Your future smartwatch

might be printed with an inkjet printer

By Gabriel

Popkin

Nov. 1, 2016, 3:00 AM

 

Imagine getting the latest

smartwatch or a high-tech heart attack warning detector from your inkjet

printer. Researchers have taken a step in this direction by printing cheap,

reliable arrays of transistors—the key components of modern electronics—and

using them to carry out elementary computing tasks. The work might someday help

usher in a new era of organic, flexible consumer electronics.

Instead of the usual silicon, the new circuits were

fashioned out of organic—or carbon-based—compounds. And whereas others have

printed and stacked organic electronic components using a mix of inkjet

printing and other deposition methods, the new work uses just an inkjet printer

for the entire process. “I cannot think of another [device with at least two

layers] where everything was done with inkjet printing,” says Ananth

Dodabalapur, an electrical engineer at the University of Texas in Austin who

was not involved in the work. “This is a good demonstration.”

New commercial electronic devices must be compact,

durable, and amenable to mass production. Nearly all mass market devices rely

on microchips of the chemical element silicon, on which manufacturers etch ever

smaller transistors—essentially electrical switches that can be used to fashion

logic circuits for computers.

But silicon chips have some disadvantages. Silicon wafers

are stiff, so it’s difficult to make silicon-based circuitry flexible. Many

think that flexible, wearable electronics built from organic

materials could open up new applications for electronics. For example, flexible

electronics could gather vital medical data such as the stiffness of arteries,

which can help predict heart attacks, and brain electrical activity, which can

signal oncoming epileptic seizures.

To help realize that potential, Sungjune Jung, an

electrical engineer at Pohang University of Science and Technology in South

Korea, and colleagues set out to see whether they could simply print working

networks of organic transistors. To cram in as many transistors as possible, they

designed transistors that could be stacked on top of each other, rather than

placed side by side on a chip, effectively packing two transistors into the

space usually occupied by one.

They printed the 3-micrometer-tall circuits one layer at

a time with an inkjet printer: On the bottom, they laid down the carbon-based

compound that would form the parts from which electrical current would flow

into and out of one transistor, then the metal electrodes that would control

the current in both transistors, and, finally, the compound that would form the

current-carrying parts of the other transistor. Between the layers of

transistors they deposited thin films of a protective material called parylene.

The device included more than 100 transistors, enough to form logical circuits

that completed several basic computations, including adding two numbers.

Jung’s device hit a number of key benchmarks. All the transistors worked, even

8 months after production—an impressive feat for organic electronics, which

often degrade quickly. Moreover, the process required temperatures no higher

than 120°C, compared with many hundreds of degrees on a typical silicon wafer

fabrication line, the team reports in ACS Nano.

Still, the printed devices are far from competing with

silicon. The team was able to pack about five transistors into a square

millimeter, whereas integrated circuit chips in today’s computers cram millions

into the same space. “Our technology, in terms of transistor density, is at the

stage of silicon technology in the late 1960s or early 1970s, when the first

microprocessors came out,” Jung says.

Because the researchers were aiming to demonstrate a

concept rather than prototype a product, Jung’s team printed its circuit on

stiff glass. But he says they have already printed similar components on

flexible plastic, and plan to publish that result soon. Dodabalapur also notes

that by some metrics, the new device lags behind what others have already

achieved with organic circuits. For example, the type of computing logic the

team used requires more transistors than other approaches, largely wiping out

gains from more closely packing the components. And the transistors operated

relatively slowly and inconsistently, he says. Moreover, although it’s possible

to use inkjet printing for every step in the manufacturing process, he says, “I

don’t see any advantage … to restrict oneself to one printing or patterning

technique.”

But such imperfections might be ironed out as a product

moves to commercialization, says Janos Veres, a flexible electronics expert at

PARC, a research institution in Palo Alto, California. He applauds the study

for showing a novel way to print and protect organic circuit components, and

imagines future labels or sensors containing stacks of not just two, but many

transistors, perhaps working in concert with silicon chips or other

technologies. “Ultimately we do see the opportunity to print microchips,” he

says.

Posted in: 

Technology

DOI: 10.1126/science.aal0325

 

http://www.sciencemag.org/news/2016/11/your-future-smartwatch-might-be-printed-inkjet-printer