The physical property of zinc oxide nanometer humidity sensing thin film
Chih Chin Yang, Shu Wei Chang, Xiang Chen You, Shang Ting Lee, and Ping Chen Wu
Department of Microelectronics Engineering, National Kaohsiung Marine University,
No. 142, Haijhuan Road, Nanzih District, Kaohsiung City 81143, Taiwan (R.O.C.),
e-mail: chchyang@mail.nkmu.edu.tw
Abstract
The zinc oxide nanostructures are being considered as prime material for the moisture detection
in improvement of life quality. The relationship between growth temperature and thin film thickness in
zinc oxide material is explored by the analysis of experimental data. It can be seen that when the
growth temperature increases, the film thickness of zinc oxide sensing material increases. We conclude
that the combined condition of oxygen source with zinc atom in zinc oxidation by increasing growth
temperature is the reason to the thickness formation of zinc oxide nanometer films. The characteristics
of nanometer zinc oxide material as a function of growth temperature from room temperature to 500℃
is also examined by the optical microscopy on the film surface. It is also found that the zinc oxide
films have stable controlled characteristics of crystal structure in growth temperature. It has been
shown that the density of nanostructure can be significantly increased by increasing the growth
temperature from room temperature to 500℃ by the measurement of optical microscopy. A typical
four point probe measurement pattern with high resistivity in low exciting current is obtained and
discussed. In the four point probe measurement, with increasing growth temperature, the resistance
characteristic of zinc oxide nanostructure first increase in proportion to growth temperature,
suggesting that nanostructure growth occurs under the oxygen rich growth condition. The resistance
characteristic of zinc oxide nanostructure finally decreases at higher growth temperature, because of
destruction of lattice stress in nanostructure. It should be noted that the resistance characteristic is
increased with increasing growth temperature shown in the value of measured resistivity, suggesting
that the poly crystallization of zinc oxide material at higher growth temperature. With increasing
growth temperature of zinc oxide thin films, the resistivity variation as a function of growth
temperature, respectively indicates the resistance characteristic of sensing structure for zinc oxide
films. A slight variation of resistance characteristic is only observed from the growth temperature
200℃ to 300℃. Compared with zinc oxide nanostructure films, the sensing characteristic is not better
below growth temperature of 200℃ and above growth temperature of 500℃, due to the lower
resistance.