IMF2017

Ferroelectrics, particularly Ba_xSr_1-xTiO₃, have shown great promise for microwave-frequency devices such as electric field tunable dielectrics. A recurring challenge has been achieving simultaneous high quality factor (Q=1/tanδ>100) while also enabling tunable capacitance by at least a factor of two. In this work, parallel plate capacitors are fabricated with Ba_0.3Sr_0.7TiO₃ thin films grown by hybrid molecular beam epitaxy on epitaxial Pt bottom electrodes. They exhibit device quality factors above 1000, which is higher than that grown by any other method. We investigate the influence of the top-electrode interface on device properties. Two different electrode deposition approaches are considered, which result in different interface quality – electron-beam evaporation at room temperature and sputter deposition after a high-temperature oxygen anneal. Using fits to the tunable capacitance, interfacial capacitances are extracted for samples with both contact deposition methods. The effective removal of the interfacial contaminant layer by using high-temperature sputtering deposition is demonstrated. While the removal of interfacial contaminants does not strongly affect quality factors, dielectric tunability is enhanced in devices with these cleaner interfaces. The combination of high tunability and high device quality factors results in record device figures of merit. We also report on the effects of different etch processes for the Ba_0.3Sr_0.7TiO₃ mesa – a high-aspect-ratio Ar ion mill and a dilute HF wet etch. While the effect on device quality factors is not significant for low biases, the damage induced by the ion mill allows leakage paths which become active at lower biases.