Fabrication of epoxy spherical microstructures by controlled drop-on-demand inkjet printing

Well-controlled spherical microstructures open new possibilities for several MEMS devices, such as hemispherical microfluidic channels or micro-optical elements. However, machining of micro-spherical shapes has proven to be difficult with conventional planar micro-fabrication processes. This paper presents a fabrication method allowing the fabrication of controlled micro-spherical cap structures with defined edge angles. Drops of 30 pL of an epoxy solution were accurately inkjet printed on circular platforms. The deposited volume is confined by the rim of the platforms. This allows a fine tuning of the spherical cap edge angle as well as its height and radius of curvature. The presented method allowed fabricating large arrays of well-controlled micro-spherical shapes of different diameters, ranging from 50 to 930 μm, with a maximum controlled edge angle tuning of 85°. Theoretical investigations of the underlying phenomena are also presented. Good agreement between experimental results and theoretical expectations has been observed, with standard deviations below 3%. Using the proposed method, several 2D arrays up to 900 micro hemispheres with an edge angle of 90° ± 2° have been fabricated with a yield above 98%.