# How MEMS Microphones Became the Standard for Mobile Audio

An episode of [The Hardware Podcast with Fexingo: Chips, Devices, and Electronics Engineering Conversations](https://invisiblenetwork.ai/podcast/1896799982), 28 Jul 2026, 7:30.

Audio: https://audio.fexingo.com/business/the-hardware-podcast/episode-0136.mp3

In this episode of The Hardware Podcast, Lucas and Luna dive into the tiny silicon chips that have replaced the electret condenser microphones in nearly every smartphone, smart speaker, and hearing aid on the market. They explore how MEMS microphones are fabricated—from an etched silicon membrane to a precision backplate—and how companies like Knowles and Infineon have scaled production to billions of units per year. The hosts discuss the key advantages: miniature size, reflow soldering compatibility, and consistent performance across temperature and humidity. They also touch on the trade-offs between sensitivity and signal-to-noise ratio, and why Apple’s adoption of triple-MEMS arrays in the iPhone pushed the entire industry forward. Finally, they look at emerging applications in beamforming and noise cancellation, asking whether the next frontier is on-chip microphone arrays for spatial audio. Listeners will come away with a clear understanding of why that tiny hole in your phone is more than just a hole—it’s a marvel of microengineering. #HardwarePodcast #FexingoBusiness #BusinessPodcast #Technology #Semiconductors #MEMS #Microphones #AudioTech #ConsumerElectronics #Smartphone #HearingAids #SmartSpeaker #KnowlesCorp #Infineon #Apple #SiliconFabrication #AcousticEngineering #Miniaturization Keep every episode free: buymeacoffee.com/fexingo

## Transcript

Lucas: You know that tiny hole at the bottom of your smartphone? That's not just a port for a paper clip or a vent. Inside it is a microscopic silicon membrane that flexes with sound pressure, changing capacitance and creating an electrical signal. That's a MEMS microphone.
Luna: MEMS meaning micro electro mechanical systems. So this is a mechanical structure etched onto a chip, not the old-school electret condenser microphone we grew up with.
Lucas: Exactly. The electret condenser mic relied on a plastic diaphragm and a permanently charged foil. It worked fine, but it was bulky, sensitive to humidity and temperature, and couldn't be reflow-soldered onto a circuit board. MEMS microphones solved all that by using single-crystal silicon as both the diaphragm and the backplate.
Luna: So how do you make a silicon diaphragm that actually moves with sound? Silicon is stiff.
Lucas: You etch it incredibly thin. A typical MEMS microphone die has a membrane that's about one micron thick—that's one one-thousandth of a millimeter. Below that membrane, there's a rigid backplate with tiny holes, like a perforated metal sheet. The gap between membrane and backplate is maybe two microns. When sound pressure hits the membrane, it deflects, changing the capacitance between the two electrodes. A charge pump and amplifier—on the same chip or a separate ASIC—converts that capacitance change into an analog voltage.
Luna: And that ASIC is usually co-packaged in the same MEMS package. One package, two dies: the microphone die and the amplifier die. That's what we call a MEMS microphone.
Lucas: Right. And the evolution has been rapid. The first commercial MEMS microphones came from Knowles in the early 2000s. They were used in hearing aids first—size and power were the killer advantages. Then in 2007, the original iPhone used an electret mic, but by the iPhone 4 in 2010, Apple had switched to MEMS for the main microphone. That was the tipping point.
Luna: What about quality? Audiophiles often complain that smartphone recordings sound thin compared to a dedicated mic.
Lucas: Fair point. The fundamental trade-off is signal to noise ratio. A larger membrane generally captures more acoustic energy, giving a cleaner signal. MEMS membranes are tiny—often less than one millimeter across—so SNR is lower than a studio condenser mic's. But in the last decade, SNR has improved from maybe 55 decibels to over 70 decibels in high-end MEMS parts. That's good enough for voice and most environmental audio.
Luna: And they come in arrays. The latest iPhones have three MEMS microphones: one at the bottom, one at the top, one on the back. That enables noise cancellation and beamforming.
Lucas: Exactly. Smart speakers like the Amazon Echo use seven MEMS microphones in a circular array to localize where a voice is coming from. And because MEMS mics are tiny—a package might be three millimeters square—you can put them anywhere. The Echo's whole array fits in a ring smaller than a dime.
Luna: Let's talk fabrication. How do you actually etch a free-standing silicon membrane?
Lucas: Standard MEMS process: start with a silicon wafer. Deposit a sacrificial layer—like silicon dioxide—on top. Then deposit the structural layer that will become the membrane, typically polycrystalline silicon, about one micron thick. Etch small holes in the membrane to allow an etchant—hydrofluoric acid vapor—to reach and remove the sacrificial layer underneath. That releases the membrane so it can move. The backplate is often a separate wafer bonded on top, or it's made from the same wafer using a deep reactive ion etch.
Luna: And you're doing this in a cmos like fab. That's what really drove costs down—the ability to manufacture these in standard semiconductor foundries with batch processing.
Lucas: Yes. Infineon and STMicroelectronics have invested heavily in MEMS fabs. Knowles actually bought a fab in China years ago. The result: a MEMS microphone die costs a few cents. The whole packaged part might be ten to twenty cents. That's why every smartphone has at least two, and sometimes three or four.
Luna: Hearing aids too. Modern behind the ear hearing aids use MEMS mics because they can fit inside the small housing and consume very little power—a few hundred microamps.
Lucas: And they can be made to withstand dust and moisture. The IP rating of many MEMS microphones is IP57 or better. That's why you can take your phone in the rain and still make calls.
Luna: What about the future? Are we going to see MEMS microphones that rival studio condensers?
Lucas: Maybe not in the same form factor. But there's work on dual-membrane designs that improve SNR by picking up differential pressure. And there are digital-output MEMS mics with built-in pulse-density modulation, which makes them easy to connect directly to a processor. Also, Apple has filed patents for MEMS microphones that are part of the phone's display—using the glass itself as the diaphragm.
Luna: That would be wild. No visible hole at all.
Lucas: Exactly. The hole itself is a design compromise. If you can make the entire display a microphone, you free up industrial design and maybe even improve water resistance.
Luna: Well, if you're listening to this episode on earbuds right now, those tiny beamforming mics are probably MEMS chips. And if you find these dives into hardware engineering useful, consider supporting the show at buy me a coffee dot com slash fexingo.
Lucas: Yeah, listener support is what keeps this ad-free. We appreciate anyone who chips in.
Luna: So back to the future: what about using MEMS microphones for ultrasound or infrasound? They have a frequency response that extends beyond the audible range.
Lucas: That's a great point. The natural frequency of a one-micron-thick silicon membrane can be in the megahertz range if you design it right. So MEMS mics can double as ultrasonic sensors. You see that in automotive for in-cabin child presence detection—using ultrasound to detect breathing—and in some gesture recognition systems.
Luna: And the same technology can be adapted for pressure sensors, accelerometers—the basic capacitive MEMS structure is incredibly versatile.
Lucas: Right. So the MEMS microphone is really just one manifestation of a broader platform. But it's the one that touches every consumer's life every day. And it's a great example of how a physics principle from the 1800s—variable capacitance—gets reinvented at the micron scale.
Luna: I think the next time I see that tiny hole on my phone, I'll have a little more appreciation for the ten-cent marvel behind it.
Lucas: Absolutely. And maybe spare a thought for the canceled electret condenser microphone—it served us well, but silicon simply does it better.

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