臺灣博碩士論文加值系統

本篇論文主要探究具有垂直與水平方向性之磁穿隧結元件之磁阻特性。微米級元件皆運用由上而下的製作方式完成，其主要製程技術主要包含黃光微影及雙角度離子蝕刻技術等等。此樣品分別以四端點式的直流與交流電性量測方式探討其磁阻特性。
在直流電性量測架構下，各層磁性層磁矩翻轉行為可以準確對照經由交換梯度磁力計所量測其磁滯曲線。透過改變量測電流極性與大小，得以討論偏壓效應對穿隧結磁阻元件的影響；隨著電流由大而小遞減，磁電阻隨之上升且磁阻率有上升趨勢，並發現其磁阻率在不同電流極性時，擁有不同的數值且高低組態電阻值在小電流區間產生轉折現象。
在交流電性量測架構下，固定輸出一微安培交流電流訊號，以量測磁穿隧結元件磁阻，並確認量測數據與直流量電性測吻合。最後，於磁穿隧結元件下電極(Ta 金屬層)施加直流電，並同時利用交流電流訊號量測其翻轉場的改變，藉以評估自旋效應。在此量測架構下，發現當下電極施加電流大於三毫安培時，造成元件崩潰。經估算，此時通過下電極的電流密度約為每平方公分具有五千萬安培，尚不足以燒毀下電極，但是沒有觀察到自旋電子流的現象，推估應為電流密度不夠大之關係，而造成元件崩潰之原因則待查。

This dissertation is focused on the magnetoresistance characteristic of the magnetic tunnel junction (MTJ) within-plan and out-of-plan magnetic anisotropy. A top-down process has been employed to fabricate the devices in micron scales. The key techniques used include photolithography and dual-angle ion-milling process. The behavior of the magnetoresistance is measured via four-probe electrical measurements.
The basic magnetization reversal behavior of each ferromagnetic layer in MTJ film stack is understood by room temperature DC MR measurements and they are in good agreement with M-Hhysteresis loop, measured by an Alternating Gradient Magnetometer (AGM). By varying the strength and polarity of the sensing current, it is discussed how the bias effect influences the magnetoresistance characteristic. When the current strength is reduced, the resistance level as well as the MR ratio are increased but with a kink in the small current region.
The electrical measurements by using an AC currentof1inthe room temperature show pretty similar MR curves with those measured by using DC measurements. We attempt to observe spin current effect by applying an DC current in the Ta bottom electrode while an AC sensing current is used for probing the MR curves of the MTJ device. The MTJ device is broken down at applied current above3, in which the corresponding current density is 5.04.Consequently, no effect of spin current is observed. This may have been due to current density being too low. The reason for breaking down the MTJ device at such condition is still unknown and more efforts are needed to explore this phenomenon.

CONTENTS

口試委員會審定書 #
誌謝 i
中文摘要 ii
ABSTRACT iii
CONTENTS iv
LIST OF FIGURES vi
LIST OF TABLES ix
Chapter 1 Introduction 1
1.1 Introduction to spintronics 1
1.1.1 Giant magnetoresistance effect (GMR) 2
1.1.2 Magnetic Tunnel Junction 4
1.2 Motivation of this dissertation 5
1.3 Reference 6
Chapter 2 Theory and literature review 7
2.1 Review of basic concepts of tunneling 7
2.1.1 Basic concepts of tunneling 10
2.1.2 General current- voltage characteristic for electron tunneling 12
2.2 Spin-dependent tunneling 17
2.2.1 Ferromagnetic metal/insulator/ ferromagnetic metal (F/I/F) junctions and Julliere model 18
2.3 Spin transfer and magnet dynamics mechanics 21
2.3.1 Spin transfer torque 21
2.3.2 Spin orbit torque 23
2.4 References 25
Chapter 3 Experimental procedure 27
3.1 Fabrication procedure 27
3.1.1 Current-in-plane magnetic tunnel junctions (CPP-MTJs) 27
3.2 Electrical measurement 31
Chapter 4 Results and discussion 33
4.1 The hysteresis curve of the sheet film 33
4.2 The RH cures of the MTJs 35
4.2.1 The reversal behaviors with different sizes MTJs 35
Chapter 5 Conclusions and Future Prospects 43

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