Fabrication, Characterization And Humidity Sensing Properties Of Radio Frequency Magnetron Sputtered Calcium Copper Titanate (CCTO) Thin Film
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Date
2018-07-01
Authors
Ahmadipour, Mohsen
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Resistance-type humidity sensor based on CCTO thin films which are capable of
sensing of humidity in the range of 30%-90% and short period of time have been
successfully fabricated by using radio frequency (RF) magnetron sputtering
technique. The CCTO thin film humidity sensor based-on resistance measurement
has never been reported before. The aim of this study is to fabricate a humidity
sensor with small size and simple structure in order to reduce the fabrication cost, to
enhance of CCTO thin film humidity sensing properties, and finally to prove the
great potential of CCTO as a humidity sensing application. CCTO thin film with 200
nm, 400 nm, and 600 nm thicknesses were deposited on alumina (Al2O3) substrates,
respectively and physically analyzed by field emission scanning electron microscopy
which is connected with energy dispersive X-ray spectroscopy (FESEM-EDAX), X ray diffraction (XRD) and atomic force microscopy (AFM) in order to understand
their microstructure and morphology. Prior to CCTO deposition, the fabrication
process was assisted by thermal evaporator to prepare the highly conductive
interdigitated silver electrode. The CCTO thin film humidity sensor electrically
tested in different relative humidity (RH) (30% to 90%) at ambient temperature.
Results exhibited that resistance of all samples decreased with increasing the CCTO
thin film thickness and also upon exposure to humidity. In addition, a quick response
time i.e., approximately less than 1 min was observed for both CCTO thin films. For
device based on 200 nm CCTO thin film, high humidity sensing properties
(Response time = 10 s, Recovery time = 450 s, Sensitivity = 75.6 %) was observed
upon exposure to humidity. When the measurements were repeated after a month, the
CCTO thin film showed remarkable stability. The possible mechanism between
humidity and CCTO thin film was proposed whereby the humidity sensing process is
correlated to adsorption and desorption water on the films surface at low RH, water
molecule will not cover the surface completely and can only chemisorb on the
available site of the CCTO surface. Furthermore, water adsorbing will not provide
electrons to sensing layers and will significantly lower the sensing properties of
CCTO thin film humidity sensor. At high RH, the larger content of water is
adsorbed, so the density of charge carrier becomes higher and hence the sensing
properties increases. Thus, the performance of the CCTO thin film electrical
properties achieved the requirement for good humidity sensor. Moreover, its ability
to detect relative humidity in range 30%-90% qualified this CCTO thin film as a very
promising potential to be applied as a practical and high performance humidity
sensor in the near future.