The studies of polymer dielectrics and electrode/active layer interface on pentacene-based organic field-effect transistors

• Main Authors: Tzung-DaTsai, 蔡宗達
• Other Authors: Tzung-Fang Guo
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/25447192534248447815

博士 === 國立成功大學 === 光電科學與工程學系 === 102 === This thesis divides into two aspects for studying. The first aspect is the manipulating the hysteresis in poly(vinyl alcohol)-dielectrics organic field-effect transistors (OFETs). The second aspect is the origins in the transformation of ambipolar to n-type pentacene-based OFETs. In the first aspect of hysteresis, it investigates the origins of hysteresis of transfer characteristics in pentacene-based OFETs under the forward and backward scan with using poly(vinyl alcohol) (PVA) as top dielectric. The experimental results confirm that the hydroxyl groups in PVA gate dielectrics are correlated re-orientated with an applied electric field. The applied gate bias partially aligns the orientations of the hydroxyl groups perpendicular to the substrate, in which the field-induced surface dipoles at the pentacene/PVA interface trap charges and cause the hysteresis. Treating PVA with an anhydrous solvent eliminates the residual moisture in the dielectrics layer, allowing for more effective control of the induced dipoles by the applied gate bias. OFETs of dehydrated-PVA dielectrics present a pronounced shift of the threshold voltage, and results in sufficient dynamic response for applications in memory elements. In the second aspect of transformation of ambipolar to n-type, the hole currents in ambipolar pentacene-based OFETs with aluminum (Al) electrodes are decreased by the magnitude of two orders in 24 hours. The experimental results confirm that the time-dependent decrease of hole current is associated with the interfacial oxidation reaction at the Al source-drain electrodes and pentacene. The time-dependent oxidization of Al and pentacene creates an interfacial barrier to suppress the hole injection from Al electrodes into pentacene, but the similar oxidation was not observed at the interface of the pentacene and silver. Therefore, through co-evaporated the pentacene and Al process, it expands the contact surface of pentacene and Al and accelerates the reaction, and results in the fabrication of n-type only pentacene-based OFETs.