Nanotechnology goes to war

David Hambling
Wouldn't it be handy if everything we needed to build the next generation of portable devices and robots were available on a microchip? You could just plug in a navigation system, a radar sensor, cryogenic cooling system, or even a miniature power unit. For laboratory applications, there would be micro versions of everything from mass spectrometers to magnetic sensors. The Defence Advanced Research Projects Agency (Darpa), the Pentagon's extreme science wing, aims to provide all this, and more, in handy "matchbook size" electronic packages.

Forty years ago, Gordon Moore, the co-founder of Intel, accurately predicted that the cost of processing power would halve every two years. We have come to expect devices to get smaller, cheaper and more powerful over time. Now the revolution is spreading to other types of device. The development of mems (microelectromechanical systems) has already paved the way for "lab-on-a-chip" chemical analysis. Such breakthroughs tend to come from the military rather than industry.

"Darpa was instrumental in helping support much of the initial development of lab-on-a-chip in the early 90s," says Jon Cooper, Wolfson chair of bioengineering at the University of Glasgow. "The technologies enabled a number of US startup companies to develop miniaturised chips for faster biological analysis, giving them the necessary long-term support to grow."

Cool runnings

Now Darpa is miniaturising many new devices. Some electronics require very low temperatures, such as superconducting circuits and infra-red sensors, and the entire component is chilled by a bulky cooling system. The low-power micro-cryogenic cooler program will cool only the exact spot needed.

The key element is a "micro-machined thermal isolation structure", a tiny deep-freeze made of bismuth telluride. This cools by the thermoelectric effect when a current is applied. The micro-cooler will chill a space of about four cubic centimetres down to 200 degrees below zero, using just 0.1 watts.

Lab-on-a-chip devices already use pumps to move gas or liquid. But these pumps are not able to maintain the "hard" vacuum required for devices such as mass detectors for analysing airborne chemicals and bolometers to measure irradiation. The chip-scale vacuum micropumps program aims to produce pumps capable of producing a pressure of one millionth of an atmosphere.

Some items are for specific applications. Microsensors for imaging will deliver an infrared video camera on a chip weighing just 10g; this is specifically for uncrewed aircraft and night-vision goggles. But most of the technology will simply be made available to industry for use in future military electronics. Other programs include an atomic clock on a chip, radar on a chip, gas analysers and other sensors, radio-frequency and photonic devices. Some would have multiple uses, such as the chip-scale atomic sensors program. These tiny, high-resolution sensors can be reconfigured instantly to measure temperature, pressure, magnetic fields or other environmental factors. It's an ambitious program, but the US defence sector has a record of getting the microtechnology it needs.

In recent years, the possibility of bioterrorism prompted Darpa to provide chip-based analytical tools for homeland security. Cooper cites several developments, including advances in rapid polymerase chain reaction (PCR) used to analyse DNA. This technology now has a much wider use in diagnosing infectious diseases. However, chip-based doesn't always mean portable.

"The concept of lab-on-a-chip is of an analytical system which benefits from its reduced size, although many instruments are chips-in-a-lab, rather than labs-on-a-chip," says Cooper. "Often the instrument needs to be plugged into the mains."

"Truly handheld lab-on-a-chip technology is still elusive," agrees Matt Mowlem of the National Oceanography Centre at Southampton. "Building stand-alone systems requires integrated systems and solutions to the problematic engineering issues surrounding system design, interconnects between the chips and off-chip systems, packaging and support systems, etc."

But Darpa wants it all to be self-contained, enthusing in budget documents about "matchbook-size, highly integrated device and micro-system architectures", including "low-power, small-volume, lightweight microsensors, microrobots and microcommunication systems". Much of the effort is to integrate different components so that "electronic, mechanical, fluidic, photonic and radio/microwave technologies" all work together on the same chip.

Socket to 'em

Then there is the need to plug into that wall socket. Darpa is addressing the need for mobile power with tiny heat engines and devices that scavenge energy from the environment. Being military, it also walks where others fear to tread. The micro isotope power source is a tiny atomic battery, occupying less than a cubic centimetre and generating 35 milliwatts.

Industrial funding is limited. Darpa, which is not looking for profit, can sink money into unlikely schemes.

"As with all blue-sky research there is a high risk of failure," says Mowlem, "but a small chance of a world-changing discovery." Darpa is not afraid of failure, and has its eye on world-changing success. After all, it did invent the internet.