ST has been struggling on the digital side of its business in recent years but its MEMS (microelectromechanical systems) business has been a resounding success, propelling the company to a leadership position with annual sales of about $900 million in 2011 and an emphasis on ninertial and membrane-based MEMS.
The system-in-package (SIP) approach adopted, whereby the company uses different manufacturing processes for sub-elements, is one reason for that success, Benedetto Vigna, executive vice president and general manager of the analog, MEMS and sensors group, said. It already allows ST to make smart MEMS that include a mechanical die, an analog signal conditioning and calibration die and, on occasion, a digital interface die with that die sometimes including a microcontroller. The next step is to add an RF transceiver.
"That's where we are aiming to and exactly where we are going," said Vigna. "We are looking at applications around the human body and in the home. There are clear use cases and we are working intensively on that program."
When asked if such wireless sensors nodes would be for medical applications, Vigna said it would be more in fitness and wellness applications, which do not need years of clinical trials to be licensed for use. He added that tire pressure monitoring systems would be another key application for MEMS components that could communicate wirelessly, although ST is not in this market at present.
ST's high volume MEMS making is for accelerometers and gyroscopes based on capacitive motion sensing and environmental sensors based primarily on moving membranes, such as pressure and microphones.
ST uses two silicon die to implement the MEMS function: one for the MEMS element and a second for analog amplification, calibration and conditioning of the signal. There is a third piece of silicon which provides the cap to the MEMS element.
ST prefers to use what Vigna calls a "stupid" cap with little or no functionality and