Modeling and Simulation of RF MEMS devices

2009

In the last 5-10 years, the high frequency (RF) applications of MicroElectroMechanical Systems (MEMS) devices have reached significant progress, because of their low price, technology, matched with the ordinary microelectronic technologies, good RF parameters and yield. The process of research, investigation and design of RF MEMS switch are presented. The results from this process, in connection with the design of ordinary RF coplanar transmission line, interrupted RF coplanar transmission line and their combination with a contacting metal electrode are shown.

The design of RF MEMS switches involves several disciplines: mechanics, materials science and electrical engineering. While significant progress has been made in the RF design of the switches, mechanical and material studies are required for mass commercialization of reliable devices. Senturia and co-workers at MIT have presented a closed form solution to describe the electromechanical behavior of a fixed-fixed switch. However, in some practical applications, multi-domain simulations are required to account for membrane shape, non-uniform state of residual stress, temperature and other effects. In this presentation, we will describe the modeling and simulation of MEMS switches and discuss their electromechanical performances. The switch, bottom electrode and surrounding air were all included and meshed in the model. Iterations between the electrostatic and structural analyses were performed until the solution converged. The developed method is applicable to all types of electrostatic switches, though the design of a capacitive coupling shunt switch has been examined.

2014 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS (DTIP), 2014

This paper presents the design, optimization and simulation of a radio frequency (RF) micro-electromechanical system (MEMS) switch. The device is a capacitive shuntconnection switch, which uses four folded beams to support a big membrane above the signal transmission line. Another four straight beams provide the bias voltage. The switch is designed in 0.35µm complementary metal oxide semiconductor (CMOS) process and is electrostatically actuated by a low pull-in voltage of 2.9V. Taguchi Method is employed to optimize the geometric parameters of the beams, in order to obtain a low spring constant and a robust design. The pull-in voltage, vertical displacement, and maximum von Mises stress distribution was simulated using finite element modeling (FEM) simulation-IntelliSuite v8.7 ® software. With Pareto ANOVA technique, the percentage contribution of each geometric parameter to the spring constant and stress distribution was calculated; and then the optimized parameters were got as t=0.877µm, w=4µm, L1=40µm, L2=50µm and L3=70µm. RF performance of the switch was simulated by AWR Design Environment 10 ® and yielded isolation and insertion loss of-23dB and-9.2dB respectively at 55GHz.

Journal of Electromagnetic Waves and Applications, 2012

This paper deals with a general analytic approach for the design of RF microelectromechanical system (MEMS) switches. The chosen configuration for these microwave devices is composed of twocoplanar transmission line sections separated by a metal membrane providing a shunt connected variable impedance. Using a bias voltage it is possible to actuate the switch. The adopted methodology for the development of the circuital model is based on the image impedance parameter representation of a two-port network. Synthesis equations are presented, and design considerations are discussed. The proposed approach is validated by means of electromagnetic simulations.

Mechanical modeling of RF MEMS switches is important for performance optimization and device reliability. 1-D, 2-D, and 3-D linear analytical models have been proposed to analyze the electrostatic pull-in of a fixed-fixed beam at small deflection. However, most RF MEMS switch structures work at large deflection range. In this paper, 1 -D, 2 -D, and 3 -D nonlinear analytical models suitable f or large structural deflection are developed in a generalized form. In some practical applications, finite element models are required to account for the effects of all the design parameters: switch geometry, non-uniform state of residual stress, temperature and etc. A 3-D finite element model between structural, electrical and thermal domains is developed. This 3 -D model is applicable to the design of all types of electrostatic actuators, though that of a capacitive coupling switch was examined.

RF-MEMS is a promising technology that has the potential to revolutionize RF and microwave system implementation for next generation telecommunication applications [1]. In this paper, a MEMS capacitive shunt type switch is design and analyzed for RF applications. This new switch design focuses on the failure mechanisms restriction, the simplicity in fabrication, the power handling and consumption, as well as controllability with electromagnetic characteristics. The MEMS switch is designed in both ON and OFF states. The proposed MEMS switch has dimension of 508 µm × 620 µm with a height of 500 µm and implemented on GaAs as a substrate material with relative permittivity of 12.9. The electrostatic and electromagnetic analyses of the designed RF-MEMS Switch have been performed using Ansoft High frequency structure simulator (HFSS) electromagnetic simulator tool.

2010 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF), 2010

An RF-MEMS capacitive switch for mm-wave integrated circuits, embedded in the BEOL of 0.25µm BiCMOS process, has been characterized. First, a mechanical model based on Finite-Element-Method (FEM) was developed by taking the residual stress of the thin film membrane into account. The pull-in voltage and the capacitance values obtained with the mechanical model agree very well with the measured values. Moreover, S-parameters were extracted using Electromagnetic (EM) solver. The data observed in this way also agree well with the experimental ones measured up to 110GHz. The developed RF model was applied to a transmit/receive (T/R) antenna switch design. The results proved the feasibility of using the FEM model in circuit simulations for the development of RF-MEMS switch embedded, single-chip multi-band RF ICs.

Advances in Science, Technology and Engineering Systems Journal

Microelectromechanical Systems (MEMS) are devices made up of several electrical and mechanical components. They consist of mechanical functions (sensing, thermal, inertial) and electrical functions (switching, decision making) on a single chip made by microfabrication methods. These chips exhibit combined properties of the two functions. The size of system has characteristic dimensions less than 1mm but more than 1μm. The configuration of these components determine the final deliverables of the switch. MEMS can be designed to meet user requirements on any level from microbiological application such as biomedical transducers or tissue engineering, to mechanical systems such as microfluidic diagnoses or chemical fuel cells. The low cost, small mass and minimal power consumption of the MEMS makes it possible to readily integrate to any kind of system in any environment. MEMS are faster, better and cheaper. They offer excellent electrical performances. MEMS working at Radio frequencies are RF MEMS. RF-MEMS switches find huge market in the modern telecommunication networks, biological, automobiles, satellites and defense systems because of their lower power consumptions at relatively higher frequencies and better electrical performances. But the reliability is the major hurdle in the fate of RF MEMS switches. Reliability mainly arises due to the presence of residual stresses, charging current, fatigue and creep and contact degradation. The presence of residual stresses in switches the S-Parameters of the switches are affected badly and the residual stress affects the final planarity of the fabricated structure. Design and simulation of an RF-MEMS switch is proposed considering the residual stresses in both on and off state. The operating frequency band is being optimized and the best possible feasible fabrication technique for the proposed switch design is being analyzed. S-Parameters are calculated and a comparison for the switches with stress and without stress is performed in FEM based HFSS software.

2008 9th International Conference on Solid-State and Integrated-Circuit Technology, 2008

In the following, we first present the results of device simulation in order to deepen our understanding of the device behavior. Then the modeling of the two types of CMOS-compatible MEMS inductors is presented, respectively. Finally, we conclude the modeling methodology of CMOS-compatible RF-MEMS devices for integrated circuit design. Fig. 1 Post-CMOS micromachining steps: (a) after completion of CMOS, (b) protective photoresist layer and anisotropic dry oxide etching, and (c) the isotropic dry silicon etching and structural release [3]. high Q inductor device as shown in Fig. 2 [4]. The details of the fabrication of this MEMS inductor can be found in [4].

Sensors and Actuators A: Physical, 2005

This work focuses on electrostatically actuated micro-electro-mechanical systems (MEMS) capacitive switches, intended for adaptive output stage of power amplifiers. These devices are particularly attractive because theoretically they are capable of very high quality factor values due to the air gap between plates and the low resistivity of lines and bridge. On the other hand, substrate parasitic effects, overlooked up to date, can seriously impair device performance. In this paper, we introduce a lumped element equivalent circuit taking into account substrate effects. Model validation is based on measurements carried out in the 50 MHz-40 GHz range.