Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio

산화물/질화물 복합구조를 이용한 유연한 전자 및 광전소자 응용

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리학과, 2020. 8. 이규철.물리적으로 강하고 유연한 그래핀과 같은 2차원 소재위에 성장된 무기물 나노소재로 구성된 복합차원 나노소재는 유연한 대면적 전자 및 광전소자로의 응용에 적합한 형태의 소재 구조이며, 실제로 이를 기반으로 한 유연한 수직형 전계효과 트랜지스터 및 발광다이오드 등을 포함한 많은 소자들이 개발되고 있다. 하지만, 처리된 정보를 저장하고 이를 사용자에게 전달하는 기능을 수행하기 위해선 보다 다양한 소자들이 개발되어야 할 필요가 있다. 본 학위논문은 이러한 수요를 충족시키기 위해, 복합차원 나노소재 기반 유연한 대면적 차세대 비휘발성 메모리 및 유연한 대면적 다파장 발광 다이오드의 개발에 대하여 다루고 있다. 복합차원 나노소재를 기반으로 차세대 비휘발성 메모리를 구현하기 위해 니켈 산화물 및 질화갈륨 이종구조로 구성된 마이크로디스크 형태의 소재를 그래핀 위에 성장하고, 본 소재의 상부 및 하부에 전극을 증착하여 전극/산화물/전극으로 구성된 형태의 산화물 기반 저항변화 메모리를 제조할 수 있었다. 마이크로디스크 형태의 소재의 사이가 떨어져있기 때문에 본 소자를 유연한 형태에서 구현하거나 1,000 회 이상의 구부림 뒤 소자의 특성을 파악할 때 소자 특성의 큰 변화 없이 정보가 안정적으로 저장되는 특성을 확인할 수 있었다. 뿐만 아니라, 니켈 산화물 기반 저항변화메모리를 동작할 때, 산화물 내부에 전도성이 높은 니켈 산화물이 필라멘트 형태로 구성되는데, 이를 발광다이오드의 나노전극으로 사용하여 저항변화메모리 내부의 필라멘트 역학에 대해서도 연구할 수 있었다. 한편, 저장된 정보를 사용자에게 정확하게 전달하기 위해선 발광다이오드의 한 픽셀 (pixel) 의 크기가 수 마이크로미터 이하로 작아야하고, 빨강, 초록, 파랑색의 빛을 발광할 수 있어야 하는데 이는 현재 이용되고 있는 픽 앤 플레이스 (pick and place) 기술을 이용하여 제조할 때 소자 제조의 효율성 및 재현성에 한계를 보이고 있다. 본 학위논문에서는 이를 극복하기 위한 방법의 하나로, 다양한 색을 발광할 수 있는 발광다이오드를 하나의 그래핀 기판위에 동시에 성장하는 방법을 제시하고 이를 유연한 다파장 발광다이오드로 구현하는 방법에 대해 기술하고 있다. 본 소자를 구현하기 위해 다양한 모양의 질화갈륨 및 산화아연 이종구조를 그래핀 위에 성장하는 방법을 개발하였는데, 산화아연 나노튜브의 간격을 다르게 설정하여 성장하고 이 위에 질화갈륨을 성장하면 질화갈륨의 성장률이 나노튜브의 간격에 따라 다르게 형성되어 다른 모양의 마이크로 발광다이오드가 성장되는 것을 이용하였다. 각기 다른 발광다이오드에 같은 전압을 가해줬을 때 성장률의 차이로 인한 다중 양자 우물 조성의 변화 및 소재 내부의 결함으로 인해 각기 다른 파장의 색이 발광되는 특성을 확인하였고, 유연한 형태에서도 안정적으로 발광특성이 유지되는 것을 확인할 수 있었다.The hybrid dimensional nanostructrures composed of high-quality inorganic nanostructures grown directly on two-dimensional (2D) materials such as graphene offers a novel material system for flexible electronics and optoelectronics. Indeed, the hybrid dimensional nanostructures have been fabricated to flexible electronics/optoelectronics and attracted many attentions with their excellent performances. Despite of the demonstration of flexible devices using the hybrid dimensional nanostructures, there remains a lot of devices that need to be further investigated in order to realize future electronics/optoelectronics such as wearable devices. This thesis presents the hybrid material system composed of oxide/nitrid heterostructures grown on graphene films and their applications on flexible non-volatile memory and flexible multi-color LEDs.Abstract Chapter 1. General Introduction 1 1.1. Motivation: Potentials of hybrid dimensional nanomaterials for flexible electronic/optoelectronic device applications 1 1.2. Thesis objective and approach 3 1.3. Thesis outline 4 Chapter 2. Literature survey 6 2.1. Oxide-based flexible electronics 6 2.1.1. Current status of oxide-based electronics 8 2.1.2. Next generation oxide-based electronics: ReRAM 12 2.1.3. Flexible ReRAM 17 2.1.3.1. ReRAM on plastic substrates 17 2.1.3.2. Transfer of ReRAM layers on flexible substrates 20 2.2. Nitride-based flexible optoelectronics 23 2.2.1. Current status of nitride-based optoelectronics 23 2.2.2. Next generation nitride-based optoelectronics: flexible & high-resolution LED 29 2.3. Hybrid dimensional material systems for flexible electronics and Optoelectronics 34 2.3.1. Growth of oxide & nitride nano-/micro-structures on graphene layers35 2.3.2. Functional devices using hybrid dimensional material Systems 45 2.3.2.1. Electronics 47 2.3.2.2. Optoelectronics 50 Chapter 3. Experimental Techniques 53 3.1. Growth techniques 53 3.1.1. Metalorganic vapor-phase epitaxy system 53 3.1.1.1. Gas delivery system 53 3.1.1.2. Reactor and temperature controller 55 3.1.1.3. Exhaust disposal system and low pressure pumping System 56 3.2. Structural characterization 57 3.2.1. Morphology inspection 57 3.2.2. Crystallographic and microstructural investigations 57 3.2.2.1. Transmission electron microscopy 57 3.3. Optical characterization 58 3.3.1. Photoluminescence & electroluminescence spectroscopy 58 3.4. Electrical characterization 59 3.4.1. Current-Voltage measurement 59 Chapter 4. Flexible ReRAM based on hybrid dimensional material systems 60 4.1. Introduction 60 4 .2. Growth of oxide/nitride hybrid structures on graphene layers 61 4.2.1. ZnO nanowall growth CVD-graphene films 62 4.2.2. Growth of GaN microdisk arrays 62 4.2.3. Growth of resistive switching layers 65 4.4. Fabrication of flexible ReRAM 65 4.5. Resistive switching characteristics 69 4.6. Discussion for the mechanism of resistive switchings using oxide/nitride hybrid structures 78 4.6.1. Fabrication of ReRAM/LED hybrid device 80 4.6.2. Real-time imaging of resistive switching dynamics 85 4.7. Summary 99 Chapter 5. Monolithic integration of morphology controlled GaN microstructures on graphene films for flexible & multi-color LEDs 101 5.1. Introduction 101 5.2. Morphology control of GaN microstructures on graphene films 103 5.2.1. Growth parameter: spacing & time 103 5.2.2. Growth behavior analysis 109 5.3. Fabrication of LEDs on graphene films 115 5.4. EL and electrical characteristics 118 5.5. High temperature operations of flexible LEDs 125 5.6. Summary 134 Chapter 6. Conclusion and Outlook 136 6.1. Conclusion 136 6.2. Future works and outlook 141 References 143 Abstract (Korean) 151Docto

Delay dynamics of neuromorphic optoelectronic nanoscale resonators: Perspectives and applications

With the recent exponential growth of applications using artificial intelligence (AI), the development of efficient and ultrafast brain-like (neuromorphic) systems is crucial for future information and communication technologies. While the implementation of AI systems using computer algorithms of neural networks is emerging rapidly, scientists are just taking the very first steps in the development of the hardware elements of an artificial brain, specifically neuromorphic microchips. In this review article, we present the current state of the art of neuromorphic photonic circuits based on solid-state optoelectronic oscillators formed by nanoscale double barrier quantum well resonant tunneling diodes. We address, both experimentally and theoretically, the key dynamic properties of recently developed artificial solid-state neuron microchips with delayed perturbations and describe their role in the study of neural activity and regenerative memory. This review covers our recent research work on excitable and delay dynamic characteristics of both single and autaptic (delayed) artificial neurons including all-or-none response, spike-based data encoding, storage, signal regeneration and signal healing. Furthermore, the neural responses of these neuromorphic microchips display all the signatures of extended spatio-temporal localized structures (LSs) of light, which are reviewed here in detail. By taking advantage of the dissipative nature of LSs, we demonstrate potential applications in optical data reconfiguration and clock and timing at high-speeds and with short transients. The results reviewed in this article are a key enabler for the development of high-performance optoelectronic devices in future high-speed brain-inspired optical memories and neuromorphic computing. (C) 2017 Author(s).Fundacao para a Ciencia e a Tecnologia (FCT) [UID/Multi/00631/2013]European Structural and Investment Funds (FEEI) through the Competitiveness and Internationalization Operational Program - COMPETE 2020National Funds through FCT [ALG-01-0145-FEDER-016432/POCI-01-0145-FEDER-016432]European Commission under the project iBROW [645369]project COMBINA [TEC2015-65212-C3-3-PAEI/FEDER UE]Ramon y Cajal fellowshipinfo:eu-repo/semantics/publishedVersio

Wide and ultra-wide bandgap oxides : where paradigm-shift photovoltaics meets transparent power electronics

Oxides represent the largest family of wide bandgap (WBG) semiconductors and also offer a huge potential range of complementary magnetic and electronic properties, such as ferromagnetism, ferroelectricity, antiferroelectricity and high-temperature superconductivity. Here, we review our integration of WBG and ultra WBG semiconductor oxides into different solar cells architectures where they have the role of transparent conductive electrodes and/or barriers bringing unique functionalities into the structure such above bandgap voltages or switchable interfaces. We also give an overview of the state-of-the-art and perspectives for the emerging semiconductor β- GaO, which is widely forecast to herald the next generation of power electronic converters because of the combination of an UWBG with the capacity to conduct electricity. This opens unprecedented possibilities for the monolithic integration in solar cells of both self-powered logic and power electronics functionalities. Therefore, WBG and UWBG oxides have enormous promise to become key enabling technologies for the zero emissions smart integration of the internet of things

Through Silicon Via Field-Effect Transistor with Hafnia-based Ferroelectrics and the Doping of Silicon by Gallium Implantation Utilizing a Focused Ion Beam System

3-dimensional integration has become a standard to further increase the transistor density and to enhance the integrated functionality in microchips. Integrated circuits are stacked on top of each other and copper-filled through-silicon VIAs (TSVs) are the industry-accepted choice for their vertical electrical connection. The aim of this work is to functionalize the TSVs by implementing vertical field-effect transistors inside the via holes. The front and back sides of 200 ... 300 µm thin silicon wafers were doped to create the source/drain regions of n- and p-FETs. The TSVFETs showed very stable saturation currents and on/off current ratios of about 10^6 (n-TSVFET) and 10^3 (p-TSVFET) for a gate voltage magnitude of 4V. The use of hafnium zirconium oxide on a thin SiO_2 interface layer as gate dielectric material in a p-TSVFET, enabled the implementation of a charge trapping memory inside the TSVs, showing a memory window of about 1V. This allows the non-volatile storage of the transistor on/off state. In addition, the demonstration of the use of gallium as the source/drain dopant in planar p-FET test structures (ion implanted from a focused ion beam tool) paves the way for maskless doping and for a process flow with a low thermal budget. It was shown, that ion implanted gallium can be activated and annealed at relatively low temperatures of 500 °C ... 700 °C.:Abstract / Kurzzusammenfassung Danksagung Index I List of Figures III List of Tables X List of Symbols XI List of Abbreviations XV 1 Introduction 1 2 Fundamentals 5 2.1 Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) 5 2.1.1 Historical Development - Technological Advancements 7 2.1.2 Field-Effect Transistors in Semiconductor Memories 10 2.2 3D Integration and the Use of TSVs (Through Silicon VIAs) 16 2.3 Doping of Silicon 19 2.3.1 Doping by Thermal Diffusion 20 2.3.2 Doping by Ion Implantation 22 3 Electrical Characterization 24 3.1 Resistivity Measurements 24 3.1.1 Resistance Determination by Four-Point Probes Measurement 24 3.1.2 Contact Resistivity 27 3.1.3 Doping Concentration 32 3.2 C-V Measurements 35 3.2.1 Fundamentals of MIS C-V Measurements 35 3.2.2 Interpretation of C-V Measurements 37 3.3 Transistor Measurements 41 3.3.1 Output Characteristics (I_D-V_D) 41 3.3.2 Transfer Characteristics (I_D-V_G) 42 4 TSV Transistor 45 4.1 Idea and Motivation 45 4.2 Design and Layout of the TSV Transistor 47 4.2.1 Design of the TSV Transistor Structures 47 4.2.2 Test Structures for Planar FETs 48 5 Variations in the Integration Scheme of the TSV Transistor 51 5.1 Doping by Diffusion from Thin Films 51 5.1.1 Determination of Doping Profiles 52 5.1.2 n- and p- TSVFETs Doped Manufactures by the Use of the Diffusion Technique 59 5.2 Ferroelectric Hafnium-Zirconium-Oxide (HZO) in the Gate Stack 81 5.2.1 Planar ferroelectric p-MOSFETs Doped by Thermal Diffusion 82 5.2.2 p-TSVFETs with Hafnium-Zirconium-Oxide Metal Gate 90 5.3 Doping by Ion Implantation of Gallium with a Focused Ion Beam (FIB) Tool 96 5.3.1 Ga doped Si Diodes 97 5.3.2 Planar p-MOSFETs Doped by Ga Implantation 108 5.3.3 Proposal for a parallel integration of Cu TSVs and p-TSVFETs 117 6 Summary and Outlook 120 Bibliography XVIII A Appendix XXXVI A.1 Resistivity and Dopant Density XXXVI A.2 Mask set for the TSVFET XXXVII A.3 Mask Design of the Planar Test Structures XXXVIII Curriculum Vitae XXXIX List of Scientific Publications XL