Low-temperature electrical characteristics of nanocrystalline BaTiO3 thin films for cryogenic applications

Abstract

Ferroelectric thin films are vital in a large number of applications due to their promising properties. Although ferroelectric films' electrical response is studied at high temperatures, their low-temperature behavior is not well understood. In the present study, the εr-V and I-V characteristics of BaTiO3 (BTO) thin films are explored at cryogenic temperatures. BTO thin films have systematically deposited different Ar/O2 ratios by RF sputtering and investigated their structural, microstructural, optical, and electrical properties. The microstructures of these films are well-packed with uniform grain growth and revealed lower rms roughness. The thickness of the films (~170 nm) is obtained by cross-sectional scanning electron microscope images and transmittance spectra. There is not much variation in the optical bandgap, which shows the full stoichiometry and similar thickness of the films. The εr-V response of the film measured at 387 K shows the asymmetry in dielectric constant maxima value. It signifies that there are movable ions and charge accumulation at the interface of film and electrodes. The dielectric response obtained as a temperature function exhibited a Tc of 387 K, indicating the phase transition from ferroelectric tetragonal phase to paraelectric cubic phase. The I-V characteristics of the film measured at 300 K revealed the leakage current of 10−6 Amp, whereas, at 43 K, it is 8.83 × 10−10 Amp. The slope of the I-V curve of the film measured between 1 and 5 V displayed the Ohmic nature. The slope of the film obtained at 6–10 V indicated the space charge limited conduction mechanism, which corresponds to discrete trap carriers. Therefore, trap carriers assisted discrete conduction mechanism is one of the leading factors controlling the conduction process in BTO oxide thin films. The acquired electrical response of the BTO films deposited at 50 Ar is promising for cryogenic devices.