PORTLAND, Ore.—The world's smallest MEMS chip—a tiny 700 square micron digital microphone—was fabricated recently by Bosch Sensortec GmbH for its subsidiary Akustica Inc. The CMOS die integrates a mechanical microphone diaphragm in a sea of mixed signal CMOS circuitry that culminates in a standard PDM (pulse density modulation) output.
The MEMS microphone market topped 695 million units in 2010, up more than 57 percent from the 441 million units shipped in 2009, according to IHS iSuppli (El Segundo, Calif.), which predicts that shipments will rise to more than 1.7 billion units, or $471 million, by 2014. Applications for MEMS microphones include mobile phones, touchscreen tablets, PCs, laptops, netbooks, video- and audio-recorders, Bluetooth headsets and camera modules.
The first chip to come from Akustica since its 2009 acquisition by Bosch Sensortec, the design team was able to squeeze another 30 percent out of the die's area—which had already been shrunk from two- to one-millimeter square—to qualify the new digital microphone as having the world's smallest MEMS die at just 700 square microns.
"Bosch's experience in shrinking high-performance circuitry enabled us to reduce the size of the die while also maintaining its low noise and improving is sensitivity," said Akustica's CEO and general manager, Stefan Finkbeiner. "For directionality and noise cancelation, it is also thin enough that you can fit multiple mics into the bezels of any PC, laptop, netbook or even the smallest tablet computer."
Akustica also plans to downsize its current 3.8-by-4.7-by-1.3 millimeter package further for handheld devices wishing to fit high-fidelity MEMS microphones into spaces too small for conventional electret microphones, such as ultra-thin cell phones. The 840-by-840 micron die is just 380 microns thick, allowing it to comfortably fit in even the smallest industry standard packages.
Using Bosch's CMOS process, Akustica has shrunk the size of its die by 80 percent, yielding five-times as many chips per wafer.