam. The calculated spring constant for this beam is used to determine the accurate actuation voltage. The size of the switch is 60 ? 110 µm2. The designed RF MEMS series switch was simulated using Intellisuite MEMS tool. He calculated actuation voltage is 4.05 V and simulated one is 4.2 V for 0.6 µm beam thickness. The calculated result is also very close with simulated one. The proposed switch compared with other electrostatic switches has low actuation voltage and small size. The RF characteristics were simulated using HFSS software and the switch has good RF performance. The insertion loss of 0.067 dB, return loss of 26 dB and isolation of 16 dB were achieved at 40 GHz.

A general theory and method are presented and employed to analyze the static behaviors of rigid and deformable electrostatic actuator systems with various electrode configurations. This method utilizes capacitance-based generalized equations and provides an easy and time-saving platform over complicated coupled finite element method (FEM) simulations for pull-in analysis of a complex system. Analytical results show that the travel range of rigid electrostatic actuators can be extended by manipulating the shape of the electrode. Even a full travel range (100%) can be realized by a general power function shaped electrode. It is found that the partial actuation can avoid pull-in and reach full travel ranges with the sacrifice of the bias voltage. Analytical results of cantilever rectangular and circular actuators with a partial electrode are in good agreement with simulation results. Actuation curves of various actuators are also derived using this method. It is found that partial actuation curves are exactly the same as full actuation curves, and all types of cantilever torsion actuators with various electrode shapes follow the same actuation curve. Analytical and FEM simulations are carried out to study the pull-in behavior of deformable electrostatic actuators of three electrode configurations. The analytical results agree with FEM simulation results. It is found that the normalized deformation curves of these three electrode configurations are independent of geometry and voltage. The fringing field is considered in this analytical method.

Microwave switches are extensively used in many wireless and satellite communication systems. They are mainly used for signal routings and reconfigurations. Recently, due to the development of micro-mechanical systems (MEMS), RF MEMS switches are being widely investigated. Although RF MEMS switches have been intensively studied, limited work was done on switches that are suitable for integration in large switching networks such as switch matrices and multi-bit phase shifters [1, 2]. These switching networks require very small switches each with independent controls. Their major existing problems are the high actuation voltage and the low switch yield. High actuation voltage is undesired as a more complicated circuitry is required to provide suitable control signal. Low yield is another drawback as it could result in malfunctioning of some of the switches and thus the entire integrated system. One of the major contributions in resulting of low yield in RF MEMS switches are their dependency to the residual stress of the fabrication process both across one wafer and across batches. This problem is much more pronounced on switches with long length as they deform to their curled shape and prevent switching. In this paper, a novel type of switch is proposed that could reduce the stress sensitivity of the switch as well as providing a low actuation voltage. The overall switch structure is design with size miniaturization.

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

This study establishes the forming limit diagram (FLD) for QSTE340 seamed tube hydroforming by finite element method (FEM) simulation. FLD is commonly obtained from experiment, theoretical calculation and FEM simulation. But for tube hydroforming, both of the experimental and theoretical means are restricted in the application due to the equipment costs and the lack of authoritative theoretical knowledge. In this paper, a novel approach of predicting forming limit using thickness gradient criterion (TGC) is presented for seamed tube hydroforming. Firstly, tube bulge tests and uniaxial tensile tests are performed to obtain the stress‐strain curve for tube three parts. Then one FE model for a classical tube free hydroforming and another FE model for a novel experimental apparatus by applying the lateral compression force and the internal pressure are constructed. After that, the forming limit strain is calculated based on TGC in the FEM simulation. Good agreement between the simulation and experimental results is indicated. By combining the TGC and FEM, an alternative way of predicting forming limit with enough accuracy and convenience is provided.

Numerical simulation of the temperature distortions in InGaP/GaAs/Ge solar cells working under high concentrating conditions due to voids presence in the solder joint

This paper presents the analytical and experimental results on optimal placement of piezoceramic actuators for shape control of beam structures. The objective is to determine the optimum piezoceramic actuator locations and voltages to minimize the error between the desired shape and the achieved shape. The analytical model for predicting beam deformation due to a piezoelectric actuator is based on the Euler-Bernoulli model. The cost function has fifth-order polynomials in the actuator locations and second-order polynomials in actuator voltages. This difference resulted in difficulty in simultaneous optimization of actuator locations and voltages. Using embedded Nader and Mead simplex algorithms to separately optimize actuator locations and voltages was found to produce reliable results, converging to the same optimum solution for a variety of initial conditions. Experimental results show that the analytical model provides a reasonable prediction of actuator performance at low input voltage, but does not account for the nonlinear behavior of the piezoceramic and effects of hysteresis.

Low Actuation Wideband RF MEMS Shunt Capacitive Switch

RF-MEMS switches may be divided into capacitive and metal-to-metal types in terms of type of connection. In capacitive switches in the OFF-state the beam does not attach to the transmission line due to the presence of a thin dielectric layer and it gets released easily. Capacitive switches are better compared with the metal-to-metal types due to their ability to transmit signals of higher frequency and power. In this paper, a novel RF MEMS shunt capacitive switch with a unique spring design is proposed. The proposed design benefits from high isolation, low loss, low actuation voltage, small size and weight compared to similar switches and is designed for application in the Ka-band. Step structure is used in the mechanical design of the switch to reduce the air gap between the bridge and the transmission line that has resulted in reduction of actuation voltage to 2.2 V. The proposed switch has been placed upon a coplanar waveguide (CPW) line with an impedance of 50 Ohms. $${\text{SiO}}_{2}$$ with a thickness of 1000 A has been used as dielectric to increase isolation and down-state capacitance. The unique design of the spring results in the reduction of stress to a minimum at all points of the switch especially the springs at the time of applying the actuation voltage. This advantage would reduce switch failures as time passes and results in increased life of the switch. Up-state capacitance is 93.3 fF and down-state capacitance is 2.64 pF. Therefore, a capacitive ratio of 28 is obtained. The dynamic behavior of the switch is studied by using the COMSOL Multiphysics software package and the RF characteristics have been obtained by using the HFSS software and show good RF performance. The results show that in the up-state, the designed switch including S11 is less than − 11.5 dB and S21 is more than − 0.85 dB at 1–40 GHz. In the down-state, the switch has excellent isolation in the Ka-band. Maximum isolation is − 71 dB that occurs at the resonance frequency of 30.5 GHz.

We report the first ever silicon carbide (SiC) nano-electro-mechanical systems (NEMS) switches capable of operation from 25 to 600degC. We have developed both laterally- and vertically-actuated designs with threshold voltages of less than 5 V. Switches have been verified to cycle more than 3 billion times at room temperature and more than 2 million times at 600degC. Plausible models to describe the contact resistance in two actuation voltage regimes are also suggested: (i) at low actuation voltage, the resistance is dominated by the native oxide which forms on the SiC surface; and (ii) at higher actuation voltages, the resistance can be described by Sharvin's model.

A vertical RF-MEMS (Radio Frequency Micro ElectroMechanical Switch) switch design is proposed in this work that features a shunt capacitive configuration and can operate at a very low actuation voltage. Besides operating on a low switching voltage, the switch behold a small value of insertion loss in Up (ON) state and offers a towering isolation factor in Down (OFF) state. A horizontal structure of bridge membrane is used in the proposed design and the switch function (with ON and OFF operating states) is provided by the vertical movement of this membrane structure that is controlled by the electrostatic actuation technique. The actuation pad is centrally fed by a Coplanar Waveguide structure. The switch performance has been analysed over a wide frequency range from 1 to 40 GHz. For obtaining a 1.5 μm vertical displacement of the bridge membrane, a sheer 3.0 Volts of pull-in voltage (VPI) is required. CoventorWare and HFSSv13 tools are used in this work for designing and analysing the proposed switch. The use of fixed-fixed flexure beam configuration is chosen for switch design. Simulation results showcase excellent RF characteristics with isolation factor of −47 dB (at 32.5 GHz) and insertion loss in range of −0.01 to −1.10 dB (for 1−40 GHz frequency).

In this work, low voltage MEMS variable capacitor was presented. Compare with other RF MEMS technologies, piezoelectric MEMS devices offer certain benefits such as low actuation voltage and fast moving, etc. The proposed structure consists of dual piezoelectric actuation bridges of in-plane polarized lead zirconate titanate (PZT) film to improve actuation voltage and reliability of devices. The PZT thin film, deposited on Au structural layer using RF magnetron sputtering method, was poled and driven with interdigitated electrodes(IDEs) to exploit dSUB33/SUB mode actuation. The in-plane polarized PZT films make it possible to develope dSUB33/SUB mode bending devices which lead to about two times improvement in strain performance. The fabricated variable capacitor shows that the tuning range is varied 100.9 to 111.2 nF with control voltage ranging from 0 to 1 V.

This paper reports the design, fabrication, electrical characterization and packaging of micromachined shunt capacitive switch with low actuation voltage. These switches are fabricated on a low resistive silicon substrate using only a four mask surface micromachining process. The co-planar waveguide is patterned using chrome/gold layer. Positive photoresist S1813 is used as the sacrificial layer. The top beam membrane is made of gold. The membranes are released through a wet release process through Piranha solution. Supercritical point drying tools were used for the top beam release after wet etching to provide anti-stiction. The switches are 300 µm long with 10 μm holes on the top membrane to lower both residual stress and pull-in voltages. These switches exhibit low actuation voltages in the range of 5.5–6.4 V. The RF characterization shows that these switches have low insertion loss and high isolation in the frequency range of interest. The packaging was carried out using commercially available surface mount style RF packages. However, the whole packaging process is performed under low temperature in order to free the MEMS structures of thermally induced stress which otherwise would affect the performance of the switch. The adhesion of the die to the bottom package is excellent and is tested by die shear test. The packaged switch has passed the non-destructive pull test.

Thermal analysis for bulk-micromachined electrothermal hydraulic microactuators using a phase change material

In the last forty years the semiconductor industry focused on the downscaling process of the CMOS (Complementary Metal-Oxide-Semiconductor) technology, trying to follow as much as possible the empirical Moore's Law. In the last five years this trend has been facing technology limits that have led to the development of a new research field, named Beyond CMOS, which investigates new electron devices concept and materials that can replace or co-integrate the standard technology, to make large scale integrated (LSI), high performance, low power devices. Carbon nanotubes (CNTs) are considered one of the most promising materials for Beyond CMOS devices, both at front-end and back-end level. The development of the research on this new organic material is due to its nanometer scale dimensions and to its outstanding electrical (metallic and semiconducting behavior, ballistic conduction, current density > 109 A/cm2) and mechanical (Young's modulus ∼1 TPa) properties, nevertheless due to its low mass (mass density ρ = 1300 kg/m3). Among the several CNT applications already reported in literature (interconnections, sensors, transistors, memory, etc.), a particular interest is on their use to build Nano-Electro-Mechanical (NEM) devices, such as resonators and switches. NEM relays based on carbon nanotubes show large-current density drive and high speed operation compared to metal-based NEMS counterparts, low actuation voltage and low power, performances which are promising for radio-frequency (RF) applications, where RF MEM devices are considered as replacement solution for their off-chip and/or solid-state counterparts in front-end transceivers. Most of the previously reported CNT NEM switches concerns relay configuration based on one single movable nanotube and its DC characterization. Despite individual proof-of-concept merits, an electromechanical switch based on a single CNT usually presents an output signal level that is too low for practical applications and a poor reliable fabrication process, which opposes the precise control at wafer level achieved by standard technology. Alternatively, a very large-scale integration of NEM devices requires the exploitation of high-density aligned arrays of nanotubes, grown in precise locations and that could be patterned into well-defined and controlled configurations. The objective of this research work was to develop LSI NEM switches based on high dense carbon nanotube arrays in the back end of the line (BEOL), with conductive and capacitive contacts and tested from DC up to high frequency (RF), in order to evaluate their performances in a wide range of operations. The synthesis process of carbon nanotubes was performed by thermal CVD and temperature, gas concentration and catalyst pretreatment were optimized to achieve high dense aligned CNT arrays. A study on the catalyst geometries and on the substrate materials were performed in order to obtain horizontal aligned arrays grown directly on metallic substrate without density change. We developed a novel surface micromachining process to suspend CNT arrays. The DC characterization of CNT NEM switches was exploited to extract the equivalent electromechanical properties of the CNT membranes, since they behave as a new body material. We extracted an equivalent flexural modulus of 8.5 GPa and a resistivity of 0.0077 Ωcm. The devices, in both configurations, present a very low actuation voltage, below 10 V, lower than typical metal NEM switch for the same dimensions and a comparable switching time. The RF characterization was performed in the telecommunication frequency range (up to 6 GHz) showing reasonably high isolation and low insertion loss. The relay shows a lower reliability than the capacitive switch, due to the elevated drive current which induces the CNTs burning at the metal-to-metal interface. The RF measurements were used to extract the parameters of the proposed devices equivalent lumped model. Several implementations of CNT NEM switches, both for DC (reconfigurable interconnects, logic functions, memories) and RF (signal routing purposes in RF system Front-Ends, phase shifting networks or digitalized capacitor banks) applications, were reported.