A MEMS microphone is a miniature microphone built on a silicon chip using the same manufacturing techniques that produce computer processors. MEMS stands for Micro-Electro-Mechanical Systems, a category of tiny devices that combine moving mechanical parts with electronic circuits on a single piece of silicon. These microphones are now the dominant type found in smartphones, laptops, earbuds, hearing aids, and smart speakers, largely because they can be made incredibly small and produced by the millions at low cost.
How a MEMS Microphone Converts Sound
Most MEMS microphones use a capacitive design. Inside the microphone, two key structures sit close together: a thin, flexible diaphragm and a rigid backplate with tiny holes in it. Together, these form a capacitor, which is a component that stores a small electrical charge. When sound waves hit the diaphragm, it flexes toward or away from the backplate. That movement changes the distance between them, which changes the capacitance, which produces a tiny fluctuating electrical signal that mirrors the original sound wave.
The diaphragm is typically made from low-stress polysilicon, a material thin and flexible enough to respond to subtle pressure changes in the air. The backplate, which needs to stay rigid, is often made from polysilicon coated in silicon nitride. The holes in the backplate allow air to pass through so the diaphragm can move freely without air pressure building up behind it.
A less common type uses piezoelectric materials instead of capacitance. In these designs, sound pressure creates mechanical strain in a cantilever or membrane, and the piezoelectric material converts that strain directly into an electrical signal. Piezoelectric MEMS microphones don’t need a bias voltage to operate, which simplifies some aspects of their design, but capacitive versions currently dominate the market because of their higher sensitivity.
What’s Inside the Package
A complete MEMS microphone package contains two chips working together. The first is the MEMS chip itself: the silicon die with the diaphragm, backplate, and air gap etched into it. The second is an ASIC (Application-Specific Integrated Circuit) that supplies voltage to the MEMS chip and converts its raw capacitance signal into a usable output. Depending on the design, the ASIC outputs either an analog voltage signal or a digital signal that can feed directly into a processor.
Both chips sit inside a small enclosure, typically a metal or laminate package with a sound port, which is simply a small hole that lets sound reach the diaphragm. The sound port can face upward (a top-port design, where sound enters from the top of a circuit board) or downward (a bottom-port design, where it enters through a hole in the board itself). The entire assembly, including both chips and the enclosure, often measures around 2.75 mm by 1.85 mm by 0.9 mm. That’s roughly the size of a sesame seed.
How They’re Manufactured
The key advantage of MEMS microphones is that they’re built using standard CMOS semiconductor fabrication, the same process used to make the chips in your phone or computer. Engineers design the diaphragm, backplate, and air gap using the thin film layers already available in a CMOS foundry, then use post-processing etching steps to release the moving parts. This means a MEMS microphone and its signal-processing electronics can be built together on a single chip, reducing the parasitic electrical noise that would come from connecting separate components with wires.
Because the process uses existing chip fabrication infrastructure, factories can produce millions of microphones with tightly matched performance characteristics. That consistency matters enormously for devices that use multiple microphones together. It also means MEMS microphones are compatible with surface-mount soldering, the automated process that places and solders tiny components onto circuit boards at high speed. MEMS microphones are tested to withstand peak temperatures of 260°C during the soldering process, though manufacturers caution against vapor phase soldering, which can damage the membrane or introduce contamination through the sound port.
Performance: What the Numbers Mean
Three specs define how well a MEMS microphone performs. Sensitivity tells you how much electrical signal the microphone produces for a given sound pressure, typically measured at 1 kHz. Commercial MEMS microphones generally fall between -38 and -40 dBV/Pa. A higher number (closer to zero) means the microphone produces a stronger signal from the same sound.
Signal-to-noise ratio (SNR) measures how much louder the desired audio signal is compared to the microphone’s own internal noise. Commercial units typically achieve 62.5 to 66 dBA. Higher SNR means cleaner audio, which is why this spec matters most for voice recording and speech recognition.
The acoustic overload point (AOP) tells you the loudest sound the microphone can handle before distortion becomes significant. Commercial MEMS microphones typically range from 124 to 133 dBSPL, with 133 dBSPL being louder than standing near a jet engine at takeoff. There’s an inherent tradeoff between SNR and AOP: designs that increase diaphragm stiffness or widen the air gap handle louder sounds better but produce less signal from quiet ones, lowering the SNR.
Why MEMS Replaced Older Microphone Technology
Before MEMS, most small devices used electret condenser microphones (ECMs). These work on a similar capacitive principle but are built from discrete mechanical parts rather than etched silicon. MEMS microphones won out in consumer electronics for several practical reasons.
Size is the most obvious. MEMS microphones take up far less space on a circuit board, and since their signal-processing electronics are built into the same package, they eliminate the need for external amplifier components that ECMs require. That reduction in both the microphone footprint and surrounding circuitry freed up valuable space inside increasingly thin phones and earbuds.
Manufacturing consistency is the second major advantage. Because MEMS microphones come from semiconductor fabrication lines, unit-to-unit variation is extremely small. Two MEMS microphones from the same production run will perform nearly identically, with closely matched and temperature-stable characteristics. ECMs, assembled from individual mechanical parts, show more variation. This consistency makes MEMS microphones particularly well suited for multi-microphone arrays, where even small differences between units can degrade performance.
ECMs do still have a niche. Their larger physical size actually makes it easier to achieve high dust and moisture protection ratings, so they remain common in rugged industrial equipment and outdoor applications where environmental sealing is the priority.
How Devices Use Multiple MEMS Microphones Together
The small size and tight manufacturing tolerances of MEMS microphones make it practical to place several of them in a single device. Your smartphone likely has two or three; smart speakers may have six or more arranged in a circular pattern. These arrays enable two capabilities that a single microphone cannot provide.
Beamforming uses the slight time differences in sound arriving at each microphone to determine where a voice is coming from. The system then digitally amplifies sound from that direction and suppresses everything else. This is how a smart speaker can pick out your voice command from across a noisy room, and why video calls sound clearer when you’re facing your laptop.
Active noise cancellation (ANC) is another array application. In hearing aids and earbuds, one set of microphones picks up the desired audio (like speech in the 300 to 3,400 Hz range), while another set captures unwanted noise at higher frequencies. The system then generates an inverted version of the noise signal to cancel it out. Research using MEMS microphone arrays for ANC has shown measurable improvements in automatic speech recognition accuracy, meaning the technology doesn’t just make audio sound better to human ears but also helps voice assistants understand you more reliably in noisy environments.