Of Bst Pyroelectric Thin Film Leakage Current

Recently, there is a growing interest in the application of BST thin films, due to its high dielectric constant, low leakage current, and good pyroelectric properties. Therefore, it is not only an important but also a challenge work to study its leakage current behavior. In this dissertation, the BST (Ba_0.8Sr_0.2TiO₃) thin films on the Pt/Ti/SiO₂/Si substrate were prepared by RF sputtering, and the leakage current characteristics were systemically investigated. The mechanisms of leakage current and dielectric breakdown of BST thin films are explained based on the theoretic of electrical transport in solids.First of all, the mechanisms of leakage current of BST thin films are investigated by analyzing the J-V (current density-voltage) characteristics, J-t (current density-time) characteristics, J-T (current density-temperature) characteristics. It is found that, when V < V_Ω, the leakage current of BST thin films obeys ohm's law: J∝V, and the relationship between leakage current and temperature is: ln J∝-1/T; when V > V_Ω, the leakage current obeys space-charge-limited-current with exponential distribution traps: J∝V^m, the relationship between current and temperature is log J∝1/T.Secondly, based on the investigation result above, time-zero dielectric breakdown and time-dependent dielectric breakdown are studied. In the case of time-zero dielectric breakdown, a new stable state (incipient breakdown) is found, and the mechanism is explained. As for time dependent dielectric breakdown, the phenomenon of soft and hard breakdown in BST thin films are observed and defined, as well as the mechanisms of them are interpreted.Finally, several methods to calculate the microcosmic parameter of BST thin films are proposed. Trap density is calculated and found to depend on trap level energy in a power law relationship, which proves the correctness of the investigated leakage current mechanism and contributes to the succedent investigation of film fabrication.