Electrical Instability of RF Sputter Amorphous In-Ga-Zn-O Thin-Film Transistors

Fung, Tze-Ching; Abe, Katsumi; Kumomi, Hideya; Kanicki, Jerzy

doi:10.1109/jdt.2009.2020611

Cited by 111 publications

(57 citation statements)

References 30 publications

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“…In the range of n 4 10 20 cm − 3 , which is typical under PBS and CS conditions, the estimated α energy barriers are 0.0-1.4 eV in good agreement with the experiments (0.08-0.95 eV). [15][16][17][18][19][20]22 The thermal activation energy for electron detrapping (E a, detrap ) (after stopping the PBS or CS) has also been measured. This value can be interpreted as the β energy barrier in the (In*-M) 2 − → NS+2e − transition.…”

Section: Undercoordinated Indium As An Intrinsic Electron-trap Centermentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

“…A negatively charged deep level has been hypothesized to be created in experiments, accompanied by a positive shift of the threshold voltage. 20 The experimentally measured thermal activation energy for electron trapping (E a,trap ) is in the range of 0.22-0.95 eV [15][16][17][18][19]22 under PBS and 0.08-0.14 eV 20 under CS. The α energy barrier in the (In*-M) 2 − formation corresponds to these values, which vary depending on the carrier concentration (Figure 4b).…”

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confidence: 99%

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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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Section: Undercoordinated Indium As An Intrinsic Electron-trap Centermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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

Nahm

Kim

2014

NPG Asia Mater

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“…Furthermore, Ψ S is almost equal to Ψ sub in the subthreshold region, and it is almost equal to Ψ abv in the above threshold region. In addition, in the subthreshold region, Ψ abv is larger than Ψ sub since the localized charges are neglected in (12). Similarly, in the above threshold region, Ψ sub is larger than Ψ abv since the free electrons are neglected in (11).…”

Section: Threshold Voltage Modelmentioning

confidence: 99%

A physics-based model of threshold voltage for amorphous oxide semiconductor thin-film transistors

Chen

Zhou

et al. 2016

AIP Advances

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In the application of the Lambert W function, the surface potential for amorphous oxide semiconductor thin-film transistors (AOS TFTs) under the subthreshold region is approximated by an asymptotic equation only considering the tail states. While the surface potential under the above-threshold region is approximated by another asymptotic equation only considering the free carriers. The intersection point between these two asymptotic equations represents the transition from the weak accumulation to the strong accumulation. Therefore, the gate voltage corresponding to the intersection point is defined as threshold voltage of AOS TFTs. As a result, an analytical expression for the threshold voltage is derived from this novel definition. It is shown that the threshold voltage achieved by the proposed physics-based model is agreeable with that extracted by the conventional linear extrapolation method. Furthermore, we find that the free charge per unit area in the channel starts increasing sharply from the threshold voltage point, where the concentration of the free carriers is a little larger than that of the localized carriers. The proposed model for the threshold voltage of AOS TFTs is not only physically meaningful but also mathematically convenient, so it is expected to be useful for characterizing and modeling AOS TFTs.

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“…Much experimental [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and theoretical [19][20][21] effort has been done to reveal the origin of the threshold voltage (V th ) instability in a-IGZO TFTs and improve the process conditions to minimize it. V th instabilities under positive gate bias stress (PBS) or negative gate bias stress (NBS) are not severe [5]. Negative gate bias stress under visible-light illumination (NBIS), however, causes huge negative V th shifts as much as a few volts within a few hours [6].…”

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Influence of gate dielectric/channel interface engineering on the stability of amorphous indium gallium zinc oxide thin-film transistors

Cho

Ryu

Kim

et al. 2014

Phys. Status Solidi A

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We report the simultaneous improvements of the threshold voltage (V th ) stabilities under the prolonged positive gate bias stress (PBS) and negative gate bias under illumination stress (NBIS) by employing the gate dielectric/channel interface engineering in the bottom-gate, DC-sputtered amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFT). In the interfacial region, a-IGZO is grown under the low oxygen partial pressure (P O2 ) condition to minimize the damage from highly energetic oxygen anion bombardment into the substrate during sputtering. Meanwhile, high P O2 is employed during the bulk growth of active film to reduce the oxygen vacancy (V O ) related defects in a-IGZO, which is known to be a main cause for the degradation of the electrical properties of TFT under NBIS. Owing to the lower damage of the gate dielectric by interface engineering during sputter deposition, the charge trapping or injection probability into the gate dielectric is diminished. Consequently, V th instabilities due to both the electron trapping under PBS and the trapping of positively charged species under NBIS are alleviated simultaneously.

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Electrical Instability of RF Sputter Amorphous In-Ga-Zn-O Thin-Film Transistors

Cited by 111 publications

References 30 publications

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

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

A physics-based model of threshold voltage for amorphous oxide semiconductor thin-film transistors

Influence of gate dielectric/channel interface engineering on the stability of amorphous indium gallium zinc oxide thin-film transistors

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