Crystal Structure and Dielectric Characterization of a (SrTiO 3 /BaTiO 3 ) n Multilayer Film Prepared by Radio Frequency
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continued drive toward greater miniaturization and integration of discrete electronic components has led to the development of thin film materials for a wide variety of applications, and among these are the thin film ferroeletrics.[1] Ferroelectric materials are the most promising capacitor materials for future high density dynamic random access memories (DRAMs). Several ferroelectric compositions, such as PbTiO3, Pb(Zr,Ti)O3, and (Pb,La)(Zr,Ti)O3, have been studied in DRAMs, while Barium titanate (BaTiO3) with some dopants has been a popular candidate for making multilayer capacitors because of the high dielectric constant.[2] BaTiO3 is one of the most important ferroelectric perovskites. It has a Curie point temperature of about 398 K (125 C), and at this temperature, the crystal lattice undergoes a tetragonal-to-cubic phase change accompanied by a sharp peak in the dielectric constant. The dielectric constant (er) of a BaTiO3 single crystal is WANG-LONG LI, Associate Professor, Institute of Nanotechnology and Microsystems Engineering, and FU-YUAN HSIAO, Master, and NAN-CHUNG WU, Professor, Department of Materials Science and Engineering, are with the National Cheng Kung University, Tainan, Taiwan R.O.C. HUEY-JIUAN LIN, Professor, is with the Department of Materials Science and Engineering, National United University, Miao-li, Taiwan R.O.C. MOO-CHIN WANG, Professor, is with the Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, Kaohsiung, Taiwan R.O.C. Contact e-mail: [email protected] Manuscript submitted June 14, 2008. Article published online February 23, 2010 1330—VOLUME 41A, MAY 2010
strongly anisotropic, with ec = 400 along the tetragonal c-axis and ea = eb = 4000 perpendicular to the c-axis at room temperature.[3] An average of er 950 to 1200 for BaTiO3 ceramics has been calculated,[4,5] and these polarize along any h100i direction of the prototype and possess an er of 1900 and 1620 parallel and perpendicular to the poling axis, respectively, under constant conditions. Therefore, BaTiO3 thin films have good potential for use in DRAMs cell capacitors compared to other gate dielectrics, such as Ta2O5 and SiO2.[2] A large number of studies have been performed to elucidate the mechanism giving rise to the ferroelectricity of BaTiO3 and to improve the related properties.[6] Perovskite compounds in the BaTiO3-SrTiO3 system are the most promising candidates for the fabrication DRAMs with very large scale integration and have been extensively studied with respect to the dielectric properties of the paraelectric phase.[7] The fabrication of superlattice materials constitutes a powerful method to control the crystal structure and ferroelectric properties artificially over a wide temperature range,[8] explore predications of giant dielectric constants,[9,10] and produce new functional devices.[11] Ferroelectric multilayer thin films, such as PbTiO3/Pt/ PbTiO3 ultrathin multilayer capacitors, have been prepared by a sol-gel process.[12] Qu et al.[13] reported that the dielectric properties of Ba
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