Impact of Particle and Crystallite Size of Ba$_{0.6}$Sr$_{0.4}$TiO$_3$ on the Dielectric Properties of BST/P(VDF-TrFE) Composites in Fully Printed Varactors

In the field of printed electronics, electronic components such as varactors are of special interest. As ferroelectric materials, Ba$_{0.6}$Sr$_{0.4}$TiO$_3$ (BST) and poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) are promising compounds to be used in functional inks for the fabrication of fully inkjet-printed dielectric layers. In BST/P(VDF-TrFE) composite inks, the influence of the particle and crystallite size is investigated by using different grinding media sizes and thermal treatments at varying temperatures. It was found that with an increasing particle and crystallite size, both the relative permittivity and tunability increase as well. However, the thermal treatment which impacts both the particle and crystallite size has a greater effect on the dielectric properties. An additional approach is the reduction in the dielectric layer thickness, which has a significant effect on the maximal tunability. Here, with a thickness of 0.9 µm, a tunability of 29.6% could be achieved in an external electric field of 34 V µm$^{−1}$.