藉由電極調整及摻雜提升氧化鋅透明性電阻式記憶體電阻轉態特性

Abstract

對於未來在非揮發性記憶體範疇中，電阻式記憶體被認為是最為可靠的選項。除此之外，穿戴式應用產品對於透明性電子元件的需求也是必須的。在此論文中，我們詳述了非揮發性記憶體中，以氧化鋅為主體的透明性電阻式記憶體的發展。然而在記憶體轉態可靠度上(記憶體高低阻態倍率、均勻度和轉態次數)，是對於氧化鋅為主體的透明性電阻式記憶體最主要的挑戰。在此篇論文中，使用曾經被發展和提出的新穎方法來解決前述的問題。首先是藉由對於上電極缺陷的調整，以提升高低阻態倍率。存在於上電極中的氧空缺需要被考慮，以達到所需的高低阻態倍率，在上電極中極度多數的空缺，可能會抽取來自轉態層的氧原子，因此導致高低阻態倍率的下降，可藉由文中的方法增強高低阻態倍率7倍。第二，利用操控首次形成燈絲的過程來加以限制燈絲。不同種的氧化鋅薄膜也被製作為轉態層，以驗證文中的方法。而文中所推崇的首次形成燈絲的方法，較傳統方法更為優異，可以達到高度穩定的轉態，且高低阻態的倍率可以達到100倍的數值。第三，藉由調整空缺和微結構，可以增強轉態可靠度上的性能。在轉態特性上，空缺的種類和結構方向扮演相當重要的腳色，而利用在轉態層中不同濃度的鈷參雜以達成前述的調整，透過使用文中的各個參數可以達到高穩定的轉態性能。另外，透過嚴格的電性及材料分析以說明文中所提出方法的現象。

Resistive memory is believed to be the most promising technology for the future nonvolatile memory. In addition, the need of transparent electronic devices is compulsory for wearable gadget application. In this thesis, we report the development of ZnO-based transparent resistive devices for nonvolatile memory application. A decent endurance performance (memory window, uniformity and switching cycles) is one of the major challenges in ZnO-based resistive random access memory (RRAM). This thesis presents novel methods that have been developed and proposed to overcome the challenges. Firstly, the approach to enhance memory window by top electrode defect modulation is studied. Oxygen vacancies defects in the top electrode need to be considered to achieve suitable memory window. An excessive amount of the defects may withdraw oxygens from the resistive layer, thus, decreasing memory window. The enhancement of memory window of 7 (seven) times can be achieved by employing this manner. Secondly, filament confinement through controlled electroforming process is investigated. Less-favorable ZnO film is intentionally fabricated as the resistive layer in order to confirm the method. Our proposed electroformed setup is found superior as compared to the traditional one. Highly stable switching with a high memory window of two order of magnitude can be achieved by employing this procedure. Thirdly, an enhanced endurance performance by defects and microstructures modulation is explored. Both defects species and structural orientation play a significant role in the switching characteristics. Various concentration of Co dopant in the resistive layer is employed to observe and control the modulation. High endurance performance can be achieved by adjusting these factors. Furthermore, electrical and materials analysis have been carefully conducted to elucidate the phenomena in the proposed methods.