By Sean Henahan, Access Excellence

ALBUQUERQUE, NM (May 8, 1996)- Originally developed to provide better security for nuclear arms, micromachines now in development offer the potential of everything from better airbags to improved drug delivery.

(Photo: A dust mite, a tiny dot to the human eye, crawls across a new micromachine. Click for larger view.)

In the past two years, researchers at Sandia National Laboratories have created a succession of increasingly powerful micromachines. Most recently, they have been able to create 'intelligent' machines capable of signaling its status and power requirements and performing tasks on and automated basis.

They have accomplished this by combining tiny motors only one millimeter square with integrated circuit "brains" on individual silicon chips. The compact design, made possible by sinking the motors in tiny etched trenches, enables the fabrication of entire electromechanical systems on a chip.

"This is definitely a substantial advance they've come up with," said Roger Howe, director of the University of California - Berkeley's Sensor and Actuator Center. "A lot of people are champing at the bit to access this technology. We hope to be early in getting adapted so that talented graduate students -- not just in Berkeley but anywhere in the country -- can invent new circuits to play around with. Once the process is tuned up, there's no shortage of people who will dive in to try it out."

Said Richard Payne, director of the advance accelerometer team at Analog Devices, the largest producer of automated airbag sensors in the U.S., in Wilmington, Mass., "We're talking with Sandia in a preliminary way to use their technology to prototype devices. The technology they've recently demonstrated is what we're working on. It's the right direction." Analog Devices interleaves the steps of circuit and microsensor creation on a single chip, but focuses on the application of airbag accelerometers.

"This will be a big enabler for a variety of new products to be produced that are small, smart and cheap," said Paul McWhorter, manager of the effort in Sandia's Microelectronics Development Laboratory. By using the semiconductor industry's fabrication methods, "We've created a generic manufacturing process."

Medical possibilities of micromachines include the creation of tiny drug delivery devices, tumor destroying robots and utlimately, machines capable of performing repairs on the cellular level, eg on damaged DNA. Other possibilities for the general-purpose process include the creation of tiny, inexpensive, long-lasting gyroscopes for civilian and military uses.

The process was originally developed to enhance the safety and security of nuclear weapons by providing smarter, more reliable locks for the devices.

The Sandia process involves etching tiny trenches in silicon chips and fabricating the machines within these depressions like pool tables in sunken living rooms. The machines, heat-treated, are then submerged in a tiny hardening sea of silicon dioxide.

"If you first sink the machine in a trench and then fill in around it, in effect you've recreated a pristine wafer for doing electronic processing," said Steve Montague, inventor of the approach. The hardened silicon dioxide re-creates a level chip surface upon which circuitry is fabricated by photolithography.

Removal of the silicon dioxide at the end of the process frees the microengines. Working systems are manufactured with a 78 percent success rate -- a reasonably high measure of production yield.

The process can produce a wide range of micromachine systems because it allows independent optimization of micromachine and microcircuit performances, achieving the "paradoxical but desirable result of larger, more powerful micromachines with smaller transistors," said McWhorter.

The inexpensive manufacturing process can be used either to produce "tens of thousands of units a day, reducing costs significantly for government or industrial users, or to do specialty work making unique motors and circuits for university or medical researchers," Sandia scientist Jeff Sniegowski said.

Circuits fabricated only microns from a machine eliminate ghost signals -- parasitic currents -- created by excess electrical capacitance in long connecting wires.

"Without this interference, by applying a mechanical load you can measure the capacitance change in the drive gear teeth as they move in and out," said Sandia engineer Ernest Garcia. "Then you know how fast the machine is moving. The sequence allows you to understand velocity."

The Sandia researchers have overcome significant technical obstacles to reach this point. The difficulty with joining a microcircuit to a micromachine on a silicon chip has been that aluminum circuit interconnectors, if formed first, melt when the micromachines are heat-treated. If the gears are not heated to approximately 900 degrees Centigrade, said Sandia scientist Jeff Sniegowski, "Like potato chips, they curl."

If micromachines are fabricated first, their elevation above the chip surface creates bumps that distort the delicate process of etching accurate microcircuits. "You can't have fine undulations or striations in the photoresist," Sniegowski said. "At that scale, five microns is a mountain, and a micromachine is five to six microns high."

BACKGROUND

The advance is the latest in a series by Sandia scientists. Last September, the Laboratories announced that its researchers -- using methods similar to those of the integrated circuit fabrication industry -- had succeeded in mass producing micromachines that could perform work. The machines turn gears each one-hundredth the weight of a dust mite -- itself seen by the human eye as a tiny dot -- at hundreds of thousands of revolutions per minute. Each gear is approximately one hundredth the thickness of a sheet of paper, and smaller in diameter than a human hair.

Sandia researchers also recently announced the creation of the world's first working microelectronic device to be made with extreme ultraviolet light. The device is a field effect transistor, a common building block of all integrated circuits. It has an electrical channel, or gate width less than 0.13 microns, a thousandth the width of a human hair, roughly three times smaller than devices on current chips.

Sandia National Laboratories is a multiprogram national laboratory operated by a subsidiary of Lockheed Martin Corporation for the U.S. Department of Energy.

Related information on the Internet

Sandia Home Page

Sandia: Microelectronics Page

Nanotechnology Sites

"Engines of Creation", Web Version of Nanotechnology Classic

Links last updated: July 2001

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