多層膜巨磁阻中鐵磁層材料之影響及其於感測器之應用

Giant magnetoresistance multilayers: effects of ferromagnetic materials and applications in magnetic sensors

王蔚鴻(Wei-Hung Wang)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

自從巨磁阻（giant magnetoresistance，GMR）效應發現之後，由於具有電阻變化大、高靈敏度、磁場操作範圍廣等優點，人們很快地將其應用在不同領域之中，包括磁紀錄媒體讀頭以及磁性感測器。在磁性與非磁性金屬多層膜系統中，在適當的非磁性層厚度下，相鄰鐵磁層的磁矩會藉由反鐵磁耦合而形成反平行排列，若施加磁場則可使其轉換為平行排列，此相鄰磁性材料磁化方向相反情況下的電阻值，明顯大於磁化方向相同時的電阻值，這種可透過磁場控制轉換高低阻態的現象，即被稱為巨磁阻效應。巨磁阻元件構造簡單、耐震性強，有較佳電阻溫度係數，對操作條件誤差以及環境的容忍度高，較不受粉塵、油漬、高濕度等汙染影響，因此對於汽車產業或工業製造等惡劣使用環境是良好的選擇；而由於巨磁阻元件易與一般半導體製程整合、可微小化，在消費性電子或生技醫藥產業亦極具應用潛力。
本研究希望透過不同材料結構與製程方法的改良，取得高穩定性、高阻值比的巨磁阻元件。我們以直流磁控濺鍍方法製備鐵磁（Co、CoFe、NiFe、NiFeCo）/非鐵磁（Cu）多層膜，找出具有最高巨磁阻及反鐵磁耦合的膜厚；引入底層緩衝層，藉由調整粗糙度，降低與自旋無關的電子散射，來大幅提升磁阻值比。藉由不同鐵磁層材料的巨磁阻多層膜系統，觀察這些鐵磁材料對磁阻以及靈敏度的影響，我們發現CoFe/Cu多層膜可以達到最高的磁阻，而以NiFeCo/Cu多層膜則是具有較好的感測靈敏度。我們亦鍍製了結合CoFe和NiFe兩種鐵磁材料的膜層結構，結合它們高磁阻與高靈敏度的特性。為驗證其作為磁感測器的潛力，我們分別使用剝離和蝕刻製程製備NiFeCo/Cu的多層膜巨磁阻元件，確認我們的元件在製程中並不會犧牲磁阻值後，藉由一磁鐵陣列驗證元件的感測能力。本實驗結果可幫助未來開發高精度且高靈敏度的巨磁阻感測器，並期望應用於儀器量測、汽車工業、自動機械、座標量測、半導體業、生醫感測、消費電子等領域。

關鍵字

巨磁阻 ； 磁性多層膜 ； 磁感測器

並列摘要

Since the discovery of giant magnetoresistance (GMR) effect, it has been applied to many fields, including read heads of magnetic recording media and magnetic sensors, for its large resistance change, high sensitivity and wide operating range. If we carefully select the thickness of the non-magnetic layers in a ferromagnetic and non-magnetic metallic multilayer system, the magnetizations of neighboring ferromagnetic layers will align in antiparallel directions through antiferromagnetic coupling. Applying a magnetic field can turn them into parallel arrangement. The resistance of the system is much higher at antiparallel state than that at parallel state. Therefore, the system can transit between high and low resistance states by an external magnetic field. This phenomenon is called GMR effect. GMR devices have relatively simple structure, high resistance to shock, good temperature coefficient of electrical resistance, high tolerance of operating error and environment and are less affected by harsh conditions such as dust, oil, high humidity, so they are a good choice for using under nasty environments, such as automobile industry and industrial manufacturing. Since GMR devices can easily be integrated with semiconductor manufacturing processes, they also have great potential to be applied in consumer electronics and biotechnological industry.
This study is aimed to obtain a GMR device with high stability and high magnetoresistance (MR) ratio from different materials and structures and improvements on fabrication processes. We sputtered ferromagnetic (Co, CoFe, NiFe, NiFeCo) /non-magnetic (Cu) multilayers and selected the thicknesses with the highest MR ratio and antiferromagnetic coupling, and we observed the effects of ferromagnetic materials on MR ratio and sensitivity. A buffer layer was introduced under the multilayers to adjust the roughness and lower the spin-independent scattering to raise MR ratio. We found that Co/Cu multilayers had the highest MR ratio an NiFeCo/Cu multilayers had the best sensitivity among the systems we investigated. We also designed layer structures with CoFe and NiFe in hopes of combing their high MR ratio and high sensitivity respectively. We fabricated NiFeCo/Cu GMR devices by lift-off and etching processes respectively to demonstrate their potentials of magnetic sensors. After verifying that the MR ratio was maintained through the fabrication processes, we showed the sensing capabilities of the devices with a patterned magnet array. The results are helpful for developing highly precise and sensitive GMR sensors, which are expected to be applied in plenty fields, e.g. instrumental measurements, automobile industries, automatic robotics, semiconductor industries, biomedical sensing and consumer electronics.

並列關鍵字

giant magnetoresistance ； magnetic multilayers ； magnetic sensor

參考文獻

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