Metal Oxide Semiconductor Research Articles

Temperature Dependent Growth of Ytterbium Oxide as Gate Dielectric on Silicon Substrate Via Combination of Nitrogen and Oxygen Ambient

The ongoing trend towards downsizing silicon (Si)-based metal-oxide semiconductor (MOS) devices has led to constraints on the silicon dioxide (SiO2) gate dielectric due to increased leakage current through the thin SiO2. In this study, ytterbium oxide (Yb2O3) as a high dielectric constant (k) gate oxide material was deposited on a Si substrate and subjected to annealing at different temperatures ranging from 400 to 1000oC in a nitrogen-oxygen-nitrogen ambient atmosphere. The successful formation of Yb2O3 was verified using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet-visible (UV-VIS) spectroscopy. The FTIR analysis indicated that Yb2O3 gate dielectrics post-annealing exhibited Yb-O bonding due to oxygen diffusion, as well as N-O bonding and NO3-bonding, demonstrating the formation of a nitrogen barrier at the interface to hinder oxygen diffusion. The optical band gap values of Yb2O3 gate dielectrics post-annealing ranged from 3.092 eV to 3.267 eV. Notably, the Yb2O3 gate dielectric annealed at 800 °C showed no breakdown within the 0–3 V range across all samples. The acquisition of a high k value of 19.40 and a low effective oxide charge (Qeff) of 5.32 x 1011 cm-2, along with the superior I-V characteristics, suggest that the Yb2O3 gate dielectric annealed at 800oC has the potential to be employed for next generation MOS applications.

An ASIC-based system-in-package MEMS gas sensor with impedance spectroscopy readout and AI-enabled identification capabilities

The main advantages of micromachined metal oxide semiconductor (MOX) gas sensors, in particular their low cost, high sensitivity, miniaturization and low power consumption, are compromised by lack of selectivity and long-term sensor signal drifts, which often hinder their application in real-world sensing applications. To increase the sensor data dimensionality, temperature cycled operation (TCO) and impedance spectroscopy (IS) readout was proposed, enabling the acquisition of large datasets from a single sensor, as suitable to be exploited by machine learning techniques. Furthermore, recent studies have shown how the IS readout minimizes the issues represented by the sensor long-term signal drift.The aim of this work is the development of a smart system-in-package, integrating a state-of-the-art micromachined MOX gas sensor based on a wafer-level nanostructured sensing layer with a novel versatile sensor interface chip, capable of high performance IS readout. We propose a miniaturized sensing device, which is a small, lightweight low power consumption chemical sensing micro-system with fast and accurate classification capabilities, suitable to be deployed in long multi-node sensing cables or on unmanned aerial vehicles. A software suite comprising a sensor training wizard was also developed, enabling users with no technical background to train the sensing system.

Development of an inductive energy storage pulsed power supply using SiC semiconductor devices for ozone production by streamer discharges

An inductive energy storage (IES) pulsed power generator driven by a silicon carbide metal oxide semiconductor field effect transistor (SiC-MOSFET) with a blocking voltage of 1.2 kV was developed. The IES pulsed power generator consists of a capacitor, a pulsed transformer and the SiC-MOSFET used as an opening switch. The influence of the turn ratio of the pulsed transformer on the output voltage was evaluated. The output voltage amplitude increased with increasing secondary turn ratio. Under the conditions of no load, a peak output voltage of 13 kV and a pulse width of 120 ns were obtained with a voltage across the drain–source terminals of the MOSFET of 1 kV. The peak voltage increased, and the peak current and pulse width decreased, with increasing load resistance and decreased capacitance. The maximum energy transfer efficiency was obtained at 500 Ω and was approximately 56%.

Silica conversion of polysilazanes by low-temperature plasma jet generated from Ar and water-vapor mixed gas

Perhydropolysilazane (PHPS), which contains no organic catalyst, chemically reacts with H2O in the atmosphere by heating it at 450 °C for more than 1 h to turn it into a SiO2 film. If silica conversion can be achieved at temperatures below 100 °C, which plastics can withstand, it may be applicable to a wide range of applications, such as flexible electronics. Here, we report a technique for forming SiO2 films with leakage current characteristics very close to those of thermally oxidized (THOX) films that works at a very low temperature of 52 °C with high speed. Using a 9-kV, 30-kHz power supply, a low-temperature plasma jet containing a gas mixture of Ar and water vapor irradiated an 8 nm thick PHPS thin film, inducing silica conversion at a maximum substrate temperature of 52 °C. The current density-electric field strength (J-E) characteristics of metal oxide semiconductor capacitors fabricated with this SiO2 film showed characteristics very close to those of THOX films. In addition, the mechanism of silica conversion of PHPS through low-temperature plasma jet irradiation using this gas mixture was clarified in real-time FT-IR measurements.

Effects of Thickness and Anisotropic Strain on Polarization Switching Properties of Sub-10nm Epitaxial Hf0.5Zr0.5O2 Thin Films

Abstract Doped HfO2-based ferroelectric (FE) films are emerging as leading contenders for next-generation FE non-volatile memories due to their excellent compatibility with complementary metal oxide semiconductor processes and robust ferroelectricity at nanoscale dimensions. Despite the considerable attention paid to the FE properties of HfO2-based films in recent years, enhancing their polarization switching speed remains a critical research challenge. We demonstrate the strong ferroelectricity of sub-10 nm Hf0.5Zr0.5O2 (HZO) thin films and show that the polarization switching speed of these thin films can be significantly affected by HZO thickness and anisotropically strained La0.67Sr0.33MO3-buffered layer. Our observations indicate that the HZO thin film thickness and anisotropically strained La0.67Sr0.33MO3 layer influence the nucleation of reverse domains by altering the phase composition of the HZO thin film, thereby reducing the polarization switching time. Although the increase in HZO thickness and anisotropic compressive strain hinder the formation of the FE phase, they can enable faster switching. Our findings suggest that FE HZO ultrathin films with polar orthorhombic structures have broad application prospects in microelectronic devices. These insights into novel methods for increasing polarization switching speed are poised to advance the development of high-performance FE devices.

Influence of isochronal heat treatment on spray-deposited mixed phase tin based thin films for ammonia gas sensor applications

The current work applied the spray pyrolysis (SP) approach to coat mixed-phase SnS thin films at 3500C, and then air annealed at 400,450,5000C for use in sensor and solar cells applications. A variety of methods were employed to evaluate the structural, morphological, compositional, optical, and electrical characteristics of synthesized mixed-phase films. Films annealed at 5000C are reported to have bigger crystal sizes, and all deposited SnS films exhibit the orthorhombic phase in addition to tetragonal phase of SnO2, with other visible secondary phases like SnS2,Sn2S3. Fourier transform infrared spectroscopy and Raman analyses verified the molecular structure and vibrational mode of SnS films. The Scanning electron microscopy tests reveal a consistent, size-varying two-dimensional flake like grain structure, while the optical studies show a variation in optical direct band-gap from 1.79-2.75eV. The Hall-effect shows that films subsequently annealed at 4000C have improved electrical properties. An efficient metal oxide semiconductor gas sensor was developed by applying mixed-SnS film on the conducting side of an indium tin oxide coated glass plate. To examine the sensor selectivity at room temperature, a variety of test gases, such as NO2, H2S, C2H5OH, NH3, were purged at different concentrations. The optimum working temperature and concentration for NH3 selective gas have been determined to be 3500C and 5ppm. The sensor sensitivity is found to be maximum at operating temperature of 2000C towards NH3 gas. An inexpensive, fabricated MOS-gas sensor based on mixed-phase SnS can be easily mass produced and may find potential applications in industrial and environmental monitoring.

Comprehensive Study of Low-Power SRAM Design Topologies

: The need for low power in portable and smart devices is the demand to be fulfilled for sustaining the semiconductor industry. Static Random Access Memory (SRAM) is the main part of the core design in chips. It is important to reduce the leakage power consumption during the steady mode of the device for the long run of the battery. This article is about the study of different modules using pre-existing low power. Application of different methods other than lowering the supply voltage leads to an increment in the number of transistors in conventional 6T (six transistor) SRAM cells like 7T to 14T. Power gating and the Multi-threshold complementary metal oxide semiconductor (MTCMOS) technique is the most relevant method. Hybrid low power techniques are in high demand because it shows better results than using individual techniques. However, the biggest challenge is to maintain the area and delay as well. FinFET came into the scenario to overcome the leakage power and short channel effect due to scaling in CMOS. Comparative study analysis shows that FinFET decreases the overall power and delay even when the number of transistors increases. A comparison was done between 6T, 8T, and 10T using FinFET and CMOS in a paper, and concluded that FinFET shows 77.792% improved write power.

Silicon rich nitride: a platform for controllable structural colors

Abstract High refractive index dielectric materials like silicon rich nitride (SRN) are critical for constructing advanced dielectric metasurfaces but are limited by transparency and complementary metal oxide semiconductor (CMOS) process compatibility. SRN’s refractive index can be adjusted by varying the silicon to nitride ratio, although this increases absorption, particularly in the blue spectrum. Dielectric metasurfaces, which utilize the material’s high dielectric constant and nano-resonator geometry, experience loss amplification due to resonance, affecting light reflection, light transmission, and quality factor. This study explores the impact of varying the silicon ratio on structural color applications in metasurfaces, using metrics such as gamut coverage, saturation, and reflection amplitude. We found that a higher SRN ratio enhances these metrics, making it ideal for producing vivid structural colors. Our results show that SRN can produce a color spectrum covering up to 166 % of the sRGB space and a resolution of 38,000 dots per inch. Fabricated samples vividly displayed a parrot, a flower, and a rainbow, illustrating SRN’s potential for high-resolution applications. We also show that SRN can provide a better CIE diagram coverage than other popular metasurfaces materials. These findings highlight the advantages of SRN for photonic devices, suggesting pathways for further material and application development.

Synthesis and Advanced Applications of Transition Metal Oxides

Transition metal oxide semiconductor materials have gained significant attention in recent years because of their unique electrical, magnetic, and optical features. Transition metal oxides (TMOs) with partially filled d-shells have a wide range of characteristics and play important roles in a variety of technological applications. They are influenced by stoichiometry changes, which alter their physical, chemical, and electrical properties. Controlled synthesis, doping, and post-synthesis treatments can all have an impact on the size, shape, crystal structure, and overall attributes of TMOs. These changes affect applications such as magnetic materials and smart windows. Effective techniques include valence state control, dopants, alloying, structure engineering, nano and defect structuring, and surface modification. This article discusses the synthesis methods, crystal structures, electrical properties, and applications of transition metal oxides, as well as their involvement in cutting-edge technologies such as electronics, optoelectronics, energy storage, and catalysis.

Gate control of superconducting current: Mechanisms, parameters, and technological potential

In conventional metal-oxide semiconductor (CMOS) electronics, the logic state of a device is set by a gate voltage (VG). The superconducting equivalent of such effect had remained unknown until it was recently shown that a VG can tune the superconducting current (supercurrent) flowing through a nanoconstriction in a superconductor. This gate-controlled supercurrent (GCS) can lead to superconducting logics like CMOS logics, but with lower energy dissipation. The physical mechanism underlying the GCS, however, remains under debate. In this review article, we illustrate the main mechanisms proposed for the GCS, and the material and device parameters that mostly affect it based on the evidence reported. We conclude that different mechanisms are at play in the different studies reported so far. We then outline studies that can help answer open questions on the effect and achieve control over it, which is key for applications. We finally give insights into the impact that the GCS can have toward high-performance computing with low-energy dissipation and quantum technologies.

High-temperature time-dependent dielectric breakdown of 4H-SiC MOS capacitors

—With the rapid applications of silicon carbide metal–oxide–semiconductor field-effect transistor (SiC MOSFET) power devices, further improving the performance of SiC MOSFET device through enhancing its gate oxide reliability is one of the crucial directions. The density of interface states in a SiC MOSFET is a significant parameter that affects the reliability of the gate oxide layer. In this paper, the SiC MOS capacitors (MOSCAPs) were prepared by the 1250 °C dry oxidation and 1350 °C NO annealing process. Then, we analyzed the mechanisms of the breakdown by two group of ramped experiment. And we still evaluated the reliability of oxide layer via the high-temperature time-dependent dielectric breakdown (TDDB) tests on the prepared MOSCAPs, meanwhile, the temperature effect on the reliability was considered. Furthermore, the E, 1/E, and E models with Weibull plotting were used to calculate the tBD lifetimes and failure analysis was carried on the failed samples finally. The results indicate that: (1) the impact of the generation and accumulation of the traps in the oxide, which is the main mechanisms of device failure; (2) The prediction of lifetime was calculated with three models at different acceleration factors; (3) at high-temperature, although the lower the density of interface states is, the Si epitaxial growth and C cluster will manifest in the oxide surface and lead to the breakdown of SiC MOSCAPs.

Enhanced water splitting on (010) facet-exposed BiVO4 photoanode with improved carrier injection efficiency

Transition metal oxide semiconductors, noted for their stability and suitable bandgap, are promising photoanodes for water splitting. Surface engineering is critical to tackle issues like low carrier mobility and charge recombination, stemming from atomic arrangement and Fermi level differences. While exposing dominant crystal facets boosts photocatalytic capability, it can hinder carrier injection into the electrolyte. In this study, BiVO4 films with various facet exposures were synthesized and characterized using scanning electron microscopy and x-ray diffraction to confirm their morphology and crystalline structure. Mott–Schottky analysis was employed to investigate changes in the band structure near the semiconductor–electrolyte interface, revealing that high (010)-BiVO4 facet exposure enhances carrier separation but reduces injection efficiency. The results from photoconductive atomic force microscopy tests demonstrated that enhanced band bending at the semiconductor interface improves hole transfer. Coating the (010)-BiVO4 photoanode with MoS2 and an amorphous ZrO2 interlayer yielded a photocurrent density of 0.6 mA cm−2 at 1.2 V (vs RHE) under AM 1.5 G illumination, tripling the pristine photoanode's performance and nearly tripling water splitting efficiency. Mechanism revealing the improved photoelectrochemical performance is attributed to a greater band bending on the BiVO4 surface, enhancing hole injection dynamics. This work provides a feasible strategy for a deeper understanding of the intrinsic mechanisms of facet engineering and improving the activity of photoanodes.

A Drosophila-inspired intelligent olfactory biomimetic sensing system for gas recognition in complex environments

The olfactory sensory system of Drosophila has several advantages, including low power consumption, high rapidity and high accuracy. Here, we present a biomimetic intelligent olfactory sensing system based on the integration of an 18-channel microelectromechanical system (MEMS) sensor array (16 gas sensors, 1 humidity sensor and 1 temperature sensor), a complementary metal‒oxide‒semiconductor (CMOS) circuit and an olfactory lightweight machine-learning algorithm inspired by Drosophila. This system is an artificial version of the biological olfactory perception system with the capabilities of environmental sensing, multi-signal processing, and odor recognition. The olfactory data are processed and reconstructed by the combination of a shallow neural network and a residual neural network, with the aim to determine the noxious gas information in challenging environments such as high humidity scenarios and partially damaged sensor units. As a result, our electronic olfactory sensing system is capable of achieving comprehensive gas recognition by qualitatively identifying 7 types of gases with an accuracy of 98.5%, reducing the number of parameters and the difficulty of calculation, and quantitatively predicting each gas of 3–5 concentration gradients with an accuracy of 93.2%; thus, these results show superiority of our system in supporting alarm systems in emergency rescue scenarios.

Modeling and Analyzing of CMOS Cross-Coupled Differential-Drive Rectifier for Ultra-Low-Power Ambient RF Energy Harvesting

This paper models and analyzes the Complementary Metal Oxide Semiconductor (CMOS) cross-coupled differential-drive (CCDD) rectifier for Ultra-Low-Power ambient radio-frequency energy harvesters (RFEHs) working in the subthreshold region. In this paper, two closed-form equations of CCDD rectifier output voltage and input resistance in the subthreshold region were derived based on BSIM4 models of NMOS and PMOS. The model give insight to specify circuit parameters according to different inputs, transistor sizes, threshold voltages, numbers of stages, load conditions and compensation voltages, which can be used to optimize the rectifier circuit. There is a good agreement between the simulation results and these models, and these models have a maximum deviation of 10% in comparison with the simulation results in the subthreshold region. The measurement results of a single-stage CCDD rectifier reported in a previous paper were adopted to verify the model. The output voltage and input resistance predicted by these models provide excellent consistency with corresponding measurement results. The model can be employed to optimize the CCDD rectifier without expensive calculation in the design stage.

Impact of monolayer WS2 surface properties on the gate dielectrics formation by atomic layer deposition

Two-dimensional transition metal dichalcogenides (2D TMDs), such as MoS2 and WS2, have emerged as promising channel materials for future generation transistors. However, carbon-based surface contaminants pose a significant challenge in the formation of high-quality metal–oxide–semiconductor gate stacks for 2D TMDs. Carbon-based surface contaminants are known to be present even on directly grown 2D TMDs that have not been in contact with polymers. These organic contaminants affect precursor adsorption during atomic layer deposition (ALD) of gate dielectrics on 2D TMDs and as such the 2D-dielectric interface. This study examines the effectiveness of predeposition annealing in mitigating carbon-based contaminants while maintaining the integrity of a directly grown WS2 monolayer on a SiO2 substrate. We show that a WS2 monolayer on a SiO2/Si substrate remains stable during vacuum annealing at temperatures up to 400 °C. Water contact angle measurements and x-ray photoelectron spectroscopy confirm that the surface concentration of carbon starts to decrease at 150 °C. Thermal anneal improves the surface coverage of Al2O3 for both conventional chemisorption-based ALD and physisorbed-precursor-assisted ALD processes by facilitating more effective Al2O3 nucleation on the WS2 monolayer. The impact of predeposition anneal on the Al2O3 growth behavior in both processes can be explained by changes in surface contaminant levels. Our results underscore the importance of surface pretreatment in dielectric deposition on 2D TMDs and demonstrate that predeposition anneal is an effective method to enhance ALD-based dielectric deposition on directly grown 2D TMDs.

Analysis and Design of an SiC CMOS Three-Channel DC-DC Synchronous Buck Converter for High-Temperature Applications

In this study, we present the design, simulation, and implementation of a DC-DC synchronous buck converter utilizing IISB’s 2 μm 4H-silicon carbide (SiC) complementary metal–oxide–semiconductor (CMOS) technology. The converter is designed to meet the demands of modern integrated circuits, particularly in the field of integrated power management. The SiC technology offers enhanced performance and reliability at high temperatures, making it especially suitable for applications that operate in these conditions, including automotive systems, and aerospace, among others. The power transistors and gate drivers are fully integrated on-chip, optimizing efficiency and minimizing footprint. Additionally, the study contributes to the understanding of SiC technology and its application in integrated circuit design. Simulation results demonstrate a peak efficiency of 86.6% at 120 mA load current and 84.8% at 300 mA load current, showing the converter performance under different operating conditions. Furthermore, at high temperatures (295 °C), the converter achieves an efficiency of 89.6%, demonstrating its robustness and versatility in extreme environments. These findings contribute to the advancement of integrated circuit design and facilitate advancements in more efficient and robust power management solutions.

Ultrathin Copper Monosulfide Films for an Optically Semitransparent, Highly Selective Ammonia Chemosensor.

Transition-metal sulfides are emerging as promising materials for chemiresistive gas sensors─a field still dominated by semiconducting metal oxides. Despite the availability of materials with tunable electronic, optical, physical, and chemical properties, few studies have moved beyond synthesis to provide strategies for enhancing gas sensing performance through material modification. Here, we present a simple, scalable synthetic strategy for developing an optically semitransparent, flexible NH3 gas sensor with a highly uniform, ultrathin CuS (covellite) active sensing layer. The optical and chemical properties of the CuS were precisely controlled near the percolation threshold of thin-film formation by varying key experimental parameters such as the Cu film thickness (<10 nm) and the sulfurization time (∼90 s) under ambient conditions. Experimental and computational studies of CuS and its NH3 sensing characteristics identify key physicochemical properties. The controlled surface chemistry and morphology of the ultrathin CuS layer demonstrate its effectiveness in functional NH3 sensing devices, which achieve a calculated detection limit of 1.38 ppm for NH3 gas at 150 °C, along with exceptional mechanical robustness and optical semitransparency in the visible-light spectrum.

Development of High-Performance Ethanol Gas Sensors Based on La2O3 Nanoparticles-Embedded Porous SnO2 Nanofibers.

Porous pure SnO2 nanofibers (NFs) and La2O3 nanoparticles (NPs)-embedded porous SnO2 NFs were successfully synthesized via electrospinning followed by calcination. These materials were systematically evaluated as gas-sensing elements in metal-oxide-semiconductor (MOS) sensors. The La2O3 NPs embedded in porous SnO2 NFs demonstrated superior gas-sensing performance compared to pure SnO2 NFs. Specifically, the incorporation of La2O3 resulted in a 12-fold enhancement in gas-sensing response towards ethanol, significantly improving both sensitivity and selectivity by tuning the carrier concentration and modifying oxygen deficiencies and chemisorbed oxygen levels. Thus, La2O3 NPs embedded in SnO2 NFs present a promising strategy for the development of high-performance ethanol gas sensors.

Wide-range and ultra-low temperature thermometer based on a silicon resonator.

In this Letter, the silicon-based microring resonator (MRR) was experimentally demonstrated for cryogenic sensing down to 10 K by overcoming the issue of acquiring the optical signals at low temperatures for on-chip optical sensors. A wide-range temperature sensor from 240 to 10 K was obtained. The experimental results show that the device sensitivity decreased from 64.7 pm/K at 240 K to 4.19 pm/K at 10 K. Theoretical analysis indicates that the reduction in sensitivity is attributed to the weakening of thermo-optic effects with the decrease in temperature, which is well consistent with the experimental results. Based on this work, the silicon-based ring resonators, featuring complementary metal oxide semiconductor (CMOS) compatibility, high-quality factors, and ease of chip-scale integration, are a potential platform for ultra-low temperature monitoring.

Revealing Enhanced Optical Modulation and Coloration Efficiency in Nanogranular WO3 Thin Films Through Precursor Concentration Modifications

Electrochromic (EC) materials allow for dynamic tuning of optical properties via an applied electric field, presenting great potential in energy-efficient technologies, such as smart windows for effective light and temperature regulation. The precise control of precursor concentration has proven to be a powerful approach in tailoring the physicochemical properties of semiconducting metal oxides. In this study, we employed a one-step electrodeposition technique to fabricate tungsten oxide (WO3) thin films, systematically exploring how varying precursor concentrations influence the material’s characteristics. X-ray diffraction analysis revealed significant changes in diffraction patterns, reflecting subtle structural modifications due to concentration variations. Additionally, scanning electron microscopy revealed significant changes in the microstructure, showing a progression from small nanogranules to larger agglomerations within the film matrix. The W-25 mM thin film delivered exceptional EC performance, efficiently accommodating lithium ions while showcasing superior EC properties. The optimized electrode, denoted as W-25 mM, showcased exceptional EC metrics, featuring the highest optical modulation at 82.66%, outstanding reversibility at 99%, and a notably high coloring efficiency of 83.01 cm2/C. These findings emphasize the importance of precursor concentration optimization in enhancing the EC properties of WO3 thin films, contributing to the advancement of high-performance, energy-efficient materials.