Engineering titanium and aluminum oxide composites using atomic layer deposition

Abaffy, N. Biluš; McCulloch, D. G.; Partridge, J. G.; Evans, P. J.; Triani, Gerry

doi:10.1063/1.3667134

Cited by 13 publications

(4 citation statements)

References 39 publications

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“…This structure cannot be upheld in a bulk crystal. In accordance with the TiO 2 -free reference Al 2 O 3 sample of ref , it is therefore concluded that all ALD-Al 2 O 3 -based films, i.e., pure films and monolayers sandwiched between SiO 2 , have only a tetrahedral O coordination. This is supported by molecular dynamics structure studies of amorphous Al 2 O 3 that calculated 85% 4-fold coordination (plus 13% 5-fold coordination) for densities of 3.0 g/cm 3 , a typical value for ALD-Al 2 O 3 deposited at elevated temperatures. , …”

Section: Resultssupporting

confidence: 80%

Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density

Hiller

Göttlicher

Steininger

et al. 2018

ACS Appl. Mater. Interfaces

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AlO on Si is known to form an ultrathin interfacial SiO during deposition and subsequent annealing, which creates a negative fixed charge ( Q) that enables field-effect passivation and low surface recombination velocities in Si solar cells. Various concepts were suggested to explain the origin of this negative Q. In this study, we investigate Al-O monolayers (MLs) from atomic layer deposition (ALD) sandwiched between deliberately grown/deposited SiO films. We show that the Al atoms have an ultralow diffusion coefficient (∼4 × 10 cm/s at 1000 °C), are deposited at a constant rate of ∼5 × 10 Al atoms/(cm cycle) from the first ALD cycle, and are tetrahedral O-coordinated because the adjacent SiO imprints its tetrahedral near-order and bond length into the Al-O MLs. By variation in the tunnel-SiO thickness and the number of Al-O MLs, we demonstrate that the tetrahedral coordination alone is not sufficient for the formation of Q but that a SiO/AlO interface within a tunneling distance from the substrate must be present. The Al-induced acceptor states at these interfaces have energy levels slightly below the Si valence band edge and require charging by electrons from either the Si substrate or from Si/SiO dangling bonds to create a negative Q. Hence, tunneling imposes limitations for the SiO and AlO layer thicknesses. In addition, Coulomb repulsion between the charged acceptor states results in an optimum number of Al-O MLs, i.e., separation of both interfaces. We achieve maximum negative Q of ∼5 × 10 cm (comparable to thick ALD-AlO on Si) with ∼1.7 nm tunnel-SiO and just seven ALD-AlO cycles (∼8 Å) after optimized annealing at 850 °C for 30 s. The findings are discussed in the context of a passivating, hole-selective tunnel contact for high-efficiency Si solar cells.

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Section: Resultssupporting

confidence: 80%

Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density

Hiller

Göttlicher

Steininger

et al. 2018

ACS Appl. Mater. Interfaces

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“…10,11 Especially Al2O3 / TiO2 nanolaminates have applications in optics, 10,19 because the Al2O3 is a low-refractive-index and the TiO2 a high-refractive-index material. 20 In mixed oxides 21 (Al2O3 and TiO2) and Al2O3 / TiO2 nanolaminates, 22 tailored optical properties varying from Al2O3 to TiO2 with gradual composition change have been demonstrated. Electrical properties 23,24 can be tuned by adjusting either the TiO2 fraction 25,26 or the bilayer thickness 27,28,29,30 or with an interfacial layers.…”

Section: Fig 1 (Color Online)mentioning

confidence: 99%

Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties

Ylivaara¹,

Kilpi²,

Liu

et al. 2016

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Atomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110–300 °C), film thickness (20–300 nm), bilayer thickness (0.1–100 nm), and TiO2 content (0%–100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon.

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“…Figure 2e shows the X‐ray absorption near‐edge structure (XANES) of the oxygen K‐edge, which mainly presents TiO 2 peaks instead of those of ALD aAlO x . [ 23 ] ALD aAlO x usually contains OH groups and carbon–oxygen (CO) molecules, resulting in oxygen vacancies. [ 13a ] The annealing process enables the OH groups to escape.…”

Section: Resultsmentioning

confidence: 99%

Chain‐Like Semiconductive Fillers for Dielectric Enhancement and Loss Reduction of Polymer Composites

Wu,

Karlin,

Beilin

et al. 2024

Advanced Materials

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Dielectric composites have attracted considerable attention because of their enhanced dielectric properties, which are highly required in electrical devices and systems. Dielectric loss is a crucial factor in determining the long‐term endurance for security and energy loss assessment. Here, chain‐like semiconductive fibers of titanium oxide, and indium, niobium‐doped titanium oxide were used for enhancing the complex dielectric properties of a polymer through composite construction, which involves significant interface enhancements. The chain‐like fibers significantly enhanced the dielectric constant owing to the special morphology of the fillers and their interfacial polarization, especially at higher temperatures. The dielectric loss and electrical conductivity of the composites were substantially reduced across the entire investigated temperature range, achieved by passivating the fiber surface with an alumina shell using atomic layer deposition (ALD). The as‐deposited alumina shell was transformed from an amorphous to a crystalline phase through thermal annealing. This results in a porous shell and more effective suppression of the loss tangent and electrical conductivity, indicating lowered interfacial polarization. A plausible mechanism for loss suppression is associated with carrier movement along the surface of the fibers and bulk (semiconductive fillers), leading to a larger loss tangent. The alumina shell blocked the carrier transport path, particularly at the interfaces, resulting in a reduced interfacial polarization contribution and energy storage loss. This study provides a method for inhibiting dielectric loss in dielectric composites by fabricating fillers with special shapes and surface chemistry.This article is protected by copyright. All rights reserved

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Engineering titanium and aluminum oxide composites using atomic layer deposition

Cited by 13 publications

References 39 publications

Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density

Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density

Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties

Chain‐Like Semiconductive Fillers for Dielectric Enhancement and Loss Reduction of Polymer Composites

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Engineering titanium and aluminum oxide composites using atomic layer deposition

Cited by 13 publications

References 39 publications

Structural Properties of Al–O Monolayers in SiO2 on Silicon and the Maximization of Their Negative Fixed Charge Density

Structural Properties of Al–O Monolayers in SiO2 on Silicon and the Maximization of Their Negative Fixed Charge Density

Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties

Chain‐Like Semiconductive Fillers for Dielectric Enhancement and Loss Reduction of Polymer Composites

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Product

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Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density

Structural Properties of Al–O Monolayers in SiO₂ on Silicon and the Maximization of Their Negative Fixed Charge Density