Hydrogen gas has attracted attention as a new energy carrier, and simple but highly sensitive hydrogen sensors are required. We fabricated an optical hydrogen sensor based on a silicon microring resonator (MRR) with tungsten oxide (WO 3 ) using a complementary metal-oxide-semiconductor (CMOS)-compatible process for the MRR and a sol-gel method for the WO 3 layer and investigated its sensing characteristics at device temperatures of 5, 20, and 30 • C. At each temperature, a hydrogen concentration of as low as 0.1 vol% was successfully detected. The gas sensitivity increased with decreasing temperature. The dependence of the sensitivity on the device temperature can be attributed to the thickness of tungsten bronze (H x WO 3 ) formed by WO 3 during exposure to hydrogen gas. In addition, a hydrogen gas sensor based on a silicon-MRR-enhanced Mach-Zehnder interferometer (MRR-MZI) is proposed and its significantly high sensing ability using improved changes in the transmittance of light is theoretically discussed.

A novel optic sensor using platinum-loaded tungsten oxide (Pt/WO 3) and a silicon microring resonator for detection of hydrogen gas at room temperature was developed and tested. The sensing principle is mainly based on the resonant wavelength shift caused by the catalytic combustion reaction of hydrogen. In a previous study, it was found that Pt/WO 3 film could not be deposited uniformly on the surface of the microring. To solve this problem, acetylene glycol surfactant was used and mixed with Pt/WO 3 precursor solution. Electron probe microanalyzer images of the device surface showed that the Pt/WO 3 layer successfully covered the target part of the microring. When this device was tested, a 580-pm resonant wavelength shift was observed after 20-min exposure to pure hydrogen gas at room temperature. When the previous device was tested under the same condition, a 160-pm resonant wavelength shift was observed, so the sensitivity (defined by the wavelength shift after 20-min exposure to sample gas) of the developed device was approximately four times larger than that of the previous one.

A silicon microring-resonator (MRR) hydrogen sensor which utilizes platinum-loaded tungsten oxide (Pt/WO3) thin film was fabricated and evaluated. The uniform film was deposited on MRR portion by using sol-gel technique. By the exposure to pure hydrogen gas, the sensor devise showed the large resonant wavelength shift at room temperature. It is suggested that the change in the optical properties of hydrogen sensitive layer results in this response.