電阻式記憶體(ReRAM)由於具有結構簡單、低功耗、高耐久度、操作速度快與CMOS製程的高兼容性等特點，使其成為新興非揮發性記憶體中最具潛力的候選之一，近年來有許多研究顯示電阻式記憶體有應用於神經運算上的潛力，所以在未來AI與大數據的時代，電阻式記憶體必將是熱門的研究主題。
本實驗使用磁控濺鍍系統將鐵酸鉍(BiFeO3)與鈦酸鋇(BaTiO3)薄膜沉積於ITO透明電極上，再利用電子束蒸鍍製備Ag做為上電極。實驗元件可分為單層切換層元件: Ag/BFO/ITO與Ag/BTO/ITO；以及三層切換層元件: Ag/BFO/BTO/BFO/ITO與Ag/BTO/BFO/BTO/ITO，為了測試三層切換層結構的穩定性，將下電極從ITO改變為FTO電極進行測試，藉由電性量測比較單層結構與三層結構ReRAM間的差異，實驗結果顯示使用三層切換層的ReRAM結構具有較高的耐久度與穩定性且在Reset過程中產生特殊的階梯型(Step-like)電流下降，階梯型的電流下降有助於實現ReRAM的多級(Multi-level)儲存功能，在電性分析中又以Ag/BFO/BTO/BFO/ITO與Ag/BTO/BFO/BTO/FTO的表現最為優秀，耐久度測試可維持1800次以上且具有良好(>103)的開關電流比(On/off ratio)。
除了單層與三層結構的電性比較外，我們測試三層結構的多級儲存功能，實驗透過改變ReRAM Set過程的限制電流(Compliance Current)與Reset過程的停止電壓(Stop Voltage)來實現。當Set的限制電流的上升，ReRAM的低阻態電阻有下降的趨勢，而在Ag/BFO/BTO/BFO/ITO與Ag/BTO/BFO/BTO/FTO的結構中高阻態電阻也會隨之下降；當Reset的停止電壓上升時，高阻態的電流值會跟著下降，為了測試各個阻態間的穩定性，將低阻態與各個高阻態量測記憶保存時間(Retention time)，結果顯示每種三層結構元件皆可穩定維持10000秒且各個高阻態間皆能清楚區別，顯示此三層結構ReRAM的穩定性與多級儲存能力。
最後為了解ReRAM的薄膜傳導機制，我們將電流與電壓值分別進行對數處理並線性擬合，由擬合結果中得出薄膜傳導機制主要為歐姆傳導與空間電荷限制電流(SCLC)所主導。

Resistive memory (ReRAM) is one of the most promising candidates for emerging non-volatile memories due to its simple structure, low power consumption, high durability, fast operation speed, and high compatibility with CMOS processes. In recent years, many studies have shown that resistive memory has the potential to be applied to neuromorphic computing; therefore, the applications of resistive memory have already found their way into the era of AI and big data in the future.
In this work, a magnetron sputtering system was used to deposit bismuth ferrite (BiFeO3) and barium titanate (BaTiO3) thin films on ITO or FTO transparent electrodes. Electron beam evaporation was adopted to prepare Ag as the top electrode. The experiment can be divided into single switching layer devices, namely, Ag/BFO/ITO and Ag/BTO/ITO; as well as tri-layer devices including Ag/BFO/BTO/BFO/ITO and Ag/BTO/BFO/BTO/ITO. To test the stability of the tri-layer ReRAM, the bottom electrode was changed from ITO to FTO, and the difference between the single-layer and the tri-layer-based ReRAM was compared by electrical measurement. The results showed that the ReRAM structure using the tri-layer structure has higher durability and stability and has a special step-like current drop during the reset process. The multi-level storage function of ReRAM can be achieved via the step-like current drop characteristic. The electrical properties of the tri-layer Ag/BFO/BTO/BFO/ITO and Ag/BTO/BFO/BTO/FTO render the best performance. In particular, their endurance can last more than 1800 switching cycles and deliver an excellent (>103) current switching ratio.
In addition to comparing the electrical parameters of the single-layer and tri-layer structures, the multi-level storage function of the tri-layer structure was tested. The experiment was realized by changing the compliance current of the ‘set’ process and the stop voltage of the ‘reset’ process. When the compliance current increases, the low-resistance state (LRS) resistance of ReRAM decreases, and the high-resistance state (HRS) resistance of Ag/BFO/BTO/BFO/ITO and Ag/BTO/BFO/BTO/FTO structures also decrease as well. On the other hand, when the stop voltage of ‘reset’ increases, the HRS current drops accordingly. To test the stability between each resistance state, the low resistance and high resistance states are used as criteria to measure the memory retention time, The results show that each tri-layer structure device can be stably maintained for 10,000 seconds and different resistance states can be distinguished from one another, which all evidently show the stability and multi-level storage capacity are well achieved with this three-layer structure ReRAM.
Finally, to understand the conduction mechanism of ReRAM, the current and voltage characteristics are logarithmically fitted to discern different conduction mechanisms involved in switching. From the fitting results, the principal conduction mechanisms are mainly dominated by ohmic conduction and space charge limited current (SCLC).

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