Papers by Author: Ichiro Matsubara

Abstract: For resistive oxygen sensor elements of Ce1-xZrxO2 (x = 0.0, 0.05, 0.1, 0.2), grain diameter was varied in the range of 86 – 300 nm by changing sintering temperature or changing Zr content. The grain diameter decreased with increasing Zr content. The response time was approximately proportional to the square of the grain diameter. In the relationship between the amplitude of sensor output, An and the frequency, f of sine wave of variation in oxygen partial pressure, the gradient in the high-frequency region of a plot of log An vs. log f in was approximately –0.5. From these results, it was concluded that the sensor response was determined by the oxygen vacancy diffusion rate. The grain diameter of Ce0.8Zr0.2O2 element was 86 nm and the response time at 1073 K was 9 ms, which result opens the door to the technological development of independent control of engine cylinders.

Abstract: For gas sensors, not only sensitivity and selectivity but also fast response speed is very important. We fabricated a restive type gas sensor using ceria (cerium oxide) porous thick film with a particle size of about 100 nm in order to improve the response speed of the sensor. First, we investigated the sensing properties for the change of oxygen partial pressure. The sensor was able to detect the variation of oxygen partial pressure in the wide range from 10-18 Pa to 105 Pa at 873 K. The response time (t90), which is defined as the time until response changes 90% of the saturated value after a sudden change of oxygen partial pressure, was about 10 ms at 1073 K. Next, we investigated the sensing properties for carbon monoxide. We developed the new sensor having two ceria thick films with and without catalyst layer to give selectivity. The sensor was able to detect carbon monoxide over 330 ppm at 773 K, and t90 was 2 s at 723 K. By using Pt/Al2O3 catalyst, the sensor hardly responded for hydrogen, so it was implied that the sensor had a good selectivity for carbon monoxide.

Abstract: The organic/MoO3 hybrid sensors show a distinct response to aldehyde gases, formaldehyde and acetaldehyde, by changing the electrical resistance, whereas they show almost no response to other VOCs. The organic/MoO3 hybrids have a potential for selective VOC detection because the sensing properties of organic/MoO3 hybrids can be controlled by the kind of interlayer organic components. In this study, we have carried out the detail characterization of the interlayer of the organic/MoO3 hybrids as well as the valence of Mo and evaluation of their sensing properties.

Abstract: Micro-thermoelectric hydrogen sensor (micro-THS) with the combination of the thermoelectric effect of Si0.8Ge0.2 thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation was prepared by microfabrication process. In the viewpoint of high sensitivity of micro-THS, the thermoelectric properties of the Si0.8Ge0.2 thin film could be improved by optimizing carrier concentration using helicon sputtering with an advantage of easy doping control, and sensitivity of the device with this thin film was investigated. As the result, the boron-doped Si0.8Ge0.2 thin film is considered to be the better choice ensuring the reliable monitoring of hydrogen concentration down to ppm level.

Abstract: To integrate the ceramic Pt/alumina catalyst on micro-hotplate of micro-thermoelectric hydrogen sensor (micro-THS), a dispenser technique was used in this study. This micro-THS with the Pt/alumina catalyst is capable of sensing wide range hydrogen concentration of 50 ppm to 3 % at room temperature. For hydrogen/air mixture gas of 50 ppm, voltage signal is measured to be 0.03 mV at room temperature.

Abstract: Micromachined sensors are a new generation of sensor technology combining existing integrated circuit fabrication technology with novel deposition and etching processing. In the viewpoint of low-power operation, high sensitivity and fast response speed of thermoelectric hydrogen sensor (THS), we prepared the micromachined thermoelectric hydrogen sensor (micro-THS) with the combination of the thermoelectric effect of SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation. The power consumption of the micro-THS was greatly reduced to be 50 mW for 100 °C operating, by the Pt-micro-heater on single membrane. The micro-THS with 40 wt.% Pt/alumina catalyst showed voltage signal of 10 mV for 1 % H2 in air.