Small is not just beautiful, but dutiful. Tim Radford reports on the coming of the almost invisible machine
The new machines are millimetres big at the most. Their moving parts are microscopic: the size of pollen grains. The first may have already saved your life on the road and the latest may already be saving your bacon while you play Tomb Raider. Any year now they’ll be ticking away in your watch, your computer, your television set.
They are the micromachines. Systems on a chip – little springs and gear levers and sensors made as part of the electronic wafer – are already being fitted to cars and computer joysticks.
Very soon, they could be running satellites, monitoring battlefield operations, and sniffing for dangerous fumes in fire emergencies. Right now, mostly what they do is trigger airbags.
It all started, says Jim Smith of Sandia National Laboratories in Albuquerque, New Mexico, as a simple sensor based on a mass on a spring, built simultaneously on an integrated circuit. “Instead of a small ball weighing a few grams, it is now a little piece of silicon a little bit bigger than the width of a human hair, weighing a microgram.
“The springs are only a micron in width, finer than a red blood cell. So you can make a mass on a spring but you can make it on the same chip as you are making electrical components. You can sense motion from the outside world, and you can pass information optically.”
You can make a decelerometer any size you like. If you make it on a chip on a scale of millionths of a metre, you have something that can sense the deceleration of the kind that might happen when cars collide at 50km/h, pass the word to its microprocessor and fire an airbag in bags of time to protect the driver.
But that is a relatively high-cost extra in an already expensive vehicle. What will kickstart the world of the micromachine is the economies of scale.
Once the devices can be made in high volumes, the components themselves will become inexpensive. The machines will then become technology in search of once-unimaginable roles.
“Once you have inexpensive components, you can afford to put them in the joystick of a computer,” says Smith. He sees them being fitted to portable tape and CD players for the jogging fraternity, to compensate for shock.
“Your average 15-year-old may only want to spend $50 on a Walkman, but boy, he’d spend $75 if it had this anti-shock feature.”
The micromachines will be welcomed in spacecraft, where every 500g of payload adds $10 000 to launch costs. Satellites have to keep antennae pointing in the right direction, and they are fitted with sensors that tell how far the spacecraft has turned, and when to turn the thrusters off.
“Right now, those types of systems weigh pounds and are the size of your fist,” says Smith. “With a set of micromachines you could do that on a system that would weigh just a gram.”
The next step is to fit them into watches. Smith and a team at Berkeley, California, have fashioned a new clock source from a micromachine.
The quartz crystals in your wristwatch are piezoelectric: they change shape and store a charge in an electric field and release it when there is no current, so electric energy sloshes back and forth between the crystal and a timing circuit in a feedback loop.
The Sandia version works electrostatically: it uses polysilicon resonators that vibrate very like a tuning fork. The difference is in the size: 10 of them would fit on a pinhead. Right now, they generate frequencies of 1MHz: soon, they will be oscillating at above 10MHz.
It is a step to getting the clock, the machine and the circuitry all on the same chip. Engineers at Sandia claim to have made a micromechanical transmission assembly with a three- million-to-one gear reduction ratio, in less than 1mm2: surely the torque of the town.
The next trick is to supply the instruments with the capacity to share intelligence. The problem is: how small can you make a battery, or antennae?
“There are some people working on fuel-cell technology, there are some people working on miniature turbines; and those technologies have a much higher energy density,” says Smith. “You might imagine one of those, you might imagine devices that scavenge fuel from the environment.
“Twenty years ago they had self- winding wristwatches – you shook your arm and you wound your watch.
“You could imagine devices like that to capture power from the environment and that would enable them to go smaller still: millimetre-sized. You’d have to crawl around on the floor to see them.”
A decade ago micromachines were laboratory curiosities. Now they are being produced in tens of millions for the electronics market: for joysticks and computer mice and inkjet printers. By early next century, the Sandia team calculate the market could grow to $30-billion, worldwide.
“I liken it to the integrated circuit industry at the end of the 1960s,” says Sandia’s Bill Miller, who has been testing them for reliability. “A lot of potential, but nobody really knew how big it could get then.”