SiO2 Thin Films Research Articles

Remarkable enhancement of thermal conductivity induced by coordination transition in SiO2 thin films

Remarkable enhancement of thermal conductivity induced by coordination transition in SiO2 thin films

Heat transport in SiCOH thin films: an experimental and molecular dynamics study

Carbon-doped silicon dioxide (SiCOH) film is currently regarded as one of the most promising low-k materials in the integrated circuits (ICs) industry for advanced technology nodes. However, there have been limited studies on the thermal properties of SiCOH compared to its electrical and mechanical properties. In this study, we investigate the thermal conductivity of SiCOH thin films through molecular dynamics simulations (MD) and experimental characterizations. Our findings indicate that the size effect on thermal conductivity at 300 K is negligible when the thickness of SiCOH film is less than 20 nm. Additionally, we observe a contrasting temperature dependence law for the thermal conductivity of SiCOH thin films compared to crystal SiO2 thin films. Furthermore, we demonstrate a significant decrease in thermal conductivity with increasing porosity in SiCOH films; specifically, an increase in porosity from 5.35% to 42.77% results in a 60% reduction in thermal conductivity. Moreover, we validate our simulation results by characterizing the thermal conductivity of SiCOH using 3 ω method.

Deposition of CdSe Nanocrystals in Highly Porous SiO2 Matrices-In Situ Growth vs. Infiltration Methods.

Embedding quantum dots into porous matrices is a very beneficial approach for generating hybrid nanostructures with unique properties. In this contribution we explore strategies to dope nanoporous SiO2 thin films made by atomic layer deposition and selective wet chemical etching with precise control over pore size with CdSe quantum dots. Two distinct strategies were employed for quantum dot deposition: in situ growth of CdSe nanocrystals within the porous matrix via successive ionic layer adsorption reaction, and infiltration of pre-synthesized quantum dots. To address the impact of pore size, layers with 10 nm and 30 nm maximum pore diameter were used as the matrix. Our results show that though small pores are potentially accessible for the in situ approach, this strategy lacks controllability over the nanocrystal quality and size distribution. To dope layers with high-quality quantum dots with well-defined size distribution and optical properties, infiltration of preformed quantum dots is much more promising. It was observed that due to higher pore volume, 30 nm porous silica shows higher loading after treatment than the 10 nm porous silica matrix. This can be related to a better accessibility of the pores with higher pore size. The amount of infiltrated quantum dots can be influenced via drop-casting of additional solvents on a pre-drop-casted porous matrix as well as via varying the soaking time of a porous matrix in a quantum dot solution. Luminescent quantum dots deposited via this strategy keep their luminescent properties, and the resulting thin films with immobilized quantum dots are suited for integration into optoelectronic devices.

Annealing effects on 100 keV silicon negative ions implanted SiO2 thin films

SiO2 thin film of thickness 300 nm grown on p-type silicon substrate was implanted with 100 keV silicon negative ions for the fluences of 1 × 1016, 5 × 1016, and 1 × 1017 ions cm−2. The implanted samples were investigated using an energy-dispersive X-ray (EDX) spectroscopic technique, and the samples were annealed at a temperature of 900 oC under N2 ambient. Ultraviolet–visible near infrared (UV-Vis-NIR) spectroscopy has been used to investigate the implanted SiO2 thin film samples before and after thermal annealing. EDX results revealed an increase in the atomic percentage and weight percentage of silicon ions as compared to oxygen ions in SiO2 thin film. This may be due to the increase in the concentration of silicon ions with the increase of implanted ion fluences within the SiO2 thin film. UV-Vis-NIR studies showed higher transmittance for thermally annealed samples as compared to non-annealed samples. This may be attributed to the creation of a new SiOx phase in the SiO2 matrix at higher temperatures. UV-Vis-NIR studies also exhibited an increase in the energy band gap value after thermal annealing. This effect may be related to the formation of silicon nanoclusters in SiO2 thin film.

Investigating the effect of SiO2 thin films with sculptured topographies on the alignment properties of liquid crystals

In the present work, sculptured thin films (STF) based on silicon dioxide (SiO2) induced on the indium tin oxide (ITO) coated substrates via glancing angle deposition (GLAD) technique using the physical vapor deposition (PVD) process. Our main motive to perform this work is to address the issues we have faced with the traditional alignment method and give a try to overcome those problems. Keeping these challenges in our mind, we are giving here an alternative to traditional method and explored this different alignment technique with GLAD process. We have fabricated a liquid crystal device (LCD) in a way of electrically-controlled birefringence (ECB) and placed the engineered substrates in anti-parallel alignment. Morphological, optical and electro-optic behaviour of resulting device has been studied in the ∼5 μm thick device. Effect of applied voltage on the morphology and electro-optic behaviour of liquid crystal has been established. Interestingly, LC material demonstrates electrically switchable birefringence colours viz. brown, green, pink, purple and mauve colour, under applied electric field in room temperature at 10X magnification under polarizing optical microscope. A very nice extinction and contrast has been obtained with fabricated ECB device, which elucidate the device quality with impeccable alignment without any disclination defects. Besides, the electro-optic characteristics it also shows a significant impact on the liquid crystal properties. The obtained results demonstrate nice optical retardation, a lower Frederick's threshold voltage i.e. 1.5 V and 19.03 dB higher contrast respectively. An impressive switching response time τon of 5.4 ms and τoff = 600 µs at 20 V has attained with respective device as well. Such change in parameters may correspond to the higher electrical torque experienced by the LC molecules on the application of applied field. Anchoring energy and pretilt angle of respective system has been calculated and correlated with observed behaviour. Thus, engineered device with this superior alignment method show remarkable electro-optic results which can open a new way for the development of fast LCD for advanced optical device applications.

Humidity sensing by tailoring light absorption of SiO2/bromophenol blue (BPB) thin film on optical fiber

The fabrication of an evanescent wave fiber optic humidity sensor based on bromophenol blue (BPB) doped SiO2 thin film was demonstrated, modulating in light intensity. The sensing film was coated on a fiber core via a single-step dip coating method, followed by sol-gel processing of the precursor. A good exponential relationship was established between output light intensity and relative humidity. The sensor exhibited a high sensitivity and fast response and recovery, as well as low hysteresis, good stability and repeatability. Adsorption of ambient water triggered a ring-opening reaction of BPB, which enhanced light absorption of the sensing film significantly and affected the transmission of the evanescent wave.

High-efficiency green light emission from InGaN/GaN using localized surface plasmon resonance tuned by combination of Ag nanoparticles and dielectric thin film

We achieved significant enhancements in green light emission (550 nm) from InGaN/GaN quantum wells (QWs) by tuning the localized surface plasmon resonance (LSPR) of self-assembled Ag nanoparticles (NPs) through the application of a SiO2 thin film. The LSPR wavelength of Ag NPs was shifted towards shorter wavelengths by 80 nm using a 5 nm SiO2 layer to separate Ag NPs from GaN surface, thereby aligning it effectively with the green region. This strategic placement of Ag NPs and a 5 nm SiO2 film resulted in significant enhancements of photoluminescence (PL) by 15- and 8.8-fold with 5 and 11 nm GaN cap layers, respectively. The LSPR of Ag NPs on a SiO2 thin film facilitated a longer possible distance for the coupling between surface plasmons (SPs) and excitons in a QW. Traditionally, the distance between SPs-generating metal and a QW has been maintained at 10 nm to achieve substantial enhancements. Remarkably, even with a 25 nm cap layer, Ag NPs on a 5 nm SiO2 film boosted PL by 3.1-fold. The enhancements attributable to Ag NPs on SiO2 films were superior, reaching up to 4.8 times greater than those of Ag NPs on GaN surfaces. Additionally, the PL enhancement factors calculated using the finite differential time domain (FDTD) method aligned closely with experimental results.

Improved Thermal Stability and Oxygen‐Barrier Performance of SiO2 Thin Films by Modifying Amorphous Network Structure

Due to low‐refractive‐index and grain‐boundary‐free features, amorphous SiO2 thin films possess inherent advantages in serving as antireflective and protective layers against atmosphere. However, under high‐temperature and/or oxidation harsh environment, the thermodynamic instability of SiO bonds and “depolymerization” process among tetrahedral units [SiO4] would result in their insufficient thermal stability and oxygen‐barrier failure. By taking amorphous network former, small element electronegativity, and high oxide dissociation energy into considerations, low‐level Zr dopant is introduced to induce short‐ and medium‐range structural modification in amorphous SiO2 thin films, aiming to shorten SiO bond length and enhance network connectivity, respectively. As expected, the fabricated SiZrO thin films exhibit superior thermal stability and oxygen‐barrier performance without sacrificing their low‐index attribute. The Zr doping significantly elevates the oxygen‐inward‐diffusion activation energy from 0.94 to 1.95 eV in SiO2 network. Further, utilizing as protective layer for W‐SiO2 cermet, the SiZrO can effectively prevent the oxidation of W nanoparticles caused by oxygen inward diffusion. Undoubtedly, the exploration of amorphous SiZrO thin films offers exciting prospects for the application of functional coatings and devices under extreme conditions.

Characteristics of highly sensitive hydrogen gas sensor based on Pt-SiO2/Si microring resonator

A hydrogen gas sensor based on a silicon microring resonator (MRR) with a Pt–SiO2 thin film as a hydrogen-sensitive film is proposed and investigated to realize a high-sensitivity hydrogen sensor. The sensor detects hydrogen on the basis of the resonant wavelength shift caused by the reaction heat generated in the Pt–SiO2 film. In the hydrogen exposure measurement, resonant wavelength shifts of approximately 5.0 and 2.4 nm were observed at hydrogen concentrations of 4.0 and 0.4 vol%, respectively, showing the high sensitivity of the proposed sensor. In addition, an MRR sensor with an upper Al2O3 cladding layer is proposed and its higher sensitivity is theoretically demonstrated.

Formation of SiO2 thin films through plasma- enhanced chemical vapor deposition using SiH4/Ar/N2O

SiO2 films and their formation technologies are critical for the fabrication of Si-based integrated circuits (ICs). SiO2 films fabricated using plasma-enhanced chemical vapor deposition (PECVD) have become increasingly important because of the increasing trend of three-dimensional (3D) architectures in ICs. SiO2 films formed by PECVD have been widely studied for over 40 years; however, owing to the complex plasma reactions and the differences in system conditions, the relationship between the experimental parameters and film characteristics are disputed. In this study, focusing on the two important characteristics (surface morphology and deposition rate) of SiO2 films for 3 D ICs manufacturing, SiO2 film growth was systematically investigated via SiH4/Ar/N2O in PECVD; a theoretical reaction process model (including gas-phase reaction, chemical adsorption, and surface reaction) bridging the experimental parameters (chamber pressure, gas ratio, radio frequency power, and substrate temperature) and characteristics (surface morphology and deposition rate) of SiO2 films was established. This study contributes to the precise formation of sub-100 nanometer SiO2 films using PECVD for manufacturing 3 D ICs.

Comparative structural study of Al2O3–SiO2 glasses and amorphous thin films

AbstractWe compared the impact of alumina doping on the structure of Al2O3–SiO2 amorphous thin films and bulk glasses using Raman spectroscopy and x‐ray diffraction. In both thin films and bulk glasses, the addition of Al2O3 is accompanied by an increase in the mean Si–O–T angle and an evolution of the ring statistics with a decrease in the proportion of small rings. We evidenced structural differences between sputtered films and fused bulk glasses. Sputtered Al2O3–SiO2 thin films are about 6%–7% denser than their equivalent Al2O3–SiO2 bulk glasses. This difference is mainly due to a change in ring statistics with the formation of small rings within the sputtered thin films. These structural differences in atomic structural organization highlight the impact of the synthesis conditions and open the door to further investigation of the structure–functional property relationships in sputtered Al2O3–SiO2 thin films.

Sol-Gel Spin Coated Transparent Single-TiO2 and SiO2 Thin Film on Glass for Opto-electronic Applications

Great attention has been given on the sol-gel synthesis and spin-coating deposition techniques for the fabrication of various thin films. Because of its simple technique to fabricate dielectric (metal oxide) films using tetraethyl orthosilicate and titanium isopropoxide precursors. In this work, transparent single layer of SiO2 and TiO2 thin film was deposited on a glass substrate and characterized by FTIR, UV-visible spectroscopy, fluorescence and scanning electron microscopy techniques. The single layer thin film was mechanically stable and strong by adhering to glass substrates. The FTIR transmittance spectrum evidenced the existence of Si-O-Si and Ti-O-Ti at ~1100 and 1400 cm-1. The UV-visible absorbance spectra of single layer of SiO2 and TiO2 thin films showed strong absorption at below 00 nm. The excitation wavelength at 380 nm, the fluorescence spectra of both thin films showed the highest emission spectrum in between 733-798 nm. The SEM studies confirmed the smooth surface in both SiO2 and TiO2 layers. Further, it could be useful for various applications such as back reflector in solar cells, anti-reflection coatings, hydrophobic and anti-fogging materials.

Investigation of optical and electrical properties of TiO2, SiO2, and Ag single and multilayer thin films using spectroscopic ellipsometry and spectrophotometry methods: prepared by spin coating and DC magnetron sputtering

In this work, spectroscopic ellipsometry was used to study the optical and electrical properties of TiO2 and SiO2 thin films deposited by spin-coating at different coating rotation speeds and annealed at various temperatures. In addition, Ag thin films of different thicknesses were deposited by DC magnetron sputtering at ambient temperature. In this method, the optical band gap for TiO2 thin films is between 3.15–3.85 eV, and for SiO2 thin films, it is between 3.2–3.8 eV. The optical properties, including reflectance, transmittance, and absorbance, of TiO2, SiO2, and Ag thin films in the form of single and multilayer thin films in the wavelength range of 200–2500 nm, were investigated using an ultraviolet-visible-near infrared (UV–vis-NIR) dual-beam spectrophotometer. In the TiO2/Ag/SiO2 multilayer thin film, the rejection was 58.6% −73.6% in the NIR wavelength range (800–2500 nm), and a transmittance of 40%–45% was achieved in the visible light range (400–700 nm).

Design and fabrication of poly-Si/SiO2 Fabry–Perot filter for nondispersive IR CO2 sensors

The relationship between the transmittance and FWHM of a Fabry–Perot filter for a nondispersive carbon dioxide (CO2) sensor was investigated as a function of the number of distributed Bragg reflector (DBR) pairs consisting poly-Si and SiO2 thin films. Given the significant prior research on the fabrication of high-performance Fabry–Perot filters, this study is focused on the relationship between the transmittance and FWHM that can be achieved by controlling the reflectance of the DBR pairs. Each layer of the filter was simulated adequately as the poly-Si and SiO2-based DBR pairs, and poly-Si and SiO2 were deposited on the soda–lime substrate by RF sputtering and low-pressure chemical vapor deposition based on the simulation results. The fabricated filter showed a transmittance of 43.7% and FWHM of 125 nm at 4.26 μm. The NDIR CO2 sensor with Fabry–Perot filter showed enhanced selectivity to CH4 and CO compared with normalized CO2 response.

Self-assembling formation of Si-QDs on SiO2 line patterns

The lateral growth of Si-quantum dots (QDs) on line-patterned SiO2 from the thermal decomposition of pure monosilane (SiH4) has been systematically examined. We confirmed that the Si-QDs diameter in the line direction of the SiO2 patterns has the same growth rate as the SiO2 thin film surface without the line patterns. Moreover, it has been found that in the growth of Si-QDs in the width direction, a surface migration of Si precursors adsorbed from space regions could contribute to dots growth on line-patterned SiO2, which results in an elliptical growth. Furthermore, we have demonstrated a one-dimensional arrangement of highly dense-elliptical shaped Si-QDs with high uniformity in size by controlling line width, CVD time, and temperature.

Effects of the thermal treatments on the optical properties of SiO2 anti-reflective coatings on sapphire windows

The SiO2 films were deposited on sapphire substrates using radio frequency (RF) magnetron sputtering to enhance the mid-wave infrared (IR) transmittance. The effects of thermal treatments by annealing and in-situ heating on the SiO2 films were investigated. After annealing at 600 °C, the surface morphology, microstructure, chemical states, and optical constants were investigated. No obvious microcracks or delamination were observed on the film surfaces, indicating excellent adhesion to the sapphire substrates. With an increase in the annealing time, gradual oxidation of Si atoms within the SiO2 thin films occurred, resulting in the release of OH groups and evaporation of moisture. The refractive index exhibited slight changes, while the extinction coefficient showed a significant reduction, thus the transmittance was improved. According to the in-situ heating tests from the annealed samples, it revealed a slight increase in average transmittance with prolonged annealing time. Finally, we assessed the performance of the annealed samples by rapid heat shock to 600 °C at a very short time, which demonstrated outstanding optical performance and heat-resistant properties. The present work supports the feasibility of applying the SiO2 films under harsh high-temperature environments.

From silicon to silica: a green chemistry approach for hollow sphere nanoparticle formation.

Herein we report on an environmentally friendly and scalable production route for hollow silica spheres (HSSs). The process is based on close to 100% conversion of non-crystalline solid Si nanoparticles (D̄ = 40 ± 9 nm) in mild alkaline solutions (pH ≤ 9.0) at ambient temperature. The Si nanoparticles are prepared using the centrifugal chemical vapor deposition (cCVD) method. Combining transmission electron microscopy (TEM) imaging and nanoparticle size analysis with hydrogen evolution data, elemental mapping, and nitrogen adsorption for surface area measurement, we show for the first time experimental data that document a Kirkendall type Si-to-HSS formation process. Our understanding is that the Si nanoparticles exposed to air form a SiO2 film, which is stable in the mild alkaline environment. Silicon from the Si nanoparticles is transported through the thin SiO2 film and is reacting with H2O/OH- species on the particle surface or in the already thickened SiO2 shell to form silicic acid that in turn rapidly gets converted to a sol-gel to continue the growing of the silica shell. We foresee that this green chemistry approach can be utilized for HSS preparation for use in batteries, insulation materials and drug delivery.

A live mammalian cells electroporation array for on-chip immunofluorescence

The detection of intracellular proteins in vitro is commonly realized with immunofluorescence techniques, through which antibodies or markers are delivered into fixed cells and recognize specific proteins. Many innovative techniques, however, avoid cells fixation by chemical compounds and, among the others, electroporation is widely used. Here we demonstrate that in situ electroporation on thin film SiO2 capacitive microelectrodes can be realized with high efficiency to deliver fluorescent markers and antibodies into mammalian cell lines and primary neuronal cells to detect intracellular proteins, like actin. The results presented in this work open the way to the use of this technique for the detection of potentially any target protein, even through subsequent electroporations.

Cerium-Doped Oxide-Based Materials for Energy and Environmental Applications

Cerium is a rare-earth metal commonly used as a dopant in various metal oxides to enhance their performances or provide optoelectronic properties. Cerium oxide (ceria) is particularly valuable owing to its unique properties and applications in various fields, such as biomedical research, photovoltaics, and industrial catalytic processes. This review focuses on the use of cerium and ceria doping in the synthesis of SiO2 and ZnO. Studies have shown that Ce-doped SiO2 thin films exhibit luminescence properties and proton shielding capabilities, and that Ce-doped ZnO has potential applications in gas sensors. In this review, we highlight the potential for controlling the luminescence and optical characteristics of these materials via cerium doping, opening up possibilities for various technological advancements and potential applications of cosmic ray shielding in space photovoltaics.

Influence of thermal annealing on silicon negative ion implanted SiO2 thin films

SiO2 thin film of thickness 300 nm grown on p-type silicon substrate was implanted with 100 keV silicon negative ions with fluences varying from 5×1015 to 1×1017 ions cm−2. The implanted samples were annealed at the temperature of 500 °C under N2 ambient. Electron spin resonance (ESR), Fourier transform infrared (FTIR), Photoluminescence (PL), and glancing angle X-ray diffraction (GXRD) techniques have been used to investigate the implanted SiO2 thin film after thermal annealing. ESR studies revealed the absence of vacancy defects after thermal annealing. FTIR studies showed variations in the vibrational modes, attributed to the formation of new structures after annealing at 500 °C. PL studies showed the presence of a peak at 720 nm with an intensity higher than that observed for the unannealed SiO2 samples. This effect showed a decrease in the non-radiative defect centers with an increase in the radiative Si:SiO2 interface states after thermal annealing. The presence of an additional peak at 692 nm may be attributed to the radiative recombination centers associated with silicon nanoclusters formed after annealing at 500 °C. GXRD studies showed a decrease in the intensity of the spectra for the samples implanted with 1×1016 and 5×1016 ions cm−2 after thermal annealing at 500 °C. This result reveals the formation of new SiOx structures in SiO2 thin film.