Organic field-effect transistors with bending radius down to 1 mm
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Organic field-effect transistors with bending radius down to 1 mm Tsuyoshi Sekitani1, Hiroshi Kawaguchi2, Takayasu Sakurai2, and Takao Someya1 1
Quantum-Phase Electronics Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan 2 Center of Collaborative Research, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan ABSTRACT We have investigated the allowed bending radius of high-quality pentacene field-effect transistors (OFETs) manufactured on a plastic substrate of a polyethylenenaphthalate (PEN) film with a polyimide gate dielectric layer. It is found that the reduction of mobility due to the application of an expansive stress with a radius of curvature (R) smaller than about 1 mm, was only 20 %. Furthermore, the mobility increase by 7 % to 0.28 cm2/Vs on a compressive stress with R=4.6 mm. We also studied the recovery performance after stressing OFETs. No significant change and residual effect in performance has been found after the removal of the compressive bending the device down to a radius of 4.6 mm (1.4 ± 0.1 % in strain). In the analysis of the mechanical flexibility, we demonstrated that our OFETs electrical properties were fairly stable during the application of an expansive and compressive stress down to several mm in bending radius. INTRODUCTION Notable advantages of organic materials attract much attention in many fields because of the inherent features [1-3], such as lightweight, low-cost processable, large-area available, and mechanical flexibility, which seems to be difficult for inorganic materials. Especially, there are almost no beings as inherently flexible without organic materials. In order to fully utilize such high potentiality, it is an inevitable to use flexible materials for a gate dielectric layer as well as a channel layer and a base film. However, a lot of organic transistors are still manufactured with inorganic and inflexible gate insulators (SiO2, Al2O3, and Ta2O5) and/or base materials (Si-base, glass), which are believed to be more reliable and stable. Recently, great progress of polymer technology has proved their reliability of new class of polyimide precursors, so that it can be widely used in electronics. In our experiments, the number of the device showing a leakage current above noise level (~100 fA at 200 mV) is less than 1 % for the devices with 540 nm
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polyimide gate dielectric layers. As a result, we have succeeded in fabricating high-performance and essentially flexible organic field-effect transistors (OFETs) utilized solution-processable polymer as a gate dielectric layer, which show the mobility as high as 1.4 cm2/Vs and an on/off current ratio of above 106 [4]. Such flexible transistors will be widely used in a lot of applications. For practical use of organic transistors and its integrated circuits, it is very important to understand the strain effect. In this work, we have performed systematic bending experiments with both expansive and compressive strains in order to unveil the strain effect of high qua
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