Metrology and Physical Mechanisms in New Generation Ionic Devices (eBook)

Umberto Celano received a M.Sc. degree in Nanoelectronics from the University of Rome ``Sapienza'', Italy and a Ph.D. degree in Physics from the KU Leuven, Belgium in 2011 and 2015 respectively. Currently, he is a researcher in the material and component analysis group of imec in Belgium. Umberto's research interests include nanometer scale issues in materials, emerging nanoelectronics and physical characterization. His goal is to explore methods and novel metrology techniques that enable the understanding of the physics in nanomaterials and nanoelectronics devices.

Supervisor’s Foreword 8
Abstract 10
Acknowledgments 11
Contents 14
Abbreviations 17
Symbols 19
1 Introduction 21
1.1 Nonvolatile Memory for Sub-15 nm Node 22
1.2 New Applications, New Needs and Old Problems 24
1.3 Resistive Switching: Bits Made of Filaments 25
1.4 Objectives and Outline of the Dissertation 26
References 28
2 Filamentary-Based Resistive Switching 30
2.1 Basic Operating Principles 30
2.2 Conductive Bridge Resistive Memory 33
2.2.1 The Electrochemistry in CBRAM 34
2.2.2 The Rate-Limiting Process 36
2.2.3 CBRAM Device Operation 37
2.2.4 Device Optimization 40
2.3 Oxide-Based Valence Change Memory 43
2.3.1 VCM Device Operation 44
2.3.2 Switching Mechanism and Electron Transport in VCM 46
2.3.3 The Filament as a Quantum Point Contact 47
2.3.4 VCM Device Optimization 49
2.4 Review of Conductive Filaments Observation 50
2.4.1 Filament Observation in CBRAM 51
2.4.2 Filament Observation in VCM 55
2.5 Summary of the Chapter 58
References 58
3 Nanoscaled Electrical Characterization 65
3.1 Overview 65
3.2 Conductive Atomic Force Microscopy 68
3.2.1 Conductive Tips 70
3.2.2 Contact Forces 72
3.2.3 Artifacts in C-AFM 74
3.2.4 Electrical Lateral Resolution 78
3.2.5 Effective Emission Area Evaluation 79
3.2.6 Extending C-AFM Current Range 84
3.3 Peak Force: Intermittent Contact Mode 85
3.3.1 Peak Force TUNA Case Studies 88
3.3.2 Electrical Tip-Contact: Dragged Versus Intermittent 91
3.4 Three-Dimensional SPM Tomography 93
3.4.1 Overview of 3D Tomography 94
3.4.2 SPM Tomography 96
3.5 Summary of the Chapter 100
References 101
4 Conductive Filaments: Formation, Observation and Manipulation 105
4.1 Tip-Induced Filament Formation and Observation 105
4.1.1 Areal Switching 106
4.1.2 Ultra-Scaled Device Sizes with C-AFM 107
4.1.3 The Role of the Tip 109
4.1.4 Resistive Switching C-AFM Versus Devices 111
4.1.5 Filament Observation 114
4.2 C-AFM Probing the Reset State 118
4.2.1 Gap Formation in Cu Filaments 118
4.2.2 Low-Defects Assisted Quantum-Point-Contact 121
4.3 Device De-Process: Filament Observation 125
4.4 Summary of the Chapter 129
References 129
5 Three-Dimensional Filament Observation 132
5.1 Scalpel SPM for Filament Observation 132
5.2 Tomographic Observation of Cu-Based Filaments 133
5.2.1 CBRAM: Low-Resistive-State Observation 134
5.2.2 CBRAM: High-Resistive-State Observation 136
5.2.3 Cu-Filament Growth Model in Low-Mobility Media 137
5.2.4 Filament Volume Modulation and Multibit Capability 139
5.3 On the Dual Nature of Cu Filament Dissolution 141
5.3.1 A Model for Broken and Nonbroken HRS Filaments 144
5.3.2 A Ruptured Filament Is Not a Conventional Tunnel Junction 146
5.3.3 Hourglass Shaped Cu Filament 147
5.4 Tomographic Filament Observation in VCM 149
5.4.1 Filament Size Modulation in VCM 153
5.5 Summary of the Chapter 156
References 157
6 Reliability Threats in CBRAM 160
6.1 Reliability Threats of Cu Filaments 160
6.2 Filament Multiplicity as Source of State Instability 161
6.3 Stuck in LRS: A Cu Filament Degeneracy 164
6.4 Summary of the Chapter 166
References 167
7 Conclusions and Outlook 168
7.1 Filaments Formation and Dissolution 168
7.1.1 Challenges with Tip-Induced Analysis 170
7.2 Filaments 3D Observation 171
7.2.1 Challenges in the Three-Dimensional Observation 173
7.3 Outlook 174
7.3.1 Improving Scalpel SPM 176
Appendix A Cellulose Nanopaper Memory 178
Curriculum Vitae 185