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The 4 M’s of MEMS Analysis Software Selection:
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By Robert Calvet
Optomechanical Engineer
SiWave, Inc.
Arcadia, CA
In designing telecommunication optical switching components using Micro Electro Mechanical Systems (MEMS) technology, I have discovered that MEMS analysis software needs to provide flexible modeling capabilities, consider multiple physical phenomena, include Mechanical Event Simulation for replication of dynamic behavior and be capable of considering components that connect the MEMS devices to the macro-scale world (i.e., "packaging").
SiWave chose the FEA and simulation package from ALGOR, Inc. because it has the modeling and analysis capabilities I need and can be used to optimize packaging as well as the actual MEMS devices.
MEMS are micromachines the size of a grain of salt or the eye of a needle that integrate mechanical elements, sensors, actuators and electronics on a common silicon substrate. In addition to optical switches within telecommunication and networking systems, MEMS applications include accelerometers in automotive airbags, inkjets in desktop printers and sensors in medical testing equipment.
Flexible modeling capabilities, including CAD support and precision finite element modeling, are important because MEMS geometry tends to be very complex. CAD software is ideal for creating the intricate features of a MEMS device and the analysis software must provide the means to capture all of those features. The CAD geometry is automatically captured in the FEA tool and is updated automatically for each design change. Once in the FEA software, however, I find it valuable to have point and click features to automatically generate a mesh, change the mesh, add or remove features for design optimization and extrude a model from 2-D profiles.
Once geometry has been acquired, the next challenge of designing and optimizing MEMS devices is to consider the multiple, interdependent physical phenomena to which MEMS are sensitive. Electrostatics, heat transfer, stress, linear dynamics and even fluid effects such as squeeze film damping are important in the design of the optical network components I work on. The more tightly these multiple physical phenomena are integrated within the same software package, the better.
Multiphysics capabilities must also be integrated with Mechanical Event Simulation (MES), which combines large-scale motion and stress analysis of a finite element model in a single process and simulates real-world deformation and failure behavior. Having MES integrated with multiphysics enables me to simulate how electrostatic forces actuate a device and how heat might cause parts to deform from thermal stresses.
MES even eliminates the need for limited kinematics software because it simulates large-scale motion. It can also include linear and nonlinear materials. A wide range of material models is important since silicon, a common material in MEMS, is orthotropic while other materials we sometimes use require nonlinear material models.
Some think that once you’ve designed the actual MEMS device, the job is done. At the end of the day, however, the device needs to function in the real world. It must be a product that you can put in an envelope and send to a customer. In MEMS design, everything that is not the actual MEMS device is grouped under the catch-all "packaging," including components that interface the device with the macro-scale world as well as the components that house and protect the device.
Designing and optimizing packaging for a device is an important part of any MEMS project – one that can benefit from analysis and simulation as much as the design and optimization of the actual MEMS device. One advantage to selecting a general-purpose FEA software such as ALGOR over MEMS-specific software is that the general-purpose software can easily be used for packaging optimization.
Other advantages to a general-purpose FEA package are the use of only finite elements, which I prefer. MEMS-specific software may also use a combination of analysis methods such as boundary elements, p-elements and finite difference instead of finite elements. In addition, many MEMS-specific software packages often require the user to know the inner workings of the analysis code, whereas general-purpose FEA software is easier to use since it is more interface-based.
Thus, FEA software like ALGOR is an effective tool for MEMS design due to its use of trusted finite element technology, flexible modeling options, multiphysics and dynamic nonlinear capabilities, Windows-based interface and ability to analyze and optimize packaging.
Robert Calvet has been using ALGOR FEA for 20 years. SiWave, Inc., is a supplier of optical switching components and subsystems. SiWave, Inc., is funded by Draper Fisher Jurvetson (www.dfj.com), the leading, early-stage information technology venture capital firm.
Click here for more on how SiWave, Inc. used ALGOR software.
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