Density of States in Amorphous In-Ga-Zn-O Thin-Film Transistor under Negative Bias Illumination Stress

Ueoka, Yoshihiro; Ishikawa, Yasuaki; Bermundo, Juan Paolo; Yamazaki, Haruka; Urakawa, Satoshi; Fujii, Mami N.; Horita, Masahiro; Uraoka, Yukiharu

doi:10.1149/2.001409jss

Cited by 37 publications

(28 citation statements)

References 32 publications

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“…Therefore, we can conclude that the no trap state was generated close to the conduction band and NBIS effects were due to the capturing of fixed charges in the insulator, similar to the reported effect for IGZO TFT38. This effect is different from the hypothesis such as elimination of dangling bonds with O 2 annealing39, and defect formation in semiconductor layer or interface between the semiconductor and gate insulator404142. The shift in the electrical characteristics is due to a similar mechanism to that known for IGZO TFTs; holes from electron-hole pairs excited by the light and heat are transported from the back channel of the semiconductor to the gate surface and are captured close to the interface between the gate insulator and the semiconductor38.…”

Section: Resultssupporting

confidence: 71%

Rare-metal-free high-performance Ga-Sn-O thin film transistor

Matsuda

Umeda

Kato

et al. 2017

Sci Rep

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Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

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Section: Resultssupporting

confidence: 71%

Rare-metal-free high-performance Ga-Sn-O thin film transistor

Matsuda

Umeda

Kato

et al. 2017

Sci Rep

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“…8 In addition, though electron-hole pairs may not be band to band generated due to low photon energy, trap-assisted hole generation could occur in a-IGZO TFTs. 9,14 Especially, ionized V O could help generation of holes by capturing electrons excited from valence band via light illumination.…”

Section: Resultsmentioning

confidence: 99%

Effect of Wavelength and Intensity of Light on a-InGaZnO TFTs under Negative Bias Illumination Stress

Kim

Lee

Cho

et al. 2016

ECS J. Solid State Sci. Technol.

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We investigated degradation mechanism of a-IGZO TFTs under NBIS with different wavelengths λ and intensities I L of light. Negative gate bias was applied for 4000 s while drain and source were grounded, and illuminations with λ = 450, 530, or 700 nm were applied. Illumination with photon energy exceeding ∼2.3 eV (530 nm) induced noticeable change in threshold voltage shift V th , which can be interpreted in terms of ionization of oxygen vacancies V O . In addition, I L of blue illumination (450 nm) was varied from 6 to 200 lux and saturation in V th was observed after exceeding a certain I L . We suggest that the saturation occurs because V O -ionization rate is saturated by outward relaxation of metal atoms in the a-IGZO film. Metal oxide-based materials have high carrier mobility, low offcurrent, and good transparency, so they are promising candidates for the channel material of thin film transistors (TFTs).1 In particular, amorphous-InGaZnO (a-IGZO) TFTs have excellent properties such as high on/off ratio, good uniformity, and low processing temperature. However, a-IGZO TFTs exhibit some instability problems.Stability of a-IGZO TFTs is affected by several factors including bias/current stress, temperature, light illumination and passivation conditions.2-5 Among several factors, bias stress is most widely studied because bias is always applied to TFTs in practical display applications. In darkness, the transfer curves of TFTs shift positively when positive bias stress (PBS) is applied to the gate, but shift relatively little when negative bias stress (NBS) is applied.6,7 Although a-IGZO TFTs remain stable under NBS, their electrical characteristics degrade when it is combined with illumination, 7,8 i.e., negative bias illumination stress (NBIS).Instability of a-IGZO TFTs under NBIS has been widely investigated and reported.7-11 Though some papers dealt with the effect of light intensity on reliability of the TFT, 12,13 the effects of wavelength λ and intensity I L of light during NBIS have not been fully explained yet, especially in terms of oxygen vacancy which is crucial factor affecting reliability of a-IGZO TFTs. In this paper, we investigated degradation mechanism of a-IGZO TFTs under NBIS with light of various λ and I L . Degradation of a-IGZO TFT under NBIS with different λ, and the saturation of threshold voltage shift V th independent of I L were identified. We propose that the saturation phenomenon can be explained by restriction in the ionization rate of oxygen vacancy V O due to their effect on the structure of a-IGZO. Method and MeasurementsWe fabricated a-IGZO TFTs with bottom gate, back channel etch structure (Fig. 1). A 500 nm-thick and 200 nm-thick SiO 2 were used as gate insulator and passivation layer, respectively. The a-IGZO active layer was formed with the channel width/length of 110 μm/6 μm. Transfer characteristics of the TFTs were measured after NBIS was applied. For bias stress, negative gate voltage was applied for 4000 s while drain and source were grounded. Illumination from white ...

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“…D i and τ i can be extracted from the peak intensity and the peak position of the G p /ω versus ω −1 curve. The DOS of an interface trap states and the interface trap time constant can be calculated using the following formula [27]:…”

Section: A Effect Of Postannealing Time On Initial Transfer Charactementioning

confidence: 99%

“…This shows that D i and τ i were interrupted at V g near the flat band voltage (V FB ). Therefore, based on the simple model of device physic [21], [27], the defects which locate above V FB are the acceptorlike interface defects. The defects which locate below V FB are the donorlike interface defects.…”

Section: A Effect Of Postannealing Time On Initial Transfer Charactementioning

confidence: 99%

Investigating Effect of Postannealing Time on Positive Bias Stress Stability of In–Ga–Zn–O TFT by Conductance Method

Hung

Wang

Furuta

2015

IEEE Trans. Electron Devices

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The conductance method was used to investigate the positive bias stress (PBS) degradation mechanism of In-Ga-Zn-O (IGZO) thin-film transistor (TFT). The effects of postannealing time on the PBS degradation mechanism were investigated. The stabilization of the donorlike interface defects was found to be the reason for the threshold voltage instability in the IGZO-TFT under the PBS test. The donorlike defects at the front channel interface and in the plasma-enhanced chemical vapor deposition (PE-CVD) SiO x acted as the electron trapping centers. The electron trapping resistance of the PE-CVD SiO x was improved by increasing the postannealing time, resulting in an improvement in the PBS stability. However, long-time postannealing-induced creation of the deep acceptorlike interface defects in the TFT under the PBS. The energy distribution of the created deep acceptorlike interface defects was revealed using the conductance measurement. Index Terms-Acceptorlike interface defects, amorphous In-Ga-Zn-O (IGZO), conductance method, donorlike interface defects, IGZO/SiO x interface, improve positive bias stress (PBS) stability, PBS, positive gate bias stress, thin-film transistor (TFT).

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Density of States in Amorphous In-Ga-Zn-O Thin-Film Transistor under Negative Bias Illumination Stress

Cited by 37 publications

References 32 publications

Rare-metal-free high-performance Ga-Sn-O thin film transistor

Rare-metal-free high-performance Ga-Sn-O thin film transistor

Effect of Wavelength and Intensity of Light on a-InGaZnO TFTs under Negative Bias Illumination Stress

Investigating Effect of Postannealing Time on Positive Bias Stress Stability of In–Ga–Zn–O TFT by Conductance Method

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