Silicon Substrate Research Articles

Sputter Deposited Crystalline MoO2 Films as a High-Capacity and Stable Electrode Material for Supercapacitors: Mechanistic/Electrochemical Insights

In this work, we have optimized and fabricated pristine molybdenum dioxide (MoO2) electrodes over the Silicon (Si) substrate and examined the impact of various ion-loaded aqueous electrolytes on their electrochemical behavior. The sputtered electrodes exhibited a high crystalline structure and a very low resistivity. These highly conductive electrodes were tested in three different aqueous electrolytes (acidic, neutral, and alkaline) to establish a relation between the electrode and the nature of the electrolyte to achieve optimal electrochemical performance and cyclability. The electrochemical kinetics showed that the charge storage mechanism was unique for all the electrolytes. The capacitive current was dominant in the neutral electrolyte, whereas it was diffusive dominant in alkaline and 70% capacitive in the acidic electrolyte. Our findings indicated that the MoO2@Si electrode exhibited superior electrochemical activity in an acidic electrolyte. The electrode showed a voltage window of 0.6 V with an areal capacity of 24 mF/cm2 at 0.1 V/s scan rate. Moreover, the electrode also demonstrated excellent cyclability and capacitance retention (∼145%) till 5000 cycles. These results highlighted that the binder-free MoO2@Si electrode showed outstanding electrochemical activity and stability, which makes it suitable for sulfuric acid electrolyte-based energy storage systems.

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]%).

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.

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.

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.

Multi-parameter terahertz metamaterial sensors based on single-layer quarter ring patterns

A terahertz metamaterial sensor based on a single-layer quarter ring pattern is proposed to realize the simultaneous measurement of temperature, refractive index, and other parameters through a metasurface consisting of a patterned quarter ring gold layer and a silicon substrate. Field finite element numerical simulations were performed to analyse the transmission and reflection spectra. A two-parameter sensor combined with electric field distribution was realized using multiple peaks, thus revealing the physical mechanisms of the interaction in metamaterial structures. In addition, the effect of each geometrical parameter on the sensor performance is also simultaneously analysed to verify the optimal selection of structural parameters. On this basis, the sensors are theoretically analysed at different incidence and polarization angles, and the results show that the transmittance is not sensitive to the polarization angle. The simulation results show that the transmittance at the resonant frequencies of 0.48 THz, 0.64 THz, 0.79 THz and 1.04 THz are 93.7 %, 79.1 %, 38.4 % and 50.8 %, respectively, and the refractive index sensitivities at the resonant frequencies are 6.84 GHz/RIU, 7.42 GHz/RIU, 8.22 GHz/RIU and 32.11 GHz/RIU, and quality factor Q of 6.76, 9.63, 15.51 and 26.28, respectively. The devices proposed in this study are simple in structure, easy to fabricate, easy to miniaturize and can be integrated for sensitivity, multi-parameter sensors. They can be functionally designed for chemical and biological sensing and other important applications.

Effect of supporting layer on electrical characteristics of field-effect transistor based on reduced graphene oxide film

The field-effect transistors (FETs) based on reduced graphene oxide (rGO) with SiO2, porous silicon (PS), and oxidized porous silicon (PSox) supporting layers were obtained. The influence of charged impurities in the silicon substrate and electrically active defects in the support layers on the electrical properties of the FETs was studied based on the capacitance-voltage characteristic analysis. Localized electron states in the SiO2, PS, and PSox supporting layers that affect the charge transfer in the rGO-based FETs were determined using thermally stimulated depolarization spectroscopy. The influence mechanisms of various supporting layers on the electrical characteristics of the obtained FETs are discussed.

Mechanically-flexible wafer-scale integrated-photonics fabrication platform

The field of integrated photonics has advanced rapidly due to wafer-scale fabrication, with integrated-photonics platforms and fabrication processes being demonstrated at both infrared and visible wavelengths. However, these demonstrations have primarily focused on fabrication processes on silicon substrates that result in rigid photonic wafers and chips, which limit the potential application spaces. There are many application areas that would benefit from mechanically-flexible integrated-photonics wafers, such as wearable healthcare monitors and pliable displays. Although there have been demonstrations of mechanically-flexible photonics fabrication, they have been limited to fabrication processes on the individual device or chip scale, which limits scalability. In this paper, we propose, develop, and experimentally characterize the first 300-mm wafer-scale platform and fabrication process that results in mechanically-flexible photonic wafers and chips. First, we develop and describe the 300-mm wafer-scale CMOS-compatible flexible platform and fabrication process. Next, we experimentally demonstrate key optical functionality at visible wavelengths, including chip coupling, waveguide routing, and passive devices. Then, we perform a bend-durability study to characterize the mechanical flexibility of the photonic chips, demonstrating bending a single chip 2000 times down to a bend diameter of 0.5 inch with no degradation in the optical performance. Finally, we experimentally characterize polarization-rotation effects induced by bending the flexible photonic chips. This work will enable the field of integrated photonics to advance into new application areas that require flexible photonic chips.

Copper tantalum nitride (CuTaN2) thin films prepared by reactive radio-frequency magnetron sputtering

RF reactive sputtering was used to deposit copper tantalum nitride (CuTaN2) films from a Cu/Ta target in an environment containing a mixture of argon and nitrogen at two different substrate temperatures: room temperature and 200 °C. The films were studied by SEM, EDS, XRD, Raman spectroscopy, spectrophotometry, and resistivity measurements. The deposition conditions significantly impacted the morphology of the films, which varied from smooth, void-free films at high nitrogen concentrations and at room temperature substrates to cauliflower-like grains with voids at low nitrogen contents and elevated substrate temperatures. Despite the target’s 1:1 Cu: Ta ratio, the stoichiometric analysis showed a lower Ta content in the deposited film. The films produced on silicon substrates were polycrystalline, whereas those deposited on glass substrates were amorphous. The band gap (0.9 eV to 1.55 eV) and film resistivity (20 kΩ-cm to 76 kΩ-cm) are strongly affected by the nitrogen fraction in the sputtering gas. Increasing the nitrogen percentage in semiconductor films results in smoother films with larger bandgaps (approximately 1.5 eV), higher resistivity, and compositions closest to those of stoichiometric CuTaN2.

Influence of inverted pyramid texturization on front metallization and performance of crystalline silicon solar cells

The silicon surface texturing is an essential part for the fabrication of crystalline silicon solar cells to increase the conversion efficiency. By adjusting the etching texturing condition, inverted pyramid (IP) and upright pyramid (UP) texturization were prepared on crystalline silicon substrates for fabrication of PERC solar cells. The surface morphology not only affects the light trapping but also impacts electrode shading loss and front electrode contact interface. The IP texturization presents better anti-reflective performance due to more common light paths and narrower silver grids owing to less flow of Ag paste on concave blocked structure, both of which results in the higher short-circuit current density (Jsc). Yet in terms of front Ag/Si contact interface, the IP texturization causes more Ag crystallites and more surface recombination under the present condition suitable for UP texturization because of more edges on the upper part of IP, which leads to the lower open-circuit voltage (Voc). The final conversion efficiency of IP solar cells (23.61 %) is 0.06 % higher than that of UP solar cells (23.55 %). An improvement about 0.07 mA/cm2 of Jsc was achieved with IP samples and Voc has a decrease of 0.3 mV caused by the surface recombination on IP texturization. In summary, the structural characteristics of IP results in lower reflectivity and less electrode shading, while Ag/Si contact interface could be optimized by adjusting the processing condition, ultimately promising the higher efficiency.

Numerical ellipsometry: Artificial intelligence for rapid analysis of indium tin oxide films on silicon

Ellipsometry is a well-known material analytical method widely used to measure thickness and optical properties of thin films and surfaces across a wide range of industrial and research applications including critical dimensions in chipmaking. The method employs the fact that light undergoes a change in polarization state upon reflection from or transmission through a material. The desired properties of the surface structure are related to measurements by the electromagnetic models expressed by Maxwell’s equations as well as models of material properties. The work here demonstrates the use of artificial intelligence in the form of a multilayer perceptron artificial neural network to apply the electromagnetic model. The reflecting surface examined here is composed of indium tin oxide (ITO) films approximately 400 nm in thickness deposited on silicon substrates. Solutions are provided by 299 artificial neural networks, one per wavelength from 210 to 1700 nm across which ITO exhibits transparent as well as absorbing characteristics. Thus, it serves as a proxy for a wide range of other materials. To train the network, simulated measurements are computed at two thicknesses which differ randomly by 1–6 nm and at three different incidence angles of 55°, 65°, and 75°. Following training, results are obtained in less than one second on a conventional desktop computer.

Molybdenum-Doped ZnO Thin Films Obtained by Spray Pyrolysis.

A batch of ZnO thin films, pure and doped with molybdenum (up to 2 mol %), were prepared using the spray pyrolysis technique on glass and silicon substrates. The effect of molybdenum concentration on the morphology, structure and optical properties of the films was investigated. X-ray diffraction (XRD) results show a wurtzite polycrystalline crystal structure. The average crystallite size increases from 30 to 80 nm with increasing molybdenum content. Scanning electron microscopy (SEM) images demonstrate a smooth and homogeneous surface with densely spaced nanocrystalline grains. The number of nuclei increases, growing over the entire surface of the substrate with uniform grains, when the molybdenum concentration is increased to 2 mol %. The estimated root mean square (RMS) roughness values for the undoped and doped with 1 mol % and 2 mol % of ZnO thin films, defined by atomic force microscopy (AFM), are 6.12, 23.54 and 23.83 nm, respectively. The increase in Mo concentration contributes to the increase in film transmittance.