Influence of stress on structural and dielectric anomaly of Bi2(Zn1/3Ta2/3)207 thin films
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Influence of stress on structural and dielectric anomaly of Bi2(Zn1/3Ta2/3)2O7 thin films Jun Hong Noh, Hee Bum Hong, and Kug Sun Hong1 School of Materials Science & Engineering, College of Engineering, Seoul National University, Seoul, Korea 1
Corresponding author, E-mail address: [email protected]
ABSTRACT Bi2(Zn1/3Ta2/3)2O7 (BZT) thin films were grown on the (111) oriented Pt/TiOx/SiO2/Si substrates using a pulsed laser deposition (PLD) technique. BZT thin films deposited at an oxygen partial pressure of 400 mTorr have the non-stoichiometric anomalous cubic phase despite the BZT target was the monoclinic phase. Compositions, the lattice mismatch, the interfacial layer and the residual stress in the film were investigated as the factors which may affect the formation of the anomalous cubic phase. Among them, the coherent interfacial layer which formed at high oxygen pressures resulted in the formation of the cubic phase by reducing the internal stress. INTRODUCTION Bi2O3-ZnO-Ta2O5 (BZT) pyrochlore ceramics have been developed for low firing temperature multilayer capacitors since they exhibit excellent dielectric properties of the large dielectric constants (k = 60~70) with low dielectric losses (tanĪ“ < 0.001) and the small temperature coefficients of capacitance (TCC = -170 ~ 60 ppm/oC) [1-3]. The BZT ternary systems have two phases with different composition; one is monoclinic Bi2(Zn1/3Ta2/3)2O7 phase and the other is cubic (Bi1.5Zn0.5)(Zn0.5Ta1.5)O7 phase [4, 5]. The dielectric constant, the dielectric loss and the TCC of the monoclinic phase are 61.4, below 0.001 and 60ppm/oC, while those of the cubic phase are 71.4, below 0.005 and -172ppm/oC, respectively. The dielectric properties of BZT pyrochlores may be controlled by combining the monoclinic and cubic phases [1]. Dielectric thin films have many potential applications because of their outstanding advantage over bulk ceramics in several aspects such as the faster response, the lower operation voltage, and feasibility for epitaxial growth [6,7]. However, thin films of the BZT pyrochlores have been rarely reported. The pulsed laser deposition (PLD) technique can synthesize the thin films with multi components at high deposition rates with a precise control of the compositions, compared to other techniques such as rf-sputtering, sol-gel and metal organic chemical vapor deposition (MOCVD) processes [8]. In this study, we fabricated the BZT thin films on (111)-oriented Pt/TiOx/SiO2/Si substrates and SrTiO3 (STO) single crystal substrates by using PLD technique. The residual
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stress varied with the oxygen partial pressure during the deposition and the influence of the internal stress on the evolution of the crystalline phase of BZT thin films and the resulting dielectric properties were discussed in terms of the interfacial layer between BZT films and substrates and the residual stress of the thin films. EXPRIMENTAL DETAILS BZT thin films were deposited on (111)-oriented Pt/TiOx/SiO2/Si substrates (Pt substrate) and (111)-oriented S
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