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Mn on BiFeO_3 base film structure and properties of

Author: YinZaiMei
Tutor: HuGuangDa
School: Jinan University
Course: Materials Physics and Chemistry
Keywords: Multiferroic Bismuth ferrite Ferroelectric thin films Piezoelectric coefficient Residual polarization
CLC: O484.1
Type: Master's thesis
Year: 2011
Downloads: 132
Quote: 1
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Abstract

BiFeO ₃ is at room temperature, with a lead-free multiferroic materials, the Curie temperature (TC ~ 850 ℃) and Neil temperature (TN ~ 370 ℃) are higher. Recent studies found that lanthanide doping and strain are able to make BiFeO ₃ had structural phase boundary (MPB) in the quasi-phase boundary exists near comparable with PZT piezoelectric response in the future information storage, sensors, micro-electromechanical systems and applications such as multi-function devices are promising to replace leaded materials. However, the use of chemical solution prepared BiFeO ₃ Films serious leakage problems, coercive field greater insulation performance and long term reliability is low, and the future requirements for device applications there is a gap . Therefore, the current key issue is to suppress BiFeO ₃ leakage of the base film, to improve the insulation performance and long term reliability, and improving film and the piezoelectric coefficients of the polarization. In this thesis, by precisely controlling the amount of reduced Mn-doped BiFeO ₃-based film leakage and maintains its piezoelectric properties of thin films by controlling the process parameters to improve the degree of crystallinity of the film, to obtain better ferroelectric properties. In this paper, the layers of metal-organic decomposition method combined annealing process in ITO / glass substrates were prepared BiFeO ₃-based films, on the one hand of Mn content on Bi _0.86 Sm _0.14 FeO ₃ thin film structure, leakage, ferroelectric and piezoelectric properties impact on; the other hand, the layer thickness of the films and annealing temperature on BiFe _0.95 Mn _0.05 O ₃ film growth mode and electrical properties. Main conclusions are as follows: deposited on ITO / glass substrate doped with different concentrations of Mn, Bi _0.86 Sm _0.14 Fe _1-x Mn _x O ₃ (x = 0.00,0.01,0.03,0.05) films with Bi _0.86 Sm _0.14 FeO ₃ thin compared to only Bi _0.86 Sm _0.14 Fe0.99Mn0.01O ₃ films exhibit lower The leakage current, smaller coercive field and greater residual polarization and piezoelectric coefficients. This suggests that in order to obtain Bi _0.86 Sm _0.14 FeO ₃ Films intrinsic ferroelectric and piezoelectric properties, doping 1 at.% Of Mn is very necessary. The resulting excess Mn-doped Bi _0.86 Sm _0.14 FeO ₃ film piezoelectric properties dropped significantly, while ferroelectric properties are to some extent destroyed. This is due to the higher concentration of Mn doping Bi _0.86 Sm _0.14 FeO ₃ thin film structure deviates from quasi-phase boundary, but also in doped more (3 at.% and 5 at.%) Mn of Bi _0.86 Sm _0.14 FeO ₃ films, aging more serious, non-180 ° domain wall movement in the irreversible also reduced. Annealing process conditions in the layers prepared with different layer thickness (42 nm, 31 nm, 25 nm) of BiFe _0.95 Mn _0.05 O ₃ film. Wherein the layer thickness of the film is 25 nm (110) - oriented preferential growth of the grain from the substrate to the upper electrode through between the columnar growth, to avoid the multi-layer structure, in which fewer defects. Layer thickness of 42 nm and 31 nm of BFMO multilayer films have demonstrated growth, wherein the grain boundary more, more defects. The drain side, with the layer thickness decreases, the leakage current density of the film is slightly increased, which is mainly due to the small thickness of the film layer large grains, the grain boundary less leakage path is short. The film has greatly improved retention performance, the film layer thickness of 25 nm is almost no loss of pulse polarization layer film having a thickness of 42 nm pulse polarization loss of 27 at.%. This is because the latter has more defects, resulting in a serious aging of the holding performance. Layer thickness of 25 nm thin rectangular hysteresis loops degree than the other two samples is much larger than, and its residual polarization is also the largest (82μC/cm2), asymmetric coercive field level is minimal. This is also the age of the sample with the relatively minor related. Therefore, the preparation BiFe _0.95 Mn _0.05 O ₃ thin films used in optimum layer thickness is 25 nm, the layer thickness is sufficient to make the film achieved through the columnar growth, the smaller the leakage current density to ensure the same time, to significantly improve the residual polarization value of the film and the film significantly improved retention performance. Annealing at different temperatures for different layer thicknesses BiFe _0.95 Mn _0.05 O ₃ film, a thin layer BiFe _0.95 Mn _0.05 O ₃ films annealed at higher temperatures, the (110) orientation is high. However, at high temperature annealing BiFe _0.95 Mn _0.05 O ₃ Films leakage density is too large, which is larger by a high temperature annealing the grain , caused by leakage path shorter. BFMO layer thicknesses for different film, the remnant polarization is increased with increasing annealing temperature, the annealing time and temperature reached 600 ℃ decreased; annealed at lower temperatures for the film, the remnant polarization With the decrease of the layer thickness increased significantly. This is aging and the result of leakage. As the temperature increases, the degree of crystallinity of the film increases, defects are reduced, reducing the residual polarization aging increases, and the high annealing temperature will bring a large leakage, which is applied to the film so that the effective voltage reduce the remanent polarization decreases. BiFe _0.95 Mn _0.05 O ₃ Films maintain performance with annealing temperature has been significantly improved, while the high annealing temperature films maintain performance have declined. Therefore, 575 ℃ is the optimal annealing temperature at 575 ℃ annealed BFMO film did not show too much leakage density, while showing a great deal of residual polarization (86μC/cm2) and excellent retention properties.

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