MEMS Microphones - A Global Technology
Most handheld consumer products requiring microphones, such as cellular phones
and portable tape recorders, use the electret condenser microphone (ECM) invented
at Bell Laboratories in the 1960s. These microphones are preferred for their
acoustical properties and low price, usually less than $1. In these devices, a vibrating
membrane picks up the sound wave, and electronic circuitry converts the vibration
into an electrical signal.
Traditional ECMs, while they have reached smaller sizes, are approaching the limits
of the technology and are unlikely to shrink much further or provide significant new
innovations. New microphone technology is needed that provides smaller
microphones with both greater ease-of-use and more design flexibility.
Silicon microphones are among a broad range of devices known as microelectromechanical
systems (MEMS), an emerging field in which various sensors and
mechanical devices are constructed on a single wafer using processes developed for
making Integrated Circuits-ICs. The chief advantage of micromachining silicon
microphones is cost. Several sensors can be processed on a chip simultaneously and
can be integrated with passive and active electronic devices.
One of the most notable differences between a MEMS microphone and an ECM is the
difference in size. The back plate and diaphragm in a MEMS microphone are
approximately 10x smaller than those in the smallest ECM. This inherent small size
allows a packaged MEMS microphone to start at approximately the same size as the
smallest ECM, with the potential to shrink much further as MEMS microphone
technology matures. A smaller microphone consumes less PCB space and requires
smaller height allowances, making it ideal for space-constrained designs
MEMS microphones are more compact than traditional microphone systems because
they capture sound and convert it to a digital signal on the same chip. When sound
waves hit the microphone's –membrane – a thin metal mesh in the middle of the –
chip – it vibrates, producing a voltage that contains information about the analogue
sound signal. But since the analogue signal is produced and converted to a digital
signal on the same chip, it never has to experience the harsh electromagnetic
environment outside the circuit. And, because interference is less of an issue,
insulation is not needed. This allows engineers to place the microphone anywhere
that a chip can fit, for example, into a laptop in which multiple microphones can even
fit in the bezel surrounding a laptop's monitor.
STUDY GOALS AND OBJECTIVES
Most microphones in consumer electronics (CE) products today are based on
technology that has remained fundamentally unchanged for 50 years. Problems with
the ECMs include noise, size and manual assembly.
However, the main challenge for the audio system designer is to achieve the lowest
overall noise in the system design. The noise of an ECM is a function of several
sources: electrical noise resulting from fluctuations in the bias voltage, noise of the
FET, board noise, acoustic self noise of the diaphragm, and external Electromagnetic
(EM) and Radio Frequency (RF) fields that are coupled into the high impedance input
of the FET.
MEMS microphone solutions developed on the CMOS (complimentary metal oxide
semiconductors) MEMS platform frees consumer electronic device designers and
manufacturers from many of the problems associated with ECMs. When electronic
circuitry is fabricated within microns of the acoustic structure, the short trace
lengths lead to an inherently improved ability to mitigate RF noise. The CMOS MEMS
microphone has a very short diaphragm to preamp distance and better input to
output isolation due to the on-chip amplification stage as opposed to the FET in an
ECM. Since there is better power supply and output signal isolation as well as a
shorter distance between the diaphragm and the preamplifier, there is less chance of
coupling EM fields into the microphone.
CMOS MEMS microphones also integrate an analogue-to-digital converter on the
chip, creating a microphone with a robust digital output. Since the majority of
portable applications will ultimately convert the analogue output of the microphone
to a digital signal for processing, the system architecture can be made completely
digital, removing noise-prone analogue signals from the circuit board and simplifying
the overall design.
CMOS MEMS microphones also solve many of the mechanical design and
manufacturing challenges associated with using an ECM. First, the monolithic nature
of the CMOS MEMS microphone enables a footprint and height that can be less than
half that of a traditional ECM. Second, the small size and mass of the CMOS MEMS
microphone diaphragm, which has a diameter of less than 0.5mm, leads to improved
vibration immunity as compared with an ECM, which has a diaphragm diameter of 4-
6mm. Third, since CMOS MEMS microphones are fabricated using standard CMOS
materials and processes, they are inherently able to withstand the high temperatures
required for surface mounting. Therefore, no mechanical interconnect is required,
which leads to another significant reduction in overall height of the microphone
system. Finally, the surface-mount and pick and place compatibility of the CMOS
silicon microphone reduces cost by eliminating manual assembly, thereby improving
reliability, manufacturing throughput and yield.
Therefore, this study focuses on MEMS microphones that can be used in mobile
phones, digicams, camcorders, laptops, automotive hands-free calling and hearing
aids. Production will be low-cost and high-volume.
This study focuses on providing market data about the size and growth of the MEMS
microphones application segments, new developments including a detailed patent
analysis, company profiles and industry trends. Also, this report provides a detailed
and comprehensive multi-client study of the market in North America, Europe,
Japan, China, India, Korea and the rest of the world (ROW) for MEMS microphones
and potential business opportunities.
The objectives include thorough coverage of the underlying economic issues driving
the MEMS microphones business, as well as assessments of new advanced MEMS
microphones that are being developed. Another important objective is to provide
realistic market data and forecasts for MEMS microphones. This report provides the
most thorough and up-to-date assessment that can be found anywhere on the
subject. The study also provides extensive quantification of the many important
facets of market developments in MEMS microphones all over the world. This, in
turn, contributes to the determination of what kinds of strategic responses companies
may adopt in order to compete in this dynamic market.
REASONS FOR DOING THE STUDY
The MEMS microphone exhibits many qualities that make it ideal for integrated
microphone array applications in laptop and desktop computers. Most importantly,
the robust digital output is immune to the EM or RF interference that can prohibit
optimal acoustic placement of a standard analogue-output microphone in a laptop
computer. The small footprint and thinness also increase the flexibility of the
microphone placement.
The widespread availability of well maintained CMOS models and simulation tools
results in products that can go from design to prototype in a matter of weeks.
Leveraging the economies of scale, high quality and maturity of the semiconductor
industry, CMOS MEMS provides cost effective solutions that can be incorporated into
mobile phones, digital devices and automotive accessories. Therefore, iRAP has
produced this detailed technology update and industry analysis in this area.
SCOPE AND FORMAT
The market data contained in this report quantifies opportunities for MEMS
microphones. In addition to product types, it also covers the many issues concerning
the merits and future prospects of the MEMS microphone business, including
corporate strategies, information technologies, and the means for providing these
highly advanced products and service offerings. It also covers in detail the economic
and technological issues regarded by many as critical to the industry’s current state
of change. The report provides a review of the MEMS microphones industry and its
structure, and the many companies involved in providing these products. The
competitive position of the main players in the MEMS microphones market and the
strategic options they face are also discussed, as well as such competitive factors as
marketing, distribution and operations.
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