||Nowadays, transparent conductive films (TCFs) are more and more important in the world. They are widely used in numbers of electronic devices, including liquid crystal displays, organic light-emitting diodes, touchscreen, and photovoltaics et al. One of the promising structures of TCFs is made of triple-layer which has a thin metal film (e.g., Ag, Cu) between two metallic oxide thin films (e.g., ITO, ZnO, TiO2). These structure gives high conductivity and also transparency. It motivates us to study the TCF with metal/metallic oxide/metal structure with sub-wavelength resonant structure. It is expected that the resonant structure can be used to fine tune the optical transmittance. Fine-tune the parameters of the resonant structure thus can be used to enhance the optical transparency while maintains a high level of electrical conductivity. |
According to the fundamental of the optics and getting deepen, the optimal thickness of metal/metallic oxide/metal structure can be calculated by the concept of interference of light. These structure can be seen as resonant cavity which makes the incident light inside reflect persistently by the different refractive index between metal layers and metallic oxide layer. With the optimal thickness, light away from the resonant cavity can form constructive interference which increase the percentage of transmission. Also, the structure have one more metal layer which can increase the electrical conductivity than the former structure. The first half of the study is to calculate the theoretical optimizing thickness with Ag/ITO/Ag structure and then fabricate the sample to testify the result from calculation.
When the Ag layer are thicker, the resistance of the sample certainly be lower, but the transparency will be decreased also. To keep the transmittance in an applicable level, thickness reduction of Ag layer is absolutely needed. However, there comes an island structure when the Ag layer is in an ultra-thin condition, which cannot transmit electron smoothly. The second half of the study is to improve the discontinuous structure condition. The methods include fabricating Ag layer by evaporation system, Inserting ultra-thin Ti or Cu seed layer below Ag layer. Amorphous ZrCu film is also used to substitute Ag layers into the structure. In the result, using Cu seed layer can make the Ag layer above continuous letting the transparent conducting film in Ag/ITO/Ag structure shows the superior behavior even better than single layer ITO thin film.