Patterning of integrated thin-film barium strontium titanate

Ferroelectric (FE) thin-film capacitors should be integrated on the chip to form a complete miniaturized circuit, with other semiconductor or thin-film components such as inductors, isolation capacitors, bias resistors, etc[1]. These components have already been developed for integration with CMOS circuits. The main effort in integrating FE with CMOS has been focused on FE memories [2]. However, many types of circuits (microwave, optical, sensing, etc) require both metal electrodes other than Pt (Cu, Al or Au) and corresponding technologically compatible patterning of FE thin films. Perovskite Ba1-xSrxTiO3 films (400 nm) were grown by in situ pulsed laser deposition [3] on Si substrates using different bottom layers and varying the deposition temperature. The wet etching process with acid solutions was used for film patterning. The process was optimized with respect to both minimal lateral under etching and low-gradient edge shape of the film, which is important to facilitate good step coverage of the top electrode. The etching regimes were found to depend both on the film microstructure and electrode material.