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Using silicon micromachining, a state-of-the-art approach for making silicon materials with microscopic features, Peter Gammel and his colleagues at Bell Labs/Lucent Technologies in New Jersey built a microphone on a silicon integrated circuit, shown above. The base has marks with an approximate size of just 100 microns (0.1millimeters).lllll Figure courtesy of Bell Labs/Lucent Technologies.
Fans of the Dick Tracy watch — a two-way, voice-activated video phone that fits around a wrist, introduced in a Jan. 13, 1946 edition of the famous comic strip — will be thrilled to hear that the device may soon become a technological reality. According to Peter Gammel, a researcher at Bell Labs, such a device contains many of the features one would like to see in portable wireless devices, including voice instruction, video capability, seamless operation and an attractive physical design. At the APS New York State Section meeting held April 20-21 at Bell Labs/Lucent Technologies in Murray Hill, NJ, Gammel described three research results which are aiding in bringing this vision closer to fruition, estimating that all the necessary components should become technologically available as early as 2005.
The first involves the development of miniature radio frequency filters. In current cell phones, the radio filter, made of a ceramic material, is by far the largest single component. In a second effort, silicon micromachining, a state of the art approach for making silicon materials with microscopic features, is used to incorporate the microphone onto a silicon integrated circuit, another step towards the single chip radio. A third effort also involves the use of silicon micromachining, this time to fabricate high quality inductors. Inductors, which are simple loops of wire, are used in part of a cellular phone which determines the proper frequency for communications. "It turns out the battery life of a cell phone is determined by a measurement in the inductors known as the 'quality factor,'" says Gammel. "High quality factor inductors, such as the ones we are making, can lower the demands on the battery, another step towards a real-life Dick Tracy watch." (For graphics, see http://www.aip.org/png/html/Dicktrcy.htm. )
Other scientists who gave invited lectures at the meeting covered such topics as optical micro-machines and plastic transistors. [The talks — which were free and open to the public — were designed for non-experts.] Marc Kastner of MIT described recent work on the Single Electron Transistor (SET), a new kind of device that turns on and off every time one electron is added to it, compared with the transistors currently used in cellular phones and laptop computers, which require about 1,000 electrons to turn on and off. "While some researchers are struggling to make these transistors commercially viable, we physicists are using them as laboratories for studying how electrons behave when they are confined to dimensions only about 200 times larger than the size of individual atoms," he said, describing experiments which demonstrate that the electrons in the SET settle into an unusual quantum state at very low temperatures, similar to the behavior of electrons on magnetic impurities in metals.
Another Bell Labs researcher, Zhenan Bao, reported on the developing of electronic devices known as MISFETs-metal-insulator-semiconductor field-effect transistors-made of thin-film and organic components. Organic thin-film MISFETs are potentially useful not only as large area flexible displays (especially for ultrathin TV screens) but also as low-cost memory devices. Some proposed applications for plastic transistors are: driving circuits for electronic papers, luggage tags, price tags, and smart cards. "Plastic transistors are not intended to replace silicon devices, but rather they offer opportunities for low cost flexible large area devices," said Bao.
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