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|Inkjet Printed MgO-Thickfilm-Layer with Embedded BST Pillars|
|Keywords: inkjet printing, barium strontium titanate, magnesium oxide, embedded structures|
|Barium strontium titanate (BST) and Magnesium oxide (MgO) are common materials for electronic applications. Because of its low permittivity MgO can be used for passivation layers. In contrast to that the high-k BST allows for building up structures with high capacitances. Bandgap and antenna applications are feasible on basis of periodic BST/MgO structures, which are e.g. woodpile shaped. Furthermore BST can be used for filter or phase shifter applications due to the dielectric constant of BST can be modified by the applied electrical field. To keep the applied voltage in a low range very fine structures are required. Thus, the attempt is to realize very fine structures by screen printing or thin film deposition of BST and MgO. In this paper the inkjet printing will be presented as an alternative method for realization of such fine structured thick films. BST particles with a particle size of 0.5 micron are deposited by inkjet printing. The BST structures are embedded in MgO layers, which are printed by inkjet as well. The corresponding, own developed inks are based on an organic nonpolar solvent. The particles are dispersed in the solvent by triple-roll-mill process and stabilized sterically. A solvent was found which is compatible to both kinds of particles as well as to the used substrates. Hence, the ink formulation differs only in the solid phase. The printed structures are processed in two steps. First the MgO layer with the included holes is printed, the BST columns are deposited afterwards. The realization of fine MgO and BST structures is demonstrated. Printing of large areas with holes or channels as well as printing of columns with a high aspect ratio is feasible. Numerous designs can be realized using inkjet printing. Any common passive devices as well as periodical structures with small dimensions and high aspect ratio are feasible.|
|Waldemar Diel, Research Assistant
Helmut Schmidt University