Simulation of Cantilever RF MEMS switch

Transcription

1 International Research Journal of Applied and Basic Sciences 2014 Available online at ISSN X / Vol, 8 (4): Science Explorer Publications Simulation of Cantilever RF MEMS switch Gholamhosein Moloudian *1, Mohammad Amin Pirbonyeh 2 Sama technical and vocational traning collage,islamic Azad Universiy, kazeroun branch kazeroun, Iran *Corresponding Author gholamhosein_movludian@yahoo.com ABSTRACT: the RF MEMS switches are series switches type and are designed using physical level approach by using 3D MEMS commercial software package, Intellisuite. These switch structures are first designed using 2D layout which then is converted to 3D model to simulate the actuation voltage. In this paper, we design and simulate RF MEMS switch in suspension cantilever mode. We chose the transmission line of type micro strip. High performance RF MEMS switch with low voltage actuation, 10 V was successfully designed and simulated. INTRODUCTION Micro-electromechanical switches, or in brief RF MEMS switches, are widely used in telecommunications and satellite communications. Switches which are manufactured by utilizing MEMS technologies and with cost much less than other switches, are the best alternative for conventional switches such as field-effect transistors made of Gallium Arsenide, as well as p-i-n diodes for utilization in telecommunication systems in rather high radio frequencies. Technological advances in radio-frequency (RF) front -ends made all the things to work under RF applications. Great effort is made in developing high frequency low scale designs to follow the trends of the market for smaller, technologically more advanced applications. The electrostatic actuation mechanism for the excitation has some merits such as fast response and simple drive electronics. RF microelectromechanical systems (MEMS) switches have demonstrated outstanding RF performance with very low insertion loss, high isolation, excellent linearity, and very low power consumption, which make them very attractive for modern radar and telecommunication applications (Ming-jer lee et al. 2010). Fixed fixed beams and cantilevers are the most popular switch structures ( G.M.rebiz et al. 2001). RF MEMS is the application of micro electromechanical systems in radio frequency circuits. The utilization of RF MEMS helps fulfill the increasing demand for more flexible and functional, lightweight, and low-power-consumption wireless systems. RF MEMS switches are one of the applications of RF MEMS (y.mafinejad et al. 2009). Radio frequency micro-electro-mechanical systems (RF MEMS) are a technology that offers low insertion loss, high isolation, and low power consumption with improved functionality. Micromachined beam structures are the basic building-block of many RF MEMS devices and components like switch, phase shifter, varactor etc. (Bao 2005; Nathason et al. 1967; Peroulis et al. 2003; Rahman et al.2009; De Los Santos 2004). In past, a large number of papers had been published on the development of RFMEMS switches based on the principle of electrostatic actuation. However, these switches operated at higher voltage than their conventional counterparts (Bao 2005; Nathason et al. 1967; De Los Santos 2004). RF MEMS Switches Basically, there are two distinct parts for an RF MEMS switch: the actuation (mechanical) section and the electrical section. Mechanical part of RF MEMS switch can be operated using four mechanisms, which is electrostatic, thermal, magnetic, and piezoelectric. However, this paper will describe the RF MEMS series using electrostatic mechanism. RF MEMS switch can also move in two directions, which is vertically or laterally, depends on the requirement and it is also can be designed in series or shunt configurations which use metal-to-metal or capacitive contact. Figure 1 shows the side view of a standard RF MEMS series switch. When a certain amount of voltage is applied between bottom electrode and the pull down electrode, electrostatic force is created and will pull the cantilever down from the arm of anchor and complete the RF signal path at down-state. Short circuit occurred between two terminals of RF transmission line has made the RF signal can pass through and transmitted. Figure 1 shows the side view of a standard RF MEMS series switch.

2 Figure 1. RF-MEMS direct contact cantilever switch. In RF MEMS switch, there are several properties need to be considered in mechanical modeling, such as spring nstant of the beam, critical stress issues, and hold-down voltage.rf MEMS can be classified into different categories on the basis of circuit configuration, actuation principle, moving structure or desired application. The most common categories ofmems switches are series and shunt switches. Fig. 2 shows the series and shunt configuration of MEMS switch. On the basis of moving structure, MEMS switches can be of cantilever and suspended bridge types. In this paper, suspended bridge configuration is taken under consideration as actuation voltage issues are more dominant in this type of configuration. Suspended bridge is mostly effective in shunt circuit configuration (G.M. Rebeiz et al. 2001). a b Figure2. (a) Series switch configuration (b) Shunt switch configuration. Electrostatic Actuation An electrostatic force is induced on the beam when a voltage is applied between a fixed-fixed or cantilever beam and the pull down electrode. The electrostatic force exists in the plates of a capacitor under applied voltage. The beam over the pull down electrode is modeled as a parallel-plate capacitor in order to approximate the electrostatic force (Haslina Jaafar et al. 2011).When the width of beam is w and the width of pull down electrode is W, the parallel capacitance is : = 0 = 0 The basis of this excitation is that by applying the voltage between panels and creating opposite charges in both panels, based on the gravity available between panels of an electric field and finally, an electrostatic force is created which causes the panels to be absorbed by each other. By applying the voltage between two panels, we create an electric force which causes the moving panel to be drawn downward and causes short circuit in the transmission path. The voltage in which, the distance between two panels is equal to 0.66 of total distance, is called pull-down voltage or V p. this voltage is one of the most important parameters in switch parameters. = 8 h h 27 2 h

3 fabrication process of RF MEMS Switch For simulating manufacturing process of RF MEMS capacitive switch, we use Intellisuite software. By using 3Dbuilder, we design the switch with several different layers. Level0 : si Level1: transmission line & post & down electrod Level2 : transmission line & post Level3: post & oxide Level4 Level5 Level6 Level7 Figure3. steps of fabrication cantilever switch After designing switches, we must perform thermo-electromechanical analysis, which is given in the next chapter. 444

4 RESULTS OF SWITCH ANALYSIS actuation voltage is one of the most important parameters in RF MEMS switch.most people who work on RF MEMS switches are looking for a way to reduce this voltage. Schematics of designed switches are given in Fig 4. Figure4. Schematic of designed switch This simulation measures the voltage needed to pull the beam down to the RF lines. This simulation used ther- mo Electro Mechanical Analysis (TEM) module to calculate the voltage needed. Figure4 show the switch design and z-displacement vs. voltage actuation result respectively. This simulation used the air gap of 1 μm. From the graph, the voltage obtained is 10 V which is low and meet the requirement. Figure5. Bending of beam Figure6. Diagram of distance of z according to applied voltage for switch CONCLUSION High frequency switches wildly have applied in defense aerospace and wireless communication, radar systems application. High performance RF MEMS switch with low voltage actuation, 10 V was successfully designed and simulated. Few switches were designed using physical level approach, 3D Builder (3DB), and were then simulated using Thermo ElectroMechanical Analysis (TEM) and Electromagnetic and RF Analysis (Emag) modules from Intellisuite. 445

5 REFERENCES Bao M Analysis and design principles of MEMS devices Elsevier Publication, Amsterdam, De Los Santos HJ Introduction to microelectromechanical (MEMS) microwave systems, 2nd edn.artech House, Boston, Haslina J, Fong LN, Nurul Amziah Md Y '' Design and Simulation of High RF MEMS Series Switch'', RSM2011 Proc.,, Kota Kinabalu, Malaysia, /11/$ IEEE Hyman D,et al '' GaAs-compatible surface-micromachined RF MEMS switch'', Electron Lett Katehi LPB, Harvey JF, Brown E MEMS and micromachined circuits for High- Frequency applications '' IEEE MTT,Vol. 50, No. 3, PP Mafinejad Y, Kouzani AZ, Mafinezhad K, Izadi D Design and Simulation of a RF MEMS Shunt Switch for Ka and V Bands and the Impact of Varying Its Geometrical Parameters, /09/$ IEEE Ming-Jer L, Yang Z, Changwon J, Mark B, Franco DF, Li GP A Novel Membrane Process for RF MEMS Switches, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 19, NO. 3, JUNE Nathason MC, Newell WE, Wickson RA, Davis JR The resonant gate transistor. IEEE Trans Elec Dev 14: , Peroulis D, Pacheco SP, Sarabandi K, Katehi LPB Alleviating the adverse effects of residual stress in MEMS switches. In:31 European microwave conference, pp 1 4, Peroulis D, Pacheco SP, Sarbani K, Katehi LPB Electromechanical considerations in developing low- voltage rf mems switches. IEEE Trans MTT 51: , Rahman H, Chan KY, Ramer R Investigation of residual stress effects and modelling of spring constant for RF MEMSswitches, Presented at microwave symposium (MMS), Rebeiz GM, Muldavin JB RF MEMS switches and switch circuits, IEEE Microw. Mag., vol. 2, no. 4, pp , Dec. Rebeiz GM, Muldavin JB RF MEMS switches and switch circuits,ieee Microwave magazine, pp