MEMS Based Lateral Mode Free-Free Beam Resonator

Transcription

1 MEMS Based Lateral Mode Free-Free Beam Resonator Jyoti Yadav 1, Neelam Yadav 2 1 Dronacharya College of Engineering, Gurgaon, 2 St. Margret Engineering College, Neemrana Abstract: MEMS based on mechanical resonators and filters contain exposed gifted characteristics in achieving high-q principles with high-quality constancy. The choice of frequency process depends on the magnitude of the construction over and above the substance used. The plan of a mechanical filter involves essential philosophy of physics, sensations, electromechanical transduction and filter circuitry. This paper presents filter designs in addition to afterward study of the structures. Laterally vibrating Free Free Beam Resonator enclose High Q factor at inferior frequency through smallest amount of anchor lossextremely suitable designed for make use of communication s-grade oscillators with frequency filters. Keywords: MEMS, Beam Resinator, filter, Q factor. 1. INTRODUCTION: Filter design is an essential fraction of some electrical arrangement plan with analysis. Electronic filters are electronic circuits which be able to execute signal processing functions, particularly to eliminate unnecessary frequency mechanism from the signal, to improve required ones, or both. Filters developed by means of dissimilar combinations of MEMS structures are MEMS filters, designed for the identical purposes. MEMS filters are to some extent dissimilar in the sense that at this time both electrical in addition to mechanical properties of structures decide the filter properties. MEMS filters can be seen as a probable complement to conventional electronic filters while it comes to convinced compensation of MEMS for example near to the ground power utilization. The design of an assortment of elements of MEMS filters is ambitious by the necessities of bandwidth along with its cut-off frequencies. The main compensation obtainable by MEMS filters are as follows: Low power consumption High Quality (Q) issue Chip integration ability Integration by means of conventional CMOS circuitry Smaller dimension The major point of the paper is to approach through designs which are reasonable by means of fabrication view intended for MEMS filters. After doing a literature survey, designs were planned by way of a quantity of adjustment. Finally analysis of a meticulous design was complete from side to side computer simulations. We design the Free Free Beam Resonator with high Q factor 2. WORKING PRINCIPAL: The electrostatic excitation mechanism and capacitive finding technique allows the straight employ of these resonators in merely electrical situation, since both input and output signals are electrical. Actually the resonator can be modeled in a straight line by means of an electrical representation whose electrical parameters are straight associated to physical parameter. Amongst the diverse excitation and readout techniques, electrostatic excitation and capacitive detection offers a straight electrical signal processing, which is favored to put back electrical components in the RF front end, low down power consumption, manufacture them potentially appropriate for battery operated and straightforward of fabrication and compatibilization in a typical CMOS technology. 2.1 PROCESS: Ordinary procedure has the universal features of a normal surface micromachining process as follows: Polysilicon is used as the structure material Deposited silicon oxide is used as the sacrificial layer, Silicon nitride is used as electrical separation between the polysilicon and the substrate, Metal (usually gold) is the top layer of the device and be able to used as conductive layer. Figure 2.1 show a very rough impression of process flow is obtainable. Merely major steps are exposed in the flow chart. Disadvantages of MEMS filters: Dispensation on Si wafer Inferior consistency lesser power handling aptitude Volume 2, Issue 6 November December 2013 Page 34

2 2.2 ELECTROSTATIC EXICITATION: This work is mostly composed on a vibrating fraction (the resonator) in addition to two permanent electrodes (the excitation electrode and readout electrode). The schematic figure of a distinctive electro statically operated two port free free beam resonator is shown in Figure Fig:2.2.1 Lateral Mode Free Free beam resonator During this topology, a time-carrying signal (V in) is functional to the excitation electrode while the resonator is biased on a unchanging DC voltage. These signals produce energy (f o ) resting on the resonator at the identical frequency of the V in signal. This f o provokes the dislocation of the resonators stipulation the practical AC signal have a incidence close to natural resonance frequency of the mechanical construction, which resolute by physical magnitude. The pressure group of the resonator changes the value of the existing capacitor flanked by resonator and readout electrode, this vibration of the capacitor generates a current in this electrode. Significant physical extent are shows: Beam Width(W r ), Beam Length(B r ), Supporting Beam Width(W s ),Supporting Beam Length(B s ), Thickness(h), Electrode Width(W e ), Dc Bias Voltage (V p ),Gap Spacing (d o ). It can be experimental that there are two capacitors present stuck between the excitation electrode and the resonator beam (C g ) as well as a different one between the resonator and read-out driver (C g ). These capacitors can be uttered (intended for small resonator beam deflection) by means of parallel plate capacitors: C g = ε A / (d 0 +x) C g = ε A / (d 0 -x) Where ε is the electrical permittivity of the medium, A is the coupling region between the resonator and the electrodes, (A= L h) and x is the displacement of the resonator. The exerted force (Allowing for very little displacement) has three components (a) DC component which deflects the beam (b) A constituent of frequency equivalent to the input signal (c) An additional to double the V i frequency. Note that a DC voltage is necessary to actuate the beam at the similar frequency than the input signal. The output current is the amount of the resonance current and the parasitic current. The merely dissimilarity is that currently, the parasitic capacitance from AC input signal to output current signal is agreed by the fringing capacitance sandwiched between excitation and read-out driver. In arrange to get hold of high Q values: high k ( i. e. stiff devices), high m (i.e. big devices also consequently of low frequency) with low damping are desirable, while for high frequency devices elevated stiffness as well as low mass are essential. Due to these constrains single of the figures of merit for MEMS resonators is the Q-frequency invention, which be obliged to the uppermost probable. 3. Theory: The resonator consists of a free-free beam balanced at its nodal locations by four flexural hold up beams. Electrodes on the sides of the resonator beam permit electrostatic excitation and capacitive detection of induced vibrations. The support beams are planned in such a method that composite beams (grouping of two support beams) resound in a subsequent mode at the fundamental mode frequency. This suppresses energy losses from free-free beam to the support anchors and as a result allows a resonator to attain a high Q. To hold back energy losses from the FF-beam to the support anchors, the support beams are actually designed so as to the composite beams attained by combining two support beams on conflicting sides of the FFbeam (from anchor-to-anchor) vibrate in a subsequent mode at the fundamental mode frequency of the FFbeam. With this design, the beam attachment locations correspond to nodal points for together the composite support beams and the FF-beam resonator, creating a far above the ground (ideally infinite) impedance location through which very small energy is transferred, hence, through which very little energy is dissolute. This allows the resonator system to achieve a very high Q, regardless of the high stiffnesses of its constituent beams. Figure 3.1shows the SEM image of lateral free free beam resonator [16]. Fig:2.2.2 Two port resonator through capacitors between resonator and excitation drivers Volume 2, Issue 6 November December 2013 Page 35

3 When the support beams are calculated as described above, the expression for resonance frequency f o of the beam in Fig takes on that for an idyllic free-free beam. The real resonance frequency will actually be a function of the electrical stiffness k e generated through the parallel-plate capacitive transducers, and is specified by Where f nom is the resonance frequency of an idyllic FFbeam in the absence of electromechanical coupling, and <k ei /k m > and <k eo /k m > are mechanical-to electrical stiffness ratios related with the input and output electrodes, correspondingly, and dependent upon the values of dc-bias voltage V P and electrode-to-resonator gap spacing d o. 3.1 Support Beam Design: For a given FF-beam resonance frequency fo= 1.03 sqrt (EW r /ρl r 2 ), the composite support beams shake in their second modes while their lengths are preferred to satisfy Where E and ρ are the Young s modulus and density, respectively, of the structural material, and Ws and Ls are indicated in Figure 3.2 Equivalent circuit: The free-free beam is modeled using 3 'Beam' components associated in series. These are the 3 horizontally aligned beams in the diagram shown in Figure. The flexural support beams are also modeled using 'Beam' components. Every support beam is modeled using a solitary linear beam. The support beams are attached to the free-free beam at nodal locations. The electrodes used for exciting the free-free beam are designed using 'Side Electrode' components from the library. There are two side electrodes (a drive and a sense) in the diagram, one on moreover side of the freefree beam. A dc' and a 'sinusodial' voltage source are used for exciting the resonator. Thermo-elastic damping is included to model energy loss in the beams. Fig 4.2 Displacement contour plot of a Free Free Beam Resonator simulated on Coventor Ware 2010 [2] 4.1 Lateral Free Free Beam Design Summary For this exacting simulation, the values of various parameters are as follows: Material: Polysilicon Design Parameters 10MHz 20 Unit MHz FF-Beam Length, L r μm FF-Beam Width, W r 2 2 μm Fig:3.2.1 Equivalent circuit of Free Free Beam Resonator Where C x, L x and R x are capacitance, inductance and motional resistance. 4. SIMULATION ON COVENTOR WARE: Architect is used to construct a fully parametric 3D model of the resonator by means of beams and side electrodes from the Parameterized Electromechanical Parts Library. Figure shows the schematic of the resonator Support Beam Length, L s μm Support Beam Width, μm W s Thickness 2 2 μm Electrode Width, W e 14 9 μm Dc Bias Voltage, V p V Gap Spacing, d A o Table: Fig: 4.1 Parameterized lateral free free beam resonator schematic in Architect Fig 4.1.1: Free Free beam structure in Architect Volume 2, Issue 6 November December 2013 Page 36

4 of the structure concerning the axis in which it is oscillating. The natural frequency of a resonating mechanical structure approximately depends on the subsequent factors: Direct variation with thickness in addition to square root of elastic modulus (in case of bending) and/or shear modulus (in case of twisting) Opposite variation with the square of the length as well as the square root of density and width. Fig 4.1.2: Purple (top): Amplitude Response (Rotation about beam length) Green (below): Phase Response The following parameters were varied one at a time: Bridge and Beam Material Beam Length and Support Beam Length Beam Width and support Beam Width Gap Spacing Bias Voltage Electrode width 4.2 Beam and Bridge Material Fixing all other parameters, different materials were tried in simulations. Sr Material Elastic Shear Densit Reson.N o. Modul us (GPa) Modulu s (GPa) g/cc ance freque ncy (MHz) 1. Polysilicon Nickel Tungsten Chromium Platinum Gold Table 4.2.1: Material with Frequency Response Fig: Free Free Beam Resonator Parameter Each measurement contributed to the overall mass and stiffness of the structure. Also the natural frequencies of oscillation depend on the elastic/shear modulus and densities of the materials. Assumptions made: Damping constant is stable as it does not have an effect on the value of natural frequencies. Applied voltage is well underneath the pull-in voltage of the structure. Natural Frequency, = ; of any structure is given by: Fig4.2.1.: Resonance frequency versus materials Remarks: Material with greater Elastic/Shear Modulus and lower density has greater resonance frequency. (A) Vary Beam Length Where K effective is the effective spring constant of the structure and I effective is the effective moment of inactivity Volume 2, Issue 6 November December 2013 Page 37

5 Fig Vary Beam Width Fig4.2.7 (D) Vary Electrode Width Fig (A) Vary Gap distance between electrode and structure Fig Remark: For maximizing the figure of merit, Q, coupling area (A), and the applied V p have to be the highest possible, whereas the parasitic capacitor (C r ), the elastic constant (k) and the electrode to resonator gap (d 0 ) must be minimized. Fig (B) Support Beam Length Fig: (C) Vary Support Beam Width Fig Vary Bias Voltage 5. Conclusion Design and analysis of MEMS filter is obtainable in this paper after observing the outcome of various parameters, the structure is planned optimally based on necessities. Note, that at this frequency the support beams swing at their second harmonic. The animation was created in Scene3D. The simulation time for this analysis is about 1 second on a 2GHz laptop. Then a frequency response of filter was calculated using coventor-ware architect. In the end perforated structure is also deliberate and its frequency response was analyzed. The work on lateral free free beam gives method to a new kind of filter design approach in MEMS. The study shows that there is a large amount of scope for innovative filter designs in MEMS which can be used in position of conventional electronic filters. Lateral free-free beam mechanical resonators with second-mode dividing supports have been established with Q s ~10,000. The usefulness of the isolating support design in maximize Q was established experimentally. However, the resonance frequency and Q of this resonator were originated to be responsive errors in support beam length. In meticulous, overshoot errors (over the preferred second-mode length) in support beam length were fairly unfavorable to the Q of the overall resonator. As a final point, the use of metal electrodes in the capacitive transducers was establish to be detrimental to the thermal Volume 2, Issue 6 November December 2013 Page 38

6 stability of the resonance frequency due to thermal growth of the electrodes, which complete electrical stiffness a function of temperature. Through adjustments to get rid of this electrode occurrence, this resonator design should show useful in civilizing the design flexibility of future mechanical transportation circuits, especially filters and oscillators. REFERENCE: [1] Journal of microelectromechanical systems, VOL. 9, NO. 3, SEPTEMBER VHF Free Free Beam High-Q Micromechanical Resonators Kun Wang, Member, IEEE, Ark-Chew Wong, Student Member, IEEE, and Clark T.-C. Nguyen, Member, IEEE [2] W. -T. Hsu, J. R. Clark, and C. T. -C. Nguyen, Qoptimized lateral free-free beam micromechanical resonators, Digest of Technical Papers, the 11th Int. Conf. on Solid-State Sensors & Actuators (Transducers 01), Munich, Germany,June 10-14, 2001, pp [3] Y.-W. Lin, S.-S. Li, Z. Ren, and C. T.-C. Nguyen, Vibrating micromechanical resonators with solid dielectric capacitive-transducer gaps, Proceedings, Joint IEEE Int. Frequency Control/Precision Time & Time Interval Symposium, Vancouver, Canada, Aug , 2005, pp [4] SEMLESSWINE-GLASS-MODE DISK MICROMECHANICAL RESONATORS Mohamed A. Abdelmoneum, Mustafa U. Demirci, and Clark T- C. Nguyen Center for Integrated Microsystems Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor, Michigan , U.S.A. [5] Electrostatic free-free beam microelectromechanical resonator by Tianming Zhang [6] High Q Low Impedance MEMS Resonators By Li- Wen Hung and Clerk Nguyen(Technical Report No. UCB/EECS ). [7] Design and Fabrication of Micromachined Resonators, Ritesh Ray Chaudhuria1, Joydeep Basub, Tarun Kanti Bhattacharyya*b a Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur, India bdept. of Electronics and Electrical communication Engg,Indian Institute of Technology,Kharagpur,India [8] Microelctromechanical resonators for radio frequency communication Application, Joydeep Basu1 and Tarun Kanti Bhattacharyya2 Department of Electronics and Electrical Communication Engineering Indian Institute of Technology Kharagpur, Kharagpur , West Bengal, India [9] RF MEMS and Si Micromachining in High Frequency circuits application, Linda P. B. Katehi, and Stephen V. Robertson Purdue University, Schools of Engineering 1280 ENAD, West Lafayette, IN USA [10] Abdelmoneum MA, Demirci MU, Nguyen CTC (2003) Stemless wine-glass-mode disk micromechanical resonators. In: Proceedings of the 16th IEEE International Conference on Micro Electro Mechanical Systems, Kyoto, Japan, Jan 2003, pp [11] Bannon FD, Clark JR, Nguyen CTC (1996) High frequency microelectromechanical IF filters. In: Technical Digest of IEEE International Electron Devices Meeting, San Francisco, CA, Dec 1996, pp [12] Basu J, Bhattacharyya TK (2011) Comparative analysis of a variety of high-q capacitively transduced bulk-mode microelectromechanical resonator geometries. Microsyst Technol 17(8): [13] Bhave SA, Di G, Maboudian R, Howe RT (2005) Fully-differential poly-sic Lame mode resonator and checkerboard filter. In: Proceedings of the 18th IEEE International Conference on Micro Electro Mechanical Systems, Miami, Florida, Jan Feb 2005, pp [14] Accepted for publication in IEEE/ASME J. Microelectromech. Syst. in either the Sept. or Dec issue. VHF Free-Free Beam High-Q Micromechanical Resonators Kun Wang, Member, IEEE, Ark-Chew Wong, Student Member, IEEE, and Clark T.-C. Nguyen, Member, IEEE [15] M. U. Demirci and C. T.-C. Nguyen, Higher-mode free-free beam micromechanical resonators, Proceedings, 2003 IEEE Int. Frequency Control Symposium, Tampa, Florida, May 5-8, 2003, pp [16] W.-T. Hsu, J. R. Clark, and C. T.-C. Nguyen, A submicron capacitive gap process for multiple-metalelectrode lateral micromechanical resonators,, Technical Digest, IEEE Int. Micro Electro Mechanical Systems Conf., Interlaken, Switzerland, Jan , 2001, pp AUTHOR Jyoti Yadav received the B.E. and M.Tech. degrees in Electronice Engineering from SMEC neemrana and Bansthali Vidhyapheet in 2007 and 2010, respectively. She now with DIoF gurgoan. Neelam Yadav received the BE. From IET, alwar and M.Tech degree in Digital communication from IET, Alwar. Now she with SMEC, Neemrana. Volume 2, Issue 6 November December 2013 Page 39