Commercial MEMS Case Studies: The Impact of Materials, Processes and Designs
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Commercial MEMS Case Studies: The Impact of Materials, Processes and Designs Jack Martin Analog Devices, Inc., Micromachined Products Division, Cambridge, MA 02139, U.S.A. ABSTRACT Minimizing risk is an important factor in new product planning because high volume breakthrough products require tens of millions of dollars to develop and bring to market. Sometimes risk can be minimized by following the IC model: build new devices on an existing process – just change the mask set. This approach obviously has limits. Adoption of new materials and processes greatly expands the horizon for “disruptive” products. This paper uses a case study approach to examine how changes in masks, materials and unit processes were used, and will continue to be used, to produce MEMS products for high volume applications. INTRODUCTION New devices typically start with an idea followed by a lab scale investigation. The next step – development focused towards a commercial product – is considerably larger. What lessons can we learn from a review of past successes and failures in commercial MEMS products? How can we build on those lessons for future products? The MEMS industry is almost as old as the IC industry. MEMS pressure sensors have been commercially available since the early ‘70s. Through the ‘70s and ‘80s, MEMS was described as being on the verge of explosive growth. For example, it was the cover story [1] of the April 1983 issue of Scientific American. Yes, that growth is occurring. However, it has taken much longer than expected. This paper starts by examining three promising MEMS product opportunities that did not succeed. It then moves onto a series of successful examples, and how they were affected by material properties, product architecture and market forces. DISCUSSION Technical excellence is not sufficient The 1983 Scientific American article described a variety of MEMS devices that had been demonstrated at an R&D level such as accelerometers, inkjet print nozzles and pressure sensors that had active circuitry integrated on the chip. However, the focus was a Stanford University gas chromatograph which had injection and carrier gas ports, a capillary column, valves, detector, exhaust port and connecting capillaries all integrated on a 2-inch silicon wafer. By minimizing system volume, this lab-on-a-chip optimized one important chromatograph design goal. Unfortunately, other performance metrics such as column separation efficiency did not match conventional chromatographs. Standard chromatographs with discrete components performed better and cost less. The wafer-level chromatograph was an impressive technology, but the resulting product could not compete in a marketplace. There is a Lesson here: MEMS integration is difficult. The example involved integration of mechanical and chemical components, but electronic integration poses similar challenges. This does not mean that integration is impossible. Indeed, Texas Instruments’ DMD image
projection products with two million independently-controlled MEMS mirrors requi
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