Thermoelectric Materials Keep Chips Cool, Enable Faster Fiber Optics, and Proteomic Chips

11-Oct-2001 12:00 AM EDT

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EMBARGOED until 2 p.m. EDT October 10, 2001

Contact: Reid Maness, crm@rti.org, 919-541-7044

New Thermoelectric Materials Can Keep Chips CoolAdvances in Fiber Optics and in Biotechnology also are Likely

New thermoelectric materials could make a life-or-death difference for the next generation of microprocessors, enable fiber optic switches 100 times faster than current ones, and even turn a car's waste heat into electricity for the air conditioner. RTI researchers report the breakthrough in Nature, October 11, 2001

Thermoelectric devices are solid state "heat pumps" that can provide cooling, heating, precise temperature control, and also can convert heat into electricity.

RTI's new material is 2.4 times more efficient and responds 23,000 times faster than existing thermoelectric materials. A thermoelectric module with just one square centimeter of RTI's new material can provide 700 watts of cooling, or nearly one horsepower, under a temperature gradient of 58 degrees F.

RTI's material cools so efficiently that dots of it, applied just to the hot spots on a microprocessor, would give better performance than cooling the whole chip, and consume less power.

The technology emerges from a Department of Defense decision in the early 1990s to take a fresh look at thermoelectric technology, which had been stagnant since the 1960s. The Office of Naval Research (ONR) and the Defense Advanced Research Projects Agency (DARPA) have funded RTI's development of the new materials and device technology since 1993.

"The potential, enabling impact of RTI's discovery is truly staggering," said Valerie Browning, Program Manager at DARPA's Defense Sciences Office. "This revolutionary development will almost certainly improve the performance and capability of many cooling and power generation systems for DoD and commercial applications."

"This marks a major advance in field that has stagnated for 30 years," added John Pazik, director of ONR's Physical Science and Technology Division.

In addition to cooling microprocessors, this "anywhere any time" cooling/heating technology also could enable telecommunications routers based on the fastest fiber-optic switches available: electroholographic devices. If cooled, the switches can operate at low voltage, which means packing more switches into a smaller space.

Some of the existing technology used to switch signals in fiber optic trunk lines, which change the direction of laser light by using heaters to change the position of a bubble of liquid, would become 100 times faster if RTI's patented planar thermoelectric technology was used. These switches also would become more efficient, reducing the cost of regenerating laser signals over long distances.

The ability to control temperatures quickly and precisely at microscopic points also could enable new tools for biotechnology. For example, with precise temperature control at each of its nodes, a DNA microarray could self-assemble, replacing a laborious process in which robotic machines make the nodes one by one.

Temperature control also could enable proteomic chips, which would act by producing messenger RNA and translating it into proteins. These reactions are temperature sensitive, so microscopic thermoelectric devices could turn them on and off. Scientists potentially could create new proteins and enzymes, as pharmaceuticals, by using thermoelectric temperature control to manipulate binding of RNA polymerase with DNA.

The power generating capability of advanced thermoelectrics might appear first in automobiles, especially those with hybrid or fuel cell engines. Capturing even a small part of an car's waste heat would provide most of the electricity it needs, and even run the air conditioner.

RTI's new materials would be cost-effective immediately for any of these applications. The new materials are almost as efficient as mechanical heat pump systems, but for applications such as refrigerators and home heat pumps, the cost must come down.

RTI is an independent, nonprofit organization dedicated to research that improves the human condition. With a staff of more than 1,900 people, RTI turns knowledge into practice in the fields of technology commercialization, health and medicine, environmental protection, decision support systems, and education and training. www.rti.org

Attachments: -- Nature News release -- Technical abstract

Nature news release, EMBARGOED until 2 p.m. EDT October 10[413597] TECHNOLOGY: GET COOL FAST (pp597-602; N&V)

A new composite described in this week's Nature can pump heat rapidly to warm or cool miniaturized devices. It could help to cool computer chips and may provide a kind of mini Bunsen burner for scaled-down industrial chemical processing.

The material, devised by Rama Venkatasubramanian and co-workers at the Research Triangle Institute in North Carolina, relies on the thermoelectric effect: the generation of an electrical current in two electrically conducting materials that are in contact when one is hotter than the other.

Passing an electric current from one conductor to another can make the interface between them hotter or colder, depending on the direction of the current.

Most commercial thermoelectric devices are for cooling. Venkatasubramanian's group has found a way to greatly increase the amount and speed of heating or cooling using superlattices: stacks of very thin films of two alternating semiconducting materials. The researchers' device generates a cooling of around 32 degrees C at room temperature. Its thinness means it acts fast - about 23,000 times faster than bulk devices.

"The material properties are 2.5 times better than the current state of the art," explains Cronin B. Vining, at ZT Services, Auburn, Alabama, in an accompanying News and Views article. He adds that this result may be good enough to "greatly expand the range of practical applications".

Technical Abstract:Venkatasubramanian, R, Siivola, E., Colpitts, T., O'Quinn, B., "Thin-film thermoelectric devices with high room-temperature figures of merit," Nature 413, 597-602 (2001).

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then - despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of ~2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices - more specifically, phonon-blocking, electron-transmitting superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W per square-cm. The localized cooling or heating occurs some 23,000 times faster than in state-of-the-art bulk thermoelectric devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, self-assembly of DNA microarrays, proteomic chips, fiber-optic switches and microelectrothermal systems. They can also serve to meet the emerging thermal management needs in advanced microprocessors, power electronics, laser devices, IR-imaging devices.

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