SiO2 Thin Films Research Articles

Dynamic modulation performance of ferroelectric liquid crystal polarization rotators and Mueller matrix polarimeter optimization

A ferroelectric liquid crystal polarization rotator (FLCPR) has been widely used in polarization measurement due to its fast and stable modulation characteristics. The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation. In this study, FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter. Strong linear and weak circular birefringence are observed during modulation processes, and all the optical parameters of FLCPR are dependent on driving voltage. A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter. The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter. The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition. A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration. Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to −4.34%. This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.

Ozone based high-temperature atomic layer deposition of SiO2 thin films

In this paper, atomic layer deposition of SiO2 thin films was investigated with Si2Cl6 and O3/O2 (400 g m−3). O3/O2 is not preferred for high-temperature (>400 °C) processes due to its lower decomposition temperature, especially in a furnace-type chamber. However, with Si oxidation test using a cold-wall chamber, we have demonstrated the reactivity of O3/O2 up to 800 °C in comparison with O2 and H2O. The ALD of SiO2 films was examined at deposition temperatures from 500 °C to 700 °C. The growth rate at 600 °C was saturated to 0.03 nm/cycle with Si2Cl6 exposure over 1.2 × 105 L. O3/O2 also showed ALD-like saturation behaviors for exposures over 2.4 × 106 L. The ALD films deposited at 600 °C exhibited relatively smooth surface roughness (<0.18 nm) and low wet etch rate (1.6 nm min−1, 500:1 HF) that are comparable with PECVD SiO2 deposited at 250 °C and LPCVD SiO2 deposited at 450 °C.

SiO2 Coated on ZnO Nanorod Arrays With UV-Durable Superhydrophobicity and Highly Transmittance on Glass.

ZnO nanorod arrays were fabricated on glass through hydrothermal way. Then a thin SiO2 film was covered on ZnO nanorod arrays using pulsed laser deposition (PLD) technique, and modified by stearic acid. It was found that SiO2 film only had slight effects on the contact angle and transmittance of ZnO nanorod arrays. However, it had brought a huge improvement in the UV durability of superhydrophobic ZnO nanorod arrays. The results showed that the water contact angle remains constantly at 160.5° even UV irradiation time exceeded 50 h when the deposition time of PLD was about 10 min. This structure with UV-durable superhydrophobicity and highly transmittance on glass substrate can be served as front materials in solar cells.

Processing technologies for sealing glasses and glass‐ceramics

AbstractThis paper embraces two different approaches for the joining of materials through glass sealants. First, the conventional method of furnace sealing in which paste technology is normally employed. The glass sealant is applied in powder form mixed with agglomerant and with the help of dispenser robots, tape casting, or screen printing. Glass‐ceramics for sealing of solid oxide fuel cells (SOFC) are described as an example of this type of processing. Glass composition, thermal properties, particle size of the glass powder, sintering and crystallization competition, and final crystalline phases together with a suitable chemical compatibility with the metallic and ceramic elements to be sealed need to be carefully adjusted for this specific application. Second, laser welding is presented as an alternative sealing technology. A general overview about laser welding through glass sealants is presented. Particularly, the welding of sapphire and fused silica glass through a BTS.2SiO2 thin film glass sealant by employment of a nanosecond‐pulsed laser is detailed. Laser parameters (frequency, power, scan speed, and number of passes) were optimized to get the best molten conditions of the BTS thin film, while allowing its crystallization. BTS crystallization upon laser welding leads to a strong blue emission upon UV excitation. Finally, both processing technologies were compared.

Dielectric Loss of Thin-Film SiO2 Samples on Al in THz–IR Range

The development of new dielectric materials for insulating layer of interconnects with low loss on high frequencies (low-k) is one of main directions of modern microelectronics. At present, various modifications of SiO2-based dielectric structures standard for modern integrated circuits differ in composition and morphological characteristics are being studied. In this work, the dielectric loss of thin-film SiO2 samples on Al substrate are studied by methods of terahertz (THz) and IR spectroscopy. It is found that the spectra of such structures are substantially different, including the resonant Berreman modes, as compared to the spectra of a bulk fused silica.

Surface modification of SiO2 thin film using high-dose ion implantation technique as a suitable manufacturing process

We studied the surface modification of SiO2 films using high-dose ion implantation. The wet etching rate of HF solution can be precisely controlled by changing the various ion species. The etching rate increases with B+ and P+ implantation and decreases with C+, N+, O+ and Si+ implantation. In particular, the wet etching rate is greatly increased by P+ implantation and is hardly etched by C+ and Si+ implantation. We also demonstrated the selective etching process using a 3D structure sample. Selective etching can be realized in a self-aligned manner using ion implantation. This technique using ion implantation can be quite useful as a suitable production process for device fabrication.

Water vapor-induced structure modification of vertically-aligned carbon nanotube arrays and successive thin film coating for enhanced field emission properties

Vertically-aligned carbon nanotubes (VCNTs) are used as electron source in various field emission applications owing to its high aspect ratio, chemical inertness, mechanical strength and electrical conductivity. Here, we demonstrate that surface structure modification along with thin film coating enhances the field emission performance, such as turn-on voltage, emission site density, and stability. In the present study, VCNTs with different heights were grown on silicon wafers by thermal chemical vapor deposition followed by the structure modification of VCNTs using capillarity-driven water vapor condensation. We obtained various surface morphologies by varying the water vapor exposure time and heating temperature. In addition, the structure-modified VCNTs surfaces were coated with W and SiO2 thin films using electron-beam evaporation. It was observed that W-coated VCNTs with modified surface morphology results in the best field emission performance.

Antireflection Coating on PMMA Substrates by Atomic Layer Deposition

Antireflection coatings (ARC) are essential for various optical components including such made of plastics for high volume applications. However, precision coatings on plastics are rather challenging due to typically low adhesion of the coating to the substrate. In this work, optimization of the atomic layer deposition (ALD) processes towards conformal optical thin films of Al2O3, TiO2 and SiO2 on poly(methyl methacrylate) (PMMA) has been carried out and a five-layer ARC is demonstrated. While the uncoated PMMA substrates have a reflectance of nearly 8% in the visible (VIS) spectral range, this is reduced below 1.2% for the spectral range of 420–670 nm by applying a double-side ARC. The total average reflectance is 0.7%. The optimized ALD coatings show a good adhesion to the PMMA substrates even after the climate test. Microscopic analysis on the cross-hatch areas on PMMA after the climate test indicates very good environmental stability of the ALD coatings. These results enable a possible route by ALD to deposit uniform, crack free, adhesive and environmentally durable thin film layers on sensitive thermoplastics like PMMA.

Unravelling local environments in mixed TiO2–SiO2 thin films by XPS and ab initio calculations

Mixed TixSi1−xO2 oxide can exhibit a partial phase separation of the TiO2 and SiO2 phases at the atomic level. The quantification of TiO2–SiO2 mixing in the amorphous material is complicated and was so far done mostly by infrared spectroscopy. We developed a new approach to the fitting of X-ray photoelectron spectroscopy data for the quantification of partial phase separation in amorphous TixSi1−xO2 thin films deposited by plasma enhanced chemical vapour deposition. Several fitting constraints reducing the total number of degrees of freedom in the fits and thus the fit uncertainty were obtained by using core electron binding energies predicted by density functional theory calculations on TixSi1−xO2 amorphous supercells. Consequently, a decomposition of the O1s peak into TiO2, SiO2 and mixed components was possible. The component areas ratios were compared with the ratios predicted by older theoretical models based on the atomic environment statistics and we also developed several new models corresponding to more realistic atomic structure and partial mixing. Based on the comparison we conclude that the studied films are mostly disordered, with only a moderate phase separation.

EFFECT OF SURFACE WETTABILITY AND SURFACE ROUGHNESS ON SiO2 AND COPPER HYBRID THIN-FILM-COATED SURFACES FOR NUCLEATE BOILING PERFORMANCE

The present scenario shows that the usages of electronics equipment are very extensive because of its performance and compactness. The concept of boiling heat transfer is applied to cool the equipment for better thermal management system. In the present experimental investigation, the copper substrates were coated by SiO2 and copper hybrid thin film by the radio frequency sputtering method. The thickness of the coating was selected as 250 nm, 500 nm, and 750 nm. The contact angle of the SiO2 and copper-coated hybrid surface was measured by goniometer, and structural studies were conducted by images from a scanning electron microscope and a stylus profilometer. The wettability of surfaces was improved significantly because of active nucleation sites created by thin-film coating. The nucleate boiling test was carried out by the pool boiling experimental setup for deionized (DI) water at saturation temperature and atmospheric pressure. The critical heat flux (CHF) and boiling heat transfer coefficient (HTC) were calculated, and compared with bare copper substrate. The results showed that the critical heat flux was enhanced by 45%, 53%, and 62%, whereas the boiling heat transfer coefficient was 63%, 97%, and 130% for 250-nm-, 500-nm-, and 750-nm-thick surfaces, respectively. The reason for this enhancement was due to increased nucleation site density which deals with the bubble formation and departure. The critical heat flux and boiling heat transfer enhancement at low wall superheat reveals a better heat transfer mechanism for an effective thermal management system.

Effect of an electric field during the deposition of silicon dioxide thin films by plasma enhanced atomic layer deposition: an experimental and computational study.

The growth, chemical, structural, mechanical, and optical properties of oxide thin films deposited by plasma enhanced atomic layer deposition (PEALD) are strongly influenced by the average-bias voltage applied during the reaction step of surface functional groups with oxygen plasma species. Here, this effect is investigated thoroughly for SiO2 deposited in two different PEALD tools at average-bias voltages up to -300 V. Already at a very low average-bias voltage (< -10 V), the SiO2 films have significantly lower water content than films grown without biasing together with the formation of denser films having a higher refractive index and nearly stoichiometric composition. Substrate biasing during PEALD also enables control of mechanical stress. The experimental findings are supported by density functional theory and atomistic simulations. They demonstrate that the application of an electric field during the plasma step results in an increased energy transfer between energetic ions and the surface, directly influencing relevant surface reactions. Applying an electric field during the PEALD process leads to SiO2 thin films with significantly improved properties comparable to films grown by ion beam sputtering.

SiO2 thin film growth through a pure atomic layer deposition technique at room temperature.

In this study, less contaminated and porous SiO2 films were grown via ALD at room temperature. In addition to the well-known catalytic effect of ammonia, the self-limitation of the reaction was demonstrated by tuning the exposure of SiCl4, NH3 and H2O. This pure ALD approach generated porous oxide layers with very low chloride contamination in films. This optimized RT-ALD process could be applied to a wide range of substrates that need to be 3D-coated, similar to mesoporous structured membranes.

Диэлектрические потери тонкопленочных образцов SiO-=SUB=-2-=/SUB=- на Al в THz-IR-диапазоне

Creation of new dielectric materials for insulating layers of interconnects with low losses at high frequencies (low-k) is one of the main directions of modern microelectronics. Currently, various modifications of standard for modern integrated circuits dielectric structures based on SiO2, differing in composition and morphological characteristics, are being investigated. In this paper, the dielectric losses of thin-film SiO2 samples on an Al substrate are studied by terahertz (THz) and IR spectroscopy. Significant differences in the spectra of such structures in comparison with bulk samples of fused quartz, including berriman resonance modes, were found.

Boiling Heat Transfer and Critical Heat Flux Enhancement Using Electrophoretic Deposition of SiO2 Nanofluid

The electrophoretic deposition (EPD) technique was used to create a uniform SiO2 thin film coating on boiling plates, 4 mm in width and 9 mm in length. Significant enhancement in critical heat flux (CHF), for the hydrophilic surfaces generated by this anodic EPD method, has been observed. In order to increase the coating strength, the plates were sintered at various temperatures. To find the thickness and uniformity of the coatings, the SEM images were captured. The captured images showed that the coating thickness uniformly increased up to 90 nm for 0.5% nanofluid percentage by the EPD method. The results show that the hydrophilic and super-hydrophilic surfaces have different boiling heat transfer (BHT) coefficients and CHF behaviors. Also, the results showed an increase of 160% in the CHF value by sintering compared to a bare surface. However, because of the setup simplicity, the shape independency, the particle-coating uniformity, and thickness controllability, the EPD technique can be an appropriate option for modification of the surface and coating on the nuclear fuel cladding.

Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO2 and SiO2 thin films and multilayers

The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO2 and TiO2 thin films as well as SiO2/TiO2 multilayers prepared by electron beam evaporation at 70° and 85° zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO2 is higher than in TiO2 nanocolumns, while the situation is closer to this latter in TiO2/SiO2 multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.

Spectroscopic and morphological studies of SiO2 graded index thin films fabricated at oblique incidence angles

The present paper reports the fabrication of single layer graded index SiO2 thin films at various oblique incidence angles by using Static glancing angle deposition (GLAD) setup. These SiO2 films have been fabricated by using the electron-beam physical vapor deposition technique via ingeniously designed jig holder by placing the substrates at different angles of incidence of the incoming plasma. The optical properties of these films were studied by using UV–Vis–NIR spectrophotometer. The coating at various incidence angles of deposition from 10 to 80° reveals that there is a variation in refractive index of the material from 1.46 to 1.38. The microstructural studies of these films were further ascertained by field emission scanning electron microscopy, which reveals increase in the porosity of the film with deposition at oblique angle of incidence. The contact angle measurement of the films indicated the decrease in contact angle of these films with increasing angle of deposition indicating the hydrophilic nature of the samples. Owing to this behavior, these films find applications in antireflection (AR) coatings for flat panel displays, protective coatings, solar cells and optoelectronic devices etc.

Experimental investigation of critical heat flux on SiO2 thin film deposited copper substrate in DI water at atmospheric pressure

Experimental investigation of critical heat flux on SiO2 thin film deposited copper substrate in DI water at atmospheric pressure

Application of the inverse method in the 3 ω method for measuring the thermal conductivity of thin films

Planar nano-materials generally refer to samples that are extremely thin in the direction of thickness, such as nanofilms, graphene, and superlattice. They are of great importance in various fields, including transistors, thermoelectrics, and optoelectronics, etc. In practice, materials’ thermal transport characteristics often play a crucial role in applications. More importantly, due to the confinement in the direction of thickness, the mechanisms of thermal transport process in planar nano-materials become very different from those at the macroscale. For example, the effective lattice thermal conductivities of nanofilms are always highly dependent on their thickness, since phonon coherence, ballistic transport, and boundary scattering effects could occur in this case. Therefore, probing thermal transport properties of planar materials has been a research hotspot in both the research and industrial communities. The 3 ω method has been proven to be a powerful tool that can measure the thermal conductivities of planar materials effectively. Particularly for a thin film on a substrate, the differential 3 ω method was developed. In this scheme, it is necessary to determine the thermal properties of substrate materials in the first step. Thus, a reference sample should be measured in addition to the target sample, which not only increases the complexity of measurement but also reduces the measurement accuracy of the thin film’s thermal transport properties. In the present work, we used the numerical simulations to demonstrate that in the 3 ω method the combination of finite element method (FEM) and inverse problem method can derive the thermal properties of thin film and substrate simultaneously. It was found that the thermal conductivities could be determined accurately despite the cutoff frequency of measurement, whereas the thermal diffusivities’ accuracy could be improved with increasing cutoff frequency of measurement. Furthermore, as a test, the thermal conductivities of silicon dioxide (SiO2) thin film on the silicon (Si) substrate were measured using the method above. In our experiments, the thickness of Si substrate was 450 μm, and the thickness of SiO2 thin film was 950 nm. The frequency of driving current was set from 100 to 5000 Hz (the cutoff frequency). The trust region reflective method was adopted in the fitting process. Moreover, it was found that the measurement uncertainty of temperature rise was less than 1% and thus its influence on the uncertainties of measured thermal properties could be ignored. As a result, the major uncertainties of thermal conductivity measurement came from measuring the thickness of SiO2 thin film. The thermal conductivity of Si substrate was 142.1 W/(m K) with a relative error equal to approximately 2%, and the thermal conductivity of SiO2 thin film was 1.01 W/(m K) with a relative error equal to approximately 2%, which could agree well with the reported value in literature. In summary, the present work demonstrated that the combination of FEM and inverse method could be employed for thermal properties measurement, and thus analytical models are not always necessary. For future work, the methodology presented in this paper can be extended to deal with the measurement of thermal transport properties of irregular-shape thin flakes on a substrate.

Oxidation resistant TiO2–SiO2 coatings on mild steel by Sol–Gel

Single and multilayer titania–silica (TiO2–SiO2) oxidation resistant dry gel thin film was applied on mild steel (MS) through sol–gel based dip coating. The coated samples were fired at 410 °C for 30 min and the coating film thickness was found to be 200–400 nm using spectroscopic ellipsometry. The structural and chemical analysis of the films was carried out by XRD, SEM–EDS and TG–DTA. The oxidation resistance of coatings was evaluated by weight gain per unit area after exposing to 400 °C for 20 h in air. Uncoated specimens exhibited a weight gain of 0.72 mg/cm2. However, the weight gain was less by 6 times for single layer and 16 times for 3 layers of coatings (deposition). Further, oxidation kinetics study revealed a reduction of parabolic oxidization rate constant by 43 times (0.026 mg2 cm−4.h−1) for single layer and 325 times (8 × 10−5 mg2 cm−4.h−1) for 3 layer coatings, compared to bare MS exposed to identical conditions. Such a high reduction in oxidation with multilayer deposition is probably due to the effective coverage of micro–cracks, which may be induced due to the thermal mismatch between the coatings and MS. An improvement in adherence of coating was confirmed due to the formation of (Fe0. 927Ti0.073)2.O3 at the interface using XRD. The addition of SiO2 to TiO2 was found to minimise the coating defects associated with sol–gel and also inhibit the formation of anatase. Thus, the present work demonstrated the application of TiO2–SiO2 thin film coating on MS through sol–gel technique to form an impervious layer to substantially enhance the oxidation resistance at elevated temperatures.

FePt Metallic Nanoparticle Dispersion-Induced Evolution of Resistive Switching Performance in SiO2-Based RRAM Devices

In order to improve the resistive switching performance of SiO2-based resistance random access memory (RRAM) devices, the evolution from pure oxide-based devices to metallic nanoparticle dispersed oxide-based devices is investigated in this paper. It is found that a high ratio of dispersed-oxide/pure-oxide and thin SiO2 film can increase the uniformity and endurance of RRAM devices. Pure TiN/SiO2/Au RRAM devices show large distributions and poor endurance for repeated resistive switching process, while the TiN/SiO2:FePt/SiO2/Au RRAM devices exhibit higher uniformity and better endurance. Moreover, the fluctuations and degradation of high-resistance state and low-resistance state are observed in the former devices; by increasing the ratio of dispersed-oxide/pure-oxide in TiN/SiO2/SiO2:FePt/SiO2/Au, high consistency resistive switching is obtained. It is believed that the random formation of conducting filaments (CFs) causes poor performance of RRAM devices, and with a higher ratio of dispersed-oxide/pure-oxide the morphology of CFs is controlled due to the local field enhancement. The results in this paper may provide a method of fabricating high-performance RRAM devices for industry application.