Advanced CAD System for Electromagnetic MEMS Interactive Analysis

2. Objectives, Approach and Significant Results
2.1 Software Development
A key objective is to develop and demonstrate fully-integrated, FEM-based prototype solver
capabilities to model behavior and fabrication process-dependency of MEMS devices. This
includes capabilities to consider multi-physics and materials dependencies as well as other
process induced factors—for example, geometry effects due to deposition/etching. The overall
tool integration strategy was targeted to develop and test key components that overcome limits
currently seen to be "bottlenecks" in CAD systems. Application-specific lumped modeling was
pursued early on in the project and used to guide the overall direction of the CAD efforts,
including improved parameter extraction schemes that cross-link device performance with
physical factors such as layout and process dependencies. The approach used here addresses the
following information flow and simulation capabilities:
1. Layered access in MEMS specification across levels--layout, process specification,
geometry definition, grid and constitutive models
2. Enhanced element technology for discretization of multi-physics systems of equations
3. Unified approach to interface geometry and gridding through use of servers.
4. Demonstration of integrated MEMS simulation capability with internet access to
modeling and open interface standards including parameter extraction
5. Prototyping of benchmark canonical RF test structures--both computationally and
experimentally--that demonstrate capabilities of models and tools.
The PhD thesis of Edward Chan [1], completed during the course of this project, describes: the
validation of a canonical benchmark device (RF switch), characterization of the contact electromechanical
phenomena, and the design of an electrostatic actuator with an extended range of
travel. Included in the thesis are analyses (through simulations) of the effects of: changes in
substrate curvature, the influences of stress gradients on fixed-fixed beams, and the importance
of considering film coverage in understanding the behavior of composite materials. Rigid-body
simulations of the electrostatic actuator with series feedback capacitor, used for extended travel,
reveal that tilting always occurs at a spacing of ~60% of the initial gap. This tilting occurs due to
asymmetry, but it is unclear why the range does not depend on degree of asymmetry or the size
of the series capacitance. One difficulty related to tilting in the electrostatic actuator with
extended range of travel is the fact that increasing the feedback or reducing asymmetry cannot
mitigate the effect.
Two aspects of the software and design capabilities developed during this research deserve
special note and discussion--web-based design of MEMS and accurate modeling of geometry
and process-flow information. In the area of web-based design, demonstrations of the final
prototype are available through the Stanford TCAD web site [2]. Subsequent to the ending of
this contract there has been substantial interest expressed by researchers at the Beckmann
Institute at the University of Illinois (Professors Narayan Aluru and Umberto Ravaioli) in
continuing efforts in this direction with computational support also coming through NCSA
(National Computational Science Alliance) co-located at Illinois. The web-based prototyping
environment now includes a more robust interface, remote process tracking to show the status of
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