Atomic force microscopy investigation of piezoelectric response of ZnO thin films deposited by HIPIMS

This work reports the effects of substrate temperature and the pressure of the deposition gas on the crystal quality and piezoelectric response of zinc oxide thin films deposited by High Power Impulse Magnetron Sputtering (HIPIMS). The effects of substrate temperature and gas pressure on piezoelectric property of the deposited ZnO films were investigated locally (with nanoscale resolution) by Piezoelectric Force Microscopy (PFM) in connection with the film structure, which was investigated by X-ray diffraction), and the film surface morphology, which was investigated by Atomic Force Microscopy (AFM). Deposition temperature and gas pressure have a strong effect on the piezoelectric response and crystallinity of the thin layers in terms of grain size, residual strain and surface roughness. Piezoelectric response and crystallinity of ZnO were improved considerably by decreasing the gas pressure and/or by increasing substrate temperature. The PFM images reveal that the ZnO films have inversion domains and pronounced grain boundaries.