Nissan Research Institute has developed a hydrogen sensor with a larger detection concentration range
The Japan Industrial Technology Research Institute (Product Research Institute) has developed a miniature thermoelectric hydrogen sensor that can be integrated into a semiconductor chip. The detection range (concentration of hydrogen in the air) is between 0.5 ppm and 5%. Used for leak detection in facilities such as hydrogen stations. In the future, sensor samples will be supplied to relevant institutions and will be applied to hydrogen facilities.
The sensor forms a platinum catalyst pattern with a ceramic support material on the thermoelectric conversion MEMS element. Compared with the past sensors, it can exert the performance of platinum catalyst, so it has good sensitivity and durability.
Because the concentration of hydrogen in the air will explode as soon as 4%, the hydrogen leak detection technology requires a hydrogen sensor to perform high-precision detection between the minimum explosion limit concentration range of ppm to 4%. However, previous contact-fired and semiconductor-type hydrogen sensors were difficult to detect in a wide range of ppm to a few percent.
For example, the contact combustion type gas sensor is detected by detecting the change in the resistance of the signal sensor, so that the detection of the high concentration region is effective, but in the low concentration region, since the sensitivity is low, it is practically impossible to detect. Specifically, when the combustion heat causes a temperature change of 0.01 ° C, the resistance change is only 0.004%, and it is practically impossible to detect, so it cannot be used as a sensor.
The newly developed thermoelectric hydrogen sensor is composed of a thermoelectric conversion film and a platinum catalyst film formed on a surface thereof, and a local temperature difference caused by a heat reaction between hydrogen and a catalyst is converted into a voltage signal by using a thermoelectric conversion film. Thus, as long as high performance thermoelectric materials are used, a signal sufficient to complete the inspection task can be obtained.
The newly developed sensor uses a combination of catalytic reaction and thermoelectric conversion function to convert the voltage generated by the component itself into a signal, which not only improves the detectable concentration range, but also is less susceptible to external temperature. The hydrogen sensor using this working principle has been successfully developed in the industrial technology research support project of NEDO (New Energy Industry Technology Development Organization)--"Development of a new hydrogen sensor using thermoelectric oxide", but to develop Low-cost, high-sensitivity sensors also require miniaturization and integration technologies for sensor components, as well as micro-heater technology.
This development mainly solves the sensor element manufacturing technology for forming a thermoelectric film, a catalyst film, an electrode, a wiring, and a heater on a semiconductor wafer. At the same time, it also improves the durability of the sensor and reduces the production cost. As a key technique of a thermoelectric conversion element, a film forming technique in which a SiGe film is formed by a sputtering vapor deposition method and then heat-treated is established. Because of the high thermoelectric properties of SiGe thermoelectric conversion materials, it is very suitable to use a semiconductor process. In order to stabilize the catalyst from the influence of water vapor in the atmosphere, the temperature is maintained at 100 °C. As a heater integration technology that maintains the temperature of the catalyst, MEMS technology is used to develop a micro-heater with high heat insulation. The three components of the thermoelectric diagram, the microheater, and the catalyst were integrated into a film having a size of about 1 × 2 mm 2 to prepare a sensor chip having a size of 4 × 4 mm 2 .
In the platinum catalyst durability test using ceramic as the support material, the newly developed micro thermoelectric hydrogen sensor was placed in a room temperature environment with a relative temperature of about 65%, and it was continuously operated for 3 months, during which it was applied to 100 ppm. The reaction characteristics of 1000 ppm and 1% hydrogen concentration were tested. The results confirmed that the performance was very stable. This time, the micro-sensor was integrated into the silicon substrate using the common semiconductor process. Therefore, the company believes that it can integrate electronic circuits for processing sensor signals in the future, thus facilitating miniaturization and reducing production costs through mass production. .
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