Demand for the detection of carbon dioxide (CO2) is increasing in various fields, including air-quality monitoring, healthcare, and agriculture. On the other hand, smart gas sensors, in which micromachined gas sensors are integrated with driving circuits, are desirable toward the development of the society of the internet of things. In this study, micromachined hotplate-based CO2 sensors were fabricated and their characteristics were investigated. The sensors have La2O3/SnO2 stacked layers as a sensing material and Pt interdigitated electrodes. A CO2 response of 2.9 for a CO2 concentration of 1000 ppm was obtained at 350 °C with low power consumption (approximately 17 mW). A relatively large response was obtained compared with previous studies even though a compact sputtered-SnO2 film was used. This high response was speculated to be due to a significant contribution of the resistance component near the electrode. Furthermore, CO2 sensing was successfully performed in the CO2 range of 200–4000 ppm with at least 200-ppm resolution.
In this study, bridge-type micro-hotplates (MHP) with an SU-8 supporting layer were proposed for smart gas sensor applications. The proposed MHP consisted of a heating membrane with an area of 140 µm × 140 µm, and a 33 µm-thick SU-8 layer deposited on its bridges. Finite element method based simulation confirmed that the proposed MHP displayed good thermal isolation properties. The proposed MHP was successfully fabricated, and the properties of the MHP were characterized. Current–voltage characteristics revealed that the MHP temperature can reach 550 °C at 5 V. The temperature of the MHP was calculated from changes in the resistance of the heater. Power consumption of the MHP approximately corresponded to 13.9 mW for heating to 300 °C. This was comparable to the power consumption reported in the previous studies. Furthermore, a stable operation under a constant voltage was observed for 100 min. The properties of the MHP indicated that it could potentially be utilized for applications related to integrated gas sensors.
We report the sequence-regulated radical additions of tert-alkyl radicals to two different olefins controlled
by a Cu catalyst,
which we term the “atom-transfer radical addition–substitution”
reaction. The reactions of α-bromocarbonyl compounds, such as tert-alkyl radical sources, with methacrylates and styrenes
occur in a sequence-regulated manner to give the corresponding three-component
product possessing skipped quaternary carbon centers. Our method provides
new insight into how to control the reactivities of tert-alkyl radicals during the synthesis of regulated aliphatic chains.
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