Tailoring growth modes by excess alkali addition in magnetron sputtered potassium sodium niobate thin films

Abstract This work reports on the deposition of thin film potassium sodium niobate sputtered from equimolar and excess alkali targets, showing that the growth mode can be shifted towards recrystallized grain growth without substrate heating, while structural and electrical material properties are improved. In particular, we investigate the influence of abnormal grain growth and its attenuation on KNN thin films. This is accompanied by a comprehensive crystallographic analysis of the obtained crystal structures involving wide-range reciprocal space mapping, temperature-dependent X-ray diffraction and elemental analysis associated with the different growth modes. Moreover, we report on the phase segregation within the processed thin film discovered by scanning transmission electron microscopy, which does not show in conventional elemental analysis of the film surface. Verification of the ferroelectric properties of the films is given by piezoresponse force microscopy, which also enables a study of the ferroelectric domains.