Multiscale 2D/3D microshaping of property-contrast polymer-derived SiCN

Polymer-derived ceramics are a unique class of materials known for their outstanding properties and versatile applicability. The liquid nature of the precursors allows easy addition of fillers in order to alter the resulting ceramics’ properties. We use a polysilazane with a thermal initiator and 0 – 60wt.% divinyl benzene to vary the final free carbon content and tune the electrical conductivity. Casting of mm-sized parts is performed in PTFE molds whereas high-resolution parts are made in KOH-etched silicon micro-molds. The latter approach allows precise dimension control due to the typical flat and smooth surfaces of KOH-etched Si. Furthermore, due to its high melting temperature, pyrolysis of the preceramic material can be conducted at 1000°C directly in the silicon mold with the additional advantage that the part is conveniently released. By means of direct laser writing, we have added sacrificial 3D microstructures at the mold bottom which replicate into the cast PDC part at high resolution and decompose during pyrolysis. Parts are manufactured with an electrical conductivity ranging from ~10^(-11) to 1 S/cm. Additionally, monolithic parts with a seamless composition and conductivity contrast have been obtained by subsequent casting and crosslinking of precursor formulations with dissimilar DVB concentrations. This approach opens new opportunities towards all-ceramic functionality integration.