SiO2 Thin Films Research Articles

Non-destructive processing of silver containing glass ceramic antibacterial coating on polymeric surgical mesh surfaces.

Surgical meshes composed of bioinert polymers such as polypropylene are widely used in millions of hernia repair procedures to prevent the recurrence of organ protrusion from the damaged abdominal wall. However, post-operative mesh infection remains a significant complication, elevating hernia recurrence risks from 3.6% to 10%, depending on the procedure type. While attempts have been made to mitigate these infection-related complications by using antibiotic coatings, the rise in antibiotic-resistant bacterial strains threatens their effectiveness. Bioactive glass-ceramics featuring noble metals, notably silver nanoparticles (AgNPs), have recently gained traction for their wide antibacterial properties and biocompatibility. Yet, conventional methods of synthesizing and coating of such materials often require high temperatures, thus making them impractical to be implemented on temperature-sensitive polymeric substrates. To circumvent this challenge, a unique approach has been explored to deposit these functional compounds onto temperature-sensitive polypropylene mesh (PP-M) surfaces. This approach is based on the recent advancements in cold atmospheric plasma (CAP) assisted deposition of SiO2 thin films and laser surface treatment (LST), enabling the selective heating and formation of functional glass-ceramic compounds under atmospheric conditions. A systematic study was conducted to identify optimal LST conditions that resulted in the effective formation of a bioactive glass-ceramic structure without significantly altering the chemical and mechanical properties of the underlying PP-M (less than 1% change compared to the original properties). The developed coating with optimized processing conditions demonstrated high biocompatibility and persistent antibacterial properties (>7 days) against both Gram-positive and Gram-negative bacteria. The developed process is expected to provide a new stepping stone towards depositing a wide range of functional bioceramic coatings onto different implant surfaces, thereby decreasing their risk of infection and associated complications.

Real-time detection of acetone gas molecules at ppt levels in an air atmosphere using a partially suspended graphene surface acoustic wave skin gas sensor.

To improve the quality of modern life in the current society, low-power, highly sensitive, and reliable healthcare technology is necessary to monitor human health in real-time. In this study, we fabricated partially suspended monolayer graphene surface acoustic wave gas sensors (G-SAWs) with a love-mode wave to effectively detect ppt-level acetone gas molecules at room temperature. The sputtered SiO2 thin film on the surface of a black 36°YX-LiTaO3 (B-LT) substrate acted as a guiding layer, effectively reducing the noise and insertion loss. The G-SAWs exhibited enhanced gas response towards acetone gas molecules (800 ppt) in a real-time atmosphere. The high sensitivity of the G-SAW sensor can be attributed to the elasticity and surface roughness of the SiO2 film. In addition, the G-SAW sensor exhibited rapid response and recovery at room temperature. This study provides a potential strategy for diagnosing different stages of diabetes in the human body.

A Study on the Gap-Fill Process Deposited by the Deposition/Etch/Deposition Method in the Space-Divided PE-ALD System

This study concerns the development of a gap-fill process technology for isolating trench patterns. There are various gap-filling techniques in the case of trench patterns; nevertheless, a processing technology adopting the DED (deposition/etch/deposition) method was developed in this study. After the etch step, an Ar/O2 (1:2) plasma treatment technology reduced the residual amount of F in the films to 0.05%. By improving the etch uniformity, the deposition uniformity after the DED process on a 12-inch flat wafer was secured within <1%, and a high-quality SiO2 thin film with a dielectric constant of 3.97 and a breakdown field of 11.41 MV/cm was fabricated. The DED method can be used for gap-filling even in patterns with a high aspect ratio by changing process parameters, such as RF power and division of etch steps, according to the shape, depth, and CD size of the pattern. This study confirmed that a void-free gap-fill process can be developed in a trench pattern with a maximum aspect ratio of 40:1.

Mesostructure and Magnetic Properties of SiO2-Co Granular Film on Silicon Substrate

Granular films SiO2(Co) exhibit unusual magnetic and magnetotransport properties which are strongly dependent on the composition of the film and material of a substrate. For example, the injection magnetoresistance (IMR) coefficient reaches a giant (GIMR) value of 105% at room temperature in SiO2(Co) films on an n-GaAs substrate. However, the IMR effect is negligible in the case of a similar granular film deposited on the n-Si substrate. In this report, the structural and magnetic properties of granular film SiO2(Co) on Si substrate are studied with the aim to understand the cause of the difference in IMR coefficients for SiO2(Co) thin film deposited on n-GaAs and on n-Si substrates. Investigations were carried out using complementary methods of Polarized Neutron Reflectometry, Grazing Incidence Small-Angle X-ray Scattering, X-ray Reflectometry, Scanning Electron Microscope, and SQUID magnetometry. It is shown that the interface layer between the granular film and Si substrate exhibits metallic rather than magnetic properties and eliminates the GIMR effect. This interface layer is associated with the Si diffusion to Co nanoparticles and the formation of the metallic cobalt silicides.

Monte-Carlo simulation and experimental study of the effect of internal charging on the electron emission yield of amorphous SiO2 thin films

A Monte-Carlo code has been developed for the transport of low energy electrons and the simulation of the internal charge buildup induced by the electron irradiation in thin films of amorphous SiO2. The code is validated with time resolved experimental Electron Emission Yield (EEY) data on 20 nm SiO2 thin films for incident electrons of 300 eV and 1 keV. As the EEY is greater than 1, this corresponds to the case of positive charging. In order to assess the impact of the charge buildup on the electron emission yield, the samples have been negatively polarized to suppress the positive external charging effects, and irradiated with a defocused beam (mm²). A direct correlation is found between the value of the EEY and the density of holes created in the material. This clearly shows that the recombination of the secondary electrons with trapped holes significantly affects the EEY of insulators.

Spray-coated SiO2/PECVD SiN[formula omitted] stack for the passivation of n[formula omitted] emitter of p-type Si solar cell

Inefficient passivation of phosphorous diffused emitter is one of the limiting factors contributing to lower efficiency in advanced p-type silicon solar cells. Stack of SiO2 and SiNx with the former as an intermediate layer beneath SiNx provides better emitter passivation in comparison to SiNx film alone. Thermal oxide is reported to provide the best passivation, but it is not industrially viable. We demonstrate spray SiO2/SiNx as a viable alternative to thermal SiO2/SiNx stack. A few nanometer thin (∼6.1 nm) spray SiO2 film was first time demonstrated on micrometer sized textured pyramid with full coverage over an entire deposited area. The passivation of symmetrical (n+-p-n+) structure shows iVoc∼660 mV and passivation uniformity over the entire wafer area for both the stacks. Voc∼630 mV is achieved on cells with spray and thermal SiO2 as a passivating layer. Similar front passivation is further verified by overlapping IQE in the shorter wavelength range. Therefore, incorporating SiO2 film deposited via an industrially viable spray-coating process as a passivating layer at the front provides overall cell performance similar to the thermally grown SiO2.

Changes in optical thicknesses of Ge and SiO thin films and spectral characteristics of narrowband filters at cryogenic temperatures

Subject of study. Two narrowband filters with Ge and SiO resonant layers were investigated both at room and cryogenic temperatures of 293 and 80 K, respectively. Aim of study. The deposition of bandpass filters with predefined deviations of optical thickness layers under operating conditions at cryogenic temperatures was considered. The presented design of an optical interference coating increases the transmission coefficient in the operating spectral ranges during its operation at cryogenic temperatures. Method. An antireflective bandpass coating constituting a pair of Ge-SiO film-forming materials was deposited onto a substrate made of an optical material using vacuum deposition. The layer thicknesses were controlled during their deposition using an optical control system. Main results. The obtained spectral characteristics of two narrowband filters are presented herein. The optical thicknesses of the filters with resonant layers made of Ge and SiO and thickness variations at the temperatures of 293 and 80 K were determined by an iteration method via the positions of the wavelengths of maximum transmission of the filters. Practical significance. The spectral characteristics of the filters with SiO resonant layers demonstrated smaller changes at cryogenic temperatures than those of the filters with Ge resonant layers.

Non-Equilibrium Growth of Surface Wrinkles Emerging in an SiO2/Si Stack during Si Melting Induced by UV Nanosecond Pulsed Laser Annealing

UV nanosecond pulsed laser annealing (UV-NLA) is demonstrating clear benefits in the emerging 3D-integrated electronic devices, where the allowed thermal budget is strictly limited to preserve underlying device performance. A possible drawback of UV-NLA is that melting a solid substrate covered by a dielectric layer, which can be found in typical CMOS device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in thermally-grown SiO2/Si structures to systematically investigate the formation of wrinkles. A classical analytical model adopted from literature shows a good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value is rapidly increasing for a thinner (roughly less than 50 nm) SiO2 film, whereas it becomes closer to unity for a thicker (roughly greater than 50 nm) SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The impact of the as-grown SiO2 film stress on the growth of wrinkles is also investigated, improving the statistics of the measurements. The results do not show any significant impact possibly because of the degree of the as-grown SiO2 film stress being negligible compared to the SiO2 shear modulus.

High efficacy of activated carbon fabric filters and masks developed to prevent the inhalation of microorganisms and particles associated with respiratory tract infections

As a major international public health emergency, COVID-19 has posed many challenges for healthcare professionals who have been heavily exposed to contamination. This article describes the development of a high-filtration capacity mask consisting of filter-element layers interspersed with super-activated carbon fiber fabric, non-woven polypropylene for dental–medical–hospital use and antiviral polyamide with nanostructured SiO2 thin film coating. The study found 98.18% particle filtration efficiency and determined 2.11 mmH2O/cm2 differential pressure, while fluid repellency complied with Brazilian standard NBR ABNT 15052:2004.

SPR based refractive index modulation of nanostructured SiO2 films grown using GLAD assisted RF sputtering technique

Low refractive index materials have always gained attention for avoiding optical losses in numerous devices like Light emitting diodes (LEDs), Distributed Bragg Reflectors (DBRs) etc. Glancing angle deposition (GLAD) has proven to be an effective method for depositing porous nanostructures with low refractive index. SiO2 has the lowest refractive index in comparison to most of the materials present in nature and is therefore utilized extensively in the fabrication of optical devices with minimum optical losses. The present work focuses on the SiO2 nanostructured thin films grown using glancing angle (GLAD) configuration in RF Sputtering technique under varying deposition conditions (glancing angle and pressure) at fixed thickness. The deposited porous SiO2 nanostructured layers have well-defined nanorods of feature size smaller than 100 nm. The refractive index corresponding to all the deposited SiO2 nanostructured films came out to be smaller than the corresponding value (1.49) mentioned in the literature for bulk SiO2. The refractive index has been observed to vary in a wide range (1.05 to 1.40). Characterization of the deposited SiO2 nanostructured films was carried out using Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive X-Ray (EDS) analysis, and Atomic Force Microscopy (AFM) to assess the qualitative properties of the deposited nanostructured SiO2 films. Surface Plasmon Resonance (SPR) and Ellipsometry studies are performed to determine the refractive index value of the deposited nanostructured SiO2 thin films. A refractive index value as low as ∼ 1.05 at a wavelength of 633 nm is achieved for SiO2 nanostructured thin film deposited at 30 mTorr deposition pressure and 80° glancing angle.

Modeling effective thermal conductivity enhanced by surface waves using the Boltzmann transport equation

The thermal management of semiconductors at the device level has become a crucial issue owing to the high integration density and miniaturization of microelectronic systems. Because surface phonon polaritons (SPhPs) exhibit long propagation lengths, they are expected to contribute significantly to the heat dissipation in microelectronic systems. This study aims to numerically estimate the heat transfer due to SPhPs in a thin SiO2 film. The one-dimensional Boltzmann transport equation (BTE) is solved using the estimated propagation length based on the SPhP dispersion curves. The temperature profiles and heat fluxes are predicted and demonstrate the size effect of the film on the effective in-plane thermal conductivity of the SiO2 film. The results indicate that the temperature distribution was constant regardless of the film length and thickness because the propagation length was much longer than the film length. In addition, the heat flux increased with decreasing film thickness owing to the depth-averaged energy transfer. The effective thermal conductivities predicted using the BTE differed by ~ 16.5% from the values obtained from the analytical expression. The numerical results of this study can provide valuable data when studying the thermal behavior of SPhPs.

Engineering a sandwiched Si/I/LNOI structure for 180-GHz-bandwidth electro-optic modulator with fabrication tolerances.

Electro-optical modulators are essential for scalable photonic integrated circuits and are promising for many applications. The convergence of silicon (Si) and lithium niobate (LN) allows for a compact device footprint and large-scale integration of modulators. We propose a sandwiched Si/I/LNOI modulator for broad modulation with CMOS-compatible fabrication tolerances. There is a thin film SiO2 spacer sandwiched between Si and LN, which is engineered to tailor optical and electrical properties and enhance index matching. Moreover, the SiO2 spacer is also exploited to inhibit the radiation loss induced by mode coupling. The modulator shows a bandwidth of ∼180 GHz with a halfwave voltage of 3 V. Such a device is considerably robust to the fabrication deviations, making it promising for massive and stable manufacturing.

Synthesis and characteristics of Sn-doped SiO2 via plasma-enhanced atomic layer deposition for self-aligned patterning

Sn-doped SiO2 thin films as a spacer for self-aligned patterning were deposited by plasma-enhanced atomic layer deposition and their characteristics were evaluated. This doping research was conducted to improve the mechanical properties of SiO2 films, which have been conventionally used as a spacer material. Because pure SiO2 films have a low Young's modulus, the pattern is stretchable and may collapse as the patterning size decreases. The ratio of the SnO2 and SiO2 deposition cycle was varied from 15(SiO2):1(SnO2) to 3(SiO2):1(SnO2) to modify the film characteristics. X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometer analyses revealed whether Sn was doped in SiO2 or became a nanolaminate. The x-ray photoelectron spectroscopy analysis showed that a greater amount of Sn in the SiO2 thin film resulted in a binding energy shift toward the lower binding energy Si2p and Sn3d peaks, and more Si–O–Sn chemical bonding, which increased the number of stiffer ionic bonds as the SnO2 cycle ratio was increased. Therefore, Young's modulus measured by using a nanoindenter increased from 39.9 GPa for SiO2 films to 90.9 GPa for 3(SiO2):1(SnO2) films. However, the hardness results showed a different tendency due to the not well-distributed nanolaminate film structure showing a tendency to decrease and then increase as doping increases. Moreover, the growth rate and film density were evaluated by XRR. The growth per cycle (GPC) of SiO2 was 1.45 Å/cycle and the GPC of SnO2 was 1.0 Å/cycle. The film density of SiO2 was 2.4 g/cm3 and the film density of SnO2 was 4.9 g/cm3. Also, the GPC and film density values of the Sn-doped SiO2 films were in between the values of pure SiO2 and SnO2. The dry etch rate was also measured by reactive ion etching using CF4 plasma with 150 W for 1 min.

Effect of multilayer anti-reflective coating on spectral emissivity of area blackbody

An area blackbody is used as a standard radiant source for calibrating equipment of non-contact infrared temperature measurement. Tailoring the spectral emissivity of area blackbody is important for improving the accuracy of a temperature measurement system. In this work, a new antireflective coating (ARC) has been proposed and the first association it with area blackbody has been made to improve the emission in the 3–14 μm wavelength range. We have compared the single, dual and triple-layer of different ARC materials with a different combination. In each category, we have optimized the SiO2, Al2O3 and Si3N4 thin films layer stack as ARC coating and then compared radiation property of area blackbody covered by ARC. Numerical simulations of the spectral emissivity of the combination reveals that double-layer ARC is taken as the most excellent stack structure, which can realize spectral emissivity exceeding 0.9 with least material in the wavelength range from 3 to 13 μm. Physical mechanisms responsible for the increasing emissivity are elucidated as due to producing the gradual variation of the refractive index and the selection of each layer material directly affects emission performance. Considering excellent radiation property of area blackbody combined with ARC, this study can help pave the way for designing ideal area blackbody.

Argon and Other Defects in Amorphous SiO2 Coatings for Gravitational-Wave Detectors

Amorphous SiO2 thin films are one of the two components of the highly reflective mirror coatings of gravitational-wave detectors. For this study, layers of amorphous SiO2 on crystalline Si substrates were produced by ion-beam sputtering (IBS), using accelerated neutralized argon ions as sputtering particles, as is the case for the actual mirror coatings of gravitational-wave detectors. The aim of this study is to investigate the possible presence of various defects in the materials in order to improve the coating quality. We provide evidence that, due to the synthesis method, about 0.2 wt.% of Ar is present in the coatings, and it can be released by means of thermal treatments, starting around 400 °C. The time and temperature to obtain the total release of Ar increases with the coating thickness; for a thickness of 100 nm, all argon is released below 600 °C, while an isotherm of one hour at 900 °C is necessary for a coating 5 μm thick. Besides the Ar atoms left from the synthesis, other defects, such as Si clusters and silicon dangling bonds, are present in the coatings. The concentration of both of them is strongly reduced by thermal treatments either in vacuum or in air. The overall thickness of the coating is slightly increased after thermal treatments, as witnessed by the change of the period of interference fringes.

IMPROVEMENT OF THE PASSIVATION PROPERTIES OF SiO<sub>2</sub> FILMS, GROWN BY THE METHOD OF RAPID THERMAL ANNEALING, AFTER CHEMICAL RCA TREATMENT

As it is known, increasing the efficiency of silicon solar cells is one of the most important tasks in modern alternative energy industry. Optimization of the antireflection and passivation layer is the most economical way to increase efficiency. In this work, the effect of pretreatment on the passivation properties of silicon dioxide (SiO 2 ) films grown by rapid thermal processing (RTP) at annealing temperatures of 900 and 950°C in a dry oxygen atmosphere, was studied. The growth of thin films of SiO 2 on the surface of monocrystalline silicon wafers was carried out in the AS-ONE 150 rapid thermal annealing chamber (France). Measurements of the lifetime of minority charge carriers by the non-contact microwave method showed that the best passivation of the samples is achieved by applying a preliminary three-stage chemical cleaning (RCA) of the surface of the n-type silicon wafers. IR spectroscopy confirmed the formation of a SiO 2 layer by the presence of an intense maximum at 1071 cm -1 , which was attributed to stretching vibrations of the "tensioncompression" type. The results of calculations of the optical constants of the obtained SiO 2 films using the reflection spectra and the SCOUT software show the presence of a silicon dioxide whose refractive index and extinction coefficient are close to the reference.

Effect of gamma irradiation on the critical heat flux of sintered nano-coated surfaces

The electrophoretic deposition (EPD) technique was used to manufacture uniform SiO2, Al2O3, ZrO2, and TiO2 thin film coatings on thin steel plates (1.5 mm by 90 mm) to study heat transport properties when in contact with water at boiling temperature. To find the thickness and uniformity of the coatings, scanning electron microscope (SEM) images were made. The captured images showed that the coating thickness is uniformly increased by the EPD method. To investigate the effect of sintering, the coated plates were placed in a furnace at various temperatures. To investigate the effect of gamma irradiation on the critical heat flux (CHF) of the coated surfaces, the test specimens were irradiated in a gamma cell with different dose rates, and then BET, SEM, and EDS analyses were performed. Significant enhancement in CHF, for the hydrophilic surfaces, can be achieved by the EPD method. The results showed that the CHF for the sintered nano-coated surfaces, SiO2, Al2O3, ZrO2, and TiO2, increase by 24%, 23%, 19%, and 10%, compared to those of unsintered nanocoated surfaces, respectively. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area, and pore volume. The CHF of the nano-coated surfaces irradiated at 300 kGy increased by 12%, 8%, 5%, and 12% for SiO2, Al2O3, ZrO2, and TiO2, respectively. Nevertheless, the effect of gamma irradiation on the sintered surfaces was insignificant.

Probing material absorption and optical nonlinearity of integrated photonic materials

Optical microresonators with high quality (Q) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator Q factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of Q, the ultimate attainable Q, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited Q factors in several photonic material platforms. High-Q microresonators are fabricated from thin films of SiO2, Si3N4, Al0.2Ga0.8As, and Ta2O5. By using cavity-enhanced photothermal spectroscopy, the material-limited Q is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate Q vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.

Investigation of Heater Structures for Thermal Conductivity Measurements of SiO2 and Al2O3 Thin Films Using the 3-Omega Method.

A well-known method for measuring thermal conductivity is the 3-Omega (3ω) method. A prerequisite for it is the deposition of a metal heater on top of the sample surface. The known design rules for the heater geometry, however, are not yet sufficient. In this work, heaters with different lengths and widths within the known restrictions were investigated. The measurements were carried out on SiO2 thin films with different film thicknesses as a reference. There was a significant difference between theoretical deposited heater width and real heater width, which could lead to errors of up to 50% for the determined thermal conductivity. Heaters with lengths between 11 and 13 mm and widths of 6.5 µm or more proved to deliver the most trustworthy results. To verify the performance of these newfound heaters, additional investigations on Al2O3 thin films were carried out, proving our conclusions to be correct and delivering thermal conductivity values of 0.81 Wm−1 K−1 and 0.93 Wm−1 K−1 for unannealed and annealed samples, respectively. Furthermore, the effect of annealing on Al2O3 was studied, revealing a significant shrinking in film thickness of approximately 11% and an increase in thermal conductivity of 15%. The presented results on well-defined geometries will help to produce optimized heater structures for the 3ω method.

Electrostatic Tuning of Ionic Charge in SiO2 Dielectric Thin Films

Dielectric thin films are a fundamental part of solid-state devices providing the means for advanced structures and enhanced operation. Charged dielectrics are a particular kind in which embedded charge is used to create a static electric field which can add functionality and improve the performance of adjacent electronic materials. To date, the charge concentration has been limited to intrinsic defects present after dielectric synthesis, unstable corona charging, or complex implantation processes. While such charging mechanisms have been exploited in silicon surface passivation and energy harvesters, an alternative is presented here. Solid-state cations are migrated into SiO2 thin films using a gateless and implantation-free ion injecting method, which can provide greater long-term durability and enable fine charge tailoring. We demonstrate the migration kinetics and the stability of potassium, rubidium, and caesium cations inside of SiO2 thin films, showing that the ion concentration within the film can be tuned, leading to charge densities between 0.1–10 × 1012 q cm−2. A comprehensive model of ion injection and transport is presented along a detailed investigation of the kinetics of alkali cations. Integrating ionic charge into dielectrics to produce controlled electric fields can enable new architectures where field effect is exploited for improved electron devices.