Papers by Keyword: Hydrogen Sensor

Abstract: A semiconductor based hydrogen sensor system was optimized by various modifications, which allow an improved detection of very low concentrations of hydrogen in air. The foundation for new investigations on the sensor structure are modifications of substrate and gate structures. Establishment of reference structures is a major aim. A possible drift compensation could be the use of aluminum or alloys for sensor system in order to stabilize signal in Metal Oxide Semiconductor (MOS) respectively Metal Electrolyte Insulator Semiconductor (MEIS) structures. Gold is more likely not capable to function for drift compensation as a pure metal. Nafion^TM treatment for cover up the palladium gate seems not to be suitable as a reference, besides could be an option to stabilize sensor signal responses and protect sensors from environmental influences.

Abstract: This paper demonstrates the ability of 3CSiC microcantilevers (μCs) to monitor binary gas mixture without sensitive coating. Here, 3CSiC is chosen in particular, as the newly designed sensor will be placed in a radioactive environment. The change in gas concentration is identified using relative shifts in the cantilever’s mechanical resonance frequency (∆f_r). The presented microcantilevers work on electromagnetic actuation and inductive detection. In this paper, the fabrication process, optical characterization results using laser Doppler vibrometry and test results under a gas mixture environment are demonstrated. The presented limit of detection shows the ability of 3CSiCμCs to detect less than 1% of hydrogen in nitrogen, which makes them suitable for the targeted application.

Abstract: Developing quality hydrogen sensitive material is the core problem of hydrogen sensor, the sensor performance was determined by sensitive response, reproducibility and recovery of hydrogen material. Palladium silver alloy was used as hydrogen sensitive material in this paper. A thin film hydrogen sensor was prepared by using magnetron sputtering system. Testing results indicate that the sensor has a good linear output performance at 0 ~ 30% hydrogen concentration range, and demonstrates a high responsiveness and good repeatability. The strength of responsive signal of the sensor decreases while temperature increases, and its responsive time was shorten as the temperature increases.

Abstract: Arrays of vertically well aligned ZnO nanorods (NRs) were prepared on nanostructured ZnO films using a low temperature hydrothermal method. We propose the use of the low cost, environmentally friendly electrophoretic deposition technique (EPD) as seeding procedure, which allows the obtaining of homogeneous, well oriented nanostructured ZnO thin films. ZnO nanorod arrays were covered with graphite in order to prepare graphite/ZnO NRs junctions. These nanostructured junctions showed promising current-voltage rectifying characteristics and gas sensing properties at room temperature.

Abstract: This paper develops a multiple membranes fiber Bragg grating (FBG) hydrogen sensor and investigates the relationship between wavelength of FBG hydrogen sensor and ambient hydrogen concentration. A physical and mathematical model is built to explain the sensor behavior when it is subjected to the changes in hydrogen concentration and in temperature. The shifts in Bragg wavelengths of the Pd-coated FBG hydrogen sensor as a function of hydrogen partial pressure is obtained. Thus the developed FBG hydrogen sensor has a linear response to hydrogen in the low concentration range. Tests were carried on to prove the relationship between wavelength shift and hydrogen concentration.

Abstract: This paper presents the development and fabrication of fiber Bragg grating hydrogen sensor by using magnetron sputtering method to overcome the problem of hydrogen embrittlement.With compact, smooth and high quality thin films deposited by magnetron sputtering, two layers have been sputtered around the fiber cladding: titanium (Ti) layer (20nm) and palladium (Pd) layer (500nm). Between the two layers, Ti is acted as adhesive coatings to ensure connection between fiber and Pd film. Finally, the performance of the developed FBG hydrogen sensor was tested in the laboratory under low hydrogen concentration. The results prove that the fabricated hydrogen sensor has a high sensitivity of 22.67pm/%H₂.

Abstract: Surface Acoustic Wave Sensor is one of the most promising detection systems due tosmaller size, lower weight, power requirements and great sensitivity. It is known from the liter-ature that Pd and ZnO are the most promising materials for detecting hydrogen. A nanoporousPd and ZnO based layered SAW sensors have been developed and investigated for hydrogen,at room temperature. The sensors were of a delay line type (quartz substrate, 70 MHz cen-tral frequency). The nanoporous sensitive layer was directly deposited onto a quartz substrateusing a picosecond laser ablation method. Lasers with picosecond pulses or a high repetitionrate leads to major changes in the ablation process and implicit in the deposited lm struc-ture. Thus, using such a regime, at a certain ambient gas pressure, we have the advantage ofdirectly obtaining a nanoporous lm. The sensor performances (sensitivity, limit of detectionand response time), for a hydrogen concentration in synthetic air of 0.015 2 % were studied.For a concentration between 0.2 - 0.8 % hydrogen/synthetic airs, the response times was 15 -44 s and 6 - 27 s in case of Pd lms and ZnO respectively. Limit of detection was about 6.3times better at Pd sensors (50 ppm) than ZnO sensors (315 ppm).

Abstract: In this article we demonstrate the high sensitivity AlGaN/GaN circular HEMT (C-HEMT) hydrogen gas sensor with new gate interfacial Pt/NiO layer. The wide band-gap III-nitride semiconductor heterostructure allows the sensor operation at elevated temperatures. Likewise, the C-HEMT sensing device is easy to prepare because the MESA insulation step can be omitted. Moreover, the I-V characteristics of ring gate diodes with a dominant thermionic emission of electrons can be easly achieved by elimination of tunneling currents induced on the MESA-etched edges. The Pt/NiO stacked gate absorption layer has nanocrystalline structure, what increases the surface-to-volume ratio. Consequently, the hydrogen gas is more efficiently dissociated at low temperature. Comparing to reference Pt/AlGaN/GaN diode sensor, the optimum operation temperature decreases from 250 oC towards 50oC and the hydrogen detection efficiency is enhanced about 10 times. This is desirable for battery-powered sensors with low current consumption. On the other hand, the fabricated sensor shows longer reaction and regeneration time constants. This is due to longer diffusion path that hydrogen atoms must overcome to reach the AlGaN semiconductor surface.

Abstract: MOS capacitor devices based on silicon carbide (SiC) are largely used as hydrogen detectors in high temperature and chemically reactive environments. A SiC MOS capacitor structure used as hydrogen sensor is analyzed by extensive simulations. The sensitivity to hydrogen detection, stability to temperature variation and dependence on interface states concentration are evaluated. The effects of structure parameters on sensors performance are also investigated. Results show that the oxide layer type and thickness and the SiC polytype have a significant influence on the detectors performance. The proposed optimum structure for high temperature hydrogen detection is based on 3C-SiC substrate and 10nm TiO₂ layer. In accordance with the simulations results, three types of masks are designed for the fabrication of SiC MOS capacitor structures.

Abstract: Researchers have successfully prepared reflection-mode hydrogen sensor by coating Palladium (Pd) alloy in the end of the fiber and it has been proved to be in good effect. Characteristics of the hydrogen sensors are influenced by several factors, such as thickness of thin film, substrate, light wavelength and the film material, etc. For best performance, an optical model of reflection-mode fiber hydrogen sensor is established. The effecting law of each factor is analyzed and discussed through model-based simulation method. The results can provide credible design methods for the reflection-mode fiber hydrogen sensor.