Jpn. J. Appl. Phys. 44 (2005) pp. 2841-2843 |Previous Article| |Next Article| |Table of Contents|
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Bending Effect of Organic Field-Effect Transistors with Polyimide Gate Dielectric Layers
Quantum Phase Electronics Center, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
(Received September 22, 2004; revised November 2, 2004; accepted November 3, 2004; published April 21, 2005)
We manufactured markedly flexible pentacene field-effect transistors (FETs) on a polyethylenenaphthalate base film with polyimide gate dielectric layers, with a mobility of 0.3 cm2/Vs and an on/off ratio of 105. The electric performance of DC current–voltage characteristics was measured by applying compressive and tensile strains while reducing the bending radius down to 3 mm. It was found that the compressive strain leads to an increase in mobility of 10% induced by the change in strain of up to 1.4±0.1%, although the tensile strain leads to a decrease in mobility of 10%. To elucidate the origin of the enhancement of mobility under the compressive strain, we also investigated the strain dependence of capacitance–voltage characteristics for a pentacene channel layer, and almost no change was observed. Our results suggest that the strains markedly affect the spacing between pentacene molecules rather than the number of induced carriers.
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- Here, we would like to discuss the strain-induced changes of the structural parameters, which can be associated with a change in transistor performance. In the geometry of the present devices, compressive and tensile strains lead to the decrease and increase in channel length (L), respectively. The magnitude of change can be described by D/2R. [rf4,rf7] Furthermore, such strains also induce the change in the thickness of polyimide gate dielectric layers due to the Poisson effect. Namely, thickness increases on compression and decreases on tension. This deformation can be estimated using the Poisson model equation, Dν/2R(1-ν). These two changes of the structural parameters mentioned above are responsible for the intrinsic changes in DC characteristics.