Effects of excess oxygen on operation characteristics of amorphous In-Ga-Zn-O thin-film transistors

Ide, Keisuke; Kikuchi, Yutomo; Nomura, Kenji; Kimura, Mutsumi; Kamiya, Toshio; Hosono, Hideo

doi:10.1063/1.3633100

Cited by 226 publications

(160 citation statements)

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“…Figure 3 shows the hysteresis curves in the transfer characteristics of the a-IGZO TFTs additionally annealed in O 2 for 8 h, swept for 3 cycles of V GS between ¹20 to 20 V. These transfer curves exhibited very large hysteresis loops, indicating that the TFT characteristics were deteriorated by formation of electron traps by the additional oxygen annealing; i.e., the electrons induced by the large positive V GS are captured by traps, the charged traps are energetically relaxed to an energy deeper than the Fermi level, and the V on is increased in the backward V GS sweep measurements. A similar behavior is observed by 300°C O 3 annealing, 11) but that is different from the present case because the high-V th state was stable at least for 12 h in that case; on the other hand, the high-V on state is quickly recovered to the initial small-V on state and the same forward-sweep characteristics are observed also in the 2nd and 3rd cycle measurements. That is, the clock-wise hysteresis suggests that the a-IGZO channel layer contains electron traps with a fast recovery time.…”

Section: Methodssupporting

confidence: 61%

“…300°C exhibited a significant deterioration and bistable behavior. 11) On the other hand, Hall mobilities (® Hall ) and field-effect mobilities (® FE ) of a-IGZO TFTs with the chemical composition of In:Ga:Zn³1:1:1 in atomic ratio are reported to be 1015 cm 2 /Vs, 1),12) but some reports have provided much larger mobilities. Based on the device physics, ® FE should be smaller than drift mobility (³® Hall ) because ® FE include the deterioration effects by electron traps in the band gap and carrier scattering at the channelgate insulator interface; 13) actually, we have confirmed that ® FE of our a-IGZO TFTs are close to or a little bit smaller than ® Hall .…”

Section: Introductionmentioning

confidence: 99%

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Apparent high mobility ~30 cm<sup>2</sup>/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

Xiao

Domen

Kamiya

et al. 2013

J. Ceram. Soc. Japan

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Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) annealed in ozone at 250°C exhibited a good subthreshold swing (S) of 123 mV/decade and a saturation mobility (® sat ) of ³10 cm 2 /Vs, but a bit large threshold voltage (V th ) of 11.6 V. Further oxygen annealing at 200°C resulted in high apparent ® sat of ³30 cm 2 /Vs and deteriorated characteristics such as a large S value and large hysteresis. The high apparent ® sat values were attributed to the electrical discharge between the gate and source electrodes. Reasonably actual ® sat values ³10 cm 2 /Vs were obtained using the actual capacitance calculated from the discharge characteristics.

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Section: Methodssupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Apparent high mobility ~30 cm<sup>2</sup>/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

Xiao

Domen

Kamiya

et al. 2013

J. Ceram. Soc. Japan

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“…42 The SR-driven doping effect is expressed in terms of the atomic rearrangement in the devices and the changes in the density of states in a-IGZO; these factors are shown in Figures 4c and d, respectively. The density of states in a-IGZO in the as-deposited state was obtained from Kamiya et al 3 and Ide et al 43 During annealing, SR results in the densification of the a-IGZO thin-films (Figure 1e and Supplementary Figure S1c) and a decrease in the free volume in a-IGZO in association with greater V O s in the dense network. Therefore, V O s in deep-donor or electron-trap states are transformed into shallow-donor states.…”

Section: Resultsmentioning

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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“…Thus, the excess O can be removed using a thermal annealing process. 36,39 Because electron trapping still occurs in the absence of excess O, there should be another cause of electron trapping.…”

Section: Introductionmentioning

confidence: 99%

“…An excess O defect model has been previously suggested to describe electron-trap centers based on ozone-treated amorphous InGaZnO 4 . 39 The excess O is characterized as a weakly binding O that results in a peak at~200°C in thermal desorption spectroscopy. Thus, the excess O can be removed using a thermal annealing process.…”

Section: Introductionmentioning

confidence: 99%

Undercoordinated indium as an intrinsic electron-trap center in amorphous InGaZnO4

Nahm

Kim

2014

NPG Asia Mater

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Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO 4 . Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*-M (M = In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2-) charge state, and we designate it as an intrinsic (In*-M) 2 − center in amorphous InGaZnO 4 . The (In*-M) 2 − centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties. NPG Asia Materials (2014) 6, e143; doi:10.1038/am.2014.103; published online 14 November 2014 INTRODUCTIONThe identification of charge-trapping defects on the atomic scale has been achieved in crystalline semiconductors. A donor can capture carrier electrons with large lattice relaxations, forming a DX (donor (D) deactivated (X)) center, 1-5 whereas an acceptor traps holes, forming an AX (acceptor (A) deactivated (X)) center. [5][6][7] However, in amorphous semiconductors, even though many charge-trapping phenomena that can modify electronic device characteristics 8 and be applied to nonvolatile memory devices 9 have been observed, the atomic and electronic structures of the charge-trapping defects lack clear understanding.Amorphous oxide semiconductors seriously suffer from chargetrapping events. 10 Thin-film transistors made of amorphous oxide semiconductors exhibit a variety of metastable changes in their transistor characteristics through carrier doping and optical [11][12][13] or electrical [14][15][16][17][18][19][20][21] (or both [21][22][23][24][25][26][27][28] ) excitation of carriers. Indium (In)-based amorphous oxide semiconductors are considered as a promising material for next-generation thin-film electronics and optoelectronics because they have high electron mobility, transparency, flexibility and uniformity. [29][30][31][32][33] However, the success of these applications has been limited by the lack of stability in their electrical properties owing to charge trapping.Investigation of the charge-trapping defects on the atomic scale is an essential prerequisite to overcome the instability issue of the indiumbased amorphous oxide semiconductors. An oxygen-vacancy (V O ) defect has been suggested as a metastable hole-trap center. 34,35 Unlike in crystalline oxides, V O and M-interstitial (M i ) (M = In, Ga, or Zn) are essentially indistinguishable in amorphous oxides. An M-M bond configuration can be understood as a V O and as anSimilarly, an O-O bond configuration can be interpreted as an M-vacancy (V M ) and as an In this paper, we find that undercoordinated indium (In*) acts as an intrinsic electron-trap center in In-based amorphous oxide semiconductors. Conduction electrons are subjected to a strong conductionelectron-ion interaction near the undercoordinated In* and trapped there, forming an In*-M bond. ...

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Effects of excess oxygen on operation characteristics of amorphous In-Ga-Zn-O thin-film transistors

Cited by 226 publications

References 15 publications

Apparent high mobility ~30 cm<sup>2</sup>/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

Apparent high mobility ~30 cm<sup>2</sup>/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

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

Undercoordinated indium as an intrinsic electron-trap center in amorphous InGaZnO4

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