MEMS hydrogen gas sensor with wireless quartz crystal resonator

Abstract

A highly sensitive hydrogen-gas sensor fabricated using MEMS technology is presented. The sensor chip consists of glass substrates, silicon substrate, and an AT-cut quartz crystal resonator, which is embedded in the microchannel constructed on the substrates. The quartz resonator has a fundamental resonant frequency of 165 MHz and a 200 nm palladium film deposited on its single surface as the hydrogen-gas sensing material. The MEMS hydrogen-gas sensor operates in a wireless manner by exciting and detecting the resonator vibration using the non-contacting antennas. The curvature induced resonant frequency change of the resonator plate caused by the expansion of the palladium film is used for the detection of the hydrogen gas. We succeeded in improving the hydrogen absorption rate and then the sensitivity for the hydrogen-gas detection by applying the air-plasma treatment method, and clarified the role of palladium oxide in lowering the energy barrier for the hydrogen-atom migration from surface to subsurface with the X-ray photoelectron spectroscopy. Thus sensitivity enhanced MEMS hydrogen-gas sensor exhibits a detection limit of 10 ppm or less at room temperature.

Machine Learning-Assisted Multifunctional Environmental Sensing Based on a Piezoelectric Cantilever

“…The development of micro-electromechanical systems (MEMS) technology promotes the miniaturization of environmental sensors, and many environmental sensors have been developed based on different principles such as optical sensors, chemiresistors, electrochemical sensors, and field-effect transistors (FETs). − Among them, a piezoelectric cantilever is one of the most promising environmental sensing platforms because of its advantages of small size, large sensing range, high compatibility with CMOS processes, and easy interfacing with digital circuits. , The piezoelectric cantilever-based environmental sensors usually consist of a cantilever with a sensing layer, whose properties, such as mass, viscoelasticity, and electrical conductivity, will be changed after its exposure to various environments. − However, the metallic top electrode of the conventional piezoelectric cantilever, which is normally covered by the sensing layer, as shown in Figure S1, usually has excellent electrical conductivity, which eliminates the effects of conductivity changes of the sensing film on the output signal of the sensor. Currently, most environmental sensors based on the piezoelectric cantilevers only detect their resonant frequency shifts after exposure to various environments, which are mainly due to the mass changes of the sensing film .…”

Multi-mode resistive spectroscopy for precisely controlling morphology of extremely narrow gap palladium nanocluster array

“…Using these characteristics, palladium-based hydrogen-gas sensors, including the nanocluster-array-based sensor, have been developed. [4][5][6][7][16][17][18][19][20][21] In the nanocluster-array-based sensor, hydrogen gas is detected from the change in the electrical resistance of the nanocluster array. The resistance change is caused mainly by two mechanisms: (i) decrease in the tunneling current between isolated nanoclusters by the hydrogen adsorption and (ii) gap closing between nanoclusters caused by the volume increment by the hydrogen absorption.…”

Self-Powered Thermoelectric Hydrogen Sensors Based on Low-Cost Bismuth Sulfide Thin Films: Quick Response at Room Temperature

“…Therefore, developing fast and accurate hydrogen sensors is of great importance for safely using hydrogen energy. Hydrogen sensors based on various structures and mechanisms have been reported in the past decade, including micro-electro-mechanical systems, semiconductors, optical, , electrochemical, TE, , and other hybrid catalytic systems. − TE hydrogen sensors (TEHs) attracted the attention of researchers for their high selectivity, fast response, low power consumption, and minimum maintenance requirements …”