Ionic and electronic defects in a‐BaTiO₃ thin films studied by transient and steady state conductivity measurements

Abstract

Conduction mechanisms in BaTiO 3 films deposited at low temperatures on Cu-electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J-E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 10 22 m -3 .1 Introduction Owing to their specific dielectric properties, barium titanate (BaTiO 3 ) thin films are promising materials for application in electronic devices [1]. However, their resistance degradation observed upon biasing constitutes a serious limitation for applications. Since this event is closely related to the charge transport mechanisms, conduction processes need to be studied in details in order to improve the reliability and the lifetime of these materials. Several reports have suggested the main effect of oxygen vacancies in resistance degradation and long-term failure [2][3][4][5]. In fact, when films were elaborated under neutral or reduced ambient, oxygen vacancies are present in the film [6] and introduce different contributions in the conduction process. In the transient regime, current response shows a peak preceding the resistance degradation. This behavior was reported earlier by Zafar [5] and then by Saha [7]. It was attributed to space charge limited transient currents related to oxygen vacancies. On the other hand, defects generated by the presence of oxygen vacancies can contribute to the leakage mechanisms in the steady regime. Many reports have been published on the electrical properties of (poly)crystalline barium titanate films, but very few on the properties of amorphous films (a-BaTiO 3 ). This is the main purpose of the present study.