Thin SiO2 Layer Research Articles

Impact of interlayer insulator formation methods on HfOx ferroelectricity in the metal–ferroelectric–insulator–semiconductor stack

It has been reported that the HfOx-based metal–ferroelectric–insulator–semiconductor (MFIS) stack is one of the most feasible structures for memory applications in ferroelectric devices. In addition, in MFIS stacks, the formation of a high-quality thin insulator is considered to be a crucial process, because it determines the device performance and reliability. In this study, the effects of different SiO2 thin interfacial layers (ILs) formed by chemical oxidation and atomic layer deposition (ALD) on the ferroelectricity of HfOx were investigated in MFIS stacks. Notably, the IL formation method affected the crystallization temperature of HfOx ferroelectricity. In particular, the chemical oxide IL sample was sufficiently crystallized only at an RTA temperature greater than 800 °C, whereas the ALD oxide IL sample began to undergo a complete ferroelectric phase transition from a low temperature (600 °C). The x-ray analysis verified that the IL formation method affected the initial film state of the HfOx layer by modulating the Hf-O bonding states, resulting in a different temperature dependence for ferroelectricity formation during the subsequent crystallization annealing stage. Consequently, it was confirmed that stable polarization (2Pr > 30 μC/cm2) could be obtained over a wide temperature range (600–800 °C) through IL material engineering; this could facilitate the integration of HfOx-based ferroelectric devices in terms of the heat budget and the application of ferroelectric devices as commercial devices.

Improving the electrical performance of vertical thin-film transistor by engineering its back-channel interface

This paper reports the effect of the properties of a back-channel region of a vertical thin-film transistor (VTFT) on its electrical performance. The deposition of a thin layer of SiO2 on a damaged back-channel region was found to improve the subthreshold swing (SS) from 0.25 to 0.12 V/dec, while maintaining the field-effect mobility. Detailed analysis of the surface morphology of the back-channel region revealed that the application of advanced photolithography resulted in a significantly smoother back-channel interface, yielding higher-performing VTFTs. The VTFT fabricated using a high-resolution, stepper photolithography system exhibited a linear mobility (μlin) of 14.60 cm2/Vs, a saturation mobility (μsat) of 23.69 cm2/Vs, and an SS value of 0.13 V/dec. Meanwhile, the VTFT fabricated using a standard projection aligner displayed μlin, μsat, and SS values of 5.74 cm2/V·s, 13.87 cm2/V·s, and 0.27 V/dec, respectively. These results revealed the electrical performance of the VTFT to be strongly influenced by the properties of the back-channel region.

HfO2/SiO2 nanolaminate-based composites prepared by ion beam sputtering for low-loss optics

HfO2 prepared by ion beam sputtering (IBS) is widely used as a high-refractive index material for making low-loss laser films. The challenge of a high-performance HfO2 film is to simultaneously obtain an amorphous morphology with low scattering and a stoichiometric structure with low absorption. Furthermore, nanometer-sized voids are commonly present in IBS films due to excessive oxygen and argon adsorption during deposition, which is the primary barrier to achieve a smooth surface and low optical loss of HfO2. Thin amorphous SiO2 layers were added periodically into HfO2 coatings using the IBS process to synthesize amorphous HfO2 / SiO2 nanolaminate-based composites. The resulting composites exhibited excellent comprehensive performance with a dense amorphous microstructure and a void-free smooth surface. High-temperature annealing was performed to ensure superior stoichiometry and lower absorption. However, the crystalline states and microstructure of some composites evolved during the gradual annealing. We present a detailed study of the crystallization, surface topography, and absorption evolution in HfO2 / SiO2 nanolaminates as a function of HfO2 sublayer thickness and thermal annealing temperature. Moreover, the interplay between crystallization, surface topography, and absorption is elucidated. The HfO2 / SiO2 nanolaminate with 19 thin layers maintained a dense amorphous structure with low absorption after annealing. Finally, a 1064-nm HfO2 / SiO2 nanolaminate-SiO2 high-performance reflector was prepared and achieved lower absorption with a smooth surface after annealing, which demonstrated the great potential of the HfO2 / SiO2 nanolaminates for considerably improving optical loss.

Microstructure dependent ablation behaviour of precursor derived SiOC ceramic foam for high temperature applications

Ablation behaviour of poly(hydridomethylsiloxane) derived open and closed porous structured SiOC ceramic foams was evaluated using oxy-acetylene flame at 1500 °C for various time durations. X-ray diffraction and scanning electron microscopy analyses of ablated SiOC ceramic foams revealed the formation of a thin protective SiO2 layer inhibiting further oxidation. The closed porous structured SiOC ceramic foams exhibited very low mass ablation rate in contrast to open porous structured SiOC ceramic foams owing to the differences in thermal energy dissipation mechanism. The feasibility of the plausible foam reduction reactions pertaining to the ablation mechanism was further investigated by computing the Gibbs energy and HR-TEM analysis. The study corroborated the significance of tailoring the microporous structured SiOC ceramic foams as potential thermal protection material for high temperature applications.

Porosity tailoring of electrophoretically derived zirconia coatings using acidic and alkaline-based sol-gel post-treatment to enhance anti-corrosion performance

In this work, the post-treatment sol-gel methods based on acidic and alkaline catalyzed tetraethylorthosilicate (TEOS) solutions were applied to refine the porosity network of electrophoretically deposited ZrO2 coating on anodically oxidized 316 L substrate to improve the corrosion resistance. The ZrO2 coating dipped in alkaline TEOS solution manifested the best barrier performance, arising from the formation of a dense continuous SiO2 interlayer at the coating/substrate interface as well as narrowing the interconnected pores in the coating's body. This was related to the easily inward diffusion of the alkaline hydrolyzed TEOS molecules with an inert surface charge into the negatively charged ZrO2 coating through the open pores toward the interface. However, the acidic-catalyzed TEOS molecules mostly preferred to form a relatively thin SiO2 layer on the surface of ZrO2 coating, which provided a poor barrier performance. This corresponded to the established electrostatic repulsion forces between the positively charged ZrO2 particles and acidic-hydrolyzed TEOS molecules with positive surface charge, which restricted the unlimited diffusion of TEOS molecules. Based on the microscopic observations and electrochemical impedance results, a possible mechanism for refinement of the porous network of ZrO2 coating and formation of SiO2 layers in the acidic and alkaline TEOS solutions was suggested.

Size dependence of charge retention in gold-nanoparticles sandwiched between thin layers of titanium oxide and silicon oxide

Nonvolatile memory technology is a necessary component in many electronic devices. With the scaling down of memory devices to achieve high density and low power consumption, floating gate devices encounter various challenges like high leakage current, which leads to reliability issues and a decrease in charge density. Therefore, the use of metal nanoparticles (NPs) as charge storage centers is becoming a promising candidate due to their excellent scalability and favorable reliability. In this work, we demonstrate the charge storage dependency on the size of a gold-nanoparticle (Au-NP) by using a contact mode atomic force microscope. The individually dispersed Au-NPs are sandwiched between a thin layer (3 nm) of TiO2 blocking layer and SiO2 (2 nm) tunneling layer thin films. The consecutive I–V sweeps on a pristine device of stacking TiO2/Au-NP/SiO2/n-Si show that the threshold voltage (ΔV) increases with the increase in the Au-NP size, whereas the retention shows much more stability time with smaller size NPs, in the range of 10 nm.

Atypical secondary electron emission yield curves of very thin SiO2 layers: Experiments and modeling

The secondary electron emission phenomenon often refers to the emission of electrons as a result of the interaction of impinging energetic electrons with the surface of a material. Although it is fairly well described for metals, with a typical shape of the total electron emission yield (TEEY) first increasing to reach a maximum and then decreasing along with the energy increase in the primary electrons, there is still a lack of data and detailed analysis for dielectrics, in particular thin layers. The present work proposes a new insight into the electron emission phenomenon from very thin dielectric layers. It reports on the TEEY from very thin SiO2 layers, less than 100 nm. It is found that a departure from the typical shape of the TEEY curve occurs for primary electrons with energy of around 1 keV. The TEEY curve presents a dip, a local minimum that might be as deep as below 1. This atypical shape depends substantially on the layer thickness. The measured TEEY is compared to an electron emission 1D-model in which we consider the combined effect of the space-charge electric field induced by trapped charges in the dielectric layer and of the processes of field-dependent conductivity and radiation-induced conductivity on the fate of secondary electrons. Those mechanisms govern the charge transport in the dielectric and, consequently, the electron emission. The effects of the SiO2 layer thickness, an incidence angle of the primary electrons, and an applied external electric field on the TEEY curves are reported.

Protection of Kapton from atomic oxygen attack by SiOx/NiCr coating

SiOx/NiCr coatings with different SiOx thicknesses were deposited by the combination of ion implantation (IIP), filter cathode vacuum arc (FCVA), and electron beam (E-beam) evaporation methods to protect flexible Kapton from atomic oxygen (AO) attack. Due to the ion stitching effect and mechanical interlocking of implanted Ni+, the ductility and supporting effect of the fcc γ (Ni-Cr) alloy layer, and the low growth stress of the SiOx, the SiOx/NiCr coatings showed high adhesion and toughness. Exposure tests indicated that the AO erosion yield of the 1 μm-thick SiOx/NiCr-coated Kapton was 5.6 × 10−26 cm3 atom−1, which was attributed to the formation of a compact and continuous thin SiO2 layer. In addition, the inherent kinetic energy and oxidation performance dissipation of AO on the thick inner walls of cracks helped to reduce the cavity cross-sectional area and maximum width in the matrix.

Wettability and interfacial reaction mechanism between Ag–Cu alloy and Si3N4 ceramics in air atmosphere

The wetting behaviour and interfacial reaction mechanism between Ag–Cu alloy fillers (with varying copper contents) and Si3N4 ceramics using reactive air brazing at 970 °C were systematically investigated. As the copper content increased, the contact angles of the Ag–Cu filler on the Si3N4 ceramics decreased. A violent boiling-like interfacial reaction was observed during the experiment, and mass spectrometry analysis identified the gaseous products as N2, NO and NO2. The solid products SiO2 and Cu–O formed at the interface, and the interfacial reactions improved the wettability of the Ag–Cu filler on the Si3N4 ceramics. Owing to buoyancy and the pushing of the gases, the interfacial products floated to the surface of the filler and their distribution increased along with the increasing copper content. Two different microstructures were formed at the interface near the triple line. Thick and thin SiO2 layers were respectively formed on the triple line interface of the fillers with low (Ag–3Cu/Ag–5Cu) and high (Ag–6.6Cu/Ag–16Cu) copper content. The interfacial bonding zones formed in Ag–5Cu, Ag–6.6Cu, and Ag–16Cu samples indicated that the corresponding Ag–Cu fillers were effectively brazed with the Si3N4 ceramics.

Application of Janus Magnetic Nanoparticle Fe3O4@SiN functionalized with beta‐cyclodextrin in thymol drug delivery procedure: An in vitro study

AbstractIn this work, a novel drug delivery system was developed for thymol. Thymol is an herbal medicine that has low chemical reactivity. The drug delivery platform was Janus Magnetic Nanoparticle. The carrier's core‐shell structure was Fe3O4 nanoparticles (Fe3O4) as core and thin layer SiO2 (SiN) as a shell. The Fe3O4 nanoparticles were synthesized using the co‐precipitation method. A thin layer of SiO2 was covered on the surface of Fe3O4 nanoparticles. The whole Janus magnetic nanoparticle, Fe3O4@SiN, was functionalized with beta‐cyclodextrin (β‐CD) and used as a drug delivery platform. The binding between thymol and the Fe3O4@SiN/β‐CD was made possible through bipolar‐bipolar and hydrogen bonding. The structure, magnetic behavior, and applicability of Fe3O4@SiN for drug delivery purposes were investigated by scanning electron microscopy, X‐ray diffraction spectroscopy, Fourier‐transform infrared spectroscopy, UV–Vis spectroscopy, vibrating sample magnetometer, and energy‐dispersive X‐ray spectroscopy. Vibrating sample magnetometer (VSM) indicated that the Fe3O4@SiN has a weak ferromagnetic behavior (Hc = 65.748G) at temperature 300 K and a permeability of 35.759 × 10−3 emu gG−1. The scanning electron microscopy (SEM) images showed that the particle size of Fe3O4@SiN is 40 nm. Finally, the Fe3O4@SiN/β‐CD was successfully applied to simulated body fluid.

Fabrication of polycrystalline silicon thin films by gold-induced crystallization of amorphous silicon suboxide

In this work, polycrystalline silicon (poly-Si) thin films were synthesized using Au-induced crystallization of amorphous silicon suboxide for the first time. The structure and elemental composition of the substrate/Au/a-SiO0.4 stacked structure annealed at 500–700°C were investigated by transmission electron microscopy (TEM), Raman, and energy-dispersive X-ray spectroscopy (EDX). TEM and Raman methods confirmed the formation of a poly-Si thin film in the bottom layer (on the substrate) as a result of annealing. At the same time, TEM and EDX studies showed the formation of a thin (barrier) SiO2 layer with a thickness of ~5 nm located between the poly-Si thin film and the upper layer consisting of Au, Si, and O. Based on the results, a mechanism for the growth of poly-Si thin films is proposed which has features (dewetting of Au films and formation of a barrier SiO2 layer) that are not characteristic of the well-known layer exchange process.

Light–matter interactions in the coupling system of quantum emitter and hyperbolic nanorod

Plasmonic nanostructures are widely applied to couple with quantum emitters (QEs), so as to improve the optical performances of QE and obtain advanced photonic devices, such as the quantum photon source, quantum circuit. However, the huge loss of plasmonic nanostructures greatly hinders the future development of plasmon–QE hybrid systems. Herein, we propose the hyperbolic nanorods (HNR) which are built by alternate Au and SiO2 thin layers. The size of HNR discussed in this paper is mainly around 40 × 50 × 60 nm3, which is a subwavelength size benefiting for device miniaturization and integration. The photonic resonant mode of HNR can be tuned by simply changing its length/width ratio. Due to the hybridization of the surface plasmon polariton resonances associated with each metal–dielectric interface, the HNR possesses the advantage of small mode volume (V) as the Au plasmonic nanorod (PNR) with similar size, and its mode quality factor (Q) can be larger due to the lower loss. Therefore, when coupled with a resonant QE, the Purcell factor in HNR/QE is ∼20 times larger than that in the PNR/QE system. Furthermore, the HNR/QE hybrid also demonstrates obvious superiority over the PNR/QE in generating strong coupling and quantum entanglement. With the features of small V and low loss, it is believed that the HNR can not only greatly improve the optical properties of QE, but also be a powerful nanostructure for studying light–matter interactions.

A nanotubular TiO2/SiOx/Si composite derived from cellulosic cotton as an anode material for lithium-ion batteries with enhanced electrochemical performance

A TiO2/SiOx/Si composite derived from cellulosic cotton as the structural template was biomimetically synthesized. Modified sol–gel deposition processes were performed to coat each cellulose nanofiber with a SiO2 thin gel layer, followed by layer-by-layer self-assembly processes to form an external TiO2 coating with controllable thickness. The resulted matter was calcined in air to obtain the TiO2/SiO2 composite, which was successively put in N2 atmosphere and treated with magnesiothermic reduction reaction, resulting in the final TiO2/SiOx/Si composite. The composite possessed a typical hierarchical three-dimensional (3D) nanotubular network microstructure precisely inherited from the cellulosic cotton template, and each nanotube had a core-shell nanostructure with Si-based matters as the core and TiO2 coating as the shell. Compared with the bare nanotubular SiOx/Si material, the TiO2/SiOx/Si composite showed a highly enhanced electrochemical performance as an anode material for lithium-ion batteries (LIBs), delivering an initial discharge capacity of 2370 mAh g−1 at a current density of 0.2 A g−1 (an initial Coulombic efficiency of 56.4%), a reversible capacity of 682 mAh g−1 after 100 discharge/charge cycles, and a discharge capacity of 241 mAh g−1 at a high current density of 2.0 A g−1. The excellent specific capacity, cycling stability and rate capability are ascribed to the synergistic effect of the unique 3D porous nanotubular network structure and the uniform TiO2 coating layer, which accommodates the volume variation of Si-based components during cycling, offers sufficient ion transport pathways and improves the electron transfer efficiency. This work provides a facile biomass-based strategy for fabrication of metal oxide/Si composites with well-defined microstructures that exhibit significant potential as anode materials for LIBs.

Pre-deposition growth of interfacial SiO2 layer by low-oxygen-partial-pressure oxidation in the Al2O3/4H-SiC MOS structure

A novel thermal oxidation method for growing a thin SiO2 layer is proposed for improving the Al2O3/4H-SiC-based MOS structure characteristics. The method combines low oxygen partial pressure and high temperature oxidation during the SiO2 layer growth process. Compared with the conventional thermal oxidation method, the experimental results show that the proposed method can effectively reduce the density of trapped charges in the oxide and at the gate dielectric/4H-SiC epilayer interface, and improve the breakdown characteristic of the MOS structure. The interface trap density (Dit) at energy level of 0.2 eV below the conduction band edge (EC) of 4H-SiC in the sample by our proposed method is reduced to 6.6 × 1012 cm−2 eV−1, which is about 4 times lower than the as deposited Al2O3/4H-SiC sample. The core reason underlying the improvement is the reduced SiO2 layer thickness and lower SiCxOy component concentration, as shown by X-ray photoelectron spectroscopy measurements.

Multi-photon 3D imaging with an electrothermal actuator with low thermal and inertial mass

Design and testing of a low-mass electrothermal vertical scanning mirror for fast axial scanning during multi-photon microscopy is presented. The mirror makes use of a novel honeycomb mechanical support structure to substantially reduce both thermal and inertial mass relative to mirror size. At the same time, undesirable mirror curvature due to residual thermal stress is controlled without adversely affecting the image quality. In addition, the support structure makes the complete mirror area usable which otherwise is not possible in devices that rely on isotropic silicon etching. A high actuator efficiency with static displacement per unit power of 2.08 μm/mW was achieved due to the reduced thermal capacitance at the actuator legs, when using a 700 nm thin structural layer of SiO2. The resulting scanning mirror achieves open loop time constant as small as 3.42 ms with both thermal and mechanical bandwidths exceeding 100 Hz. Mirror surface non-idealities related to the mirror structure and their influence on image quality are discussed. Sample 3D multi-photon images captured by performing remote scanning in both lateral and axial direction on a benchtop testbed are presented. The efficacy of remote axial scan is ascertained by comparisons with images obtained by moving specimens relative to the objective.

Rapid Detection of Salmonella typhimurium in Drinking Water by a White Light Reflectance Spectroscopy Immunosensor.

Biosensors represent an attractive approach for fast bacteria detection. Here, we present an optical biosensor for the detection of Salmonella typhimurium lipopolysaccharide (LPS) and Salmonella bacteria in drinking water, based on white light reflectance spectroscopy. The sensor chip consisted of a Si die with a thin SiO2 layer on top that was transformed into a biosensor through the immobilization of Salmonella LPS. The optical setup included a reflection probe with seven 200 μm fibers, a visible and near-infrared light source, and a spectrometer. The six fibers at the reflection probe circumference were coupled with the light source and illuminated the biosensor chip vertically, whereas the central fiber collected the reflected light and guided it to the spectrometer. A competitive immunoassay configuration was adopted for the analysis. Accordingly, a mixture of LPS or bacteria solution, pre-incubated for 15 min, with an anti-Salmonella LPS antibody was pumped over the chip followed by biotinylated secondary antibody and streptavidin for signal enhancement. The binding of the free anti-Salmonella antibody to chip-immobilized LPS led to a shift of the reflectance spectrum that was inversely related to the analyte concentration (LPS or bacteria) in the calibrators or samples. The total assay duration was 15 min, and the detection limits achieved were 4 ng/mL for LPS and 320 CFU/mL for bacteria. Taking into account the low detection limits, the short analysis time, and the small size of the chip and instrumentation employed, the proposed immunosensor could find wide application for bacteria detection in drinking water.

Ti3SiC2 interphase coating in SiCf/SiC composites: Effect of the coating fabrication atmosphere and temperature

The SiC fibers were coated with Ti3SiC2 interphase by dip-coating. The Ti3SiC2 coated fibers were heat-treated from 900 °C to 1100 °C in vacuum and argon atmospheres to comparatively analyze the effect of temperature and atmosphere on the microstructural evolution and mechanical strength of the fibers. The results show that the surface morphology of Ti3SiC2 coating is rough in vacuum and Ti3SiC2 is decomposed at 1100 °C. However, in argon atmosphere, the surface morphology is smooth and Ti3SiC2 is oxidized at 1000 °C and 1100 °C. At 1100 °C, Ti3SiC2 oxidized to form a thin layer of amorphous SiO2 embedded with TiO2 grains. Meanwhile, defects and pores appeared in the interphase scale. As a result, the fiber strength treated in the argon was lower than that treated in vacuum. The porous Ti3SiC2 interphase fabricated under vacuum was then employed to prepare the SiCf/SiC mini composite by chemical vapor infiltration (CVI) combined with precursor infiltration pyrolysis (PIP), and can effectively improve the toughness of SiCf/SiC mini composite. The propagating cracks can be deflected within the porous interphase layer, which promotes fiber pull-outs under the tensile strength.

Photocatalytic Activity of Multicompound TiO2/SiO2 Nanoparticles

Multicompound TiO2/SiO2 nanoparticles with a diameter of 50–70 nm were generated using a liquid flame spray (LFS) nanoparticle deposition in a single flame. Here, we study the photocatalytic activity of deposited multicompound nanoparticles in gas-phase via oxidation of acetylene into carbon dioxide that gives new insight about the multicompound nanoparticle morphology. A small addition of SiO2 content of 0.5%, 1.0% and 3.0% significantly suppressed the photocatalytic activity by 33%, 44% and 70%, respectively, whereas 5.0% SiO2 addition completely removed the activity. This may be due to a formation of a thin passivating SiO2 layer on top of the of the TiO2 nanostructures during the LFS nanoparticle deposition. Surface wetting results support this hypothesis with a significant increase in water contact angle as the SiO2 content is increased.

Selective Lithium Adsorption of Silicon Oxide Coated Lithium Aluminum Layered Double Hydroxide Nanocrystals and Their Regeneration.

Silicon oxide-coated lithium aluminum layered double hydroxide (Lix Al2 -LDH@SiO2 ) nanocrystals (NCs) are investigated to selectively separate lithium cations in aqueous lithium resources. We directly synthesized Lix Al2 -LDH NC arrays by oxidation of aluminum foil substrate under a urea and lithium solution. Various lithium salts, including Cl- , CO3 2- , NO3 - , and SO4 2- , were applied in aqueous solution to confirm the anion effect on the captured and released lithium quantity of the Lix Al2 -LDH NCs. In a 5% solution of sulfate ions mix with lithium chloride, the Lix Al2 -LDH NCs separated a larger quantity of lithium than in other anion conditions. To enhance regeneration stability and lithium selectivity, thin layers of SiO2 were coated onto the Lix Al2 -LDH nanostructure arrays for inhibition of nanostructure destruction after desorption of lithium cations in hot water. The Lix Al2 -LDH@SiO2 nanostructures showed enhanced properties for lithium adsorption, including increase of stable regeneration cycles from three to five cycles, and they showed high lithium selectivity in the Mg2+ , Na+ , and K+ cation mixed aqueous resource. Our nanostructured LDH lithium adsorbents would provide a facile and efficient application for cost-efficient and large-scale lithium production.

Interface engineering of a hierarchical ZnxCd1-xS architecture with favorable kinetics for high-performance solar water splitting.

Manipulating the charge carrier transport in photoactive materials is a big challenge toward high efficiency solar water splitting. Herein, we designed a hierarchical ZnxCd1-xS architecture for tuning the interfacial charge transfer kinetics. The in situ growth of ZnxCd1-xS nanoflakes on ZnO backbones provided low interfacial resistance for charge separation. With this special configuration, the optimized Zn0.33Cd0.67S photoanode achieved significantly enhanced performance with a photocurrent density of 10.67 mA cm-2 at 1.23 V versus RHE under AM1.5G solar light irradiation, which is about 14.1 and 2.5 times higher than that of the pristine ZnO and CdS nanoparticle decorated ZnO photoanodes, respectively. After coating a thin SiO2 layer, the photostability of the hierarchical Zn0.33Cd0.67S photoanode is greatly enhanced with 92.33% of the initial value retained under 3600 s continuous light illumination. The prominent PEC activity of the hierarchical ZnxCd1-xS nanorod arrays can be ascribed to an enhanced charge transfer rate aroused by the binder-free interfacial heterojunction, and the improved reaction kinetics at the electrode-electrolyte interface, which is evidenced by electrochemically active surface area measurements and intensity modulated photocurrent spectroscopy analysis. This interfacial heterojunction strategy provides a promising pathway to prepare high performance photoelectrodes.