Monolithic integration of patterned BaTiO₃ thin films on Ge wafers

Titanates exhibit electronic properties highly desirable for field effect transistors such as very high permittivity and ferroelectricity. However, the difficulty of chemically etching titanates hinders their commercial use in device manufacturing. Here, the authors report the selective area in finestra growth of highly crystalline BaTiO₃ (BTO) within photolithographically defined openings of a sacrificial SiO₂ layer on a Ge (001) wafer by molecular beam epitaxy. After the BaTiO₃ deposition, the sacrificial SiO₂ can be etched away, revealing isolated nanoscale gate stacks circumventing the need to etch the titanate thin film. Reflection high-energy electron diffraction in conjunction with scanning electron microscopy is carried out to confirm the crystallinity of the samples. X-ray diffraction is performed to determine the out-of-plane lattice constant and crystal quality of the BTO film. Electrical measurements are performed on electrically isolated Pt/BaTiO₃/SrTiO₃/Ge capacitor devices.