| AVS 61st International Symposium & Exhibition | |
| Electronic Materials and Processing | Friday Sessions |
| Session EM+NS+TF-FrM |
| Session: | Transparent Electronics |
| Presenter: | Toshihide Nabatame, NIMS, Japan |
| Authors: | T. Nabatame, NIMS, Japan H. Yamada, Shibaura Institute of Technology, Japan A. Ohi, NIMS, Japan T. Oishi, Shibaura Institute of Technology, Japan T. Chikyo, NIMS, Japan |
| Correspondent: | Click to Email |
The In0.9Sn0.1Ox (ITO) films is widely used as transparent electrodes in optical and optoelectronic devices. The work function (WF) of the ITO film was generally evaluated by optical measurements such as ultraviolet photoemission spectroscope and Kelvin probe. However, the optically measured WF differs from the effective work function (EWF) estimated by electrical measurement. The influence of oxygen diffusion in ITO film on EWF change has not been also understood. In this paper, we systematically investigate EWF change of ITO film by oxidation and reduction annealing. We also examine oxygen diffusion coefficient (D) of ITO film, using isotope 18O tracer, to discuss influence of oxygen diffusion of ITO film on EWF change.
The ITO films were prepared under an Ar/O2 by sputtering using an In0.9Sn0.1Ox target. The ITO-gated metal-oxide-semiconductor (MOS) capacitors with HfO2 and SiO2 gate insulators were fabricated to estimate EWF value of ITO film. The ITO (150 nm)/SiO2/Si films were annealed at 300 – 500 °C for 30 min under 104 Pa of 18O isotope (99%) gas to obtain D value.
The resistivity of ITO film, which consists of cubic structure, shows an almost same value regardless of oxidation and reduction annealing temperatures. The EWF of ITO-gated MOS capacitors significantly changes from 4.4 to 5.2 eV as the oxidation annealing temperature increases from 250 to 350 °C. The EWF change is saturated at 350 °C. On the other hand, the EWF value decreases in reduction annealing temperature ranging from 200 to 350 °C. This must be due to oxygen introduction and removal in ITO film during oxidation and reduction annealing, respectively. To understand the mechanism of oxygen transfer in the ITO film, we examine D behavior of ITO film. The ITO film has a large D value of about a 1.1X10-20cm2/s at 300 °C and a small activation energy (Ea) of about 1.4 eV. We found that the D and Ea values are similar to those of grain boundary in monoclinic ZrO2. This results indicate that oxygen diffusion of ITO film occurs even at low temperature of 300 °C and affects to the EWF change during oxidation and reduction annealing at around 300 °C.