Sensor stability is defined as the ability to maintain a relatively stable and repeatable signal over a sufficient period. Long-term stability for gas sensors is an essential capability for carrying out long-term data collection of human exhaled breath, environmental monitoring and other gas detection in the modern electronic information age. This article reviews the research advances on the stability of metal oxide semiconductor gas sensors in the past five years. The impact of structure, environment, toxicity and sensor array on the sensor stability are discussed. Then, the improvement schemes of existing materials and structure design are summarized. The achievements of structure doping, humidity, anti-poisoning and photoactivation are overviewed. Finally, the great significance of elucidating the sensing mechanism and carrying out the life acceleration test for future research and development is pointed out.

Stability of Metal Oxide Semiconductor Gas Sensors: A Review

Novel combined waveform temperature modulation method of NiO-In2O3 based gas sensor for measuring and identifying VOC gases

Selective methane sensing properties of VO2 at different temperatures: A first principles study

Micro-hotplate gas sensors are widely used in air quality monitoring, identification of hazardous chemicals, human health monitoring, and other fields due to their advantages of small size, low power consumption, excellent consistency, and fast response speed. The micro-hotplate gas sensor comprises a micro-hotplate and a gas-sensitive material layer. The micro-hotplate is responsible for providing temperature conditions for the sensor to work. The gas-sensitive material layer is responsible for the redox reaction with the gas molecules to be measured, causing the resistance value to change. The gas-sensitive material film with high stability, fantastic adhesion, and amazing uniformity is prepared on the surface of the micro-hotplate to realize the reliable assembly of the gas-sensitive material and the micro-hotplate, which can improve the response speed, response value, and selectivity. This paper first introduces the classification and structural characteristics of micro-hotplates. Then the assembly process and characteristics of various gas-sensing materials and micro-hotplates are summarized. Finally, the assembly method of the gas-sensing material and the micro-hotplate prospects.

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Research Progress on Coating of Sensitive Materials for Micro-Hotplate Gas Sensor

Abstract Flexible sensors used to detect NO 2 gas generally have problems such as poor repeatability, high operating temperature, poor selectivity, and small detection range. In this work, a new spraying platform with a simple structure, low cost, and good film-forming consistency was designed and built to make a sensitive film (rGO/SnO 2 ) for NO 2 gas sensors. The relationship between the solid content of rGO and SnO 2 nanoparticles, annealing temperature, and sensor performance was studied. The results show that the interdigital electrode-sensitive film formed by spraying 0.25 ml of a 0.4 wt% rGO/SnO 2 mixture and annealing at 250 °C exhibited the best comprehensive performance for NO 2 detection. The sensor’s response value for 100 ppm NO 2 gas was 0.2640 at room temperature (25 °C), and the response time and recovery time were 412.4 s and 587.3 s, respectively. In the range of 20–100 ppm, the relationship between the response and NO 2 concentration was linear, and the correlation coefficient was 0.9851. In addition, a soft-monitoring node module with an overlimit warning function for NO 2 gas was designed and manufactured based on flexible electronics. Finally, the flexible sensor and node module were embedded into woven fabric that could be used to make a mask or a watch that could detect NO 2 gas, realizing the practical application of flexible NO 2 gas sensors in the field of wearable electronics. 

/pdf/a-flexible-and-wearable-no2-gas-detection-and-early-warning-2fd3nsl8.pdf

A flexible and wearable NO2 gas detection and early warning device based on a spraying process and an interdigital electrode at room temperature

The disadvantages of poor selectivity, thermal instability and nonlinear output for metal oxide semiconductor (MOS) gas sensors restrict their detection accuracy for flammable and toxic gases. In this paper, a low frequency dynamic temperature modulation detection method using rectangular wave was designed and first proposed herein. The temperature modulation detection mechanism was also provided in detail. The flammable gases CH4 and CO were detected successfully using this method by self-made indirectly Pt/SnO2 sensors. The results show that the response time of the Pt/SnO2 sensors is 9 s and 8 s, and the recovery time is 25 s and 23 s for 100 ppm CH4 and CO, using the rectangular wave temperature modulation with a working temperature of 335-382 °C and an optimized frequency of 100 mHz. The temperature modulation has more advantages than steady-state constant temperature method in power consumption and working temperature. The temperature-modulated response for CH4 and CO, are highly linear with the gas concentration without using the log coordinates. The selectivity of the Pt/SnO2 sensors for 500 ppm CH4 and CO is enhanced from 2.03 using the traditional steady-state constant temperature detection to 2.56 using the temperature modulation method. Compared with the steady-state constant temperature method, both the selectivity and linearity of the response output for the Pt/SnO2 sensors are improved by this method, and an effective detection can be realized for a wide gas concentration range of 0–500 ppm CH4 and CO. It provides a new potential detection pathway for MOS-based gas sensors.

Optimized Low Frequency Temperature Modulation for Improving the Selectivity and Linearity of SnO 2 Gas Sensor

Air pollution is one of the major threats to human health. The monitoring of toxic NO2 gas in urban air emission pollution is becoming increasingly important. Thus, the development of an NO2 sensor with low power consumption, low cost, and high performance is urgent. In this paper, a planar structural micro hotplate gas sensor based on an AlN ceramic substrate with an annular Pt film heater was designed and prepared by micro-electro-mechanical system (MEMS) technology, in which Pt/Nb/In2O3 composite semiconductor oxide was used as the sensitive material with a molar ratio of In:Nb = 9:1. The annular thermal isolation groove was designed around the heater to reduce the power consumption and improve the thermal response rate. Furthermore, the finite element simulation analysis of the thermal isolation structure of the sensor was carried out by using ANSYS software. The results show that a low temperature of 94 °C, low power consumption of 150 mW, and low concentration detection of 1 to 10 ppm NO2 were simultaneously realized for the Nb-doped In2O3-based gas sensor. Our findings provide a promising strategy for the application of In2O3-based sensors in highly effective and low concentration NO2 detection.

https://www.mdpi.com/1424-8220/19/17/3719/pdf

A Low-Temperature Micro Hotplate Gas Sensor Based on AlN Ceramic for Effective Detection of Low Concentration NO 2 .

Phase transition and relaxor nature of BaTiO3 ceramics induced by Li/Ga Co-doping

Highly Sensitive NO2 gas sensor with a low detection limit based on Pt-modified MoS2 flakes

Transition metal borides (TMBs) are promising catalysts for hydrogen evolution reaction (HER). While the commercially available TMBs indicate poor HER performance due to powder electrode and low activity sites density, optimizing commercial TMBs for better HER performance is urgent. To break through the challenge, a new strategy is proposed to compose integral bulk electrodes with needle surfaces in TMBs. The integral bulk electrodes in TiB2, ZrB2, and HfB2 are formed under high pressure and high temperature (HPHT), and the nanoneedle morphology is constructed by chemical etching. In the three materials, the smallest overpotential is 346 mV at 10 mA cm−2 in the HCl etched bulk TiB2 electrode, which is about 61.9% higher than commercial TiB2 powder. Better performance arises from better conductivity of the integral bulk electrode, and the nano morphology exposes the edge sides of the structure which have high activity site density. This work is significant for developing new kinds of bulk TMBs catalysts.

https://www.mdpi.com/2073-4344/12/2/222/pdf?version=1644991635

Dan Xu

Papers

Optimized Low Frequency Temperature Modulation for Improving the Selectivity and Linearity of SnO 2 Gas Sensor

A Low-Temperature Micro Hotplate Gas Sensor Based on AlN Ceramic for Effective Detection of Low Concentration NO 2 .

Phase transition and relaxor nature of BaTiO3 ceramics induced by Li/Ga Co-doping

Highly Sensitive NO2 gas sensor with a low detection limit based on Pt-modified MoS2 flakes

Surface Modification towards Integral Bulk Catalysts of Transition Metal Borides for Hydrogen Evolution Reaction