Fabrication And Study Of Micro- And Nano- Structures On Flexible Substrate

Nanoimprint lithography is one of next generation nanometer pattern preparation technologies with low cost, high throughput, and has a broad application prospect. According to the different methods of curing resist, it can be divided into thermal nanoimprint lithography (T-NIL) and UV cured nanoimprint lithography (UV-NIL). Because thermal nanoimprint lithography needs to use high temperature and high pressure in the process, the different thermal expansion coefficients of template and resist can easily cause the distortion of imprinted patterns. However, UV curing nanoimprint lithography uses transparent templates to copy patterns at low pressure and room temperature, and it can fabricate structure in large area with high resolution. So the application of UV cured nanoimprint lithography is more extensive.In this paper we used hard UV-cured resist to form controllable wrinkles on flexible polydimethylsiloxane (PDMS) substrate. A hard film layer was formed on a stretched PDMS by curing the UV-resist. The film would form sine-shaped fold structures perpendicular to the tensile direction after the stress was released from the PDMS. Through the analysis of the morphology of the wrinkles, it can be found that the thinner thickness of hard layer and the larger pre-strain ratio of PDMS substrate, the periodicity of the wrinkles will be denser, that is with smaller cycles. On the other hand, the hard film layer of UV-resist has high elastic modulus, when the stress on the substrate is released, the hard film layer can form cracks due to modulus mismatch of the double-layer system. It is concluded that the formation of cracks is related to the thickness of the hard layer and the pre-stretching ratio of the substrate, the thicker thickness of hard layer, the bigger pre-stretching ratio, can produce cracks.Based on double layer nanoimprint technology and combined with reactive ion etching, electron beam evaporation coating process, we achieved pattern transfer from rigid silicon wafer to the flexible polydimethylsiloxane (PDMS) surface. The elastomeric tunable metal gratings were successfully fabricated on flexible substrate. With polyvinyl alcohol (PVA) as sacrificial layer, adjusting the parameters of the etching, we first fabricated PVA patterns on silicon substrate, and then coated metal on PVA patterns. We cover PDMS onto the sample to form PDMS/metal/PVA sandwich structure on silicon substrate. Water bath was used to dissolve PVA layer, thus metal lines were transferred to the flexible PDMS substrate, and the periodical tunable metal grating were achieved. Optical tests show that by adjusting the PDMS substrate tension between 0-20%, we can modulate metal grating period effectively.Based on aforementioned transfer method of hard film, we formed hard UV-resist and flexible PDMS double layer system, and fabricated nano-structure of UV-resist at the same time. By controlling whether stretching the substrate before transferring the hard UV-resist layer, we could get different morphologies. With pre-stretching substrate before transfer, we could get the nested structure of nano-strucrure and wrinkles after releasing the PDMS substrate. With no-stretching substrate before transfer, we could change the morphology of nano-structures by stretching elastic PDMS substrate. Hard film layer is composed of silicon-containing material,and the sample can be used as a hybrid mold after O2 RIE treatment and a coating of fluoroalkyltrichlorosilane release agent. Different nanostructure patterns would occur under different stain ratios of PDMS substrate, and we can get different patterns using the mold under stretching. We used one grating pattern mold to form grating of different periods with the stretching ratio changed, so as to realize a single period template changing to controllable variable period templates.