在本研究中，將焦點著重於以氧化鉿薄膜之電阻式記憶體特元件的轉態物理機制。由於氧化鉿已經廣泛應用在CMOS 的製程中，所以它在CMOS 製程上有相當好的相容性。因為氧化鉿當成電阻式記憶體元件時的轉態特性很穩定，所以我們可以進一步地去研究電阻式記憶體在轉態過程中的變化。所以我們藉由不同的限制電流和reset 停止電壓來達到Multi-states，並由不同阻態的電流-電壓曲線的載子傳導機制探討，可以得知電阻式記憶體在set 與reset 過程中的轉變。大部分的電阻式記憶體都需要經過一個forming 的行為才會使元件具有電阻切換的特
性，接下來我們結合示波器去設計出一個等效電路來觀測forming 的行為。此外我們利用脈衝產生器給一個極短時間的脈衝來對元件進行forming。在不同的forming 行為中我們可以發現到一個overshoot 的現象，並藉由電荷的計算可以知道forming 過程中通過的電荷量決定電阻式記憶體的傳導路徑。
我們針對脈衝forming 的元件做研究，首先對set 與reset 的電阻轉態機制中可以知道電流傳導的路徑是不連續的，並藉此不對稱的電壓-電流曲線的傳導機制探討和模擬電場的搭配下可以證明脈衝forming 的元件的載子傳輸是藉由一個不連續的傳導路徑。

This study is focuses on the resistance switching physical mechanism in hafnium oxide (HfO2) of resistive random access memory (RRAM). HfO2 was taken as the resistance switching layer because HfO2 is extremely compatible with the prevalent complementary metal oxide semiconductor (CMOS) process. The detail physical mechanism is studied by the stable RRAM device (Ti/HfO2/TiN), which is offered from Industrial Technology Research Institute (ITRI). In this study, the resistance switching property of two different forming conductions are compared, including DC sweeping forming and AC pulse forming. In general, forming is a pivotal process in resistance
random access memory (RRAM) to activate the resistance switching behavior. However, over forming would lead to device damage. The overshoot current has been considered as a degradation reason during the forming process. The circuit design is used to obtain the overshoot effect of DC sweeping forming by oscilloscope and semiconductor parameter analyzer system. The quantity of charge through the switching layer has been proven as the key element in the formation of the conduction path. Ultra-fast pulse
forming can form a discontinuous conduction path to reduce the operation power.

Acknowledgement………………………………………….i
Abstract (Chinese)…………………………………............ii
Abstract (English)................................................................iii
Contents……………………………………………………iv
Figure captions……….......................................................vii
Table captions……............................................................xiii

Chapter1 Introduction
1-1.The evolution of memory.............................................1
1-2.Motivation........................................................................2
Chapter2 Literature
2-1.Introduction of memory................................................4
2-1-1.FeRAM (Ferroelectric RAM)....................................6
2-1-2.MRAM (Magnetic RAM)............................................7
2-1-3.PCRAM (Phase Change RAM)..............................8
2-1-4.RRAM (Resistance RAM).....................................10
2-2.The materials of Resistance RAM...........................11
2-2-1.Perovskite...............................................................11
2-2-1-1.PrCaMnO3 (PCMO).........................................12
2-2-1-2.SrTiO3 and SrZrO3..........................................13
2-2-2.Transition metal oxides........................................14
2-2-3.Organic materials..................................................16
2-3.The switching mechanism of Resistance RAM....17
2-3-1.Filamentary model................................................18
2-3-1-1.Joule heating effect.........................................18
2-3-1-2.Redox reaction with cation migration...........20
2-3-1-3.Redox reaction with anion migration...........21
2-3-2.Charge trap in small domain..............................22
2-3-3.Modified Schottky-like barrier model..................23
2-4.The mechanism of current conduction...................23
2-4-1.Ohmic conduction.................................................24
2-4-2.Schottky emission.................................................25
2-4-3.Poole-Frenkel emission......................................26
2-4-4.Tunneling conduction...........................................27
2-4-5.Space charge limited current..............................27
2-4-6.Hopping conduction..............................................28
Chapter3 Study of the Resistance Switching Physical Mechanism
3-1.Results for Ti/HfO2/TiN device.................................43
3-1-1.Experimental procedures....................................43
3-1-2.Basic characteristic of HfO2................................44
3-2.Multi-state characteristic............................................46
3-3.Analyses of carrier transport mechanism..............46
3-3-1.Current-Voltage curve for fitting...........................46
3-3-2.Current-Voltage curve for fitting in Multi-state...47
3-3-3.Discussion for carrier transport mechanism...49
3-4.Extraction of relevant parameters............................50
3-4-1.Schottky barrier height and switch thickness..50
3-4-2.Barrier height and Hopping distance................51
3-5.Extraction parameters and discussion..................52
3-5-1.Set process............................................................52
3-5-2.Reset process.......................................................54
Chapter4 The Overshoot of Forming Process
4-1.Study of overshoot......................................................73
4-1-1.Experimental procedures....................................73
4-1-2.Compare the different forming process...........74
4-2.Compared of the different forming device.............75
4-2-1.Calculation quantity of electricity........................75
4-2-2.Current-voltage curve for fitting...........................76
4-2-3.Variable-temperature measurements in LRS.76
4-3.Discussion...................................................................77
Chapter5 Study of Pulse Forming Device
5-1.Basic characteristic of pulse forming device.........87
5-1-1.The current-voltage curve with DC voltage
sweeping...........................................................................87
5-1-2.Multi-set states characteristic.............................88
5-2.Analyses of set process............................................88
5-2-1.Current-voltage curve for fitting in Multi-set
states..................................................................................88
5-3.Analyses of reset process.........................................91
5-3-1.Stage by stage of resistance state.....................91
5-3-2.Current-voltage curve for fitting...........................91
5-3-3.Schottky barrier height and switch thickness...92
5-4.Study of the PN bias asymmetric phenomenon...94
5-4-1.Basic characteristic...............................................94
5-4-2.Current-voltage curve for fitting...........................94
5-4-3.Hopping barrier high and Hopping distance in
LRS.....................................................................................95
5-4-4.Schottky barrier high and switch thickness in
HRS....................................................................................95
5-5.Discussion with energy band...................................97
5-5-1.Barrier lowering with electric field......................97
5-5-2.Hopping barrier lowering and hopping
distance.............................................................................97
5-5-3.Schottky barrier lowering.....................................98
5-5-4.Schottky emission become Hopping conduction
............................................................................................99
5-6.Discussion................................................................100
Chapter6 Conclusion.....................................................118
References.......................................................................121

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