Metal Oxide Semiconductor Research Articles

Effect of the Chemical Structure of a Self-Assembled Monolayer on the Gas-Sensing Behavior of SnO2 Nanowires.

In this study, detailed investigations of the selective sensing capability of semiconducting metal oxide (SMO)-based gas sensors with self-assembled monolayer (SAM) functionalization were conducted. The selective gas-sensing behavior was improved by employing a simple and straightforward postmodification technique using functional SAM molecules. The chemical structure of the SAM molecules promoted interaction between the gas and SAM molecules, providing a gas selective sensing of SnO2 nanowires (NWs). In addition, a bundle of SnO2 NWs provided a large surface area that could act as a sensing site. SAM functionalization was confirmed by infrared spectroscopy and thermogravimetric analysis, and the selective gas-sensing behaviors were investigated under different sensing conditions. With variations in the chemical structures of the SAM molecules, the selective gas-sensing behaviors also changed as the corresponding intermolecular interaction forces were different. This integration of selective gas sensing and passivation of a sensing surface provides a straightforward approach for the preferred gas sensing of SnO2 NWs. Furthermore, owing to the universal binding characteristics of SAM molecules to the metal oxide surface, this approach can be expanded to other SMO-based gas-sensing platforms.

Application of MOS gas sensors for detecting mechanical damage of tea plants

Mechanical damage of tea plant is a serious problem in tea production. This work employed metal oxide semiconductor (MOS) gas sensors and gas chromatography-mass spectrometer (GC-MS), as an auxiliary technique, to detect tea plants with different types of mechanical damage in different severities. Various algorithms were applied. The results showed the uniformity of the results of gas sensors and GC-MS. While, it was hard for gas sensors to discriminate among tea plants with different types of mechanical damage. However, the feasibility of gas sensors for predicting the damage severity in different damaged types based on gas sensors was proven, which was more meaningful. Finally, multi-layer perceptron neural networks (MLPNN) was employed and the results showed that the correct discrimination accuracy rate for damage severity was 99.07% for the training set and 95.83% for the testing set, which indicated that MLPNN was an excellent algorithm for damage severity determination. This study provided a new technique for mechanical damage of tea plant detection and was very meaningful for tea plant protection.

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.

Insights into Selective Sensitivity of In2O3-CuO Heterojunction Nanocrystals to CH4 over CO and H2: Experiments and First-Principles Calculations.

Metal oxide semiconductor gas sensors have demonstrated exceptional potential in gas detection due to their high sensitivity, rapid response time, and impressive selectivity for identifying various sorts of gases. However, selectively distinguishing CH4 from those of CO and H2 remains a significant challenge. This difficulty primarily stems from the weakly reducing nature of CH4, which results in a low adsorption response and makes it prone to interference from stronger reducing gases in the surroundings. Herein, we synthesized In2O3-xCuO nanocomposites using a hydrothermal method to explore their gas sensing properties toward CH4, CO, and H2. Characterization tests confirmed the successful preparation of In2O3-xCuO nanocomposites with different In:Cu molar ratios and the formation of a p-n heterojunction. The gas sensing test results indicated that the In2O3-2.1CuO nanocomposites calcined at 500 °C and measured at 350 °C displayed a p-type response for CH4 and an n-type response for CO and H2, allowing for accurate differentiation of CH4 from CO and H2. Moreover, the In2O3-2.1CuO sensor also showed excellent stability and reproducibility across all three gases. First-principles calculations revealed distinct changes in the electronic structure of the In2O3-CuO heterojunction upon adsorption of CH4, CO, and H2, a finding that aligns with empirical evidence. The gas selectivity mechanism was effectively explained by variations in the energy band gap, driven by electrical behavior during the adsorption process. This work suggests a promising approach for developing selective gas sensors capable of detecting weakly reducing gases.

Low dark current and low voltage germanium avalanche photodetector for a silicon photonic link

Germanium (Ge)-silicon (Si)-based avalanche photodetectors (APDs) featured by a high absorption coefficient in the near-infrared band have gained wide applications in laser ranging, free space communication, quantum communication, and so on. However, the Ge APDs fabricated by the complementary metal oxide semiconductor (CMOS) process suffer from a large dark current and limited responsivity, imposing a critical challenge on integrated silicon photonic links. In this work, we propose a p-i-n-i-n type Ge APD consisting of an intrinsic germanium layer functioning as both avalanche and absorption regions and an intrinsic silicon layer for dark current reduction. Consequently, a Ge APD with a low dark current, low bias voltage, and high responsivity can be obtained via a standard silicon photonics platform. In the experimental measurement, the Ge APD is characterized by a high primary responsivity of 1.1 A/W with a low dark current as low as 7.42 nA and a dark current density of 6.1×10−11 A/μm2 at a bias voltage of −2 V. In addition, the avalanche voltage of the Ge APD is −8.4 V and the measured 3 dB bandwidth of the Ge APD can reach 25 GHz. We have also demonstrated the capability of data reception on 32 Gbps non-return-to-zero (NRZ) optical signal, which has potential application for silicon photonic data links.

Domain-limited surface oxygen vacancy in rutile TiO2 for enhancing photocatalytic hydrogen evolution

Defect engineering is an effective strategy for enhancing the photocatalytic performance of semiconducting metal oxides. In this study, we demonstrate a simple method to engineer oxygen vacancies (OVs) on the surface of rutile TiO2 by the use of thiourea. No bulk phase defects or heteroatom doping are introduced during the hydrothermal reaction, while preserving the original morphology of rutile TiO2. It was observed that the structural synergies with surface OVs significantly alter the electronic structure, thereby extending the absorption region of rutile TiO2 and promoting efficient separation and transport of photogenerated carriers to the surface. The rutile TiO2 with OVs on its surface exhibits highly photocatalytic H2 evolution activity as 54.7 mmol·g-1·h-1 (with 1 wt% Pt loading), with an apparent quantum efficiency (AQY) of 24.7% at 380 nm.

IGBT Overcurrent Capabilities in Resonant Circuits

The control of IGBT (insulated gate bipolar transistor) and MOSFET (metal oxide semiconductor field effect transistor) is of great interest nowadays as they are widely used in electric vehicles, photovoltaic applications, and a multitude of systems. The field of power electronics and their correct activation ensures that the transistors are operated without being destroyed. In this work, a double resonant transformer was built and used to produce very high currents. These currents are switched by a full bridge of resonant IGBT transistors to demonstrate the feasibility of exceeding the maximum permissible transistor currents in a resonant system. The system is controlled by the feedback from two current sensors. In this case the currents exceed in a 170% the peak current of the transistor without problems. In this way, resonant circuits with IGBT transistors can be designed with currents lower than the maximum currents of the resonant circuit, therefore reducing the cost of the circuit and reducing the switching losses to nearly zero.

A breathable, waterproof and battery-free wearable e-nose with high flexibility based on MEMS gas sensors for accurate identification of volatile aromatic hydrocarbons

Benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS) are harmful gases indoors and in the cabin. Electronic nose (e-nose) technology has shown great potential in detecting BTEXS. However, to maintain the normal operation of the e-nose and improve the recognition accuracy, it often employs a large array of metal oxide semiconductor (MOS) gas sensors, along with extensive signal processing circuits and high-power solid-state batteries. The bulky structure makes it difficult for the e-nose to realize the portable real-time detection of BTEXS. Herein, a breathable, waterproof, battery-free, and highly flexible wearable e-nose (BWBFW e-nose) is fabricated for BTEXS detections. In detail, we first prepare a combination scheme of n-type and p-type MOS for forming four MEMS gas sensors, exhibiting differentiated response characteristics. Subsequently, a wireless supply module and a wireless signal processing module are designed on a flexible porous circuit board. Then, a waterproof and breathable membrane by electrospinning was adopted to encapsulate the flexible circuit board, endowing the e-nose with high safety. Finally, accurate identification and low-error concentration prediction of BTEXS are achieved with the help of a 1D Convolutional Neural Network (1DCNN) algorithm. We believe the e-nose reported here will shed new light on the design of new devices for detecting BTEXS.

High-Sensitivity, High-Resolution Miniaturized Spectrometers for Ultraviolet to Near-Infrared Using Guided-Mode Resonance Filters

Miniaturized spectrometers have significantly advanced real-time analytical capabilities in fields such as environmental monitoring, healthcare diagnostics, and industrial quality control by enabling precise on-site spectral analysis. However, achieving high sensitivity and spectral resolution within compact devices remains a significant challenge, particularly when detecting low-concentration analytes or subtle spectral variations critical for chemical and molecular analysis. This study introduces an innovative approach employing guided-mode resonance filters (GMRFs) to address these limitations. Functioning similarly to notch filters, GMRFs selectively block specific spectral bands while allowing others to pass, maximizing energy extraction from incident light and enhancing spectral encoding. Our design incorporates narrow band-stop filters, which are essential for accurate spectrum reconstruction, resulting in improved resolution and sensitivity. Our spectrometer delivers a spectral resolution of 0.8 nm over a range of 370–810 nm. It achieves sensitivity values that are more than ten times greater than those of conventional grating spectrometers during fluorescence spectroscopy of mouse jejunum. This enhanced sensitivity and resolution are particularly beneficial for chemical and biological applications, facilitating the detection of trace analytes in complex matrices. Furthermore, the spectrometer’s compatibility with complementary metal oxide semiconductor (CMOS) technology enables scalable and cost-effective production, fostering broader adoption in chemical analysis, materials science, and biomedical research. This study underscores the transformative potential of the GMRF-based spectrometer as an innovative tool for advancing chemical and interdisciplinary analytical applications.

Pd nanoislands-modified ZnO nanowire-network for sensitive and linear hydrogen sensing

To facilitate the safety use of hydrogen fuel in aerospace applications and in hydrogen fuel cell vehicles, there is a high demand for hydrogen sensing technology with both merits of high sensitivity and high linearity. However, it is hard to integrate these two advantages together in just one device. Here, we designed and developed a hydrogen-sensitive Pd nanoislands-modified ZnO nanowire-network structure (Pd-ZnO nanoisland structure) for sensitive and linear hydrogen sensing. By optimizing the size-to-gap ratio of Pd nanoislands, we enhanced the response of the Pd-ZnO nanoisland structure sensor (Pd-ZnO sensor) more than 12 times larger than that of the pure ZnO nanowire-network sensor (without Pd nanoislands), and decreased its limit of detection down to 100 ppb at 150 °C low temperature. On the premise of high sensitivity, the sensor also has a remarkable sensing linearity (R2 >0.9969) in the whole detecting range and the full operating temperature range as designed. The high sensitivity together with high linearity can maximize the signal-to-noise ratio and facilitate the calibration of sensors. For example, only the single calibration at a specific concentration can meet the sensing of Pd-ZnO sensors in the whole concentration range. This study of utilizing noble metal nanoislands to modify metal oxide semiconductors provides an opportunity for hydrogen sensors with high sensitivity and high linearity to be integrated into one device.

Dual-gated MOSFETs of α-In2Se3 monolayer for high performance and low power logic applications

As a well-known van der Waals 2D material with entangled ferroelectricity and semiconductivity, α-In2Se3 has garnered significant attention in recent years to develop novel nonvolatile (photo) electronic devices mainly based on its ferroelectricity. However, the ability of its semiconductivity to design 2D transistors for high-performance (HP) and low-power (LP) logic applications remains unclear. Herein, this article reveals the potential of α-In2Se3 as a semiconductor in sub-10 nm 2D transistors. We analyze a dual-gated metal–oxide–semiconductor field-effect transistor (MOSFET) based on monolayer (ML) α-In2Se3 with a 5 nm channel-length, utilizing density functional theory (DFT) in combination with non-equilibrium Green’s function method. The transport performance indicators of n-type MOSFET along the zigzag direction can satisfy or nearly satisfy the HP and LP application requirements of the International Technology Roadmap for Semiconductor (ITRS) 2013, while p-type MOSFET along the armchair direction exhibits an outstanding on-current attributed to effective mass and the density of states modulation. The p-type MOSFETs also exhibit ultralow leakage current and subthreshold swing below 60 mV/dec. Meanwhile, our simulated MOSFETs demonstrate large on-current and high ON/OFF ratios. These findings highlight the application prospect of α-In2Se3 as a conventional 2D semiconductor material for further 2D FETs in HP and LP logic applications.

Design, Fabrication and Characterization of Disk Resonator Gyroscope with Vibration and Shock Resistance

This paper presents a comprehensive optimization of an outer frame anchor disk resonator gyroscope (DRG) with enhanced resistance to vibration and shock, achieved by increasing the resonant frequency of the tub and translation modes. Furthermore, the wineglass mode retains a high quality factor, enhancing sensitivity and reducing the angle random walk (ARW). The performance of the proposed DRG is analyzed using dynamic equations, and its structural parameters are optimized through finite element analysis (FEA). The prototype device was fabricated using a two-mask silicon-on-insulator (SOI) process on (100) single-crystal silicon (SCS), which is better suited for complementary metal-oxide–semiconductor (CMOS) integration compared to (111) SCS. Experimental results show an ARW of and a bias instability (BI) of , with no significant performance degradation observed under vibrational environments, indicating potential for tactical-grade performance.

Fabrication and Reflow of Indium Bumps for Active-Matrix Micro-LED Display of 3175 PPI

Indium is acknowledged as a preferred material for micro-light-emitting diodes (micro-LEDs) flip-chip bonding within the industry, due to its favorable economic characteristics and low melting point. However, indium bumps fabricated via photolithography and thermal evaporation often exhibit irregular shapes and varying heights, and they readily oxidize in air to form a tightly adhered oxide layer (In2O3), leading to flip-chip bonding failures and blind pixels. The reflow process can not only remove the oxide layer but also enhance bump uniformity. Nevertheless, literature on indium reflow predominantly focuses on planar substrates, with limited studies on high-resolution micro-LED chips for flip-chip bonding. This paper details the preparation of micro-LED chips with a pixel density (pixel per inch, PPI) of 3175. An indium bump array with a diameter of approximately 5 μm was prepared on the micro-LED chips using thermal evaporation technology. The influence of reflow time and temperature on indium bumps was thoroughly investigated by the formic acid reflow process, revealing that under the conditions of 270 °C and 180 s, the indium bumps with a narrower size distribution could be reflowed into spherical shapes on the micro-LED structure. Furthermore, an inversely proportional relationship was discovered between mesa/metal layer height and indium bump growth, which influenced the reflow effect. Ultimately, micro-LED chips were integrated with si complementary metal–oxide–semiconductor (CMOS) driver chips through flip-chip bonding technology, resulting in the successful functioning of the devices.

Review of Voltage Balancing Techniques for Series-Connected SiC Metal–Oxide–Semiconductor Field-Effect Transistors

Review of Voltage Balancing Techniques for Series-Connected SiC Metal–Oxide–Semiconductor Field-Effect Transistors

Gold‐Assisted Exfoliation of Large‐Area Monolayer Transition Metal Dichalcogenides: From Interface Properties to Device Applications

AbstractSemiconductor transition metal dichalcogenides (TMDs), such as MoS2, are currently regarded as key‐enabling materials for sub‐1 nm channel transistors, beyond‐complementary metal–oxide–semiconductor electronic and optoelectronic devices and sensors. Owing to this wide application potential, several bottom‐up and top‐down synthesis approaches for these materials have been explored so far. Despite the huge progresses in scalable deposition methods (such as chemical vapor deposition, metal–organic chemical vapor deposition), exfoliated layers from bulk crystals still represent the benchmark for record electronic properties of TMDs. Among exfoliation approaches, metal‐assisted mechanical exfoliation emerges as the most effective method to separate large‐area (mm2 to cm2) single‐crystalline monolayer membranes of TMDs (and many other 2D materials) from the parent bulk crystals. This paper reviews the state‐of‐the‐art in this field, from current understanding of MoS2 exfoliation mechanisms on Au (considered as a model system), to the main device applications of as‐exfoliated and transferred large‐area MoS2 membranes (including Au/MoS2/Au memristors, MoS2 photodetectors, and field‐effect transistors). Perspectives of this method in the realization of arrays of 2D heterojunction devices, including Moirè superlattice devices, and open challenges for its widespread application are finally discussed.

Recent advances in nanomaterial-enabled chemiresistive hydrogen sensors.

With the growing adoption of hydrogen energy and the rapid advancement of Internet of Things (IoT) technologies, there is an increasing demand for high-performance hydrogen gas (H2) sensors. Among various sensor types, chemiresistive H2 sensors have emerged as particularly promising due to their excellent sensitivity, fast response times, cost-effectiveness, and portability. This review comprehensively examines the recent progress in chemiresistive H2 sensors, focusing on developments over the past five years in nanostructured materials such as metals, metal oxide semiconductors, and emerging alternatives. This review delves into the underlying sensing mechanisms, highlighting the enhancement strategies that have been employed to improve sensing performance. Finally, current challenges are identified, and future research directions are proposed to address the limitations of existing chemiresistive H2 sensor technologies. This work provides a critical synthesis of the most recent advancements, offering valuable insights into both current challenges and future directions. Its emphasis on innovative material designs and sensing strategies will significantly contribute to the ongoing development of next-generation H2 sensors, fostering safer and more efficient energy applications.

Low-frequency noise analysis on asymmetric damage and self-recovery behaviors of ZnSnO thin-film transistors under hot carrier stress

The need for understanding the low-frequency noise (LFN) of metal oxide semiconductor thin-film transistors (TFTs) is increasing owing to the substantial effects of LFN in various circuit applications. A focal point of inquiry pertains to the examination of LFN amidst bias stress conditions, known to compromise TFT reliability. In this study, we investigate the effects of hot carrier stress (HCS) on zinc tin oxide (ZTO) TFTs by low-frequency noise (LFN) analysis. Asymmetric damage caused by HCS is analyzed by measuring the power spectral density at the source and drain sides. The excess noise generated by the HCS is analyzed with consideration of trap density of states (DOS). It is revealed that the needle defects are generated during the HCS, significantly affecting the LFN characteristics of the ZTO TFTs. Additionally, we observe a self-recovery behavior in the devices and demonstrate the relevant changes in the LFN characteristics following this phenomenon. This study provides valuable insights into the LFN characteristics of ZTO TFTs under HCS conditions and sheds light on the underlying mechanisms.

Progress in the Sputtering Preparation of Hf0.5Zr0.5O2 Ferroelectric Films and Memories

AbstractSince the first report of ferroelectric HfO2 in 2011, researchers are making rapid progress in the understanding of both material properties and applications. Due to its compatibility with complementary metal oxide semiconductor, high coercivity voltage and the fact that ultrathin films remain ferroelectric, it is developed for applications in non‐volatile memories for data storage in different polarization states. As the most representative hafnium‐based ferroelectric materials, Hf0.5Zr0.5O2 has received a great deal of attention due to its various of outstanding properties. Magnetron sputtering is a promising method for the preparation of ferroelectric HfO2 films. This paper reviews recent developments in preparing Hf0.5Zr0.5O2 ferroelectric films and memories. Meanwhile, due to the many advantages of sputtering, such as higher throughputs, low cost and no carbon contamination, this review mainly focused on the preparation of Hf0.5Zr0.5O2 ferroelectric thin films by sputtering and explored its working mechanism and optimization strategy. In addition, the factors affecting the reliability of the memories, the mechanism of action, the solution ideas are introduced. These provide the basis for the design and optimization of Hf0.5Zr0.5O2 ferroelectric films and memories.

Investigation of ultrasmall sidewall-insulated GaN via with large aspect ratio for the strategy of vertically stacked full-color Micro-LEDs

Micro light-emitting diode (Micro-LED) is considered as an ideal candidate for near-eye, outdoor display, and light field photography applications. At present, the commercialization of full-color Micro-LED is limited by the mass transfer of red, green, and blue (R-B-G) sub-pixels. Hence, we proposed a full-color scheme of vertically stacked tricolor Micro-LED layers to avoid mass transfer, which owns over 1000 PPI (pixel per inch). In this solution, the sidewall-insulated via in the epilayer plays a critical role to achieve the electrical and mechanical integration of three monochromatic Micro-LEDs with Si-based complementary metal-oxide semiconductor (CMOS) driver. Therefore, the via processes of GaN-based epilayer were investigated systematically using available semiconductor processes in this article. The inductively coupled plasma (ICP) etching was employed to create the ultra-small micro-structure array using SiO2 thin film as hard mask. Sidewall-insulated vias were fabricated with different aperture sizes (9.3, 7.5, and 3.4 μm) and a depth of about 4-μm. The vias with large aspect ratio are completely satisfy the requirement of designed vertical interconnection. This study aims to provide valuable reference for the commercial progress of high-resolution and full-color Micro-LEDs.

Reservoir Computing System with Diverse Input Patterns in HfAlO-Based Ferroelectric Memristor.

Ferroelectric memristors, particularly those based on hafnia, are gaining attention as potential candidates for neuromorphic computing. These devices offer advantages over perovskite-based ferroelectric memristors owing to their simpler structures, compatibility with complementary metal-oxide semiconductor technology, and low-power consumption characteristics. Additionally, improvements in ferroelectric memristor's performance, such as enhancing tunneling electro resistance (TER) and polarization retention, can be achieved using methods like aluminum doping and insulating film deposition. In this study, we implement a physical reservoir computing (RC) system utilizing the metal-ferroelectric-insulator-semiconductor-structured ferroelectric memristor based on Al-doped HfO2 as an artificial synapse. Specifically, we ensure the universality and diversity of the system by experimentally demonstrating a robust reservoir layer capable of handling various types of input pulses. To utilize the ferroelectric memristor in the reservoir layer of the RC system, we employ partial polarization switching of ferroelectric materials. We measure the retention loss characteristics of the device for pulse amplitude, interval, and width, and quantify the time constant values by fitting them to a stretched exponential function. Additionally, we validate the suitability of the fabricated device as an artificial synapse by mimicking various short-term plasticity functions of biological synapses. Furthermore, we experimentally demonstrate various applications related to learning and memory of the brain, such as image training and Pavlov's experiment, utilizing the short-term memory characteristics of the fabricated device. Lastly, we evaluate the robustness of the RC system under various input conditions by employing the fabricated device as a reservoir layer.