By Tom Cheyney, Small Times Senior Contributing Editor
October 16, 2007 — After successful applications in the automotive, medical, and industrial markets, micromachined motion and voice sensors have begun to ride what Benedetto Vigna calls the “MEMS consumerization wave.” Citing the successful integration of multiple-axis devices in such products as Nintendo’s Wii game console and emerging markets with unit-volumes ranging in the hundreds of millions to billions of pieces per year, the STMicroelectronics executive noted the adoption of accelerometer and silicon microphone devices by a growing number of consumer OEMs over the past two years: “Motion sensors are revolutionizing the way people use handheld devices.” Vigna’s comments came during his presentation at the recent International MEMS/MST Industry Forum, held in conjunction with Semicon Europa in Stuttgart, Germany.
To catch and stay on the fast-changing consumer product wave, successful MEMS companies must learn how to manufacture increasingly miniaturized devices in high volumes with quick product turnarounds, according to Vigna. STMicro’s recently opened 200-mm state-of-the-art development and production facility near Milan, Italy represents an investment of several hundred million Euro, but is “the most economically viable solution” for consumer applications, he said. Other reasons noted for making the transition from 150- to 200-mm wafer processing included better access to leading equipment suppliers, both in terms of best-in-class tools and the higher quality of service that comes with them.
The ramp of the new manufacturing facility has not been without its challenges. Vigna said that product and technology teams have had to deal with an assortment of equipment, process integration, and yield issues, leveraging STMicro’s chipmaking expertise where they could. “It was very, very difficult at times. Some problems were known, others were discovered along the way,” he said.
The company has several new processes running in the fab, including Vensens, a technology that creates a very thin monolithic monosilicon sensor with a micron-sized hermetic air cavity and 10-micron membrane, without the need for silicon membrane–glass/silicon-wafer bonding steps. In the packaging area, he described “a LEGO approach for fast time to volume,” where STMicro uses building-blocks of MEMS as well as analog and digital semiconductors to achieve small-form-factor, system-in-package devices.
One key advantage of the fast-growing silicon microphone consumer segment is the devices’ ability to be fabricated on CMOS lines, according to Troy Chase of Akustica. He believes that fabless MEMS companies can benefit from distributed “cost of fab facilities and processes across a broader and larger group of users,” which then results “in a greater variety of products with faster time to market.”
Chase explained that “Akustica’s CMOS MEMS is a standard process that allows MEMS products to scale up in manufacturing capacity, scale down in die and product size, and scale across into different MEMS applications.” Akustica’s post-CMOS MEMS processing steps employ standard semiconductor front- and backside dry plasma etching processes, which have been demonstrated in 12 different technology nodes from nine different foundries, he claimed. As further evidence of the inherent scalability of its product line, Chase stated that the company will soon ship its two-millionth device, only three months after hitting the million-unit mark, which took 15 months to achieve after the microphone product launched last year.
“The long-term success of the foundry model in the MEMS market depends on two main factors: the higher complexity of the technologies involved and the emergence of high-volume applications,” said Volker Herbig of analog/mixed-signal foundry X-FAB. He cited several historical differences between MEMS and semiconductor manufacturing, such as the uniquely specific processes of many MEMS products as well as their more demanding test/assembly/packaging steps. He then pointed out the clear trend toward increased CMOS-MEMS integration, which will make it difficult for pure-play MEMS foundries to “address the market segment due to the high entrance barriers involved,” including the smaller contract manufacturers’ lack of 200-mm manufacturing capability. Analog/mixed signal foundries and IDMs will be increasingly able to compete, using their comprehensive “customer-owned tooling technology” model to profitably fabricate CMOS-integrated MEMS-enabled sensors for a growing number of fabless companies.
Herbig said X-FAB has developed application-specific approaches for the MEMS space and has started several business-development projects with MEMS customers. He expects that part of the company’s portfolio to “double in the next three years.”