Page 55 - MEMS Mechanical Sensors

44 MEMS Simulation and Design Tools

solution of the simultaneous equations typically involves complex matrix algebra
that requires the use of computers. Such computing power is readily accessible today,
with even basic PCs being capable of solving complex FEA problems.

3.2.2.1 CoventorWare
CoventorWare [9] is a fully integrated design environment for MEMS design. The
latest version is the CoventorWare 2003.1 running on Sun Solaris and Windows. It
is process independent and consists of four bundles:

1. Designer: design, specify, and model MEMS structures, including
two-dimensional layout creation and editing, process emulation,
three-dimensional generation of solid models from two-dimensional masks,
finite element meshing.
2. Analyzer: the specialty solvers creates electrical, mechanical, thermal, and
fluidic solutions for MEMS-specific in-depth numerical analysis using
mechanical simulation (FEM), electrostatic simulation (BEM), and coupled
electromechanical simulation for complex multidomain.
3. Integrator: extracts reduced order models of physical effects (stiffness,
damping, and inertia) found in most dynamic systems.
4. Architect: creates schematic models of MEMS designs and runs rapid
simulations in other system-level simulators (Saber/Simulink).

CoventorWare generally follows a simulation and design procedure starting with
the drawing of device layout, then the definition of the fabrication flow, generating a
two- and three-dimensional solid model, meshing the structure, analysis, and detailed
simulation, and optionally a reduced order system level model can be derived.
The first step is to create the two-dimensional layout of a MEMS design using
Designer’s layout editor, which is a full-featured two-dimensional mask-drawing
tool capable of all-angle construction and curve creation for MEMS geometries, and
parameterized layout generators. The layout editor supports true-curve structures
and handles irregular MEMS solid components, which can be auto-meshed without
partitioning, and it can also edit design subsections in any level of the hierarchy.
Layout creates a .cat format file and supports the format used by other lay-
out software such as GDS II, CIF, IGES, and DXF. Figure 3.4 is an example
of the layout of a single-axial micromachined accelerometer with dimensions of
4.8 × 4.0 × 0.06 mm.
In the second step the fabrication steps for a MEMS device are defined and
emulated. The process editor supplies the information needed to create a three-
dimensional MEMS model from the two-dimensional mask information provided
by the layout editor. The depth information is defined by the various material layers
in a sequence of deposit and etching steps with control of bulk and thin-film geome-
tries. Materials for each process layer for the MEMS device are chosen from a mate-
rial property database; the material properties include elasticity, stress, density,
viscosity, conductivity, dielectric, piezoelectric, and thermal characteristics. The
fabrication process parameters are defined by material thickness, deposition type
(stacked, conformal, or planar), sidewall profiles of angular slope, mask perimeter
offset, and mask polarity.