Al2O3 Diffusion Barrier Research Articles

Effect of oxide diffusion barrier and substrate on the reliability of stainless-steel-based CIGS solar cells

This paper investigates the effect of the oxide diffusion barrier and substrate on the residual stress and the delamination at the CIGS/Molybdenum (Mo) interface when stainless-steel-based CIGS solar cells cool down to room temperature from the CIGS deposition process (500 °C) and hotspot conditions (100, 200, 300, and 400 °C). The focus is on the performance of Al2O3 and SiO2 oxide diffusion barriers and SS 304, SS Duplex, and SS 430 substrates. Through Finite Element method (FEM) and Machine Learning (ML) simulations, we calculated the energy release rate (J integral) of the CIGS/Mo interface crack and residual stress of the CIGS layer while concurrently varying the thickness of the diffusion barrier layer from 0.1 to 3 μm and the SS substrate from 25 to 200 μm. ML algorithms were used to predict the J integral at the CIGS/Mo interface and the CIGS residual stress for arbitrary CIGS deposition temperatures. Our simulation method is validated by the agreement between some of our simulation results and experimental findings from other researchers. Based on the simulation results, the following key findings were observed 1) A thinner diffusion barrier (for both SiO2 and Al2O3) is more effective in preventing the delamination at the CIGS/Mo interface, but a thicker diffusion barrier is more effective in reducing the stress in the CIGS layer 2) SiO2 diffusion barrier is better suited for preventing the CIGS/Mo interface delamination, while an Al2O3 diffusion barrier is better suited for reducing the residual stress in the CIGS layer 3) The thickness of stainless steel substrate significantly alters the residual stress in the CIGS layer (up to ∼30 times) 4) The SS 430 substrate is better suited for minimizing the residual stress in the CIGS layer and preventing delamination at the CIGS/Mo interface. The proposed methodology can be applied to other flexible solar cells to enhance their reliability.

Highly reliable bipolar resistive switching of tantalum oxide-based memory using Al2O3 diffusion barrier layers

We present a novel bipolar resistive switching memory based on TaOx, featuring a Ru/Al2O3/Ta2O5/TaOx/Al2O3/W structure. Thin Al2O3 layers play a crucial role as diffusion barriers, preventing undesirable interfacial reactions at the top and bottom interfaces. They support the stable formation of the Schottky barrier near the Ru top electrode through redox reactions during operation, resulting in highly reliable bipolar resistive switching. The device exhibits excellent memory performance, including a fast operation speed (∼10 ns), good switching endurance (∼106 cycles), and robust data retention (>104 s at 200 °C).

Preparation and Corrosion Resistance of an Al2O3/Ni Coating on 316 Stainless Steel in Molten 52MgCl2-48NaCl Chloride Salt

In this paper, in order to improve the corrosion resistance of 316 stainless steel (316 SS) in molten chloride salt, an in situ grown Al2O3 diffusion barrier is prepared through, first, electrodepositing an inner Ni-Al/NiO composite transition layer and an outer Ni layer through double-pulse composite electroplating technique, followed by annealing at 800°C for 12 h under Ar. The obtained Al2O3/Ni composite coating is dense and shows good adherence to the substrate. Then the corrosion resistance of Al2O3/Ni composite coating in molten 52MgCl2-48NaCl (wt%) is measured through electrochemical technique and immersion tests and the corrosion mechanism is also discussed. The results show that the 316 SS is effectively protected by the Al2O3/Ni composite coating from the corrosion of molten chloride salt.

Preparation and properties of α-Al2O3 diffusion barrier on stainless steel 316

A compact and adherent Al2O3 diffusion barrier was obtained between a Ni coating and stainless steel 316 (316SS) through double-pulse composite plating coupled with in-situ thermal growth. To promote the formation of α-Al2O3 at low temperature, a Cr2O3 film was firstly prepared by pre-oxidation of 316SS. Then a Ni-Al/NiO composite coating was deposited on 316SS in a modified Watts’ bath with a Zeta potential of about +21.89 mV, a favorable condition for the co-deposition of double particles and nickel, followed by heat treatment in Ar at 800 ℃ for 12 h. Results of diffusion resistance tests at 750 and 800 ℃ for 100 h in Ar suggest that the Ni/α-Al2O3 composite coating changes slightly during the annealing treatment and significantly prevents the diffusion of Fe and Cr from 316SS substrate to the upper Ni layer. Furthermore, corrosion resistance of the composite coating is higher than that of the 316SS/Ni sample.

Diffusion barrier effect of Al2O3 layer at the interface between Mo-Si-B coating and Nb-Si based alloy

An oxidation-resistant composite coating, including Mo-Si-B layer and Al2O3 diffusion barrier, was prepared on Nb-Si-based alloy by a two-step method. The Al2O3 film was fabricated by firstly deposition of Al on the alloy through pack cementation, and then by in situ oxidation of the aluminide coating. Mo-Si-B coating was then prepared on the Al2O3 film by spark plasma sintering. The Mo-Si-B coating is mainly composed of MoSi2 and a small amount of MoB and SiO2 particles. After long-term exposure at 1250 °C, the growth of the interdiffusion zone (IDZ) was suppressed effectively at the interface with the Al2O3 diffusion barrier. The results indicate that the diffusion barrier can significantly inhibit the outward diffusion of Nb, Ti and Cr alloying elements as well as the sluggish inward consumption of Si element. The Mo-Si-B coating with Al2O3 diffusion barrier exhibited a good oxidation resistance with a mass gain of about 0.97 mg/cm2 after 500 h of oxidation.

Al2O3 Diffusion Barrier: In‐Situ Observation of the Formation of NiSi/Ni2Si Heterojunction in SiGe Nanowire with Al2O3 Diffusion Barrier Layer (Adv. Mater. Interfaces 14/2021)

In article number 2100422, Yu-Chuan Lee, Lian-Ming Lyu, and Ming-Yen Lu demonstrate the manipulation of the phases of Ni silicides when Ni diffuses into SiGe nanowire (NW) with the introduction of Al2O3 diffusion barrier. Since the diffusion barrier is very thin (≈5 nm), Ni atoms can pass through the barrier and form the NiSi/Ni2Si heterojunction with SiGe NW. This study provides the insights for fabrication of semiconducting devices.

Interdiffusion behavior of Mo-Si-B/Al2O3 composite coating on Nb-Si based alloy

Mo-Si-B/Al2O3 composite coating was applied to Nb-Si based alloys by plasma spray-physical vapor deposition (PS-PVD) followed by spark plasma sintering (SPS). Interdiffusion behavior of the coating at 1200, 1250 and 1300 °C in dry air was investigated. The results indicate that the thickness of the interdiffusion zone (IDZ) in the composite coating is smaller than that in the Al2O3-free coating. The Al2O3 diffusion barrier effectively restrains coating-substrate interdiffusion. The activation energy for IDZ growth is increased to 367 kJ/mol correspondingly, and the interdiffusion coefficient of Si is decreased by one order of magnitude.

Potential-Induced Degradation Depends on Leakage Current and Light/Electrical Bias in Cu(In,Ga)Se2 Devices

Potential-induced degradation (PID) of encapsulated Cu(In,Ga)Se2 (CIGS) solar cells was studied for different substrates: soda-lime glass (SLG), SLG with an Al2O3 diffusion barrier, and borosilicate glass (BSG). The Al2O3 and BSG samples increased the time to PID failure by 5x and 30x, respectively. The relationship between PID and coulombs transferred from the substrate to the device through leakage current differed depending on the sample type. When the (unrepresentative) dark PID stress test was interrupted to characterize devices with light/electrical bias, PID was partially reversed. In addition, applying high voltage stress to open-circuit devices was less damaging, relative to forward-biased and short-circuited cells. Light/electrical bias may therefore reduce PID by driving alkali metal cations away from the p-n junction to diminish their degrading effects. These results show that device light/electrical bias should be carefully controlled during CIGS PID testing, as it affects PID in addition to leakage current.

Dissimilar Joining of Pure Aluminum to SiCp/Al-MMCs Using an AlMgGaLi Active Interlayer Foil

To broaden the application of advanced metal matrix composites in the electronic packaging industry, a lead-free AlMgGaLi interlayer was developed for active soldering of aluminum to aluminum metal matrix composites. The effect of joining pressure on the microstructure evolution, interfacial wettability and mechanical properties of the dissimilar joints was investigated. The experimental results indicated that as the joining pressure increased, the mean thickness of the bond seam was 46.02 μm, and solidification of a solid solution occurred (detected by SEM/XRD analysis). The composition of the Al-based solid solution (in atom%) was 86.52% Al, 9.32% Mg, 2.56% O, 1.5% Ga and 0.1% Si. The pressure improved the interfacial wettability by enhancing the atom diffusion between the interlayer and parent materials. The joint shear strength initially increased and then decreased, and a sound joint with a maximum shear strength of ~ 45 MPa was produced at 450 °C and 0.75 MPa. The fracture crack initially occurred at the interfaces of the Al/filler metal and then propagated mainly along the Al2O3 layer on the Al side. A novel model describing the pressure-induced microstructure changes within the joint and the formation of an Al2O3 diffusion barrier layer at the Al/filler metal interface is proposed.

A strategy for increasing the energy release rate of aluminum by replacing the alumina passivation shell with aluminum iodate hexahydrate (AIH)

Aluminum iodate hexahydrate (AIH) is an oxidizing salt that can be synthesized on the surface of nano-aluminum (nAl) particles, replacing the inherent alumina (Al2O3) passivation shell. For nAl particles encapsulated by AIH, rates of reaction have been shown to be on a time scale relevant to a detonation. Yet, little is known about the reaction mechanism between AIH and Al or how the Al2O3 passivation shell encapsulating nAl particles affects the reaction mechanism. This study explores the reactive nature of AIH and nAl by examining ignition and energy transfer of two different AIH + nAl formulations. The first is AIH synthesized on the surface of nAl particles to a concentration ratio of 80 wt% AIH to 20 wt% nAl. This composite particle lacks the Al2O3 shell that inherently passivates nAl and replacing it with AIH, these particles will be referred to as ParticleAIH+Al. In comparison, a discrete mixture of 80 wt% AIH powder combined with 20 wt% nAl powder is also examined and the mixture is referred to as MixAIH+Al. Laser ignition studies show ignition and burn times are reduced for ParticleAIH+Al compared to MixAIH+Al, owing to the presence of the Al2O3 diffusion barrier that inhibits ignition in the MixAIH+Al. Also, flame speed measurements reveal that ParticleAIH+Al propagate at 3062 m/s while the MixAIH+Al at 1366 m/s. Further analysis using thermal equilibrium calculations show hydrogen gas generation may facilitate heat transfer and energy propagation. Equilibrium analysis using differential scanning calorimetry also show the decomposition energy of pure AIH is nearly the same as the ignition energy of ParticleAIH+Al but twice that energy is required to ignite MixAIH+Al. All of these results provide a stronger foundation for the impedance of the Al2O3 passivation shell on the rate of energy release for Al reaction under equilibrium and non-equilibrium conditions.

(Invited) Advances in Testing Inorganic & Hybrid Organic Thermoelectric Thin Films

In this work, a novel Si-based Lab-on-a-Chip test platform is introduced to perform in-plane ZT measurements of various classes of thermoelectric films with a complete set of thermoelectric test structures. The electrical conductivity σ, the Seebeck coefficient S, the thermal conductivity κ, and the power factor PF and the figure of merit ZT values can be experimentally determined in a single simultaneous measurement run as a function of temperature. It is shown that this Lab-on-a-Chip test system can be applied to classic inorganic thermoelectric films such as PbTe and PbSe and also to hybrid inorganic-organic films such as SURMOF films and as well as to conducting organic PEDOT:PSS films. Generally, the thermoelectric film can be deposited in the exposed test area of the chip by using a shadow mask. All the parameters can be measured in the temperature range of 300 K to 370 K with a 1 T magnet field. Applications are demonstrated for all three film material categories. Here, PbTe and PbSe thin films and double-layer PbTe/PbSe films were synthesized by Atomic Layer Deposition (ALD) technology directly on the pre-structured Si chip. A thin Al2O3 protection and diffusion barrier layer was applied to avoid oxidation and degradation of PbTe/PbSe films. The Seebeck coefficient, electrical conductivity and thermal conductivity for PbTe, PbSe and double-layer PbTe/PbSe film were measured simultaneously by applying in-pane ZT chips. Furthermore, this Lab-on-a-Chip test system can be extended to Surface Anchored Metal-organic-framework (SURMOF) films, which consist of quasi-liquid phase epitaxially grown highly ordered crystalline films. MOF films are designed scaffold-like compounds that consist of metal ions connected by organic ligands. Furthermore, the example of a complete thermoelectric characterization of a conductive organic polymer thin film material will be discussed.

Effects of Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings at 1100 °C

In this research, the effects of thin Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al2O3 diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al2O3/nanostructured YSZ coating at 1100 °C.

Interfacial Evolution Behavior of ZrO2(ZrB2) Active Diffusion Barrier

Two sample groups, N5/(ZrB2+ZrO2)/NiCrAl and N5/ZrO2/NiCrAl, were prepared on Ni-based single crystal alloy (Rene N5) substrate by electron beam physical vapor deposition (EB-PVD). Both sample groups were exposed to isothermal oxidation at 900 °C for 5 h and at 1000 °C, for 250 h, 300 h or 350 h. The microstructural evolution and deterioration failure behavior was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results suggest that the introduction of ZrB2 decelerates the interfacial reaction rate of the active diffusion barrier of Al2O3 but does not affect the final formation of the Al2O3 diffusion barrier with anti-diffusion properties. Moreover, the introduction of ZrB2 prolongs the service life of active diffusion barrier structure and changes its failure mode.

Formation of Al2O3 diffusion barrier in cold-sprayed NiCoCrAlY/Ni multi-layered coatings on 304SS substrate

Abstract This work deals with a double-layer coating for the corrosion protection of stainless steel (SS) structures used in molten fluoride salt reactors for energy production. It aims to mitigate the dissolution of chromium from stainless steel structures into the molten salts. On 304SS substrates, three coating layers consisting of NiCoCrAlY, Ni(O), and the nickel layer on the top were deposited by cold spraying. The Ni(O) coating was made by using a powder containing active oxygen and prepared by mechanical-alloyed pure Ni powders in ambient atmosphere. The Al 2 O 3 diffusion barrier was evolved by annealing the cold-sprayed coating system in argon at temperatures ranging from 800 to 1000 °C at the interface between NiCoCrAlY and Ni(O) layers. During the annealing, the Al 2 O 3 layer formed with a growth following a parabolic law, resulting from the reaction of the oxygen in the Ni (O) layer with the aluminium in the NiCoCrAlY layer. The coating test conducted at 900 °C for 100 h in argon showed that the Al 2 O 3 layer changed little during annealing and could effectively prevent the diffusion of Fe and Cr from the SS substrate to the upper Ni layer.

Inhibition of Rh sintering and improved reducibility of Rh on ZrO2 nanocomposite with an Al2O3 diffusion barrier

To enhance the durability of Rh catalysts for vehicle emissions control, a novel support, Nd-A80ZL, was designed. This support was composed of La2O3-stabilized ZrO2 particles that contained a Nd2O3-enriched surface layer and nanosized Al2O3 particles, which acted as a diffusion barrier. Nd2O3 was mainly loaded on ZrO2 after high-temperature aging, as anticipated. Then, Rh was also mainly loaded on the ZrO2 with the Nd2O3 surface enrichment; the inhibition of Rh sintering during the aging test suggests that the surface Nd2O3 functioned as anchoring sites for Rh. The results of the hydrogen temperature-programmed reduction showed that Rh on the Nd-A80ZL support was more easily reduced than that on a La2O3-stabilized ZrO2 support with Nd2O3 surface enrichment (Nd-ZL). Rh/Nd-A80ZL also had a more appropriate solid basicity than Rh/Nd-ZL. These results showed that the introduced Al2O3 diffusion barrier in Nd-A80ZL controlled the basicity derived from the addition of Nd2O3 and balanced the inhibition of Rh sintering and Rh reducibility.

Roll-to-roll atomic layer deposition process for flexible electronics encapsulation applications

At present flexible electronic devices are under extensive development and, among them, flexible organic light-emitting diode displays are the closest to a large market deployment. One of the remaining unsolved challenges is high throughput production of impermeable flexible transparent barrier layers that protect sensitive light-emitting materials against ambient moisture. The present studies deal with the adaptation of the atomic layer deposition (ALD) process to high-throughput roll-to-roll production using the spatial ALD concept. We report the development of such a process for the deposition of 20 nm thickness Al2O3 diffusion barrier layers on 500 mm wide polymer webs. The process uses trimethylaluminum and water as precursors at a substrate temperature of 105 °C. The observation of self-limiting film growth behavior and uniformity of thickness confirms the ALD growth mechanism. Water vapor transmission rates for 20 nm Al2O3 films deposited on polyethylene naphthalate (PEN) substrates were measured as a function of substrate residence time, that is, time of exposure of the substrate to one precursor zone. Moisture permeation levels measured at 38 °C/90% relative humidity by coulometric isostatic–isobaric method were below the detection limit of the instrument (<5 × 10−4 g/m2 day) for films coated at web moving speed of 0.25 m/min. Measurements using the Ca test indicated water vapor transmission rates ∼5 × 10−6 g/m2 day. Optical measurements on the coated web showed minimum transmission of 80% in the visible range that is the same as the original PEN substrate.

Controlled aluminum-induced crystallization of an amorphous silicon thin film by using an oxide-layer diffusion barrier

Aluminum-induced crystallization (AIC) of amorphous silicon with an Al2O3 diffusion barrier was investigated for controlling Si crystallization and preventing layer exchange during the annealing process. An Al2O3 layer was deposited between the a-Si and the Al films (a-Si/Al2O3/Al/Glass) and was blasted with an air spray gun with alumina beads to form diffusion channels between the Si and the Al layers. During the annealing process, small grain SixAl seeds were formed at the channels. Then, the Al2O3 diffusion barrier was restructured to close the channels and prevent further diffusion of Al atoms into the a-Si layer. A polycrystalline Si film with (111), (220) and (311) crystallization peaks in the X-ray diffraction pattern was formed by annealing at 560 °C in a conventional furnace. That film showed a p-type semiconducting behavior with good crystallinity and a large grain size of up to 14.8 µm. No layer conversion occurred between the Si and the Al layers, which had been the fundamental obstacle to the applications in the crystallization of a-Si films by using the AIC method.

High temperature stability of electrically conductive Pt–Rh/ZrO2 and Pt–Rh/HfO2 nanocomposite thin film electrodes

Nanocomposite films made up of either Pt–Rh/ZrO2 or Pt–Rh/HfO2 materials were co-deposited using multiple e-beam evaporation sources onto langasite (La3Ga5SiO14) substrates, both as blanket films and as patterned interdigital transducer electrodes for surface acoustic wave sensor devices. The films and devices were tested after different thermal treatments in a tube furnace up to 1,200 °C. X-ray diffraction and electron microscopy results indicate that Pt–Rh/HfO2 films are stabilized by the formation of monoclinic HfO2 precipitates after high temperature exposure, which act as pinning sites to retard grain growth and prevent agglomeration of the conductive cubic Pt–Rh phase. The Pt–Rh/ZrO2 films were found to be slightly less stable, and contain both tetragonal and monoclinic ZrO2 precipitates that also helps prevent Pt–Rh agglomeration. Film conductivities were measured versus temperature for Pt–Rh/HfO2 films on a variety of substrates, and it was concluded that La and/or Ga diffusion from the langasite substrate into the nanocomposite films is detrimental to film stability. An Al2O3 diffusion barrier grown on langasite using atomic layer deposition was found to be more effective than a SiAlON barrier layer in minimizing interdiffusion between the nanocomposite film and the langasite crystal at temperatures above 1,000 °C.

Structural Evolution and the Control of Defects in Atomic Layer Deposited HfO2–Al2O3 Stacked Films on GaAs

The structural characteristics and interfacial reactions of bilayered dielectric stacks of 3 nm HfO2/2 nm Al2O3 and 3 nm Al2O3/2 nm HfO2 on GaAs, prepared by atomic layer deposition (ALD), were examined during film growth and the postannealing process. During the postdeposition annealing (PDA) of the Al2O3/HfO2/GaAs structures at 700 °C, large amounts of Ga oxides were generated between the Al2O3 and HfO2 films as the result of interfacial reactions between interdiffused oxygen impurities and out-diffused atomic Ga. However, in the case of the HfO2/Al2O3/GaAs structures, the presence of an Al2O3 buffer layer effectively blocked the out-diffusion of atomic Ga, thus suppressing the formation of Ga oxide. Microstructural analyses showed that HfO2 films that were deposited on Al2O3/GaAs had completely crystallized during the PDA process, even at 700 °C, because of the Al2O3 diffusion barrier. Capacitance-voltage measurements showed a relatively large frequency dispersion of the Al2O3/HfO2/GaAs structure in accumulation capacitance compared to the HfO2/Al2O3/GaAs structure due to a higher interface state density. Conductance results revealed that the Al2O3 buffer layer on GaAs resulted in a significant reduction in gap states in GaAs. The induced gap state in the Al2O3/HfO2/GaAs structure originated from the out-diffusion of atomic Ga into the HfO2 film. Density functional theory calculations supported this conclusion.

M-13 Determination of Wear Behaviour of Titanium Alloys Implant Materials Blasted With Mixture of Zirconia/Silica/Hydroxyapatite Powders

In this research, the effects of thin Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al2O3 diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al2O3/nanostructured YSZ coating at 1100 °C.