Effects of strontium doping on microstructure and functional properties of solution-derived potassium sodium niobate thin films

Abstract

The effects of strontium doping (0-2 mol%) on structure, microstructure and functional properties of potassium sodium niobate (KNN) thin films deposited on Pt(111)/TiOy/SiO2/Si substrates were investigated. Incorporation of Sr up to 1 mol% into the KNN crystal lattice hindered the grain growth, vertical roughness and contributed to the fine-grained and dense thin film microstructure with monoclinic crystal syngony. This effectively reduced leakage current and improved ferroelectric characteristics. Higher doping content (2 mol%) led to the formation of secondary phases and complete deterioration of functional properties. Stabilization of 1 mol% Sr-doped KNN solution with diethanolamine resulted in the film with dielectric constant and losses of 394 and 0.018 at 100 kHz, respectively, leakage current of 3.8 · 10−8 A/cm2 at 100 kV/cm and well saturated ferroelectric hysteresis with Pr of 6.8 µC/cm2 and low Ec of 85 kV/cm. Benefiting from improved leakage current characteristics at high electric fields and less defect structure, the film showed maximal local piezoelectric coefficient, d33 ∼ 110 pm/V determined by piezo-response force microscopy (PFM), ability to reach fully saturated local hysteresis under low switching DC voltage of 15 V, and good ferroelectric domain mobility proven by successful in-situ poling of chosen area using PFM lithography.