以原子層沉積程序製備擬自旋閥奈米結構及相關磁性質之探討

Preparation of Pseudo-Spin Valve Nanostructures with Atomic Layer Deposition Processes and Study of relevant Magnetic Properties

陳敏騰(Min-Teng Chen)

指導教授 ： 呂世源

國立清華大學/工學院/化學工程學系/碩士(2006年)

摘要

本研究以原子層沈積系統來製備pseudo-spin valve之三明治奈米結構，其三層結構分別為Si(100)/FM1/Au/FM2，其中FM1與FM2為陶鐵磁性氧化鐵奈米薄膜，且固定FM1與Au之薄膜厚度而改變FM2氧化鐵之薄膜厚度。由於在低溫下以原子層沉積之氧化鐵薄膜為非晶相結構，因此必須經過煅燒過程，且在真空環境下通入氫氣，使非晶相之氧化鐵薄膜還原成Fe3O4之晶相結構。並可研究與討論FM2在不同沉積週期數下與煅燒前後所展現磁性之相關特性，並且藉由SEM與AFM來觀察氧化鐵薄膜其表面微結構之變化。由於氧化鐵薄膜必須經過煅燒、氫氣之還原程序才可轉變成Fe3O4之陶鐵磁特性，因此可以藉由XRD與XPS來偵測薄膜是否已經完全還原成Fe3O4之晶相結構。而在磁性量測方面，可以藉由振動樣品磁力計及四點探針在外加磁場的環境下，來量測擬自旋閥(pseudo-spin valve)之磁滯曲線與磁阻值之大小。由SEM及AFM結果顯示，在煅燒前後，氧化鐵薄膜其表面粗糙度會明顯地增加，且表面薄膜結構有轉變成顆粒狀聚集之現象。而由XRD與XPS結果顯示，非晶形之氧化鐵經過煅燒還原之後，已完全地還原成Fe3O4之晶相。而磁滯曲線之量測結果顯示，由於在煅燒還原之前，氧化鐵是非晶形結構，因此其淨磁化量為零，而沒有磁滯之曲線，但經過煅燒還原之後，由於已還原成Fe3O4之晶相，因此有磁滯之曲線的呈現。而從磁阻之量測結果顯示，在煅燒還原前後均有磁阻值之顯現，且隨著第二層氧化鐵之沉積週期數的增加，磁阻值均有增加之趨勢。

關鍵字

原子層沈積 ； 自旋閥結構 ； 自旋電子學 ； 鐵磁性材料 ； 磁鐵礦

並列摘要

The present research focused on the fabrication of sandwiched nanostructure of pseudo-spin valve via the atomic layer deposition process. The structures of the three layer thin films included Si(100)/FM1/Au/FM2. The FM1 and FM2 were nano-thin films of ferrimagnetic iron oxide and we fixed the thicknesses of the FM1 and Au thin films but varied the thickness of the FM2 iron oxide thin film. Since iron oxide thin films prepared at low temperatures via the atomic layer deposition process were amorphous, the structure was heat treated with hydrogen gas (H2) in reduced pressure environment, to reduce the amorphous iron oxide to crystalline Fe3O4. The resulting structures were then studied for the relevant magnetic characteristics subject to variations in thickness of FM2 and application of the reductive heat treatment process. The surface morphology of the oxide thin films was observed and characterized with SEM and AFM. Amorphous iron oxide thin films were transformed into ferrimagnetic Fe3O4 crystal films via reductive heat treatment in hydrogen atmosphere. The crystalline structures of the reduced thin films were confirmed with XRD and XPS. For magnetic measurements, hysteresis curves and magneto-resistances were measured with the vibrating sample magnetometer (VSM) and 4-point probe in an applied magnetic field, respectively. From the results of SEM and AFM, the surface roughness of the iron oxide thin films increased significantly due to growth and aggregation of Fe3O4 crystals after the reductive heat treatment. And from the results of XRD and XPS, the amorphous iron oxide was successfully reduced to Fe3O4 crystals with the reductive heat treatment. Before the reductive heat treatment, the iron oxide films were amorphous, the corresponding net magnetization was equal to zero and no hysteresis was observed. But after the reductive heat treatment, the iron oxide was transformed into Fe3O4 crystals and showed hysteresis phenomena. As to the magneto-resistance, the pseudo-spin valve structures before and after the reductive heat treatment both showed magneto-resistances. And with increasing of deposition cycle numbers of the second layer iron oxide, magneto-resistance values all have the tendency of increase.

並列關鍵字

atomic layer deposition ； spin valve structure ； spintronics ； ferromagnetic material ； magnetite

參考文獻

3. 張慶瑞、衛榮漢‚2003‚“單自旋金屬材料的性質與應用”.

4. Hsiao C. T, 2002.

Winkler, J.; Seidel, T. E. Thin Solid Films 2002, 402,

6. Juppo, M. “Atomic Layer Deposition of Metal and

Spectrometry Studies”, Academic Dissertation 2001,