利用射頻磁控濺鍍系統製備鉍鐵氧化物/鈦酸鍶超晶格薄膜結構與性質之研究

Preparation and characterization of artificial BiFeO3/SrTiO3 superlattices by radio-frequency sputtering

邱上睿(Shang-Jui Chiu)

指導教授 ： 喻冀平 ； 黃嘉宏 ； 李信義

國立清華大學/原子科學院/工程與系統科學系/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00316

摘要

本論文主要是探討應變效應，參雜效應以及底電極對於鉍鐵氧化物/鈦酸鍶超晶格之影響。鉍鐵氧化物/鈦酸鍶超晶格，及鑭參雜鉍鐵氧化物/鈦酸鍶超晶格使用雙靶射頻磁控濺鍍技術以最佳參數法製鍍。藉由X光繞射及反射圖譜，我們可以確認超晶格薄膜具有良好磊晶性質。鉍鐵氧化物/鈦酸鍶超晶格於本實驗中被證實當薄膜成長溫度介於600到700度之間時，具有優良的結晶性、趨近於臨界應變值(~1.42%)之應變量(~1.3%)、以及優良之鐵電性質。由超晶格薄膜之殘留極化量(Pr) 、壓電係數(d33) 以及漏電流量測結果顯示，超晶格之鐵電性質可藉由控制薄膜應變量改善。藉由控制超晶格介層之厚度於極薄的情況，我們可以維持超晶格薄膜之pseudo-cubic結構，在此種類似tetragonal之結構下，超晶格薄膜得以藉由應變效應有效改善薄膜鐵電性質。鉍鐵氧化物超晶格結構藉由適度鑭參雜(5 atomic %)於鉍鐵氧化物層可以改善薄膜整體的漏電性質。當鑭參雜鉍鐵氧化物超晶格薄膜以相同製程參數被鍍著於鎳酸鑭底電極上時，其鐵電遲滯曲線有著明顯的改善；極化曲線有著明顯的飽和現象。此外壓電係數(d33)結果顯示超晶格薄膜鍍著於鎳酸鑭底電極可改善鐵電性質，這證明薄膜鍍著於鎳酸鑭底電極上，有助於量測其本質之鐵電性質而不受過大的底電極電阻干擾。

關鍵字

鉍鐵氧化物 ； 超晶格 ； 濺鍍 ； 應變效應 ； 鐵電性質

並列摘要

The objective of the study is to investigate effects of strain state, ion doping, and bottom electrode on BiFeO3 (BFO)/SrTiO3 (STO) superlattice structure. The BFO/STO and La-doped BFO/STO superlattice were deposited by radio frequency magnetron sputtering with optimized coating conditions. The epitaxial growth of superlattice films was confirmed by X-ray reflection and diffraction patterns. The BFO/STO superlattice with a well defined crystal structure, large strain state ~1.3% which approaches the critical value of 1.42% and large remnant polarization value at deposition temperature 600-700oC. The measurements of Pr values, piezoelectric coefficient d33, and the leakage current density of superlattice films demonstrate that ferroelectric properties of BFO/STO superlattice thin films could be enhanced with increasing in-plane strain. The BFO/STO superlattice with small BFO/STO sublayer thickness exhibits a pseudo-cubic structure without strain relaxation. Similar with tetragonal structure, superlattice films with pseudo-cubic structure exhibit a clear strain improvement on ferroelectric properties. The substitution of La (5 atomic %) in BFO sublayer can improve the leakage property of superlattice films. The La-doped BFO/STO superlattice films exhibited excellent and saturated hysteresis loops, larger piezoelectric coefficient (d33) on LaNiO3 (LNO) electrode than films on Nb-doped doped STO substrate. High leakage property of La-doped BFO sublayer and suitable resistivity of LNO bottom electrode are the major factor of enhancement of ferroelectric properties of superlattice films.

並列關鍵字

BiFeO3 ； superlattice ； sputtering ； strain effect ； ferroelectric property

參考文獻

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