原子層化學氣相沉積之氧化鉿材料於電阻式記憶體之改善與應用

Atomic Layer Deposition of HfO2 Materials for Resistive Random Access Memory Improvement and Application

彭慶翔(Ching-Shiang Peng)

指導教授 ： 林樹均

國立清華大學/工學院/材料科學工程學系/博士(2013年)

https://doi.org/10.6843/NTHU.2013.00121

摘要

本論文中，內容著重在於氧化鉿基電阻式記憶體的改善以及應用。所有電阻式記憶體元件皆由氧化鉿為主要材料，且皆由原子層化學氣相沉積方法製備。
氧化鉿為一過渡金屬，因其卓越的物理性質，如:高介電常數、能帶寬度適宜以及優異的熱穩定度，被廣泛應用於半導體產業中。除了應用在高介電常數/金屬閘極的疊層中，以氧化鉿為基礎的電阻式記憶體也引起廣泛注意並被視為下一世代非揮發性記憶體的重要材料。氧化鉿基電阻式記憶體內部傳導是由電致生成導電細絲，並擁有優良的雙極性電阻轉換效應，在未來的電阻式記憶體應用中備受期待。然而，不明確的電阻傳導機制以及不穩定的電阻轉換行為是電阻式記憶體遲遲無法實際應用的原因。電阻式記憶體中不穩定的電阻轉換行為是由於在每次的電阻轉換時，將使薄膜內部傳導路徑不規則分布，進而影響轉換電壓及電阻之穩定性。因此，如何提升電阻轉換效應的穩定度是電阻式記憶體在實際應用上的主要課題。在本文之第4章以及第5章，採用摻雜以及嵌入金屬層的方法控制導電細絲生成，提升了氧化鉿基電阻式記憶體的穩定度。藉由原子層化學氣相沉積方法摻雜鋁於氧化鉿薄膜後，使得Hf-Al-O鍵結形成，降低了氧空缺生成能，鋁離子附近形成可控制之導電路徑。而嵌入鉿金屬層不只可改善電阻換效應，更使得操作極性反轉。Pt/Hf/HfO2/TiN電阻式記憶體原件中產生之HfOx介面層，不僅是讓氧化還原反應固定在介面層，控制了傳導路徑，更使得導電機制由法蘭克-普爾穿隧轉換為空間電荷侷限電流，進而影響了操作極性反轉。第6章則提出Pt/NiO/HfO2/TiN氧化物選擇器，施加交互電壓後，可使其具有穩定且類似臨界轉換特性。施加交互電壓可平衡薄膜之內部缺陷，呈現類似臨界轉換的揮發記憶體特性。此具有臨界轉換特性的揮發性氧化物選擇器，預計可相容於雙極性電阻式記憶體之高密度堆疊。

關鍵字

電阻式記憶體 ； 電阻轉換效應 ； 原子層化學氣相沉積 ； 氧化鉿

並列摘要

In this thesis, we focus on HfO2-based resistive random access memory (RRAM) researches in improvement and application. All the RRAM devices using HfO2 as a main material are prepared by the atomic-layer-deposition (ALD) technique with remote-plasma system.
The transition metal oxide, HfO2, is already widely used in semiconductor industries because of its superior physical properties, such as large permittivity, subsequent band gap, and excellent thermal stability. In addition to its use as high-k/metal gate stacks, HfO2-based RRAM has attracted significant attention for its potential in next-generation nonvolatile memory. HfO2-based RRAM devices are formed by an electric-field induced conductive filaments formation/rupture process, and possess superior bipolar resistive switching for future RRAM applications. However, the indefinite resistive switching mechanism and unstable resistive switching behaviors prevent RRAM from being put into practice. The localized filamentary conducting paths in the thin films are diverse in each switching, leading to the nonuniform distributions of switching voltages and resistance states, which result in irresolvable errors in the RRAM operations. Thus, how to effectively improve the stability of switching behavior is an essential issue for practical application of the RRAM. In Chapter 4 and Chapter 5, we use methods of doping and inserting metal layer to control the filaments formation and to stable the resistive switching behaviors of HfO2 RRAM devices. By the ALD doping of Al:HfO2 films, Hf-Al-O bonding formed in the Al:HfO2 films decreases the formation energy of oxygen vacancies and forms controllable conducting filaments along Al atoms. Inserting a Hf metal layer not only improves resistive switching characteristics but also makes polarity operation reversed. The interface HfOx generated in the Pt/Hf/HfO2/TiN devices makes redox fixed near the interface and the conduction mechanism switch to SCLC mechanism from Poole-Frenkel emission, leading to a polarity reversion. Chapter 6 proposes an oxide selector (Pt/NiO/HfO2/TiN) which was verified to exhibit similar, stable threshold switching characteristics by applying mutual bias. The mutual bias could balance the internal defects, which are produced by the interaction between conductive NiO and HfO2 thin films, to present such a similar threshold switching behavior. This volatile oxide selector with a similar threshold switching property is compatible with bipolar RRAM crossbar array applications.

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