NSF Sponsored Workshop on Structured Design Methods for MEMS

Digital Data Interchange Languages


Introduction

Standard digital data interchange representations (e.g., Caltech Intermediate Form (CIF)) have had a beneficial effect on the development of structured design methods for VLSI. It enabled the development of design tools to address issues at all levels of abstraction, and provided access to technology that was otherwise unavailable to a wide community of electronics designers. The resulting innovations ranged from powerful new digital design tools, to computer architectures that spawned new corporations. The simplified design tools in turn made VLSI design accessible to all university students interested in computer science and electrical engineering. The standard interface to manufacturing produced an economy of scale that could not be achieved by individual researchers or educators.

Some of the lessons that were learned in VLSI might be beneficially applied to the MEMS community. An examination of a typical design and manufacturing flow in mechanical systems reveals certain similarities in data interfaces between major modules where the VLSI approach might be emulated. Figure 7 (Mechanical Design Process Flowchart.) illustrates a typical mechanical system design process. However, the mixture of mechanical and electronic components and functions will require new research to develop the multi-domain, multi-dimensional representations required.

Five specific areas where research work on standard representations will benefit the development of MEMS are:

  1. 3-D solid modeling representation;
  2. Interfaces between design tools (e.g., between 3-D modeling, analysis, and process design);
  3. Representations for mask-layout, process specification, and metrology;
  4. Interfaces between design and fabrication (e.g., between process design tools and fabrication);
  5. Representation for function ({e.g., the MEMS equivalent of digital VLSI's Boolean logic).

Findings and Recommendations

Common data representations which are widely used are critical to rapid innovation in MEMS.

Mask Layout Geometry vs. Desired 3-D Shape

In VLSI, currently, the mask describes the final desired (2-D) geometry. The fabricators take into account the details of their fabrication process and pre-distort the mask so that once fabricated, the desired shape emerges. This establishes the "clean separation" between design and fabrication.

In MEMS, currently, the required pre-distortion is geometrically complex (due to the 3-D nature of most MEMS) and generally unknown. Therefore MEMS mask layout geometry is used as the mask directly. The required pre-distortion (compensation, etc.) must be determined by the MEMS designer, generally over many prototype cycles and with much experimentation. Furthermore, this experimentation does not usually, at present, result in a generalized understanding that can be applied to different MEMS devices.

At issue is whether the MEMS designer can be (or should be) insulated from the details of the fabrication processes. If this is desirable and/or possible, then the geometry that is communicated to the fabricator should be the desired (3-D) geometry. Conversely, if the relationship between mask layout geometry and final shape is too complex, MEMS designer must have available accurate fabrication simulations so that the required pre-distortion of the mask can be determined with the smallest number of fabricated prototypes possible.

Closure

While the challenges in developing structured design methods for MEMS that preserve the "clean separation" are significant, the benefits of such methods will greatly enhance MEMS developments in those areas where the design and fabrication communities can make use of such methods.

Summary

Much about the historical development of digital VLSI suggests that a common interchange language (CIF) greatly facilitated the rapid advances. While MEMS developers commonly use CIF to describe mask-layout geometry, CIF lacks many elements needed for a complete data interchange language. The development of a common interchange language for MEMS is likely to play a pivotal role in accelerating the advances in MEMS.


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