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Brad Petersen
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2052 ECE Building
306 N. Wright Street
Urbana, IL 61801
Phone: (217) 244-6376
bradp@illinois.edu

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Meg Dickinson
Communications Specialist
2016 ECE Building
306 N. Wright Street
Urbana, IL 61801
Phone: (217) 300-6664
megd@illinois.edu

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Recent News

New ECE class gives students an in-depth look at the engineering process

New ECE class gives students an in-depth look at the engineering process

Starting this semester, ECE ILLINOIS will offer students an opportunity to study the engineering design process and possibly get a head start on their Senior Design projects with a new class called ECE 398, Special Topics in ECE.

Microdischarge devices shed light on variety of applications

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By Laura Schmitt
January 1, 2002

  • Using standard micromachining and silicon processing technology, ECE researchers have developed light-emitting gas-discharge devices small enough to be integrated on a millimeter-sized chip.
  • "We've made an entire family of devices that are about five orders of magnitude smaller than fluorescent tubes used in overhead lighting," said ECE Professor Gary Eden.

Using standard micromachining and silicon processing technology, ECE researchers have developed light-emitting gas-discharge devices small enough to be integrated on a millimeter-sized chip. These devices, which are able to produce light from the far infrared to the soft x-ray region, may someday replace much larger and more expensive light sources for a variety of applications, including cancer detection and treatment and new gas and liquid sensors.

Left: Four 15x15 arrays of microdischarge devices made in silicon are shown next to a dime to illustrate their size. Each of the 900 devices has a cathode, which is an inverted square pyramid 50 microns square at the surface. Eden's group has made silicon devices as small as 10 Ám 2.
Left: Four 15x15 arrays of microdischarge devices made in silicon are shown next to a dime to illustrate their size. Each of the 900 devices has a cathode, which is an inverted square pyramid 50 microns square at the surface. Eden's group has made silicon devices as small as 10 Ám 2.

"We've made an entire family of devices that are about five orders of magnitude smaller than fluorescent tubes used in overhead lighting," said ECE Professor Gary Eden. "The emission we generate depends on the gas or gas mixture we use."

According to Eden, a major application area for the gas-discharge devices is flow cytometry, a medical technique for sorting healthy cells from bad cells by illuminating them with visible or ultraviolet light and then examining the spectrum they produce. Currently, a large laser costing as much as $50,000 is used as the light source.

"Our technique appears to be a very attractive way of mounting a light source directly into a cytometry system on a chip," Eden said. Not only that, but Eden's inexpensive optical array could produce light at various wavelengths, resulting in the capability to also destroy the undesirable cells.

Another medical application for Eden's devices is photodynamic therapy (PDT), a fairly new treatment that uses a fixed-frequency laser light and a photosensitizing agent to destroy certain types of cancerous cells.

"PDT is used all over the world, but its use has been limited because it requires a laser and not too many clinics can afford that," Eden said. "What we have in mind is a flexible array that would be inexpensive and could be wrapped around a patient's arm or chest with a Velcro strip. [The light source] lifetime is not the key issue. It doesn't have to last a thousand hours, it has to last two."

Eden is collaborating with ECE Assistant Professor Chang Liu, postdoctoral researcher Sung-Jin Park, and graduate research assistants Clark Wagner, Nels Ostrom, Scott McCain, Min Cai, and Jack Chen. They make one type of their discharge devices by chemically etching square pyramids upside down in a silicon wafer. A cavity having the same dimensions as the pyramid is also formed through an insulating film (dielectric) and a conducting film (anode). They then fill the cavity with a gas or mixture of gases and apply a voltage from the conducting film to the silicon, producing light.

"It lights up like a Roman candle," Eden said. "For 40 years, researchers have been trying to develop an intense optical source in silicon. The irony is that we've effectively done that, using the plasma or gas as an energy converter."

Eden's team has arranged multiple devices together in as many as four 15 x 15 arrays. These arrays have a radiating area of two square millimeters and include 900 individual devices, each measuring 50 microns on a side. In addition to silicon, the devices can be integrated on ceramic and other material substrates.

For example, Eden, ECE Adjunct Professor Bruce Vojak, and researchers at Motorola in Tempe, AZ, are developing ceramic devices based on Motorola's multi-layer technology originally developed for use in wireless circuit components.

"Because we use standard processing technology, these devices are straightforward to make and they're inexpensive," Eden said.

Packaging the arrays or devices is a challenge that Eden and his students are currently investigating. Laminating an array between two sheets of plastic is one inexpensive, yet not quite perfect, solution.

"Our devices currently last only 15 minutes not because they fail, but because the gas inside the devices becomes poisoned with organic vapors that bleed out from the plastic laminate," said Eden, who thinks this is not a major problem. "We need to deposit a transparent barrier on the laminating sheet to block the diffusion of the vapors into the microdischarge devices."

An electron micrograph of a 15 x 15 array of silicon microdischarge devices. Each device produces intense emission when filled with a gas or gas mixture and excited electrically.
An electron micrograph of a 15 x 15 array of silicon microdischarge devices. Each device produces intense emission when filled with a gas or gas mixture and excited electrically.

Eden's former student Cy Herring, who earned his PhD in physics in 1998, cofounded a company in Urbana, to explore commercial applications for the devices. According to Herring, Caviton is developing microdischarge devices for a variety of sensors that could be used in an environmental pollutant monitoring system, an oil and engine analysis instrument, and a portable gas and liquid analyzer.

"These sensors are small, lightweight, and use little power, so portable devices are a prime use of the technology," said Herring, who is working with Ju Gao (PhD '98) and biochemistry doctoral candidate David Kellner at Caviton.

Eden has three patents for his micro- discharge technology already, and he and his colleagues have filed for four more. Several display manufacturers have recently expressed an interest in Eden's technology, as have some lighting companies.

Editor's note: media inquiries should be directed to Brad Petersen, Director of Communications, at bradp@illinois.edu or (217) 244-6376.

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