A novel, non-volatile, organic capacitive memory device called p-i-n-metal-oxide-semiconductor (pinMOS) memory is demonstrated with multiple-bit storage that can be programmed and read out electrically and optically. The diode-based architecture simplifies the fabrication process, and makes further optimizations easy, and might even inspire new derived capacitive memory devices. Furthermore, this innovative pinMOS memory device features local charge up of an integrated capacitance rather than of an extra floating gate.
Before the device can perform as desired, the leakage current due to the lateral charge up of the doped layers outside the active area needs to be suppressed. Therefore, in this thesis, lateral charging effects in organic light-emitting diodes (OLEDs) are studied first. By comparing the results from differently structured devices, the presence of centimeter-scale lateral current flows in the n-doped and p-doped layers is shown, which results in undesirable capacitance increases and thus extra leakage currents. Such lateral charging can be controlled via structuring the doped layers, leading to extremely low steady-state leakage currents in the OLED (here 10-7 mA/cm2 at -1 V). It is shown that these lateral currents can be utilized to extract the conductivity as well as the activation energy of each doped layer when modeled with an RC circuit model.
Secondly, pinMOS memory devices that are based on the diode with structured doped layers are investigated. The memory behavior, which is demonstrated as capacitance switching for electrical signals, and light emission for optical signals, can be tuned either by the applied voltage or ultraviolet light illumination, respectively. The working mechanism is explained by the existence of quasi steady-states as well as the width variation of space charge zones. The pinMOS memory shows excellent repeatability, an endurance of more than 104 write-read-erase-read cycles, and currently already over 24 h retention time. Furthermore, an early-stage investigation on emulating synaptic plasticity reveals the potential of pinMOS memory for applications in neuromorphic computing. Overall, the results indicate that pinMOS memory in principle is promising for a variety of future applications in both electronic and photonic circuits. A detailed understanding of this new concept of memory device, for which this thesis lays an important foundation, is necessary to proceed with further enhancements.:1 Introduction 1
2 Fundamentals of organic semiconductors 5
2.1 Electronic states of a molecule 5
2.1.1 Atomic orbitals and molecular orbitals 5
2.1.2 Solid states 9
2.1.3 Singlet and triplet states 12
2.2 Charge transport 13
2.2.1 Charge carrier mobility 13
2.2.2 Charge carrier transport 14
2.3 Charge injection 17
2.3.1 Current limitation 17
2.3.2 Charge injection mechanisms 20
2.4 Doping 22
3 Organic junctions and devices 25
3.1 Metal-semiconductor junction 25
3.1.1 Schottky junction 25
3.1.2 Surface states 27
3.2 Metal-oxide-semiconductor capacitor 29
3.3 Junctions and diodes 31
3.3.1 PN junction and diode 31
3.3.2 PIN junction and diode 32
4 Organic non-volatile memory devices 35
4.1 Basic concepts 35
4.2 Organic resistive memory devices 37
4.2.1 Device architecture and switching behavior 38
4.2.2 Working mechanisms 38
4.3 Organic transistor-based memory devices 41
4.3.1 Organic field-effect transistor and memory devices based thereon 41
4.3.2 Floating gate memory 43
4.3.3 Charge trapping memory 45
4.4 Organic ferroelectric memory devices 46
4.4.1 Ferroelectric capacitor memory 47
4.4.2 Ferroelectric transistor memory 48
4.4.3 Ferroelectric diode memory 49
5 Experimental methods 53
5.1 Device fabrication 53
5.2 Device characterization 55
5.3 Materials 57
6 Lateral current flow in semiconductor devices having crossbar electrodes 61
6.1 Introduction 61
6.2 Device architecture 62
6.3 Characteristics comparison between unstructured and structured devices 63
6.3.1 Charging measurement 63
6.3.2 Current-voltage characteristics 64
6.3.3 Capacitance-frequency characteristics 67
6.4 Influence of conductivity of doped layers 69
6.4.1 Dependence on doped layers thickness 69
6.4.2 Dependence on temperature 73
6.5 Lateral charging simulation 74
6.5.1 Analytical description 74
6.5.2 RC circuit simulation 76
6.5.3 Parameters for doped layers gained by simulation 79
6.6 Pseudo trap analysis 81
6.6.1 The pseudo trap density of states determination 81
6.6.2 The pseudo trap analysis under simulated identical conditions 84
6.7 Summary 85
7 The pinMOS memory: novel diode-capacitor memory with multiple-bit storage 87
7.1 Introduction 87
7.2 Device architecture 88
7.2.1 Dependence on layout and pixel 89
7.2.2 Fundamental memory behavior characterization 93
7.3 Working mechanism 96
7.3.1 Working mechanism of quasi-steady states 97
7.3.2 Working mechanism of dynamic states 101
7.4 Tunability of the memory effect 105
7.4.1 Operation parameters 106
7.4.2 Photoinduced tunability 108
7.4.3 Intrinsic layer thickness 110
7.5 Potential in neuromorphic computing application 111
7.5.1 Extracting capacitance at 0 V sequentially 112
7.5.2 Mimicking the long-term plasticity (LTP) behavior 113
7.6 Summary 114
8 Optoelectronic properties of pinMOS memory 117
8.1 Introduction 117
8.2 Measurement setup 117
8.3 pinMOS memory emission intensity 118
8.4 Pulse characteristics and device brightness 119
8.5 Conclusion 124
9 Conclusion 125
Bibliography 129
List of Figures 145
List of Tables 151
List of Abbreviations 153
Publications and Conference 157
Acknowledgment 159 / Es wird ein neuartiges, organisches kapazitives Speicherelement demonstriert, das p-i-n-Metalloxid-Halbleiter (pinMOS) Speicher genannt wird und eine Mehrfachbitspeicherung besitzt, die elektrisch und optisch programmiert und ausgelesen werden kann. Die auf einer Diode basierende Architektur vereinfacht den Herstellungsprozess sowie die weitere Optimierung und könnte sogar Inspiration für neue kapazitive Speichermedien sein. Darüber hinaus basiert dieses innovative pinMOS Speicherelement auf der lokalen Aufladung einer integrierten Kapazität und nicht auf einem zusätzlichem “Floating Gate”.
Bevor das Speicherelement wie gewünscht funktioniert, muss der Leckstrom, der durch die laterale Aufladung der dotierten Schichten außerhalb des aktiven Bereichs verursacht wird, unterdrückt werden. Deshalb werden in dieser Arbeit zuerst die lateralen Aufladungseffekte in organischen Leuchtdioden (OLEDs) untersucht. Beim Vergleich verschiedener Device-Strukturen wird die Existenz von lateralen Stromflüssen im Zentimeterbereich in den n- und p-dotierten Schichten gezeigt, was zu einer unerwünschten erhöhten Kapazität und folglich einem höheren Leckstrom führt. Diese laterale Aufladung kann durch die Strukturierung der dotierten Schichten kontrolliert werden, was zu extrem geringen Gleichgewichtsleckströmen in den OLEDs (10-7 mA/cm2 bei -1 V) resultiert. Es wird auch gezeigt, dass die lateralen Ströme genutzt werden können um die spezifische Leitfähigkeit sowie die Aktivierungsenergie der einzelnen dotierten Schichten zu extrahieren, wenn diese mit einem RC-Modell modelliert werden.
Im zweiten Teil werden pinMOS Speicherelemente, die auf der Diode mit strukturierten dotierten Schichten basieren, untersucht. Das Speicherverhalten, dass durch Kapazitätsschaltung für elektrische Signale und als Lichtemission für optische Signale gezeigt wird, kann entweder durch die angelegte Spannung, beziehungsweise durch die Belichtung mit ultraviolettem Licht eingestellt werden. Die Wirkungsweise wird durch die Existenz quasistatischer Gleichgewichte sowie durch die Größenänderung der Raumladungszonen erklärt. Der pinMOS Speicher zeigt eine hervorragende Wiederholbarkeit, eine Beständigkeit über mehr als 104 Schreiben-Lesen-Löschen-Lesen Zyklen und aktuell schon eine Retentionszeit von über 24 h. Weiterhin offenbaren erste Versuche in der Nachahmung von Neuronaler Plastizität das Potenzial von pinMOS Speichern für Anwendungen im “Neuromorphic Computing”. Insgesamt deuten die Ergebnisse an, dass pinMOS Speicher prinzipiell vielversprechend für eine Vielzahl von zukünftigen Anwendungen in elektronischen und photonischen Schaltkreisen ist. Ein tiefgreifendes Verständnis von diesem Konzept neuartiger Speicherelemente, für das diese Arbeit eine wichtige Grundlage bildet, ist notwendig, um weitere Verbesserungen zu entwickeln.:1 Introduction 1
2 Fundamentals of organic semiconductors 5
2.1 Electronic states of a molecule 5
2.1.1 Atomic orbitals and molecular orbitals 5
2.1.2 Solid states 9
2.1.3 Singlet and triplet states 12
2.2 Charge transport 13
2.2.1 Charge carrier mobility 13
2.2.2 Charge carrier transport 14
2.3 Charge injection 17
2.3.1 Current limitation 17
2.3.2 Charge injection mechanisms 20
2.4 Doping 22
3 Organic junctions and devices 25
3.1 Metal-semiconductor junction 25
3.1.1 Schottky junction 25
3.1.2 Surface states 27
3.2 Metal-oxide-semiconductor capacitor 29
3.3 Junctions and diodes 31
3.3.1 PN junction and diode 31
3.3.2 PIN junction and diode 32
4 Organic non-volatile memory devices 35
4.1 Basic concepts 35
4.2 Organic resistive memory devices 37
4.2.1 Device architecture and switching behavior 38
4.2.2 Working mechanisms 38
4.3 Organic transistor-based memory devices 41
4.3.1 Organic field-effect transistor and memory devices based thereon 41
4.3.2 Floating gate memory 43
4.3.3 Charge trapping memory 45
4.4 Organic ferroelectric memory devices 46
4.4.1 Ferroelectric capacitor memory 47
4.4.2 Ferroelectric transistor memory 48
4.4.3 Ferroelectric diode memory 49
5 Experimental methods 53
5.1 Device fabrication 53
5.2 Device characterization 55
5.3 Materials 57
6 Lateral current flow in semiconductor devices having crossbar electrodes 61
6.1 Introduction 61
6.2 Device architecture 62
6.3 Characteristics comparison between unstructured and structured devices 63
6.3.1 Charging measurement 63
6.3.2 Current-voltage characteristics 64
6.3.3 Capacitance-frequency characteristics 67
6.4 Influence of conductivity of doped layers 69
6.4.1 Dependence on doped layers thickness 69
6.4.2 Dependence on temperature 73
6.5 Lateral charging simulation 74
6.5.1 Analytical description 74
6.5.2 RC circuit simulation 76
6.5.3 Parameters for doped layers gained by simulation 79
6.6 Pseudo trap analysis 81
6.6.1 The pseudo trap density of states determination 81
6.6.2 The pseudo trap analysis under simulated identical conditions 84
6.7 Summary 85
7 The pinMOS memory: novel diode-capacitor memory with multiple-bit storage 87
7.1 Introduction 87
7.2 Device architecture 88
7.2.1 Dependence on layout and pixel 89
7.2.2 Fundamental memory behavior characterization 93
7.3 Working mechanism 96
7.3.1 Working mechanism of quasi-steady states 97
7.3.2 Working mechanism of dynamic states 101
7.4 Tunability of the memory effect 105
7.4.1 Operation parameters 106
7.4.2 Photoinduced tunability 108
7.4.3 Intrinsic layer thickness 110
7.5 Potential in neuromorphic computing application 111
7.5.1 Extracting capacitance at 0 V sequentially 112
7.5.2 Mimicking the long-term plasticity (LTP) behavior 113
7.6 Summary 114
8 Optoelectronic properties of pinMOS memory 117
8.1 Introduction 117
8.2 Measurement setup 117
8.3 pinMOS memory emission intensity 118
8.4 Pulse characteristics and device brightness 119
8.5 Conclusion 124
9 Conclusion 125
Bibliography 129
List of Figures 145
List of Tables 151
List of Abbreviations 153
Publications and Conference 157
Acknowledgment 159
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:72161 |
| Date | 17 September 2020 |
| Creators | Zheng, Yichu |
| Contributors | Lakner, Hubert, Mannsfeld, Stefan, Vandewal, Koen, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | info:eu-repo/grantAgreement/Deutsche Forschungsgemeinschaft/German Excellence Initiative/194636624//EXC 1056: Center for Advancing Electronics Dresden (cfAED) |
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