Before Micro Electro Mechanical &stems (MEMS) can achieve their full potential, design tools for these systems must be made available to members of other disciplines, and not restricted only to those with the in-depth processing knowledge required to make the devices. To make this technology available will require a substantial abstraction away from the details of processing and toward system-level design. The abstraction from processes to devices will require characterization and modeling of the devices. If device models are to be developed, either we need to develop simulation tools which can model all processes, or we need to pick specific processes and study them in detail. Because the former option seems optimistic at best, it seems clear that what is needed is a set of standardized, general-purpose processes which integrate a sufficiently rich set of components to be widely useful.
Integrated electromechanical systems require four physical components: sensors to monitor the state of the system and the environment, actuators to affect the state, electronics to drive the sensors and actuators, and mechanical structures to support all of the above. There are several major problems which need to be addressed when developing a process that integrates these components. Most of these problems are associated with the three dimensional nature of the universe and the two dimensional nature of IC processing. There are a wide variety of tricks which can be used to sculpt the two dimensional surface of a wafer into the desired three dimensional part, but the combination of tricks appropriate for one device can only rarely be used without modification to make a different device. As a result, every new device requires a new process, and every new process requires a designer skilled in the art of micromachining. It is the lack of knowledge of the art of micromechanical process development which currently excludes the uninitiated from MEMS design. The development of a standard process shields the designer from the details of the process.
Once an integrated process is established, the behavior of individual components can be characterized and mathematical models can be developed to describe them. At this level of abstraction it becomes possible to write CAD tools which assist in the design and analysis of MEMS, and it is these CAD tools which will enable members of other disciplines to produce practical devices and systems of their own design.
September 30, 1992
Pister, K. S. J. (1992). Hinged Polysilicon Structures with Integrated CMOS Thin Film Transistors. (n.p.): University of California, Berkeley.