(IEEE), is necessary to support commercialization and foundry technologies. An effective fabrication facility needs to be able to provide a valid assessment of the characteristics and behavior of materials and processes that potential customers can use as a basis for comparing facilities. The same parameters can be used to facilitate reasonable modeling and simulation of designs prior to fabrication. The ability to deposit, characterize, and test a material or device must not depend on the skill or equipment of a single organization.

MODELING

A particular challenge for MEMS is the establishment of a self-contained, complete, and integrated modeling and simulation suite appropriate to its computational analysis requirements. Most MEMS analyses to date have required numerical techniques based on methods using discrete data. Commercial mechanical-engineering and finite-element analysis (FEA) software has proven useful for modeling a variety of parameters (e.g., displacement, stress, electric field, magnetic field, temperature, and fluid velocity) under a wide variety of conditions. For example, FEA-based modal analysis has often been used to model the mechanical-vibration modes of structures.

MEMS-specific tools will be required, however, and these tools will have to be integrated into an environment where complete structural, as well as operational, analysis can be performed. Academic research systems (e.g., MEMCAD [Senturia et al., 1992] and CAEMEMS [Crary, Juma, and Zhang, 1991]) and small-business spin-offs from academe (e.g., IntelliSense and Microcosim)-many of which are supported by general and newly CAD-focused programs at DARPA-have begun to address the need for an easy-to-use interface between modeler and numerical tools. But much remains to be done.

The need for numerical tools that deal efficiently with cross-energy domain modeling is also beginning to be addressed (e.g., Wachutka, 1995). Commercial tools are coming to market that can treat some problems involving the coupled solutions of displacement, stress, electrostatic, and temperature fields (IntelliSense). But these tools are in early development. Accurate predictions of the energy dissipation and mechanical quality factors of MEMS structures are still elusive and also require further research.

COMPUTER-AIDED DESIGN SYSTEMS

MEMS devices have not yet been designed using CAD and computer-aided engineering (CAE) tools directly, in contrast to the more mature IC devices (Antonsson, 1996). Computer tools familiar in the IC-design world, such as schematic capture, schematic-to-layout generation, automatic routing, and design verification, need to be developed for MEMS. There is also a need for software tools designed for different tasks (e.g., layout, solid modeling, discretization, numerical computation, and visualization) that can function synergistically under a consistent user interface. Newer software techniques, such as object-oriented methods, will make it easier for solutions developed in one domain to be adopted in several others. For MEMS to flourish, computer descriptions will be needed for geometric, kinematic, and field views, as well as for layout and function. Other desirable features of an evolving system for CAD/CAE for MEMS include efficient interactive operation; modularity; flexibility to allow for changes; reliability; accuracy control, including error propagation from material-property and geometric uncertainties; and methods for discretization and for estimating numerical errors. Designers will eventually need to be able to determine such information as the cost of manufacture or the expected time to failure. A MEMS compiler that can start from a user specification and produce masking and processing information as outputs also needs to be developed.

Existing commercial CAD frameworks can provide a starting point for a MEMS CAD system (Broenink, Bekkink, and Breedveld, 1992; Gilbert et al., 1993; Beerschwinger et al., 1994; Senturia, 1995), but the great diversity of MEMS devices and implementations means that libraries of parameterized MEMS devices will be very large. Systems will have to be able to manipulate and gain access to very large data banks of hundreds of types of devices, with tens to hundreds of parameters each. Thus, an efficient means of library generation, organization, and accessibility is essential. Detailed process and materials information to model and simulate MEMS devices and systems accurately are also required. Unfortunately, material parameters change from fabrication facility to fabrication facility, so the CAD package will have to keep track of where the devices are to be made.

FOUNDRY INFRASTRUCTURE

To assure industry and government users that they will be able to manufacture future MEMS products at competitive rates, the United States will have to develop a MEMS foundry-technology base similar to the base that supports the IC markets. Several elements of the infrastructure will have to be developed concurrently to create this technology base, the most important being the CAD infrastructure, which is the backbone of the foundry interface. A processing base must be developed so that foundries will be able to provide "technology files" to prospective users. These files must adequately describe the foundry technologies in terms of layout rules, modeling and simulation parameters, and behavioral characteristics (e.g., materials parameters). Qualified data regarding behavioral characteristics need to be made available to the user, who can then independently develop a system and



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