tesi R. Miscioscia.pdf - EleA@UniSA

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146 Conclusions gate leakages in case of thin dielectrics, the security mechanism had to be hardwired into the process flowchart without relying on the effects of annealing. For these reasons, the optimized layout designed and adopted to build OTFTs had patterned gates and reduced the overlap area between contacts and OSC. The utilization of gate leakage model also enabled us to estimate mobility-pentacene grain size trend relationship. In the case of PMMA devices and other thin dielectrics, the dependence of field-effect mobility from gate field made the performance analysis not affordable if faced with a simple circuital model. In these cases a model used in inorganic electronics for leaky dielectrics has been adopted after Palestri, Esseni et Al. Such distributed-parameter model proved to be effective also with OTFTs and was employed to investigate grain sizemobility trend for an extended class of devices. The utilization of PMMA as thin gate dielectric evidenced a low mobility value, thus we worked on this parameter by changing the nature and surface state of the insulator. From this point of view, we developed a novel gate insulator material PFTEOS:TEOS which is and organic-inorganic material processable by sol-gel technique from a solution. Devices based on this kind of material exhibited improved performances respect to the plain dielectrics but break the relationship between grain dimensions and mobility. Anomalies which have been noticed for PFTEOS:TEOS and its optimized version PFTEOS:TEOS/PMMA obtained from buffer layer deposition have been investigated and compared to other polymeric dielectrics with their varying nature and thickness. In order to do this, thermal analyses have been performed. A Meyer-Neldel rule general observation was found to be obeyed in every analyzed case, thus activation energy and Meyer Neldel temperature were exploited to characterize energetic disorder at OSC/insulator interface by Gaussian disorder model for Density of Band states. In conclusion the behavior of a novel sol-gel gate insulator has been characterized and analyzed comparing it to plain cases and finding an original behavior of EMN/mobility/Activation energy which exhibits an inverse (decreasing) trend between energetic disorder and charge transport. This has been completely opposite to trends found for PMMA devices encouraging studying, exploiting and
Introduction 147 characterizing more in depth this material for Organic Electronics purposes. The development of the organic thin film transistors is evolving quickly and most of the efforts are being focused on the overcoming of the technological limits which make the employment of these devices in integrated circuits complex, in particular in large area applications (typical characteristic of flexible display). Further efforts are to be invested whereas it is possible to glimpse the possibility of improvement concerning the development of n-type channel materials, the addressing of the structures patterning issues, problems related to surface upscaling and device downscaling. Also further researches have to be done in self-aligned processing (consequent reduction of gate overlaps). Low-cost and highproductivity deposition methods should be developed by vacuum-free deposition techniques and finally the implementation of highefficiency complementary logics should be reached. The research on the OE field has to face all these challenges and even more, other ones, so that this new technology can assert itself and become competitive covering the market sectors left still partially unexplored by the inorganic electronic technology.
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Università degli Studi di Salerno
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Acknowledgments It is a pleasure to
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In loving memory of my uncle, Profe
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Introduction Nowadays, it has becom
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Introduction 3 The drawbacks of org
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Introduction 5 Artificial Skin (OTF
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Introduction 7 structure has been d
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Chapter 1 Working principles An Org
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Chapter 1 11 1.1 A model for DC beh
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Chapter 1 13 hp. 4) Decoupling betw
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Chapter 1 15 figure 2: integration
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Chapter 1 17 eq. 11 − = Then, bei
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Chapter 1 19 The formula in eq. 18
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Chapter 1 21 and behaves as a resis
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Chapter 1 23 eq. 22 I DS = μ C ins
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Chapter 1 25 In eq. 27, kB is the B
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Chapter 1 27 eq. 30 · Thu
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Chapter 2 A survey on the state of
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Chapter 2 31 emphasizing the role p
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Chapter 2 33 Only after those years
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Chapter 2 35 In fact, usually the m
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Chapter 2 37 Examples of top-gate b
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Chapter 2 39 deposition process of
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Chapter 2 41 region is patterned by
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Chapter 2 43 figure 11: Non-Relief-
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Chapter 2 45 factor analysing, in p
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Chapter 2 47 In literature results,
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Chapter 2 49 It is clear that the c
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Chapter 2 51 In figure 17 the impro
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Chapter 2 53 figure 19: OFET trans-
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Chapter 2 55 figure 22: Comparison
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Chapter 2 57 channel and gate in Pe
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Chapter 2 59 figure 28: Pentacene b
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Chapter 2 61 figure 31: OTFT realiz
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Chapter 2 63 materials, the higher
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Chapter 2 65 The effect of the barr
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Chapter 2 67 figure 36: potential p
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Chapter 2 69 From table 2, it is ea
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Chapter 2 71 thermal-budget treatme
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Chapter 2 73 in particular in OLEDs
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Chapter 2 75 One interesting charac
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Chapter 2 77 figure 48: electrical
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Chapter 2 79 The research on the OE
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Chapter 2 81 photolysis). In this p
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Chapter 2 83 [26] Facchetti, Wasiel
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Chapter 3 Gate-leakages in polymeri
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Gate-leakages 87 determined by XRD
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Gate-leakages 89 The results are:
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Gate-leakages 91 It has to be consi
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Gate-leakages 93 figure 8: Output c
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Page 103 and 104: 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
Page 129 and 130: Chapter 4 123 mobility with the dim
Page 131 and 132: Chapter 4 125 As it can be observed
Page 133 and 134: Chapter 4 127 eq. 4 Where r
Page 135 and 136: Chapter 4 129 3.4.3 Thermal charact
Page 137 and 138: 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 )
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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.
Page 151: Conclusions In this PhD dissertatio
Page 155 and 156: Table of acronyms and symbols Symbo
Page 157: Table of acronyms and symbols _____
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