Yoshinobu Matsuura

Metal oxide semiconductor NO2 sensor

Abstract A newly developed sensor for NO 2 has been investigated from a practical point of view. Various metal oxide semiconductors have been examined and as a result it is found that WO 3 shows the highest potentiality as an NO 2 sensor for air-quality monitoring. Several approaches, such as introducing SiO 2 binder, microprocessing techniques, heat-cleaning techniques and adopting a filter material, have been carried out, and consequently the performance of the WO 3 sensor for NO 2 is improved enough for practical use.

Toward the realization of an intelligent gas sensing system utilizing a non-linear dynamic response

Abstract We report on a trial to construct an intelligent gas sensing system based on the information embedded in a non-linear dynamic response, an application that has possibilities for various kinds of practical usage. By applying a sinusoidal voltage to a heater attached to SnO 2 , a characteristic time-dependent trace of the sensor resistance is obtained as a response to environmental gases. In order to evaluate the characteristic response in a quantitative manner, Fast Fourier Transform (FFT) is performed for the dynamic response. Higher harmonics, obtained by performing the FFT, were processed using an Artificial Neural Network (ANN). It is shown that with these procedures one can simultaneously distinguish and quantify individual gas components. Actually, we show that eight different gases (methanol, ethanol, acetone, diethyl ether, benzene, iso -butane, ammonia and ethylene) as well as natural air can be identified with a single sensor, and can also be quantified with an accuracy of less than 30%. It has been confirmed that our system exhibits long-term reproducibility, and the ability for discrimination and quantification.

Highly sensitive and selective H2S gas sensor from r.f. sputtered SnO2 thin film

Abstract A highly sensitive and selective H 2 S gas sensor has been developed. An SnO 2 thin film is deposited on an alumina substrate by the r.f. reactive sputtering method. The influence of the preparation conditions, such as the calcination temperature and the film thickness, has been examined. The sensitivity and the selectivity to H 2 S are improved by increasing the calcination temperature from 500 to 600°C and by decreasing the film thickness. The optimized sensor shows high sensitivity and good selectivity to H 2 S, a short response time and long-term stability over 90 days. The relationship between the preparation conditions and the morphologies of SnO 2 thin films is also discussed.

Stabilization of SnO2 sintered gas sensors

Abstract In order to improve the long-term stability of SnO2 sintered gas sensors, 31 kinds of metal elements have been added and their stability over a long period of time studied. Sensor materials with metal element dopants are characterized by measurements of hydrogen oxidation reactivity and X-ray diffractometry. The addition of rhenium and vanadium results in excellent stability, reducing the changes in hydrogen oxidation reactivity of the sensor elements over a long period of time. The X-ray analysis indicates that these addition effects are independent of the inhibition of SnO2 crystallite growth.

Battery operated semiconductor CO sensor using pulse heating method

Abstract To develop the pulse heated semiconductor CO sensor which operates on a 9 V alkaline battery for 2 years (power consumption; approximately 0.1 mW), the current sensor structure was refined. The results regarding thermal analysis of the current sensing element convinced us that temperature gradients of this element was so large that only a small area was cleaned by heating. Furthermore, it was found that the loss due to heat conduction, mainly from Au electrodes, was larger than expected. From these results, the element size was reduced from 0.5×0.5 to 0.3×0.3 mm and Pt was used for the electrode material. Compared with the current sensor, the modified sensor was drastically improved as to the long term stability under battery operating conditions.

Development of semiconductor fluorocarbon gas sensor

Abstract To improve the sensitivity to fluorocarbon, surface-modification effects on fluorocarbon detection of a gas sensor based on metal oxides such as SnO2, ZnO, In2O3, Fe2O3 and WO3 have been examined. It is proved that SnO2 is the most suitable material for fluorocarbon detection. 39 kinds of elements have been investigated as the additives to SnO2, which significantly affect its sensing characteristics. It is confirmed that sulfur is the most effective modifier to improve the sensitivity. The surface modification of SnO2 with 1.0 mol% of sulfur induced the enhancement of sensitivity by a factor of 6.5 for CCl2FCClF2 (R-113). Furthermore, the selectivity is also improved by this modification. The sensor doped with 1.0 mol% of sulfur can even detect gas leakage as low as 5 ppm of CH2FCF3 (R-134a) and shows no impairment in long-term stability. IR results have convinced us that the doped sulfur exists in bidentate coordinated form as the sulfate ion (SO42-) on the Sn atom. The sulfur acts as an active site to decompose fluorocarbon (the severance of CCl and CF bond sin fluorocarbon molecules).

Identification for gaseous indoor air-pollutants using NDV

Abstract Four types of tin oxide gas sensors are used to identify indoor air-pollutants in a domestic environment. They are a combustible gas, ammonia gas, carbon monoxide gas and nitrogen oxide gas sensors. Eight pollutants are investigated using these sensors. This system can identify one kind of pollutant out of these pollutants. Three NDVs are adopted to identify a pollutant. NDV is a value which an output of a gas sensor is divided by the output of combustible gas sensor, namely NDV = V( a sensor ) V( combustible gas sensor ) . The characteristic of NDV varies with a pollutant. It becomes clear that three types of NDVs are effective in identifying one of these eight indoor air-pollutants.

A new and environmentally friendly liquid electrolyte gas sensor

For the purpose of making an electrochemical sensor for CO gas detection, by mixing an ion conductor into the catalyst layer and by unique application of a separator, the amount of noble metal catalyst and the density of electrolyte can be reduced. The result is a new electrochemical CO gas sensor possessing improved characteristics with the advantage of being more environmentally friendly, made possible by a neutral/very low concentration alkaline electrolyte and an extremely low amount of noble metal catalyst.