Merja Teirikangas

Multilayer BST-COC Composite with Enhanced High Frequency Dielectric Properties

The 0–3 composites with a mixture of randomly dispersed and separated ceramic particles and thermoplastic polymers provide flexible method to fabricate RF devices with adjusted mechanical and electrical properties. However, high ceramic loading levels are required to achieve high relative permittivity which, on the other hand, dramatically degrades the mechanical properties of the composite. In this work vertical and horizontal 2–2 type multilayer structures were fabricated by hot lamination of injection moulded 0–3 BST-COC composite materials with different loading levels of paraelectric ceramic (Ba 0.55 Sr 0.45 Ti 1.01 O 3 ). Each layer and the structures with gradient in permittivity and loss were characterized up to 1 GHz by impedance analyzer. The relative permittivity for the vertical and horizontal gradient structure with identical layer order and average ceramic loading of ∼ 16 vol.% was 6.54 and 10.60 at 1 GHz, respectively. The results showed that especially the horizontal structure is able to provide higher relative permittivity values than a vertical one with similar ceramic loading levels and with competitive dielectric losses. Since the introduced structure is composed of combination of ductile and brittle layers, it also offers a way to fabricate devices with improved mechanical properties.

Room temperature curable zirconium silicate dielectric ink for electronic applications

A facile formulation of room temperature curable and screen printable zirconium silicate (ZrSiO4) ink has been developed. The ZrSiO4 ink printed on the flexible BoPET (biaxially-oriented polyethylene terephthalate) substrate showed a surface roughness of ∼160 nm for a printed layer thickness of 25 μm. The screen printed ZrSiO4 layer on the BoPET substrate has a relative permittivity of 3.01 and a dielectric loss of 0.0058 at 10 GHz. It showed a temperature coefficient of relative permittivity of 55 ppm per °C in the temperature range of 25–60 °C at 15 GHz. The room temperature curability, low dielectric loss, low relative permittivity, mechanical and temperature stability of microwave dielectric properties of the printed ZrSiO4 layer make it suitable for printed microwave applications.

Polymer-ceramic composite filler selection using mixing rules

In this work, classical Bruggeman symmetric and Looyenga mixing rules were used together with a general mixing model to estimate the permittivities and loss tangents of polymer composites in order to make rational filler selections. Eight different fillers were used and compared with theoretical polymer composites. Permittivity levels of the composites were between 2.1 and 70 in the frequency range of 2.5−8 GHz. Results showed that rational selections of fillers also provided better properties of composites when using low permittivity instead of high permittivity filler. However, in certain permittivity targets, better properties were achieved with high permittivity filler. The selections were based on the required volume ratios of fillers and total loss tangents of the composites. Theoretical results correlated well with previously reported values.

Extrinsic Influences of the Polymer Matrix on Electrical Properties of High Frequency Composites

The effect of different polymer matrices on composites with homogenously distributed BaSrTiO 3 (BST) particles was researched. BST-COC, BST-PPS and BST-epoxy composites with the maximum filler loading exhibited relative permittivity and losses at 1 GHz of 10.0, 13.5, 35.7 and 0.0006, 0.003, 0.035, respectively. The characteristics of the composites were analysed by using a modified Lichtenecker model and effective-medium theory (EMT), showing variation of the correction factors as a function of loading level. Moreover the level of the factors varied greatly for different polymers thus suggesting the significant influence of extrinsic effects on the electrical characteristics of the composites.

Microwave Characterization of Printed Inductors with Ferrimagnetic BaFe12O19 Composite Layers

Microwave properties of a novel and functional composite inorganic materials based on barium hexaferrite (BaFe12O19) were measured and simulated. Three different inks with flake and sphere shape particles were developed and printed on the top of meander-shaped microwave inductor on alumina substrate. Several types of meandered inductors with a different number of turns were investigated for the verification of obtained results. The results show relative permeability values of 1.3, 2.2, and 1.5 for composite layers printed from the inks with flake shape at 41.5 wt.%, flake shape plus dodecyl benzene sulphonic acid (DBsa) at 44.4 wt.%, and sphere-like shape at 55.6 wt.% of BaFe12O19, respectively, at 3 GHz. Corresponding magnetic loss tangents were 0.015, 0.04, and 0.02. This novel inductor composite material can be applied for mobile telecommunication operations at 0.5 to 3 GHz frequency range.