Aluminum Thin Films Research Articles

Demonstration of Single Photon Detection in Amorphous Molybdenum Silicide / Aluminium Superconducting Nanostrip

Single photon detectors (SPD) are largely used when the signal to be measured is particularly low or if high accuracy, timing resolution and low noise are required. About twenty years ago, a new type of SPD based on superconducting materials appeared, and today these devices present the best performances in terms of efficiency, noise, counting rate, detectable wavelength, dead time, and timing jitter. In this work, we first describe the working principle of Superconducting Nanostrips Single Photon Detectors (SNSPDs) and provide a brief overview of the main properties and applications. Then, we present the results of the fabrication and characterization of Molybdenum Silicide SNSPDs with a cover layer of a thin Aluminium film (MoSi/Al). MoSi has already been adopted to fabricate SNSPDs, and in this work, we prove that the additional Al layer enhances the operating conditions without compromising the detection likelihood and leaving unaltered the properties of the device, even over a temporal window of two years and after several thermal cycles.

N–doping of alumina thin film support to improve the thermal stability of Catalysts: Preparation and investigation

This article presents the procedure for N – doping of alumina thin film grown on a metal substrate surface. The modification mechanism for model alumina by nitrogen during film formation is studied by in situ X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The preparation procedure, based on NO treatment of the growing alumina film, allows for nitrogen content control by NO pressure at a substrate temperature of 670 °C. The proposed N – doped model alumina support is suitable for catalysis oriented surface science studies devoted to enhancing supported metal particle resistance to thermal driven sintering.

Deterioration behavior of aluminum pouch film used as packaging materials for pouch-type lithium-ion batteries

Pouch-type lithium-ion batteries are packed into an aluminum pouch film (Al-Pouch). They are used as power sources for large-scale energy storage systems or electric vehicles because of their attractive features. However, the packaging materials of Al-pouch are prone to contamination from electrolyte containing lithium salt during the electrolyte injection process, a key part of their manufacturing process. This electrolyte contamination can be fatal to the long-term reliability or durability of pouch-type LiBs. Here, therefore, we study of how Al-pouch are damaged by electrolyte contamination; understanding this mechanism is critical for ensuring the long-term reliability and durability of pouch-type LiBs. We find that the nylon film comprising the outer layer of Al-pouch is damaged when it reacts with an electrolyte containing lithium salt in the presence of atmospheric moisture. This leads to cracking, followed by nylon locally peeling off from the Al-pouch. This peeling exposes the underlying thin aluminum film that comprises the middle layer of Al-pouch. Once partially exposed to the atmosphere, severe pitting corrosion occurs on the thin aluminum film. High volumes of moisture to easily penetrate pouch-type LiBs through these corroded pits, showing the detrimental effects of electrolyte contamination on pouch-type LiBs’ long-term cycle life and reliability.

Al2O3 and HfO2 Atomic Layers Deposited in Single and Multilayer Configurations on Titanium and on Stainless Steel for Biomedical Applications

Thin films of alumina and hafnia were prepared by atomic layer deposition, with the aim of investigating the use of such films in biomedical applications. Films were deposited on commercially pure titanium and on medical stainless steel. Two configurations were prepared: single alumina films, 20 nm and 60 nm thick, and a multilayer film, 60 nm thick, consisting of alumina/hafnia/alumina layers, each 20 nm thick. The morphology, structure and composition of the coated alloys were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. In addition, ellipsometry and atomic force microscopy coupled with scanning Kelvin probe force microscopy, were used to study the thickness and the topography with surface potential properties. An improvised method, involving the Vickers hardness test, was applied to assess the delamination of the deposited films. Coated specimens, as well as bare substrates, were tested at 37 °C in simulated body fluid, using potentiodynamic polarization and electrochemical impedance spectroscopy as techniques for assessing corrosion susceptibility. In general, single and multilayer thin films possess excellent barrier properties and are worth investigating further for biomedical applications. The degree of protection is dependent mainly on film thickness and on the type of substrate, and less on configuration.

Inside Front Cover

AbstractMultispectral fluorescence imaging is performed under the laser illumination of multiple wavelengths simultaneously. A plasmonic metasurface is designed to perform colour filtering, composed of an arrangement of circular and elliptical nanoholes etched into an aluminium thin film. The resultant mosaic colour filter array is flip‐chip bonded onto a single‐photon avalanche diode (SPAD) array. High fidelity, full‐colour fluorescence images are reconstructed from as few as three photons per pixel from a variety of biological samples.Further details can be found in the article by P.W.R. Connolly, J. Valli, Y.D. Shah, Y. Altmann, J. Grant, C. Accarino, C. Rickman, D.R.S. Cumming, and G.S. Buller (e202000505) image

Influence of the Voltage on Pore Diameter and Growth Rate of Thin Anodic Aluminium Oxide (AAO) Pattern on Silicon Substrate

By applying dual anodization procedures of aluminum (Al) thin film over silicon substrate under controlled anodizing process conditions, a thin anodic alumina (AAO) pattern with hexagonal honeycomb-like arrangement nano-pores and highly-regular aligned arrays was created. Anodizing DC voltage was thought to have an effect on pore size dimensions. With anodizing DC voltage, the pore diameter (30 - 110nm) showed a linear change. The rate of vertical growth of the nanopores was found to be proportional to the anodizing voltage. To achieve open-through pore nanostructure and ensure homogeneous electrochemical deposition of various nanostructures onto AAO pattern, a bottommost barrier layer of the AAO pattern was detached during dropping the DC voltage in the final period of the anodization process, followed by a pore widening wet treatment for numerous minutes at ambient temperature atmosphere. The features of the AAO pattern were inspected by using the field emission scanning microscope (FESEM) linked with an electron dispersive x-ray spectrometer (EDX) for chemical elements investigation.

Mathematical model of the charging of thin aluminum film in the space plasma

In this paper the generalization of model of a film charging which takes into account its bilateral form and partial permeability is made. Also the system of the equations for the determination of the density of the charge induced on the film surfaces is obtained and results of calculations of the charge density in plasma of a solar wind and in the radiation belt for different reflection factors of sunlight are given.

Preparation of transparent alumina thin films deposited by RF magnetron sputtering

Alumina (Al2O3) thin films were prepared by RF magnetron sputtering technique using Al2O3 ceramic target. Effects of sputtering powers and oxygen gas mixtures were investigated and the optimized coating condition was applied on semi-precious gemstones. RF sputtering powers were varied to optimize the transparency of the films. Besides, the oxygen gas mixtures were also studied at the optimized sputtering power with a constant sputtering pressure. Optical and physical properties of the thin films were investigated using UV-Vis Spectrophotometer, FESEM, XRF, GIXRD, XRR including a microscratch tester. The Al2O3 films were highly transparent in the visible region in form of an amorphous phase with granular structure of the surface morphology. Thickness of the films decreased significantly with an introduction of the oxygen gas in the sputtering process but slowly decreased with further addition of the oxygen gas. Density of the film changed linearly with the variation of the oxygen gas mixtures. The semi-precious gemstones gained higher scratch resistance after the Al2O3 thin films coating. To enhance the scratch resistance and maintain the aesthetic appearance of the semi-precious gemstones, the most optimum deposition condition for the Al2O3 thin film coating was determined for the RF magnetron sputtering technique at room temperature.

High-Q Silicon Nitride Drum Resonators Strongly Coupled to Gates.

Silicon nitride (SiN) mechanical resonators with high quality mechanical properties are attractive for fundamental research and applications. However, it is challenging to maintain these mechanical properties while achieving strong coupling to an electrical circuit for efficient on-chip integration. Here, we present a SiN drum resonator covered with an aluminum thin film, enabling large capacitive coupling to a suspended top-gate. Implementing the full electrical measurement scheme, we demonstrate a high quality factor ∼104 (comparable to that of bare drums at room temperature) and present our ability to detect ∼10 mechanical modes at low temperature. The drum resonator is also coupled to a microwave cavity, so that we can perform optomechanical sideband pumping with a fairly good coupling strength G and demonstrate mechanical parametric amplification. This SiN drum resonator design provides efficient electrical integration and exhibits promising features for exploring mode coupling and signal processing.

Atomic layer deposition of aluminum (111) thin film by dimethylethylaminealane precursor

We report the growth of aluminum (111) thin film by atomic layer deposition (ALD) technique with dimethylethylaminealane (DMEAA) as a precursor. It is found that the metallic underlayer is essential to grow uniform aluminum films by DMEAA precursor. As a titanium thin film is used as the underlayer, grown aluminum thin film shows (111) orientation irrespective of substrates. The lattice constant and superconducting transition temperature of the aluminum thin films are the same as the bulk one. These findings suggest that ALD technique provides high quality of the aluminum thin films and have potential for the applications of superconducting devices. We discuss ALD technique with DMEAA precursor is the promising method for fabricating vertical small Josephson tunnel junctions, which can be used as the superconducting quantum bits.

An investigation of adhesion mechanisms between plasma-treated PMMA support and aluminum thin films deposited by PVD

The metallization of polymers has been the subject of several scientific studies Polymethylmethacrylate PMMA is known to have very bad adhesion to plasma deposited aluminum thin films. This study focuses on understanding the phenomena of adhesion between PMMA and metallic aluminum films deposited by magnetron sputtering. Before deposition, in situ pulsed DC plasma pre-treatment was performed in various atmospheres. We showed that oxygen-rich and short duration plasma pre-treatment considerably increase PMMA’s adhesives properties. Contact angle measurements showed a significant increase in the wettability of plasma pre-treated samples. XPS analysis revealed that the interaction between plasma species and polymer surface results in two simultaneous phenomena: surface functionalization by the introduction of oxygenated chemical functions such as carbonyl groups (CO) and surface degradation by the splitting of carbon chains by plasma UV radiation. Moreover, AFM analyses showed that the slight increase in surface roughness leads to best adhesion between PMMA and aluminum.

Influence of seed layers on the reflectance of sputtered aluminum thin films.

The fabrication of highly reflective aluminum coatings is still an important part of current research due to their high intrinsic reflectivity in a broad spectral range. By using thin seed layers of Cu, CuOx, Cr, CrOx, Au, and Ag, the morphology of sputtered (unprotected) aluminum layers and, consequently, their reflectance can be influenced. In this long-term study, the reflectance behavior was measured continuously using spectrophotometry. Particular seed layer materials enhance the reflectance of aluminum coatings significantly and reduce their long-term degradation. Combining such seed layers with evaporation processes and suitable protective layers could further increase the reflectance of aluminum coatings.

Light-harvesting enhancement in ultrathin film silicon solar cells using photonic and plasmonic nanostructures

Past few decades, nanostructures are useful in the active region and light-harvesting layers in thin film solar cells. In this work, the high reflectance alternative Si/SiO2 distributed Bragg reflectors (DBRs), and aluminum (Al) thin film layers were integrated as a backside reflectors in ultrathin film silicon solar cells to improve the light trapping mechanism using finite-difference time-domain (FDTD) method. DBR is known as one-dimensional photonic crystal (1DPC) used as backside reflectors with the addition of SiO2 buffer layer. Further, the transverse electric (TE) and magnetic (TM) field distribution shown the strong light scattering in the silicon active layer region by integration of top (ITO) and bottom (Al) nanogratings. Both polarization conditions yielded the highest current density (Jsc) of 22.03 (TE) and 30.42 mA/cm2 (TM) achieved within 50 nm active region thickness.

Formation of Nanoscale T-Shaped Gates Using Directional Angular Deposition of Thin Aluminum Films

Formation of Nanoscale T-Shaped Gates Using Directional Angular Deposition of Thin Aluminum Films

Electrical and Optical Characteristics of WOx, ZrHfO, and Tri-Layer WOx Embedded ZrHfO High-k Based SSI-LEDs

The solid state incandescent light emission device (SSI-LED), which can emit the broadband warm white light, is made from the high-k MOS capacitor after the dielectric breakdown [1-4]. Electrical properties of the capacitor, such as interface defect density (Dit ), oxide trapped charge density (Qot ), equivalent oxide thickness (EOT), and leakage current density (Jleakage ) are important to the dielectric breakdown process and eventually the optical properties of the emitted light. Since the zirconium hafnium oxide (ZrHfO) high-k material has superb gate dielectric properties, e.g., high crystallization temperature, low interface state density, oxide trapped charges, and high effective k value, it has been used as the gate dielectric layer of the MOS capacitor [5,6]. On the other hand, the WOx dielectric-based MOS capacitor and SSI-LED has been studied. The latter emitted light with relative high intensity due to the high emissivity coefficient of the W component [7]. However, the capacitor has a high leakage current which can be a reliability concern. In this paper, three types of MOS capacitors, i.e., with gate dielectrics made of ZrHfO, WOx, and ZrHfO/WOx/ZrHfO/WOx/ ZrHfO/WOx/ZrHfO, separately, have been fabricated into SSI-LEDs and studied for electrical and optical properties.MOS capacitors were prepared on a DHF pre-cleaned p-type <100> silicon (1015 cm-3) wafer. For the ZrHfO capacitor, the gate dielectric layer was sputter-deposited from the Zr/Hf (12/88 wt%) target in Ar/O2 (100:100 sccm) at 5 mTorr and 60 W for 12 min. The WOx layer was sputter-deposited from the W target (99.999 %) in Ar/O2 (40:100 sccm) at 5 mTorr and 60 W for 12 min. For the WOx embedded capacitor, the ZrHfO (2 min)/WOx (2 min)/ZrHfO (2 min)/WOx (2 min)/ ZrHfO (2 min)/WOx (2 min)/ZrHfO (2 min) stack was deposited in one pump down under the same conditions as each individual layer. The post-deposition annealing (PDA) was conducted at 900 ̊C under the O2 atmosphere for 5 min in furnace. An 80 nm thick ITO was sputter deposited and wet etched into round gate electrodes using an aqua regia solution. Then, the backside of the wafer was deposited with an aluminum thin film and annealed at 400 ̊C under H2/N2 (10/90) for 5 min. The dielectric breakdown voltage of the capacitor was determined from the current density-gate voltage (J-V) curve. The light emission characteristics the SSI-LED were measured from an optical emission spectrometer (OES, StellarNet).Electrical characteristics of the capacitors before and after the dielectric breakdown were discussed with respect to the gate dielectric material properties. Figure 1 shows the emission spectra of the 3 SSI-LEDs. They all emit broad band light in the range of UV to near IR. They are similar to the visible wavelength region of the solar light. The peak lengths λpeak’s of the ZrHfO, WOx, and WOx embedded devices are 638 nm, 687.15 nm, and 663 nm, respectively. The WOx SSI-LED has the highest emission intensity. It was reported that the emissivities of the pure (99.99 %) tungsten and the hafnium-3 wt% zirconium materials were 0.434 [8] and 0.30 [9] at 2000 K, respectively. Therefore, the inclusion of W component in conductive path may increase the light emission intensity of SSI-LED. According to the emission spectra, the CIE chromaticity chart has been prepared. The color correlation temperatures (CCT’s) and color rendering indices (CRI’s) were calculated. Y. Kuo, ECS Trans., 69, 23-29 (2015).C.-C. Lin and Y. Kuo, ECS J. Solid State Sci. Technol., 3, Q182 (2014).C.-C. Lin and Y. Kuo, J. Vac. Sci. Technol. B, 32, 011208 (2014).Y. Kuo and C.-C. Lin, Appl. Phys. Lett., 102, 031117 (2013).T.-C. Chang, F.-Y. Jian, S.-C. Chen and Y.-T. Tsai, Materials today, 14, 608-615 (2011).G. E. Moore, Cramming more components onto integrated circuits, McGraw-Hill New York, NY, USA (1965).M. Lorenz, H. von Wenckstern and M. Grundmann, Adv. Mater., 23, 5383-5386 (2011).R. D. Larrabee, JOSA, 49, 619-625 (1959).P.-F. Paradis, T. Ishikawa and S. Yoda, Int. J. Thermophys., 24, 239-258 (2003). Figure 1

Effect of thermal annealing on the dielectric, passivation and pH detection properties of aluminium oxide thin films deposited by plasma-enhanced atomic layer deposition

The dielectric properties of aluminium oxide (Al2O3) thin films obtained by plasma-enhanced atomic layer deposition (PEALD) from Al(CH3)3/O2 precursors were investigated while focusing on the influences of thermal annealing under a dioxygen (O2) ambient. PEALD-Al2O3-based metal-insulator-silicon structures/capacitors and pH-sensitive chemical field effect transistors were fabricated to deal respectively with microelectronic applications and measurement in liquid phase. Antagonist results were thus evidenced. On the one hand, dealing with high-k gate materials, optimized dielectric properties, i.e. low fixed charge density (4 × 1012 cm−2), high dielectric constant (εr = 10.2), Fowler-Nordheim conduction and high breakdown electric fields (Ebd = 8.75 MV/cm) were obtained for polycrystalline PEALD Al2O3 films annealed at high temperature (T > 750 °C). On the other hand, pH detection properties, i.e. quasi-Nernstian sensitivity (59 mV/pH), low drift (< 1 mV/day) and long lifetime (> 180 days), were optimized for unannealed amorphous PEALD Al2O3 films. These phenomena were associated germination/crystallization phenomena in the deposited amorphous alumina structure as well as to related charge trapping and leakage currents in water-based solutions related to the final Al2O3 polycrystalline structure.

High-quality remote plasma enhanced atomic layer deposition of aluminum oxide thin films for nanoelectronics applications

Here, we report comprehensive investigations of aluminum oxide (Al2O3) high-κ gate oxides deposited via remote plasma enhanced atomic layer deposition (Re-PEALD) with mesh configuration in a commercial 100 mm ALD reactor. Trimethylaluminum (Al(CH3)3), dioxygen (O2) plasma, and Argon (Ar) are used as the metal precursor, oxidant, and carrier/purge, respectively. The growth rate per cycle and non-uniformity of Al2O3 thin films is analyzed with the variation in duration of (Al(CH3)3) pulse, O2 plasma, post-precursor purge, post-oxidant purge, RF power, and substrate temperature. High-quality monolayer type Al2O3 thin films with a growth rate of ~ 1.1 Å/cycle are achieved for a wide temperature range from ~ 100 °C to ~ 300 °C suitable for various nanoelectronics applications ranging from flexible substrates to low thermal budget and high mobility alternate semiconductor substrates. Further, the Al/Re-PEALD-Al2O3/p-Si, metal-oxide-semiconductor (MOS) structures are investigated for capacitance-voltage, capacitance-frequency, and leakage current-voltage characteristics to demonstrate the quality of Re-PEALD-Al2O3 thin films. The Al/Re-PEALD-Al2O3/p-Si, MOS structures revealed excellent electrical characteristics with ultralow minimum interface trap density (Dit) ~ 9.9 × 109 eV−1cm−2, negative effective oxide charges (Neff) ~ 5.52 × 1012 cm−2, low leakage current density of ~ 4.1 nA/cm2 at −1 V, hysteresis-free, insignificant Vth shift, and trivial frequency dispersion. Moreover, the chemical analysis using XPS depth profiling disclosed that Re-PEALD deposited Al2O3 thin films results in a high-quality gradient Al2O3/SiOx/Si interface rather than an abrupt Al2O3/Si interface, and the oxygen rich thin films due to the oxygen (O2−) interstitials close to the interface are the sources of negative fixed oxide charges in Re-PEALD-Al2O3/Si, system. These results intend to boost the investigations of Re-PEALD Al2O3 ultrathin films for low thermal budget high mobility alternate semiconductor substrates for nanoelectronics applications.

Saturation profile measurement of atomic layer deposited film by X-ray microanalysis on lateral high-aspect-ratio structure

Atomic layer deposition (ALD) of aluminum oxide thin films were applied on lateral high-aspect-ratio silicon test structures. The leading front of the film thickness profile is of interest, since it is related to deposition kinetics and provides information for ALD process development. A deposited profile was characterized using energy-dispersive electron probe X-ray microanalysis (ED-EPMA) and the results were analyzed using Monte Carlo simulation. A new procedure for obtaining relative film thickness profile from X-ray microanalysis data is described. From the obtained relative thickness profile, penetration depth of film at 50% of initial thickness and corresponding slope of thickness profile were determined at the saturation front. Comparison of the developed procedure was performed against independent measurements using optical reflectometry. ED-EPMA characterization of saturation profiles on lateral high-aspect-ratio test structures, supported by Monte Carlo simulation, is expected to prove useful tool for ALD process development.

A comparative study on the electrical and tribological characteristic of magnetron sputtered Ag, Cu and Al films under current-carrying friction

Purpose The purpose of this paper is to compare the electrical conductivity and tribological properties of magnetron sputtered silver (Ag), copper (Cu) and aluminum (Al) thin films under conductive grease lubrication. Design/methodology/approach Three types of silver (Ag), copper (Cu) and aluminum (Al) thin films were prepared by magnetron sputtering. Current-carrying friction tests were carried out by a ball-on-plate reciprocating friction and wear tester. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were used to observe and analyze the worn surface and cross-section morphology of the films. Findings Silver and Cu films exhibited good conductivity and tribological properties, which were mainly attributed to the synergy of the protective tribofilm generated by conductive grease, current-induced thermal effect and magnetron sputtered films effect. Al film was worn through. Large pitting storing lubricate were only found in Ag film. Cu film showed a similar surface uniformity with Ag film. Originality/value This study provides a reference for the design and application of conductive grease and investigates the current-carrying friction behaviors of magnetron sputtered films as electrical contact materials. The comparison of current-carrying friction behaviors of the three films was rarely covered in previous studies.

Effects of annealing temperature towards properties of black silicon fabricated by aluminium-assisted chemical etching

Black silicon (b-Si) is a promising absorber material for photovoltaic (PV) application. This paper studies the effects of annealing temperature towards surface morphological and optical properties of b-Si fabricated by aluminium-assisted chemical etching (AACE) process. In this work, the AACE process is realized by depositing aluminium (Al) thin film with 12 nm thickness on crystalline silicon (c-Si) wafers by direct current (DC) sputtering, followed by annealing the wafers at 250–450 °C in nitrogen (N2) atmosphere. Subsequently, the wafers are etched in a wet chemical solution containing hydrofluoric acid (HF), hydrogen peroxide (H2O2) and deionized (DI) water for 20 min at room temperature. From the findings, annealing the sample at 400 °C leads to formation of b-Si nanopores with the deepest nanopores and the highest surface coverage. This temperature also leads to the lowest broadband reflection within 300–1100 nm wavelength region. As a result, the highest average absorption enhancement of 1.61 is achieved when the absorption of the b-Si annealed at 400 °C is normalized to the absorption of the planar c-Si reference.