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RF MEMS ApplicationsThe term RF MEMS encompasses several distinct types of devices, including RF switchesand relays, resonators, varactors (variable capacitors) and inductors. Applications of RFMEMS include all types of wireless communications, radar, satellites, military radio,instrumentation and test equipment. Compared to conventional RF components, RF MEMSoffer significant benefits, including lower power consumption, lower insertion loss, lower costand smaller form factor. RF MEMS have come to market more recently than other types ofMEMS, but the RF MEMS market is now growing rapidly.

Coventor has worked closely with leading semiconductor companies, specialty RFcomponent suppliers, and research organizations to support their development of RF MEMS.Our commercial and university customers have used CoventorWare to design an amazingvariety of RF switches, relays, resonators and varactors.

RF Switches and RelaysCoventorWare offers a comprehensive environment for designing and analyzing RF switchesand relays, and comes with an extensive tutorial on RF switch design. ARCHITECT is theplace to start for switches and relays that are actuated with electrostatic or piezoelectriceffects. ARCHITECT is unique in offering a single environment where you can perform all

phases of design and analysis: high-level concept exploration, detailed geometry design,coupling with control circuitry, and evaluation of S-parameters. With its comprehensiveelectromechanical component library, you can quickly assemble a fully parameterized design.Steady-state (DC) simulations to determine pull-in and lift-off voltage run almostinstantaneously. But thats just the start. Fully coupled, transient simulations of the switchoperation take only a few seconds. You can simulate complex behavior like bouncing whenthe switch closes. With the full parameterization of the design and fast simulation times, youcan quickly explore a broad parameter space to optimize the design. Then, with the built-intransmission line solver, you can compute the S-parameters of the switch in both closed andopen positions, for export to your favorite RF simulation environment.

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ARCHITECT schematic of an ohmic RF switch

ANALYZER also has much to offer for RF switch design. For designs that are electrostaticallyactuated, the CoSolve-EM module can be used to accurately compute pull-in and lift-offvoltages. Unlike some competing FEA tools, the hybrid finite element / boundary elementapproach used by CoSolve-EM fully captures electrostatic fringing fields, assuring accurateresults. And the sophisticated Abaqus finite-element solver in MemMech accuratelycomputes contact deformation in the switch-closed position. Other actuation methods, suchas piezoelectric and thermoelectric actuation, can be simulated in MemMech as well.MemDamping offers a comprehensive, unique approach to analyzing damping; it fully exploitsthe physical effects that are characteristic of MEMS, such as squeeze films and low Reynolds

number, to deliver accurate answers quickly. Results from MemDamping can be used inARCHITECT or MemMech to perform transient simulations of switch operation.

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This 3D model of ohmic RF switch was automatically generatedfrom the ARCHITECT Schematic shown in the preceding figure

VaractorsMEMS varactors are variable capacitors in which the capacitance is controlled by varying thegap between two plates, typically by means of electrostatic force. Both ARCHITECT and the

ANALYZER are suitable for simulating varactors both tools will fully account for electrostaticfringing fields, unlike some competing FEA tools, which neglect fringing fields. In particular,the MemMech, MemElectro and CoSolve-EM modules in ANALYZER are applicable toelectrostatically actuated varactors.

InductorsMEMS fabrication processes can be used to build spiral inductors that stand off from thesubstrate, with the benefits of reducing parasitic capacitance and dielectric losses. TheMemHenry module in ANALYZER can be used to compute resistance and inductance (RL) ofspiral inductors, and the MemElectro module can be used to compute the parasiticcapacitance (C).

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ResonatorsResonators are the fundamental building block for more complex components like duplexers,filters, and oscillators (frequency or timing sources). MEMS resonators for duplexers andfilters typically exploit Bulk Acoustic Wave (BAW) resonance modes in a suspended orotherwise isolated volume of material. The MemMech solver in ANALYZER is ideal forsimulating BAW-based resonators, including those characterized as Film Bulk AcousticResonators (FBARs). Oscillators tend to rely on mechanical resonance modes (bendingmodes in beam- or plate-like parts, possibly in combination with mass effects). ARCHITECTis the ideal tool for mechanical resonators, because it enables simulation not only of the

resonant mode shapes and frequencies, but the full frequency response of the resonator,including Rayleigh and gas damping effects. Behavior such as temperaturesensitivity/stability and nonlinearity can easily be included in ARCHITECT simulations. TheMemMech solver in ANALYZER can be used to verify mode shapes and frequency predictedby ARCHITECT.

Saddle mode of a square resonator,simulated with the MemMech solver in ANALYZER

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Designer and MEMulatorAs always, the automated 2D-to-3D solid model builder and mesh generation in Designerhave been optimized for the multi-layered construction that is typical of RF MEMS inertialsensors, whether fabricated with dedicated processes, or as pre- or post-processing steps ona standard CMOS process. Designer can export solid models in ACIS .SAT format. Thisexport capability is useful for exporting the geometry of a MEMS switch in open and closedpositions to 3rd-party electromagnetics field solvers, such as HFSS from Ansoft.

When its time to send your design to the fab, youll find that MEMulator quickly proves itsworth, both for communicating and resolving fabrication issues. Because it builds highlyrealistic, 3D models of the fabricated device, starting from GDSII layout, its often possible toidentify potential fabrication issues before tape out. MEMulator also provides a quick way tounderstand the impact of manufacturing variations.