Speed, Accuracy and Automation in MEMS Simulation and Development C. J. Welham, Coventor, Paris

Transcription

1 Speed, Accuracy and Automation in MEMS Simulation and Development C. J. Welham, Coventor, Paris

2 MEMS Design & Simulation Challenges Overview Simulation Challenges and Approaches Validation Case Studies Conclusion

3 Demand for MEMS is Changing MEMS have evolved from DLP, inkjet and airbag applications to high volume Consumer Electronic devices >20% CAGR Democratization of MEMS causing a shift in business growth from traditional MEMS companies to semi-foundries and fabless design houses. Consumer Electronic applications require shorter product development cycles. Pressure to reduce size of MEMS components whilst increasing performance and integration. Market data from Yole Development

4 Simulation Challenges MEMS-based products are becoming smaller and more integrated 1-axis accel. 2-axis accel. 3-axis accel. IMU: 3-axis accel. + 3-axis gyro Decreasing size and greater integration pressures require more sophisticated models and simulations More sensitive spurious coupling between components More important to consider non-linearities More sensitive to parasitic effects More chance of design errors in interconnect Simulations must include more coupled physics, non-linearity, parasitic effects and the connected circuit/system

5 Two Approaches Conventional Low Order FEA - General Elements 3D Geometry High Order FEA - Designed for MEMS High-order, coupled physics elements Library of generic, low-order finite elements Mesh Generator Brick, tet, shell, and beam elements 3D Design Entry in Graphical UI or Scripting in MATLAB or Python Meshed Model Large 10k to 10M DOF Meshed Model Small 10 to 1000 DOF

6 High Order Benefits High Order FEA - Designed for MEMS High-order, coupled physics elements Parameterization Speed and Accuracy 3D Design Entry in Graphical UI or Scripting in MATLAB or Python Meshed Model Compatibility Small 10 to 1000 DOF

7 Compatibility Models with a small number of DOF can run directly in MATLAB, Simulink and Cadence Enter Design in 3D Simulate and Analyze Internal Simulator Visualize Results in 3D MATLAB Simulink Virtuoso VerilogA High Order Finite Element Library: MEMS coupled-physics specific, 3D, high-order, parametric

8 Compatibility Models that run directly in other simulators allow MEMS and IC Designers to collaborate easily MEMS Designers Design Capture High Order FEA High Order Elements allow the automatic transfer of models for use by IC or System Designers IC Designers Algorithmic Level (Simulink) Behavioral Level (Virtuoso) Transistor Level (Virtuoso) Model Export Physical Level (Virtuoso)

9 Parameterization High Order Models can be inherently parametric Explore design envelope Manufacturing/Sensitivity Analysis CD loss Sidewall Angle Mass thickness

10 Parameterization Results from Monte Carlo Analysis Random input variables defined from mean and std. deviation Modal Analysis, 1000 samples 7s per sample Mode Y Mode Z Mode X Variation of of Frequency Y Z Samples Variation of Frequency X Samples

11 Speed and Accuracy Electrostatic MEMS element 100s of times faster Comb Finger - Element Level Validation High Order Model Low Order BEM Model *Self-aligned Vertical Electrostatic Comb drives for Micromirror Actuation, Krishnamoorthy, U., Lee, D., Solgaard, O., JMEMS2003

12 Validation Device Level Compare both approaches and measurement Energy Harvester - Coupled-Physics, Multi-Domain *Experimental Validation of Aluminum Nitride Energy Harvester Model with Power Transfer Circuit S. Matova, D. Hohlfeld, R. van Schaijk, C. J. Welham, S. Rouvillois Eurosensors XXIII conference 2009

13 Validation - Process Virtual fabrication MEMS device Voxel modelling for robust model build Voxel Model Silicon accurate 3D geometry Test design is correct before tape-out Communication with Foundry Process development Based on Chipworks teardown Release Oxide Polysilicon Electrode Epitaxial Polysilicon Hard Mask Bulk Silicon Thermal Oxide Release Oxide Deposition Via to Electrode Epi-poly growth and Planarization DRIE Release Etch

14 Case Study - Gyroscope Benefits of MEMS specific element approach The power of high order element models allows very rapid design studies and optimize the design A 3D parametric study in low order conventional FEA can take significant time, even though point simulations (modal) only take minutes. With high order element models simulations take seconds: total simulation time is therefore much lower Geometry variation is more difficult in conventional FEA. Key challenges solved by Model Export Writing a (VerilogA) model takes weeks and requires significant expertise. Enhancements (e.g. spurious modes, parasitic Cs) and design variations takes time, which is not always available. Simple hand written analytical models miss non-linearities and other second order effects. Upgrading and maintaining hand written models for ASIC design partners is painful

15 Case Study - Microphone Perform noise analysis Model supports noise analysis in Cadence Spectre and accurately predict thermo-mechanical noise Model supports all relevant noise sources in your MEMS+IC system, enabling you to evaluate noise cancelling strategies Microphone Model includes mechanics, electrostatics and fluidic effects Cadence Virtuoso schematic Noise analysis in Cadence Spectre

16 Case Study - Switch Switch Dynamic Response High order elements are very fast and can easily combine mechanical, electrical and fluidic effects in a transient simulation Simulated gas pressure on electrodes as RF switch closes Tip position (m) RF switch tip position, closing and opening Time (s)

17 Other Examples Accelerometer, 67 DoF Gyroscope, 96 DoF Ring Gyro, 345 DoF DLP mirror, 11 DoF Ring Resonator, 727 DoF RF Switch 119 DoF The High Order approach is general: it has been used to create compact, accurate models of many real-world designs

18 Conventional FEA Is there a place for conventional FEA models YES! Some problems are better modelled with conventional FEA Stress, packaging, multi-conductor, parasitic and damping problems TED, Gas, Anchor Some geometries are not suited to high order elements Simulate FBAR Simulate package Simulate stress

19 In Conclusion Use High Order FEA for Speed, Accuracy and Automation MEMS-specific geometries and coupled physics Benefits over traditional FEA Much faster simulations due to reduced degrees of freedom Parameterization enables rapid design exploration and optimization Compatible with MATLAB, Simulink and Cadence simulators Simulate the full dynamic response of sensors and actuators Simulate closed-loop operation of sensors Deliver models of MEMS devices to system and IC designers Perform noise analysis of sensors Conventional FEA still useful for certain design tasks Leverage Process Modeling Validate design with process prior to tape out