Nov 30, 2012
Phenomenological model uses CAFM to characterize tunnel-junction-like devices
Researchers have used conductive atomic force microscopy (CAFM) to develop a phenomenological model for studying the topographical and electrical characteristics of conducting/insulator bilayers. The model allows critical parameters to be obtained for the development of tunnel-junction-like devices (which include magnetic tunnel junctions, spin filters or even superconducting Josephson junctions). Such parameters include the energy barrier, the attenuation length of charge carriers and the critical barrier thickness required to totally cover the electrodes.
In the study, the proposed method was used to analyse the electrical transport through ultra-thin SrTiO3 layers grown over YBa2Cu3O7 electrodes. This work contributes in a direct way to optimizing the growth of insulating barriers over high Tc superconductor electrodes, which helps to improve the performance of high critical temperature devices.
Using the approach, which was based on the theoretical Simmons model, the group found that the tunnelling of the carriers seems to be the main mechanism for the electrical transport in these systems. In general, a SrTiO3 barrier thickness of at least 1.6 nm (4 u.c.) is required to obtain a good insulation of the YBa2Cu3O7 electrode for small areas. The SrTiO3 layers present an energy barrier of 0.9 eV with an attenuation length of 0.23 nm, indicating their good insulating properties.
Controlled pulsed laser deposition allows high-quality ultra-thin STO layers to be grown over high Tc superconducting electrodes, with very good control of the barrier thickness for the fabrication of Josephson junctions.
Full details can be found in the journal Nanotechnology.
About the author
The study was conducted by research teams from the Instituto Balseiro and Centro Atómico Bariloche, Bariloche, Argentina; Centro Atómico Constituyentes, Buenos Aires, Argentina; Universidad de Concepción, Concepción, Chile; UMP-CNRS/THALES, Université Paris Sud 11, France, LPEM, UMR/CNRS, ESPCI ParisTech, France; and LPN-CNRS, Marcoussis, France. The scientists are focused on the fabrication of micro- and nanostructured tunnel junctions. Luis Avilés Félix is a PhD student in physics at the Instituto Balseiro and Centro Atómico Bariloche, Bariloche, Argentina, under the supervision of Martin Sirena, PhD. He is developing micro- and nano-templates for the fabrication of tunnel junction devices. L Agüero, J González and S Pons are undergraduate students at the Universidad de Concepción, Chile. L B Steren, PhD, is a researcher at the Centro Atómico Constituyentes, Argentina. Rozzen Bernard, Juan Trastoy and Javier Villegas are working in the High Tc Superconductors and Signal processing group headed by Javier Briático, which developed the growth of the samples. Nicolas Bergeal and Jérôme Lesueur are researchers at the LPEM/ESPCI, France and G Faini is a researcher at the LPN Marcoussis France. The teams are members of an international collaboration project in the framework of the ECOS Argentine/France co-operation program.