Fabin Qiu

Thermoelectric Properties of RF-Sputtered SiGe Thin Film for Hydrogen Gas Sensor

Phosphorus-doped Si0.8Ge0.2 thin films were deposited on the Si3N4/SiO2/Si substrate by the RF sputtering. Thermal annealing was carried out to crystallize as-deposited, amorphous-like SiGe thin films. With increasing annealing temperature and time, the crystallization of the SiGe thin films progressed, resulting in a high carrier mobility and a large absolute value of Seebeck coefficient. The SiGe thin film deposited on the Si3N4/SiO2/Si substrate and then annealed at 850°C for 5 h at an argon flow rate of 150 cc/min showed a Seebeck coefficient of -198 µV/K, a Hall mobility of 10.54 cm2/Vs, a carrier concentration of 1.1×1018 cm-3 at 100°C. The thermoelectric hydrogen sensor with the SiGe thin film annealed at 850°C for 5 h showed a voltage signal of 5.81 mV, a catalyst activity of 16.17°C and a response time, corresponding to 90% voltage signal of 50 s for 3% H2 in air. The sensor operating at 100°C detected hydrogen in air at concentrations from 0.01 to 3%, and showed a good linearity between voltage signal and gas concentration.

Hydrogen sensor based on RF-sputtered thermoelectric SiGe film

Si0.8Ge0.2 thin film was sputtered on an alumina substrate by the RF-sputtering method. After annealing in flowing Ar atmosphere, platinum film, which acts as a catalyst of the combustible sample gas, was further sputtered on half the surface area of SiGe film. The hydrogen-sensing properties were investigated for the development of potential applications of the device structure as a hydrogen sensor that makes use of the thermoelectric (TE) effect. The measurement results indicate that a reliable output voltage signal was successfully realized when the element was exposed to an environment with a certain hydrogen concentration. The operating temperature for the device was around 100°C, and the response and recovery time corresponding to 90% voltage change were both shorter than 50 s on switching the atmosphere from synthetic air to 3% H2. The detectable concentration of the device ranged from 0.01% to 3%. Furthermore, a good selectivity to hydrogen was also exhibited.

Investigation of thermoelectric hydrogen sensor based on SiGe film

A novel hydrogen sensor with the working principle of thermoelectric effect was prepared. It was composed of a rf-sputtered SiGe film, and a rf-sputtered Pt catalyst film atop the half-surface area of the SiGe film. The molar ratio of Si and Ge component in the SiGe film is 4:1, and the alumina substrate was utilized for the preparation of the stacked-film structure. Due to the amorphous structure of the as-deposited SiGe film, an annealing process for the crystallization of SiGe film was conducted. The annealing effect on the phase structure of SiGe film and hydrogen sensing properties of the sensing device was investigated. In addition, some factors essential to the sensing properties, such as the operating temperature of the sensing device and the preparing condition of Pt catalyst as well as the detectable concentration range of hydrogen gas were all examined in detail.

Static characteristic of planar-type CO2 sensor based on NASICON and with an inner-heater

Abstract The structure and the static characteristic of planar-type solid electrolyte CO 2 sensor are introduced. It was fabricated by the combination of carbonate auxiliary phase with a NASICON chip (2.5×0.5 mm), while a passage of Pt wire coiled into suitable form acting as inner-heater was pressed into the chip. When being measured in static state, it exhibited stable EMF response to 100–2000 ppm CO 2 in air over a current range of 200–300 mA, and its characteristic was almost independent of partial pressure of O 2 . The 90% response time were less than 10 and 50 s, respectively when the heating current was kept at 270 mA. Furthermore, the difference in characteristic due to different carbonate auxiliary phase and its sensing mechanism are also preliminary investigated.

Study on ethanol sensitivity of nanocrystalline La0.7Sr0.3FeO3-based gas sensor

Abstract La 0.7 Sr 0.3 FeO 3 nanocrystalline material was synthesized with citrate method, and an indirect-heating sensor was fabricated based on it. After measurement and analysis of its characteristics, this new kind of device showed us high sensitivity, selectivity and stability against disturbing gases, the response and recovery times of it was also found be much shorter than conventional devices.

Investigation of a new catalytic combustion-type CH4 gas sensor with low power consumption

Abstract The sensitive composite material was prepared by doping Pd and some metal oxides such as MgO into SnO 2 –In 2 O 3 –TiO 2 matrix material. The technique for fabricating the direct-heating-type sensor and a surface-modifying process were employed to prepare the CH 4 gas sensor. Its sensitive properties and working mechanism are presented.

Property analysis and humidity sensitivity of the composite material of BaTiO3 and RMX

Nanocrystal BaTiO3 and polymer (R)nM+X− are mixed to make a composite material. IR and XPS spectra of the composite material were analyzed and compared with those of BaTiO3. The humidity sensor made of the composite material shows better humidity sensing properties than the BaTiO3 sensor such as higher sensitivity and smaller humidity hysteresis.

Thermoelectric CO Gas Sensor Using Thin-Film Catalyst of Au and Co3 O 4

Thin-film catalysts of gold and cobalt oxide were prepared by magnetron radio frequency sputtering deposition on magnesia substrate by cosputtering Au and Co 3 O 4 . We investigated the catalytic activity of this thin-film catalyst for CO gas and found that the catalytic activity was influenced strongly by the contents of the supported oxides in the thin film. Using this catalyst, a thermoelectric gas sensor of [Au, Co 3 O 4 ]/SiGe/magnesia was developed to detect carbon monoxide gas. When this sensor is exposed to the gas mixture of air and CO, the catalytic reaction oxidation of CO heats up the catalyst-coated surface and then thermoelectric voltage builds up along the hot and cold region of the thermoelectric film of SiGe. The sensor of [Au, Co 3 O 4 ]/SiGe/magnesia showed a temperature increase of about 6.6°C in the hot region and an output voltage signal of about 0.63 mV for 3% CO in air at 200°C. The sensor showed a clear voltage signal with good linearity for the target gas content in the range 0.05-3.0% and high selectivity for CO gas at 200°C.

Preparation and humidity-sensitive properties of nanocrystalline BaTiO3 thick film fabricated on Teflon substrate by using pressing method

Abstract Nanocrystalline BaTiO 3 precursor has been synthesized by using the stearic acid gel (SAG) method. After calcining the precursor at above 600 °C for 0.5 h, nanocrystalline BaTiO 3 powder with cubic perovskite structure is obtained. The powder is compacted further into solid material under a pressure of 0.1 to 2.0 GPa or fabricated into thick film by pressing on a Teflon substrate at room temperature and 200 °C. The powder and film samples are characterized by XRD, TEM and SEM. The results show that the average grain size of the powder is between 20 and 60 nm, and the thickness of the compacted film is about 56 μm. The investigation on the humidity-sensitive properties of nanocrystalline BaTiO 3 thick film shows that a compacted thick-film sample possesses higher humidity sensitivity, simpler preparation process, and enhanced adhesion strength on the Teflon substrate in comparison with a coated sensor, and the grain size and pressing pressure have obvious influence on its properties. In addition, the solid reaction mechanism and pressure effect on the material in the course of processing are also discussed.

Investigation of the synthesis, compacting density and hot-pressed sintering density for Y2O3-stabilized zirconia nanocrystalline materials

Abstract Precursors for the synthesis of 10 mol.% Y2O3-stabilized zirconia have been prepared by using polyethylene glycol as a protecting material of the colloidal particles obtained via the gel process. After the solid phase reaction at 550–800°C for 1 h, nanocrystalline composite oxide samples with a grain size of 3–10.8 nm were obtained. The morphology and properties of the materials were characterized by X-ray powder diffraction, thermal analysis and transmission electron microscopy. The compacting and hot-pressed sintering density for the sample of grain size 10.8 nm were investigated. The result indicated that compacting or sintering after compacting can increase the initial relative density and the final relative density for the sample, but they cannot make the sample reach much higher density below 1150°C sintering temperature. The pressed sintering process can increase the relative density of the samples to 98.4% of the theoretical density at 800°C and 2.0 GPa for 20 min.