具低操作電流與自我限流特性之氧化鋅奈米柱陣列/氧化銅薄膜異質接面結構之雙極性電阻轉換行為

Abstract

本論文在研究氧化鋅奈米陣列與氧化銅PN異質接面的製程與電阻轉換行為。首先利用水熱法在ITO基板上生長氧化鋅奈米柱陣列，接著將銅薄膜沉積在氧化鋅奈米柱陣列的頂端，並以熱氧化法形成氧化銅，其中我們將氧化鋅奈米柱之間的空隙用光阻層填滿作以減少漏電流；並利用掃描式電子顯微鏡，光激螢光，以及X射線繞射圖型分別作幾何結構、發光結構和成分上的分析 電壓電流的量測結果觀察到PN接面二極體的整流特性，並且在經過forming process後，我們可以明顯地觀察到雙極性電阻轉換行為，以及大約相差10倍的高低阻態之電流比例。我們元件運作的整體操作電流非常小，約在10-7安培的電流等級。此外，不論於SET或者RESET的步驟中、都可以觀察到元件自我限流的特性；即在SET與RESET的過程中，電流同時都有減少的趨勢。 為了瞭解電極對於元件電阻轉換的影響，我們將不同種類的電極蒸鍍在樣品上，結果顯示轉換的行對於不同的電極幾乎沒有影響。最後，我們提出一個模型，推測電阻轉換行為是因為於空乏區的空缺遷移導致，並且成功地解釋了所觀察到的實驗結果。

The growth and bipolar resistive switching behavior of ZnO nanorods / CuO PN heterojunction are reported in this thesis. ZnO nanorods were grown on ITO substrate by using hydrothermal method. A Cu layer was then grown on top of the ZnO nanorods and oxidized to become CuO, but before the growth of the Cu layer, the empty spaces between nanorods were filled with photo-resist to prevent current leakage. Scanning electron microscope, Photoluminescence and X-Ray diffraction were used to study the surface morphology and the crystalline structure of the sample and the results indicate that the sample have good crystalline quality and optical properties. Typical PN junction rectifying behavior was observed for the sample in the current- voltage measurement. After the forming process, the bipolar switching behavior can be clearly observed with a high/low ratio of about 10 between high resistance state and low resistance state. The operation current is very low in our device, and it can be operated at a current level of 10-7 A. In additions, current self- compliance is observed in both the set and reset processes; the current in the device decreases in both the set and rest processes. Several different kinds of electrodes were deposited on the samples to study the effect of the electrodes on the switching behavior of the devices, and the results indicate that the switching behavior is electrode-independent. A model which takes into account of the migration of vacancies in the depletion region is proposed and can explain successfully the observed experimental results.