| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 93 === Abstract
The Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin film is one of the most developed ferroelectric materials for the nonvolatile ferroelectric random acess memories. In this study, the cosubstitution of A-site Na+ acceptor/B-site Ta5+ donor is incorporated into the (Bi3.15Nd0.85)Ti3O12 ferroelectric thin films. The purpose of cosubstituting donor and acceptor is to create the additional coulombic interaction between the negatively charged NaBi’’ on the 12-coordinated A site and the positively charged TaTi• on the 6-coordinated B site, in the hope of tilting the triple-layered TiO6 octahedral chains, increasing their off-center displacement, and enhancing the remanent polarization. There were four kinds of (Na, Ta)-codoped BNT films prepared by magnetron sputtering with the sputtering targets of (Bi0.83Nd0.17-naNana)4.35(Ti3-nbTanb)Ox (a= 0.00365, b= 0.0575), n= 1, 2, 3, 4. After the sample preparation, the co-doping effects on the electric properties, crystal structure, and microstructure were investigated.
From the experimental result, the increase in the doping amount led to a worse ferroelectric property. The best result was obtained for the (Na, Ta)-BNT films with the sputtering target having the composition at n=1, after crystallization at 750oC for 20 min in air. The value of remanent polarization (Pr) is 9 µC / cm2 and the value of coercive field (Ec) is 155 kV / cm. The fatigue property is not bad, Pr decrease only 10% after 1010 measurements. All Leakage currents were under 10-6 amp. However, the co-doping effect for lowering crystallization temperature and better ferroelectric properties is not displayed in this study, which can be attributed to the difficulty in composition controls for a multi-component system by using magnetron sputtering.
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