Rubrene Single-crystal Organic Field Effect Transistor with Laser Ablated BaTiO 3 Epitaxial Growth Thin-film as High-k I
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0965-S08-04
Rubrene Single-Crystal Organic Field Effect Transistor with Laser Ablated BaTiO3 Epitaxial Growth Thin-Film as High-k Insulator Nobuya Hiroshiba1, Ryotaro Kumashiro1, Taishi Takenobu2, Naoya Komatsu1, Yusuke Suto1, Yoshihiro Iwasa2, Kenta Kotani 3, Iwao Kawayama 3, Masayoshi Tonouchi 3, and Katsumi Tanigaki1 1 Department of Physics, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, 980-8578, Japan 2 IMR, Tohoku University, Sendai, 980-8578, Japan 3 Osaka University, Osaka, 565-0871, Japan
ABSTRACT High quality BaTiO3 thin film epitaxially grown on a Nb-doped SrTiO3 (BTO/Nb-STO) substrate by a laser ablation technique is employed as a high-k gate insulator for a field-effect transistor of a rubrene single crystal in order to search for the possibility of high carrier accumulation. The high dielectric constant of 280 esu for the prepared BaTiO3 thin film accumulates 0.1 holes/rubrene-molecule, which is 2.5 times as high as the maximum carrier number of 0.04 holes/rubrene-molecule attained in the case of SiO2 gate insulator. Important parameters of rubrene single crystal FETs on BTO/Nb- STO are also described in comparison with those on SiO2/doped-Si. INTRODUCTION Organic field effect transistors (OFETs) are currently being studied with lots of enthusiasm [1–5], because they are important considering for the future applications to electronic devices as well as for the fundamental interests in creating intriguing physical properties. Continuous tuning in the carrier concentration both for electrons and holes are expected to be very important to give rise to intriguing physical properties that are very difficult to observe under the normal tuning in the chemical compositions of materials. For attaining intriguing electronic properties of metal-insulator transitions such as charge density wave (CDW), spin density wave (SDW) and moreover superconducting transition, triggered by the change in the band filling, the carrier concentration of 0.2 to 1.0 electrons or holes per molecule is at least needed in the case of the conventional molecular solids. The current situation of organic FETs reported in literature so far has unfortunately shown much lower values than such requirements in the case of SiO2 as a gate insulator. In general, the carrier concentration N is proportional to (εS/ed)VG, where e is the Coulomb charge of an electron, S and d are the surface area and the thickness of gate insulators, ε is the dielectric constant of gate insulators and VG is the applied gate voltage. Therefore, the important parameter is the product of ε and VG. Such situation has been exemplified for inorganic semiconducting FETs as viewed. As a result, in order to overcome the conventional
limitation of the carrier injection in organic FETs, application of gate insulating materials with higher dielectric constants can be considered to be one of the most realistic solutions. Along with this guideline, some experiments were made for organic FETs fabricated using higher dielectric gate insulators than SiO2 [6–8]. However, the
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