Robert Bosch GmbH claims to be the world's largest manufacturer of micoelectromechanical-system-based sensors, with production levels that exceed 100 million MEMS chips per year. In 2005 the company spun off subsidiary Bosch Sensortec GMbH to expand its MEMS offerings beyond automotive applications and into consumer and other products. Bosch has also licensed its proprietary deep-reactive ion-etching MEMS production technique to SiTime Corp. to manufacture oscillators and timing chips. Robert Bosch sensor engineering vice president Horst Münzel and Bosch Sensortec general manager and CEO Frank Melzer recounted the history of MEMS development at Bosch and shared its plans for the technology in a conversation with contributing editor R. Colin Johnson.
EE Times:When did you begin MEMS development work?
Horst Münzel:We began our research on micromachining over 20 years ago, but of course our very earliest work did not lead directly to products. When I joined in 1989, we were only four MEMS engineers. Today we have over 350 engineers working exclusively on MEMS chips.
EE Times: When did you introduce your first MEMS chip?
Münzel: In 1993. [It was] an integrated pressure sensor housed in a metal can for engine management. The sensor had a better than 1 percent precision across its temperature range. Automobile makers used it to measure manifold air pressure so reliably that it is still in volume production today.
EE Times: How is it constructed?
Münzel:We use bulk micromachining to make a silicon membrane about 15 microns thick and 1 square millimeter large. The membrane is built into the center of a bipolar chip. Then we use a smart trimming technology, which is very cost-effective.
EE Times: What was your next micromachined product?
Münzel: Another bulk micromachined MEMS part--a mass flow sensor with a very thin membrane, which is also used for engine management. It utilizes a calorimetric principle to measure airflow. It was a breakthrough product for us--so fast and accurate at measuring mass in airflow that it dramatically lowered fuel consumption and emissions, resulting in much higher efficiency of engine performance.
EE Times: Is this MEMS sensor also still manufactured today?
Münzel: Yes, after 11 years it is still in high-volume production. This is one of the characteristics of the automotive business: You need to spend a lot of time up front making a very low-cost and reliable device, but once it has proved itself in automotive production, you can continue making it for many many years. [In fact] you have to continue production, since the lifetime of a car is very long.
EE Times: When did your first start researching surface micromachining?
Münzel: In 1992, [but] the state of the art in surface micromachining in those days was not manufacturable in high volumes.