We have prepared single crystalline epitaxial PbZr_0.52Ti_0.48O₃ (PZT) thin films on single crystalline epitaxial SrRuO₃ (SRO) thin films grown on SrTi0₃ (100) (STO) substrates. PZT and SRO thin films were grown using high-pressure on-axis sputtering. The film thickness ranged between 12 to 165 rim. Their excellent structural properties, surface smoothness and interface sharpness were demonstrated by XRay Diffraction measurements (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Rutherford Backscattering Spectrometry and Channeling measurements (RBS/C) were used to analyze stoichiometry and crystalline quality. Ferroelectric hysteresis loops were obtained for all films of a thickness down to 12 rim showing an increase in the coercive field E, towards thinner film thickness. The decrease in the remanent polarization Pr, however, was found to depend on the patterning method. Furthermore tunnel junctions with a PZT barrier thickness of 3-6 nm have been prepared. Reproducible bi-stable I-V-curves and bias dependence of the conductance were obtained suggesting an influence of the ferroelectric properties of the barrier material on the tunnel current.