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Title: Electrical Characterization of Functional Oxides for Resistive RAM Memory Applications (Elektrische karakterisatie van functionele oxiden voor resistieve RAM applicaties)
Other Titles: Electrical Characterization of Functional Oxides for Resistive RAM Memory Applications
Authors: Chen, Yangyin; S0181579
Issue Date: 18-Jun-2013
Abstract: This Ph.D study mainly focuses on transition metal oxide based filamentary resistive random access memory (RRAM) technology, as to screen out a stable switching material stack, assess its scalability and characterize its reliability at scaled dimension. A reliable switching system HfO2 / Hf in scaled dimension was successfully demonstrated, and its technology feasibility of NAND replacement or other types of application was evaluated. Detailed endurance and retention reliability degradation study was also performed, gaining more in-depth understanding for further device improvement.
Table of Contents: Table of Contents



1 General Introduction 1
1.1 Memory device history 1
1.1.1 History of information storage 1
1.1.2 Digital storage era 5
1.1.3 HDD vs. NAND-flash SSD 8
1.2 Solid state Semiconductor memory technology: floating gate, NAND and NOR .11
1.2.1 Flash memory history 11
1.2.2 Scaling limit of NAND flash 15
1.3 Resistive switching memory 22
1.3.1 History of resistive switching memory 22
1.3.2 RRAM category 23
1.3.3 Filamentary RRAM and its working principles 26
1.4 Thesis contents overview 28
1.4.1 Thesis objective 28
1.4.2 Thesis outline 29

2 Material and Device Optimization 41
2.1 Material and device optimization guideline 42
2.1.1 Selection of the oxide materials 42
2.1.2 Selection of electrode materials 46
2.2 Active electrode system 47
2.2.1 Device processing and experimental details 47
2.2.2 Pt electrode as active electrode 48
2.2.3 Summary 53
2.3 Alternative electrode system beyond Pt 54
2.3.1 Device processing and experimental details 54
2.3.2 Switching behavior of Ni-containing BE / HfO2 / TiN TE stack 55
2.3.3 Evidence of Ni diffusion in as-deposited Ni-containing BE / HfO2 / TiN stacks 56
2.3.4 Ab-initio simulation for Ni-containing BE / HfO2 / TiN stacks 58
2.3.5 Switching models for Ni-containing BE / HfO2 / TiN stacks 59
2.3.6 Reliability aspects of Ni-containing electrodes / HfO2 / TiN stacks 61
2.4 Oxygen vacancy drift based system 63
2.4.1 Switching scenario of Vox based system 64
2.4.2 Hydrogen reduction of HfO2 67
2.4.2.1 Device processing and experimental details 67
2.4.2.2 Switching properties and reliability 69
2.4.2.3 Physics analysis of indentifying hydrogen in the HfO2 70
2.4.3 HfO2 with Hf metal cap as oxygen scavenging layer 73
2.4.3.1 Device processing and experimental details 73
2.4.3.2 Electrical switching properties 74
2.4.3.3 First-principle simulation and XPS spectrum 75
2.5 Conclusion 79

3 Endurance Reliability Analysis 91
3.1 Device processing and experiment details
93
3.2 Balancing the SET / RESET pulse conditions 95
3.2.1 Impact of the SET / RESET pulse tuning on endurance failure 96
3.2.2 Impact of the SET / RESET pulse width on endurance failure 98
3.2.3 1010 cycles by balancing the SET / RESET pulse conditions 101
3.3 Recovery of the LRS / HRS endurance failure 102
3.4 Endurance degradation analysis of the unbalanced SET / RESET operations 103
3.5 Intrinsic endurance degradation under balanced SET / RESET pulse conditions 105
3.5.1 Brief description of the hour-glass model 106
3.5.2 LRS dependence of endurance failure lifetime 109
3.5.3 Pulse Period tcycle dependence of endurance failure 110
3.6 Endurance failure analysis through monitoring Vtrans 112
3.6.1 Vtrans shift during endurance cycling 112
3.6.2 Vtrans shift during baking test 113
3.6.3 The usage of the Vtrans shift as a thermometer 114
3.7 Local atomic relaxation of HfO2 117
3.8 Possible techniques to improve the endurance 118
3.9 Summary 121

4 Retention Reliability Analysis 125
4.1 Retention failure behavior and the physics behind it 127
4.1.1 LRS dependence of the retention degradation 128
4.1.2 LRS retention degradation: Vox out diffusion 130
4.2 Monte-Carlo simulation of the LRS retention degradation 132
4.2.1 Monte-Carlo simulation set-up environment 133
4.2.2 Experiment and simulation corroboration 134
4.3 Process and device tuning to improve the retention 136
4.3.1 Tuning of passivation schemes to minimize the sidewall oxidation 136
4.3.2 LRS Tuning of the thermal budget to improve the LRS retention 139
4.4 Post-cycling retention 142
4.5 Summary 146

5 Impact of Cap Layer Materials on Endurance / Retention of HfO2 based RRAM 151
5.1 Thermodynamics of oxygen scavenging by metal caps from HfO2 152
5.2 Large area device results 154
5.2.1 Experimental details 154
5.2.2 Results and Discussions 155
5.3 Pulse endurance comparison on 1T1R HfO2 / metal cap cells 161
5.4 LRS retention comparison on 1T1R HfO2 / metal cap cells 163
5.5 Different Vox profile and filament constriction geometry 166
5.5.1 Different Vox profile 166
5.5.2 Different filament constriction geometry 167
5.5.3 Correlation of the filament constriction with endurance / retention performance 169
5.6 Summary 172

6 Summary and Outlook 175
6.1 Summary of Ph.D 175
6.1.1 Major scientific contributions of this Ph.D 175
6.1.2 Wafer turns during this Ph.D 177
6.1.3 RRAM research worldwide (2004’ ~ 2012’) 178
6.2 Outlook of RRAM R&D activity 181
6.3 RRAM: time to market, who, how and when? 183

Appendix 189
Appendix.I Summary of Physical Analysis Techniques to Study the RRAM Devices 189
ISBN: 978-94-6018-662-2
Publication status: published
KU Leuven publication type: TH
Appears in Collections:ESAT - MICAS, Microelectronics and Sensors
Electrical Engineering - miscellaneous

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