Inkjet printing of SU-8 for high-aspect ratio spherical polymeric microstructures

SU-8 exhibits interesting mechanical and optical properties for various MEMS applications, such as the development of micro lens and ball-like lens arrays. One of the most common method to fabricate such structures, is thermal reflow. However, a promising alternative is inkjet printing. It is generally reported that inks with a dynamic viscosity below 40 mPa•s and a surface tension from 10-3 to 10-1 N•m-1 can be inkjetted. The ability of inkjet printing SU-8 based material and fabricate micro lens has already been demonstrated. Another area of interest for SU-8 is MEMS packaging. Once the MEMS active parts are fabricated, it is often important to protect them from environmental damages or perturbations affecting their functionality. In this work, SU-8 based material has been inkjet printed for the development of optical micro lenses with controlled contact angle and for MEMS like parts embedding. Chemical functionalization and dedicated topographical features allows self-alignment of the deposited drops, and using the fabrication method described in high drop confinement is also performed. It was possible to fabricate spherical shapes with different radius of curvature on practically 1 mm diameter round platforms in a controlled manner. The experimental standard deviation is below 1.5% from theoretical expectations. Furthermore a precise positioning of the inkjetted drop can be used to micromachine overhanging ball-like lens structures with edge angle up to 160°. This paper will present three case studies; a) the fabrication of micro lens arrays, with a controlled radius of curvature and thus controlled focal lens, b) the possibility to prototype ball like lens structures and c) the ability to precisely encapsulate MEMS parts.