Search Results (43)

Chemical warfare agents (CWAs), including hydrogen cyanide (AC), 2-[fluoro(methyl)phosphoryl]oxypropane (GB), 3-[fluoro(methyl)phosphoryl]oxy-2,2-dimethylbutane (GD), ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate (VX), and di-2-chloroethyl sulfide (HD), pose a great threat to public safety; therefore, it is important to develop sensing technology for CWAs. Herein, a sensor array consisting of 24 metal oxide semiconductor (MOS)-based MEMS sensors with good gas sensing performance, a simple device structure (0.9 mm × 0.9 mm), and low power consumption (<10 mW on average) was developed. The experimental results show that there are always several sensors among the 24 sensors that show good sensing performance in relation to each CWA, such as a relatively significant response, a broad detection range (AC: 5.8–89 ppm; GB: 0.04–0.47 ppm; GD: 0.06–4.7 ppm; VX: 9.978 × 10⁻⁴–1.101 × 10⁻³; HD: 0.61–4.9 ppm), and a low detection limit that is lower than the immediately dangerous for life and health (IDLH) level of the five CWAs. This indicates that these sensors can meet the needs for qualitative detection and can provide an early warning regarding low concentrations of CWAs. In addition, features were extracted from the initial kinetic characteristics and dynamic change characteristics of the sensing response. Finally, principal component analysis (PCA) and machine learning algorithms were applied for CWA classification. The obtained PCA plots showed significant differences between groups, and the narrow neural network among the machine learning algorithms achieves a prediction accuracy of nearly 100.0%. In summary, the proposed MOS-based MEMS sensor array driven by pattern recognition algorithms can be integrated into portable devices, showing great potential and practical applications in the rapid, in situ, and on-site detection and identification of CWAs. Full article

Due to its advantages of fast response, low cost, low power consumption, and easy integration, Metal Oxide Semiconductor (MOS) gas sensor is widely used in the electronic nose system (E-nose). However, the MOS sensor has cross-sensitivity to different gases, which can impair the performance of the E-nose. Another key factor affecting the E-nose performance is the extraction method of gas features. In order to overcome the above shortcomings, an E-nose system that can modulate the operating temperature of gas sensors during the gas detection was designed in this paper, and a new gas feature extraction algorithm named Boruta-Recursive Feature Elimination (Boruta-RFE) was proposed based on the designed system. In order to verify the effectiveness of the designed system and the gas feature extraction algorithm, they were applied to the identification of different categories of apple juice. The experimental results show that more gas features can be obtained by modulating the operating temperature of the gas sensors, and the Boruta-RFE algorithm can effectively reduce the dimensionality of the original gas feature dataset, and can quickly select the key gas features, so as to effectively improve the identification accuracy of the E-nose system. Full article

We report the results of a zinc oxide (ZnO) low-power microsensor for sub-ppm detection of NO₂ and H₂S in air at 200 °C. NO₂ emission is predominantly produced by the combustion processes of fossil fuels, while coal-fired power plants are the main emitter of H₂S. Fossil fuels (oil, natural gas, and coal) combined contained 74% of USA energy production in 2023. It is foreseeable that the energy industry will utilize fossil-based fuels more in the ensuing decades despite the severe climate crises. Precise NO₂ and H₂S sensors will contribute to reducing the detrimental effect of the hazardous emission gases, in addition to the optimization of the combustion processes for higher output. The fossil fuel industry and solid-oxide fuel cells (SOFCs) are exceptional examples of energy conversion–production technologies that will profit from advances in H₂S and NO₂ sensors. Porosity and surface activity of metal oxide semiconductor (MOS)-based sensors are both vital for sensing at low temperatures. Oxygen vacancies (${\mathbf{V}}_{\mathbf{O}}^{••}$) act as surface active sites for target gases, while porosity enables target gases to come in contact with a larger MOS area for sensing. We were able to create an open porosity network throughout the ZnO microstructure and simultaneously achieve an abundance of oxygen vacancies by using a heat treatment procedure. Surface chemistry and oxygen vacancy content in ZnO were examined using XPS and AES. SEM was used to understand the morphology of the unique characteristics of distinctive grain growth during heat treatment. Electrical resistivity measurements were completed. The valance band was examined by UPS. The Engineered Porosity approach allowed the entire ZnO to act as an open surface together with the creation of abundant oxygen vacancies (${\mathbf{V}}_{\mathbf{O}}^{••}$). NO₂ detection is challenging since both oxygen (O₂) and NO₂ are oxidizing gases, and they coexist in combustion environments. Engineered porosity ZnO microsensor detected sub-ppm NO₂ under O₂ interference, which affects mimicking realistic sensor operation conditions. Engineered porosity ZnO performed better than the previous literature findings for H₂S and NO₂ detection. The exceptionally high sensor response is attributed to the high number of oxygen vacancies (${\mathit{V}}_{\mathit{O}}^{••}$) and porosity extending through the thickness of the ZnO with a high degree of tortuosity. These features enhance gas adsorption and diffusion via porosity, leading to high sensor response. Full article

As the mainstream type of gas sensors, metal oxide semiconductor (MOS) gas sensors have garnered widespread attention due to their high sensitivity, fast response time, broad detection spectrum, long lifetime, low cost, and simple structure. However, the high power consumption due to the high operating temperature limits its application in some application scenarios such as mobile and wearable devices. At the same time, highly sensitive and low-power gas sensors are becoming more necessary and indispensable in response to the growth of the environmental problems and development of miniaturized sensing technologies. In this work, hierarchical indium oxide (In₂O₃) sensing materials were designed and the pulse-driven microelectromechanical system (MEMS) gas sensors were also fabricated. The hierarchical In₂O₃ assembled with the mass of nanosheets possess abundant accessible active sites. In addition, compared with the traditional direct current (DC) heating mode, the pulse-driven MEMS sensor appears to have the higher sensitivity for the detection of low-concentrations of nitrogen dioxide (NO₂). The limit of detection (LOD) is as low as 100 ppb. It is worth mentioning that the average power consumption of the sensor is as low as 0.075 mW which is one three-hundredth of that in the DC heating mode. The enhanced sensing performances are attributed to loose and porous structures and the reducing desorption of the target gas driven by pulse heating. The combination of morphology design and pulse-driven strategy makes the MEMS sensors highly attractive for portable equipment and wearable devices. Full article

This study introduces a rectenna, functioning as an RF envelope detector, utilizing a 16 nm bulk MOS transistor (metal-oxide-semiconductor field-effect transistor) for nonlinear detection. A circuit architecture is presented alongside a detailed design methodology and simulations. The detector efficiently demodulates a 2.4 GHz OOK (On/Off Keying) encoded signal, comprising a 32-bit word, within 320 μs. Remarkably, the circuit operates passively, requiring no voltage supply or bias current, and functions effectively with $-53$ dBm input power at the antenna. This capability enables the decoding of 32-bit unsigned integer radio packets as a wakeup radio event. The effectiveness of the envelope detector is substantiated through comprehensive simulations. Full article

An adaptive high-efficiency light-emitting Diode (LED) backlight driver scheme has been proposed to address the issue of additional power loss caused by LED forward voltage variation. In this scheme, the peak current and the duty cycle of each LED channel are adjusted separately through an adaptive control algorithm to minimize the voltage drop on the linear current regulator (LCR) of each LED channel to reduce the excessive power loss in each LED channel and enhance the total power efficiency. A linear current regulator, suitable for adaptive control, is designed on a 0.18 μm 5V complementary metal-oxide-semiconductor (CMOS) process. Simulation results demonstrate that the linear current regulator can achieve a linearly adjustable channel current ranging from 0 to 48 mA with a current resolution of 0.2 mA. Across different process corners and temperatures, the maximum error for the full current range is less than 0.1%. The core area of chip layout is about 0.1 mm². The complete driver prototype comprises the LCR chips, external power MOS transistors, digital module, and LED chains. The test results show that the power loss of the linear current regulator has been significantly reduced, and the power efficiency of each LED channel has been measured at around 98.1%. Full article

Carbon monoxide can cause severe harm to humans even at low concentrations. Metal Oxide Semiconductor (MOS) carbon monoxide gas sensors have excellent sensing performance regarding sensitivity, selectivity, response speed, and stability, making them very desirable candidates for carbon monoxide monitoring. However, MOS gas sensors generally work at temperatures higher than room temperature, and need a heating source that causes high power consumption. High power consumption is a great problem for long-term portable monitoring devices for point-of-care or wireless sensor nodes for IoT application. Room-temperature MOS carbon monoxide gas sensors can function well without a heater, making them rather suitable for IoT or portable applications. This review first introduces the primary working mechanism of MOS carbon monoxide sensors and then gives a detailed introduction to and analysis of room-temperature MOS carbon monoxide sensing materials, such as ZnO, SnO₂, and TiO₂. Lastly, several mechanisms for room-temperature carbon monoxide sensors based on MOSs are discussed. The review will be interesting to engineers and researchers working on MOS gas sensors. Full article

TID effects occur in MOS-gated transistors in radiation environments where proton and gamma-rays irradiate the devices. TID effects seriously affect the electrical characteristics of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). They can eventually result in the malfunction of power systems when exposed to long-term radiation conditions. We irradiated gamma-rays and protons into 1.2 kV SiC MOSFETs and evaluated the change in electrical properties to analyze the TID’s effects. As a result of the experiment, the threshold voltage (V_T) and on-resistance (R_on) of 1.2 kV SiC MOSFETs decreased because positive fixed charges inside the oxide increased depending on the radiation dose of the gamma-ray and fluence of the proton irradiations. The degradation of breakdown voltage (BV) occurred owing to a change in the depletion curvature at the edge of termination regions owing to the trapping of the charge in the field’s oxide. Full article

While wireless sensor node (WSNs) have proliferated with the rise of the Internet of Things (IoT), uniformly sampled analog–digital converters (ADCs) have traditionally reigned paramount in the signal processing pipeline. The large volume of data generated by uniformly sampled ADCs while capturing most real-world signals, which are highly non-stationary and sparse in information content, considerably strains the power budget of WSNs during data transmission. Given the pressing need for intelligent sampling, this work proposes an extrema pulse generator devised to trigger ADCs at significant signal extrema, thereby curbing the volume of data points collected and transmitted, and mitigating transmission power draw. After providing a comprehensive signal-theoretic rationale, we construct and experimentally validate these circuits on a system-on-chip field-programmable analog array in a 350 nm complementary metal-oxide-semiconductor (MOS) process. Operating within a power range of 4.3–12.3 µW (contingent on the input bandwidth requirements), the extrema pulse generator has proven to be capable of effectively sampling both synthetic and natural signals, achieving significant reductions in data volume and signal reconstruction error. Using a nonideality-resilient reconstruction algorithm, that we develop in this work, experimental comparisons between extrema and uniform sampling show that extrema sampling achieves an 18-fold lower normalized root mean square reconstruction error for a quadratic chirp signal, despite requiring 5-fold fewer sample points. Similar improvements in both the reconstruction error and effective sampling rate objectives are found experimentally for an electrocardiogram signal. Using both theoretical and experimental methods, this work demonstrates the potential of extrema-triggered systems for extending Pareto frontiers in modern, resource-constrained sensing scenarios. Full article

This article describes a low-voltage, low-power fractional-order low-pass filter (FO-LPF) of order 1 + α, which is implemented using a voltage differencing differential difference amplifier (VDDDA). The VDDDA structure is implemented using the bulk-driven metal oxide semiconductor transistor technique. The transistors operate in the subthreshold region to maintain low-supply voltage and low-power consumption. The FO-LPF structure implemented using this VDDDA structure is compact. It includes three VDDDAs and three grounded capacitors along with two active resistors implemented using MOS transistors. In addition, this filter structure provides electronic tuning of its order and cut-off frequency through the bias current of the active component used. The effects of tracking error and parasitics on the functionality of the proposed FO-LPF were investigated. The VDDDA and filter operate at ±300 mV and dissipate only 207 nW and 663 nW of power, respectively. Thus, the VDDDA structure and filter are suitable for low-voltage and low-power operation. Layouts of the proposed VDDDA as well as the FO-LPF were designed in the Cadence Virtuoso environment. Post-layout simulation results of the designed circuits imply that they are suitable for fabrication. Noise, total harmonic distortion, Monte-Carlo, and PVT analyses were also performed. Full article

High power semiconductor laser is a kind of photoelectric device with high efficiency and high stability, the performance of its drive system directly affects its output characteristics and service life. In order to solve the problems of stability and robustness of the output power of the semiconductor laser, a semiconductor laser driving power supply with high efficiency, low ripple and strong anti-interference ability was developed. In this paper, the topology of the LCC resonant converter is adopted (LCC refers to the type of resonant converter, because its resonator is composed of an inductor L and two capacitors C, it is called LCC resonant converter). The power supply adopts full-bridge LCC resonant power topology. Firstly, a mathematical model is established to analyze the relationship between LCC resonator parameters and output current gain. Secondly, an LCC resonator parameter design method is proposed to reduce the current stress of components, and the variable frequency phase shift (PFM-PWM) composite control strategy and linear active disturbance rejection control (LADRC) algorithm are proposed, which not only ensures the zero voltage (ZVS) conduction of MOS (Metal-Oxide-Semiconductor) tube, but also reduces the on-off loss of MOS tube. The PFM-PWM composite control strategy and LADRC algorithm not only improve the power efficiency of the drive power supply, suppress the output current ripple, but also ensure that the output current of the drive power supply is stable when the input voltage, load and parasitic parameters of the circuit change. Finally, the simulation and experimental results show that the power supply can be continuously adjustable in the output current range of 0–40 A, the current ripple is less than 0.8%, and the working efficiency is up to 92%. It has the characteristics of high stability, small ripple, high efficiency, low cost and good robustness. Full article

Metal oxide semiconductor (MOS) gas sensors are widely used for gas detection. Typically, the hotplate element is the key component in MOS gas sensors which provide a proper and tunable operation temperature. However, the low power efficiency of the standard hotplates greatly limits the portable application of MOS gas sensors. The miniaturization of the hotplate geometry is one of the most effective methods used to reduce its power consumption. In this work, a new method is presented, combining electron beam lithography (EBL) and focused ion beam (FIB) technologies to obtain low power consumption. EBL is used to define the low-resolution section of the electrode, and FIB technology is utilized to pattern the high-resolution part. Different Au⁺⁺ ion fluences in FIBs are tested in different milling strategies. The resulting devices are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS). Furthermore, the electrical resistance of the hotplate is measured at different voltages, and the operational temperature is calculated based on the Pt temperature coefficient of resistance value. In addition, the thermal heater and electrical stability is studied at different temperatures for 110 h. Finally, the implementation of the fabricated hotplate in ZnO gas sensors is investigated using ethanol at 250 °C. Full article

Device physics and accurate transistor modeling are necessary to reduce the operating voltage near the threshold for power-constrained circuits. Conventional device modeling for metal-oxide-semiconductor (MOS) transistors focuses on operations in either strong or weak inversion regimes, and the electrostatics at gate biases near the threshold voltage is rarely studied. This research proposed an analytical model to describe the distribution of the surface potential along the channel for near-threshold operation. Numerical device simulations were also performed to investigate the electrostatics near the threshold voltage. The numerical simulation with constant carrier mobility showed an overshoot in the transconductance due to decay of the lateral electric field with gate bias. The decay of the lateral electric field was predicted by the proposed analytical surface potential model which considered widening the channel length with flooding of the inversion carriers in the channel and gate overlap regions. The channel length widening effect saturated as the gate bias further increased. Therefore, evident transconductance overshoot was observed near the threshold voltage in short-channel devices. Full article

The electrical and physical properties of the SiC/SiO₂ interfaces are critical for the reliability and performance of SiC-based MOSFETs. Optimizing the oxidation and post-oxidation processes is the most promising method of improving oxide quality, channel mobility, and thus the series resistance of the MOSFET. In this work, we analyze the effects of the POCl₃ annealing and NO annealing processes on the electrical properties of metal–oxide–semiconductor (MOS) devices formed on 4H-SiC (0001). It is shown that combined annealing processes can result in both low interface trap density (D_it), which is crucial for oxide application in SiC power electronics, and high dielectric breakdown voltage comparable with those obtained via thermal oxidation in pure O₂. Comparative results of non-annealed, NO-annealed, and POCl₃-annealed oxide–semiconductor structures are shown. POCl₃ annealing reduces the interface state density more effectively than the well-established NO annealing processes. The result of 2 × 10¹¹ cm⁻² for the interface trap density was attained for a sequence of the two-step annealing process in POCl₃ and next in NO atmospheres. The obtained values D_it are comparable to the best results for the SiO₂/4H-SiC structures recognized in the literature, while the dielectric critical field was measured at a level ≥9 MVcm⁻¹ with low leakage currents at high fields. Dielectrics, which were developed in this study, have been used to fabricate the 4H-SiC MOSFET transistors successfully. Full article

This paper reports on improved AlGaN/GaN metal oxide semiconductor high-electron mobility transistors (MOS-HEMTs). TiO₂ is used to form the dielectric and passivation layers. The TiO₂ film is characterized using X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The quality of the gate oxide is improved by annealing at 300 °C in N₂. Experimental results indicate that the annealed MOS structure effectively reduces the gate leakage current. The high performance of the annealed MOS-HEMTs and their stable operation at elevated temperatures up to 450 K is demonstrated. Furthermore, annealing improves their output power characteristics. Full article