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November 11, 2010

2 Min Read
Flat and Flexible Organic ICs Can Monitor Contents of Catheters

IC1.JPG

A thin, flat organic transistor and complementary IC is flexible enough to be wrapped around a catheter, enabling measurements of properties inside the device.

Japanese researchers have developed thin, flat, and flexible organic transistors and complementary integrated circuits (ICs). Incorporated into a thin polyimide sheet, the ICs can be wrapped around a catheter, enabling measurement of physical or chemical properties inside the device. "Flexible organic ICs are biologically friendly, so they can be used potentially in wearable and implantable electronic [products]," remarks Takao Someya, an electronic engineering professor at the University of Tokyo. The research results will be published in the December issue of Nature Materials.

Working together with Hagen Klauk at the Max-Planck-Institut für Chemische Physik fester Stoffe (Dresden, Germany), the University of Tokyo scientists have developed the the material, which can function without degradation even after being folded into a shape with a radius of 100 µm. The researchers used 12.5-µm-thick polyimide as a base (gate insulator film) and developed technologies to achieve a smooth planar coating at the atomic level. They also built a hybrid encapsulation stack, which places the transistors in the neutral strain position. This structure imparts flexibility and bending stability to the IC sheet.

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IC2-web

The flexible IC design can be crumpled like a handkerchief.

Flexible electronic circuits are essential for the development of biodegradable electronics and for applications with unconventional form factors. A circuit typically can be bent no more than a few millimeters before the active circuit elements are subject to strain-induced damage. Although bending-induced damage can be avoided by placing the circuit elements on rigid islands connected by stretchable wires, the presence of rigid areas within the substrate limits the bending radius. Someya's team not only overcame the flexibility challenge, but it also achieved a low operating voltage, a breakthrough for practical applications.

"This sheet can be crumpled like a handkerchief," Someya remarks. "You can wrap it around the catheter and continuously monitor oxygen concentration and pressure distribution within the blood vessels. Our study has proven that this sheet can be integrated into a catheter."

While Someya's group introduced ultraflexible organic field-effect transistors in 2005 based on 500-nm-thick organic polyimide with a bending radius of 0.5 mm, a 40-V power source was needed. This limitation prevented the device's commercialization," Someya says. This time, however, the team has  developed special coating technologies that enable the device to operate at 2 V. "With this technique, you can also design a variety of unique medical devices," Someya notes.

The researchers are now testing the durability of this device under continuous bending. At a bending radius of about 1 mm, it resists more than 1000 folding operations, according to Someya.

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