Design and Simulation of Micro-cantilever

Transcription

1 Design and Simulation of Micro-cantilever Suresh Rijal 1, C.K.Thadani 2, C.K.Kurve 3,Shrikant Chamlate 4 1 Electronics Engg.Dept.,KITS,Ramtek, 2 Electronics and Comn.Engg.Dept.,KITS,Ramtek, 3 Electronics Engg.Dept.,KITS,Ramtek, 4 Electronics and Comn.Engg.Dept.,KITS,Ramtek, Abstract Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common substrate through the utilization of micro-fabrication technology or micro-technology. By definition A cantilever is a beam supported on only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevered beams are the most ubiquitous structures in the field of micro-electromechanical systems (MEMS). MEMS cantilevers are commonly fabricated from silicon (Si), silicon nitride (Si 3 N 4 ), or poly-silicon. The fabrication process typically involves undercutting the cantilever structure to release it, often with an anisotropic wet or dry etching technique. Keywords MEMS, cantilevers, anisotropic etching, ansys. I. INTRODUCTION The term MEMS refers to a collection of micro-sensors and actuators which can sense its environment and have the ability to react to changes in that environment with the use of a microcircuit control[1]. An effort to miniaturize sensors and actuators for the purposes of reducing size, weight, energy consumption, and fabrication cost. Integrating micro-machines and microelectronics on the same chip is possible. In many cases, obtain better device performance than macro equivalent. MEMS made micro-sensors are used for measuring physical parameters. Transducer is a basic building block of a sensor, which senses the physical change and gives corresponding response which is measureable and converts the measureable response into electrical signal with use of specific transduction principle. Micro-cantilevers and beams are very useful transducer elements,using which many physical changes can be measured. The main principle is the deflection of the beam and cantilever structures. The deflections are sensed either by capacitive or piezoresistive measurement [2]. The difference between a beam and a cantilever is that a beam is fixed at both the ends whereas a cantilever is fixed at only one end. This paper shows the effects of variation in different materials and compares the output simulation results for silicon, poly-silicon, and silicon nitride using Ansys13.0. II. DESIGN PARAMETERS OF CANTILEVER BEAM Cantilever beam has one end fixed and second is freely moveable to deflect as per provided load. The cantilevers have more length as compare to width and have optimal thickness. Without load the cantilever is at the resting state and therefore initially it is horizontal and straight [3]. When force is applied the horizontal axis of the beam is deformed into a curve. Deflection of cantilever depends on length of cantilever, cross-sectional shape of beam and type of material used. Cantilever deflection also depends on the point where load is applied and supporting mechanism of the beam. A Micro-cantilever is a device that can be used as physical, chemical or biological sensor by detecting the changes in cantilever bending or vibrational frequency. DOI: /IJRTER SGT0A 197

2 Among those two equations first one is Stone s equation, which relates cantilever end deflection δ to applied stress σ and it indicates that the end deflection of cantilever beam is directly proportional to the applied stress. Where ϑ is Poisson s ratio, E is the Young s modulus, L is the beam length and t is the cantilever thickness [4]. The second formula relates the spring constant k to the cantilever dimensions and material constants: δ = ( ) (1) K = = (2) Where F is the force and w is the cantilever width. The deflection of the cantilever beam depends up on the dimensions of the beam i.e., length, width, thickness and also depends on various properties of the material used to build the cantilever. Equations for deflection of cantilever, when load is applied at the end: d(x) = () (3) Equations for maximum deflection of cantilever, when load is applied at the end: dmax = d(l) = (4) Equation for deflection of cantilever, when point load is applied at the intermediate point: d(x) = 0 x a (5) = $ a x L (6) ($) Equation for maximum deflection of cantilever, when point load is applied at the intermediate point: dmax = d(l) = $ ($) (7) III. Design of Micro-cantilevers A popular method of designating planes and orientations is the Miller indices. These indices are effectively used to designate planes of materials in cubic crystal families [5]. The comparative analysis of change in material of the cantilevers is performed and the change in stress, strain, and total deformation of cantilevers is formed, which proves the provided equations. Table1. Respective change in resultant stress, strain and total deformation with change in material of cantilevers. Material Properties Material Names SiO 2 Si 3 N 4 Poly-si Young s Modulus(Pa) 70E9 250E9 160E9 Density(Kg/m 3 ) Poisson s Ration Length(µm) Width(µm) Height(µm) Force(N/m 2 ) 1 1 All Rights Reserved 198

3 Equivalent 2.54E E E12 Stress (Max.) Equivalent Strain(Max) Total Deformation(Max) Figure 1: Micro-cantilever ansys geometry view Figure 2: Micro-cantilever total deformation for SiO All Rights Reserved 199

4 Figure 3: Micro-cantilever equivalent stress for SiO 2. Figure 4: Micro-cantilever equivalent elastic strain for SiO 2. IV.CONCLUSION With the change in materials of cantilevers respective change in total deformation, equivalent stress and equivalent elastic strain is All Rights Reserved 200

5 II III IIII IIV IV REFERENCES Suryansh Arora, Sumati, Arti Arora, P.J George, Design of MEMS based Microcantilever using Comsol Multiphysics, Applied Engineering Research, Vol.7 No.11, Maziar Norouzi, Alireza K, Design of Piezoelectric microcantilever Chemical Sensor in Comsol Multiphysics Area, Electrical and Electronics, Vol.2, issue 1, No.184, Nitin S.Kale, V.Ramgopal Rao, Design and Fabrication Issues in Affinity Cantilevers for biomems Applications,Micro Electro Mechanical Systems,VOL.15,NO.6,2006. Anchit J.Kaneria, D.S.Sharma, R.R.Trivedi. Static Analysis of Electrostatically Actuated Micro Cantilever Beam, Procedia Engineering 51, 2013, pp Robert Littrell et.al. : Modelling and Characterization of cantilever based MEMS piezoelectricsensors and actuators, JournalofMicroelectromechanical Systems Vol.21 No.2 pp All Rights Reserved 201