| Micro hydrogen sensors,which hasthe compact size,ultra low power and simple working mode,is urgenty needed in aerospace,weapon systems and other industrial fields.In addition,when Pd and Pd-based alloys meet with hydrogen,PdHx compound is formed and lead to the variation of the resistivity.As a result,the concentration of the hydrogen could be determined by measuring the resistance of Pd and Pd-based alloys.In this thesis,PdNi thin film hydrogen sensors were fabricated by micro-manufacturing technology and the properties were characterized.and the main results are as follows:First,the PdNi alloy thin films were deposited on the silica substrates by DC magnetron sputtering.The influence of the processing parameters on the resistivity of the film was studied.The results showed that when Ni content increased from 6.15 at.%to 21.71 at.%,the deposition rate is decreased from 9.5 nm/min to 7.0 nm/min,and the resistivity increased from 2.15×10-5?·cm to 2.89×10-5?·cm.After vacuum annealing at 350°C,the intensity of the diffraction peak of PdNi thin film was enhanced,indicating improved crystallization.The temperature coefficient of resistance of the PdNi alloy thin film was 1.22×10-3/K.Pt thin film was also deposited on the silicon oxide substrate by DC magnetron sputtering.and the temperature coefficient of resistance of Pt thin film was 2.17×10-3/K.Second,the thin film hydrogen sensor was designed and fabricated.PdNi film was used as the sensitive material of hydrogen detection and Pt thin film was applied as the temperature resistor.The sensor was consisted of silica substrate,Si3N4 hydrogen barrier layer,Pt temperature resistor layer,and PdNi sensitive layer.The dimension of the sensor was 1 mm×1 mm×0.5 mm.PdNi hydrogen sensing film and Pt/Si3N4temperature resistor were designed:the line width was 40?m,and the resistance of PdNi hydrogen sensor and Pt temperature resistor was 500?and 100?,respectively.The sensor was fabricated by photolithography and peeling off process.The thicknesses of the Si3N4 bottom layer,the Pt/Si3N4 temperature sensing layer,the PdNi hydrogen sensitive layer and the Au pads layer were 50 nm,80 nm/25 nm,100 nm and 280 nm,respectively.Third,a hydrogen measuring system was designed and built.The system was composed of a sample chamber,an automatic gas-mixer,a digital source meter,a computer,test software,a heating system,and the gas cylinders.During the test process,the hydrogen and nitrogen mixed gase with different hydrogen concentrations were mixed in the gas mixer,and the digital source meter was applied to measure the resistance in the constant current mode.The interval of the signal acquisition was 1 s.Finally,the properties of the fabricated hydrogen sensor were investigated.The output response of the sensor increased from 0.17%to 0.39%when the hydrogen concentration increased from 0.5%to 2%.The response time decreased from 18.34 min to 10.34 min,and the recovery time decreased from 41.85 min to 25.51 min.Moreover,the sensor demonstrated excellent repeatability.And the output response of the sensor only varied from 0.40%to 0.42%under 3%hydrogen concentration.It should be noted that the vacuum annealed sensor exhibits better repeatability that the hydrogen annealed sample,and the maximum difference of the output response was only 0.03%.The output response of the hydrogen sensor decreased with the increasing temperature.After the temperature correction,the fluctuation of resistance of the hydrogen sensor was less than 0.448?,indicating that the influence of the temperature on the performance of the fabricated sensor was significantly reduced. |
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