Thin films of In2O3/SiO for Humidity Sensing Applications

Detection of Methanol with Fast Response by Monodispersed Indium Tungsten Oxide Ellipsoidal Nanospheres

Indium tungsten oxide ellipsoidal nanospheres were prepared with different In/W ratios by using a simple hydrothermal method without any surfactant for the first time. Sensors based on different In/W ratios samples were fabricated, and one of the samples exhibited better response to methanol compared with others. High content of defective oxygen (Ov) and proper output proportion of In to W might be the main reasons for the better gas sensing properties. The length of the nanosphere was about 150-200 nm, and the width was about 100 nm. Various techniques were applied to investigate the nanospheres. Sensing characteristics toward methanol were investigated. Significantly, the sensor exhibited ultrafast response to methanol. The response time to 400 ppm methanol was no more than 2 s and the recovery time was 9 s at 312 °C. Most importantly, the humidity almost had no effect on the response of the sensor fabricated here, which is hard to achieve in gas-sensing applications.

An All Oxide-Based Imperceptible Thin-Film Transistor with Humidity Sensing Properties

We have examined the effects of oxygen content and thickness in sputtered InSnO (ITO) electrodes, especially for the application of imperceptible amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) in humidity sensors. The imperceptible a-IGZO TFT with 50-nm ITO electrodes deposited at Ar:O₂ = 29:0.3 exhibited good electrical performances with V_th of −0.23 V, SS of 0.34 V/dec, µ_FE of 7.86 cm²/V∙s, on/off ratio of 8.8 × 10⁷, and has no degradation for bending stress up to a 3.5-mm curvature. The imperceptible oxide TFT sensors showed the highest sensitivity for the low and wide gate bias of −1~2 V under a wide range of relative humidity (40–90%) at drain voltage 1 V, resulting in low power consumption by the sensors. Exposure to water vapor led to a negative shift in the threshold voltage (or current enhancement), and an increase in relative humidity induced continuous threshold voltage shift. In particular, compared to conventional resistor-type sensors, the imperceptible oxide TFT sensors exhibited extremely high sensitivity from a current amplification of >10³.

Liquid exfoliated pristine WS2 nanosheets for ultrasensitive and highly stable chemiresistive humidity sensors

WS₂ nanosheets have been synthesized by ultrasonication in a binary mixture of acetone and 2-propanol, with a volume ratio of 80:20. Hansen solubility parameters were taken into consideration as part of the process. These nanosheets have been characterized by electron microscopy, atomic force microscopy, and x-ray diffraction, along with spectroscopy such as ultraviolet-visible spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. The nanosheets were further used as a sensing material to fabricate a humidity sensor on interdigitated aluminum electrodes, realized over Si/SiO₂ substrate using a conventional photolithography technique. The response for our sensor varied from 11.9 for 40% RH to as high as 37.5 for 80% RH. Response and recovery time were found to be 13 ± 2 s and 17 ± 2 s respectively. The suspended nanosheets were also treated with UV light in a nitrogen environment. The response for UV treated nanosheets shows better linearity, however its response decreases in the presence of humidity. This is due to a decrease in oxygen content of the UV treated sample. Furthermore, the effect of sonication time has been investigated, and it was found that samples with 10 h sonication are better than others due to their high surface-to-volume ratio. The repeatability and stability of the sensor have been investigated and found to be excellent. The hysteresis in the sensors was also explored. The mechanism of humidity sensing has been discussed in detail.

Humidity sensors principle, mechanism, and fabrication technologies: a comprehensive review

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

Toward a new generation of photonic humidity sensors

This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors.

Wireless remote weather monitoring system based on MEMS technologies

This study proposes a wireless remote weather monitoring system based on Micro-Electro-Mechanical Systems (MEMS) and wireless sensor network (WSN) technologies comprising sensors for the measurement of temperature, humidity, pressure, wind speed and direction, integrated on a single chip. The sensing signals are transmitted between the Octopus II-A sensor nodes using WSN technology, following amplification and analog/digital conversion (ADC). Experimental results show that the resistance of the micro temperature sensor increases linearly with input temperature, with an average TCR (temperature coefficient of resistance) value of 8.2 × 10⁻⁴ (°C⁻¹). The resistance of the pressure sensor also increases linearly with air pressure, with an average sensitivity value of 3.5 × 10⁻² (Ω/kPa). The sensitivity to humidity increases with ambient temperature due to the effect of temperature on the dielectric constant, which was determined to be 16.9, 21.4, 27.0, and 38.2 (pF/%RH) at 27 °C, 30 °C, 40 °C, and 50 °C, respectively. The velocity of airflow is obtained by summing the variations in resistor response as airflow passed over the sensors providing sensitivity of 4.2 × 10⁻², 9.2 × 10⁻², 9.7 × 10⁻² (Ω/ms⁻¹) with power consumption by the heating resistor of 0.2, 0.3, and 0.5 W, respectively. The passage of air across the surface of the flow sensors prompts variations in temperature among each of the sensing resistors. Evaluating these variations in resistance caused by the temperature change enables the measurement of wind direction.