Sandia National LaboratoriesAlbuquerque, N. Mex.

Double Electron Layer Tunneling Transistor

Fooling Mother Nature at her own game isn't easy. For two decades scientists have explored the possibility of building a transistor that would allow electrons to slip through seemingly impenetrable physical barriers inside the device itself. Their ultimate goal? Create a semiconductor that's faster and far more efficient than anything available today. Last February scientists at Sandia National Laboratories in Albuquerque announced that they had made just such a breakthrough. Expected to operate at roughly 10 times the speed of the fastest transistor circuits presently in use, the device, dubbed Double Electron Layer Tunneling Transistor (DELTT), could pave the way for dramatic performance improvement in telecommunications, desktop and mainframe computing, electronic measurement devices, and an array of specialized applications. Because DELTT might also detect infrared light far better than any existing device and is completely tunable, it also promises to revolutionize automobile collision avoidance, chemical and biological weapons detection, and industrial monitoring -- including the appearance of chemical or biologic agents in food or agricultural products. The compact size of the quantum transistor means that it can be built into much smaller machines than currently exist. "The device has far reaching implications and can be used in a wide array of industries and applications," says Jerry Simmons, head of the Nanoelectronics Group in Sandia's Semiconductor Physics Dept. He and a team of eight colleagues have worked on the project for nearly five years. In 1997 they finally proved that the principal was viable. Although other companies, including Texas Instruments, Motorola, IBM, and Lucent Technologies, have experimented with quantum transistors over the last two decades, it wasn't until Sandia embarked on the project that a major breakthrough occurred. DELTT succeeds by taking advantage of quantum effects that don't normally occur in transistors. The device consists of two layers of gallium arsenide 15 nanometers thick and separated by an aluminum-gallium-arsenide barrier 12.5 nanometers wide. Simmons likens it to a pair of houses separated by a six foot high fence. Ordinarily the electrons wouldn't have the strength to climb over the barrier and into the other yard. But, in this case, because the barrier is so thin, electrons can act more like waves and pass through the fence when the right electrical field exists. Although Sandia has demonstrated a real circuit that works and can be easily fabricated, actual commercial development of the device is still a few years away, says Simmons. Nevertheless, DELTT has already begun to attract interest and attention. "The true significance of this device is that researchers have felt like they were running into a brick wall when it comes to future semiconductor development. Using conventional transistors, it would soon be impossible to build devices any smaller or faster. The DELTT technology is a way to break through the bottleneck and usher in a new era of semiconductor development," he boasts. Simmons believes that telecommunications -- particularly satellite communications, digital radar, and cellular phones -- represent one of the biggest potential applications for the technology. He points out that mobile communication is currently constrained by spectrum problems and bandwidth limitations. Because the DELTT chip would use a different part of the spectrum, it could usher in higher speed wireless data communications. On the industrial front, it could eventually lead to wristwatch-sized mobile spectrometers that could take the place of today's awkward three-foot-long behemoths. These spectrometers could sniff out food borne bacteria such as salmonella or ensure the chemical purity of pharmaceutical drugs. The same capability could allow scientists to map toxic-waste sites. And for businesses and consumers, the performance boost could lead to sophisticated new PCs able to handle high-level speech recognition and pattern recognition. DELTT chips could also lead to tiny electronic medical implants and hearing aids with ultra-low power consumption capabilities. That could translate into units that would last years inside the human body and provide a higher level of dependability. "We could build specialized chips to serve all sorts of functions. It's a technology that has real commercial value," Simmons explains. "Recently, scientists have been discussing the limitations of today's technology. Now we're pondering the possibilities of the next generation of transistors."

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