A vacuum food sealer. Image: FoodSaver |
One day in 2010, Rutgers University physicist Vitaly Podzorov
watched a store employee showcase a kitchen gadget that vacuum-seals food in
plastic. The demo stuck with him. The simple concept—an airtight seal around
pieces of food—just might apply to his research: Developing flexible
electronics using lightweight organic semiconductors for products such as video
displays or solar cells.
“Organic transistors, which
switch or amplify electronic signals, hold promise for making video displays
that bend like book pages or roll and unroll like posters,” said Podzorov. But
traditional methods of fabricating a part of the transistor known as the gate
insulator often end up damaging the transistor’s delicate semiconductor
crystals.
Drawing inspiration from the
food-storage gadget, Podzorov and his colleagues tried an experiment. They
suspended a thin polymer membrane above the organic crystal and created a
vacuum underneath, causing the membrane to collapse gently and evenly onto the
crystal’s surface. The result: a smooth, defect-free interface between the
organic semiconductor and the gate insulator.
The researchers reported their
success in the journal Advanced Materials. In the article, Podzorov and three colleagues
describe how a single-crystal organic field effect transistor (OFET) made with this
thin polymer gate insulator boosted electrical performance. The researchers
further reported that they could remove and reapply membranes to the same
crystal several times without degrading its surface.
Organic transistors electrically
resemble silicon transistors in computer chips, but they are made of flexible
carbon-based molecules that can be printed on sheets of plastic. Silicon
transistors are made in rigid, brittle wafers of silicon.
Fabricating single crystal organic field-effect transistors using ultra-thin polymer membrane for a gate insulator. In the upper row, the membrane is stretched over the transistor before vacuum is applied. In the lower row, the vacuum has been applied and the membrant is adhering to the organic crystal. Photos on the right are close-up views of the transistor, with the organic semiconductor crystal in red. Image: H. T. Yi, et. al. |
The methods that scientists
previously applied to organic transistor fabrication were based on silicon
semiconductor processing, explained Podzorov, assistant professor in the Department of Physics and Astronomy, School of Arts and Sciences. These involved high temperatures,
high-energy plasmas, or chemical reactions, all of which could damage the
delicate organic crystal surface and hinder the transistor’s performance.
“People have tendencies to go
with something they’ve known for a long time,” he said. “In this case, it
doesn’t work right.”
Podzorov’s innovation builds upon
a decade of Rutgers research in this field,
including his invention of the first single crystal organic transistor in 2003.
While his latest innovation is still a ways from commercial reality, he sees an
immediate application in the classroom.
“Our technique takes 10 minutes,”
he said. “It should be exciting for students to actually build these devices
and immediately see them work, all within one lab session.”
Podzorov was actually trying to
solve another problem when he first recalled the food packaging demo. He was
thinking about how to protect organic crystals from airborne impurities when
his lab shipped samples to collaborating scientists in California and overseas.
“We could place our samples
between plastic sheets and pull a vacuum,” he said. “Then I thought, ‘why don’t
we try doing this for our gate insulator?'”
