COOL JETS: MICRONOZZLES SPLATTER
APPLICATIONS BEYOND INKJET PRINTER

By Jack Mason
Small Times Correspondent

Jan. 17, 2002 — Inkjet technology, one of the first applications of microfluidics, is finding many uses beyond the printed page.

Microjets are being put to work printing “plastic” circuitry, fabricating display screens from organic light-emitting diodes (OLEDs) and laying down microarrays for DNA research and drug discovery.

The virtues of inkjet tech are simple: It offers a well-developed process for depositing small, precise quantities of material quickly, accurately and

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Seiko-Epson and Cambridge Display
Technology is commercializing light-
emitting polymer (LEP) display screens
that can be applied on glass with inkjets.
inexpensively. And unlike other deposition or fabrication technologies, inkjetting doesn’t require expensive vacuum equipment.

Some enterprises taking advantage of inkjet virtues:

In November, Kodak was awarded a patent for incorporating scents into an inkjet-printed image. This month, Purdue University chemical engineering professor Osman Basaran and graduate student Alvin Chen reported a technique that enables inkjet nozzles to use 10 times less fluid per tiny drop.

Plastic Logic Inc., a year-old U.K. startup spun out of Cambridge University’s Cavendish Laboratory, is aiming to print electronic circuits out of semiconducting organic polymers with inkjet equipment. Target products include active-matrix backplanes for flat-panel displays and electronic labels that could serve as “smart” successors to product barcodes.

While plastic electronics aren’t likely to challenge silicon in pure performance anytime soon, marketing manager Tracey Stephens said that inkjet fabrication offers opportunities for circuit customization and small volume or specialty production.

By contrast, silicon chip-making based on photolithography requires an intricate (read: expensive) and unalterable physical “mask” to define a circuit’s pattern. Inkjet-printed circuit designs could be changed more quickly and inexpensively in software.

“We could conceivably alter the circuitry with every pass of the inkjet, or run multiple small batches or variations on a product,” Stephens said.

Formed in 1992 and headquartered in England, Cambridge Display Technology (CDT) is commercializing light-emitting polymer (LEP) display screens that can be applied on glass with inkjets. Such “plastic” screens (also being developed in “small molecule” form by Kodak) promise to be brighter, thinner, lower-powered, more flexible and less expensive than existing liquid crystal displays. The first commercial displays from CDT licensees are expected in cell phones by this summer.

In December, CDT acquired Pleasanton, Calif.-based Litrex Corp., developer of a highly precise inkjet technology it calls Piezo Micro Deposition. Stewart Hough, CDT’s vice president of business development, said that inkjet deposition should help his company get LEP screens to market faster by increasing production throughput and yields as well as offering lower capital costs. However, he notes that inkjet production for LEP displays will require continuing improvement to reach its full market potential.

“The organic polymers we’re using are more volatile and sensitive than standard ink,” said Hough. “We have to carefully control the volume, velocity and direction of how they are deposited on the substrate.” Hough explained that each circular drop of polymer is sprayed onto a rectangular pixel area. The borders of the pixel “well” are doped with hydrophilic (water-attracting) material that “stretch” the round droplet into a rectangle as it dries.

Agilent Technologies and PerkinElmer Inc. are in a growing field of companies using inkjets to build microarrays for analyzing DNA, proteins and other biomolecules. PerkinElmer has acquired Packard BioScience’s patented PiezoTipnology, an inkjet-type system that doesn’t heat the liquid during deposition.

Agilent, a Hewlett-Packard spinoff, is drawing on HP’s inkjet expertise to precisely position as many as 16,000 droplets of DNA segments in solution onto 1-by-1-inch squares of glass. The inkjets can also go back and customize the length or character of the DNA in all locations by chemical synthesis. “It’s really a very sophisticated microreagant delivery system,” said R&D section manager Doug Amorese.

It’s also meant to be a massively parallel research tool that saves on expensive reagents. One of these microarrays, which range in price from $500 to more than $1,000, can effectively perform thousands of simultaneous experiments.

“The alternative is to do thousands of gene expression tests one after the other,” Amorese said. “And that’s just not economical or practical.”

What other microjet-enabled technologies look promising? Purdue’s Basaran believes microencapsulation — in which one fluid is squirted around another by two inkjets — has the potential to help develop drugs with long time-release properties. Similarly, “drop-by-drop manufacturing” that uses inkjets to produce particles with unique chemical characteristics could hold advantages over “solution” chemistry where compounds interact by mechanical mixing.

Further down the road, “nanojets” with nozzles as small as 6 nanometers, such as those investigated by Georgia Tech physics professor Uzi Landman, may deliver genes into cells or function as fuel injectors in microscopic motors.

And who knows? If Kodak’s scented inkjet patent pans out, you may some day pop a digital photo of Mom fresh out of the printer smelling like her home-baked cookies.

Maybe they should call it a “stinkjet.”

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