Printed plastic electronics could cut future cleanroom stringency
By Mark A. DeSorbo
MISSIAUGHA, Ontario—Researchers at Xerox Corp. and Infineon Technologies say their potential alternative to silicon transistors, printed plastic electronics, could slash costs, pave the way for a new generation of products and eliminate the need for cleanrooms.
“This material is bendable, an active component of transistors and is not sensitive to oxygen,” says Beng Ong, a research fellow at Xerox Corp.'s Research Center of Canada. “Therefore, you do not have to take any precautionary measures with high temperature or pressure, and you can eliminate the photolithography process.”
Ong, who manages the printed organic electronics group here, says the team formulated the material by first understanding the polymer structural features responsible for limitations in existing materials. Then, the group developed design rules to get around those limitations, he says, declining to elaborate.
The materials were then evaluated in simple devices at Xerox, with further testing and experimental printing at its Palo Alto Research Center (PARC) and select electronics firms around the world.
Ong, along with Tony Paine, a venture principal at Xerox, believes the material will also bring the world one step closer to portable, poster-like television screens and monitors made of a single sheet of flexible plastic.
“We're trying to make electronic paper for e-books and newspapers and make the smart card more accessible to the public in terms of cost,” Ong says.
“We're taking the technology we have in ink jet printing and making printed, plastic electronic circuits,” adds Paine.
Meanwhile, Munich, Germany-based Infineon has also developed organic transistor-based electronic circuits on various substrates. According to the chipmaker, the organic circuits have achieved performance capability levels that its researchers say were previously unattainable.
 Beng Ong is leading a group of Xerox Corp. researchers exploring ways to print integrated circuits on a plastic sheet instead of etching them on silicon wafers. |
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Thin-film transistors, according to a company report, use organic molecules as the active layer and achieve charge carrier mobilities in excess of one square centimeter per Volt second (1 cm2/Vsec).
According to Infineon: “While the manufacture of integrated circuits using silicon or other crystalline semiconductors requires a large number of sequential processes with expensive equipment and is, therefore, tedious and relatively expensive, polymer electronics can be manufactured rapidly, at low cost and in large quantities.”
Among the applications envisioned by Infineon for polymer electronics are wireless radio frequency (RF) identification badges, flat-panel displays, large sensor arrays and biochemical sensors.
“The latest research results at Infineon show that plastic-based integrated circuits (ICs) can be a potential addition to silicon chips in high volume and extremely cost-critical applications,” says Dr. Soenke Mehrgardt, Infineon's chief technical officer. “Possible applications for low-cost polymer IC's are RF ID tags as an alternative to barcodes or for use in the wearable electronics area.”
Infineon researchers developed a process portfolio that can be combined in a variety of ways and can be used to manufacture high-quality organic transistors and circuits using conventional deposition processes and photolithographic patterning techniques.
Infineon scientists have also used micro-contact printing—a relief printing method similar to flexographic printing—to pattern transistors and circuits, with feature size and electrical performance similar to those of transistors and circuits fabricated by photolithography.
Xerox's Paine points out that polymers are suited for powering such electronic devices as flat-panel displays, saying the material conducts low voltage at a slow rate.
“This is more applicable to large-area electronics, like drivers for screen, not for things like Pentium chips,” he says, adding that Philips Electronics N.V. has already revealed a two-inch screen driven by organic electronics.
While the material aims at innovating large-area electronics, Paine says an easy-to-manufacture silicon alternative is equally appealing.
“Usually you are spending billions for a fab. It can cost $200 to $500 per square foot, but with organic electronics, it is about $5 per square foot,” he says. “With organic electronics, you won't be using photolithography, you can use a roll-to-roll machine process. It's this kind of opportunity that is causing people to investigate this field.”
Under a National Institute of Standards and Technology grant, scientists from Xerox are collaborating with teams at Motorola Labs and Dow Chemical to “develop novel organic electronic materials and processing technologies … to enable the fabrication of large-area electronic devices, such as displays, using relatively inexpensive printing technologies in lieu of semiconductor lithography.” lll
 The uses for plastic thin-film transistors range from wearable identifications tags to electronic newspapers and books. |
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Clarification
The Lymtech photograph featuring Lymsat wipers ran in the incorrect column. The photograph should have appeared with the Lymtech Scientific entry entitled “Presaturated wiper” instead of the Value-Tek entry. For a corrected version of the listing, go to Product Spotlight, January 2003, at www.cleanrooms.com.
IEST publishes new residue recommendation
New RP categorizes cleanrooms according to average deposition rates
By Hank Hogan
ROLLING MEADOWS, Ill.—No matter how stringent a contamination defense you've established, into every cleanroom a little contamination must fall. A key concern for cleanroom personnel is the rate at which that unwanted, but inevitable, contamination residue appears.
The Institute of Environmental Sciences and Technology (IEST) has published IEST RP-CC016.2: The Rate of Deposition of Nonvolatile Residue in Cleanrooms, a new recommended practice (RP) that categorizes cleanrooms according to average deposition rates.
The 10-point scale is logarithmic, so moving up one level signifies a tenfold increase. The baseline rate is a picogram per square meter per second, which is assigned a rate level of 0.
“In order to judge cleanrooms, we want to define the deposition rate down to very low levels,” explains Gene Borson of Swales Aerospace (Beltsville, Md.) and chair of the IEST working group that created the new document. RP-CC016.2 replaces a decade-old predecessor, which Borson says was based on the needs and techniques of the aerospace industry.
Some of these technological changes over the past 10 years have resulted in increased sensitivity to contamination, and that, Borson says, is reflected in the breadth of the average deposition rates covered in RP-CC016.2. The baseline rate, for example, would take about 30 years to build up one molecular monolayer on a surface. The exact time depends on a number of assumptions. At the other end of the scale, however, a monolayer is deposited in less than a tenth of a second.
Borson says he is unsure how applicable such low deposition rates will be across all cleanroom industries. Pharmaceutical and food processing groups, he notes, are typically concerned when hazardous materials are involved; otherwise, they don't worry about depositing a monolayer over scores of years. On the other hand, electronics, optics and aerospace industries are more likely to be alarmed by such low deposition rates.
According to Borson, one reason the base rate of a picogram per square meter per second was selected is because it's less than what is required by almost any application.
The RP doesn't specify a particular measurement method. Instead, it describes various measurement techniques, such as the use of witness plates that collect contaminants for testing or quartz crystal microbalances that change frequency as residue accumulates upon a surface. It's up to cleanroom end users to select a method that best fits a particular situation.
The new RP complements established standards on allowable nonvolatile residue and molecular contaminants on products, such as IEST-STD-CC1246D: Product Cleanliness Levels and Contamination Control Program.
The new document can only be obtained from the IEST. For more information, visit the IEST website at www.iest.org. lll
Cause of outbreak eludes FDA, hospital to release its findings
Mark A. DeSorbo
PITTSBURGH—Officials at Allegheny General Hospital say they have yet to receive a report validating the Food and Drug Administration's (FDA) claim that a “user problem” with sterilizers used to clean bronchoscopes caused the outbreak of pseudomonas aeruginosa, a potentially deadly lung infection.
“There's been an ongoing discussion with the FDA's Office of Compliance, and in the very near term, we are going to release our findings and what we think our issues are,” says Tom Chakurda, the hospital's vice president of communications.
The outbreak is blamed for the death of Earl W. Foster, 58. The Allegheny County Coroner's Office, however, ruled his death accidental, and hospital officials said four other patients who were infected with the bacteria died from unrelated causes. In all, 15 people were infected after undergoing bronchoscopies, an examination of the lungs.
The FDA did not immediately return calls placed by CleanRooms magazine, but the agency believes that proper sanitization procedures might not have been followed when the sterilization machines were cleaned initially.
“The FDA has been conducting investigations at the hospital and at the [bronchoscope] manufacturer,” says Wally Pellerite, assistant to the director for the Office of Compliance for the FDA's Center of Devices and Radiological Health (CDRH). “We were not able to rule out user error and we are still looking at the [manufacturing] firm. We do know for sure there is history with all kinds of scopes, and nobody really knows what the exact cause of that spike is.”
Pellerite also referred to comments made by FDA spokesperson Sharon Snider, who told Pittsburgh's Tribune-Review that proper sanitization may have been the problem, and not the bronchoscopes. Snider, who indicated there was no timetable to finish the investigation, also emphasized that the findings do not necessarily point to human error, and it has not been determined who is to blame for the supposedly faulty cleaning procedure.
“It was somewhat misleading in the newspapers, but it's not a fact that it was user error,” Pellerite adds. “The agency and state departments and the hospital are still looking into this. We may never figure out what the problem was, and at this point in time, we just don't know.”
That's what troubles officials at Allegeny General.
“[The agency] makes the statement of it being a user problem, but then she says the findings are not conclusive. We believe the issue will rest in other areas,” Chakurda says, declining to elaborate.
Allegheny General disclosed the outbreak in mid-October after an in-house investigation that focused on sterilization techniques instead of the bronchoscopes. [See “Hospital tracks virus,” Oct. 22, 2002, www.cleanrooms.com.]
“Our investigation centered on three areas: the cleaning process, the filters and the actual sterilizer,” Chakurda adds. “We did this proactively, and those three areas continue to get equal looks.”
The hospital used several different brands of bronchoscopes, some of which were recalled by such manufacturers as Olympus America Inc. (Melville, N.Y.) for faulty, contamination-trapping valves.
In the case of the Olympus bronchoscopes, the FDA left the recall up to the manufacturer, an effort the medical profession said Olympus botched and, in turn, put thousands of patients at risk [See “Botched recall investigation continues,” CleanRooms, May 2002, p. 1].
Allegheny General has since replaced the bronchoscopes with new devices. lll
Bronchoscopes from Woburn, Mass.-based Bryan Corp have not been subject to recalls ordered by the FDA's Center for Devices and Radiological Health (CDHR) and undergo a rigorous, manufacturer-recommended sanitization schedule that includes pre-sterilization cleaning, chemical disinfection, ethylene oxide (ETO) sterilization and steam, or autoclave, sterilization. (Photo copywrite Bryan Corp.)