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博碩士論文 etd-0725106-141008 詳細資訊
Title page for etd-0725106-141008
論文名稱
Title
鎳奈米點非揮發性記憶體電性與物理機制之研究
Study on the Electrical Analysis and Physical Mechanism of Nonvolatile Memory with Ni Nanodots
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
75
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2006-07-06
繳交日期
Date of Submission
2006-07-25
關鍵字
Keywords
記憶體、鎳奈米點
Nonvolatile Memory, Ni Nanodots
統計
Statistics
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中文摘要
傳統的非揮發性記憶體是利用複晶矽浮停閘(floating gate)做為載子儲存的單元,當浮停閘儲存由通道注入的電子之後,元件的起始電壓就會發生改變,利用起始電壓的差異作為記憶體0和1邏輯的定義。然而,由於浮停閘是連續的一層半導體薄膜,在反覆的操作下,一旦穿隧氧化層(tunnel oxide)出現漏電路徑,儲存的電荷全部流失,記憶體就會失效,因此穿隧氧化層的厚度無法縮減下來,操作電壓無法降低,速度也無法增快。一般認為當元件通道長度達到65 nm時,便是此種結構的極限。本研究利用半導體或金屬奈米點作為電荷儲存的單元,可以減少穿隧氧化層的厚度,而不損失可靠性,進而降低操作電壓,並使元件縮小密度提高,操作速度增快。 利用半導體或金屬奈米點作為電荷儲存的單元。在元件的反覆操作下,即使穿隧氧化層產生缺陷或漏電路徑,所損失掉的儲存電子,僅是單一奈米點的電子漏失,對整體元件特性的影響並不明顯。因此,穿隧氧化層的厚度得以縮減,使得操作速度提升,元件積集度增加,元件可操作的次數(endurance)以及保存時間(retention)也同時得到改善。
當電子儲存在奈米點時,由於庫倫阻絕(Coulomb blockade)效應,儲存的電子會限制後續電子的注入。奈米點的庫倫阻絕效應使得記憶體元件的儲存及操作更加的穩健。當閘極偏壓使通道產生反轉層後,通道的電子藉由直接穿隧效應或是F-N穿隧效應通過穿隧氧化層,而讓奈米點捕獲,是為寫入動作。當閘極偏壓反向時,儲存的電子便經由穿隧氧化層回到通道,是為抹除動作。藉由電容-電壓(C-V)量測,當電子注入奈米點之後,元件之起始電壓會發生偏移,此偏移的量即定義為記憶體元件的記憶窗。
近幾年來,具有奈米點儲存單元的非揮發性記憶體元件被廣泛的提出來克服傳統浮動閘極記憶體在操作上及可靠度上的問題。良好的記憶體元件需要具備好的元件耐力,保存時間長及操作電壓小等特性。在眾多奈米點記憶體元件中,金屬奈米點的記憶體受到廣泛的研究而有機會成為新一代記憶體元件結構。金屬點的特色主要有高狀態密度、強通道耦合能力、可調變金屬功函數以及不易受載子侷限效應所引起的能階擾動。在元件設計上金屬奈米點不但可減少操作電壓、增加抹除寫入速度與電子保存時間,最重要的是我們可以控制奈米點尺寸以及低溫製作。此項優點能應用於薄膜電晶體液晶顯示器上,如面板上製作驅動IC與邏輯IC可以增加面板多變性,開關電晶體旁增加影像儲存記憶體來節省電源損耗以增加可攜帶性。
本論文主要以高功函數金屬作為記憶體儲存元件為研究,利用高溫氧化、低溫氧氣退火條件形成奈米點,並用材料分析與電性分析來研究金屬奈米點的電荷儲存效應。
Abstract
In a conventional nonvolatile memory, charge is stored in a polysilicon floating gate (FG) surrounded by dielectrics. The scaling limitation stems from the requirement of very thin tunnel oxide layer. For FG, once the tunnel oxide develops a leaky path under repeated write/erase operation, all the stored charge will be lost.Therefore, the thickness of the tunnel oxide can not be scaled down to about 7 nm.
To alleviate the scaling limitation of the conventional FG device while
preserving the fundamental operating principle of the memory, we have studied the distributed charge storage approach such as the nanocrystal nonvolatile memory. Each nanodot will typically store only a handful of electrons; collectively the charges stored in these dots control the channel conductivity of the memory device. Nanocrystal charge storage offers several advantages, the main one being the potential to use thinner tunnel oxide without sacrificing non-volatility. This is a quite attractive proposition since reducing the tunnel oxide thickness is a key to lowering operating voltages and/or increasing operating speeds. The improved scalability results not only from the distributed nature of the charge storage, which makes the storage more robust and fault-tolerant, but also from the beneficial effects of Coulomb blockade. A local leaky path will not cause a fatal loss of information for the nanocrystal non-volatile memory device. Also, the nanocrystal memory device can maintain good
retention characteristics and lower the power consumption.
In recent years, nonvolatile memory with nanocrystals cell have widely applied to overcome the issue of operation and reliability for conventional floating gate memory. The excellent electrical characteristics of memory device need good endurance, long retention time and small operation voltage. Among numerous memory devices with nanocrystals, the memory device with metal nanocrystals was widely researched. It will be a new candidate for flash memory. The advantages of metal nanocrystals has have higher density of states around Fermi level, stronger coupling with conduction channel, wide range of available work functions and smaller energy perturbation due to carrier confinement. So metal nanocrystals can reduce operate voltage, and increase write/erase speed and endurance. Most important of all, we can control the sizes of nanocrystals dot and manufacture at low temperature。This advantage can apply to thin film transistor liquid crystal display; it fabricates driving IC and logical IC on panel for diverseness and adds memory beside switch TFT as image storage to reduce power consumption for portability.
In this thesis, we will discuss metal nanocrystals as memory storage medium. And we can use high temperature oxidation, low temperature annealing with oxygen to form nanocrystals. Most importantly, we analyze the effect of electron storage at metal nanocrystals by means of material and electrical analysis.
目次 Table of Contents
Contents
Chapter 1 Introduction………………………………………………………………...1
1.1 General background…………………………………………………….1
1.2 Motivation………………………………………………………………4
1.3 Organization…………………………………………………………….6
1.4 Reference………………………………………………………………..7

Chapter 2 The Electrical Characteristics of Nonvolatile Memory Devices and Metal Nanocrystals Memory
2.1 Programming/Erasing Mechanism……………………………………...9
2.1.1 Hot electron injection……………………………………………10
2.1.2 Lucky electron model……………………………………………11
2.2 Tunneling Injection……………………………………………………12
2.2.1 Direct Tunneling…………………………………………………13
2.2.2 Fowler-Nordheim Tunneling…………………………………….15
2.2.3 Modified Fowler-Nordheim Tunneling………………………….16
2.2.4 TrapAssistant Tunneling…………………………………………16
2.2.5 Band to Band Tunneling Injection……………...……………….17
2.3 Nonvolatile Memory Reliability………………………………………18
2.3.1 Retention………………………………………………………...19
2.3.2 Endurance………………………………………………………..20
2.4 Metal Nanocrystal Memory……………………………………………23
2.4.1 Work Function Engineering……………………………………..25
2.4.2 Dielectric Engineering…………………………………………...29
2.5 Conclusion……………………………………………………………..31
2.6 Reference………………………………………………………………33

Chapter 3 A Novel Approach of Fabricating Nickel and Nickel-Silicide Nanocrystals for Nonvolatile Memory Application
3.1 Introduction……………………………………………………………38
3.2 Experimental Procedures………………………………………………39
3.2.1 Sample 1…………………………………………………………39
3.2.2 Sample 2&3……………………………………………………...42
3.3 Conclusion……………………………………………………………..46

Chapter 4 The Electrical Analysis of Metal Nanocrystals Memory
4.1 The Write and Erase Efficiency………………………………………..48
4.1.1 Sample 1…………………………………………………………48
4.1.2 Sample 2.…………………………………………………….. …50
4.1.3 Sample 3…………………………………………………………53
4.2 Retention………………………………………………………………56
4.2.1 A proposal technique of measuring accurate retention…………..57
4.2.2 The retention of Ni nanocrystals memory……………………….58
4.3Endurance………………………………………………………………63
4.4Conclusion…………………………………………………….………..65
4.5Reference……………………………………………………………….66
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