Hybrid gate insulator for OTFT using dip-coating method Jina Hwang a , Jinho Lee b , Yeonok Kim b , Eunju Lee b , Yuedan Wang a, b , Hongdoo Kim b, * a Department of Chemistry, Kyung Hee University, Gyungkido 449-701, Republic of Korea b Department of Display Materials Engineering, Kyung Hee University, Gyungkido 449-701, Republic of Korea article info Article history: Received 31 October 2010 Received in revised form 16 January 2011 Accepted 24 January 2011 Available online 14 July 2011 Keywords: OTFT Hybrid dielectrics Dip-coating Metal alkoxide abstract With metal alkoxide(Ti, Ta, Zr) and copolymer, hybrid insulator film between 10 nm and 100 nm was prepared by dip-coating method on Si substrate and showed better frequency performance in terms of dielectric characteristics than did the copolymer. Also, the dielectric constant of hybrid dielectrics became larger as the content of metal alkoxide increased. With very thin hybrid dielectrics, OTFT with pentacene as organic semi-conductor can be operated below 10 V. From the transfer characteristics, the mobility of OTFT performance and sub-threshold were 3.5 cm 2 /V, 0.09 V/dec, respectively, and on/off current ratio was w2.9  10 7 . Dipping process to make thin hybrid gate insulator has been confirmed to be easy and versatile. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Organic thin-film transistors (OTFTs) have a number of advan- tages for electronics applications, and recent attention has focused on developing OTFTs for practical use. The fabrication of OTFTs is a relatively simple process and may proceed at low temperature, although the electronic performance of OTFTs is generally low due to low field effect mobility. A strategy for improving the mobility of organic semi-conductor requires interface matching between the organic semi-conductor and the gate insulator layer. Many studies have tried to find better gate dielectrics with polymeric materials [1,2], inorganic/organic hybrids [3e6], inorganic/organic bilayers [7], and crystalline inorganic hybrids via solegel reaction [8]. The choice of dielectric material is one of crucial importance in device performance. For example, the operating voltage of OTFT depends on the characteristics of the dielectrics. In the case of a polymer dielectric film, one of the drawbacks is the high oper- ating voltage in devices due to its thickness and low dielectric constant compared with inorganic dielectrics. To solve this problem, high-K inorganic materials such as Al 2 O 3 and Ta 2 O 5 had been used as gate insulators due to their dielectrics which are much higher than those of polymers [9,10]. But, metal oxide has relatively high leakage current and these films can be produced with the application of vacuum techniques, such as chemical vapor deposition, sputtering or flame hydrolysis. Vacuum equipment is not suitable for a low temperature and low cost process. The sol- egel method can be an alternative for coating techniques at ambient temperature [3]. In this work, ultra thin film was obtained using organ- iceinorganic hybrid materials by dip-coating method; the perfor- mance of the low voltage operated OTFT as gate insulator was tested. 2. Experimental Metal alkoxides (Ti, Ta, Zr) and monomers (Aldrich, U.S.A.) and pentacene (Polysis, Korea) were used as received without any further purification. By mixing 1:2 mol ratio of MMA(methyl methacrylate) and phenylmaleimide, copolymer MP1 was synthe- sized in tetrahydrofuran (THF) as a solvent at 70  C, under N 2 atmosphere. AIBN was used as an initiator. After 24 h, copolymer was precipitated in methanol and dried in a vacuum oven. To prepare the organic/inorganic hybrid precursor solution, metal alkoxides(Ti, Ta, Zr) were mixed with copolymer MP1, denoted as MP1-Ti, MP1-Ta, and MP1-Zr, respectively. To measure the dielectric constant and leakage current of the MP1-xx samples, 0.1% wt% solution of MP1 and metal alkoxides were prepared for dip-coating using PEGMEA as solvent. The content of the metal alkoxide was adjusted to 7 wt % film compo- sition. For OTFT measurement, poly (melamine-co-formaldehyde)/ titanium isopropoxide/isopropanol mixture was used to prepare the gate insulator layer with concentrations in the range of 20 g/ * Corresponding author. E-mail address: hdKim@khu.ac.kr (H. Kim). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.01.054 Current Applied Physics 11 (2011) S154eS157