ST extends Thelma MEMS process
ST has used its Thick Epi-poly Layer for Micro-gyroscopes and Accelerometers (Thelma) surface-micromachining fabrication process for a number of years but it has generally been limited to about 25-microns depth. For deep etches MEMS manufacturers have used an alternative process called deep reactive ion etching (DRIE), which provides a much faster etch rate but is a complex process.
These processes are used for accelerometers, gyroscopes, microphones, and pressure sensors.
ST claims that Thelma60 delivers deeper etches, greater suspended masses and sensor sensitivity, similar to bulk micromachining but at the cost of near-surface micromachining.
"The introduction of ST’s Thelma60 surface-micromachining process starts a new era for inertial sensors. As already proven by a number of design wins that are now entering production, Thelma60 is the ideal solution to increase cost efficiency for challenging applications that demand high sensitivity like implantable medical devices and high-end sensors for aerospace systems and seismic exploration – once the exclusive domain of bulk micromachining,” said Benedetto Vigna, general manager of the analog, MEMS and sensors group at ST.
One of the limits of using surface micromachining for deep etches was the slow speed of etch and the consequent dwell time on the machine, which has a direct bearing on component cost. ST did not indicate that they have got round this issue.
The implication would be that ST can offer more sensitive inertial sensors, microphones and pressure sensors but at increased cost.
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