磁控濺鍍氧化鏑與鉭鈮酸鍶鉍鐵電薄膜製備及其性質研究

Abstract

本篇論文，分別以調整成長時系統的氧分壓即氧與氬氣混合的莫耳數比為變數，利用單槍磁控濺鍍法沈積氧化鏑薄膜於Si(111)單晶基板；及雙槍磁控濺鍍法沈積鉍系層狀鉭鈮酸鍶鉍鐵電薄膜於Pt/SiO2/ Si(100)基板，控制雙槍不同輸出能量，成長鉍含量不同的薄膜，並對所製備出的薄膜進行晶相結構及電性方面的研究。 氧化鏑(Dy2O3)薄膜於500oC不同氧分壓比(OMR=2.5% ,5%, 9%,13% 16%及20%)氣氛下沈積時，以氧分壓比13%所沈積之薄膜具有最佳之結晶性。且在氧分壓比13%時由於沈積薄膜原子移動性及薄膜被氧原子撞擊效應相互配合的結果，使其表面粗糙度達到一最小值，這些薄膜介電常數值皆在20-24間。氧化鏑膜漏電流密度隨著氧莫耳數比增加而減少，並在氧分壓比13%時有一最小值(1.2x10 -9A/cm2 於100 kV/cm電場下)，而其漏電流導電機制為蕭基特發射。 另以雙槍磁控濺鍍法沈積鉍系層狀鐵電薄膜，一個靶為鉭鈮酸鍶鉍(Sr0.8Bi2.2Ta1.2Nb0.8O9+X)，一個靶為氧化鉍(Bi2O3)，作為高溫沈積時鉍揮發的補償，在600℃ Pt/SiO2/Si(100)基板上成長出 Sr0.8BiXTa1.2Nb0.9O9+y薄膜(x=1.7， 2.0，2.5，2.7，2.9及3.2)。這些膜的主要晶面為(115)且具有柱狀結構。由於這些薄膜所具有C軸的晶面非常少故矯頑電場(2EC)非常低，約為30 kV/cm。此外Sr0.8Bi2.5Ta1.2Nb0.9O9+y膜的永久極化值(2Pr)較其他成份的膜為大；在35 kV/cm電場下為52 μC/cm，此外分析Sr0.8Bi2.5Ta1.2Nb0.9O9+y薄膜之X光光電子能譜，得知在膜的表面及內部鉍及鈮以Bi+3及Nb+5狀態存在，而薄膜中鉍在鍶位置取代仍是以+3價存在，並沒有較低價數的鉍存在。

Magnetron sputtering technique is employed to prepare dysprosium oxide thin films on Si(111) substrates and strontium bismuth niobium tantalate(SBTN) thin films on Pt/ SiO2 /Si(100) substrates. The effect of oxygen to argon mixing ratio on the properties of dysprosium oxide and the effect of bismuth content on the properties of layered structure strontium bismuth niobium tantalate ferroelectric thin films are investigated. The dysprosium oxide films prepared at oxygen to argon mixing ratios of 2.5%, 5%, 9%, 13%, 16%, and 20% are of a polycrystalline structure, which shows (002) and (101) highly oriented hexagonal structure. The film prepared at oxygen to argon mixing ratio of 13% has the smallest root mean square surface roughness. This phenomenon can be partly attributed to the value of atomic mobility among the films surface during deposition and partly to the rate of re-emission from the deposited film. The dielectric constants of the films are between 20 and 24. The leakage current density has the minimum value at oxygen to argon mixing ratio of 13% films, and the mechanism of conduction process is Schottky emission. On the other hand, the Sr0.8BiXTa1.2Nb0.9O9+Y ( SBTN, x=1.7, 2.0, 2.5, 2.7, 2.9, and 3.2 ) films are in situ grown on Pt/SiO2/Si substrates by using two-target off-axis radio-frequency magnetron sputtering at a substrate temperature of 600oC. The films are crystallized with a high (115) diffraction intensity and exhibit a columnar microstructure. Experimental results indicate that the root mean square surface roughness of the film increases with an increase of the bismuth content. In addition, the ferroelectric properties of the films heavily rely on the bismuth content. Moreover, the 440 nm thick Sr0.8Bi2.5Ta1.2Nb0.9O9+Y films exhibit maximum remanent polarization (2Pr) of 52 μC/cm2 and minimum coercive field(2Ec) of 28 kV/cm at an applied voltage of 1.5V. X-ray photoelectron spectral studies reveal that except for Bi+3, no lower valence state bismuth exists in the Sr0.8Bi2.5Ta1.2Nb0.9O9+Y film and bismuth substituted in the strontium site still remains in its +3 valence state.