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MEMS+, Bringing MEMS into the Electronic World

MEMS+, Bringing MEMS into the Electronic World
by Paul McLellan on 09-19-2014 at 1:59 pm

 One of the things about MEMS devices is that they almost always live on a chip that also contains the electronics necessary to process the output from the sensor. For example, an on-chip accelerometer for a car airbag deployment will contain the electronics necessary to process the signal from the sensor and end up with something much closer to “we’re crashing, deploy the airbags” versus “we’re OK, don’t fire off the airbags.”

The design of the MEMS devices themselves are typically done with some form of finite-element analysis (FEA), a very general approach to designing mechanical structures. However, these models of the device are very complex and slow to evaluate due to the huge number of degrees of freedom. This is fine for designing the device itself but for working with the electronics a simpler model of the device is required that is accurate enough for the purpose but is also fast to evaluate.

What is required is a model that can be imported into Mathworks/Simulink or Cadence/Virtuoso and allows the circuits being designed to be evaluated with the MEMS device in place. In effect we want the input to the electrical simulation to be the input to the MEMS device, which is typically mechanical/force/temperature not the electrical signal it produces. So we input deceleration and then can see the signals that the sensor creates, how they are processed all the way up, potentially, to how the software in a microcontroller reacts. Other MEMS devices are more on the output side, such as mechanical switches or DLP mirrors, but the same idea remains. The electronics and the MEMS devices need to be cosimulated with enough accuracy on the MEMS side to ensure that the electronics is designed correctly but without requiring a model with such fidelity that the simulation is prohibitively slow. The traditional approach to doing all this has been to hand-craft a model. To make it possible to even do that, tye model is often over-simplified which can lead to errors slipping through the cracks.

Coventor’s MEMS+ and other products are the tool of choice for MEMS designers. Over half the top 10, half the top 20 and half the top 30 are Coventor customers. So what is MEMS+? It is a tool for creating high order finite element models that run in MATLAB, Simulink, and Cadence instead of proprietary field solvers. It allows models of MEMS components to be constructed from parametric finite elements such as rigid shapes, flexible shapes, side electrodes, interdigitated combs and more. The basic building blocks of MEMS devices. Then models can automatically be generated for use in MATLAB/Simulink and Cadence. The models include mechanical, electrical and gas damping effects, and are small and fast enough for transient simulations, simulating in minutes on a standard laptop.

The models are parametric so it is straighforward to vary the design to take account of, for example, manufacturing variability. For example, an interdigitated comb can take account of the thickness of the elements, the height, the sidewall incidence from over-etching etc.

MEMS+ 5.0 was announced by Coventor recently. The key new features are:

  • Improved Reduced Order Model generation and export
  • Now exports Verilog-A and MATLAB/Simulink models (up to 100X faster than complete nonlinear models )
  • MATLAB/Simulink ROM’s support 3D result visualization
  • New option to include mechanical nonlinearities for frequency hysteresis (Duffing effect) and quadrature
  • Improved model library

    • New comb models for movable flexible structures
    • Improved side electrode and contact models
    • New squeezed film damping models for side electrodes
    • Support for modeling out-of-plane structures such as corrugations
    • New charge output for piezo-electrical layers
    • New generic spring and damper
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