Effect of annealing atmosphere pO2 on leakage current in 80(Bi0.5Na0.5)TiO3-20(Bi0.5K0.5)TiO3 piezoelectric thin films

Abstract

Ferroelectric 80(Bi0.5Na0.5)TiO3–20(Bi0.5K0.5)TiO3 thin films were fabricated by chemical solution deposition on Pt/TiO2/SiO2/Si substrates. Films were post-annealed after crystallization at four different oxygen partial pressures (pO2): O2, air, N2, and H2/N2, given by order of decreasing pO2. In general, post-annealing in more oxidizing atmospheres will decrease the concentration of positive charged oxygen vacancies, thus either increasing the number of electron holes or decreasing the number of electrons. In principle, this allows for the determination of the majority electronic carrier type by studying the conductivity of the films. The DC conductivity was measured as a function of electric field, and the results were found to be consistent with n-type conduction. Also, while the leakage current is generally space charge-limited, there are several key features of the current density-electric field characteristics which were affected by the post-anneal pO2. For instance, while remaining space charge is limited, the characteristics show that the trap energy distribution changes with the post-annealing treatment. The H2/N2 post-annealed films showed a reduction in the dielectric constant and ferroelectric polarization relative to the O2 post-annealed films.