Sol-Gel Synthesis of Low-Loss MgTiO 3 Thin Films by a Non-Methoxyethanol Route Kuzhichalil P. Surendran, † Aiying Wu, † Paula M. Vilarinho,* ,† and Victor M. Ferreira ‡ Department of Ceramics and Glass Engineering and Department of CiVil Engineering, CICECO, UniVersity of AVeiro, 3810-193 AVeiro, Portugal ReceiVed October 28, 2007. ReVised Manuscript ReceiVed April 11, 2008 A cost-effective and hazard-free sol-gel method for the synthesis of single-phase MgTiO 3 thin film is reported here, using (MgNO 3 ) 2 · 6H 2 O and TiC 16 H 36 O 4 as precursors and employing either acetic acid or acetyl acetone as the stabilizers for titanium n-butoxide. The effect of the stabilizers on the structure, microstructure and electrical properties is evaluated. Acetyl-acetone-based films have a denser and more homogeneous microstructure than the acetic-acid-derived films, which is directly reflected in their dielectric properties. Acetyl acetone derived films annealed at 700 °C exhibit a dielectric constant, ε r ) 16.3 and dielectric loss, tan δ ) 0.0021 at 1 MHz. The differences are attributed to the lower reactivity of acetyl- acetone-stabilized sols and higher crystallization temperature of acetyl acetone derived films. 1. Introduction Over the last two decades, the global telecommunication industry is growing toward faster, thinner, and lighter technologies, which has culminated in the development of novel 4G mobile technology. 1 In mobile phones, global positioning systems (GPS), and satellite communications, the demand for monolithic microwave integrated circuit tech- nologies (MMIC) utilizing low-loss dielectrics has been exponentially increasing. Ilmenite structured MgTiO 3 is a promising low-loss dielectric 2 with high quality factor (Q above 20 000 at 8 GHz) and intermediate dielectric constant (ε r ) 17), but with a negative temperature coefficient of resonant frequency (τ f )-50 ppm/°C) which could be tailored to zero using suitable doping. 3 This dielectric is widely used in many microwave applications like transverse electromagnetic mode quarter wave resonators, 4 band-pass filters, 5 90° hybrid couplers, 6 multilayer capacitors, 7 and so forth. Apart from its microwave resonator applications, magnesium metatitanate could also be used for optical communication in planar lightwave circuits (PLC) as a buffer layer for sapphire and LiNbO 3 . 8 However, most of the studies on pure and doped MgTiO 3 dielectrics are limited to its bulk ceramic form and there is a surprising scarcity of literature on thin film characteristics of MgTiO 3 . Despite the technological interest of this material, obtaining phase purity in MgTiO 3 is difficult both in solid state and solution methods because of its narrow range of phase stability. The sol-gel process has been frequently used in thin film technology for different microelectronic systems, because of its versatility as an effective technique to fabricate high-quality dielectric and ferroelectric films. This methodol- ogy possesses many advantages including low processing temperature, together with high purity and homogeneity of the product. The synthesis of pure phase MgTiO 3 using sol-gel methods was greatly constrained by the formation of additional phases. The low solubility of magnesium alkoxides is believed as the primary impediment for sol-gel synthesis of this complex oxide, which has to be addressed by suitable modifications at the precursor level. 9 In a recent report on sol-gel synthesis of MgTiO 3 powders by Miao et al., 10 impurity phases like MgTi 2 O 5 and Mg 2 TiO 4 appeared up to 600 °C disappearing at 700 °C, with the appearance of extra TiO 2 , consequent to the decomposition of the former. But from a thin film technology perspective, only very few reports are available. Using a modified sol-gel method, Choi and Lee 11 fabricated MgTiO 3 thin films. However, their objective was to test the adaptability of MgTiO 3 as a cladding layer to LiNbO 3 and silica, in thin film optical waveguide. In the recent past, MgTiO 3 thin films were prepared by rf- sputtering, but the observed high dissipation factor (0.041 at 10 MHz), 12 which obviously hinders the practical ap- plication of these films, demands several modifications in the fabrication process. For the synthesis of MgTiO 3 powders by sol-gel process- ing, the most frequently used methodology is the one that involves 2-methoxyethanol (2-MOE), because of the ability * Corresponding Author: paula.vilarinho@ua.pt. † Department of Ceramics and Glass Engineering, CICECO, University of Aveiro. ‡ Department of Civil Engineering, CICECO, University of Aveiro. (1) Gow, G. A.; Smith, R. K. Mobile and Wireless Communications: An Introduction Open University Press: Berkshire, U.K., 2006. (2) Wakino, K. Ferroelectrics 1989, 91, 69. (3) Ferreira, V. M.; Baptista, J. L. Mater. Res. Bull. 1994, 29, 1017. (4) Wakino, K.; Nishikawa, T.; Ishikawa, Y.; Matsumoto, H. IEEE IT-S Cat. No. 81CH1592-5. 1981, 185. (5) Huang, C.-L.; Tsai, C.-M.; Yang, A.; Hsu, A. MicrowaVe Opt. Lett. 2005, 44, 421. (6) Tanaka, H.; Banba, N.; Arai, S.; Nishikawa, T. IEEE MTT-S Digest 1994, 903. (7) Bernard, J.; Houivet, D.; El Fallah, J.; Haussonne, J. M. J. Eur. Ceram. Soc. 2004, 4, 1877. (8) Choi, Y. H.; Lee, J. Thin Solid Films 2001, 385, 43. (9) Abothu, I. R.; Rao, A.V. P.; Komarneni, S. Mater. Lett. 1999, 38, 186. (10) Miao, Y.-M.; Zhang, Q.-L.; Yang, H.; Wang, H.-P. Mater. Sci. Eng., B 2006, 128, 103. (11) Lee, J.; Choi, C. W. Jpn.J. Appl. Phys. 1999, 38, 3651. (12) Huang, C.-L.; Chen, Y.-B. Jpn. J. Appl. Phys. 2005, 44, 6736. 4260 Chem. Mater. 2008, 20, 4260–4267 10.1021/cm703088m CCC: $40.75  2008 American Chemical Society Published on Web 06/06/2008