Abstract
Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe3O4 nanoparticle lines with in-plane and out-of-plane directions.
Highlights
In the last two decades, SU-8 has proven to be of great value for microelectromechanical systems (MEMS) fabrication thanks to its Young’s modulus of 4.02 GPa, chemical and mechanical stability in addition to its simple wafer-scale processing, relatively low cost, and capability to reach high aspect ratio [1]
This paper presents the fabrication by DOD inkjet printing (IJP) of fully cured SU-8 based superparamagnetic polymer composite (SPMPC) microstructures by thermal crosslinking with high aspect ratio and thickness up to 88.8 μm
The drop-on-demand inkjet printing of superparamagnetic polymer composite containing Fe3O4 nanoparticles has been demonstrated for the fabrication of spherical cap structures onto flat and pre-patterned glass substrates
Summary
In the last two decades, SU-8 has proven to be of great value for microelectromechanical systems (MEMS) fabrication thanks to its Young’s modulus of 4.02 GPa, chemical and mechanical stability in addition to its simple wafer-scale processing, relatively low cost, and capability to reach high aspect ratio [1]. It has already been successfully used for a broad range of applications, such as among others, micro cantilevers [2], micro-optics [3], for microcapsule fabrication [4], as master for PDMS-based microfluidic setups [5], or as stamps for bio-medical purposes [6]. Suter et al have developed an SU-8-based superparamagnetic composite (SPMPC) containing Fe3O4 NP presented in [14] which enables actuation, shown by Ergeneman et al [15], and compatible with both shadow-mask photolithography [16,17] and two-photon polymerization as shown Peters et al [18]
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