Field-effect Transistors of Tetracene Single Crystal on top of a Flexible Substrate
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0920-S02-04
Field-effect Transistors of Tetracene Single Crystal on top of a Flexible Substrate Tae-Heon Kim, Joon Ho Lee, Jin heon Kim, and Chang Seoul Department of Advanced Fiber Engineering, Division of Nanosystems Engineering, Inha University, 253, Yong-hyun Dong, Nam-Gu, Incheon, 402-751, Korea, Republic of ABSTRACT Tetracene single crystals were prepared by the vapor transport method. The polyimide films were used for both substrate and gate dielectric layer. The single-crystal FETs should perform better than thin film transistors. Very thin crystals (~1 µm) were adhered to the substrate by due to electrostatic forces. The mobility of tetracene single-crystal field-effect transistors reaches the room-temperature value of 5×10-4 cm2/Vs.
INTRODUCTION Organic Field-Effect Transistors (FETs), based on conjugated small molecule, have been invegtigated. Organic electronics have the advantages of being inexpensive, and suitable for large-area production. However, in case of organic thin films, they have a considerable amount of structural imperfections and low mobility than organic single crystal. [1] At the same, organic thin films need to deposition techniques. The performance of transistors is affected by surface roughness, structural imperfections and quality of organic materials. So devices using the single crystal of high quality promise better performance than thin film devices. In this letter, we discuss the fabrication of field-effect transistors on tetracene single crystals. Polyimide film used substrate and gate dielectric was flexible and semitransparent.
EXPERIMENTAL DETAILS The source material is 98% pure tetracene purchased from Sigma-Aldrich. Tetracene single crystals were grown by physical vapor growth method. [2] N2 gas flow rate was 50 cc/min. The temperature in each one of the three zones (gas preheating, source, crystal growth) was
℃ ℃
℃
310 , 330 and 260 , respectively. Tetracene single crystals were obtained after 1 day. The flexible polyimide films were used for substrate and gate dielectric layer. Prior to electrode deposition, the substrates have been rinsed with isopropyl alcohol and acetone and dried in N2 gas flux. The gate and source/drain electrode was fabricated by continuous shadow-mask deposition. The thickness of gate and source/drain electrode was 60 nm. The
deposition rate was 1 Å/s.
DISCUSSION The performance of single-crystal transistors indicated good mobility and efficiency compared with organic thin film transistors. In addition, the fabrication of single crystals was easier than thin film deposition techniques. However single crystals were very fragile and their size was limited by about 1~5mm. So single-crystal organic devices demande great caution.
Figure 1. (a) Schematic overview of single crystal growth system. (b) Strructure of the fieldeffect transistor. The schematic overview of single crystal growth system was shown in Fig. 2 (a). The source material was located in the hottest region of the reactor. Figure 1 (b) shows the structure of the device. A 50 µm-t
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