Kieran P. Harney

A History of Consumer Microphones: The Electret Condenser Microphone Meets Micro-Electro-Mechanical-Systems

On a bright fall morning last October there was a historic meeting among three industry stalwarts that was of particular interest to the acoustics community. Gerhard Sessler and James West returned to New Jersey, the home state of Bell Labs where they both started their professional careers, to be inducted into the “New Jersey Inventors’ Hall of Fame.” Ray Stata, founder of Analog Devices and a pioneer of Micro-Elecro-MechanicalSystems (MEMS) devices, was passing through on business. The three got together at the beautiful Reeves-Reed arboretum in Summit, New Jersey for a discussion on the evolution of consumer microphones towards MEMS (see Fig.1). Drs. Sessler and West invented the Electret Condenser Microphone (ECM) at Bell Labs in the early 1960’s. The low cost and small size of the ECM has enabled the production of modern consumer devices such as cell phones, headsets, and video cameras. As a result, in excess of 2 billion ECM microphones shipped in 2008. In 1965, Ray Stata founded Analog Devices, a world leader in semiconductor converter and amplifier microchips today. In the early 1990’s Ray Stata played a key role in evangelizing MEMS technology, enabling the manufacture of small, low cost accelerometers and gyroscopes for automotive and consumer markets. More recently, he, with his company, developed world-leading MEMS microphone technology. In the 1980’s Dr. Sessler did much of the early academic research in MEMS microphones at the University of Darmstadt, Germany. Dr. Sessler is recognized as one of the earliest advocates for research in the field of silicon microphones. Amid the beauty of the autumnal foliage of the Reeves-Reed Arboretum, Sessler, West, and Stata sat down to discuss the evolution of microphones and consider what the future might hold.

Standard semiconductor packaging for high reliability low cost MEMS applications

Microelectronic packaging technology has evolved over the years in response to the needs of IC technology. The fundamental purpose of the package is to provide protection for the silicon chip and to provide electrical connection to the circuit board. Major change has been witnessed in packaging and today wafer level packaging technology has further revolutionized the industry. MEMS (Micro Electro Mechanical Systems) technology has created new challenges for packaging that do not exist in standard ICs. However, the fundamental objective of MEMS packaging is the same as traditional ICs, the low cost and reliable presentation of the MEMS chip to the next level interconnect. Inertial MEMS is one of the best examples of the successful commercialization of MEMS technology. The adoption of MEMS accelerometers for automotive airbag applications has created a high volume market that demands the highest reliability at low cost. The suppliers to these markets have responded by exploiting standard semiconductor packaging infrastructures. However, there are special packaging needs for MEMS that cannot be ignored. New applications for inertial MEMS devices are emerging in the consumer space that adds the imperative of small size to the need for reliability and low cost. These trends are not unique to MEMS accelerometers. For any MEMS technology to be successful the packaging must provide the basic reliability and interconnection functions, adding the least possible cost to the product. This paper will discuss the evolution of MEMS packaging in the accelerometer industry and identify the main issues that needed to be addressed to enable the successful commercialization of the technology in the automotive and consumer markets.