Electrical property and phase transition analysis of KNN-based leadfree ferroelectric film

The electrical properties, phase construction, thermal stability and phase transition behavior are investigated in 0.95(K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O3–0.05BaZrO3with 2 wt% MnO2 (KNNLT-BZM) lead-free epitaxial ferroelectric film on LaNiO3 (LNO)-coated SrTiO3 (STO) (001)substrate. The x-ray diffraction results show that a mixed orthorhombic (O) and tetragonal (T) phase is obtained in KNNLT-BZM film. The MnO2 doping can effectively suppress its leakage current, which greatly improves the electrical performance featured by a lower leakage value of 8 × 10–11A cm−2 , a twice remnant polarization of 44.7 μC cm−2 , and frequency-dependent ferroelectricity between 50 Hz and 10 kHz. Strikingly, the KNNLT-BZM film maintained ferroelectric nature up to 200 °C, and exhibit a phase transition from O + T mixed phase to T phase (TMix-T) at 300 °C with a high Curie temperature above 440 °C. These results suggest great application potentials of KNN-based films in lead-free micro-electronic devices.本研究针对沉积于镀有LaNiO₃（LNO）的SrTiO₃（STO）(001)衬底上、掺杂2 wt% MnO₂的0.95(K₀.₄₉Na₀.₄₉Li₀.₀₂)(Ta₀.₂Nb₀.₈)O₃–0.05BaZrO₃（KNNLT-BZM）无铅外延铁电薄膜，系统研究了其电学性能、相结构、热稳定性及相变行为。X射线衍射（X-ray Diffraction）结果表明，KNNLT-BZM薄膜呈现正交晶相（O）与四方晶相（T）的混合相结构。MnO₂掺杂可有效抑制薄膜的漏电流，显著优化其电学性能：其漏电流密度低至8×10⁻¹¹ A·cm⁻²，剩余极化强度达44.7 μC·cm⁻²（为未掺杂样品的两倍），且在50 Hz至10 kHz频段内表现出频率依赖性铁电性。值得注意的是，KNNLT-BZM薄膜在200 ℃下仍可保持铁电性，并在300 ℃时发生由O+T混合相向T相的相变（TMix-T），其居里温度高于440 ℃。上述研究结果表明，KNN基无铅薄膜在无铅微电子器件领域具备优异的应用潜力。