Electrical transport across nanometric SrTiO₃and BaTiO₃barriers in conducting/insulator/conducting junctions

Abstract

We report the electrical transport properties of conducting / insulator / conducting heterostructures by studying current -voltage IV curves at room temperature. The measurements were obtained on tunnel junctions with different areas (900 µm 2 , 400 µm 2 and 100µm 2 ) using a conducting atomic force microscope. Trilayers with GdBa 2 Cu 3 O 7 (GBCO) as the bottom electrode, SrTiO 3 or BaTiO 3 (thicknesses between 1.6 nm and 4 nm) as the insulator barrier, and GBCO or Nb as the top electrode were grown by DC sputtering on (100) SrTiO 3 substrates For SrTiO 3 and BaTiO 3 barriers, asymmetric IV curves at positive and negative polarization can be obtained using electrodes with different work function. In addition, hysteretic IV curves are obtained for BaTiO 3 barriers, which can be ascribed to a combined effect of the FE reversal switching polarization and an oxygen vacancy migration. For GBCO/ BaTiO 3 / GBCO heterostructures, the IV curves correspond to that expected for asymmetric interfaces, which indicates that the disorder affects differently the properties at the bottom and top interfaces. Our results show the role of the interface disorder on the electrical transport of conducting/ insulator/ conduction heterostructures, which is relevant for different applications, going from resistive switching memories (at room temperature) to Josephson junctions (at low temperatures).

Improving the Josephson energy in high-Tc superconducting junctions for ultra-fast electronics

“…STO is a cubic perovskite with a=0.3905 nm. The crystalline structure of GBCO/STO/GBCO trilayers was previously discussed in [26]. In our research, the GBCO thickness of 16 nm was selected by considering a trade-off between T c and the presence of smooth surfaces [22,26].…”

“…The crystalline structure of GBCO/STO/GBCO trilayers was previously discussed in [26]. In our research, the GBCO thickness of 16 nm was selected by considering a trade-off between T c and the presence of smooth surfaces [22,26]. The low surface roughness of the electrodes is critical to be able to fabricate JJ with ultra-thin insulating barriers (i.e.…”

“…The STO surface displays steps which are mainly originated by the roughness of the bottom GBCO electrode (typical 1 unit cell ∼1.2 nm) [22]. The barrier thickness displays typical fluctuations of around 1 STO unit cell [26]. In addition to the thickness fluctuations, the properties of the junctions may be affected by the stacking order at the interfaces, oxygen vacancies and by crystalline defects [27,28].…”

Josephson coupling in high-Tc superconducting junctions using ultra-thin BaTiO3 barriers

“…The roughness in the films increases adding the BTO and GBCO capping layers. The GBCO / BTO bilayers show a surface topology with uniform terraces and some 3D defects mainly originated in defects coming from the bottom electrode [31,32]. The borders of 3D defect usually display higher electrical conductivity than terraces increasing the inhomogeneity in the properties of barrier [30,31].…”

“…The electrical conductivity across the barrier decreases as the thickness increases. IV curves performed at room temperature show that tunneling and oxygen vacancy migration (OVM) contribute to the conductivity in BTO barriers [32]. The latter suppresses as the temperature reduces [33].…”