Abstract
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 (WO3) using a complementary metal-oxide-semiconductor (CMOS)-compatible process for the MRR and a sol-gel method for the WO3 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 (HxWO3) formed by WO3 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.
Highlights
Hydrogen gas has attracted attention as a new energy carrier
If we assume that the microring resonator (MRR) is the same as that previously discussed (K = 0.2, Q-factor = 4220), the temperature of the MRR increases by approximately 2.0 °C for 0.1 vol% hydrogen gas at Tsen = 20 °C, and a change in the extinction ratio larger than 40 dB is obtained if the operation wavelength is set at a suitable value, which is much larger than that of the simple MRR
We fabricated an optical hydrogen sensor based on a silicon MRR with a WO3/SiO2 layer using a complementary metal-oxide-semiconductor (CMOS)-compatible process for the MRR and a sol-gel method for the WO3 layer and investigated its sensing characteristics at device temperatures of 5, 20, and 30 °C
Summary
Hydrogen gas has attracted attention as a new energy carrier. hydrogen has an ignition temperature of as high as 585 ◦ C in air, it is flammable, its ignition energy is as small as 0.002 mJ, and its explosive range is from 4.0 to 75 vol%. Optical hydrogen sensors using optical fibers and nanostructures have been developed [15,16,17,18,19], and hydrogen gas with a concentration as low as 0.1 vol% has been detected [2]. A WO3/Si-MRR hydrogen sensor has already been proposed and hydrogen gas with a in the WO3 film. A WO3 /Si-MRR hydrogen sensor has already been proposed and hydrogen gas with concentration of 1 vol% was successfully detected [20]. We have obtained sensing characteristics for (100 vol%) hydrogen using a WO3/Si-MRR sensor [30]. The MRR sensor has realized the highest sensitivity and the fastest response at room temperature as an optical hydrogen sensor based on optical waveguides to the best of our knowledge.
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