垂直磁異向性PrFeB薄膜的製備 垂直磁異向性PrFeB薄膜的製備及其顯微結構與磁性質之研究

Abstract

本研究以磁控濺鍍的方式製備具有垂直磁異向性之PrFeB薄膜，並探討在各種濺鍍參數(如溫度、瓦數、氬壓、厚度、時間等)下其顯微結構與磁性質的改變，以利於未來應用於垂直磁紀錄媒體。研究結果發現，金屬保護層較Si3N4陶瓷保護層更能幫助PrFeB薄膜磁性質的提升，因為Ta金屬在晶界具有較佳的移動力而促進薄膜矯頑磁力的增加。而熱處理方式的不同也會影響薄膜的磁特性。研究結果顯示基板加熱鍍膜的方式較常溫鍍製再退火的製程更有助於Pr原子的移動而得到硬磁相。同時在基板加熱的過程中，我們也嘗試改變PrFeB的濺鍍環境來控制薄膜中Pr原子的含量，結果發現當Pr成分落在17-20 at.%範圍時可得到良好的磁性質，而PrFeB磁性層的厚度為125nm、Ta緩衝層的厚度為50nm時，薄膜的垂直磁異向性及矯頑磁力可再進一步改善。然而，濺鍍PrFeB時若基板溫度較高，再施予後退火卻只會增加晶粒尺寸及表面粗糙度而弱化原本的磁性質，所以高溫基板鍍製的PrFeB薄膜不需要再施予後退火的熱處理。 本研究中所製備最佳磁性質之PrFeB薄膜的濺鍍之參數為基板溫度600℃、RF150W、氬壓40mtorr、厚度125nm，再搭配Ta緩衝層50nm，此薄膜不需再後退火即可得到良好的垂直磁異向性，其Hc⊥=10.5kOe、Hc//=10.9kOe、S⊥=0.91、S//=0.29，相當有潛力發展成垂直磁記錄媒體材料。

In this study, PrFeB thin films with perpendicular magnetic anisotropy were deposited by magnetron sputtering. The effects of sputtering parameters (temperature, sputtering power, Ar working pressure, thickness of the film, annealing time etc.) on microstructure and magnetic properties were investigated. From the results, Ta metal capping layer improved the magnetic properties of PrFeB thin films, due to higher atomic mobility of Ta atoms in grain boundary. Besides, the hard magnetic phase can be obtained by in-situ annealing process (substrate heating) indicating hard phase formed easily on hot substrate. From the composition characterization, a film with good magnetic property usually contents Pr of 17-20 at.%. The perpendicular magnetic anisotropy and coercivity of the thin films could be further improved when the thickness of PrFeB magnetic layer as well as Ta buffer layer were 125nm and 50nm, respectively. Further post-annealing the PrFeB thin films only increased the grain size and the surface roughness, that degraded the magnetic performance. Thus post-annealing process was not necessary for formation of hard phase. In this study, the optimal sputtering parameters of PrFeB thin film are substrate temperature 600℃, RF power 150W, Ar gas pressure 40mtorr, thickness of PrFeB and Ta buffer layer are 125nm and 50nm, respectively. Good perpendicular magnetic properties of Hc⊥=10.5kOe, Hc//=10.9kOe, S⊥=0.91, and S//=0.29 were obtained with the film structure of Ta(50nm)/PrFeB(125nm)/Ta(20nm).