MEMS mike pioneers keep the faith

One of the perks of this job is that I get to meet some really interesting people. Last week was no exception, as I got to meet two engineers who pioneered the research for the electret condenser microphone (ECM) when they worked for Bell Labs in the early 1980s. They are James West and Gerhard Sessler. The pair was in town as they were being inducted into the New Jersey Inventors Hall of Fame (who knew New Jersey had an Inventors Hall of Fame?). Because the team was also instrumental in the development of the MEMS-based microphone, Ray Stata, the founder and chairman of Analog Devices, joined the meeting. Stata pioneered some of the early MEMS work at Analog Devices more than 15 years ago. This made the meeting that much more fun.

Sessler joined Bell Labs in 1959, a time when the primary driver for microphone development was for telephones. His development work on MEMS-based microphones occurred in the 1980s at the University of Darmstadt, where he designed the first condenser microphones based on silicon micromachining. West was simultaneously working on a similar concept at Bell Labs. In the mid 1970s, MEMS were used mainly for pressure sensing. But according to Sessler, "microphones simply measure pressure. They're just a lot more sensitive."

According to West, the evolution of microphones started with a carbon version, which was invented by Thomas Edison (also in New Jersey). However, the story goes that Edison never got the credit (or financial reward) for the carbon microphone because it was held up in the patent process by the Bell Labs legal team. The carbon mike was followed by the ECM, then a silicon version, and finally the MEMS model.

Left to right: James West, Ray Stata, and Gerhard Sessler after West and Sessler were inducted into the New Jersey Inventors Hall of Fame.

The first patent for a MEMS-based microphone was granted in 1983. At the time, there was a lot of resistance to the MEMS mike, as it cost about 10X compared with the carbon existing technology, and were not as reliable, as they were expected to have a life of only about one year. In fact, Sessler's bosses told him not to bother even trying to get a patent because it wouldn't be worth the effort. But Sessler thankfully forged ahead anyway.

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