Study On Titanium Dioxide Based Thin Film Optical Humidity Sensor

Humidity plays an important role in industry,agriculture,scientific research and other fields of national economy and people's life.With the growing demand for humidity monitoring and controlling,the research on humidity sensor has made great progress after years of efforts.Humidity sensitive material is the core of most humidity sensors,which directly determines the performance of humidity sensors.At present,porous films and nanotubes are the most commonly used humidity sensitive materials,because porous structures and nanotubes are conducive to adsorbing more water molecules,which improves the sensitivity of the sensor.But it is not beneficial to the rapid desorption of water molecules,which will increase the recovery time.In the result of the excellent physical properties and chemical stability of titanium dioxide,a series of titanium dioxide based thin film optical humidity sensors based on intensity modulation are designed and fabricated in this paper.The crystal structure,surface morphology and wettability of the humidity sensitive materials are characterized.The performance of the optical humidity sensor is studied.The influence of the number of film layers and annealing temperature on the sensor performance is also explored.The sensing mechanism is verified and the conclusions are as follows:?1?The titanium dioxide thin film prepared by the modified dip coating method annealed at 400?is anatase,with smooth surface,RMS roughness of 2.6±0.3 nm and average grain size of 20.8 nm.It shows super hydrophilicity without UV irradiation.?2?The optical humidity sensor based on the single-layer titanium dioxide thin film annealed at 400?has better performance:the fitting degree is 0.994 and 0.990 in the range of low humidity and high humidity respectively,which shows a good linear relationship;the sensitivity is 1.309?w/%RH;the response and recover time is 27 s and 23 s respectively with good stability and repeatability.?3?The output power through the humidity sensitive material decreases with the increase of relative humidity,which is mainly due to the absorption of water molecules on the surface of TiO₂film,making the incident light scatter.In the range of low humidity,water molecules are mainly chemically adsorbed on the surface of humidity sensitive film,and the weak light scattering effect leads to lower sensitivity;in the range of high humidity,a large number of water molecules are adsorbed on the surface of TiO₂ thin film,forming water drops,and the strong scattering effect makes the light intensity drop rapidly,obtaining higher sensitivity.?4?The optical humidity sensor based on TiO₂-ZrO₂ thin film has obvious linear relationship in the range of low and high humidity respectively,but the output power has no obvious change with relative humidity changing in the range of low humidity.