Akustica was the first company to produce a CMOS-based MEMS microphone, allowing it to place the signal processing electronic circuitry around the MEMS diaphragm (right) instead of the standard solution of wire bonding the two MEMS die side-by-side with the ASIC in the same package (left). Click here for larger image
Akustica's most original designs, since its first models in 2006, used a proprietary CMOS process to fabricate the MEMS microphone diaphragm on the same chip alongside the CMOS signal processing circuitry and analog-to-digital (A/D) converter. This patented technology, originating at nearby Carnegie Mellon University, enabled Akustica to deliver the worlds smallest MEMS microphone die. However, since its acquisition by Bosch in 2009, Akustica took advantage of the surface micro machining expertise and patent portfolio of its parent company. Using Bosch's process the MEMS diaphragm is fabricated in polysilicon on top of a silicon substrate using¬†deposition and sacrificial etching to release the mechanical diaphragm. The ASIC is then fabricated using standard CMOS manufacturing techniques¬†on a separate silicon die then wire-bonded to the MEMS die in the same package. As a result, the packages are slightly larger, but the ability to mix-and-match MEMS diaphragms with ASICs cuts costs and allows a bigger catalog to be built.
— R. Colin Johnson is the Advanced Technology Editor at EE Times, where he has written about MEMS microphones for over 10 years; in the early days of MEMS mics, his colleagues were baffled by his fascination with them, but his interest has since been vindicated.
All your arguements for digital outputs are valid, and in fact the first startup's first microphone (Akustica) had digital outputs. Unfortunately, its kind of like the VHS versus Beta video take war--if you can remember that far back--everybody was already set up for analog mics (electrets) so much so that even Akustica has had to acquiesce a prodeuce analog models. But I am with you, and think hat eventually all MEMS mics will be digital.
It would be interesting to know how far digital microphones (DMICs) -- MEMS mics that include the A/D converter -- have penetrated within the overall MEMS mic market. From an interface perspective, integrating the A/D into the same package as the MEMS makes so much more sense -- especially for applications requiring many microphones (beam-forming arrays, etc.). From the perspective of the audio processor at the receiving end, the two-wire PDM data & clock interface from a DMIC is so much easier to handle than a low-level analog signal, that it's probably well worth the extra cost of the MEMS mics with built-in A/D converters.
Oh that's an answer with fact figures; my estimation was based on the observation of my own. But yes it is very true that MEMS Mics will be having more chances of acceptance in other left out application with possible use of it for betterment.
Your are right too. Even though there are MEMS mics with HD quality, here is the breakdown on where they are used today (according to IHS)-- mobile phones (70 percent), tablets (13 percent), MEMS mics in headphones that manufacturers supply with their smarphones (9 percent), laptops (6 percent) and wearables (2 percent).
You are right many applications of MEMS Mic array are under development in many different areas, in the filed of mechanical engineering, environmental science, medical electronics etc. Soon many products will be in the market using MEMS Mic arrays. Although these Mics are still not being tried as conventional microphones that are used in live performances.
Beside smartphones, tablets all use MEMS microphones, also many PCs are switching over because they can locate mutiple MEMS in the bezel for noise cancelling and beam stearing. Apple's smart watch due this fall will use MEMS microphones also video camera, still cameras and digital recorders are all moving to MEMS mics. For the next generation, wearables will use MEMS mics and portable medical devices and the list goes on.
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