The content of the following thesis involves the creation and study of multiferroic tunnel structures. Together with a deep investigation and optimization of the individual processes, emphasize will be put on the importance of interface-phenomena that will be discussed in detail. The experimental results include electric transport measurements, characterization methods with synchrotron radiation and several microscopic approaches. In particular the development of a new description for the model of tunnel electroresistance will be presented. In this case, a tunnel structure based on lead titanate will give many insights in the physics of resistive tunneling phenomena that might occur mainly at the interfaces. Temperature and magnetic field dependent measurements enable insights into the nature of a spin filter junction with four resistive states that are addressable via the application of magnetic and electric fields.