Sputtering Process Research Articles

Deeper Insight into the Mechanisms Behind Sputter Damage in Silicon Solar Cells Based on the Example of Nanocrystalline Silicon Carbide

AbstractTransparent conducting oxides, like indium tin oxide, enable lateral charge carrier transport in silicon heterojunction solar cells. However, their deposition can damage the passivation quality in the solar cell. This damage during the sputter deposition is a complex issue that has not been fully understood, particularly in various silicon‐based materials like amorphous silicon, polycrystalline silicon, or nanocrystalline silicon carbide. The degradation in passivation quality observed in, for example, amorphous silicon is not only explainable by UV light degradation. This study explores the origin of this degradation based on the example of hydrogenated nanocrystalline silicon carbide by combining simulations with experimental analyses. It delves into potential sources of damage during the sputtering process and determines that neither primary nor secondary effects from plasma luminescence or electron bombardment are likely contributors to the damage. Similarly, the implantation of ions, as well as the creation of vacancies and ionization of lattice atoms, are also considered improbable causes. It is, however, proposed that the transfer of energy to the crystalline silicon interface via phonons can factor into the degradation of the passivation quality. This transfer might be a plausible explanation for the damage observed in the passivation layers during the sputtering process.

In-situ optimization of lateral film uniformity in PVD system by using Fiber Bragg grating temperature sensors

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496–1616 ns), deposition pressure (3.1 × 10−3–1.9 × 10–2 mbar) and sputtering power (25–250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Implementation of 8-bit reservoir computing through volatile ZrOx-based memristor as a physical reservoir

In this study, we employed a sputtering process to construct a memristive device within the ITO/ZrOx/TaN structure for implementing neuromorphic computing. Initially, we scanned the basic electrical properties of the ITO/ZrOx/TaN device using a DC voltage sweep on the top ITO electrode. A highly uniform gradual resistive switching phenomenon was observed over 100 cycles. The current decay in the low-resistance state was effectively controlled by the volatile memory properties. Gradual conductance changes for potentiation and depression were achieved by applying electrical pulses, enabling the establishment of multi-level conductance states. In addition, the emulation of various synaptic functions was achieved by following the learning rules of SRDP, EPSC, STDP, ADSP, Pavlovian associative learning, and PPF. Finally, 8-bit reservoir computing was demonstrated in cost-effective pattern generation and recognition, highlighting the ITO/ZrOx/TaN device’s advantageous memory storage properties for synaptic characteristics.

Effect of neural firing pattern on NbOx/Al2O3 memristor-based reservoir computing system

The implementation of reservoir computing using resistive random-access memory as a physical reservoir has attracted attention due to its low training cost and high energy efficiency during parallel data processing. In this work, a NbOx/Al2O3-based memristor device was fabricated through a sputter and atomic layer deposition process to realize reservoir computing. The proposed device exhibits favorable resistive switching properties (>103 cycle endurance) and demonstrates short-term memory characteristics with current decay. Utilizing the controllability of the resistance state and its variability during cycle repetition, electrical pulses are applied to investigate the synapse-emulating properties of the device. The results showcase the functions of potentiation and depression, the coexistence of short-term and long-term plasticity, excitatory post-synaptic current, and spike-rate dependent plasticity. Building upon the functionalities of an artificial synapse, pulse spikes are categorized into three distinct neural firing patterns (normal, adapt, and boost) to implement 4-bit reservoir computing, enabling a significant distinction between “0” and “1.”

Structural, linear/nonlinear optical characteristics and radiation shielding effectiveness of Cu4O3/Cu2O dual-phase thin films: Influence of oxygen flow rate in reactive sputtering process

In the present work, we investigated the impact of oxygen flow rate on the structural, linear, and nonlinear optical characteristics while also evaluating the radiation shielding effectiveness during reactive radio frequency (rf) sputtering in the deposition of Cu4O3/Cu2O dual-phase thin films. Microstructural analysis revealed distinct changes with increased OFRs, switching from a Cu2O cubic structure phase to a Cu4O3 tetragonal structure phase. The XRD patterns revealed good crystallinity, and the crystallite size of the film reduced from 28 nm to 22 nm, and the microstrain exhibited an opposing trend as the oxygen flow rate increased. In contrast, investigating the optical properties of dual-phase Cu4O3 and Cu2O thin films using UV–Vis–NIR spectroscopy revealed intriguing trends in the absorbance spectra, absorption coefficient, and extension index. The apparent bandgap increases from 2.0 eV to 2.62 eV with increasing oxygen flow rates. In addition, nonlinear optical parameters, including the nonlinear refractive index n2 linear, nonlinear sensitivity (χ1 and χ3), and nonlinear absorption coefficient βc were calculated to demonstrate the applicability of these materials. The dual-phase structure of the films enhances their potential for effective radiation shielding. Our findings provide valuable insights into the design of properties of Cu4O3/Cu2O dual-phase thin films for applications ranging from photoelectric and nonlinear optical devices to radiation shielding effectiveness.

High Sensitivity CH4 and CO2 Gas Sensor Using Fiber Bragg Grating Coated with Single Layer Graphene

This article outlines the development of a Fiber Bragg Grating (FBG) intended for use as a sensor for CH4 and CO2 gases. Following fabrication, the FBG was effectively treated with a layer of Graphene Material through a modified RF Sputtering process. This coating procedure involved introducing argon gas into the chamber and subjecting the FBG, securely held by two vacuum stages, to a temperature range of 27°C to 600°C by adjusting the power supplied to the cathode and anode, ranging from 0 to 125 Watts. Subsequently, the FBG was employed as a key sensing element within an experimental setup aimed at measuring gas concentrations within a confined space. The assessment involved analyzing the reflected signal of the FBG using an Optical Interrogator System, which demonstrated a shift in the Bragg wavelength of the reflected signal corresponding to varying gas concentrations. This study indicates promising outcomes for the Graphene-coated FBG as a gas sensor. The sensor’s sensitivity was evaluated based on the Bragg wavelength shift resulting from gas presence within the chamber. The Graphene-coated FBG exhibited sensitivities of 3.3 ppm for CH4 and 3.7 ppm for CO2, surpassing those reported in prior research efforts.

Assessing the Effect of Twisting and Twisting Fatigue on ZnO:Al Thin Film Performance on PEN and PET Substrates.

This study examines the electromechanical characteristics of aluminium-doped zinc oxide (AZO) films. The films were produced using the RF magnetron sputtering process with a consistent thickness of 150 nm on various polymer substrates. The study focuses on assessing the electro-mechanical failure processes of coated segments using flexible substrates, namely polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), with a specific emphasis on typical cracking and delamination occurrences. This examination involves conducting twisting deformation together with using standardised electrical resistance measurements and optical microscope monitoring instruments. It was found that the crack initiation angle is mostly dependent on the mechanical mismatch between the coating and substrate. Higher critical twisting angle values are observed for the AZO/PEN film during twisting testing. Relative to the perpendicular plane of the untwisted sample, it was found that cracks initiated at a twist angle equal to 42° ± 2.1° and 38° ± 1.7° for AZO/PEN and AZO/PET, respectively, and propagated along the sample length. SEM images indicate that the twisting motion results in deformation in the thin film material, leading to the presence of both types of stress in the film structure. These discoveries emphasise the significance of studying the mechanical properties of thin films under different stress conditions, as it can impact their performance and reliability in real-world applications. The electromechanical stability of AZO was found to be similar on both substrates during fatigue testing. Studying the electromechanical properties of various material combinations is important for selecting polymer substrates and predicting the durability of flexible electronic devices made from polyester.

Preparation of high-density and excellent bending strength pure tungsten target by hot oscillatory pressing sintering and its magnetron sputtering coating

The high-strength, high-density pure tungsten (W) targets were fabricated using hot oscillatory pressing (HOP) sintering. This study examined the influence of sintering temperature, oscillation frequency, amplitude, and median pressure on the relative density, grain size, and bending strength of the tungsten targets. A tungsten target exhibiting a relative density of 99.51%, a grain size of 2.95 μm, a bending strength of 1200.1 MPa, and a purity of 99.95% was synthesized at a sintering temperature of 1600 °C, an oscillation pressure of 60 ± 15 MPa, and a frequency of 1 Hz. Grain rearrangement and plastic deformation (dislocation movement and grain boundary slip) were identified as the primary mechanisms for grain refinement and densification, respectively. The key strengthening mechanism was sub-grain boundary strengthening. The optimal tungsten target was utilized for magnetron sputtering on a reduced activation ferritic/martensitic (RAFM) steel substrate. The effects of sputtering time, power, deposition pressure, and substrate temperature on the crystallinity, roughness, thickness, and bonding force of the tungsten films were investigated. The optimal magnetron sputtering process was achieved by sputtering for 45 min at a power of 60 W, a deposition pressure of 15 Pa, and a substrate temperature of 100 °C. This resulted in dense W films with excellent comprehensive properties, including a roughness of Ra = 8.73 nm, Rq = 3.34 nm, a thickness of 999.05 nm, and a bonding force of 2.57 N.

Influence of Sputtering Power on the Properties of Magnetron Sputtered Tin Selenide Films.

The ecofriendly tin selenide (SnSe) is expected to find multiple applications in optoelectronic, photovoltaic, and thermoelectric systems. This work is focused on the thermoelectric properties of thin films. SnSe single crystals exhibit excellent thermoelectric properties, but it is not so in the case of polycrystalline bulk materials. The investigations were motivated by the fact that nanostructuring may lead to an improvement in thermoelectric efficiency, which is evaluated through a dimensionless figure of merit, ZT = S2 σ T/λ, where S is the Seebeck coefficient (V/K), σ is the electrical conductivity (S/m), λ is the thermal conductivity (W/mK), and T is the absolute temperature (K). The main objective of this work was to obtain SnSe films via magnetron sputtering of a single target. Instead of common radiofrequency (RF) magnetron sputtering with a high voltage alternating current (AC) power source, a modified direct current (DC) power supply was employed. This technique in the classical version is not suitable for sputtering targets with relatively low thermal and electrical conductivity, such as SnSe. The proposed solution enabled stable sputtering of this target without detrimental cracking and arcing and resulted in high-quality polycrystalline SnSe films with unprecedented high values of ZT equal to 0.5 at a relatively low temperature of 530 K. All parameters included in ZT were measured in one setup, i.e., Linseis Thin Film Analyzer (TFA). The SnSe films were deposited at sputtering powers of 120, 140, and 170 W. They had the same orthorhombic structure, as determined by X-ray diffraction (XRD), but the thickness and microstructure examined by scanning electron microscopy (SEM) were dependent on the sputtering power. It was demonstrated that thermoelectric efficiency improved with increasing sputtering power and stable values were attained after two heating-cooling cycles. This research additionally provides further insights into the DC sputtering process and opens up new possibilities for magnetron sputtering technology.

Microstructure, mechanical properties, and wear behaviors of CrSiN films on oxynitriding-treated Vanadis 60 high-speed steel by the direct current magnetron sputtering process

This study utilized the direct current magnetron sputtering technique within the physical vapor deposition process to apply a chrome silicon nitride (CrSiN) coating onto the oxynitrided surface of Vanadis 60 high-speed steel. The experimental parameters include various deposition bias voltages (0, -25, -50, -75, and -100 V), a gas flow rate of 45/30 (Ar/N2) sccm, a power of 100 W, a voltage of 400 V, a deposition time of 2.5 h, and a deposition temperature of 225 °C. The research results show that the substrate formed an oxynitriding layer with a thickness of about 30 μm, while the surface hardness increased to about 1300 HV0.05. When the coatings were deposited at a bias voltage of -100 V, the CrSiN coatings possessed the highest hardness (5.74 GPa) and elastic modulus (110.94 GPa), thus, it had the best wear resistance (specific wear rate was 1.19×10−5, and 7.29×10−5 mm3·m−1·N−1 under the loads of 1.5 N and 3 N), and good corrosion resistance (corrosion current was 3.28×10−5 A·cm−2, and polarization resistance was 793.18 Ω·cm2 in a 0.1 N H2SO4 solution). Furthermore, transmission electron microscopy observations confirm that the CrSiN coatings had a significant amorphous structure.

Effect of sputtering power and substrate bias on microstructure, mechanical properties and corrosion behavior of CoCrFeMnNi high entropy alloy thin films deposited by magnetron sputtering method

The CoCrFeMnNi high entropy alloy thin films with crystalline (solid solution) structure or amorphous state were fabricated by magnetron sputtering process at different target powers and different substrate bias. Effects of the target power and substrate bias on the characteristics of the CoCrFeMnNi thin films such as microstructures, morphology and surface topography, as well as mechanical properties and corrosion behavior were studied. Phase prediction was calculated by using thermodynamic and kinetic criteria under various deposition conditions. The enthalpy, entropy, δ and Ω parameters, and electronegativity differences influenced the solid solution stability of thin films. These parameters led to the formation of solid solutions with crystalline or amorphous structures under specific limits, which corresponded to the practical XRD and TEM analysis results. Using a substrate bias in the deposition of CoCrFeMnNi thin film changed the amorphous structure to a crystalline (solid solution (BCC + FCC)) at higher target powers (200 and 300 W). On the other hand, the film structure was entirely amorphous at all sputtering target powers without the substrate bias. The mechanical properties, such as hardness, Young's modulus, film strength, and fracture toughness of CoCrFeMnNi thin film, can be enhanced by using the substrate bias and increasing the sputtering power. The potentiodynamic polarization test in 3.5 wt% NaCl aqueous solution indicated that the deposition of CoCrFeMnNi thin films at different sputtering powers and without substrate bias could increase the corrosion resistance of 304 stainless steel substrate. Using the substrate bias of −100 V in the fabrication of CoCrFeMnNi thin film decreased the corrosion current density and increased its polarization resistance.

Level set simulation of focused ion beam sputtering of a multilayer substrate.

The evolution of a multilayer sample surface during focused ion beam processing was simulated using the level set method and experimentally studied by milling a silicon dioxide layer covering a crystalline silicon substrate. The simulation took into account the redeposition of atoms simultaneously sputtered from both layers of the sample as well as the influence of backscattered ions on the milling process. Monte Carlo simulations were applied to produce tabulated data on the angular distributions of sputtered atoms and backscattered ions. Two sets of test structures including narrow trenches and rectangular boxes with different aspect ratios were experimentally prepared, and their cross sections were visualized in scanning transmission electron microscopy images. The superimposition of the calculated structure profiles onto the images showed a satisfactory agreement between simulation and experimental results. In the case of boxes that were prepared with an asymmetric cross section, the simulation can accurately predict the depth and shape of the structures, but there is some inaccuracy in reproducing the form of the left sidewall of the structure with a large amount of the redeposited material. To further validate the developed simulation approach and gain a better understanding of the sputtering process, the distribution of oxygen atoms in the redeposited layer derived from the numerical data was compared with the corresponding elemental map acquired by energy-dispersive X-ray microanalysis.

Compliance-free, analog RRAM devices based on SnOx

Brain-inspired resistive random-access memory (RRAM) technology is anticipated to outperform conventional flash memory technology due to its performance, high aerial density, low power consumption, and cost. For RRAM devices, metal oxides are exceedingly investigated as resistive switching (RS) materials. Among different oxides, tin oxide (SnOx) received minimal attention, although it possesses excellent electronic properties. Herein, we demonstrate compliance-free, analog resistive switching behavior with several stable states in Ti/Pt/SnOx/Pt RRAM devices. The compliance-free nature might be due to the high internal resistance of SnOx films. The resistance of the films was modulated by varying Ar/O2 ratio during the sputtering process. The I–V characteristics revealed a well-expressed high resistance state (HRS) and low resistance states (LRS) with bipolar memristive switching mechanism. By varying the pulse amplitude and width, different resistance states have been achieved, indicating the analog switching characteristics of the device. Furthermore, the devices show excellent retention for eleven states over 1000 s with an endurance of > 100 cycles.

Design and preparation of L-band multilayer low-group delay filter based on inner sputtering

Article propose a design for an L-band multi-layer MEMS cross-finger filter based on pore interior wall sputtering. Article analyze the structural parameters, such as resonator thickness and TSV structure, using HFSS simulation software. Findings indicate that the filter has a central frequency of 1.5 GHz, a bandwidth of 140 MHz, a band loss of less than 1 dB, return loss is greater than 25 dB, and a band group delay of less than 800 ps. Furthermore, Article conduct process design optimization and finished product testing for the filter, including optimizing the TSV process for the hole inner wall sputtering process. These results demonstrate the filter's broad application prospects.

Controllable Preparation and Mechanism Study of Easy‐Peel High‐Density and Vertically Aligned Carbon Nanotube Forests

The stripping of carbon nanotube forests (CNTF) is an urgent problem in terms of its application in thermal management and semiconductor devices. The easy‐peel and vertically aligned CNTF is prepared in a two‐step process of high vacuum magnetron sputtering and chemical vapor deposition. Based on the thick alumina buffer layer, CNTF with heights of 100 μm, 300 μm, and 500 μm was prepared by adjusting the magnetron sputtering power. Through SEM observation and calculation, the corresponding densities were 2.5 × 109 cm−2, 6.4 × 109 cm−2, and 1.21 × 1010 cm−2, with an average curvature of 1.64 × 102 m−1, 1.35 × 102 m−1 and 0.53 × 102 m‐−1, respectively. The TEM, XPS, Raman, and TGA were used to investigate the growth mechanism of CNTF. The experimental results show that the catalyst particles annealed under high sputtering power refined with high density can grow a low‐defect, well‐oriented, and high‐density CNTF, and confirm the tip growth route. Further analysis shows that the easy‐peel properties of CNTF depend on the thickness of the alumina layer, the tip growth route, and the tight entanglement between the nanotubes. This paper provides technical guidance and support for the preparation, stripping, and application of monolithic CNTF.

Assessing mechanical properties and stability of silver-doped carbon-coated urethral stent application

Carbon coatings doped with Ag nanoparticles (a-C/Ag) are promising materials to enhance ureteral stents' biological, mechanical, and tribological properties. This paper aims to assess the degradation profile and mechanical behaviour of silicone stents coated with a-C and a-C/Ag films under simulated physiological conditions. a-C coating containing about 5 at. % Ag was deposited on silicone stent substrates by magnetron sputtering. The chemical composition, roughness, and wettability of the coatings were analysed. The morphology and mechanical properties of the coatings were characterised before and after 30 days of immersion in synthetic urine. Remarkably, the a-C/Ag coating demonstrated exceptional resistance to degradation, exhibiting no signs of film delamination even after 30 days of incubation under accelerated degradation conditions. Moreover, the stability of the a-C/Ag coating was evaluated by monitoring its release in synthetic urine, revealing an initial rapid release within the first two days, followed by a controlled and gradual release of silver ions from the coating. Additionally, the a-C/Ag coating practically kept the breaking force of the silicone stent (∼5 % loss) with a significant diminution in elongation at break due to the substate embrittlement during the sputtering process. Overall, this study provides valuable insights into the performance of a-C/Ag coating on silicone stents, highlighting their ability to maintain structural integrity, resist degradation, and withstand substantial forces. These findings support the promising potential of a-C/Ag coating in enhancing the reliability and durability of urological stents.

Helium plasma irradiation on Nickel: Nanostructure formation and electrochemical characteristics

Nanotechnology offers new avenues for the design, fabrication, and application of novel materials. Helium plasma exposure is a technique that can be used to fabricate self-supported metallic nanostructures. In this work, we explore the plasma irradiation conditions for fabricating various morphologies on planar nickel surfaces, and evaluate the electrochemical performance of these surfaces for oxygen evolution reaction (OER) in alkaline media. The preferential growth towards certain morphologies such as nano-pillars, nano-blocks, and micro-structures, is found to be primarily influenced by the applied plasma conditions and two counteracting processes of sputtering and annealing. The plasma treatment increased the electrochemical surface area of the modified samples by approximately 3 to 4 times as compared to the planar/unmodified surfaces, along with an increase in the OER performance for all morphologies. However, in addition to the increased surface area, the electrochemical performance was found to be dependent on the shape, size and thickness of the nano/micro-features. Moving ahead, the ability of this technique to achieve control over the feature size along with its effectiveness for a broad range of metals offers new routes for nanostructuring and functionalization of emerging materials.

Effect of process parameters on microstructure and Raman characteristics of magnesium doped ZnO thin films

MgxZn1-xO thin films were prepared on glass substrates by radio frequency magnetron sputtering under different sputtering processes. The surface morphology, microstructure, and Raman characteristics of the films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman Spectrometer. The results show that an increase in the O/Ar ratio decreases the surface smoothness of the thin film and worsens the particle uniformity. The particles of undoped Magnesium doped Zinc Oxide (ZnO) films are small and uniform, and the uniformity of the particles in the films becomes worse after doping. Moreover, there are multiple diffraction peaks in the magnesium doped Zinc Oxide films, presenting a polycrystalline state, but the diffraction peak positions do not significantly change with the concentration and intensity of magnesium doped. The Raman characteristic peak undergoes a blue shift with the increase of magnesium doping concentration, and the peak position shifts from 573 cm−1 to 607 cm−1.

Wear performance of Ti-based alloy coatings on 316L SS fabricated with the sputtering method: Relevance to biomedical implants.

This investigation was conducted to encapsulate 316L SS with a Ti-based alloy coating. The aim was to fabricate a coating using TiN, TiO2, and TiCoCr powders on 316L SS through the physical vapor deposition (PVD) sputtering process. The powders were consecutively coated on 316L SS through the PVD sputtering process with coating durations of 30, 60, and 90 min. Further microhardness, surface roughness, microabrasion, and adhesion strength tests were also carried out. A 60% improvement in abrasion resistance was observed in TiCoCr-coated samples compared to the uncoated substrate. The X-ray diffraction results confirmed the optimal formation of Ti alloy coatings with corresponding orientation over the SS substrates. Moreover, TiCoCr with a 90 min coating duration had much better surface characteristics than TiO2 and TiN. The 90 min coating duration should be optimal for coating in steel for bio-implants.

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

Boron nitride-silicon dioxide (BN–SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN–SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN–SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δ m) of the two BN–SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δ m values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN–SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.