Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO<sub>4</sub> Thin-Film Transistors

Takechi, Kazushige; Nakata, Masaya; Eguchi, Toshimasa; Yamaguchi, Hirotaka; Kaneko, Shigeo

doi:10.1143/jjap.48.010203

Cited by 132 publications

(105 citation statements)

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“…It has been pointed out that the threshold voltages of a-IGZO TFTs are shifted markedly by exposure to light, even at subgap energies [78,79]. For photonic devices, the strong photoresponse may be good news, and the photoexcited carriers in a-IGZO fi lms appear to have long lifetimes.…”

Section: Summary: Present and Future Issuesmentioning

confidence: 99%

Material characteristics and applications of transparent amorphous oxide semiconductors

2010

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A morphous semiconductors have created a new area of electronics known as 'giant microelectronics' typifi ed by devices such as solar cells and active-matrix (AM) fl at-panel displays. Single-crystalline semiconductor technology, typifi ed by crystal silicon electronics, is unsuitable for such applications, whereas amorphous or polycrystalline fi lms can be easily formed over large areas of greater than 1 m 2 at low temperature (e.g. < 400 °C) on both glass and plastic substrates, facilitating these new applications. Due to carrier scattering and trapping at defects on grain boundaries in polycrystalline materials (the grain boundary problem), hydrogenated amorphous silicon (a-Si:H) has been used more widely than polycrystalline silicon (p-Si) for practical large-size applications. However, the critical obstacles to be overcome to realize a-Si:H in future applications are low mobility (< 1 cm 2 /V s) and instability against electric stress and photo-illumination.In late 2004, we reported that an amorphous oxide semiconductor (AOS) with the composition a-InGaZnO 4 (a-IGZO) can be applied in the fabrication of fl exible, transparent thin-fi lm transistors (TFTs) having much improved performance compared to conventional TFTs based on a-Si:H and organic materials [1]. AOS materials have superior characteristics to conventional semiconductors, and therefore AOS TFT technology has grown very rapidly toward the realization of TFT backplanes for next-generation flat-panel displays. As summarized in Figure 1, a variety of prototype AM displays have been demonstrated by several companies within the last fi ve years since the fi rst report of AOS TFTs. Herein, we review the unique characteristics of AOS materials in relation to their TFT characteristics, and discuss why AOSs have such attractive electrical properties related to the electronic structures specifi c to transparent oxides. Active-matrix displays and circuits based on AOS TFT arraysTh e fi rst AOS-TFT was reported in late 2004 (see Figure 1). Just one year later, Toppan Printing quickly followed with the fi rst AM display based on AOS as a fl exible black-and-white electronic paper (e-paper) using a-IGZO TFTs

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Section: Summary: Present and Future Issuesmentioning

confidence: 99%

Material characteristics and applications of transparent amorphous oxide semiconductors

2010

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“…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.…”

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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“…Takechi et al reported that these traps are light-induced oxygen interstitials. 12 The trapped charges enhance the TFT conductance and remain for a long period of time leading to a persistent photoconductivity (PPC). G€ orrn et al 13 and Gosain et al…”

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Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistors

Kiazadeh

Gomes

Barquinha

et al. 2016

Applied Physics Letters

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The impact of a parylene top-coating layer on the illumination and bias stress instabilities of indium-gallium-zinc oxide thin-film transistors (TFTs) is presented and discussed. The parylene coating substantially reduces the threshold voltage shift caused by continuous application of a gate bias and light exposure. The operational stability improves by 75%, and the light induced instability is reduced by 35%. The operational stability is quantified by fitting the threshold voltage shift with a stretched exponential model. Storage time as long as 7 months does not cause any measurable degradation on the electrical performance. It is proposed that parylene plays not only the role of an encapsulation layer but also of a defect passivation on the top semiconductor surface. It is also reported that depletion-mode TFTs are less sensitive to light induced instabilities. This is attributed to a defect neutralization process in the presence of free electrons.

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Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO₄ Thin-Film Transistors

Cited by 132 publications

References 13 publications

Material characteristics and applications of transparent amorphous oxide semiconductors

Material characteristics and applications of transparent amorphous oxide semiconductors

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

Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistors

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Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO4 Thin-Film Transistors

Cited by 132 publications

References 13 publications

Material characteristics and applications of transparent amorphous oxide semiconductors

Material characteristics and applications of transparent amorphous oxide semiconductors

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

Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistors

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Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO₄ Thin-Film Transistors