Nanoscale BaTiO$_{3}$ MOSCAP formation for ferroelectric field effect transistor application

Titanates are an important class of materials with many interesting functional properties and applications for non-volatile memory, i.e. BaTiO$_{3}$, which is a promising candidate for the realization of a ferroelectric field-effect transistor. However, the difficulty of chemically etching titanates has hindered their commercial use in device manufacturing so far. Here, we report a technique to circumvent this problem. Using molecular beam epitaxy, we grew compressively strained ferroelectric BaTiO$_{3}$, within photolithographically defined openings of a sacrificial SiO$_{2}$ layer on germanium (001) with Pt as a top electrode. Etching away the sacrificial SiO$_{2}$ can reveal isolated nanoscale gate stacks circumventing the need to etch the titanate thin film. Using X-ray diffraction we find that the BaTiO$_{3}$ film is tetragonal with the longer $c$-axis being out of plane, which is a requirement for the ferroelectric field effect transistor. The crystal quality of the BaTiO$_{3}$ films grown in the openings is confirmed using RHEED and cross-sectional transmission electron microscopy. Focused ion beam etching of the Pt layer is then used to electrically isolate a Pt/BaTiO$_{3}$/SrTiO$_{3}$/Ge stack to perform electrical measurements.