Fabrication and device characteristic of oxide thin film for resistance random access memory applications

應用於電阻式記憶體之氧化物薄膜製程與元件特性研究

張文淵(Wen-Yuan Chang)

指導教授 ： 吳泰伯

國立清華大學/工學院/材料科學工程學系/博士(2010年)

摘要

We focus on the fabrication and resistive switching characteristics of ZnO films for nonvolatile memory applications. The unipolar and bipolar resistive switching characteristics of highly (002)-oriented and columnar-grained ZnO thin films were observed, respectively. Based on the pad size effect and temperature dependence of LRS, it can be realized that the LRS is related to the conduction though local metallic filament. The top electrode material dependence on resistive switching characteristics of ZnO was also investigated. The existence of oxygen ions in electrode and ZnO films would play an important role in resistance switching behavior.
The influence of crystalline constituent on electrical and resistive switching properties of TiO2 was investigated. The leakage current in HRS is sensitive to the crystal phase composition of the TiO2 matrix; however, the current flowed through the films in LRS is hardly affected. Besides, the improvement of resistive switching characteristics in TiO2 films with embedded Pt nanocrystals was also investigated.
So far, the resistive switching behaviors have investigated not only in ZnO thin films, but also in ZnO nanorods (NRs). The distinct geometry of ZnO NRs leads to an excellent nonvolatile behavior with a narrow dispersion of HRS/LRS ratio due to the formation of straight and extensible conducting filaments along the direction of each vertically aligned ZnO NR.

關鍵字

電阻式記憶體 ； 氧化物薄膜 ； 非揮發性記憶體

並列摘要

本研究成功開發氧化鋅基電阻式記憶體之製程與元件特性，分別開發出具有單極性與雙極性電阻轉換特性之製程，均具有良好的操作特性與非揮發記憶特性。我們針對雙極性電阻轉換特性進一步探討，由電阻值對電極面積相關性以及對量測溫度相依性，推測其工作機制為局部導電的燈絲理論。我們亦探討電極材料對於氧化鋅基電阻式記憶體之影響性，研究發現選用具儲存氧離子或易氧化之電極材料是一大重要關鍵，其中以鉻電極具有最佳操作穩定性。
本研究亦開發二氧化鈦基電阻式記憶體之製程與元件特性，利用磁控濺鍍法鍍膜氣氛調控二氧化鈦薄膜之結晶結構，探討其對於電阻轉換特性之影響性。結果發現高電阻值受薄膜結晶結構影響，但低電阻值卻保持定值不變，推測工作機制為燈絲理論。此外，我們在二氧化鈦薄膜中加入白金奈米粒子，以此創新的奈米複合結構開發出更優異之電阻轉換特性。研究結果發現鑲埋白金奈米粒子之元件，其具有更穩定的操作特性，對於元件的耐久性與記憶特性大為提升。
本研究亦利用水熱法生成垂直陣列之奈米線，成功開發氧化鋅奈米線電阻式記憶體。 研究發現由於導電燈絲容易沿著奈米線表面垂直生成，故此奈米結構具有更佳電阻轉換穩定性。

並列關鍵字

resistance random access memory (RRAM) ； oxide thin film ； nonvolatile memory

參考文獻

1. C. Muller, IEEE Computer Society Annual Symposium on VLSI, 2008, 3.

2. C. H. Chen, Master thesis, National Tsing Hua University, 2009.

3. A. Sawa, Materials Today, 11, 28 (2008).

4. F. Chen, New Non-volatile Memory Workshop, 2008.

8. W. Y. Chang, J. H. Liao, Y. S. Lo, and T. B. Wu, Appl. Phys. Lett. 94, 172107 (2009).