tesi R. Miscioscia.pdf - EleA@UniSA

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6 Introduction Motivation and purpose of this thesis The theme of the present PhD thesis is the role played by the gate dielectric in the electrical performance of organic transistors and is based on the research activities described above. When talking about performances, not just charge mobility has to be considered but also it’s necessary to take into account gate capacitance, threshold voltages, gate leakages and static power dissipations, operating voltages, drain currents and so on in order to get a deeper insight of what kind of specifications an OTFT device should obey to be suitable for industrial/commercial purposes. In particular, in the present work the characteristics of the OTFTs have been analyzed in relation to manufacturing parameters and processes, focusing on non-ideal behaviors and aiming to optimize the characteristics of the transistor acting on morphologies, geometries and process conditions. Excluding this introduction and the conclusions, the thesis is divided into four chapters. The first chapter is a brief discussion about the working principles of OTFTs. The approach aims to reduce the complexity of the analysis in order to discuss the basic tools to study OFETs from the electrical point of view. In the second chapter, a broad overview of the state of the art of technology for innovative methods of manufacturing for OTFTs shows topologies, materials and processing technology and integration issues and compares strengths and weaknesses to guide the experimental work subsequently documented by means of process recipes and details. In the third chapter gate-leakage non-idealities are analyzed by changing the dielectric material in comparable structure topologies modeling the device by means of a circuital equivalent. The fourth chapter is devoted to gate field-mobility and thermal analyses performed to investigate the main parameters changes in OTFT devices. In detail, by acting on dielectric material and gate insulator surface, we analyzed the a relationship between the nature of gate dielectric-semiconductor interface and the insulator itself. In order to accomplish this, a common device reference
Introduction 7 structure has been designed and developed on the basis of chapter 2 and 3 considerations. The study was addressed by characterizing the devices by measuring the static curves of output characteristics and gate-drain (input-output) trans-characteristics. Activation energy of the mobility of charge carriers in thermal measurements have also is extracted in the aim to investigate charge transport at dielectric-channel interface. The tools employed in the proposed analyses are based on the model parameters of field effect transistors (mobility, threshold voltage, saturation current) and non-ideal factors linked to leakage currents but also gate-field dependent mobility models have been studied and introduced to model the presence of trap levels in disordered semiconducting mediums like in our case. Among the adopted models, particular attention was paid to the extraction tools, modeling and analysis of gate leakage. The introduction of an equivalent circuit of the studied TFTs to separate intrinsic behaviors from non ideal-drifts has been performed. The developed simple model has been applied to characterize the thermal annealing effects on complete devices and to make consideration about the drift of gate currents. Specific data concerning the development of manufacturing processes of OTFT were provided showing the routes that have enabled it to increase integration level and overall performance of studied transistors. The survey on the major sources of non-idealities related to the dielectric-dielectric interface and channel modeling and characterization and analysis has led to the identification of morphological and process factors that can influence the mobility and current saturation in OTFT considered. Finally, an innovative inorganic dielectric deposited by liquid-phase using sol-gel process has been introduced to reveal specific characteristics compared to the data acquired so far. This was made possible by the methods of extraction of physical parameters such as current channel the energy of Meyer-Neldel without which it would not be possible to identify these correlations and the found exceptions.
Page 1 and 2: Università degli Studi di Salerno
Page 3 and 4: Acknowledgments It is a pleasure to
Page 5 and 6: In loving memory of my uncle, Profe
Page 7 and 8: Introduction Nowadays, it has becom
Page 9 and 10: Introduction 3 The drawbacks of org
Page 11: Introduction 5 Artificial Skin (OTF
Page 15 and 16: Chapter 1 Working principles An Org
Page 17 and 18: Chapter 1 11 1.1 A model for DC beh
Page 19 and 20: Chapter 1 13 hp. 4) Decoupling betw
Page 21 and 22: Chapter 1 15 figure 2: integration
Page 23 and 24: Chapter 1 17 eq. 11 − = Then, bei
Page 25 and 26: Chapter 1 19 The formula in eq. 18
Page 27 and 28: Chapter 1 21 and behaves as a resis
Page 29 and 30: Chapter 1 23 eq. 22 I DS = μ C ins
Page 31 and 32: Chapter 1 25 In eq. 27, kB is the B
Page 33 and 34: Chapter 1 27 eq. 30 · Thu
Page 35 and 36: Chapter 2 A survey on the state of
Page 37 and 38: Chapter 2 31 emphasizing the role p
Page 39 and 40: Chapter 2 33 Only after those years
Page 41 and 42: Chapter 2 35 In fact, usually the m
Page 43 and 44: Chapter 2 37 Examples of top-gate b
Page 45 and 46: Chapter 2 39 deposition process of
Page 47 and 48: Chapter 2 41 region is patterned by
Page 49 and 50: Chapter 2 43 figure 11: Non-Relief-
Page 51 and 52: Chapter 2 45 factor analysing, in p
Page 53 and 54: Chapter 2 47 In literature results,
Page 55 and 56: Chapter 2 49 It is clear that the c
Page 57 and 58: Chapter 2 51 In figure 17 the impro
Page 59 and 60: Chapter 2 53 figure 19: OFET trans-
Page 61 and 62: Chapter 2 55 figure 22: Comparison
Page 63 and 64:
Chapter 2 57 channel and gate in Pe
Page 65 and 66:
Chapter 2 59 figure 28: Pentacene b
Page 67 and 68:
Chapter 2 61 figure 31: OTFT realiz
Page 69 and 70:
Chapter 2 63 materials, the higher
Page 71 and 72:
Chapter 2 65 The effect of the barr
Page 73 and 74:
Chapter 2 67 figure 36: potential p
Page 75 and 76:
Chapter 2 69 From table 2, it is ea
Page 77 and 78:
Chapter 2 71 thermal-budget treatme
Page 79 and 80:
Chapter 2 73 in particular in OLEDs
Page 81 and 82:
Chapter 2 75 One interesting charac
Page 83 and 84:
Chapter 2 77 figure 48: electrical
Page 85 and 86:
Chapter 2 79 The research on the OE
Page 87 and 88:
Chapter 2 81 photolysis). In this p
Page 89 and 90:
Chapter 2 83 [26] Facchetti, Wasiel
Page 91 and 92:
Chapter 3 Gate-leakages in polymeri
Page 93 and 94:
Gate-leakages 87 determined by XRD
Page 95 and 96:
Gate-leakages 89 The results are:
Page 97 and 98:
Gate-leakages 91 It has to be consi
Page 99 and 100:
Gate-leakages 93 figure 8: Output c
Page 101 and 102:
Gate-leakages 95 figure 12: electri
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Gate-leakages 97 3.4 Advanced circu
Page 105 and 106:
Gate-leakages 99 figure 16: SEM ima
Page 107 and 108:
Gate-leakages 101 modeled with a co
Page 109 and 110:
Gate-leakages 103 eq. 11 • Shadow
Page 111 and 112:
Gate-leakages 105 References [1] R.
Page 113 and 114:
Chapter 4 Morphology-mobility relat
Page 115 and 116:
Chapter 4 109 insulators to increas
Page 117 and 118:
Chapter 4 111 3.2 General device st
Page 119 and 120:
Chapter 4 113 Pentacene islands are
Page 121 and 122:
Chapter 4 115 For the preparation o
Page 123 and 124:
Chapter 4 117 figure 3: PFTEOS:TEOS
Page 125 and 126:
Chapter Chapter 4 4 119 (a): (a):
Page 127 and 128:
Chapter 4 121 3.4 Device’s charac
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Chapter 4 123 mobility with the dim
Page 131 and 132:
Chapter 4 125 As it can be observed
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Chapter 4 127 eq. 4 Where r
Page 135 and 136:
Chapter 4 129 3.4.3 Thermal charact
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Chapter 4 131 Ea(eV) 0.50 0.45 0.40
Page 139 and 140:
Chapter 4 133 I D (A) 100.0n 80.0n
Page 141 and 142:
Chapter 4 135 μ (cm 2 V -1 s -1 )
Page 143 and 144:
Chapter 4 137 T MN (K) 2400 2200 20
Page 145 and 146:
Chapter 4 139 Such results, supply
Page 147 and 148:
Chapter 4 141 References [1] O. D.
Page 149 and 150:
Chapter 4 143 [26] P. Palestri, D.
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Conclusions In this PhD dissertatio
Page 153 and 154:
Introduction 147 characterizing mor
Page 155 and 156:
Table of acronyms and symbols Symbo
Page 157:
Table of acronyms and symbols _____
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