Toward High-Performance Amorphous GIZO TFTs

Barquinha, Pedro; Pereira, L.; Gonçalves, Gonçalo; Martins, Rodrigo; Fortunato, Elvira

doi:10.1149/1.3049819

Cited by 241 publications

(169 citation statements)

References 33 publications

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“…12,13 These results indicate that oxygen vacancies (V O s), which are inherent chemical defects, act as the dominant electron donors. Interestingly, the V O s can act as deep donors 8 (that is, limited donation of free electrons), electron traps 3,6 and shallow donors, whose electronic states are determined by the local atomic environment.…”

Section: Introductionmentioning

confidence: 99%

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

et al. 2016

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The electronic states of oxygen vacancies (V O s) in amorphous oxide semiconductors are shallow donors, deep donors or electron traps; these are determined by the local atomic structure. Because the amorphous phase is metastable compared with the crystalline phase, the degree of structural disorder is likely to decrease, which is referred to as structural relaxation (SR). Thus SR can affect the V O electronic state by changing the local atomic conditions. In this study, we demonstrated that electron doping is possible through the SR of amorphous oxides without redox reactions using a novel device structure that prevents extrinsic reactions with electrodes and ambient atmosphere during annealing. The concentration of V O s in the shallow-donor state in amorphous In-Ga-Zn-O (a-IGZO) increases from~10 16 to~10 19 cm − 3 with increasing annealing temperatures between 300 and 450°C. The SR-driven doping effect is strongly dependent on the annealing temperature but not on the annealing time. The Arrhenius activation energy of the SR-driven doping effect is 1.76 eV, which is similar to the bonding energies in a-IGZO. Our findings suggest that the free volume in a-IGZO decreases during SR, and the V O s in either deep-donor or electrontrap states are consequently transformed into shallow-donor states. NPG Asia Materials (2016) 8, e250; doi:10.1038/am.2016.11; published online 25 March 2016 INTRODUCTION Amorphous metal oxides, such as amorphous indium gallium zinc oxide (a-IGZO), have become mainstream materials for large-area and flexible electronics because the long-range structural disorder enhances the uniformity of the electrical properties and mechanical flexibility compared with crystalline metal oxides. 1-5 A notable characteristic of amorphous oxides, relative to their crystalline counterparts, is that these materials contain structural disorder-related defects (for example, free volume) in addition to non-stoichiometric defects (for example, oxygen vacancies), which significantly affect the corresponding electrical properties. 3,[6][7][8] Moreover, the degree of structural disorder in amorphous metal oxides is always likely to decrease to form more stable structures because internal atomic rearrangement occurs even below the glass transition temperature (T g ). This process is known as structural relaxation (SR) 9-11 and results in continuous changes in the electrical properties. Thus understanding the effects of SR on the electrical properties of amorphous oxides is important for applications in future electronics.In addition to uniformity and flexibility, amorphous metal oxides exhibit tunable electrical conductivity through redox reaction control

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Section: Introductionmentioning

confidence: 99%

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

et al. 2016

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“…Metal oxide semiconductors, in particular, are very attractive for implementation into thin-film transistors (TFTs) [1][2] mainly because of their high charge 2 carrier mobility, high optical transparency, excellent chemical stability, mechanical stress tolerance and processing versatility [3][4][5] . Oxide semiconductors are usually grown using vacuum-based techniques such as sputtering [6][7][8] , pulsed laser deposition [9] , chemical vapour deposition [10] , and ion-assisted deposition [11][12] . Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] .…”

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confidence: 99%

“…Oxide semiconductors are usually grown using vacuum-based techniques such as sputtering [6][7][8] , pulsed laser deposition [9] , chemical vapour deposition [10] , and ion-assisted deposition [11][12] . Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] .…”

mentioning

confidence: 99%

“…Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] . Many of these materials have been investigated for applications in thin-film electronics where transistors with electron mobilities up to 140 cm 2 /Vs have been demonstrated [7,[11][12][13][14][15][16] . Despite the great promise however, the application of vacuum-based technologies for the deposition of complex oxide semiconductors suffers from incompatibility with large-area substrates and hence high manufacturing cost.…”

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Spray‐Deposited Li‐Doped ZnO Transistors with Electron Mobility Exceeding 50 cm²/Vs

et al. 2010

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The ever increasing demand for high performance electronic devices that can be fabricated onto large-area substrates employing low manufacturing cost techniques has given a boost to the development of alternative types of semiconductor materials, such as organics and metal oxides, with desirable physical characteristics that are absent in their traditional inorganic counterparts. Metal oxide semiconductors, in particular, are very attractive for implementation into thin-film transistors (TFTs) [1][2] mainly because of their high charge 2 carrier mobility, high optical transparency, excellent chemical stability, mechanical stress tolerance and processing versatility [3][4][5] . Oxide semiconductors are usually grown using vacuum-based techniques such as sputtering [6][7][8] , pulsed laser deposition [9] , chemical vapour deposition [10] , and ion-assisted deposition [11][12] . Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] . Many of these materials have been investigated for applications in thin-film electronics where transistors with electron mobilities up to 140 cm 2 /Vs have been demonstrated [7,[11][12][13][14][15][16] . Despite the great promise however, the application of vacuum-based technologies for the deposition of complex oxide semiconductors suffers from incompatibility with large-area substrates and hence high manufacturing cost. To this end, the development of alternative deposition methods based on solution processing paradigms could provide a breakthrough in both cost and performance by marrying fabrication simplicity with high-throughput manufacturing.In recent years a wide variety of soluble precursors compounds have been examined as potential alternatives for the fabrication of oxide-based TFTs using large area deposition methods including spin casting, dip coating and spray pyrolysis. For example, metal oxides such as zinc oxide (ZnO) [17][18][19][20][21][22] , indium oxide (In 2 O 3 ) [23][24] , indium gallium oxide (InGaO) [25] , indium zinc oxide (InZnO) [18][19][20][21][22][23][24][25][26] and zinc tin oxide (ZnSnO) [27] have been synthesised using soluble precursors and implemented into TFT structures. Despite the process simplicity, excellent charge carrier mobilities have been achieved, clearly demonstrating the significant potential of this alternative processing methodology. Here we show how spray pyrolysis (SP) can be used for the deposition of doped ZnO films and the fabrication of high electron mobility TFTs onto large area substrates under ambient atmosphere. Doping is achieved by simple physical blending of the soluble precursor compounds in water or alcohol based solutions. Among the various dopants studied, transistors fabricated using Li doped ZnO were 3 found to yield the best performance with maximum electron mobility > 50 cm 2 /Vs and on/off current modulation ratio exceeding 10 6 .Preparation of the Li doped precursor solutions is described in th...

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“…Amorphous gallium-indium zinc oxide ͑GIZO͒ thin-film transistors ͑TFTs͒ have attracted attention for their possible applications to flat, flexible, and transparent displays, [1][2][3][4] especially when processed at low temperatures. However, like the other TFTs' technologies, they also suffer from a stability phenomena known as gate-bias stress.…”

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Gate-bias stress in amorphous oxide semiconductors thin-film transistors

Lopes

Gomes

Medeiros

et al. 2009

Applied Physics Letters

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A quantitative study of the dynamics of threshold-voltage shifts with time in gallium-indium zinc oxide amorphous thin-film transistors is presented using standard analysis based on the stretched exponential relaxation. For devices using thermal silicon oxide as gate dielectric, the relaxation time is 3 ϫ 10 5 s at room temperature with activation energy of 0.68 eV. These transistors approach the stability of the amorphous silicon transistors. The threshold voltage shift is faster after water vapor exposure suggesting that the origin of this instability is charge trapping at residual-water-related trap sites. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3187532͔ Amorphous gallium-indium zinc oxide ͑GIZO͒ thin-film transistors ͑TFTs͒ have attracted attention for their possible applications to flat, flexible, and transparent displays, 1-4 especially when processed at low temperatures. However, like the other TFTs' technologies, they also suffer from a stability phenomena known as gate-bias stress. 5,6 This effect manifests itself as a continuous increase in threshold voltage ͑V th ͒ when the gate bias is kept constant over time. This limits the application of these TFTs in demanding applications, such as active matrix organic light emitting displays. The increase in V th lowers the luminance of individual pixels over time, causing display nonuniformity. 7 As an example, using current technologies several driving transistors per pixel are necessary to compensate for the V th shift. Hence, a proper understanding of the stressing mechanism is of paramount importance.Gate-bias stress effects are commonly reported in the literature for a variety of transistors, a-Si TFTs, 8 organic transistors, 9-11 and recently also in amorphous oxide semiconductors TFTs. [12][13][14][15] The effect has been explained as a slow trapping of charge carriers in defects of unknown origin located at the semiconductor/dielectric interface. 13 It is known that the current degradation is faster when the devices are exposed to atmosphere 15,16 and that the stability improves after annealing. 1 Also, it has been reported that the effects can be reduced by the insertion of a passivation layer, either between the dielectric and the semiconductor 17 or on top of the semiconductor in bottom-gate structures. 16 This work provides a quantitative study of the gate-bias stress instability as a function of temperature and environment conditions. The results allow a comparison with competing TFTs technologies. Furthermore, it also provides evidences that water vapor contamination enhances this instability. Therefore, there is no conceptual limitation for the stability of GIZO based TFTs. This is in contrast to hydrogenated amorphous silicon TFTs where the instability is caused by the creation of intrinsic defects, unsaturated valence states into which electrons are trapped.The device fabrication process has been described in detail elsewhere. 18 Briefly, the TFTs were produced with a staggered bottom gate configuration on silicon wafers, which a...

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Toward High-Performance Amorphous GIZO TFTs

Cited by 241 publications

References 33 publications

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

Spray‐Deposited Li‐Doped ZnO Transistors with Electron Mobility Exceeding 50 cm²/Vs

Gate-bias stress in amorphous oxide semiconductors thin-film transistors

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Toward High-Performance Amorphous GIZO TFTs

Cited by 241 publications

References 33 publications

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

Structural-relaxation-driven electron doping of amorphous oxide semiconductors by increasing the concentration of oxygen vacancies in shallow-donor states

Spray‐Deposited Li‐Doped ZnO Transistors with Electron Mobility Exceeding 50 cm2/Vs

Gate-bias stress in amorphous oxide semiconductors thin-film transistors

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Spray‐Deposited Li‐Doped ZnO Transistors with Electron Mobility Exceeding 50 cm²/Vs