Capacitors humidity-sensitive

Li, D., Y. Jiang, Z. Wu, X. Chen, and Y. Li. 2000. Fabrication of a prototype humidity-sensitive capacitor via layer-by-layer self-assembling technique. Mater Sci Eng C 11 117. 

Mica and plastic film (polycarbonate, polyester, or polystyrene) are most often the types of capacitors used to determine the frequency characteristics or timing behavior of discrete op-amp circuits. Ceramic disc or electrolytic capacitors should generally not be used in these applications. Ceramic disc capacitors are sensitive to temperature and humidity, and electrolytic capacitors are sensitive to temperature and conduct small amounts of DC current. However, ceramic disc and electrolytic capacitors are used for power supply bypassing duties. 

The fabrication of humidity sensors on silicon chips has recently become possible using 1C. production technology [37, 49], This realizes a small, low cost humidity sensor, and makes it possible to integrate the humidity sensor with other sensors or signal-handling circuitry on the same chip. A new integrated temperature and humidity sensor developed by Yamamoto et al., consists of a polymer capacitor on the p-n diode of a temperature sensor [50] as illustrated in Figure 20-33. A thin film of polyimide is used as the moisture-sensitive material... 

Conductometric relies on the measurement of either conductivity or resistivity. This type of sensor comprises a capacitor that changes its capacitance when exposed to the desired analyte. The capacitance of the sensor changes due to a selectively absorbing material such as polymers or other insulators. These absorbing materials serve as the dielectric layer of the capacitor and their permittivity changes with exposure to the analyte. These sensors are commonly used to detect humidity as well as carbon dioxide and volatile organic compounds (Patel et al., 2003). In the humidity sensor case, the dielectric layer comprises a water-sensitive polymer (Lazarus and Fedder, 2011). 

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