Diamond -- Engineering News: Vanderbilt University School of Engineering

Vanderbilt University School of Engineering News

Diamond
Crown Jewel of Microelectronics

It turns out that diamonds might be an engineer's best friend, too.
Long known for their hardness; their superior ability to conduct heat and electricity; and their resilience in the face of chemical, radiation, and thermal attacks, diamonds have been eyed covetously for years by engineers who would like to put the material to work in computers, sensors, and actuators.
How to do that proved to be a problem, however. The mineral occurs naturally as crystals, but for decades there seemed to be no way to produce a thin film of diamond needed to replace or augment silicon layers in integrated circuitry.
High-energy gas chemistry research in the 1960s led to the discovery that diamond could be layered onto a substrate by applying intense and precisely directed forces of heat, pressure, and microwaves to make a plasma of hydrogen mixed with a carbon-bearing gas-like methane, says J. L. Davidson, professor of electrical and computer engineering. This chemical vapor deposition (CVD) process of layering diamond became more feasible in the 1980s as equipment to apply thin diamond films over an area larger than a square foot was refined.
"Today diamond is considered a likely candidate for the next generation of semiconductor materials," Davidson says. "Not only can it replace silicon in many applications, diamond film also makes possible the design of microelectronic vacuum tubes that can replace solid state transistors with faster, cooler transistors that are electrically 'harder', being very resistant to temperature and radiation."

J. L. Davidson, left, professor of electrical and computer engineering, and W. P. Kang, associate professor, head the Vanderbilt diamond research and development team.
Photo by David Crenshaw

VUSE Leads in Technology

Vanderbilt School of Engineering is a leader in the development of this technology that produces superior solid state and vacuum microelectronics, microsensors, electric power devices, microactuators, and microelectromechanical cooling systems.
The diamond research and development team is headed by Davidson and W. P. Kang, associate professor of electrical engineering and computer engineering. Kang's work on tips and sensors combines well with Davidson's research on diamond film properties and processes. Another faculty member, Tim Fisher, assistant professor of mechanical engineering, is investigating a new area of developing diamond devices that convert energy efficiently. The research team conducts modeling, design development, fabrication, analysis, and testing of diamond devices.
Kang's expertise in sensors and emitter tips led to the development of diamond film microemitter arrays. Vanderbilt is the only institution that makes microemitter diamond array structures, Davidson says.
The technology can be used, for example, to produce bright, durable, and efficient flat panel displays for computers, and its advantages in switching and sensor devices will have a profound and lasting impact on defense and industry.

Diamonds Take the Heat

The group is working on several projects that will use diamond's sensing capabilities at high temperature and pressure.
A project funded by NASA involves developing a diamond film pressure sensor to measure pressure on wings of hypersonic aircraft expected to travel from coast to coast in the U.S. in 30 minutes.
The aircraft, which will travel half of the time in the atmosphere, half of the journey in space at speeds in excess of Mach 15, will sustain extreme conditions in temperature and pressure. Diamond-film pressure sensors can monitor pressure at temperatures in excess of 1,000 F and at high frequencies of vibration, providing more details about pressure on the wing that can help designers

Microscopic diamond emitter tips can emit electrons more efficiently than any other technique.

develop more efficient, durable designs.
The U.S. Air Force is interested in diamond's durability in developing sensors that can help air-to-ground missiles be more accurate and effective. VUSE is developing motion sensors for use in accelerometers that can profile the 10,000 -- 50,000 G event of a missile's impact on a target. "The accelerometer's ability to precisely sense deceleration will help 'smart bombs' know when they've gone through a protective outer wall versus when they've reached the inner target itself," Davidson says. The smart-sensor technology can also be used to develop better automobile air bags.
Diamond's ability to continue performing chemically and electrically in extreme temperatures makes it a good material for a chemical sensor that measures carbon monoxide in automobile engines.
The U.S. Department of Energy is funding VUSE research into designing a diamond film chemical sensor that makes sensitive calibrations and adjustments in fuel-to-oxygen proportions enabling engines to burn more efficiently. "Silicon loses its sensing properties over 200 F, but diamond continues to work well in combustion temperatures of over 1000 F," Davidson says. --Vivian Cooper-Caps