Characterization of vanadyl phthalocyanine based surface-type capacitive humidity sensors

Abstract

This study presents the fabrication and characterization of novel surface-type capacitive humidity sensors using vanadyl phthalocyanine (VOPc) as the active material. The devices, which comprise three different thicknesses, have been fabricated using the thermal evaporation technique. A thin film of VOPc is deposited on thoroughly cleaned glass substrates with pre-patterned Ag electrodes. The capacitive effect of the samples under humidity has been investigated. Comparison of the samples with different thicknesses shows that the thinnest device seems more sensitive towards humidity. The humidity dependent capacitance properties of the sensor make it beneficial for use in commercial hygrometers.

Humidity sensing and dielectric properties of mesoporous Bi3.25La0.75Ti3O12 nanorods

“…At low RH (11%, 33%, and 54%), only a small amount of water molecules are chemisorbed on the sensing layer. In chemisorption, the water molecules are doubly bonded, resulting the water molecules can hardly be polarized and hence causing the capacitance to increase scarcely [38]. With increasing the RH (75%, 85%, and 95%), more and more water molecules are physically adsorbed on the chemisorbed layer [39], which are singly bonded, thus can be easily polarized and hence cause the capacitance to increase [38].…”

“…In chemisorption, the water molecules are doubly bonded, resulting the water molecules can hardly be polarized and hence causing the capacitance to increase scarcely [38]. With increasing the RH (75%, 85%, and 95%), more and more water molecules are physically adsorbed on the chemisorbed layer [39], which are singly bonded, thus can be easily polarized and hence cause the capacitance to increase [38]. Moreover, as water exhibits high dielectric constant at room temperature (~80) [40], the effective dielectric constant of M-BLT nanorods sensing layer increases which gives rise to increased capacitance of the humidity device [41].…”

Investigating sensing properties of poly-(dioctylfluorene) based planar sensor

“…Moreover, the properties of these materials alter drastically due to the interaction of molecules with environmental parameters such as temperature, humidity, pressure and gases. Keeping in mind the response of organic semiconductors, several humidity [3][4][5] and multifunctional [6,7] thin film sensors have been investigated.…”

“…resistive, capacitive, gravimetric, hygrometric, integrated and optical types [11][12][13]. Resistive and capacitive type sensors are the two important classes of organic based humidity sensors [4]. The resistance and capacitance of sensor change by adsorbing water vapors in pores of the film, with change in humidity level of the environment.…”

Capacitive-resistive measurements of cobalt-phthalocyanine organic humidity sensors

“…Humidity sensors have -several categories based on their measuring principles, which include capacitive, resistive, hygrometric, gravimetric, optical, and integrated types [4 6]. Organic --based humidity sensors are divided into two types: resistive and capacitive [7]. The capacitive-type humidity sensors show good linearity and exhibit better stability at higher humidity levels as compared to resistive humidity sensors.…”