Grown Silicon Dioxide Research Articles

Highly sensitive refractive index sensing based on nanostructured porous silicon interferometers

In this study, we present the experimental evidence demonstrating the utility of electrical double layer (EDL)-induced ion accumulation, using sodium (Na+) ion in water as model substances, on a negatively charged nanostructured surface, specifically thermally grown silicon dioxide (SiO2). This novel approach, termed Ion Surface Accumulation (ISA), aims to enhance the performance of nanostructured porous silicon (PSi) interferometers in optical refractometric applications. The experimental results show that the electrical double layer-induced ion surface accumulation (EDL-ISA) on oxidized PSi interferometers enables remarkable amplification of the interferometer output signal (the spectral interferogram), even when the bulk refractive index variation is below 10-3 RIU. This substantial signal enhancement translates into an increase in sensitivity of up to two orders of magnitude, facilitating the reliable measurement of refractive index variations with both a detection limit (DL) and resolution (R) as low as 10-4 RIU. This achievement elevates the performance of PSi interferometers in photonics and plasmonics-based refractive index platforms.

Modeling of Charge-to-Breakdown with an Electron Trapping Model for Analysis of Thermal Gate Oxide Failure Mechanism in SiC Power MOSFETs.

The failure mechanism of thermal gate oxide in silicon carbide (SiC) power metal oxide semiconductor field effect transistors (MOSFETs), whether it is field-driven breakdown or charge-driven breakdown, has always been a controversial topic. Previous studies have demonstrated that the failure time of thermally grown silicon dioxide (SiO2) on SiC stressed with a constant voltage is indicated as charge driven rather than field driven through the observation of Weibull Slope β. Considering the importance of the accurate failure mechanism for the thermal gate oxide lifetime prediction model of time-dependent dielectric breakdown (TDDB), charge-driven breakdown needs to be further fundamentally justified. In this work, the charge-to-breakdown (QBD) of the thermal gate oxide in a type of commercial planar SiC power MOSFETs, under the constant current stress (CCS), constant voltage stress (CVS), and pulsed voltage stress (PVS) are extracted, respectively. A mathematical electron trapping model in thermal SiO2 grown on single crystal silicon (Si) under CCS, which was proposed by M. Liang et al., is proven to work equally well with thermal SiO2 grown on SiC and used to deduce the QBD model of the device under test (DUT). Compared with the QBD obtained under the three stress conditions, the charge-driven breakdown mechanism is validated in the thermal gate oxide of SiC power MOSFETs.

Effects of Varying Annealing Ambient towards Performance of Ternary GaxCeyOz Passivation Layers for Metal-Oxide-Semiconductor Capacitor

In this work, different annealing ambient (nitrogen-oxygen-nitrogen (N2-O2-N2), forming gas-oxygen-forming gas (FG-O2-FG), and argon-oxygen-argon (Ar-O2-Ar)) were explored to investigate the feasibility of employing the annealed ternary GaxCeyOz passivation layer (PL) for development of Si-based metal-oxide-semiconductor (MOS) capacitors. The impact of nitrogen and/or hydrogen in hindering the growth of silicon dioxide (SiO2) interfacial layer (IL) was quantitatively evaluated. The combination of effects brought by nitrogen attached to oxygen vacancies, nitrogen-silicon bonding, and nitrogen accumulation at the GaxCeyOz/Si interface effectively minimized the formation of SiO2 IL. Consequently, among all the samples, the GaxCeyOz PL annealed in N2-O2-N2 ambient exhibited superior MOS characteristics in terms of low effective oxide charge, slow trap density, interface trap density, and interface state density, which have translated into good leakage current density-electric field characteristics.

Intense pulsed light annealing of solution-based indium–gallium–zinc–oxide semiconductors with printed Ag source and drain electrodes for bottom gate thin film transistors

In this study, an intense pulsed light (IPL) annealing process for a printed multi-layered indium–gallium–zinc–oxide (IGZO) and silver (Ag) electrode structure was developed for a high performance all-printed inorganic thin film transistor (TFT). Through a solution process using IGZO precursor and Ag ink, the bottom gate structure TFT was fabricated. The spin coating method was used to form the IGZO semiconductor layer on a heavily-doped silicon wafer covered with thermally grown silicon dioxide. The annealing process of the IGZO layer utilized an optimized IPL irradiation process. The Ag inks were printed on the IGZO layer by screen printing to form the source and drain (S/D) pattern. This S/D pattern was dried by near infrared radiation (NIR) and the dried S/D pattern was sintered with intense pulsed light by varying the irradiation energy. The performances of the all-printed TFT such as the field effect mobility and on–off ratio electrical transfer properties were measured by a parameter analyzer. The interfacial analysis including the contact resistance and cross-sectional microstructure analysis is essential because diffusion phenomenon can occur during the annealing and sintering process. Consequently, this TFT device showed noteworthy performance (field effect mobility: 7.96 cm2/V s, on/off ratio: 107). This is similar performance compared to a conventional TFT, which is expected to open a new path in the printed metal oxide-based TFT field.

Comparative Study of Surface Activation Steps for Thermally Grown Oxide Interface and Optimal Silanization

Silanization is one of the widely explored surface modification strategies for biofunctionalization of oxide interfaces. For biosensor applications, silanes with active terminal groups such as amine, thiol, carboxylic, and aldehyde groups are utilized in routine. In near‐field sensing schemes like biologically sensitive field‐effect transistors, it is crucial to generate a homogeneous layer of silane to confine the biointeractions in close vicinity of the sensor interface. The homogeneity of such biofunctional layer is determined by the surface activation and silanization protocol being applied. Herein, the impact of the surface activation process and silanization on electrical characteristics of field‐effect devices is studied comprehensively using an electrolyte‐oxide‐semiconductor (EOS) capacitor with a high‐quality gate oxide. The thermally grown silicon oxide (SiO2) interface is activated using acidic mixtures and plasma treatment, while the subsequent silanization steps are investigated comparatively using two different silanes (3‐aminopropyl triethoxysilane (APTES) and 3‐glycidyloxypropyl trimethoxysilane (GPTMS) in wet‐chemical and vapor‐phase processes. Furthermore, the optimized silanization process is utilized to immobilize an oligo strand at the EOS capacitor surface, followed by the hybridization of complementary oligo strands. The optimized protocol holds the potential for large‐scale production of functional oxide interfaces for various applications.

A Method for Improving Heat Dissipation and Avoiding Charging Effects for Cavity Silicon-on-Glass Structures

Anode bonding is a widely used method for fabricating devices with suspended structures, and this approach is often combined with deep reactive-ion etching (DRIE) for releasing the device; however, the DRIE process with a glass substrate can potentially cause two critical issues: heat accumulation on the suspended surface and charging effects resulting from the reflection of charged particles from the glass substrate. In particular, for torsional bars with narrow widths, the heat accumulated on the suspended surface may not dissipate efficiently, leading to photoresist burning and, subsequently, resulting in the fracture of the torsional bars; moreover, once etching is finished through the silicon diaphragm, the glass surface becomes charged, and incoming ions are reflected towards the back of the silicon, resulting in the etching of the back surface. To address these issues, we proposed a method of growing silicon oxide on the back of the device layer. By designing, simulating, and fabricating electrostatic torsional micromirrors with common cavity silicon-on-glass (SOG) structures, we successfully validated the feasibility of this approach. This approach ensures effective heat dissipation on the suspended surface, even when the structure is over-etched for an extended period, and enables the complete etching of torsional bars without adverse effects due to the overheating problem; additionally, the oxide layer can block ions from reaching the glass surface, thus avoiding the charging effect commonly observed in SOG structures during DRIE.

Complications of Charge Pumping Analysis for Silicon Carbide MOSFETs

Unexpected behavior is observed when charge pumping is performed on silicon carbide MOSFETs with a thermally grown silicon dioxide gate dielectric. Supported by experimental evidence, two root causes are proposed: the trap density and the channel non-equilibrium. These are difficult to overcome experimentally due to limitations by oxide breakdown and doping variation along the channel, respectively. A correct interpretation then requires a 2D model.

Vertical Emitting Nanowire Vector Beam Lasers.

Due to the peculiar structured light field with spatially variant polarizations on the same wavefront, vector beams (VBs) have sparked research enthusiasm in developing advanced super-resolution imaging and optical communications techniques. A compact VB nanolaser is intriguing for VB applications in miniaturized photonic integrated circuits. However, determined by the diffraction limit of light, it is a challenge to realize a VB nanolaser in the subwavelength scale because the VB lasing modes should have laterally structured distributions. Here, we demonstrate a VB nanolaser made from a 300 nm thick InGaAs/GaAs nanowire (NW). To select the high-order VB lasing mode, a standing NW as-grown from the selective-area-epitaxial (SAE) growth process is utilized, which has a bottom donut-shaped interface with the silicon oxide growth substrate. With this donut-shaped interface as one of the reflective mirrors of the nanolaser cavity, the VB lasing mode has the lowest threshold. Experimentally, a single-mode VB lasing mode with a donut-shaped amplitude and azimuthally cylindrical polarization distribution is obtained. Together with the high yield and uniformity of the SAE-grown NWs, our work provides a straightforward and scalable path toward cost-effective co-integration of VB nanolasers on potential photonic integrated circuits.

Enhanced Stretchability of Wavy‐Structured Thermally Grown Silicon Dioxide Films for Stretchable Encapsulation

AbstractAligned wavy‐structured thermally grown silicon dioxide films are fabricated for stretchable encapsulation films. Uniaxial stretchability is investigated with micromechanics modeling, which can elucidate the stretchability arising from the wavy structure and the properties of the materials. The wavy‐structured films with optimum combinations of film thickness and wavy structure show 20.1% of uniaxial stretchability and 1.11 × 10−6 g m−2 day−1 of water vapor transmission rate (WVTR), simultaneously. It shows highly reliable barrier properties even after 1000 stretching cycles at 90% of their stretchability.

Numerical simulation of thermal silicon dioxide growth in the gap between stacked wafers

Stacking of wafers for thermal processing enables a strong increase of the throughput and thus offers a high potential for cost reduction in solar cell production. In previous studies, the high temperature stack oxidation (HiTSOx) approach showed promising solar cell results and homogeneous thermal oxide growth over the wafer surface within the stack. In this work, we investigate the thermal oxide growth in the gap between stacked wafers where the wafer surfaces touching each other. We perform finite element method (FEM) simulation to identify the mechanism for the oxygen transport inside the gap and compare the simulated layer thickness to experimental data. In this simulation, the gap height is an important parameter. Therefore, we present a gravimetric-density approach to experimentally determine the gap height. Further, passivated emitter and rear (PERC) solar cells are fabricated using the HiTSOx approach. A high open-circuit voltage of Voc = 694 mV confirms the high quality of the surface passivation achieved in the stack oxidation.

Ultra-thin thermally grown silicon dioxide nanomembrane for waterproof perovskite solar cells

Recently, perovskite solar cells (PSCs) have been attracting attention as the most promising alternative to conventional photovoltaics, mainly due to their high power conversion efficiency (PCE) of 25.7%. However, prior to commercialization, problems with their long-term stability caused by moisture should be solved. Accordingly, encapsulation is a crucial strategy for enhancing the long-term stability of PSCs, meaning a well-established strategy that includes an excellent barrier that protects them from the external environment while minimizing any damage during encapsulation is required. In this study, a room temperature thin-film encapsulation (RT-TFE) strategy is applied by transferring a defect-free thermally grown silicon dioxide nanomembrane (t-SiO2 NM), which is a well-known superior water molecule barrier, onto the PSCs. The average PCE of the devices decreased by only 0.012% with a standard deviation of 0.4249 during the entire encapsulation process, which was achieved by minimizing any thermal degradation of the photovoltaic components, including the perovskite and hole transport layers. This t-SiO2 NM successfully protected the PSC from external water molecules in an underwater condition for 31 days at room temperature, which is the longest reported survival time of encapsulated PSCs. As a result, the RT-TFE PSC maintained more than 98% of the initial efficiency.

A thermally erasable silicon oxide layer for molecular beam epitaxy

We present a systematic study of the oxidation and deoxidation behaviours of several kinds of ultrathin silicon oxide layers frequently used in silicon (Si) technology, which in this work serve as surface protecting layers for molecular beam epitaxy (MBE). With various characterization techniques, we demonstrate that a chemically grown silicon oxide layer is the most promising candidate for subsequent removal in an ultra-high vacuum chamber at a temperature of 1000 ∘C, without making use of a reducing agent. As a demonstration, a tensile-strained Ge(100) layer is epitaxially grown on the deoxidised wafer with an atomically flat surface and a low threading dislocation density of 3.33 × 108 cm−2. Our findings reveal that the ultra-thin oxide layer grown using a chemical approach is able to protect Si surfaces for subsequent MBE growth of Ge. This approach is promising for the growth of III/V-on-Si (using Ge as a buffer) and all group-IV related epitaxy for integration on the Si photonics platforms.

P‐2: Nitrogen Behaviors in PEALD‐Grown SiO2 Films Using N2O Plasma Reactant and Its Application in ALD‐IZO TFTs

We studied nitrogen (N) behaviors in plasma‐enhanced atomic layer deposition (PEALD)‐grown silicon dioxide (SiO2) using nitrous oxide (N2O) plasma reactant. The gradually improved breakdown phenomenon is attributed to N contents. However, although increase in the N contents, excess plasma power is degraded electrical characteristics. For applications of the SiO2 films using N2O plasma reactant, we fabricated indium‐zinc oxide top‐gate thin film transistors with SiO2 gate insulator (G.I). The stable both transfer characteristics and instability results are originated from decrease in oxygen vacancy in active layer by N2O plasma treatment during the G.I deposition.

Enhanced Stretchability of Wavy-Structured Thermally Grown Silicon Dioxide Films for Stretchable Encapsulation

Enhanced Stretchability of Wavy-Structured Thermally Grown Silicon Dioxide Films for Stretchable Encapsulation

Direct electrodeposition of various metal nanocrystals on silicon oxide dielectric layer and insights into electrochemical behavior

AbstractElectrochemistry of thermally grown silicon oxide can address many interesting features and it was further embellished by the development of defective 200 nm thermal oxide grown on highly n‐doped silicon (n+‐Si/SiO2). However, there are still space to uncover underlying conduction mechanism and applications, specifically for defective 200 nm n+‐Si/SiO2 electrode. These could be addressed by direct electrodeposition, so various kinds of metal nanocrystals, Fe, Cr, Ir, Ru, Co, Pd, Cu, Ni, and Ag, were electrodeposited on it. Their shapes were characterized by SEM and electrodeposited amounts were quantified by ICP‐MS. Furthermore, voltammetry was conducted to provide insights into the direct electrodeposition mechanism of either H atom mediated electrochemistry or electron transfer through percolation paths. This work can further provide intuition toward the development of metal‐supported catalysts.

Flexible InGaP/GaAs Tandem Solar Cells Encapsulated with Ultrathin Thermally Grown Silicon Dioxide as a Permanent Water Barrier and an Antireflection Coating

The lifetime and stability of flexible photovoltaic (PV) devices are crucial factors in the production of sustainable and eco-friendly energy. However, flexible PV devices are usually constructed with a thin active material integrated onto a soft substrate, the surfaces of which are prone to moisture and heat damage, making devices unreliable in terms of their lifetime and stability. Here, we built flexible InGaP/GaAs tandem solar cells with an ultrathin thermally grown silicon dioxide layer as a permanent water barrier and an antireflection coating (ARC). By transferring an ultrathin thermally grown silicon dioxide onto flexible InGaP/GaAs tandem solar cells, there was no performance degradation even after soaking the solar cells in water at 70 °C for 10 days. Furthermore, the energy conversion efficiency of the solar cell with a thermally grown silicon dioxide layer was improved by 2.24% due to antirefletion effect compared with that of the solar cells without the silicon dioxide layer. Such device technology establishes a stable energy source not only for vehicles, satellites, and drones exposed to harsh environments but also for underwater operating systems and sensors.

The Mechanism of Surface Passivation Degradation in SiO2/SiNx Stack Under Light and Elevated Temperature

In this article, a significant degradation of the surface passivation was observed in Czochralski silicon (Cz-Si) lifetime samples using effective lifetime measurements during 1 sun illuminated treatment at 130 °C–175 °C. The samples are passivated by plasma-enhanced chemical vapor deposited silicon nitride (SiNx) and thermally grown silicon oxide (SiO2). Samples showed strong variations in the kinetics of the surface passivation degradation depending on the passivation stacks, phosphorus diffusion, and bulk doping. Recovery of the surface passivation was only observed on samples passivated by a single silicon nitride layer. To further investigate the observed behavior, corona charging capacitance-voltage measurements were performed. It is shown that surface degradation arises from a combination of changes in interface defect density ( Dit ) and fixed charge density ( Qf ). We show that two separate degradation channels contribute to the degradation in surface passivation, where the fixed charge density continuously declines, while the interface defect density increases to a maximum and subsequently decreases. The decrease in interface defect density leads to a recovery of surface passivation.

Study of the Role of Void and Residual Silicon Dioxide on the Electrochemical Performance of Silicon Nanoparticles Encapsulated by Graphene.

Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO2 layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO2 nps and Si/SiO2 nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO2 were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO2 layer limits the formation of rich LiXSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes.

Impact of chemically grown silicon oxide interlayers on the hydrogen distribution at hydrogenated amorphous silicon/crystalline silicon heterointerfaces

We studied the impact of oxidizing pre-treatments (OPT) and post deposition annealing (PDA) on the passivation performance and the hydrogen distribution near the interface between crystalline silicon (c-Si) and hydrogenated amorphous silicon (a-Si:H), the critical functional region in Si heterojunction solar cells. The OPT prior to deposition of the a-Si:H layer consists of immersing the c-Si substrates into hydrogen peroxide solutions, which forms a silicon oxide interlayer. Spectroscopic ellipsometry (SE) indicates that slightly thicker a-Si:H layers result from OPT. The refractive index and the extinction coefficient are increased by inserting the oxide interlayers, suggesting that less deficient and denser a-Si:H layers can be formed. Under optimum conditions, OPT leads to at least 2-fold improvement of the effective photo-generated carrier lifetime. PDA at 200 °C further improves the passivation performance of samples with an interlayer. Hydrogen profiling with nuclear reaction analysis clarifies that higher hydrogen concentrations are present around the heterointerfaces of samples with an interlayer and that these hydrogen concentrations are maintained after PDA. Our results suggest that the oxide interlayer can suppress hydrogen desorption in the initial growth stage of high-quality a-Si:H layers and during subsequent PDA, resulting in excellent passivation performance.

PCB mounted sensor with high sensitivity SWNT-Based devices for gas sensing applications

In this paper, the fabrication of aligned semiconducting single-walled carbon nanotube (SWNT) devices on a thermally grown silicon dioxide (SiO2) over silicon (Si) substrate is presented. The SWNTs are aligned between the nickel fingers that are patterned on the substrate. Subsequently, the fabricated devices are bonded onto a low-cost printed circuit board (PCB) with wire bonder. The mounted sensors have been tested for carbon dioxide (CO2) gas, acetone, and isopropyl alcohol (IPA) vapor sensing at room temperature. The sensitivity values of 27% for the concentration of 15000 ​ppm of CO2, 52% for the concentration of 7000 ​ppm of acetone, and 67% for the concentration of 900 ​ppm of IPA have been observed with good response and recovery times. The fabricated sensors show better performance than the already reported sensors.