Ceramic processing for multi-material devices with complex geometry

Abstract

Recent antenna designs, as shown in figures 1 and 2, have a complex 3D distribution of different materials that must form a cohesive, and often highly asymmetric entity. The distinct materials in such designs have special dielectric and magnetic properties, and often low electromagnetic losses. This implies that the materials of choice are mainly oxides that are made by ceramic routes for practical reasons. Ceramic routes start from powders that are consolidated into a pre-designed, "green," shape, followed by thermal processing to realize the target micro-structure. Thermal processing can be described as a sequence of drying to remove volatile processing liquids, removal of binders and other additives, and finally sintering. Sintering is the process of gradual densification of particulate compacts in which individual particles merge into bigger grains while, simultaneously, the void space (porosity) between the particles disappears. The equivalent porosity of green compact is 30…80%, while the final porosity should be 0…5% for most RF materials. This makes that the linear dimensions of the sintered shape are 10…40% less than the initial dimensions of the green compact. Practical ceramic compacts exhibit unwanted deviations from ideal shrinkage behavior such as cracking, warping, delamination and bloating. It is an ongoing and major challenge in state-of-the-art ceramics to keep these deviations within acceptable limits.Thermal processing behavior of single phase compacts strongly depends on chemical composition and powder particle morphology. This has the result that attempts to make complex devices in one commensurate process require major innovations and efforts in process design, analysis and optimization. An addi-Layer 4 ε = 15 Layer 1 Layer 2 Layer 3 ε = 15 ε = 20 ε = 70 α-Al 2 O 3 /TiO 2 composite @ diff. ratios Layer 4 ε = 15 Layer 1 Layer 2 Layer 3 ε = 15 ε = 20 ε = 70 α-Al 2 O 3 /TiO 2 composite @ diff. ratios Figure 1: Mulitiple Textured Layers design with 4 6×6 cm layers. Layers 1…3 are built from an inhomogeneous distribution of 2×4 mm quasi-homogeneous blocks with 3 different ε's. 0.75mm 1.25mm 0.25mm Ø = 0.5mm 0.75mm 12.5º 50mm 10-40 units 50mm 1 st layer TiO 2 ceramic rods 2 nd layer of same TiO 2 ceramic rods, but rotated 12.5º 3 rd layer of CVG ferrite One cell MPA structure 0.75mm 1.25mm 0.25mm 0.75mm 1.25mm 0.25mm Ø = 0.5mm 0.75mm 12.5º Ø = 0.5mm 0.75mm 12.5º 50mm 10-40 units 50mm 50mm 10-40 units 50mm 1 st layer TiO 2 ceramic rods 2 nd layer of same TiO 2 ceramic rods, but rotated 12.5º 3 rd layer of CVG ferrite One cell MPA structureFigure 2: Magnetic Photonic Assembly (MPA) design [1] consisting of 10…40 cells with 5×5 cm in-plane dimensions. The cells are built of two layers of parallel TiO 2 ceramic rods and one layer ferrite (CVG).