The Industrial Technology Research Institute of Japan has developed a miniature thermoelectric hydrogen sensor that can be integrated into a semiconductor chip. The detection range (the concentration of hydrogen in the air) is between 0.5ppm and 5%. Used for leak detection of facilities such as hydrogen stations. In the future, sensor samples will be provided to relevant agencies and they will be used in hydrogen facilities.

The sensor is formed with a platinum catalyst pattern of a ceramic support material on a thermoelectric conversion MEMS element. Compared with the past sensor, it can play the performance of platinum catalyst, so it has good sensitivity and durability.

Because once the concentration of hydrogen in the air reaches 4%, it will explode, so hydrogen leak detection technology requires hydrogen sensors to be able to detect with high precision in the range of ppm to 4% of the lowest explosive limit concentration. However, the previous contact combustion type and semiconductor type hydrogen sensors are difficult to detect in a wide range of ppm to several percent.

For example, a contact combustion type gas sensor is effective in detecting a high concentration region because it detects a change in resistance of a detection signal sensor, but it cannot be actually detected at all in a low concentration region because of low sensitivity. Specifically, when the temperature changes by 0.01°C due to combustion heat, the resistance change is only 0.004%, which is practically undetectable and therefore cannot be used as a sensor.

The newly developed thermoelectric hydrogen sensor is composed of a thermoelectric conversion film and a platinum catalyst film partially formed on its surface. The local temperature difference caused by the heating reaction of hydrogen and the catalyst is converted into a voltage signal by the thermoelectric conversion film. Thus, a signal sufficient for the detection task can be obtained only by using a high-performance pyroelectric material.

The newly developed sensor adopts the working principle of the combination of catalytic reaction and thermoelectric conversion function, and converts the voltage generated by the element itself into a signal, which not only improves the detectable concentration range, but also is not easily affected by the external temperature. Hydrogen sensors using this working principle have been successfully developed in the industrial technology research support project carried out by NEDO (New Energy Industry Technology Comprehensive Development Agency)-"Development of New Hydrogen Sensors Using Thermoelectric Oxides". However, in order to develop low-cost and high-sensitivity sensors, miniaturization and integration technologies and micro-heater technologies for sensor elements need to be developed.

This development mainly solves the sensor element manufacturing technology of forming thermoelectric thin film, catalyst film, electrode, wiring and heater on semiconductor wafer. At the same time, the durability of the sensor is improved and the production cost is reduced. As a key technique of the thermoelectric conversion element, a thin film forming technique of forming a SiGe film by a sputtering deposition method and then performing a heat treatment has been established. Since the SiGe thermoelectric conversion material has high thermoelectric characteristics, it is very suitable to use a semiconductor process. In order for the catalyst to function stably without being affected by water vapor in the atmosphere, the temperature should be maintained at 100°C. As a heater integration technology to maintain the catalyst temperature, MEMS technology is used to develop a micro heater with high thermal insulation. The thermoelectric diagram, micro heater and catalyst are integrated into a thin film with a size of about 1 × 2mm2, and a sensor chip with a size of 4 × 4mm2 is made.

In the durability test of platinum catalyst with ceramic as supporting material, the newly developed miniature thermoelectric hydrogen sensor was placed in a room temperature environment with a relative temperature of about 65% and worked continuously for 3 months. During this period, its reaction characteristics to 100ppm,1000ppm and 1% hydrogen concentration were tested. The results confirm that the performance is very stable. This time, using ordinary semiconductor technology, the micro sensor is integrated into the silicon substrate. Therefore, the company believes that the electronic circuit for processing sensor signals can also be integrated in the future, so it is convenient for miniaturization and reduces production costs through mass production, which has great practical potential.