Paper NS-ThP16
High Fidelity and Sustainable Anti-reflective Moth-eye Nanostructures and Large Area Sub-wavelength Applications

Thursday, October 25, 2018, 6:00 pm, Room Hall B

The eyes of moths own a feature of unique significance that they reflect little or no light. The dome-like patterns in a depth of approximately 200 nm with pitches of about 200 nm function as a surface with graded refractive index to reduce the reflections.

In recent years, the booming of large screen TVs and smart phones brings increasing attentions for the AR moth-eye structures in sub-wavelength for panels. The AR moth-eye structures applied on smart phone glass displays require finer high resolution and well-oriented patterns, as well as much higher ability to sustain finger frictions and environmental contamination. However, the ideal moth-eye like structure is acknowledged to be parabolically curved domes, which has been rarely systematically demonstrated, and the reported methods suffer from the long-term sustainability. Formed by coating, those reported nanoparticles spheres can be easily peeled off from the surface inevitably by scratching or sticking in either hard or soft pressing from the first steps. The sustainability and reproducibility, thus the reduction of total cost of ownership, are strongly hindered as a consequence. Therefore, such critical issues have not been properly tackled.

An attempt has been made in this work to focus on the sustainability and reproducibility of the moth-eye structures fabricated in profile of parabolically curved domes. A master defining the resolution of the sub-wavelength structures is prepared, commonly by means of EBL. The transfer of large area moth-eye nanostructures is conducted by soft UV-NIL. The next critical step is to etch the substrate for sloping sidewalls, i.e. in an isosceles trapezoid from a cross-sectional view. After that, the silicon substrate is thermally oxidized, in which way the domes can be achieved taking advantage of the variation of oxidation rate at the structure corner, sidewall and bottom. By this step, a template featuring highly ordered moth-eye nanostructures in profile of parabolically curved dome of sub-wavelength resolution is well defined. The moth-eye patterns will be transferred onto the target glass substrate though soft UV-NIL and subsequent processing. The dome structures are made eventually in the substrate via covalent bonding, rather than physical adhesion in case of nanoparticle spheres. Loss of nanoparticles due to pressing, sticking, scratching and so on is hardly an issue.

The moth-eye nanostructures patterned in glass are expected to show improved reflectivity of the incident sunlight in sub-wavelength application of portable electrical devices such as smart phone glass displays. Soft UV-NIL enables its potential for direct large area replications.