P3.5 - Impact of Dopants on the Characteristics of Thin-Film Humidity Sensor Elements

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P3 - Temperature / Humidity
S. Kozhukharov, M. Machkova - University of Chemical Technology and Metallurgy (Bulgaria), T. Nenov, Z. Nenova - Technical University of Gabrovo (Bulgaria)
738 - 742


Humidity measurement in mixtures of gases – and in the air in particular – is a widely researched topic in a number of scientific and technical fields. Air humidity or the humidity of a technological gas is one of the important parameters, determining the quality of the products of a multiple of technological processes. Therefore it is important to improve the already existing and develop new humidity sensors. One of the directions for addressing this is the use of new materials and technologies for preparing sensor elements.
The present paper presents the results from the study of thin-film humidity sensor elements on the basis of TiO2 obtained by a sol-gel method and doped with various compounds. The elements used as dopants are V, Bi and Na. The impact of the dopants on the sensor characteristics have been investigated. Titanium n-butoxide is used as a starting material for the preparation of the experimental samples. Bismuth acetate, vanadium acetylacetonate and sodium butoxide have been used as doping agents.
The film is applied through the dip-coating method of the ceramic substrates in the obtained filmforming solution with subsequent drying in air environment. The ceramic substrates from Al2O3 have been prepared in advance with interdigitated silver-paladium electrodes. The experimental samples are dipped in the sol three times for 20 minutes and was allowed to dry between dippings. After preparation and drying of the samples they were sintered at 400° C for 30 minutes to obtain a ceramic thin film. The dependence of resistance on humidity, sensitivity, hysteresis and reaction time of the sensor were investigated. Impedance diagrams were obtained and the change of the phase angle in response to humidity was studied.
Samples doped with vanadium have high sensitivity in the whole range of change of relative humidity. For these sample the phase angle changes with around 30° in the whole range of change for humidity.Samples doped with sodium have good sensitivity in the in the 30% to 95% range. For them the phase angle changes significantly above 70% RH (the change is around 70°).From the results obtained one can conclude that doping with bismuth does not influence considerably the humidity sensitivity of the thin film ceramic sensors obtained. The greater sensitivity in the whole range of change of relative humidity is attributed to sensor elements, which are doped with vanadium.