鈦酸鉍鈉與鈦酸鋇之固溶與堆疊薄膜鐵電特性之比較分析研究

Comparison of the ferroelectric properties between the solid-solution and layered thin films of (Bi0.5Na0.5)TiO3 and BaTiO3

鄭鈞右(Jyun-You Jheng)

指導教授 ： 謝宗霖

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202003366

摘要

本研究的主旨在於設計由(Bi0.5Na0.5)TiO3 (簡稱BNT)、BaTiO3 (簡稱BT)所形成之(Bi0.5Na0.5)TiO3/BaTiO3 (簡稱BNT/BT)層狀薄膜，並將以此層狀薄膜為基礎，與成分位在MPB (Morphotropic Phase Boundary)內之(Bi0.5Na0.5)0.935Ba0.065TiO3 (BNT-6.5BT)薄膜作鐵電性質的比較。所使用的製程為溶膠凝膠法(sol-gel)以及旋轉塗佈法(spin-coating)，並利用快速熱退火製程使薄膜結晶成相；而選用的基材為Pt/Ti/SiO2/Si基材以及SUS301不鏽鋼基材。
本研究首先製備BNT、BT於具高化學穩定性的Pt/Ti/SiO2/Si基材，並製備Pt、Au、Cu之不同上電極。透過電流-電壓曲線之分析，結果顯示BNT具有較BT更高的漏電流值且BNT與BT皆與所有金屬上電極形成良好的Schottky介面。其中，BNT與BT皆與Pt上電極形成具最小漏電流的介面，且於電滯曲線量測下表現出最高之殘餘極化量及最大極化量。因此本研究嘗試製備BNT/BT層狀薄膜並以Pt作為薄膜之上下電極，形成金屬鐵電層金屬(metal-insulator-metal)之結構。透過微結構、結晶相、電流-電壓曲線以及電滯曲線等分析方法，結果顯示BNT/BT層狀薄膜中的BT能夠改善BNT的結晶性以及降低BNT的漏電流表現並且提升材料內部電偶極極化的能力。藉由positive-up negative-down電滯曲線的量測，以扣除漏電流與電偶極伸縮所貢獻的極化量，得到在相近電場強度施加下BNT/BT層狀薄膜的兩倍殘餘極化量(2Pr)達20.78 μC/cm2，較BNT-6.5BT薄膜的2Pr = 15.36 μC/cm2優異。
不鏽鋼基板因為具有可撓性，可以承受較大程度的形變量而使鐵電材料的上下表面誘發更高的極化電荷輸出，具較佳的壓電行為表現。且其材料成本較低，適合作為壓電元件的基材。本研究透過製備LaNiO3薄膜於不鏽鋼基板作為緩衝層，成功將BNT薄膜、BNT/BT層狀薄膜及BNT-6.5BT薄膜製備於不鏽鋼基材上，結果顯示BNT/BT層狀薄膜能夠改善材料內電偶極的極化能力，使其表現出更低的矯頑電場以及更高的最大極化量，且BNT/BT層狀薄膜展現出較BNT-6.5BT薄膜更為出色的鐵電性質。透過positive-up negative-down電滯曲線量測，在相近的電場強度下，BNT/BT層狀薄膜的2Pr = 41.18 μC/cm2，較BNT-6.5BT薄膜的2Pr = 36.72 μC/cm2優異。

關鍵字

(Bi0.5Na0.5)TiO3 ； BaTiO3 ； LaNiO3 ； 鐵電性 ； 層狀薄膜 ； 形變相界

並列摘要

The main goal of this study is to design a ferroelectric layered thin film composed of (Bi0.5Na0.5)TiO3 (BNT) and BaTiO3 (BT) layers (i.e., BNT/BT) and compare it with (Bi0.5Na0.5)0.935Ba0.065TiO3 (BNT-6.5BT) solid-solution ferroelectric thin film, which is an MPB (Morphotropic Phase Boundary) composition of the BNT-BT solid solution. The sol-gel, spin-coating, and rapid thermal annealing methods were adopted to prepare the ferroelectric thin films on two different substrates: Pt/Ti/SiO2/Si and SUS301 stainless steel substrates.
BNT and BT thin films were first prepared on the Pt/Ti/SiO2/Si substrate with different upper electrodes: Pt, Au, and Cu. The current-voltage (I-V) analysis has shown that BNT had a higher conductivity than BT, and BNT and BT both formed a good Schottky contact with the selected upper electrodes. Among them, films with the Pt upper electrode exhibited the smallest leakage current density and the largest remanent and maximum polarizations. Therefore, in this study, the Pt top electrode was selected to prepare the Pt/BNT/BT/Pt metal-insulator-metal (M-I-M) layered structure for characterizing the BNT/BT thin films, which include SEM, XRD, and the I-V and polarization-electric field (P-E) measurements.
The experimental results showed that the BT layer in the BNT/BT layered thin film was able to improve the crystallinity and reduce the leakage of the BNT layer, resulting in a better polarization switching ability, hence a larger and softer ferroelectric P-E hysteresis. Based on the results of positive-up negative-down (PUND) measurements, the double remanent polarization value (2Pr) of the BNT/BT layered thin film was 20.78 μC/cm2, about 35% higher than that of the BNT-6.5BT MPB thin film (2Pr = 15.36 μC/cm2).
Because of its flexibility, the stainless steel substrate can withstand larger flexural movements and cantilever-type piezoelectric devices based on the stainless steel substrate can typically produce higher current outputs via direct piezoelectricity. In this study, we introduced LaNiO3 as a buffer layer on the SUS301 stainless steel substrate to facilitate the deposition of the BNT, BNT/BT, and BNT-6.5BT thin films. The films exhibited a single-phase perovskite structure without secondary phases. The XRD and P-E measurements showed that the BT layer in the BNT/BT layered thin film could improve the crystallinity of the BNT layer; hence, the BNT/BT layered thin film exhibited a lower coercive field and a higher maximum polarization than those of the BNT thin film. Based on the PUND measurements, the 2Pr value of the BNT/BT layered thin film on the SUS301 stainless steel substrate was 41.18 μC/cm2, about 12% higher than that of the BNT-6.5BT MPB thin film (2Pr = 36.72 μC/cm2).

並列關鍵字

(Bi0.5Na0.5)TiO3 ； BaTiO3 ； LaNiO3 ； Ferroelectricity ； Layered thin films ； Morphotropic phase boundary

參考文獻

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