電阻式隨機存取記憶體(RRAM) 已經引起相當大的關注於下一代非揮發性記憶體的應用，由於其結構簡單可應用於高密度積體電路，也可以兼容於傳統的互補式金屬氧化物半導體(CMOS)，並且具有低操作功率、開關轉換速度快及長時間數據記憶，因此於過去十年RRAM已成為非揮發性記憶體中最有潛力的候選者之一 。然而，電阻轉換之確切機制仍然有待定論，因此於商業化使用前，RRAM必須在更加優化。
本實驗研究以多元氧化物(MCO) (ZrCuAlNi)Ox, Zr1-yCuyO2-3y/2 (ZCO), Zr1-rNirO2-r (ZNO) 及 非晶 ZrCuOk (a-ZCO) 薄膜為主之記憶體元件的電阻轉換特性及機制。厚度約15奈米的多元氧化物活性層具有非晶結構，是以濺鍍方式沉積而並無基材加熱或經退火處理。其元件展現無電致成形(forming-free)的單極電阻轉換性質(ROFF/RON~22)並具有低操作電壓(<1.7V) 、資料保存時間長、好的重複讀寫能力及高電阻值比。其電阻轉換性質是由於氧空缺存在於非晶薄膜中形成導通細絲傳導所造成。
為了研究多元金屬氧化物的成分對於電阻轉換及其機制的影響，我們將靶材成分由原本四元減少為二元金屬。因此我們接著研究欠氧的鋯銅氧化物(ZCO)薄膜作為RRAM的活化層，結果發現初鍍膜及快速退火後的ZCO薄膜皆呈現單極電阻轉換，並具有長時間資料記憶、無電致成形(forming-free)、低操作電壓(<1.9V)及薄的厚度(約11奈米)。高真空快速退火處理至150°C有助於改善薄膜的電阻轉換次數(自286次提升到6,405次)及電阻比(自13提升到25)，其退火後元件的電阻轉換特性改善是由於薄膜中具有適量及較均勻的氧空缺及較佳的薄膜品質，此外我們利用導電原子力顯微鏡 (CAFM) 觀察元件於高電阻態及低電阻態的電流影像，其電流密度於高電阻態及低電阻態分別為 ~3.0x102 nA/μm2 及 ~3.3x10-2 nA/μm2，因此我們推斷元件的電阻轉換機制歸因於氧空缺形成導電細絲的成形與斷裂。
另一方面，我們也研究鋯鎳氧化物(ZNO)薄膜作為RRAM元件的介電層，包括Pt/Zr1-rNirO2-r/Pt 記憶體元件的電阻轉換行為及機制。Zr1-rNirO2-r 薄膜是由濺鍍方式沉積，厚度僅約7奈米，且並無基材加熱或經退火處理，此元件呈現無電致成形(forming-free)的單極電阻轉換性質，包括低操作電壓(<1.9V)、長時間資料記憶、較佳的重複讀寫能力及大於兩個數量級的電阻比，研究分析顯示元件的電阻轉換機制是由於氧空缺形成導電細絲的成形與斷裂。另一方面，利用氧化物靶材濺鍍 a-ZCO 薄膜，並與由二元金屬靶材所鍍出來的 ZCO 薄膜進行比較，結果顯示，以 a-ZCO 為主的元件呈現無電致成形的單極性轉換性質並具有較低的操作電壓 (<1.8V) 、長時間資料保存及好的重複讀寫能力。
本論文研究新興 ZrOx 基隨機存取式記憶體元件的電阻轉換性質及電阻轉換參數，其具有無電致成形、低功率、較長時間的資料保存及較薄的厚度，因此 ZrOx 基薄膜於未來低功率應用具有潛力，並實現於奈米級微電子元件之應用

Resistive switching random access memory (RRAM) has attracted great interest for the application in next generation nonvolatile memory. RRAM has gained significant interest in the past decade as one of the most promising candidates as a nonvolatile memory device due to its potential for high density integration, low operating power, fast switching speed, long data retention time, simple structure and compatibility with conventional CMOS process. However, the resistive switching (RS) mechanism is still under debate, and the devices have to be optimized before they can be used commercially.
In this work, RS characteristics and mechanism of multicomponent oxide (MCO) (ZrCuAlNi)Ox, Zr1-yCuyO2-3y/2 (ZCO), Zr1-rNirO2-r (ZNO) and amorphous ZrCuOk (a-ZCO) thin film-based memory devices are studied. MCO-based on an amorphous active layer with a thin thickness of ~15nm is sputter deposited without substrate heating or post-annealing. The device shows forming-free unipolar RS properties of low operation voltage (<1.7V), long retention time, good endurance and resistance ratio of 22. The RS property is considered to be dominated by the filamentary conduction due to the presence of oxygen vacancies in the grain boundary-free structure.
To further investigate the dominant substances for the RS behavior and mechanism in the MCO film, we reduce the composition of the target to binary metals. Then, the thin oxygen deficient ZCO films are investigated for nonvolatile memory applications. Both the as-deposited ZCO and rapid thermal annealed (RTA) A-ZCO samples show unipolar resistive switching, good retention time, forming free, low voltage (<1.9V) and thin thickness (~11 nm). The high vacuum RTA treatment at 150°C for 30 minutes is beneficial to improve the switching cycles from 286 to ~6.4x103 and the resistance ratio from 13 to 25. The improved characteristics of the RTA`ed-samples are achieved due to appropriate defect concentration and film quality improvement. The current images in the low resistance state (LRS) and high resistance state (HRS) of the device observed using CAFM. The current density of LRS and HRS are ~3.0x102 nA/μm2 and ~3.3x10-2 nA/μm2, respectively. The RS mechanism of the device is attributed to the formation and rupture of conduction filaments (CFs) based on defects (oxygen vacancies).
Also, this work includes the fabrication and characterization of ZNO thin film-based RRAM devices. The RS behaviours and mechanism of Pt/Zr1-rNirO2-r/Pt memory device are studied. Zr1-rNirO2-r active layer with a thin thickness of ~7nm is sputter deposited without substrate heating or post-annealing. The device shows forming-free unipolar RS properties of low operation voltage (<1.9V), long retention time, good endurance and more than two-order resistance ratio. The analysis shows that the RS property initiates from the formation and rupture of CFs due to the presence of defects (oxygen vacancies) in the oxide films. In addition, a-ZCO films were prepared from oxide target to compare the result with ZCO samples which were prepared from binary metal target. The a-ZCO-based devices show forming-free unipolar RS properties of low operation voltage (<1.8V), good retention time and endurance.
Therefore, RS properties and switching parameters of emerging ZrOx-based RRAM devices for forming-free, low power, longer data retention and thinner thickness nonvolatile memory devices are studied. A potential application of ZrOx-based thin films in future low power, nanoscale microelectronic device applications is realized from this study.

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