利用濺鍍法製備氧化鋁薄膜記憶體元件

Abstract

近年來，對於下世代記憶體之研究，諸如鐵電記憶體(FeRAM)、磁阻式記憶體(MRAM)、相變化記憶體(PCM)與電阻式記憶體(RRAM)…等已十分廣泛。當中由於電阻式記憶體具有結構簡單、操作速度快、低耗能以及與現今半導體製程技術相容等優點，極可能成為下世代非揮發性記憶體之主流。然而，電阻式記憶體確也存在著下列缺點，像是高形成電壓(high forming voltage)、良率低(low yield)與記憶狀態在操作過程中會發生變異及寫入失敗等問題。 本論文以濺鍍法製備氧化鋁電阻轉換薄膜，搭配白金上下電極，在上電極與氧化鋁間置入一鈦金屬層。其結構為白金/鈦/氧化鋁/白金(Pt/Ti/Al2O3/Pt)，厚度各為60奈米，20奈米，20~30奈米及80奈米。實驗中發現此電阻式記憶結構其記憶耐久度、高溫穩定性、非破壞性讀取與高溫操作下等特性均為十分優異，然而卻具有形成電壓過高(9V~14V)之缺點。製程中進一步利用鈦(Ti)金屬強烈吸氧之能力，於高溫爐管中進行不同溫度之熱處理，其分別為400度、500度、600度下歷時一小時，當中發現於600度下一小時之熱處理後，氧化鋁薄膜便不再需要形成過程(即形成電壓為零)，且其依舊具有良好的電阻轉換特性。最後，由電學性質、穿透式電子顯微鏡之能量散射光譜儀(TEM-EDS)與二次離子質譜儀(SIMS)等分析相互佐證之下，進而提出以下機制：利用鈦之吸氧能力，在電阻轉換薄膜內創造許多氧空缺；當氧化鋁內某區域單位體積內之氧空缺濃度高於一程度時，就會造成類似崩潰現象，進而完成形成過程。此外，實驗中間接證明了氧化鋁之電阻轉換現象與內部氧缺陷有關，並為電阻轉態進一步地提出一個較明確之原理及機制。

In this thesis, next-generation nonvolatile memory will be introduced and from those we focus on resistance random access memory (RRAM) research. The RRAM has bistable resistive switching characteristic which can exhibit two states of different resistance for logic level. Therefore, RRAM can be next-generation memory by this characteristic. Owing to RRAM has excellent characteristics of high-speed operation, low-power, and high-density integration. In addition, its simple cell structure (metal-oxide-metal tri-layer), CMOS-friendly materials and low process temperature all are advantages for next-generation memory application. RRAM is fabricated with aluminum oxide thin film deposited on Pt bottom electrode by RF magnetron sputter and chose Ti for top electrode. First, some material analyses of aluminum oxide thin films are proposed. The physical, electrical properties and reliability issue of RRAM are observed. From those analyses, conduction mechanism and switching mechanism could be driven. Finally, a solvent is proposed to improve the disadvantage of electrical characteristics for our device. It made the device potential for next-generation memory application