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Academia and Company collaboration and technology transfer in Advanced POLYmers

Periodic Report Summary - ACAPOLY (Academia and company collaboration and technology transfer in advanced polymers)

During the 24 months in ACAPOLY the main activity was centred on the materials preparation and structuring technology, successfully following the work schedule and according to the different work packages. The main objective of the project is the development of a new set of polymer materials for micro/nanosystems technologies with an associated process library to be processed using different technologies: Direct laser writing (DWL) and Ink-jet printing (IJP).

The aim of WP1 is the development of epoxy-based resists that can be patterned by DWL with a high throughput and yielding structures with a high optical stability in terms of refraction index and loss of thermal mass. SU-8 has been selected as standard starting material because it has well-known properties as well as excellent lithographic performance with high aspect ratio up to 15. However, SU-8 has no sensitivity at wavelengths above 370 nm. Therefore, in the WP1, epoxy-based resists has to be modified and optimised to be used for DWL at 413 nm.

During the first 24 months of the project, three generations of DWL materials sensitive at wavelengths over 400 nm were prepared and lithographically investigated at MRT with UV broad band exposure and @ EPFL with laser DWL. The composition of the resist mixtures were optimised and tested for layer thicknesses up to 85 μm, approaching a thickness of 100 μm, aimed within ACAPOLY.

Patterning of test structures of epoxy resin based resists has also been successfully achieved. Fabricated structures have shown high aspect ratio and high resolution, especially for the dense micropatterns. Using Kr laser it has been possible to double the highest aspect ratio (for the best of our knowledge) obtained in an epoxy material with standard UV lithography. The aspect ratio over 40 have been obtained with structures of 2 μm width and 85 μm thickness and aspect ratio of 40 have been observed for structures of 1 μm width and 40 μm thickness. Obtained results show the good behaviour of both the development material and technique, further from the development of concrete application in the ACAPOLY frame, the obtained material will be studied as subject for development of a commercial product.

The aim of this WP2 is the development and characterisation of suitable materials to be used for microlenses fabrication using ink-jet printing (IJP) tool. The starting point of the project is modifying the standard polymers by adding commercially available materials with known properties such as chemical, mechanical, and optical properties. WP3 in the frame of inkjet printing work covers the fabrication of microlens arrays, their optical characterisation, reproducibility tests and upscaling manufacturability.

Two types of new materials, also called inks, based on epoxy resins and ormocers were developed and successfully tested by IJP at room temperature, InkEpo and InkOrmo. The ink-jet parameters for a stable one drop formation modes were determined and optimised for each given ink. Secondary electron microscopy, light microscopy and white light interferometry methods were used to determine the geometrical shapes of the lenses and material constants. The manufactured lenses exhibit a symmetrical, convex lens shape, their height to diameter ratio is can be controlled decreased by using the same number of drops per lens and substrate treatment. Various shape and diameter microlens arrays have been fabricated by tuning the substrate properties. Finally, in the area of applications, WP3 first series of microlens arrays are currently under investigation for optical properties and reproducibility.

The future fork will be concentrated on the optimisation of the selected inks, tabulation of the chemical, physical and optical properties of IJP microlens arrays. Furthermore, the fabrication of microoptical components, such as astigmatic microlenses and microlens-micromirror arrays for parallel microscopy is planned.