二氧化錳與氧化鋁應用於電阻式轉態記憶體之特性研究與電性分析

Abstract

電阻式非揮發性記憶元件具有低功率消耗、高密度、高操作速度、及微縮能力高等優點，使其成為新世代非揮發性記憶元件的熱門人選。研究中使用了二氧化錳及氧化鋁來當作電阻式記憶體的電阻轉換層，並且探討兩者的電性及轉換機制。 對二氧化錳而言，分別製作不同上電極的電阻式轉態記憶體並呈現其電流-電壓特性。根據二次質譜儀對元素含量之縱深分析，不同材料之上電極和二氧化錳之介面氧含量分布的不同。此分析可看出電極和二氧化錳之介面對於轉態行為扮演了重要的角色。其中以鈦當作上電極的鈦/二氧化錳/鉑結構在電性操作上具有可重複性,並且室溫量測能夠操作1000次以上。此外將溫度升至85℃量測元件的耐操度，在0.2伏特的讀取電壓所量測到的電阻值能夠維持一定值至104 秒，並且高低阻態的電阻值差了將近100倍。由此結果可推測資料能夠在沒有供給電壓的情況下儲存，並且說明鈦/二氧化錳/鉑結構具有潛力能夠應用於非揮發性記憶體。 對氧化鋁而言，主要討論不同電極對電性的改變。我們分別製作上電極材料為鉑、鈦而下電極為鉑、氮化鈦的電阻式記憶體，比較各個電極對轉態特性的影響。首先以鉑當下電極，上電極鈦的電性好於上電極鉑。以氮化鈦為下電極，上電極鉑的電性好於上電極鈦。根據以上電性的比較，不同上下電極可能的轉態機制模型被提出。 最後，我們提出在鈦/氧化鋁/鉑結構之電阻式轉態記憶體中埋入鎳奈米點。並且比較氧化鋁電阻轉換層有無埋入奈米點之條件，從電性的量測上得知埋入鎳奈米點能夠穩定轉態電壓之分佈。

The resistive switching random access memories (RRAMs) have advantages of low power consumption, high-density integration, and high speed operation as one of the next-generation nonvolatile memory candidates. In this study, electrical properties and switching mechanism of manganese dioxide (MnO2) and aluminum oxide (Al2O3) as the resistive switching layer are investigated. For MnO2-based resistive switching memory, the current-voltage characteristics with various top electrodes are presented. Secondary ion mass spectrometry (SIMS) depth profile reveals that different top electrodes react in different oxygen concentration distribution at the interface between the electrodes and MnO2. It suggested that the interface play an important role on the resistive switching behavior. The device structure of Ti/MnO2/Pt shows reproducible and stable resistive switching behavior traced over 1000 times at room temperature. Besides, the retention behavior at 0.2V read voltage of the memory in Ti/MnO2/Pt device at 85℃ is investigated. The resistance ratio between LRS and HRS is close to 102 and is stable for 104 sec retention time. It can say that the data can store completely without supplying power. These indicate that the Ti/MnO2/Pt device is a great candidate for non-volatile memory application. Electrode effects are also considered in Al2O3 as the resistive switching layer. We have used Pt or Ti as the top electrodes and Pt or TiN as the bottom electrode. Hence, there are four different structures, Pt/Al2O3/Pt, Ti/Al2O3/Pt, Pt/Al2O3/TiN, and Ti/Al2O3/TiN. By comparing electrical characteristics of different structures, the influence of electrode materials on the resistive switching properties of Al2O3-based resistive switching film can be investigated. With Pt as the bottom electrode, the electrical characteristics of Ti top electrode are better than Pt top electrode. With TiN as the bottom electrode, the electrical characteristics of Pt top electrode are better than Ti top electrode. The probable switching models of different top and bottom electrodes have been proposed in this study. Furthermore, nonvolatile memory characteristics of Ti/Al2O3/Pt embedded with Ni nanocrystals are also investigated. Compared to the Al2O3 without Ni nanocrystals, the resistive switching random access memories with Ni nanocrystals can stabilize the distribution of SET voltage.