Dry aerosol deposition of barium neodymium titanate microwave dielectric

Abstract

Additive manufacturing is of interest for prototype and integrated RF/microwave components. Low-loss microwave dielectrics (MWDs) are increasingly important in resonant filter and antennae designs as operational frequency increases with millimeter-wave technology. Miniaturization and design flexibility demand higher relative permittivity (ε_r) than is currently available with 3D-printed polymers. This paper describes the use of dry aerosol deposition (DAD) to build thick films of MWD barium neodymium titanate on a variety of substrates including printed circuit board. Films range in thickness from 11 to 150 µm, and cross-sectional imaging reveals a dense, ultrafine grain structure. Dielectric properties are reported over the frequency range 1 kHz–1 GHz. Relative permittivity shows a thickness dependence, with ε_r = 44 for the thickest films. Dielectric loss is reasonably low at midrange frequencies (tan(δ) ∼ 0.01), but increases at the high end of the spectra, likely due to extrinsic effects. Compared to sintered bulk ceramic of the same composition (ε_r = 81, tan(δ) ∼ 0.001), the dielectric properties of the films are impressive considering that DAD is a room temperature process. Results suggest that DAD offers a promising approach for on-demand manufacturing of MWD ceramics for applications in telecom and sensing.