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MEMS MICROPHONES – A GLOBAL TECHNOLOGY, INDUSTRY AND MARKET ANALYSIS
Publish Date: Jul 2007,   Pages: 97,   Report Code: ET-105
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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 electromgnetic 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 industrys 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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