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Using UV light to tune the performance of the flexible polymer devices

A team of researchers at the Institute of Scientific and Industrial Research "SANKEN" at Osaka University and Joanneum Research has succeeded in precisely tune the electronic properties of organic polymer by exposing it to UV light. Their work "Heterogeneous Functional Dielectric Patterns for Charge-Carrier Modulation in Ultraflexible Organic Integrated Circuits" can help in commercializing the flexible electronics that are used in healthcare monitoring and data processing.

"While the integrated circuits inside your smartphone are quite impressive, they lack certain important features. Because the electronics are silicon-based, they are very rigid, both in the literal sense of being inflexible, as well as having chemical properties that are not easily altered. Newer devices, including OLED displays, are made from carbon-based organic molecules with chemical properties that can be tuned by scientists to produce the most efficient circuits. However, controlling the characteristics of organic transistors usually requires the integration of complex structures made of various materials. The team has used UV light to precisely change the chemical structure of a dielectric polymer called PNDPE. The light breaks specific bonds in the polymer, which can then rearrange into new versions, or create crosslinks between strands. The longer the light is on, the more the polymer gets altered. By using a shadow mask, the UV light is applied to just the desired areas, tuning the circuit behavior. This method can pattern transistors of the desired threshold voltage with high spatial resolution using just a single material".

"This study demonstrated the formation of the HFDP with the use of PNDPE as an ultrathin polymer gate dielectric to modulate the behavior of the charge carriers. The HFDP are obtained with a high-resolution of less than 18 µm. With the charge-carrier modulation via the photo-Fries rearrangement in the PNDPE gate dielectrics, the Vth of the PNDPE-based transistors were programmably controlled over a wide range from −1.5 to +0.2 V at an operational voltage of 2 V, indicating that both the enhancement and depletion transistors are arbitrarily fabricated. The modulated Vth remained unchanged over a period of 140 days during the LED exposure test and under a bias duration of 1800 s. The charge-carrier modulation was achieved by controlling the acceptor-like traps. The PNDPE forms dense and uniform gate dielectrics due to the catalytic ring-opening metathesis polymerization, resulting in ultrathin PNDPE films of a thickness of 14 nm. The transistor also exhibited high mechanical flexibility, in which the characteristics did not significantly vary even at a bending radius of 0.3 mm."

"In the future, we may see smart versions of almost everything, from medicine bottles to safety vests. "Meeting the computational demands of 'the Internet of Things' will very likely require flexible electronic solutions," senior author Tsuyoshi Sekitani says. In particular, this technology can be applied to ming methods for ultra-lightweight wearable healthcare devices."O



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