Tomiharu Yamaguchi

Dual-Gate Field-Effect Transistor Hydrogen Gas Sensor with Thermal Compensation

We developed a dual-gate field-effect transistor (FET) hydrogen gas sensor for application to hydrogen vehicles. The dual-gate FET hydrogen sensor was integrated with a Pt-gate FET to detect hydrogen and a Ti-gate FET as the reference sensor in the same Si chip. The Ti-FET had the same structure as the Pt-FET except for the gate metal. The Pt-FET showed a good response to hydrogen gas above 10 ppm in air, while the Ti-FET did not show any response to hydrogen gas. The differential output voltage between the Pt-FET and the Ti-FET was stable in the temperature range from room temperature to 80 °C because of the same temperature dependence of the current–voltage (I–V) characteristics. In addition, the temperature of the integrated hydrogen sensor was controlled by an integrated system consisting of a heater and a thermometer at any given temperature under severe weather conditions.

A Proton Pumping Gate Field-Effect Transistor for a Hydrogen Gas Sensor

A proton pumping field-effect transistor (FET), consisting of a triple layer gate structure of a Pd/proton conducting polymer/Pt, has been developed. The hydrogen sensitivity was controlled by the bias change between Pt and Pd. Furthermore, two kinds of methods for the readout of DC and AC modulation can be achieved. According to the decrement of the bias frequency, the modulated output was increased. This characteristic realizes a gas sensor with a self-check function.

Hydrogen Response Mechanism of a Proton Pumping Gate FET Gas Sensor

We developed a new type hydrogen sensor for a proton pumping gate FET with a triple layer of Pd / proton conducting polymer / Pt. Compared with conventional type FET with a single catalytic metal gate, the selectivity was improved. Furthermore, two different output signals of DC and AC modulation were obtained. According to increments of the upper gate voltage to a lower gate, the sensitivity was increased. When modulation voltage was added to the upper gate voltage, AC modulation output was obtained. The response mechanism of the new type FET was investigated using several hydrogen gases and with modulation conditions. Consequently, the hydrogen response mechanism can be explained by a hydrogen dissociation reaction occurring at the upper gate, and the hydrogen gas and generated proton can pass through the proton conducting polymer, and finally an equilibrium hydrogen reaction occurs at the lower gate. These complex mechanisms can be controlled by the gate bias and modulation voltage.