tesi R. Miscioscia.pdf - EleA@UniSA

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122 Exceptions in morphology-mobility relationship eq. 1 Where Cins is the insulator surface-specific capacitance as calculated from the knowledge of the dielectric thickness (tins and the relative permittivity) in eq. 2. eq. 2 Channel microstructure-related properties (see [4],[25] and their references) involve charge transport and trapping, in our case by using the previous relationship and the subtended model in the case of amorphous or polycrystalline semiconductors, we expect a gatevoltage dependence of the mobility (µFET=µ (VGS)). The behavior of µFET versus the gate electrical field, has the ability to reveal the electrical, thermodynamic and material-related features of OSC/dielectric interface in the channel area. Then, a correct estimation of channel mobility can be performed only if we have knowledge of dielectric constants of adopted insulators. For these reasons, an HP4192A impedance analyzer has been employed to make capacitance voltage measurements (C/V) to extract the dielectric permittivity at low frequencies (10 2 -10 3 Hz). If this step could be overcome for commercial insulators like Polyimides etc., particular attention should be kept for in house made materials like PFTEOS:TEOS which, as far as we know, has still not be investigated as a dielectric for OTFTs. As a result of our measurements, we found PFTEOS:TEOS showing an elevated value if compared with polymeric low-k dielectrics (see table 6). PMMA εr=3.6 PFTEOS:TEOS εr=5.1 table 6: measured dielectrics relative permittivities at f=100Hz 3.4.2 Morphology-mobility relationship Starting from SEM imaging results on the pentacene layers grown on the top of selected dielectrics it has been possible to relate the
Chapter 4 123 mobility with the dimension of grains and thus of grain boundaries as Horowitz et Al. [3] have shown for thiophenes and also in previous works. The analysis of mobility curves versus gate bias (gate voltagedependent mobility) has been performed for PMMA samples and extended for a 225nm PMMA insulator treated in CF4 plasma and subsequently in PFTEOS:TEOS and a bufferized PFTEOS:TEOS/PMMA sample. In the case of PMMA/CF4 treated sample the gate voltage dependent µFE has showed a typical behavior of dielectrics when surface treatments are performed. A maximum in the µFE and a value higher than the equivalent untreated sample can be observed in figure 8. μ (cm 2 /Vs) 0.20 0.15 0.10 0.05 0.00 -0.05 -20 -15 -10 -5 0 5 V G (V) figure 8: the effect of CF4 plasma surface treatment on PMMA dielectric. The mobility exhibits a maximum point and values greater than a plain PMMA OTFT. (PMMA thickness: 225nm) As it can be seen in figure 8, the untreated PMMA dielectric exhibits a behavior almost linear for higher gate fields, obeying to the Necliudov’s empirical model[28] reported in eq. 3 which was already known for amorphous silicon (a-Si)[30] and its subsequent developments for PMMA-based OTFTs[29]. eq. 3 PMMA 225nm PMMA 225nm - CF4
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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
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
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: Chapter 4 121 3.4 Device’s charac
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 )
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.
Page 151 and 152: 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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