Contributed by: Sinjin Dixon-Warren
MEMS microphones appear in smartphone and tablet products from all the major suppliers, including in Apple and Samsung products. According to IHS, Apple is a major driver for MEMS microphone product growth. The iPhone 6, for example, contains three MEMS microphones, while the iPhone 6s contains four. The need for three or four microphones is driven by hands-free calling, voice commands for Siri, better audio fidelity in video recording, noise cancellation, and improved call and recording performance.
Knowles is the leading manufacturer of MEMS microphone technology in the market today, with about 59% market share for packaged devices, according to IHS. They are the major supplier for both Apple and Samsung. Chipworks has catalogued the components found inside nearly 80 samples of the iPhone 6 product family and we have found design wins from Knowles in 42% of the samples; from two Asian suppliers, AAC Technologies and GoerTek Inc in 31% and 17% of the samples, respectively, and from STMicroelectronics in 10% of the samples. It would appear that MEMS microphones are now a commodity product and that Apple is able to source equivalent devices from multiple vendors.
Knowles has been making MEMS microphones for over 10 years. In 2006, Chipworks analyzed one of their early products, the SP0103BE3 . This device features a MEMS microphone die that was 1.6 mm square and featured a single 0.65 mm diameter diaphragm, with s2.14 die markings. The microphone diaphragm occupied only 13% of the die area in this early Knowles microphone.
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Knowles has been progressively shrinking the size of the MEMS microphone dies down to about 1 mm square, while keeping the size of the MEMS diaphragm constant. Recently, they have been adding additional diaphragms. The Knowles KSM1 and KMM1 microphones, found in recent iPhone 6 phones, feature two 0.64 mm diameter MEMS diaphragms on a single die. The die is 1.1 mm x 1.7 mm and the two active MEMS diaphragms occupy nearly 35% of the die area, which is more than double the percentage in the 2006 SP0103BE3 device.
Chipworks has also seen Knowles devices with four microphone diaphragms on a single die, such as the Knowles K0614 found in the iPhone 5, where the microphone diaphragms occupy 36% of the die. All the Knowles microphones are based on capacitive sensing with two thin polysilicon plates forming the MEMS diaphragm  . According to Yole, Knowles uses Sony to fabricate their microphone dies using six-inch wafers. The 1.1 mm x 1.7 mm die size would yield about 7,700 die per wafer.
The iPhone 6 product family also includes microphones made by AAC Technologies and GoerTek. In all cases, these manufacturers use 1.4 mm x 1.4 mm MEMS dies fabricated by Infineon. The MEMS diaphragm is larger than on the Knowles devices, at 1.0 mm in diameter, corresponding to 40% of the die area.
Chipworks analyzed an earlier version of the Infineon microphone in 2008. The Infineon MEMS microphone uses capacitive sensing and was also fabricated with a two-poly process, but the top poly back plate was thicker than the poly 1 flexible plate of the MEMS diaphragm  .
STMicroelectronics’ MEMS microphones were found in about 10% of the iPhone 6 products analyzed. The STMicroelectronics microphone modules feature MEMS microphone dies fabricated by Omron. The 1.3 mm x 1.4 mm Omron die features an unusual 0.73 mm square MEMS microphone diaphragm, which occupies approximately 29% of the die area.
Exploring the genealogy trees for products, components and dies is effortless with the genealogy feature of Inside Technology. From form factors and process nodes to foundries and libraries, Inside Technology reveals why today's winning consumer products are using the hottest components.
For example, a search for the iPhone 6 reveals that the MG4P2LL/A model use GoerTek, Knowles, and AAC Technologies MEMS microphones. Inside Technology also provides images, schematics and reports; compare components; navigate the hierarchy of product/component/die relationships; and much more. See how it’s done.
MEMS microphones are a relatively mature semiconductor product. Capacitive sensing is used by all the major vendors and there continues to be considerable innovation in the ASIC circuitry required to sense the tiny MEMS microphone signal. The market is dominated by Knowles, with Infineon also commanding significant market share for the MEMS die fabrication. Infineon no longer makes their own MEMS microphone solution, but rather serves as a foundry source for several other vendors. STMicroelectronics, InvenSense (who purchased Analog Devices microphone  business), and Akustica  (owned by Bosch) are relatively minor players in this market.
- “Knowles Acoustics SP0103BE3 Zero Height Amplified SiSonic™ Microphone Process Review,” Chipworks, PPR-0608-801
- “Knowles Acoustics KSM1 SiSonicTM MEMS Microphone from the iPhone 6 Module 3: MEMS Structural Analysis,” Chipworks, MPR-1603-802-03
- “Infineon SMM310E6433XT Integrated Silicon Microphone MEMS Process Review,” Chipworks, MPR-0804-801
- “AAC Technologies 00ALP3 MEMS Microphone with Infineon E2222K MEMS Die MEMS Process Analysis,” Chipworks, CWR-1512-902
- “Analog Devices ADMP403 MEMS Microphone Package Analysis,” Chipworks, PKG-1005-901
- “Akustica AKU2000 MEMS Microphone MEMS Process Review,” Chipworks, MPR-0704-802