Low-temperature crystalline lead-free piezoelectric thin films grown on 2D perovskite nanosheet for flexible electronic device applications

A monolayer of Sr₂Nb₃O₁₀ (SNO) is deposited on the Pt/Ti/SiO₂/Si (Pt-Si) or Pt/Ti/polyimide (Pt-PI) substrate by using the Langmuir-Blodgett method and employed as a seed-layer for the growth of a crystalline (Na_1-xK_x)NbO₃ (NKN) film at 350 ℃. The crystalline NKN film is grown along the [001] direction on the SNO/Pt-Si (or SNO/Pt-PI) substrate. Due to the presence of oxygen vacancies in the SNO seed-layer, the NKN film exhibits low ferroelectric properties and large leakage current. To ameliorate these properties, the SNO/Pt-Si substrate is annealed in a 50 Torr oxygen atmosphere at 300 ℃, which removes the oxygen vacancies. Consequently, the NKN film deposited on this substrate exhibits promising electrical properties, namely a dielectric constant of 278, dissipation factor of 1.7%, a piezoelectric constant of 175 pm·V^-1, and a leakage current density of 6.47 × 10^-7 A·cm^-2 at -0.2 MV·cm^-1. Similar electrical properties are obtained from the NKN film grown on the flexible SNO/Pt-PI substrate at 350 ℃. Hence, the NKN films grown on the SNO seed-layer at 350 ℃ can be applied to electronic devices with flexible polymer substrates.