What Is a MEMS Microphone?
A MEMS microphone is a microphone that consists of MEMS components at the point of voice conversion.
MEMS microphone is an acronym for micro-electro-mechanical systems.
In the case of microphones, MEMS microphone plays the role of a transducer that converts sound waves into electrical signals by creating a diaphragm on a Si substrate using thin-film microfabrication technology. The MEMS device can also integrate ICs on the same substrate.
Uses of MEMS Microphones
Typical uses of MEMS microphone are microphones for smartphones. They are used not only in smartphones but also in a wide variety of audio and applications. They are also used in machinery, including biotechnology, medicine, and automobiles, and have attracted much attention in recent years.
With the recent rapid spread of smartphones and other electronic devices, microphone technology has also developed. In order to muffle noise and make calls in crowded places, electronic devices need to be equipped with multiple microphones.
This has led to a situation where MEMS microphones are attracting attention as a compact and high-performance alternative to conventional ECMs (electret condenser microphones).
Principle of MEMS Microphones
The principle of MEMS microphone is to detect the change in the capacitance value of the diaphragm, which is a MEMS element, when it is vibrated by sound waves, and to convert it into an electrical signal for output. The MEMS microphones are often amplified by the IC and handled as analog signal voltage/current values, or processed with digital signal processing (ADC) to perform highly efficient pulse width modulation (PWM) processing.
The MEMS microphone itself consists of a substrate covered by a cover, which has a single small hole to allow audio to enter the microphone and be detected by the MEMS element, MEMS microphones offer numerous advantages over conventional ECM microphones, including smaller size, higher heat resistance, reflow soldering capability, higher sound quality, improved reliability, longer battery life, and lower cost.
Applications where MEMS microphones are particularly well suited are those in environments with a lot of electrical noise. In environments where there is a lot of vibration, the relatively low output impedance of MEMS microphones and their superior noise rejection, combined with digital signal processing in integrated ICs, can reduce the harmful noise level caused by this mechanical vibration.
Other Information on MEMS Microphones
1. Comparison of ECM and MEMS Microphones
Compared to MEMS Microphones, ECMs are more difficult to use when mounted on high-density electronic devices because they are more difficult to miniaturize and reflow, etc. On the other hand, ECMs have many advantages that current MEMS microphones do not have, such as they have been used for a long time, they are available in a wide variety of types, so it is easy to utilize past design assets, they have a very wide range of specifications such as supply voltage range, and there are products with excellent sound directional characteristics. There are products with excellent sound directionality, which are not yet available with current MEMS microphones.
ECMs may be better suited for some applications than MEMS microphones, so it is important to choose the right one for your situation.
2. Examples of Application to AI Speakers
As of FY2022, many electronic devices, especially smartphones, are now equipped with numerous MEMS microphones. Until now, users have had little experience with the performance of MEMS microphones, and many users have not been aware of the fact that ECMs are being replaced by MEMS microphones in the market.
AI speakers, which have become a hot topic in recent years, requiring high-performance microphones, should benefit from MEMS microphones because they are directly linked to the quality of the user experience. In fact, a MEMS microphone that is cloud-free and capable of AI detection of several dozen keywords with an AI chip in the IC inside the MEMS microphone is being researched and developed by one manufacturer.
In the near future, it will not be too far off in the future when AI speakers that are commonly found in homes and cars will realize that their operation and sound quality are technologically supported by the high-performance technology of MEMS microphones.