Reactive sputtering of dense yttria-stabilized zirconia

Abstract

Yttria-stabilized zirconia (YSZ) is an O2- ion conducting material via vacancy hopping. This property enables the use of YSZ as a typical electrolyte in solid oxide fuel cells. However, this ability is also interesting for the use in thin film oxygen ion batteries. In both applications, YSZ thin films are attractive in order to achieve low cell resistance. In this work, two methods to deposit YSZ thin films were tested. One method was reactive radio frequency magnetron sputtering and the other was reactive direct current magnetron sputtering. The produced thin films were analyzed by electrochemical impedance spectroscopy, scanning electron microscopy, X-ray fluorescence spectroscopy, grazing incidence X-ray diffraction and laser induced breakdown spectroscopy. Furthermore, profilometer measurements were conducted to evaluate the thin film thickness.In the course of the sputter depositions, a process to reproducibly generate electronically insulating YSZ thin films over the whole sputtered area was developed. The crucial aspect of the preparation procedure involves conducting two distinct sputter depositions with a cleaning step in between. This process resulted in approximately 800nm thin films with a yttrium content of about 9.3mol.The developed procedure was used to successfully produce a thin film oxygen ion battery. The battery was repeatedly charged and discharged with currents between 10 to 1000μA at a temperature of 350°C. The contribution of the electrolyte to the overpotential of the battery was estimated to be less than 20%.