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  • 學位論文

自旋穿遂電阻元件的磁阻抗效應

Magnetoimpedance Effect of Spin Dependent Tunnel Junction

指導教授 : 林敏聰

摘要


量測自旋穿隧電子元件 (the spin dependent tunnel junction)的磁電阻行為通常是利用直流電源來提供電流或電壓。在本論文實驗中,磁性穿隧接面 (magnetic tunneling junction, MTJ) CoFe/Al2O3/CoFe/NiFe 使用HP4294A 提供40 Hz~110 MHz交流電流源,利用四點量測方式,在室溫下量測MTJ的磁阻抗 (magnetoresistance) 行為,我們可提供的磁場最大可達一千高斯左右。 當MTJ在交流電源中,由於MTJ結構關係由於MTJ結構關係我們將不只單單考慮穿隧電阻部分,電容所扮演的角色將會影響MTJ磁阻抗效應隨著頻率變化的關係,其中電容值得大小是與形狀和材料所決定的,但是我們發現,當外加不同磁場時,電容的大小會受到磁場而改變•另外在量測高頻阻抗行為時,我們也發現阻抗的實部大小會由正數轉電成負數,會產生此種現象是類似於因為四點量測所產生的電流分布效應,當我們MTJ的導線電阻與穿隧電阻大小相近時,電流分布效應集會產生,並有可能量到負的電阻值,然而交流電源系統中,電流分布效應的產生就必須考慮與頻率的關係。在製作MTJ絕緣層的步驟中,穿隧位障的形成是使用氧氣電漿來氧化鋁膜,我們可以控制氧化過程的時間,來製作不同大小的有效穿隧電阻,並觀察發生負實部阻抗的特徵頻率會與不同大小的穿隧電阻有何關係。也由於負的實部阻抗產生,造成我們會量到一個趨近正負無窮大的實部磁阻抗率 (TM-Re)。另外我們也觀察加上不同大小的直流偏壓與交流振幅,除了觀察磁阻抗在不同頻率中所受到的影響,並可以估計出穿隧電阻與電容受電壓增加時,分別是會下降與升高。

關鍵字

自旋 穿遂電阻 磁阻抗效應

並列摘要


The electronic properties of the spin dependent tunnel junction (STJ) are usually measured by direct current (DC) source. In our measurement, the MTJs CoFe/Al2O3/CoFe/NiFe was measured by a four-probe method at room temperature in the frequency range from 40 Hz to 110 MHz, with the external magnetic field ranging in strength up to 500 Oe. At high frequency, the capacitance will play an important role to affect the measured result. Generally speaking, the capacitance is determined by the geometry and materials. But We observed that the effective capacitance changes with the application of an external magnetic field. The magnetocapacitance ratio can get up to 15%. At high frequency, The real part of impedance was found to change from positive to negative. The phenomenon is similar to the inhomogeneous current distribution effect that derived from the electrode resistances comparable to or higher than the junction resistance. The MTJs with a tunnel barrier formed by O2 plasma. We control the time of O2 plasma sputerring in forming the tunnel barrier is effective for achieving a different junction resistance and for causing the oxidation degree of the bottom electrode during plasma oxidation in MTJs. By the way to caculated the critical frequency that the real part cahege sign. At this critical frequency, the real part of magetoimpedance (TM-Re) have a huge increase.

並列關鍵字

Magnetoimpedance Spin Tunnel Junction

參考文獻


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