Characterisation of microwave non-linear effects inmultilayer structures of YBa2Cu3O7 / SrTiO3 / LaAlO3

摘要

The strontium titanate SrTiO3 in its para-electric phase isassociated to the superconducting material YBa2Cu3O7 to obtain agilepassive components for microwave applications: filters, oscillators, phaseshifters. The limitation of these devices is the value of the dielectric lossin the SrTiO3 thin films (<500nm) which is one order of magnitude higherthan the one measured in bulk single crystal (tgδ10-4). Nevertheless aquality factor of 1000 and 10 % of agility can be obtained. Anotheressential parameter for the end-users is the level of the non-linear effectsin the device. These effects are due to the materials (SrTiO3 andYBa2Cu3O7) and their origin can be related to the intrinsic properties or tothe extrinsic issues as crystal defects generated during the growth, stressesand strains from technological processes. In this paper, we attempt toseparate the various contributions by optimising the parameters oftechnological steps. The device under test is a resonator consisting in twointerdigitated combs patterned in the superconducting film. We determinethe characteristics of the material SrTiO3 (εr, tgδ) by measuring theresonant frequency and the quality factor. When the microwave power inthe resonator is increased, a broadening, a tilting and a frequency shift ofthe resonant line are observed. To separate the contributions from thesematerials, two different type of samples were used : YBa2Cu3O7 / LaAlO3resonators patterned by ion milling for studying the influence of theresonator line edges and YBa2Cu3O7 / SrTiO3 / LaAlO3 multilayerresonators elaborated by chemical etching for studying the influence ofSrTiO3, under a DC electric bias.