899 The Polymer Society of Korea www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673 Macromolecular Research, Vol. 21, No. 8, pp 899-904 (2013) Synthesis of Polymetalloxanes and Their Properties as Gate Insulator for Organic Thin Film Transistors Yuedan Wang 1 , Kyungmin Lee 2 , Jihong Oh 2 , Sinhee Kim 2 , Minkyu Lee 1 , and Hongdoo Kim * ,2 1 Department of Chemistry, 2 Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Gyeonggi 446-701, Korea Received August 16, 2012; Revised October 23, 2012; Accepted October 25, 2012 Abstract: We report here the synthesis and dielectric properties of polymetalloxane dielectric materials for organic field-effect transistor applications. The gate insulators were obtained from polymetalloxanes by condensation poly- merization of metal chelates and silicic acid. The solution shows an appreciable stability to self-condensation and a good coating quality. A high dielectric constant 6.16-8.27 was obtained for the prepared films. Organic thin film transistors with this gate dielectric were found to exhibit high performances, including carrier mobility as large as 1.77 cm 2 /Vs, on-off current ratios above 1×10 4 , threshold voltages below -0.13 V, and subthreshold swing as low as 0.1 V/decade. In addition, the operating voltage ranges as low as 5 volts was obtained. Keywords: organic thin film transistor (OTFTs), hybrid dielectrics, polymetalloxane, sol-gel process. Introduction Organic thin film transistor (OTFT) is an intensively pur- sued subject because it would play a key role in the promis- ing era of organic and particularly flexible electronics. 1-5 A major goal in the development of OTFTs is to achieve higher carrier mobility so that higher current output can be obtained to drive other components in an organic electric device. There are many studies on the effect of structure of the gate dielec- tric on the mobility of a molecular film. 6 Materials of high capacitance have been used in the organic FETs to reduce the gate bias required to turn on the transistors. 7 One of the representative insulators with high dielectric constant is inorganic metal oxide such as TiO 2 8 and TaO 2 . 9 However, inorganic insulators may be cracked when bent. In addition, the film preparation requires a high temperature vacuum process, which is not compatible with flexible substrates. To overcome these problems, polymeric materials are promising candidates as insulators in OTFTs. 10-12 Nevertheless, poly- mers, in general, exhibit relatively low dielectric constant (~3), which limits the OTFT performance. Therefore, it is nec- essary to design and develop a high capacitance film with economical and easy method. To obtain non-breakable high dielectric material, met- allosiloxane 13,14 composed of Si-O-M bond is one of the candidates. There has been many works on the synthesis and properties of metallosiloxane 14 which are expected to be a model compound for the inorganic polymers. It shows an excellent thermal stability since the typical linkage Si-O-M is similar to the backbone structures of silicate minerals. In this study, SiO 2 -M x O y R 2 (M=Ti, Zr, R=acetylacetone) gels were synthesized by the condensation polymerization of silicic acid and acetylacetonate chelates of metals such as titanium and zirconium as shown in Scheme I, and used as gate dielectric layer by solution process. We also investi- gated the electric properties of polymetalloxane gate dielec- trics and the performance of OTFTs. Experimental Materials. All reagents were analytical reagent. Silicic acid (SA) was prepared as 0.85M SA-THF solution according to the previous paper. 15 Aqueous hydrochloric acid (37%), 1-butanol (99.5%) and n-propanol were purchased from Duksan pure chemicals (Korea). Sodium metasilicate hydrate (Na 2 SiO 3 ·9H 2 O), bis-(2,4-pentanedionato) titanium diiso- propoxide (PTP), zirconium n-propoxide (Zr(OPr n ) 4 ) and ethacrylic acid were purchased from Sigma-Aldrich (U.S.A.). Tet- rahydrofuran (THF) was purchased from J.T. Baker. Bis (2,4-pentanedionato) zirconium diisopropoxide (PZP) were synthesized by the method described in the literature. 16 All materials were used as received. Preparation and Characterization of Films. A mixture of 0.02, 0.01, or 0.005 mol of PTP and 5 mL of methanol was dropped into a solution of 0.01 mol of 0.85 M SA-THF solution containing 5 mL methanol with stirring. Then, the mixture was refluxed for 20 min-1 h, and the solvents were distilled off in vacuum to give highly viscous solution of DOI 10.1007/s13233-013-1102-x *Corresponding Author. E-mail: hdkim@khu.ac.kr