MEMS microphone technology adapting to changing use cases

April 13, 2017 // By Masahito Kanaya
Owners of devices such as smartphones and tablets continually want to be able to use their gadgets in new ways, and at the same time expect extremely high performance. On-board audio functionality is a prime example. People want to be able to record social events, music performance and expect accurate, lifelike playback, or to enjoy high voice-call quality free of background noise even when outside or travelling in a car. There is also demand for high audio quality when capturing sounds further from the microphone.

These trends call for higher-performing microphones, and some handsets also feature noise cancellation or 3D sound in video modes by using two or more microphones. In addition, the advent of intelligent digital assistants that respond to the user’s voice is changing the ways in which people interact with computers, and could drive high-performing audio subsystems into more products like wearables and IoT devices in the future.

As a result, there is rising demand for MEMS (Micro Electro-Mechanical Systems) microphones, which deliver high performance and fidelity with reliability, within compact dimensions suitable for use in portable devices. The market for MEMS microphones is expected to rise from 3.6 billion units in 2015 to over 6 billion units in 2019, according to market research company IHS Technology.

 

Recap on MEMS microphone architecture and operation

The MEMS microphone contains a moveable diaphragm and static backplate fabricated on a silicon-wafer substrate using familiar processes including deposition and selective etching. The backplate has perforations that allow air to pass through without causing deflection.

The diaphragm is designed to flex in response to changes in air pressure caused by sound waves. This flexing causes the diaphragm to move relative to the backplate, producing a proportionate change in capacitance. A companion IC co-packaged with the MEMS transducer translates this capacitance change into an electrical signal in either analog or digital format.

There are markets for MEMS microphones with analog or digital output. Analog microphones, which essentially contain the MEMS transducer and companion analog-amplifier IC, are a popular solution for small handheld devices such as feature phones and entry to mid-level smartphones.

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