RF Sputtered BZN Pyrochlore Thin Films for Voltage Tunable Dielectric Device Applications
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RF Sputtered BZN Pyrochlore Thin Films for Voltage Tunable Dielectric Device Applications Young Pyo Hong†, Seok Ha, Ha Yong Lee, Young Cheol Lee and Kyung Hyun Ko Department of Materials Science and Engineering, Ajou University, Suwon, Korea † [email protected] Dong Wan Kim*, Hee Bum Hong* and Kug Sun Hong* * School of Materials Science and Engineering, College of Engineering, Seoul National University, Seoul, Korea ABSTRACT The BZN pyrochlore thin films were prepared on platinized Si substrates using a reactive RF magnetron sputtering. The structures, surface morphologies, dielectric properties and voltage tunable properties of films with deposition parameters were investigated. The BZN thin films have a cubic pyrochlore phase and secondary phases of zinc niobate, bismuth niobate when crystallized at 600℃ ~ 800℃. The dielectric constant and tunability of thin films are O2/Ar ratio and post-annealing temperature dependent. The BZN thin films sputtered in 15% O2 and annealed at 700℃ had a dielectric constant of 153, tan δ of ~0.003 and maximum tunability of 14% at 1,000kV/cm. INTRODUCTION Ferroelectric thin film such as SrTiO3, Ba1-xSrxTiO3 has been exploited as voltage tunable dielectric materials [1-6]. Suggested applications of these thin films are planar capacitors, coplanar waveguides, tunable phase shifters and tunable filters, etc. But, ferroelectric thin films have an inherently capacitive hysteresis in the microwave region resulting in large dielectric losses. Therefore, it is necessary to develop new paraelectric tunable materials without hysteresis. Bi2O3-ZnO-Nb2O5 (BZN) pyrochlore systems are paraelectric with medium dielectric constant and low dielectric loss [7]. There are two main phases in the BZN system depending on composition; a cubic pyrochlore structure( base composition of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 )and pseudo-orthorhombic pyrochlore structure( base composition of Bi2(Zn⅓Nb⅔)2O7). These two compositions are members of the general family of (Bi3xZn2-3x)(ZnxNb2-x)O7, with x=1/2 and x=2/3, respectively [8]. Previous studies on the BZN pyrochlore ceramics have been focused mostly on the applicability to low firing temperature multilayer capacitors as a bulk form [9]. Recently, several studies on the dielectric tunability and dielectric property of BZN thin film prepared by metalorganic deposition (MOD) [10] and pulsed laser deposition (PLD) [11] process has been reported. It was found that the composition of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 thin films prepared by MOD process have voltage tunable dielectric properties, while the composition of Bi2(Zn⅓Nb⅔)2O7 thin films were nearly field independent. From a current industrial point of view, it might be necessary to investigate another process technique other than PLD or MOD process. In that case, the sputtering deposition technique would be another highly attractive process for commercial production. In this work, we report on the fabrication and dielectric properties of BZN thin films by conventional reactive RF magnetron sputtering and the correlation
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