Preparation and characterization of sol-gel derived (Li,Ta,Sb) modified (K,Na)NbO3 lead-free ferroelectric thin films

Highlights: → We prepare KNN based ferroelectric thin films using sol-gel and spin-coating method. → We optimize the processing conditions by means of XRD, DSC, SEM and AFM. → The stress in the film could be almost relieved as films thicker than 150 nm. → The 300 nm-thick films annealed at 750 deg. C exhibit good electrical properties. - Abstract: Lead-free ferroelectric thin film with a composition of (K0.4425Na0.52Li0.0375) (Nb0.8825Sb0.08Ta0.0375)O3 (KNLNST) has been successfully prepared on Pt/Ti/SiO2/Si substrate using sol-gel and spin-coating method. Polycrystalline perovskite films were obtained through pyrolysis at 400 deg. C and subsequent calcination at 700-800 deg. C for 30 min, which were optimized by means of X-ray diffraction and thermal analysis. The morphology on the top surface and fractured cross section of KNLNST films was observed by an atomic force microscope and a field-emission scanning electron microscope. Raman spectrum indicated that the film is almost stress-free as the film is thicker than 150 nm. The 300 nm-thick KNLNST film annealed at 750 deg. C exhibited a dielectric permittivity of 341, a loss tangent of 0.05 (1 kHz), a remanent polarization of 9.5 μC cm-2 and a coercive field of 31.8 kV cm-1, as compared to the remanent polarization of 25.6 μC cm-2 and the coercive field of 10 kV cm-1 for bulk ceramics.