Advanced CAD System for Electromagnetic MEMS Interactive Analysis

efforts into developing a new extensible 3-D format [13] for internet applications. The second
attempt for portable geometry and mesh visualization was to use a visualization package named
JGV [14], an applet implemented in pure Java. The viewer was less elaborate than the VRML
viewers, but did not require special plugins and is only 100 kilobytes in size, small enough to be
transmitted with the geometry over low bandwidth links such as a 56 Kbps modem.
The server side framework is implemented as a collection of PERL and Tcl CGI scripts that
manage the transmission and storage of data and control other simulation tools on the server. To
organize the information maintained on the server, the idea of a “project” is employed. A project
consists of all of the files needed as input (e.g. process flow and masks), the desired output files
of the simulation tools (e.g. visualization files), files that maintain the current state of the device
(e.g. if mesh generation is completed), and log files (e.g. files detailing the success or failure of a
desired operation). Currently this is handled transparently to the user by having the server track
the needed files and storing them physically in a single directory for the given project. The client
controls the projects via a submenu in the interface that permits the fundamental operations of
creating, deleting, renaming, and copying a project. The user is constantly reminded of the
current project name since it is clearly displayed in a separate frame of the web-browser (see Fig.
3-3). Since the server tracks the varying states of projects, the user can change between projects
or interact with multiple projects via addition windows of the web browser. The main
application called by the server scripts, named Geodesic, is detailed in the following section.
3.1.4 Geodesic framework
Geodesic consists of an extensible framework to create MEMS geometry of varying degrees of
physical accuracy using multiple geometric simulation techniques. It has an integrated meshing
layer that permits automatic tetrahedral mesh generation. In addition, it can create input files
automatically for a finite-element code, based on the ProPHLEX finite-element kernel [15],
which permits hp-adaptive finite element simulation of the coupled electromechanical problem.
Fig. 3-4 depicts the architecture of Geodesic. The input to Geodesic consists of a set of masks
(defined in a CIF file) and a process flow (specified using the Composite CAD Process
Definition Specification [11]). The geometry is then built in a layer by layer fashion by
emulating and/or simulating the processing steps used to build the actual device (i.e. “virtual
fabrication” or “vfab”). Currently only geometric steps are supported, though these are sufficient
for the devices targeted by this contract. When fabrication steps such as implants and diffusions
alter the mechanical behavior of the device, they can be approximated by using distinct
geometric regions for regions of significantly different doping.
The challenges of integrating diverse tools such as solid modelers and mesh generation software
into a unified framework involves tasks of varying computational expense and algorithmic
challenge. In addition, in a research setting it is desired to have a tool that permits rapid
prototyping and quick testing of new algorithms. For this reason, Geodesic uses Tcl/Tk as a
front-end integration environment. Tcl/Tk combines the ease of a powerful scripting language
with the ability to imbed C/C++ code for computationally intensive operations. There are four
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