The case for “harsh environment MEMS” -- devices that can operate at extreme pressures, temperatures, and in corrosive backgrounds -- is that they can be deployed in potentially lucrative applications and markets that cannot be served with traditional silicon-based MEMS. Over two years ago here in the MEMS Investor Journal, Professor Roya Maboudian of the University of California Berkeley gave an excellent overview of research efforts in silicon carbide MEMS and the technical challenges in their development. However, since that article was published there has been little progress in their commercial deployment.
Why is this? Clearly there are challenges in advancing the technology -- silicon carbide, diamond, and other “harsh environment” compatible materials are by definition “tough” and require new manufacturing methods. But also there is not yet an agreed-upon “killer app” that justifies the large investment required to scale-up the silicon carbide MEMS manufacturing infrastructure.
Technology development continues both at universities as well as in several small companies. Sporian Microsystems (Lafayette, Colorado) has used a novel ceramic material and funding from the US Navy and Air Force to develop high-temperature and pressure sensors for gas turbine and jet engine applications. Boston Microsystems (Woburn, Massachusetts) provides silicon carbide MEMS foundry services, and recently received NSF funding to continue development of a chemical sensor for automotive emissions as well. FLX Micro (Cleveland, Ohio) was developing silicon carbide MEMS but is no longer in business.
In the long run, the automotive market could become a major customer for harsh environment MEMS. Although today automotive is MEMS’ second largest market overall, MEMS sensors are used primarily outside of the engine. Compact, in-situ sensors in the engine and exhaust stream could be used to provide real-time feedback and control of combustion, leading to increases in fuel efficiency and reductions in emissions.
Some automotive companies and suppliers are already looking at this scenario. Both the US and EU are mandating substantial reductions in nitrogen oxide (NOx) emissions from diesel engines beginning in 2013. Selective catalytic reduction (SCR) can provide active (real-time) control and reduction of NOx emissions, but it requires a sensor in the exhaust stream that does not yet exist at the industry’s desired price and performance points. And although MEMS sensors could meet this need, there is a substantial gap between where the technology is today and where it needs to be -- in terms of performance, reliability, and cost -- for the automotive industry to sign up en masse.
How can we get there? Applications in alternative energy may provide the bridge. The US Department of Energy’s National Energy Technology Laboratory (NETL) is actively funding research in harsh environment MEMS sensors with the goal of enabling alternative fossil fuel technologies such as “clean coal”, syn-gas (synthetic gas), large-scale fuel cells, and alternative combustion techniques. According to NETL this will require sensors that can operate at temperatures as high as 1700°C and at pressures as high as 1000 psi. Although the performance requirements will be challenging, if successful, a MEMS-based product for monitoring coal gasification or natural gas production quality could be both the basis of a stand-alone business -- current “stack gas” monitoring equipment can sell for $10,000 to $40,000 -- as well as an important interim step in getting to high-volume harsh environment sensors, much like aerospace applications paved the way for earlier MEMS products into mass market use in the automotive industry.
Copyright 2010 MEMS Investor Journal
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