Silicon Substrate Research Articles

Effects of TMAl predose time on the quality of submicron-thick GaN on Si

Submicron-thick (∼350 nm) gallium nitride (GaN) thin films with lower dislocation densities are grown on silicon (Si) substrate by metal organic chemical vapour deposition (MOCVD). Prior to the growth, a trimethylalluminum (TMAl) predose is performed. The effects of different TMAl predose time on the surface morphology and crystalline quality of submicron-thick GaN are investigated in this study. With prolonged TMAl predose time, the surface becomes rougher, while the screw dislocation densities both for GaN and aluminum nitride (AlN) are reduced. The edge dislocation densities tend to decrease first then increase again when the TMAl predose time is elongated from 90 s over 135 s–180 s. From the high resolution transmission electron microscopy (HRTEM), we found the thickness of amorphous layer between Si and AlN decreases with the increase of TMAl predose time. Such an amorphous layer should play an important role in the surface morphology and crystalline quality of submicron-thick GaN. A possible mechanism has also been proposed to elucidate the effects of TMAl predose time.

Investigations of the growth and physical characteristics of ZNF2-DOPED GA2O3 thin films

This study began by preparing gallium oxide (Ga2O3) doped with zinc fluoride (ZnF2) and manufacturing a target material. Subsequently, electron beam (e-beam) deposition was employed to coat silicon substrates with the prepared material. Different heat treatment conditions were applied to the deposited films, followed by material and electrical property analyses. The investigation explored the impact of pre-sintering Ga2O3 at 950°C to transform it into a more stable [Formula: see text]-phase. For comparative purposes, some samples underwent annealing at 600°C in a nitrogen–hydrogen (95% N[Formula: see text] H2, abbreviated as N[Formula: see text]) mixed gas, which was used as a reduction atmosphere, to increase oxygen vacancies in the ZnF2-doped Ga2O3 thin films and consequently enhance their conductivity. The deposited ZnF2-doped Ga2O3 thin films initially exhibited an amorphous phase, with diffraction peaks appearing only after a 600°C annealing process. Pre-sintering Ga2O3 powder at 950°C promoted the emergence of the [Formula: see text]-phase, and the bandgap value increased after annealing. Measurements using B1500A revealed that sintering and annealing ZnF2-doped Ga2O3 thin films were essential steps to enhance their conductivity. X-ray photoelectron spectroscopy (XPS) further confirmed a significant correlation between the conductivity variation and the concentration of oxygen vacancies. Additionally, it was observed that the use of an N[Formula: see text] mixed gas further increased the presence of oxygen vacancies in the films. The results of this study provide an important method to make Ga2O3 thin films with conductivity, which can be utilized in the fabrication of Ga2O3 thin-film-based semiconductor devices in the future.

Highly reproducible and CMOS-compatible VO2-based oscillators for brain-inspired computing.

With remarkable electrical and optical switching properties induced at low power and near room temperature (68°C), vanadium dioxide (VO2) has sparked rising interest in unconventional computing among the phase-change materials research community. The scalability and the potential to compute beyond the von Neumann model make VO2 especially appealing for implementation in oscillating neural networks for artificial intelligence applications, to solve constraint satisfaction problems, and for pattern recognition. Its integration into large networks of oscillators on a Silicon platform still poses challenges associated with the stabilization in the correct oxidation state and the ability to fabricate a structure with predictable electrical behavior showing very low variability. In this work, the role played by the different annealing parameters applied by three methods (slow thermal annealing, flash annealing, and rapid thermal annealing), following the vanadium oxide atomic layer deposition, on the formation of VO2 grains is studied and an optimal substrate stack configuration that minimizes variability between devices is proposed. Material and electrical characterizations are performed on the different films and a step-by-step recipe to build reproducible VO2-based oscillators is presented, which is argued to be made possible thanks to the introduction of a hafnium oxide (HfO2) layer between the silicon substrate and the vanadium oxide layer. Up to seven nearly identical VO2-based devices are contacted simultaneously to create a network of oscillators, paving the way for large-scale implementation of VO2 oscillating neural networks.

Molecular Dynamics Analysis of Adhesive Forces between Silicon Wafer and Substrate in Microarray Adhesion

With the development of the electronics industry, the requirements for chips are getting higher and higher, and thinner and thinner wafers are needed to meet the processing of chips. In this study, a model of the adhesion state of semiconductor wafers in the stacking–clamping process based on microarray adsorption was established, the composition adhesion was discussed, the microarrays of different materials and pressures were experimentally studied, and a molecular dynamics model was established. The molecular dynamics analysis showed that the adhesion force was only related to the type of atom, and the applied pressure did not change the adhesion force. According to the simulation results, the tangential adhesion between the metal and the wafer is greater than that between the ceramic and the wafer, the adsorption force between the aluminum–magnesium alloy and the silicon wafer is shown in the normal direction, and the repulsion force between other materials and the silicon wafer is shown in the normal direction. During the pressure process, the metal is in the elastic deformation stage between the metal and the wafer, the wafer is plastically deformed in the silicon carbide ceramic and wafer, and the wafer is elastically deformed in the alumina ceramic and wafer. In this paper, the adhesion between the substrate and the wafer is studied, a method of constructing microarrays to enhance adhesion is proposed, and the tangential deformation of the array unit under pressure is studied, which provides theoretical support for increasing the adhesion by constructing microarrays.

Synthesis and characterization of ZnO tetrapod-like nanorods without catalyst by wet thermal evaporation and applied on dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) continue to attract as one of the most important renewable energy technologies due to their simple production, environmentally friendly, and lower-cost fabrication process compared to the most common types of solar cells. Zinc oxide (ZnO) nanostructures have motivated researchers to fabricate DSSCs as photo-anodes due to their unique properties, such as different types of structures, appropriate optical properties, proper energy bandgap, and high electron transfer characteristics. This article reports the simple preparation of ZnO tetrapod-like nanorods using the wet thermal evaporation method on porous silicon substrate PS/Si and applied as a photoanode on DSSCs. ZnO nanostructures were characterized by using grazing-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) measurements. A significant difference in the performance of DSSCs has been investigated by using a standard dye di-tetrabutylammonium cis–bis(isothiocyanate)bis(2,2[Formula: see text]-bipyridyl-4,4[Formula: see text]-dicarboxylato) ruthenium (II) (N719) reloaded on ZnO tetrapod-like nanorods ([Formula: see text], [Formula: see text], [Formula: see text]%, and [Formula: see text]%) being more efficient than the ZnO spherical nanoparticles as a reference solar cell ([Formula: see text], [Formula: see text], [Formula: see text]%, and [Formula: see text]%).

Investigations of In2O3 Added SiC Semiconductive Thin Films and Manufacture of a Heterojunction Diode

This study involved direct doping of In2O3 into silicon carbide (SiC) powder, resulting in 8.0 at% In-doped SiC powder. Subsequently, heating at 500 °C was performed to form a target, followed by the utilization of electron beam (e-beam) technology to deposit the In-doped SiC thin films with the thickness of approximately 189.8 nm. The first breakthrough of this research was the successful deposition of using e-beam technology. The second breakthrough involved utilizing various tools to analyze the physical and electrical properties of In-doped SiC thin films. Hall effect measurement was used to measure the resistivity, mobility, and carrier concentration and confirm its n-type semiconductor nature. The uniform dispersion of In ions in SiC was as confirmed by electron microscopy energy-dispersive spectroscopy and secondary ion mass spectrometry analyses. The Tauc Plot method was employed to determine the Eg values of pure SiC and In-doped SiC thin films. Semiconductor parameter analyzer was used to measure the conductivity and the I-V characteristics of devices in In-doped SiC thin films. Furthermore, the third finding demonstrated that In2O3-doped SiC thin films exhibited remarkable current density. X-ray photoelectron spectroscopy and Gaussian-resolved spectra further confirmed a significant relationship between conductivity and oxygen vacancy concentration. Lastly, depositing these In-doped SiC thin films onto p-type silicon substrates etched with buffered oxide etchant resulted in the formation of heterojunction p-n junction. This junction exhibited the rectifying characteristics of a diode, with sample current values in the vicinity of 102 mA, breakdown voltage at approximately −5.23 V, and open-circuit voltage around 1.56 V. This underscores the potential of In-doped SiC thin films for various semiconductor devices.

Fabrication and application of two-dimensional tungsten disulfide thin film

To form a tungsten disulfide film, a tungsten trioxide film is deposited first and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high-temperature environment. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment and the bias voltage during each process was monitored. In this experiment, a sapphire substrate and a silicon substrate with 200[Formula: see text]nm silicon dioxide are used. Then use optical instruments such as Raman optics, ellipsometers and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Moreover, two-dimensional tungsten disulfide thin film has a response to light, gas and pH and related devices have been successfully fabricated in experiments. Among them, comparing the single-layer film and the double-layer film, the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.

Micropatterning MXene/TiO2 Nanocomposite Ink for Gas Sensing

This work describes the preparation, characterization, and micropatterning of MXene(Ti3C2)/TiO2 nanocomposite inks. MXene nanopowder was oxidized to form MXene/TiO2 nanocomposite powder using an air-aging method. The MXene/TiO2 inks were prepared using deionized water (H2O) as the solvent/dispersant and polyvinylpyrrolidone (PVP) as the surfactant. Various techniques were utilized to characterize the MXene/TiO2 nanocomposite material, and the BET results showed the preferential adsorption of butane of the MXene/TiO2 coating. Utilizing an ultrasonic dispersion printer in conjunction with a stencil mask, the MXene/TiO2 nanocomposite ink was successfully printed onto a 10mm*10mm gold-plated silicon substrate. This process achieved millimeter-level precision control, enabling the printing of fine lines with a width of 1μm and a spacing of 0.05mm. Furthermore, this technique demonstrated the ability to render various complex patterns, thus exemplifying the potential of MXene/TiO2 nanocomposite ink in the field of micro- and nano-manufacturing.

Penetration depth and critical fields in superconducting NbTi thin films grown by co-sputtering at room temperature

We present a study on the superconducting properties of 300 nm thick NbTi thin films grown by co-sputtering on silicon substrates at room temperature. The samples exhibit a Nb (50 at%) and Ti (50 at%) chemical composition, revealing a polycrystalline structure textured along the (110) axis of the body-centered cubic structure. The measured superconducting critical temperature (T c ) was 9.65 K, and the upper critical field extrapolated to zero temperature reached approximately 15 T, resulting in a coherence length at zero temperature of approximately 4.7 nm. The penetration depth was determined through local magnetic force microscopy measurements conducted at temperatures from 4.25 to 7 K. The obtained values range from (250 ± 15) nm at 4.25 K to (370 ± 20) nm at 7 K. Extrapolating these measurements to zero temperature, we obtained an estimated value of (230 ± 20) nm. To extend the performance and potential applications of NbTi, we additionally grew a 150 nm thick sample on flexible polyimide. In this case, we observed that the films preserved their superconducting properties, displaying a decrease in T c to 9.2 K and a similar upper critical field compared to samples grown on silicon. The feasibility of growing NbTi alloys at room temperature, with superconducting parameters comparable to or superior to metallic Nb for the upper critical field, renders this system promising for cryogenic applications, particularly in the development of high-performance electronic devices on both rigid and flexible substrates.

Enhanced ferroelectric properties in BiAlO3 modified lead‐free Mn‐doped Bi0.5(Na0.8K0.2)0.5TiO3 thin films

AbstractMn‐doped (1‐x)Bi0.5(Na0.8K0.2)0.5TiO3‐xBiAlO3 (Mn:BNKT‐xBA) thin films were synthesized on lanthanum nickelate‐coated silicon substrates by sol‐gel method. The second phase issue of the film can be effectively addressed by optimizing the substrate, and the maximum polarization and breakdown strength can be increased by introducing the proper amount of Al3+, which is advantageous for the film for energy storage. The results have shown that the Mn:BNKT‐0.03BA film exhibits superior ferroelectric properties (with remanent polarization (Pr) of 23.72 µC/cm2, maximum polarization (Pmax) of 75.37 µC/cm2), which could be an excellent candidate for ferroelectric thin film capacitors.

Research and improvement of cyanoacrylate on bonding properties of silicone adhesive material

Cyanoacrylate adhesives represent the earliest discovered and most widely utilized adhesives known to date, boasting exceptional bonding properties such as the ability to cure at room temperature, rapid curing rates, and strong adhesion. However, shortcomings persist in practical applications, notably in addressing inert materials like silicone that pose challenges for ideal adhesion. To enhance the bonding performance of cyanate ester adhesives with silicone materials, this study delves into two aspects: modifying cyanate esters and pre-treating silicone surfaces to reduce surface energy. Following internal modifications, the maximum bonding strength to silicone sheets reached 2.33 MPa, while pre-treating the silicone substrate surface enabled a maximum bonding strength of 6.10 MPa. Utilizing SEM, ATR, EDS, and other analytical techniques, the mechanisms behind the improvement in silicone substrate bonding strength are characterized, revealing changes in properties pre- and post-treatment. This research paves a novel path and direction for future scientific investigations and advancements in adhesive formulation and enhancement.

A Wide Bandwidth Vivaldi Antenna Suitable for 5G/6G Communication Utilizing a CMOS 0.18 μm Process

This text proposes a Vivaldi structure array antenna, using a power divider structure. The composition includes an antenna array with four antennas, suitable for a wideband array structure antenna in the 100 GHz frequency band. The goal is to address the challenges faced by monolithic systems in modern wireless communications, particularly the issue of the inapplicability of antennas on silicon substrates. The Vivaldi antenna was chosen for its wide bandwidth, high efficiency, and stable radiation pattern. It combines the characteristics of a wide scanning angle and ultra-wide bandwidth. Through integration with CMOS technology, the developed antenna achieved a bandwidth of 85.47–102.40 GHz. The peak gain reached −4 dBi, corresponding to a bandwidth of 17.7%. And the antenna volume was only 1.2 mm × 1.2 mm, demonstrating its immense potential in high-frequency wireless applications.

Aerosol deposition of dense alumina coatings on micropillar-patterned Si substrates

Fabricating dense ceramic layers without cracks is challenging, especially on structured surfaces and under low process temperatures. Aerosol deposition (AD) is a promising technique for producing dense ceramic coatings at room temperature. Film formation on smooth and flat substrates by AD has been explored in the field, but deposition on patterned surfaces was rarely studied. In this work, we describe dense alumina coatings deposited on flat and micropatterned silicon substrates using AD. We demonstrate that the patterned substrates with 1–2 μm pillars can reduce or eliminate the formation of horizontal micro-cracks in the coatings. The impact of pillar walls on coating quality and deposition rate diminishes when the pattern size exceeds the powder agglomerate size. The deposited layers cover the substrate patterns completely and give uniform coating surfaces, which opens the way for AD in applications such as hole-filing and 3D micro-energy devices.

Direct growth of highly oriented GaN thin films on silicon by remote plasma CVD

We report on low-temperature (500 °C) and low-pressure (0.3 mbar) direct growth of GaN thin films on silicon (100) substrates using remote plasma chemical vapour deposition (RP-CVD). In the custom-designed reactor, an RF inductively coupled plasma is generated remotely from the substrate’s area to facilitate the decomposition of group-V precursor, N2 with added H2, while group-III precursor trimethylgallium (TMGa), is directly injected into the growth chamber mixed with H2 carrier gas. Growth parameters such as RF power, process pressure and gas flow rates have been optimized to achieve a film growth rate of about 0.6 µm h−1. Several characterization techniques were used to investigate the plasma and the properties of the grown thin films in terms of their crystallinity, morphology, topography, and composition. The films are highly textured with a preferential orientation along the c-axis of the wurtzite structure. They present a small roughness in the nanometer range and a columnar microstructure with a grain size of one hundred nanometer, and a gallium polarity (+c plane oriented). Rutherford backscattering spectrometry and nuclear reaction analysis show that the chemical composition is homogeneous through the depth of the layer, with a III/V ratio close to 1, a very low content of oxygen (below the detection limit ∼1%) and a carbon content up to 11%. It was shown that the increase of plasma power helps to reduce this carbon contamination down to 8%. This research paves the way for a growth method compatible with cost reduction of III–V thin film production achieved through reduced gas consumption facilitated by RP-CVD operation at low pressure.

Properties investigation of ZnS/porous silicon heterojunction for gas sensing

In this work, the gas sensing properties of ZnS/Porous silicon heterostructures have been investigated. . Zinc sulfide(ZnS) with high gas sensing performance is successfully synthesized over the Porous silicon substrate by the spray pyrolysis method. The properties of the as-prepared samples were characterized X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform spectrum (FTIR) and optical properties. The results reveal that the properties of the ZnS/Porous silicon heterostructures enhanced when the when the ZnS concentration is increased. The performance ZnS/Porous silicon as a gas-sensing show that the maximum sensitivity is found to be 5.11 at ZnS concentration of 0.5 M and etching time of 15 min compared to the other sensitivities. The ZnS-PSi heterojunction based gas sensor may be used for UV-light photo-detectors due to a valuable properties such as high sensitivity and fast response.

Anisotropic Fourier Heat Conduction and phonon Boltzmann transport equation based simulation of time domain thermo-reflectance experiments

The anisotropic Fourier Heat Conduction Equation (FHCE) and the multidimensional phonon Boltzmann Transport Equation (BTE) were solved numerically in cylindrical coordinates and in time domain to simulate a Time Domain Thermo-Reflectance (TDTR) experimental silicon/aluminum substrate/transducer setup. The out-of-phase response of the probe laser was predicted at various beam offset distances for a pump laser pulse frequency of 80 MHz and modulation frequency of 10 MHz and compared against experimental measurements for a silicon substrate. The isotropic FHCE was also solved for comparison. Results show that the isotropic FHCE with bulk thermal conductivity of 145 W/m/K significantly underpredicts the out-of-phase temperature difference, particularly at smaller beam offsets. With an isotropic thermal conductivity of 105 W/m/K, the computed results match experimental data at smaller beam offsets well, but overpredicts the experimental data at larger beam offsets. An almost-perfect match is obtained by using an anisotropic thermal conductivity wherein the radial (in-plane) thermal conductivity is set to 85 W/m/K and the axial (through-plane) conductivity is set to 130 W/m/K. The multidimensional frequency and polarization dependent phonon BTE is next solved. The BTE results for the out-of-phase temperature difference match experimental observations well at small and intermediate beam offsets, but overpredicts the experimental data at larger beam offsets. FHCE results are fitted to the BTE predictions, and the extracted (best fit) thermal conductivity is found to be 110 W/m/K.

4 inch Gallium Oxide Field‐Effect Transistors Array with High‐k Ta2O5 as Gate Dielectric by Physical Vapor Deposition

Field‐effect transistors (FETs) with ultra‐wide bandgap semiconductor Ga2O3 have been fabricated by physical vapor deposition with advantages of low cost, wafer scale, and rapid production. The insulator‐like pristine Ga2O3 is converted to semiconductor by co‐sputtering Sn with post‐annealing, which demonstrates a 5.6 × 107 times higher on‐state current. Importantly, this Sn‐doped Ga2O3 sample shows a high breakdown voltage near 500 V. Furthermore, a 4 inch array of Sn‐doped Ga2O3 FETs with high‐k Ta2O5 gate dielectric has been fabricated on a silicon substrate, successfully showing a large on‐current density of 1.3 mA mm−1, a high ION/IOFF of 2.5 × 106, and a low threshold voltage of 3.9 V, which are extracted from the average 350 devices. This work paves a promising way for Ga2O3‐based nanoelectronics to serve medium‐high voltage with low cost, rapid, and wafer‐scale production.

Obtaining and studying the composition, structure and properties of nanophases and nanolayers of CoSi2

ABSTRACT The processes of formation of a thin film of cobalt disilicide on the silicon surface due to the formation of several nuclei of atomic thickness on the surface of the silicon substrate are presented. To create these structures, the ion implantation method was used. The dependence of the depth of penetration of ions into the substrate during ion implantation on temperature and ion dose was determined. In the case of implantation of Co+ ions into Si at room temperature silicon uniformly combines with Co atoms at a depth of 3.5–4 nm, the Co concentration in these layers is 45–50 at. %. Co has been shown to form chemical bonds with Si atoms in the sample containing 40–45 atomic % of Co. When implanting Co+ into Si at 600 K, it was found that the depth of the same added layer is 2.5–3 nm, and CCo forming bonds with Si atoms increases to 85–90%.

Mechanically programmable substrate enable highly stretchable solar cell arrays for self-powered electronic skin

Development of stretchable solar cells to accommodate large strain without sacrificing the power conversion efficiency is challenging. This study presents a novel approach to manufacture highly stretchable solar cell arrays, which can be integrated into wearable medical devices to operate under challenging environments. Overcoming the limitations of rigid metal wires, liquid metal wires are employed to connect single crystal silicon solar cells, ensuring both high conversion efficiency and exceptional stretchability (up to 100%). The manufacturing process introduces embedding electrospinning films into elastic silicone substrates to create a tight bond between rigid solar cells and stretchable substrates with programmable strain capabilities. Notably, a stretchable interconnect wire is efficiently fabricated using the semi-liquid metal template printing technique and demonstrates remarkable conductivity (up to 6 × 106 S/m). Individual structural unit of solar cell presents an impressive tensile rate of 200%, and endures up to 5000 cycles of tensile testing. The overall solar cell array exhibits outstanding adaptability to extensive bending and twisting, with a mere 0.1% short-circuit current reduction in its maximum stretched state. The stretchable photovoltaic device is successfully employed in creating self-powered electronic skin for continuous real-time monitoring of parameters, showcasing its valuable potential in wearable medical electronic devices and comprehensive sports health monitoring.

Micromechanical effects of substrate hardness on graphene nano-cutting quality

In the nanocutting process of graphene, the mechanism on the atomic scale of the effect of substrate hardness on the edge quality of graphene nanoribbons has not been thoroughly investigated. In this paper, we construct a diamond probe (radius of 5 Å) to cut graphene (190 Å × 113 Å) models with different substrates (silicon/sapphire/silicon carbide), molecular dynamics simulations were used to study the effect of substrate hardness and cutting depth on the atomic structure of graphene nanoribbon edges by observing the atomic morphology, the number of C-C bonds, the radial distribution function and friction. The results show that during the nanoindentation stage, when graphene is in the critical damage state, the substrate with high hardness has high deformation strength, the substrate deformation is small, and graphene undergoes deformation is also small, but the force Fz on the probe, the critical graphene stress σz and the equivalent stress are all large, and the number of C atoms with CN=3 is large; At the nano-cutting stage, the breakage of C-C bonds and the generation of edge defects are caused by local stress concentration, and the graphene stress σxx along the x-direction has a clear directionality. With the same cutting depth (critical damage depth of silicon substrate), silicon substrate hardness is small, the graphene nanoribbon obtained has less number of circular defects generated at the edge, less total number of defective atoms, more number of CN=3 atoms, large peak of radial distribution function of graphene after cutting, and graphene integrity is better. The hardness of the silicon carbide substrate is large, and the number of C-C bond breaks in graphene during the cutting process is high. Each substrate is cut at its own critical damage depth, and the substrate hardness has no significant effect on the number of C-C bond breaks, the number of circular defects, the total number of defective atoms, and the number of CN=3 atoms in graphene. When the silicon substrate was used, the stable force of the probe is small, the edge structure of graphene has little impact, the edge effect obtained is good. The cutting depth and substrate hardness have little effect on the graphene temperature during the nano-cutting process. In this paper, the atomic structure of graphene edges after cutting is analysed and investigated on the atomic scale, and the above results are combined to provide theoretical guidance for obtaining efficient and high-quality and low-damage graphene nanoribbon cutting.