Metal Oxide Semiconductor Research Articles

2D porous hexaniobate-bismuth vanadate hybrid photocatalyst for photodegradation of aquatic refractory pollutants

Metal oxide semiconductors are highly promising due to their excellent photocatalytic performance in the photodegradation of industrial waste containing refractory chemical compounds. A hybrid structure with other semiconductors provides improved photocatalytic performance. In this work, porous and two-dimensional (2D) hexaniobate-bismuth vanadate (Nb6-BiVO4) Z-scheme hybrid photocatalysts are synthesized by chemical solution growth (CSG) of BiVO4 over electrophoretically deposited Nb6 thin films. The structural and morphological analysis of Nb6-BiVO4 hybrid thin films evidenced the well-crystalline uniform growth of monoclinic scheelite BiVO4 over lamellar Nb6 nanosheets. The Nb6-BiVO4 hybrid thin films exhibit a highly porous randomly aggregated nanosheet network, creating the house-of-cards type morphology. The Nb6-BiVO4 hybrid thin films display a strong visible light absorption with band gap energy of 2.29 eV and highly quenched photoluminescence signal, indicating their visible light harvesting nature and intimate electronic coupling between hybridized species beneficial for photocatalytic applications. The visible-light-driven photodegradation performance of methylene blue (MB), rhodamine-B (Rh-B) dyes, and tetracycline hydrochloride (TC) antibiotic over Nb6-BiVO4 hybrid are studied. The best optimized Nb6-BiVO4 thin film shows superior photocatalytic activity for photodegradation of MB, Rh-B dyes, and TC antibiotic with photodegradation rates of 87.3, 92.8, and 64.7 %, respectively, exceptionally higher than that of pristine BiVO4. Furthermore, the mineralization study of Nb6-BiVO4 thin film is conducted using chemical oxygen demand (COD) analysis. The optimized Nb6-BiVO4 thin film shows superior percentage COD removal of 83.33, 85.42, and 61.36 % for MB, Rh-B dyes and TC antibiotic, respectively. The present results highlight the expediency of hybridization in enhancing the photocatalytic activity of pristine BiVO4 by minimizing its charge recombination rate and improving chemical stability.

Introducing oxygen vacancies into WO3 thin film for improving hydrogen sensing performance of Pd/WO3-x/AAO sensors

Introducing oxygen vacancy into semiconducting metal oxides (SMOs) is a strategic approach to promote their gas sensing performances. In this paper, the WO3-x thin films were meticulously deposited onto an anodic aluminum oxide (AAO) substrate, and the oxygen vacancies concentrations of WO3-x thin films were changed by adjusting the ratio of flux of Ar to O2 in magnetron sputtering process. Sequentially, a layer of palladium (Pd) was deposited on the WO3-x/AAO films, creating a nano-mesh structured hydrogen sensor with Pd as the catalytic element. The resulted amorphous WO3-x samples with varying concentration of oxygen vacancies were thoroughly analyzed using XPS and ESR, which confirmed that the oxygen vacancies concentration escalated with an increase in the ratio of flux of Ar to O2. The hydrogen sensitivity of prepared Pd/WO3-x/AAO sensors were examined. Our findings revealed an enhancement in hydrogen sensitivity for the sensors with an optimal concentration of oxygen vacancies. However, an excess of these vacancies was found to deteriorate their hydrogen sensing performance. Notably, the optimized Pd/WO3-x/AAO sensor exhibited a marked response even at a hydrogen concentration as low as 100 ppb, demonstrating its high sensitivity and selectivity towards hydrogen detection.

Gas sensing performance regulating of ZIF-8 encapsulated WO3 nanosheets

Reasonably regulating the adsorption properties on the surface of metal oxide semiconductors (MOS) to enhance sensor selectivity remains a challenge, limiting their application in detecting diseases biomarkers in human exhaled gas. To address this, we proposed a metal-organic frameworks (MOFs) encapsulated strategy to provide a gas-selective permeable nano-filtration layer for MOS gas sensors. By adjusting the coating thickness of ZIF-8, we successfully modulate the sensing properties of WO₃ to different potential biomarkers. The optimized WO₃/ZIF-8 composite shows improved selectivity and response to various disease biomarkers compared to WO₃ alone. The unique porous structure of ZIF-8 and the heterojunction of WO3/ZIF-8 synergistically promote the gas adsorption performance. QCM test results confirm that ZIF-8 modification effectively regulates gas adsorption on the WO₃ surface. This study provides a valuable reference for designing exhaled gas sensor arrays for detecting serious diseases.

Scalable Atomic Arrays for Spin-Based Quantum Computers in Silicon.

Semiconductor spin qubits combine excellent quantum performance with the prospect of manufacturing quantum devices using industry-standard metal-oxide-semiconductor (MOS) processes. This applies also to ion-implanted donor spins, which further afford exceptional coherence times and large Hilbert space dimension in their nuclear spin. Here multiple strategies are demonstrated and integrated to manufacture scale-up donor-based quantum computers. 31PF2 molecule implants are used to triple the placement certainty compared to 31P ions, while attaining 99.99% confidence in detecting the implant. Similar confidence is retained by implanting heavier atoms such as 123Sb and 209Bi, which represent high-dimensional qudits for quantum information processing, while Sb2 molecules enable deterministic formation of closely-spaced qudits. The deterministic formation of regular arrays of donor atoms with 300nm spacing is demonstrated, using step-and-repeat implantation through a nano aperture. These methods cover the full gamut of technological requirements for the construction of donor-based quantum computers in silicon.

Wafer-Scale Atomic Layer-Deposited TeOx/Te Heterostructure P-Type Thin-Film Transistors.

There is an increasing demand for p-type semiconductors with scalable growth, excellent device performance, and back-end-of-line (BEOL) compatibility. Recently, tellurium (Te) has emerged as a promising candidate due to its appealing electrical properties and potential low-temperature production. So far, nearly all of the scalable production and integration of Te with complementary metal oxide semiconductor (CMOS) technology have been based on physical vapor deposition. Here we demonstrate wafer-scale atomic layer-deposited (ALD) TeOx/Te heterostructure thin-film transistors with high uniformity and integration compatibility. The wafer-scale uniformity of the film is evidenced by spatial Raman mappings and statistical electrical analysis. Furthermore, surface accumulation-induced good ohmic contact has been observed and explained by the unique band alignment of the charge neutrality level inside the Te valence band. These results demonstrate ALD TeOx/Te as a promising p-type semiconductor for monolithic three-dimensional integration in BEOL CMOS applications incorporated with well-established n-type ALD oxide semiconductors.

An analytical I-V model of SiC double-gate junctionless MOSFETs

Silicon carbide(SiC) double gate junctionless metal oxide semiconductor field-effect transistors(DG JL MOSFETs) have attracted significant attention due to their ideal high temperature characteristics and radiation resistance. Therefore, it is meaningful to exploit an I-V model for SiC DG JL MOSFETs. In this article, we make a linear approximation to describe the relationship between the surface mobile charge density and the surface electron concentration of the device. Based on this approximation and using the one-dimensional Poisson’s equation, we solve for the potential distribution of a SiC DG JL MOSFET in the subthreshold region. From this solution, we derived a functional relationship between the surface mobile charge density in the channel and the channel quasi-Fermi potential. Then we successfully developed a unified I-V model for the SiC DG JL MOSFETs. Based on the drain to source current calculation formula, the calculation expressions for the device’s transconductance and output conductance are derived. By comparing our model with the results from the two-dimensional numerical simulation software Silvaco Atlas, our model’s calculations closely match the two-dimensional numerical simulation results from the subthreshold region to the accumulation region. This model has reference significance for SiC DG JL MOSFETs in the high temperature electronic circuit application field.

Ion-migration-induced synaptic plasticity in high ion-storable fluorine graphdiyne for information processing

Neuromorphic devices encounter constraints associated with complementary metal–oxide–semiconductor technology, such as intricate electronics and high power consumption. Recently, solid polymer electrolytes (SPE) have gained attraction in electronic devices for constructing artificial synapses, primarily due to their low-voltage operation enabled by ion-assisted signal transmission. This study presents a two-terminal artificial synapse fabricated using fluorine graphdiyne (F-GDY) synthesized through chemical vapor deposition and ion-doped SPE. The device architecture consists of Au/SPE/F-GDY/Si, which operates by ion migration induced by external potential pulses. Electrical measurements are conducted to depict the synaptic plasticity of the devices. Among devices employing different ion-doped SPEs (Li-SPE, Na-SPE, K-SPE, and Ca-SPE), the one utilizing Li-SPE demonstrates the highest synaptic weight. This is attributed to the superior Li+ ion storage capacity of F-GDY; hence, Li-SPE/F-GDY was chosen for in-depth examinations of synaptic activity presenting long-term potentiation, short-term depression, and pair-pulse facilitation. The device has good durability and stability and can respond to low action potential with power consumption at the pJ level. Furthermore, Modified National Institute of Standards and Technology simulations reveal its learning and pattern recognition capability with 91.3 % accuracy after 10 training epochs. Finally, flexible substrate-based SPE/F-GDY devices integrated with gate electrodes were fabricated to record physiological signals, showing promise for in-sensing applications. This work shows the potential of F-GDY/Li-SPE devices for low-power neuromorphic computing, though real-time parallel processing and multimodal integration (e.g., visual, auditory) remain unexplored. However, the biocompatibility and efficient ion-assisted transmission of F-GDY suggest promising future applications in these areas.

Dielectric Material and Thermal Optimization in Sidewall Spacer Design for Junctionless Nanosheet FETs at Sub- 5 nm Technology Node: An Insight into Device and Circuit Performance

This study focuses on the design and analysis of Junctionless (JL) NSFETs, with an emphasis on the influence of spacer materials and temperature variations. A different number of materials such as Air, SiO2, Si3N4, HfO2, and TiO2 are examined for sidewall spacer compatibility in the JL-NSFET. The same materials are used for dual material spacers with combinations of: Air+HfO2, Air+TiO2, SiO2+HfO2, and SiO2+TiO2. The investigations revealed that the usage of TiO2 material gives better digital and analog performance with reduced leakage currents and subthreshold swing (SS), higher on/off ratio, voltage gain of ∼79.7 dB. Exploring the dual-k spacers produced better analog performance, gate control and reduced leakages for SiO2+TiO2 owing to the usage of higher dielectric material towards the gate. Further, the reduction of temperature from 400 K to 250 K for all the single-k and dual-k spacer materials revealed that the designed JL-NSFET is a suitable candidate at lower temperatures to improve the digital and analog performance whereas not recommended for RF performance improvement. Moreover, the SiO2+HfO2 spacer-based CMOS inverter is noticed to have better gain (∼15 V/V), noise margin, and lower delays (∼5.1 ps) when compared to TiO2 spacer-based complementary metal oxide semiconductor inverter making it suitable for digital IC applications.

Development of smart molecularly imprinted tetrahedral amorphous carbon thin films for in vitro dopamine sensing

This study investigates how varying the thickness of tetrahedral amorphous carbon (ta-C) thin films and incorporating a titanium adhesion layer influences the structural and electrochemical properties of molecularly imprinted ta-C thin film-based sensing platforms, aiming to develop a molecularly imprinted ta-C electrochemical sensor for dopamine (DA) detection with physiologically relevant sensitivity. This electrochemical sensing platform was designed by integrating ta-C with molecularly imprinted polymers (MIPs). The process involved depositing a ta-C thin film onto boron-doped p-type silicon wafers through a filtered cathodic vacuum arc (FCVA) system. Subsequently, the ta-C sensing platforms were electrochemically coated with the MIP layer (DA-imprinted polypyrrole). We evaluated three configurations: (i) a 15 nm ta-C layer, (ii) a 7 nm ta-C layer with a 20 nm titanium adhesion layer, and (iii) a 15 nm ta-C layer with a 20 nm titanium adhesion layer. Comprehensive structural and electrochemical characterization was performed to understand how these modifications affect sensor performance. The optimized MIP/ta-C sensor demonstrated a sensitivity of 0.16 μA μM−1 cm−2 and a limit of detection (LOD) of 48.6 nM, suitable for detecting DA at physiological levels. Leveraging the synergistic effects of ta-C coatings and molecular imprinting, as well as its compatibility with common complementary metal–oxide–semiconductor (CMOS) processes underlines its potential for integration into microanalytical systems, paving the way for miniaturized and high-throughput sensing platforms.

Recent trends in neuromorphic systems for non-von Neumann in materia computing and cognitive functionalities

In the era of artificial intelligence and smart automated systems, the quest for efficient data processing has driven exploration into neuromorphic systems, aiming to replicate brain functionality and complex cognitive actions. This review assesses, based on recent literature, the challenges and progress in developing basic neuromorphic systems, focusing on “material-neuron” concepts, that integrate structural similarities, analog memory, retention, and Hebbian learning of the brain, contrasting with conventional von Neumann architecture and spiking circuits. We categorize these devices into filamentary and non-filamentary types, highlighting their ability to mimic synaptic plasticity through external stimuli manipulation. Additionally, we emphasize the importance of heterogeneous neural content to support conductance linearity, plasticity, and volatility, enabling effective processing and storage of various types of information. Our comprehensive approach categorizes fundamentally different devices under a generalized pattern dictated by the driving parameters, namely, the pulse number, amplitude, duration, interval, as well as the current compliance employed to contain the conducting pathways. We also discuss the importance of hybridization protocols in fabricating neuromorphic systems making use of existing complementary metal oxide semiconductor technologies being practiced in the silicon foundries, which perhaps ensures a smooth translation and user interfacing of these new generation devices. The review concludes by outlining insights into developing cognitive systems, current challenges, and future directions in realizing deployable neuromorphic systems in the field of artificial intelligence.

Low-pressure oxidation for improving interface properties and voltage instability of SiO2/4H-SiC MOS capacitor

The impact of high-temperature sub-atmospheric oxidation pressure on the interface properties of n-type 4H-SiC metal–oxide–semiconductor capacitors has been systematically investigated in this report. The bias temperature instability measurement was used to calculate the mobile ions and near-interface trap density that led to device instability at high temperatures. The density of near interface traps decreased from 88.3 × 1011 cm−2 to 10.2 × 1011 cm−2 when the growth pressure of SiO2 was reduced from 1 atm to 0.1 atm, while the mobile ions density decreased from 83.5 × 1011 to 4.18 × 1011 cm−2. The results show that SiO2 growing under lower oxidation pressure has better interfacial quality. The underlying mechanism was explored by secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). It is speculated that the SiO2/SiC interface was reconstructed under low-pressure oxidation: the excess Si-related defects near the interface, such as SiOxCy, were released while O atoms were accumulated to promote a complete oxidation reaction, thereby effectively reducing the number of defects in the SiO2 film and improving device performance.

Design of a Portable Spectrophotometer Based on Raspberry Pi for Tea Type Classification Using Machine Learning

Abstract The use of spectrophotometers in food and beverage quality analysis has become common. However, portability and high cost have long been a problem for food industry players and small-scale laboratories. In this study, a more compact and low-cost spectrophotometer has been developed using raspberry pi. To validate its performance, the prototype was used to classify green tea, black tea, and oolong tea types. The research started with designing and assembling the hardware using a raspberry pi camera with Complementary Metal Oxide Semiconductor (CMOS) sensor, Digital Versatile Disk (DVD) as diffraction grating, white LED as light source and 3D printer as casing. The prototype was then used to acquire data from green tea, black tea and oolong tea solutions. In the tea type identification process, Principal Component Analysis (PCA) was applied to the data obtained. The experiment involved 30 solution samples of each of the three types of tea. The light source was directed past the sample towards the slit and DVD, then the spectrum image of the light source was displayed through a user interface built using python programming. This research resulted in a spectrophotometer with dimensions of 260 mm x 120 mm x 63 mm that is capable of capturing light spectra in the range of 400 - 700 nm. Based on the experimental results, the classification accuracy of the three types of tea using CNN and Decision Tree reached 100%.

Impact of Deposition Temperature on Structural and Electrical Properties of Sputtered AlN/ Si (111) for CMOS compatible MEMS

Aluminium nitride (AlN) thin films are grown by reactive sputtering on Silicon (Si) with (111) orientation at low temperature (< 450 °C) for piezoelectric-based micro-electromechanical systems (MEMS). The grown AlN thin films were polycrystalline wurtzite hexagonal structure with a high texture coefficient for the (002) plane of orientation. The leakage current density by the current-voltage (I-V) measurement was found to be as low as 1.6 ×10-6Acm−2 in the grown films. The trapped charges are crucial in controlling these electrical characteristics, and low interface trap density (6.72 ×1010cm−2 eV) was observed for the sputtered AlN grown at a substrate temperature of 300 °C. This study on the structural and electrical properties of AlN/Si (111) at low substrate temperature is compatible with the complementary metal oxide semiconductor (CMOS) process for constructing piezoelectric-based MEMS devices for various applications.

Fabrication and evaluation of a CMOS-based energy harvesting chip integrating photovoltaic and thermoelectric energy harvesters

This study explores the development of an energy harvesting chip (EHC) using a complementary metal oxide semiconductor (CMOS) process, addressing the need for efficient micro-scale energy harvesters in modern electronics. The EHC integrates a thermoelectric energy harvester (TEH) and a photovoltaic energy harvester (PEH) to maximize energy conversion efficiency. A key challenge in TEH design is enhancing power output, which is addressed by suspending the cold ends of 41 thermocouples within the TEH structure through post-processing. Experimental methods were employed to assess the performance of the TEH, revealing an output voltage of 21.4 mV and a maximum output power of 9.32 nW under a 3 K temperature difference. The TEH demonstrated a voltage factor of 8.9 mV/(mm2·K) and a power factor of 1.3 nW/(mm2·K2). The PEH was designed with novel patterned p-n junctions, integrating lightly doped n-type regions with interdigitated p-type doping to increase junction density, resulting in high conversion efficiency. The experimental results confirm the effectiveness of the EHC design, showcasing its potential in energy harvesting applications.

Constructing a Z-scheme heterojunction of oxygen-deficient WO3-x and g-C3N4 for superior photocatalytic evolution of H2

Semiconductor-based photocatalytic water splitting enables the conversion of abundant solar energy to green and renewable hydrogen energy. Graphitic carbon nitride (g-C3N4) is synthesized using a straightforward method, demonstrating stable physicochemical properties and possessing an optimal bandgap, thus positioning it as a promising photocatalyst in the realm of environmental sustainability. Oxygen vacancies are extensively employed to modulate light absorption and surface properties of metal-oxide semiconductors. In this study, g-C3N4 nanosheets were coupled with oxygen-deficient tungsten trioxide (WO3-x) to form heterojunction photocatalysts (X-WOCN). Comprehensive material characterization results demonstrated that the constructed heterojunction extended the visible light absorption range, improved photogenerated electron-hole separation efficiency, and thus augmented photocatalytic activity. Notably, the optimum hydrogen evolution rate of 6%-WOCN was enhanced by 5.4-fold compared to that of g-C3N4. Furthermore, we propose a Z-scheme heterojunction charge separation mechanism mediated by oxygen defects and support this mechanism through detection of surface-active substances •O2− and •OH. This study offers novel propositions into the function of oxygen defects in facilitating charge separation within Z-scheme heterojunction.

Sensitive and real-time monitoring of microbial growth using a dielectric sensor with a 65-GHz LC-oscillator array and polytetrafluoroethylene membrane

In this study, we report a sensitive real-time microbial growth monitoring technique using a complementary metal-oxide semiconductor (CMOS) dielectric sensor with a polytetrafluoroethylene (PTFE) membrane. The sensor comprised an LC oscillator array operating at 65-GHz, whose resonant frequency was altered according to the dielectric properties of the region approximately 15 μm from the surface. We previously reported the rapid detection of viable Escherichia coli suspended in a liquid medium using the dielectric sensor; however, sensing growing cells was challenging owing to their tendency to float outside the effective sensing area in the suspended medium. To address this, we propose a new method to enhance the sensitivity of the device using a PTFE membrane that retains cells inside the effective area during measurement. Experiments using Escherichia coli suggested that the use of the membrane more than doubled sensitivity, reducing inspection times for practical applications. Furthermore, experiments with Lactococcus lactis, Staphylococcus epidermidis, and Saccharomyces cerevisiae demonstrated that this method can be used to monitor the growth of various microbes. In addition, variations in the output values of each oscillator facilitated the determination of microbial characteristics, such as cell size and growth distribution. This microbial growth monitoring technique is expected to find applications across a wide range of fields, such as food inspection, environmental hygiene monitoring, antibiotic susceptibility testing, new drug discovery, and the exploration of beneficial microbes.

Observation on Switching Properties of WO3-Based H2 Sensor Regulated by Temperature and Gas Concentration.

Transition metal oxide semiconductors have great potential for use in H2 sensors, but in recent years, the strange phenomena about gas-sensitive performance associated with their special properties have been more widely discussed in research. In some cases, the resistance of transition metal oxide gas sensors will emerge with some changes contrary to their intrinsic semiconductor characteristics, especially in gas sensor research of WO3. Based on the hydrothermal synthesis of WO3, our work focuses on the abnormal change of tungsten oxide resistance to different gases at low temperature (80-200 °C) and high temperature (above 200 °C). Through in situ FT-IR and in situ XPS, combined with density functional theory calculations, a new reasonable explanation of WO3 is proposed for the abnormal resistance change caused by temperature and the strange response due to gas concentration. The occurrence of these findings can be attributed to the synergistic effect resulting from the presence of two contributing factors. One of them is attributed to the alteration in the surface valence state of WO3 induced by gas, resulting in the reduction of W6+. The other one is due to the reaction between gas and adsorbed oxygen on the surface of WO3. This work presents a novel and rational concept for addressing the reaction mechanism between gas and transition metal oxide semiconductors, thereby paving the way for the development of highly efficient gas sensors based on transition metal oxide semiconductors.

Pseudo-source gated beta-gallium oxide MOSFET

This study demonstrates pseudo-source-gated beta-gallium oxide (β-Ga2O3) metal oxide semiconductor field effect transistors (MOSFETs). The proposed pseudo-source gated transistor (pseudo-SGT) architecture has a thin (∼11 nm) recessed channel design, effectively emulating conventional SGT characteristics without significantly compromising on-current. The fabricated devices exhibit remarkable intrinsic gain of 104, low output conductance of 10−8 S/mm, transconductance of 10−3 S/mm, and drain saturation voltage of ∼1.5 V, while maintaining a drain current of 1.3 mA/mm. These enhanced performance metrics significantly expand the potential of β-Ga2O3 MOSFETs for the development of Ga2O3 monolithic power integrated circuits.

Selective-Area Growth of Hexagonal-to-Cubic GaN as an n-Type Metal–Oxide–Semiconductor Field-Effect Transistor Drain on a Nanogrooved Si(100) Substrate

Selective-Area Growth of Hexagonal-to-Cubic GaN as an n-Type Metal–Oxide–Semiconductor Field-Effect Transistor Drain on a Nanogrooved Si(100) Substrate

Precharge switch based on metal–oxide–semiconductor‐controlled thyristor for power relay assembly of battery electric vehicles

AbstractThe power relay assembly (PRA) is an essential component to ensure the safety of an electric vehicle. We propose a semiconductor‐based precharge switch to overcome the shortcomings of the conventional mechanical relay, which is currently used as the precharge switch in the PRA. The gate‐driving circuit uses a photocoupler instead of a gate‐driving integrated circuit to reduce complexity and cost. Five devices, namely, two insulated‐gate bipolar transistors (IGBTs), two silicon carbide metal–oxide–semiconductor field‐effect transistors (SiC MOSFETs), and one metal–oxide–semiconductor‐controlled thyristor (MCT) are tested as candidate precharge switches. Each device is analyzed under varying battery voltage and fixed measurement conditions. The IGBT and SiC MOSFET burn below 600 V, while the MCT exhibits normal operation up to 800 V. The MCT precharge switch can solve shortcomings of the conventional mechanical relay and increase the performance with a simple gate‐driving circuit. Furthermore, the PRA with an MCT precharge switch can reduce the volume, weight, and cost while improving reliability.