Oral: Structural and electrical characterization of ultra thin SrTiO3 tunnel barriers grown over YBa2Cu3O7 electrodes for the development of high Tc Josephson Junctions

M. SIRENA; L. AVILÉS FÉLIX; L. A. AGÜERO GUZMÁN; J. GONZÁLEZ SUTTER; S. PONS VARGAS; L. B. STEREN; R. BERNARD; J. BRIATICO; N. BERGEAL; J. LESUEUR; G. FAINI

Rodas

Conferencia; XI International Conference on Nanostructures Materials, Nano 2012; 2012

A superconductor-insulator-superconductor Josephson junction (JJ) is formed by two superconductor electrodes separated by a very thin insulating barrier of few atomic layers of thickness. If a constant voltage is applied on the junction, an alternating current with a frequency in the range of 1 to 1000 GHz will be generated in the system. This phenomenon has many technological applications, such as the fabrication of a volt standard, SQUIDs and other magnetic sensors, quantum computing (qubits), and the fabrication of ultra-fast superconducting microelectronics based on rapid single flux quantum logic. In the last years, conductive atomic force microscopy (CAFM) has become an important technique to study and characterize insulating barriers of tunnel junction devices, such as magnetic tunnel junctions  or spin filters. However, little work has been done that uses CAFM for the electrical characterization of JJ. In this work, we have studied by CAFM the transport properties of ultra thin SrTiO3 (STO) layers grown over YBa2Cu3O7 (YBCO) electrodes for the development of High Temperature JJ. A phenomenological approach was recently developed, that allows to obtain critical information for this system using CAFM, e.g. the barrier thickness required to totally cover the superconducting electrodes and the physical properties of the barrier (its thickness distribution, the attenuation length and the barrier?s energy). Moreover, the model allows to evaluate and consider in a simple way, the influence of the image forces and the dielectric constant of the barrier in the tunnelling properties in these systems. A very good control of the barrier thickness with a low roughness (~ 0.5 nm) of the STO layer was achieved during the deposition process. However, due to the growth mechanism of the superconducting layer, an important density of outgrowths was found on the surface of the samples. The STO layers present an energy barrier of 0.9 eV at 1.25 V and an attenuation length of 0.23 nm, indicating its good insulating properties for the development of Josephson junctions of high quality