ST’s microphone-assembly process ensures good electrical and acoustic performance, mechanical robustness, and slimmer form factors, but has also helped to reduce the microphone chip size to 2×2 mm in devices that will soon arrive in the market. It is hoped that this technology development will pave the way to introducing microphones embedded in silicon cavities as the ultimate step in device miniaturization.
ST’s MEMS microphones are suitable for assembly on flat-cable printed-circuit boards that simplify design in space-constrained consumer devices. The patented package technology allows equipment manufacturers to place the ‘sound hole’ either on the top or the bottom of the package to ensure the slimmest possible design and shortest acoustic path from the environment to the microphone. While the microphones with the sound hole on the top (top-port) suit the size and sound-inlet position requirements of laptops and tablets, the bottom-port microphones are mostly used in mobile phones.
Stringent compression and drop tests have shown that microphones in plastic packages also outperform traditional metallic-lid devices in durability. When subjected to a force of 40N – equivalent to placing a 4kg weight on the tiny chip – microphones in metallic packages have tended to collapse, whereas devices in plastic packages have remained intact. Similar results were obtained when devices from both categories were exposed to 40 drops from a height of 1.5m with a static force of 15N applied on the package. The superior robustness holds for both flat-cable printed-circuit boards (PCB) and traditional rigid PCB designs.
ST’s plastic-package microphones integrate an internal shielding cage for electromagnetic immunity and are compatible with standard surface-mount assembly machinery and conventional pick-and-place equipment.
ST’s MEMS microphones can be used in a wide variety of audio applications across existing and emerging market segments, including mobile phones, laptops and tablets, portable media players, gaming equipment and cameras, as well as noise-cancelling headphones and potentially even hearing aids. The microphones are able to pair with the company’s Smart Voice processors for multi-microphone applications and Sound Terminal audio processing chips, providing a one-stop offering for advanced sound-input applications.