Influence of active layer thickness and annealing in zinc oxide TFT grown by atomic layer deposition

Ahn, Cheol Hyoun; Woo, Chang Ho; Hwang, Sooyeon; Lee, Jun Young; Cho, Hyung Koun; Cho, Hyoung Jin; Yeom, Geun Young

doi:10.1002/sia.3357

Cited by 21 publications

(18 citation statements)

References 14 publications

(8 reference statements)

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“…So, this may be related to the lack of chemical bonding sites such as O-H groups on the surface of SiO 2 34. In previous study3536, it is reported that more ALD cycles are required for full coverage of the ZnO layer on SiO 2 surface, due to deficient O-H groups on the surface of the SiO 2 . In general, it is well known that the surface of untreated Al 2 O 3 is hydrophilic due to an abundance of hydroxyl (OH − ) groups.…”

Section: Resultsmentioning

confidence: 98%

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Ahn

Senthil

Cho

et al. 2013

Sci Rep

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High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm2/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers.

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Section: Resultsmentioning

confidence: 98%

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Ahn

Senthil

Cho

et al. 2013

Sci Rep

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“…On one hand, oxygen vacancy defects with high coordination or that are negatively charged serve as shallow donors that donate free carriers to the conduction band and contribute to the conduction of the film, which are favorable for some applications such as transparent conductive oxide film. However, oxygen vacancy defects need to be carefully controlled in some applications such as TFTs, where the free carrier concentration should be controlled at a low level so that they can be depleted to achieve the off-state of the TFTs [18][19][20]. On the other hand, oxygen vacancy defects with low coordination, that are neutrally or positively charged, serve as deep trap states in the band gap.…”

Section: Introductionmentioning

confidence: 99%

Suppression of Oxygen Vacancy Defects in sALD-ZnO Films Annealed in Different Conditions

et al. 2020

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Zinc oxide (ZnO) has drawn much attention due to its excellent optical and electrical properties. In this study, ZnO film was prepared by a high-deposition-rate spatial atomic layer deposition (ALD) and subjected to a post-annealing process to suppress the intrinsic defects and improve the crystallinity and film properties. The results show that the film thickness increases with annealing temperature owing to the increment of oxide layer caused by the suppression of oxygen vacancy defects as indicated by the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectra. The film transmittance is seldom influenced by annealing. The refractive index increases with annealing temperature at 300–700 °C, possibly due to higher density and crystallinity of the film. The band gap decreases after annealing, which should be ascribed to the decrease in carrier concentration according to Burstein–Moss model. The carrier concentration decreases with increasing annealing temperature at 300–700 °C since the oxygen vacancy defects are suppressed, then it increases at 800 °C possibly due to the out-diffusion of oxygen atoms from the film. Meanwhile, the carrier mobility increases with temperature due to higher crystallinity and larger crystallite size. The film resistivity increases at 300–700 °C then decreases at 800 °C, which should be ascribed primarily to the variation of carrier concentration.

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“…It is well‐known that the electrical performances of TFT devices, including the V th , μ FE , and I On/Off ratio, strongly depend on the electrical properties of the channel layers. In this study, the as‐grown ZnO thin film has a carrier density of 8 × 10 18 cm −3 and an electrical conductivity of 1.25 × 10 2 [Ω∙cm] −1 before postannealing, which is too high to be used as a channel layer in an oxide TFT . The high background carrier density in the ZnO layers is related to oxygen vacancies and can be artificially controlled by post‐thermal treatment at oxygen ambient.…”

Section: Resultsmentioning

confidence: 99%

Extremely Thin Al₂O₃ Surface‐Passivated Nanocrystalline ZnO Thin‐Film Transistors Designed for Low Process Temperature

Ahn

Kim

et al. 2016

J. Am. Ceram. Soc.

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Nanocrystalline ZnO (nc-ZnO) thin-film transistors (TFTs) exhibit inherent instability under bias/photo stresses, which originates from the oxygen molecules adsorbed on the surface of the crystal grains. The space charge region at nanocrystal surfaces that is induced by adsorbed oxygen molecules produces a high electrical potential barrier and significantly interrupts charge transport between the source and drain in nc-ZnO TFTs. In this article, we developed high-performance TFTs via the continuous deposition of an extremely thin Al 2 O 3 layer on a nc-ZnO channel. These devices were fabricated by atomic layer deposition at an extremely low process temperature of 150°C, including both the deposition and postannealing temperatures. The nc-ZnO TFT with an extremely thin Al 2 O 3 layer (1.8 nm) showed a significantly higher mobility (25 cm 2 /Vs) compared to devices without an Al 2 O 3 layer (3.6 cm 2 /Vs). This dramatic difference was ascribed to the suppression of the chemisorption of oxygen molecules at the nanocrystal surface during thermal annealing (reducing the potential barrier width/ height between adjacent nanocrystals). Furthermore, ultrathin Al 2 O 3 -covered nc-ZnO TFTs exhibited considerably enhanced electrical/photo stability due to the reduction in adsorption/ desorption events of oxygen molecules on the nanocrystal surfaces (with no change in the depletion width after illumination) under gate bias or illumination stress.

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Influence of active layer thickness and annealing in zinc oxide TFT grown by atomic layer deposition

Cited by 21 publications

References 14 publications

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Suppression of Oxygen Vacancy Defects in sALD-ZnO Films Annealed in Different Conditions

Extremely Thin Al₂O₃ Surface‐Passivated Nanocrystalline ZnO Thin‐Film Transistors Designed for Low Process Temperature

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Influence of active layer thickness and annealing in zinc oxide TFT grown by atomic layer deposition

Cited by 21 publications

References 14 publications

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

Suppression of Oxygen Vacancy Defects in sALD-ZnO Films Annealed in Different Conditions

Extremely Thin Al2O3 Surface‐Passivated Nanocrystalline ZnO Thin‐Film Transistors Designed for Low Process Temperature

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Product

Resources

About

Extremely Thin Al₂O₃ Surface‐Passivated Nanocrystalline ZnO Thin‐Film Transistors Designed for Low Process Temperature