1 ANSYS MEMS Features MEMSCAP ® Yiching Liang March 6, 2002 2 2 Finite Element Analysis ¤ 3D models built and exported from MEMS Pro – .ANF format: ANSYS neutral format – .SAT format: ACIS text format (compatible with most FEA, RF & solvers) ¤ Preprocessing in ANSYS – Boundary conditions/loads – Meshing – Material/element properties ¤ ANSYS solver ¤ MEMS Pro add-ons in ANSYS – 3D to layout – Reduced order modeler 3 3 ANSYS MEMS Initiative ¤ ANSYS/Multiphysics ¤ MEMS analysis requirements – Devices are inherently multiphysics – System of units applicable to small scale – Meshing of high aspect ratio devices & features – Unique material properties – Lumped parameter extraction (into SPICE, VHDL-A/MS) – Capability to model large field domains associated with electromagnetics & CFD 4 4 ANSYS MEMS Related Features ¤ Electrostatics ¤ Electrostatic-Structural Coupling ¤ Trefftz Electrostatics ¤ Capacitance Matrix Extraction ¤ Reduced Order Macro Modeling ¤ Piezoelectric ¤ Pre-stressed modal ¤ Fluid-Structural Coupling ¤ Free Surface Fluids ¤ High Frequency Electromagnetics ¤ Composite Beams ¤ Initial/Residual Stress ¤ System of Units 5 5 Electrostatics ¤ Important in MEMS – To determine both capacitance and electrostatic forces – Typically used to actuate devices such as comb drives and switches ¤ Open domain modeled either using infinite boundary elements (INFIN110, and INFIN111) or Trefftz domain technology 6 6 Adaptive P-Elements ¤ 3D P-elements for electrostatics – SOLID128 Brick/Wedge elements – SOLID127 Tetrahedral elements ¤ Polynomial order of element increased automatically to satisfy convergence to a prescribed degree of accuracy – P-order may extend from 2 - 8 ¤ Supports – All electrostatics boundary conditions and loads – node coupling and constraint equations – Trefftz Domain & CMATRIX.
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ANSYS MEMS Features
MEMSCAP®
Yiching LiangMarch 6, 2002
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Finite Element Analysis¨ 3D models built and exported from MEMS Pro
– .ANF format: ANSYS neutral format– .SAT format: ACIS text format (compatible with most FEA, RF &
solvers)
¨ Preprocessing in ANSYS– Boundary conditions/loads– Meshing– Material/element properties
– Devices are inherently multiphysics– System of units applicable to small scale– Meshing of high aspect ratio devices & features– Unique material properties– Lumped parameter extraction (into SPICE, VHDL-A/MS)– Capability to model large field domains associated with
electromagnetics & CFD
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ANSYS MEMS Related Features¨ Electrostatics¨ Electrostatic-Structural Coupling¨ Trefftz Electrostatics¨ Capacitance Matrix Extraction¨ Reduced Order Macro Modeling¨ Piezoelectric ¨ Pre-stressed modal¨ Fluid-Structural Coupling¨ Free Surface Fluids¨ High Frequency Electromagnetics¨ Composite Beams¨ Initial/Residual Stress¨ System of Units
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Electrostatics¨ Important in MEMS
– To determine both capacitance and electrostatic forces – Typically used to actuate devices such as comb drives and
switches
¨ Open domain modeled either using infinite boundary elements (INFIN110, and INFIN111) or Trefftz domain technology
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Adaptive P-Elements¨ 3D P-elements for electrostatics
– SOLID128 Brick/Wedge elements– SOLID127 Tetrahedral elements
¨ Polynomial order of element increased automatically to satisfy convergence to a prescribed degree of accuracy– P-order may extend from 2 - 8
¨ Supports – All electrostatics boundary conditions
and loads– node coupling and constraint equations– Trefftz Domain & CMATRIX.
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Electrostatic Analysis with P-Elements¨ Adaptive P-element study on comb drive structure
– Color code on elements: polynomial orders– Electrostatic field contour plot
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Electrostatic-Structural Coupling¨ Allows the actual electrostatic actuation of a MEMS
device to be simulated ¨ Three methods for electrostatic -structural simulation
– ESSOLV macro tool: a sequential coupled field macro– TRANS126: Reduced order macro model element– Manual sequential coupled: using the ANSYS APDL macro
– Comb drives: 2 Trans126 elements (EMT1 & EMT2) – Folded springs: 1 spring element (K1)– Proof mass: 1 mass element (M1)– Squeeze film damping: 1 damper element (D1)
– Large deformations – Typically more efficient actuator performance than both
electrostatic and thermal actuators
¨ Piezoelectric capabilities:– Geometric nonlinearities: large deflections/rotations – Stress stiffening– Pre-stressed modal and harmonic analyses– Accurately accounts for changes in the electromechanical field in
bending motion– Direct input of the piezoelectric strain matrix [d] – Calculation of the correction to the permittivity matrix [epsT]-
[epsS]
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Beam Steerer Example¨ The two support arms have a layer of piezoelectric
material that move the square-shaped reflecting surface
Courtesy Waveprecision, a division of GSI Lumonics
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Pre-Stressed Modal Analysis¨ In MEMS, pre-stress is sometimes used to adjust or
fine tune the response of the structure– Can compensate for variations in device geometry and material
properties (primarily due to fabrication process variations)
¨ ANSYS/Multiphysics supports the following types of pre-stressed modal analysis:– Mechanical pre-stress directly applied as a mechanical load– Electrostatic pre-stress applied via Trans126 EMT element– Piezoelectric pre-stress applied as a voltage to the piezoelectric
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Pre-Stressed Examples¨ Piezoelectric pre-
stressed modal analysis– First four modes
¨ Electrostatic pre-stressed modal analysis– First mode
– At higher velocity the fluid does not have enough time to move and is simply compressed
– Fluid damping changes drastically when the transition from compressible to incompressible flow occurs
– Can change the structural response of MEMS devices
¨ FSSOLV macro automates the simulation– Mesh morphing– Convergence monitoring
¨ Capabilities– Allows for large deformations – Time transient problems: user-specified displacement & velocity
time history for moving body– Computes both lift and drag forces– Incompressible and compressible flow– Equivalent resistance and damping terms can be extracted as
macro models2626
Mirror Example¨ End view of a parallel plate capacitor/mirror assembly
– Upper plate rotates – Blue areas is the meshed fluidic domain