Atomic Layer Deposition Al2O3 Research Articles

A flexible and free-standing silicon-based anode with a rational yolk-shell structure for high-performance lithium-ion batteries

Silicon is arousing considerable interest as a potential material for the anode of lithium-ion batteries (LIBs) owing to its proper discharge voltage and outstanding specific capacity. However, the inferior electrical conductivity, enormous volume variation, and slow Li+ propagation kinetics of Si severely hinder its application. Here, a free-standing and flexible silicon/carbon nanofibers composite with a yolk-shell structure (Si@void@CNFs) is designed, which consists of a yolk synthesized by sodiothermic reduction of SiO2 at a comparatively low temperature (450 ºC), a shell generated via electrospinning technique, and a void formed through etching atomic layer deposition (ALD) Al2O3 coating with dilute HCl. The as-prepared Si@void@CNFs anode employed in LIBs displays a large initial discharge capacity of 2828 mAh g−1 with a perfect Coulombic efficiency of 71 % at 0.2 A g−1, significantly improved cycle stability retaining a large specific capacity of 952 mAh g−1 after 200 cycles, and remarkable rate performance (1725, 1567, 1391, 1121, and 719 mAh g−1 at 0.2, 0.5, 1, 2, and 4 A g−1). The superior electrochemical behaviour of the free-standing Si@void@CNFs is imputed to the cooperative effects of the mechanically robust CNFs shell, the porous silicon yolk, and the rational yolk-shell structure.

Molecular Mechanism of Selective Al2O3 Atomic Layer Deposition on Self-Assembled Monolayers.

Area-selective atomic layer deposition (AS-ALD) of insulating metallic oxide layers could be a useful nanopatterning technique for making increasingly complex semiconductor circuits. Although the alkanethiol self-assembled monolayer (SAM) has been considered promising as an ALD inhibitor, the low inhibition efficiency of the SAM during ALD processes makes its wide application difficult. We investigated the deposition mechanism of Al2O3 on alkanethiol-SAMs using temperature-dependent vibrational sum-frequency-generation spectroscopy. We found that the thermally induced formation of gauche defects in the SAMs is the main causative factor deteriorating the inhibition efficiency. Here, we demonstrate that a discontinuously temperature-controlled ALD technique involving self-healing and dissipation of thermally induced stress on the structure of SAM substantially enhances the SAM's inhibition efficiency and enables us to achieve 60 ALD cycles (6.6 nm). We anticipate that the present experimental results on the ALD mechanism on the SAM surface and the proposed ALD method will provide clues to improve the efficiency of AS-ALD, a promising nanoscale patterning and manufacturing technique.

Nucleation dependence of atomic layer deposition on diamond surface termination

Surface termination and interfacial interactions are critical for advanced solid-state quantum applications. In this paper, we demonstrate that atomic layer deposition (ALD) can both provide valuable insight on the chemical environment of the surface, having sufficient sensitivity to distinguish between the common diamond (001) surface termination types and passivate these interfaces as desired. We selected diamond substrates exhibiting both smooth and anomalously rough surfaces to probe the effect of morphology on ALD nucleation. We use high resolution in situ spectroscopic ellipsometry to monitor the surface reaction with sub-angstrom resolution, to evaluate the nucleation of an ALD Al2O3 process as a function of different ex and in situ treatments to the diamond surface. In situ water dosing and high vacuum annealing provided the most favorable environment for nucleation of dimethylaluminum isopropoxide and water ALD. Hydrogen termination passivated both smooth and rough surfaces while triacid cleaning passivated the smooth surface only, with striking effectiveness.

Rational selection of the oxygen source for atomic layer deposition Al2O3 insulators

Insulating gate dielectric is an important component of thin film transistors (TFT) and non-volatile memories, whose properties directly affect the electrical performance of the devices. In this study, the Al2O3 insulators were prepared by atomic layer deposition (ALD) using different oxygen sources and their properties were systematically studied. Based on the two-step oxidation method (H2O + O3), the Al2O3 thin films exhibited a small gate leakage current and a big breakdown field of 9 MV/cm. However, the use of the O3 increased the C-related impurities causing a large sweep hysteresis voltage of the TFTs, i.e., 8.65 V and 4.66 V for that with Al2O3 (O3) and Al2O3 (H2O + O3), respectively. Attributed to a small amount of impurities in the Al2O3 (H2O) insulators as well as the appropriate amount of Al element diffusion at the Al2O3/ZnO interface, the TFTs using Al2O3 (H2O) as insulators presented a high mobility of 36.1 cm2V−2s−1, a subthreshold swing of 0.25 V/dec and a small sweep hysteresis voltage of 0.42 V. Therefore, the properties of the ALD-Al2O3 films can be easily controlled by changing the type of the oxidizer. The Al2O3 thin films with H2O as oxidant can be used as the insulators of the TFTs, while the Al2O3 thin films based on O3 have great potential as the charge trap layer of the memories.

In Vitro Study of Zirconia Surface Modification for Dental Implants by Atomic Layer Deposition.

Zirconia is a promising material for dental implants; however, an appropriate surface modification procedure has not yet been identified. Atomic layer deposition (ALD) is a nanotechnology that deposits thin films of metal oxides or metals on materials. The aim of this study was to deposit thin films of titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), and zinc oxide (ZnO) on zirconia disks (ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn, respectively) using ALD and evaluate the cell proliferation abilities of mouse fibroblasts (L929) and mouse osteoblastic cells (MC3T3-E1) on each sample. Zirconia disks (ZR; diameter 10 mm) were fabricated using a computer-aided design/computer-aided manufacturing system. Following the ALD of TiO2, Al2O3, SiO2, or ZnO thin film, the thin-film thickness, elemental distribution, contact angle, adhesion strength, and elemental elution were determined. The L929 and MC3T3-E1 cell proliferation and morphologies on each sample were observed on days 1, 3, and 5 (L929) and days 1, 4, and 7 (MC3T3-E1). The ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn thin-film thicknesses were 41.97, 42.36, 62.50, and 61.11 nm, respectively, and their average adhesion strengths were 163.5, 140.9, 157.3, and 161.6 mN, respectively. The contact angle on ZR-Si was significantly lower than that on all the other specimens. The eluted Zr, Ti, and Al amounts were below the detection limits, whereas the total Si and Zn elution amounts over two weeks were 0.019 and 0.695 ppm, respectively. For both L929 and MC3T3-E1, the cell numbers increased over time on ZR, ZR-Ti, ZR-Al, and ZR-Si. Particularly, cell proliferation in ZR-Ti exceeded that in the other samples. These results suggest that ALD application to zirconia, particularly for TiO2 deposition, could be a new surface modification procedure for zirconia dental implants.

Carrier Recombination Dynamics of Surface-Passivated Epitaxial (100)Ge, (110)Ge, and (111)Ge Layers by Atomic Layer Deposited Al2O3

Germanium (Ge) and its heterostructures with compound semiconductors offer a unique optoelectronic functionality due to its pseudo-bandgap nature, that can be transformed to a direct bandgap material by providing strain and/or mixing with tin. Moreover, two crystal surfaces, (100)Ge and (110)Ge, that are technologically important for ultralow power fin or nanosheet transistors, could offer unprecedented properties with reduced surface defects after passivating these surfaces by atomic layer deposited (ALD) dielectrics. In this work, the crystallographically oriented epitaxial Ge/AlAs heterostructures were grown and passivated with ALD Al2O3 dielectrics, and the microwave photoconductive decay (μ-PCD) technique was employed to evaluate carrier lifetimes at room temperature. The X-ray photoelectron spectroscopy analysis reveals no role of orientation effect in the quality of the ALD Al2O3 dielectric on oriented Ge layers. The carrier lifetimes measured using the μ-PCD technique were benchmarked against unpassivated Ge/AlAs heterostructures. Excitation wavelengths of 1500 and 1800 nm with an estimated injection level of ∼1013 cm–3 were selected to measure the orientation-specific carrier lifetimes. The carrier lifetime was increased from 390 ns to 565 ns for (100)Ge and from 260 ns to 440 ns for (110)Ge orientations with passivation, whereas the carrier lifetime is almost unchanged for (111)Ge after passivation. This behavior indicates a strong dependence of the measured lifetime on surface orientation and surface passivation. The observed increase (>1.5×) in lifetime with Al2O3-passivated (100)Ge and (110)Ge surfaces is due to the lower surface recombination velocity compared to unpassivated Ge/AlAs heterostructures. The enhancement of carrier lifetime from passivated Ge/AlAs heterostructures with (100)Ge and (110)Ge surface orientations offers a path for the development of nanoscale transistors due to the reduced interface state density.

Ga2O3@Al2O3 Core–Shell Nanowires for High-Performance Solar-Blind Photodetectors

High-performance solar-blind photodetectors (SBPDs) have been indispensable in both military and civilian applications. Herein, Ga2O3@Al2O3 core–shell nanowires (NWs) are synthesized by plasma-enhanced atomic layer deposition (PEALD) Al2O3 layer on the surface of Ga2O3 nanowires. The Ga2O3@Al2O3 NW has a length of tens of micrometers, and the thickness of Ga2O3 and Al2O3 layers in the NW is approximately 30 and 5 nm, respectively. The PEALD method passivates surface defects to improve the crystal quality of Ga2O3. The metal–semiconductor–metal (MSM) Ga2O3@Al2O3 NW-based SBPDs exhibit a superhigh sensitivity of 1.07 × 103 A/W and a high response speed of less than 83 ms at 5 V bias voltage under 254 nm irradiation. Additionally, the Ga2O3@Al2O3 NW PDs exhibit a superhigh specific detectivity of 3.38 × 1011 Jones, an external quantum efficiency (EQE) of 5.22 × 105%, and a high deep ultraviolet (DUV)/visible responsivity rejection ratio (R254/405) of 4.81 × 102. These results suggest that this method is an effective way to design and prepare high-performance photonic devices.

Plasma-enhanced atomic layer deposited SiO2 enables positive thin film charge and surface recombination velocity of 1.3 cm/s on germanium

The excellent field-effect passivation provided by aluminum oxide (Al2O3) on germanium surfaces relies on the high negative fixed charge present in the film. However, in many applications, a neutral or a positive charge would be preferred. Here, we investigate the surface passivation performance and the charge polarity of plasma-enhanced atomic layer deposited (PEALD) silicon oxide (SiO2) on Ge. The results show that even a 3 nm thick PEALD SiO2 provides a positive charge density (Qtot, ∼2.6 × 1011 cm−2) and a relatively good surface passivation (maximum surface recombination velocity SRVmax ∼16 cm/s). When the SiO2 thin film is capped with an ALD Al2O3 layer, the surface passivation improves further and a low midgap interface defect density (Dit) of ∼1 × 1011 eV−1 cm−2 is achieved. By varying the SiO2 thickness under the Al2O3 capping, it is possible to control the Qtot from virtually neutral (∼2.8 × 1010 cm−2) to moderately positive (∼8.5 × 1011 cm−2) values. Consequently, an excellent SRVmax as low as 1.3 cm/s is obtained using optimized SiO2/Al2O3 layer thicknesses. Finally, the origin of the positive charge as well as the interface defects related to PEALD SiO2 are discussed.

Interfacial Diffusion Mechanism between ALD Al2O3 passivation/Cu in Direct Bonded Copper Substrate for Power Electronics

Direct bonded copper(DBC) substrate requires surface treatments for oxidation prevention and adhesion enhancement to die-attachment. Conventional surface treatment, electroless nickel immersion gold (ENIG) has a cost and environmental problems, and immersion silver is sensitive to temperature and humidity. To solve these problems, this study presents the invention of aluminum oxide (Al2O3) passivation for DBC Cu pads, which meets the requirements of oxidation prevention and adhesion enhancement to die-attachment. Ultrathin Al2O3 passivation layers (~20nm) by atomic layer deposition(ALD) were coated on DBC Cu pads for replacing conventional ENIG and immersion silver surface finishes. This paper presents bondability and interfacial diffusion mechanism between ALD Al2O3 passivation/Cu in DBC substrate.

Tailoring the electronic states of Pt by atomic layer deposition of Al2O3 for enhanced CO oxidation performance: Experimental and theoretical investigations

Herein, atomic layer deposition (ALD)-Al2O3 films were applied as a medium to modulate the electronic states of the supported Pt. Based on the sacrificial template of ZIF-67, the ternary Co3O4/Pt/Al2O3 catalyst exhibited better performance in catalytic CO oxidation than the binary Co3O4/Pt catalyst. Both experimental and calculation results indicate the existence of charge transport between the Pt and the ALD-Al2O3 films, leading to electron-rich Pt, enhanced O2 affinity, and reduced activation energy. Interestingly, the oxidation resistance of Pt nanoparticles was visualized when annealing Co3O4/Pt/Al2O3 catalyst at high temperatures. Mechanism studies indicate the typical LH mechanism occurred in CO oxidation, showing that the co-adsorbed CO and O2 could be converted to carbonate-type *OCOO intermediates via low energy barriers. At low temperatures, CO2 was mainly produced by the lattice oxygen-mediated M-vK mechanism based on isotope labeling experiments. Our findings provide an alternative way to regulate the electronic states of noble metals by the ALD technique.

MIL-101-NH2(Fe)-Coated Nylon Microfibers for Immobilized Photocatalysts in RhB and Cr(VI) Removal.

MIL-101-NH2(Fe) is one of the effective photocatalytic metal-organic frameworks (MOFs) working under visible light. However, its powder-type form inhibits reusability in practical applications. In this study, we immobilized MIL-101-NH2(Fe) on a polymeric microfiber mesh to improve reusability while minimizing the loss of catalytic performance. To overcome the lack of surface functionality of the nylon fibers, an atomic layer deposition Al2O3 layer and NH2-BDC linker were introduced to facilitate uniform coating of the MOF on the fiber surface. The reactions of the metal precursor to the nylon substrate and NH2-BDC ligand of the MOF allow chemical bonding from the core to the shell of the entire hybrid catalytic materials. The resulting fiber-immobilized MOFs (Nylon@Al2O3@MOF) demonstrated high photocatalytic performance in the removal of RhB and Cr(VI) as representatives of organic dyes and heavy metals, respectively, while retaining over 85% of its efficiency after five cycles.

Electrical insulation improvement from interface regulation for high-temperature thin-film sensors on superalloy substrate

The stability and durability of insulation structure is crucial for the operation of thin-film sensors, especially at high temperature. However, it still faces great challenges in practical applications owing to the insulation failure during thermal cycles. In this study, an ALD Al2O3 film was introduced into the traditional TGO-sputtered Al2O3 insulation structure for interface regulation. After five thermal cycles up to 1000 °C, the modified insulation structure survived, while the control structure failed. The ALD Al2O3 layer could form denser equiaxed crystal during high-temperature crystallization, thereby preventing the propagation of cracks in sputtered Al2O3 due to volume shrinkage in phase transition. Furthermore, the ALD Al2O3 acted as a transition layer by forming semi-coherent interface with TGO Al2O3, stabilizing the multilayer insulation structure. Finally, Pt-PtRh thin-film thermocouples were fabricated on the modified insulation structure, which exhibited outstanding thermoelectric performance and stability at high temperature. Therefore, the interface regulation strategy proposed in this work could provide significant guidance for the development of high-temperature electrical insulation.

Surface Passivation of Germanium with ALD Al2O3: Impact of Composition and Crystallinity of GeOx Interlayer

Germanium is an excellent material candidate for various applications, such as field effect transistors and radiation detectors/multijunction solar cells, due to its high carrier mobilities and narrow bandgap, respectively. However, the efficient passivation of germanium surfaces remains challenging. Recently, the most promising results have been achieved with atomic-layer-deposited (ALD) Al2O3, but the obtainable surface recombination velocity (SRV) has been very sensitive to the surface state prior to deposition. Based on X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED), we show here that the poor SRV obtained with the combination of HF and DIW surface cleaning and ALD Al2O3 results from a Ge suboxide interlayer (GeOx, x < 2) with compromised quality. Nevertheless, our results also demonstrate that both the composition and crystallinity of this oxide layer can be improved with a combination of low-temperature heating and a 300-Langmuir controlled oxidation in an ultrahigh vacuum (LT-UHV treatment). This results in a reduction in the interface defect density (Dit), allowing us to reach SRV values as low as 10 cm/s. Being compatible with most device processes due to the low thermal budget, the LT-UHV treatment could be easily integrated into many future devices and applications.

Dispersion Engineering of Waveguide Microresonators by the Design of Atomic Layer Deposition

In this work, we demonstrate dispersion engineering of silicon nitride waveguide resonators with atomic layer deposition (ALD). We conducted theoretical and experimental analyses on the waveguide dispersion with air cladding, hafnium oxide (HfO2) cladding, and aluminum oxide (Al2O3) cladding. By employing ALD HfO2 as the cladding layer, the dispersion of waveguide can be tuned to a finer degree in the normal regime at a wavelength of 1550 nm. On the other hand, using ALD Al2O3 cladding provides the waveguide dispersion that spans regimes in normal, near-zero, and anomalous dispersion.

Buried Interface Passivation of Perovskite Solar Cells by Atomic Layer Deposition of Al2O3

Despite having long excited carrier lifetimes and high mobilities in hybrid halide perovskite materials, conventional (n-i-p) devices exhibit significant interfacial nonradiative recombination losses that are little understood but limit the radiative efficiency and the overall open-circuit potential. In this Letter, we reveal that the process of spiro-OMeTAD coating on perovskite gives rise to buried defect states, which are detrimental to the devices’ operational stability. We subsequently report a method to passivate these deleterious buried defect states by atomic layer deposition of Al2O3 through controlled precursor dosages on fully functional devices. The process results in notable improvements in the overall device performance, but the underlying root-cause analysis is what we essentially aimed to elucidate here. The reported passivation technique results in (a) an increase in the efficiency primarily due to an increase of VOC by ∼60–70 mV and consequently (b) enhanced photoluminescence and higher electroluminescence quantum efficiency and (c) overall device operational (MPPT) stability under ambient and, exclusively, even under high vacuum (>300 h) conditions, which is otherwise challenging.

In situ x-ray photoelectron spectroscopy analysis of the atomic layer deposition of Al2O3 on SiO x /Si: Interface dipole and persistent surface groups

Atomic layer deposition (ALD) has become an essential technology in many areas. To better develop and use this technology, it is of the pivot to understand the surface chemistry during the ALD film growth. The growth of an ALD oxide film may also induce an electric dipole at the interface, which may be further tuned to modulate the flat band voltage for electronic device applications. To understand the associated surface chemistry and interface dipole formation process, we herein employ an in situ x-ray photoelectron spectroscopy technique to study the ALD growth of Al2O3, from trimethylaluminum and H2O, on the SiO x /Si surface. We find that an electric dipole is formed at the Al2O3/SiO x interface immediately after the first Al2O3 layer is deposited. We also observe persistent surface methyl groups in the H2O half-cycle during ALD, and the amount of the persistent methyls is particularly higher during the initial Al2O3 ALD growth, which suggests the formation of Si−CH3 on the surface. These findings can provide useful routes and insights toward interface engineering by ALD.

Area-selective atomic layer deposition of Al2O3 using inkjet-printed inhibition patterns and lift-off process

Area-selective atomic layer deposition (AS-ALD) has been studied as an alternative method for metal oxide ALD film patterning in the microelectronics industry. To perform AS-ALD, area-deactivation or -activation processes should be implemented in advance using selective surface modification through a photography-based lift-off process and printing techniques. This study introduces a novel approach for Al2O3 AS-ALD using inkjet-printed inhibition patterns. ALD-inhibition patterns with two-layer structures of fluorocarbon (FC) thin film and photoresist (PR) were patterned by inkjet printing. Low surface energy FC thin films were used to block the Al2O3 nucleation and growth during the ALD process, and PR was patterned to easily remove ALD-inhibition patterns using a lift-off process. To demonstrate AS-ALD, an Al2O3 thin film approximately 10 nm thick was deposited via an in-house built system with a multiple-slit gas source. The proposed AS-ALD method was evaluated for topological analysis using atomic force microscopy and surface composition analysis using a time of flight secondary ion mass spectrometry after Al2O3 deposition and a lift-off process. Finally, a 6 nm thick Al2O3 film was selectively patterned by the lift-off process using an inkjet-printed 1.28 μm thick FC-covered PR inhibition pattern.

Al2O3 Ultra-Thin Films Deposited by PEALD for Rubidium Optically Pumped Atomic Magnetometers with On-Chip Photodiode

This communication shows the recipe for plasma-enhanced atomic layer deposition (PEALD) Al2O3 ultra-thin films with thicknesses below 40 nm. Al2O3 ultra-thin films were deposited by PEALD to improve the rubidium optically pumped atomic magnetometers’ (OPMs) cell lifetime. This requirement is due to the consumption of the alkali metal (rubidium) inside the vapor cells. Moreover, as a silicon wafer was used, an on-chip photodiode was already integrated into the fabrication of the OPM. The ALD parameters were achieved with a GPC close to 1.2 Å/cycle and the ALD window threshold at 250 °C. The PEALD Al2O3 ultra-thin films showed a refractive index of 1.55 at 795 nm (tuned to the D1 transition of rubidium for spin-polarization of the atoms). The EDS chemical elemental analysis showed an atomic percentage of 58.65% for oxygen (O) and 41.35% for aluminum (Al), with a mass percentage of 45.69% for O and 54.31% for Al. A sensitive XPS surface elemental composition confirmed the formation of the PEALD Al2O3 ultra-thin film with an Al 2s peak at 119.2 eV, Al 2p peak at 74.4 eV, and was oxygen rich. The SEM analysis presented a non-uniformity of around 3%. Finally, the rubidium consumption in the coated OPM was monitored. Therefore, PEALD Al2O3 ultra-thin films were deposited while controlling their optical refractive index, crystalline properties, void fraction, surface roughness and thickness uniformity (on OPM volume 1 mm × 1 mm × 0.180 mm cavity etched by RIE), as well as the chemical composition for improving the rubidium OPM lifetime.

Surface functionalization of microporous carbon fibers by vapor phase methods for CO2 capture

The removal of excess CO2 from the atmosphere is expected to play a major role in the mitigation of global warming. Solid-state adsorbents, consisting of CO2-binding functionalities on porous supports, can provide high CO2 capture capacities with low energy requirements. In this contribution, we report on the vapor-phase functionalization of porous carbon fibers with amine functionalities. Functionalization occurs either via direct exposure to cyclic azasilane molecules (2,2-dimethoxy-1,6-diaza-2-silacyclooctane) or by the atomic layer deposition of Al2O3 followed by exposure to azasilane. XPS analysis and SEM/energy-dispersive x-ray spectroscopy (EDX) measurements confirmed Al2O3 deposition and amine functionalization. Yet, the two different functionalization approaches led to different amine loadings and distinct differences in porosity upon functionalization, which affected CO2 capture. Combining Al2O3 and amine functionalization resulted in fast CO2 sorption with superior capturing efficiency. In contrast, direct functionalization resulted in strong reduction of the surface area of the porous support and limited gas exchange. We attribute the superior capture efficiency to the porosity level achieved when combining Al2O3 and amine functionalization demonstrating that this approach might be valuable for compact high-throughput direct air, CO2 capture systems.

Room-temperature bonding of Al2O3 thin films deposited using atomic layer deposition

In this study, room-temperature wafer bonding of Al2O3 thin films on Si thermal oxide wafers, which were deposited using atomic layer deposition (ALD), was realized using the surface-activated bonding (SAB) method. Transmission electron microscopy (TEM) observations indicated that these room-temperature-bonded Al2O3 thin films appeared to work well as nanoadhesives that formed strong bond between thermally oxidized Si films. The perfect dicing of the bonded wafer into dimensions of 0.5 mm × 0.5 mm was successful, and the surface energy, which is indicative of the bond strength, was estimated to be approximately 1.5 J/m2. These results indicate that strong bonds can be formed, which may be sufficient for device applications. In addition, the applicability of different Al2O3 microstructures in the SAB method was investigated, and the effectiveness of applying ALD Al2O3 was experimentally verified. This successful SAB of Al2O3 thin films, which is a promising insulator material, opens the possibility of future room-temperature heterogenous integration and wafer-level packaging.