| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Posters Session II |
| Presenter: | Takahisa Kawaguchi, Kogakuin University, Japan |
| Authors: | T. Kawaguchi, Kogakuin University, Japan I. Takano, Kogakuin University, Japan |
| Correspondent: | Click to Email |
Currently, commercial temperature and humidity sensors have a low sensitivity for both sides of a high humidity and a low humidity. Moreover, because the main parts of these sensors are manufactured using polymer materials, there is the problem of a short life in environments such as high temperature or high humidity. Therefore, the next-type sensors are required in a longer life and a higher sensitivity.
As a material satisfying some of the above-mentioned function, TiO2 was adopted. TiO2 is an n-type oxide semiconductor, and has the stable photo-excited state and causes no autolysis. In addition, TiO2 shows the hydrophilicity under ultraviolet irradiation. The next-type sensor with a high sensitivity is promised by the suitable junction of between a TiO2 layer and a Cu2O (p-type oxide semiconductor) layer.
In this study, the investigation of TiO2 thin films on sensor characteristics and the improvement of the sensor sensitivity by using the TiO2/NiO/Cu2O multi-layer thin film were carried out. The rutile-type TiO2 thin film (TiO2-R) with a thickness of 200 nm, the anatase-type TiO2 thin film (TiO2-A) with a thickness of 200 nm and the TiO2/NiO/Cu2O (200/10/200 nm) thin film were prepared by reactive magnetron sputtering. The electric resistance of each sample was measured by changing a voltage from 0 V to 10 V. The resistance changes for a temperature and a humidity were measured by changing a temperature from 25 ℃ to 60 ℃, by changing a humidity from 30 % to 60 %. As the characteristic relating to the humidity, a water contact angle was measured by the θ/2 method. In these experiments, the photoreaction on a semiconductor characteristic was examined by irradiating the white-LED light or UV-LED light to the sample surface.
The resistances of the TiO2-R thin film and the TiO2-A thin film decreased by the photo-excitation under the UV-LED light irradiation. The resistance of the TiO2/NiO/Cu2O thin film under the white-LED light irradiation showed the value as well as that of UV-LED. The temperature coefficient of resistance of the TiO2-R thin film, the TiO2-A thin film and the TiO2/NiO/Cu2O thin film were -8354×10-6 [/K], -5264×10-6 [/K] and -16390×10-6 [/K], respectively. In the case of a humidity characteristic, there was no large change in the electric resistance against the humidity change for any sample. In addition, the improvement of hydrophilicity by light irradiation was not confirmed from the water contact angle examination.
The TiO2/NiO/Cu2O thin film showed a superior temperature characteristic in comparison with the TiO2-R thin film or the TiO2-A thin film.