SILICON TECHNOLOGY

Microelectronics based on silicon and its oxides underlies all of today's high-technology industries, from computers to communications to biotechnology. Microelectronics has also become common in our day-to-day lives, in applications ranging from automobiles and banking to control of household appliances.

Although silicon and germanium were used in radar detectors in the early 1940s, very little was known about the physics and materials science of these semiconductors. Scientists at Bell Laboratories soon recognized that a deeper understanding of these materials was necessary for rapid application to communications. Materials research in the mid-1940s ultimately enabled the invention of the transistor in 1947. Extensive, long-term research, along with the unexpected discovery in 1959 that silicon dioxide can passivate (protect) the surface of silicon, led to the invention of metal-oxide-silicon (MOS) transistors. The MOS transistor, combined with the increased understanding of the physics and materials science of semiconductor materials and devices that resulted from almost twenty years of intensive research and development, ultimately led to the invention of the integrated circuit.

FIGURE 2.12 Intricate layers of aluminum and tungsten wiring on an integrated circuit memory chip are revealed by etching away the interlayer dielectrics and then imaging the chip with a scanning electron microscope. The width of this image is about 10 microns (0.001 cm). A chip can contain as many as 50 million connections like those shown here in an area 1 cm on a side. (Courtesy of Lucent Technologies Bell Laboratories.)

Perhaps no other device has had as large an impact on day-to-day life as the silicon-based integrated circuit (IC). Although the IC was based on many years of condensed-matter and materials research at large industrial laboratories, the acceleration of its development and use was driven by government needs. Enabled by stable, long-term research stretching over almost two decades and stimulated by government funding, the discovery of the IC spawned the modern microelectronics industry, which is now a global enterprise. In 1995, IC sales exceeded $150 billion and supported an electronics industry with sales approaching $1 trillion. Without transistors and ICs, none of this would be possible.

INTEGRATED MICROSYSTEMS

The microelectronics industry has grown explosively over the last forty years. Such phenomenal growth has not been experienced in any other field in history. A key element behind the success of microelectronics has been integration. Integration of electronic functions on ever greater length scales leads to the low cost of production and assembly and high reliability. Miniaturization allowed for integration and simultaneously resulted in increased performance.

In the early 1980s researchers unveiled the first micromachined motor, demonstrating that the tools, facilities, and infrastructure developed to fabricate microelectronic circuits could also be used to build miniature mechanical systems. Though many research problems must be surmounted before microsystems can become as ubiquitous as the integrated circuit, this demonstration raised the hope that complex microsystems that integrate physical and chemical sensing and mechanical response with control and communications electronics can be mass produced at low cost. High-performance microsystems at lower prices would create markets for many products. In transportation, they could be used for position sensing, collision avoidance, navigation, and reliable airbag deployment. Environmental monitoring could be performed in hostile environments with inexpensive, disposable detectors. Microsystems could also be used in areas as diverse as biomedical applications and consumer products. They will probably have a profound effect on our lives and the lives of our children.

FIGURE 2.13 A prototype micromechanical mirror for use in optical communications systems. Either side of the flat hinged structure in the middle can be used as the mirror. The gears at the upper left are just just 50 microns in diameter. (Courtesy of Sandia National Laboratories.)



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