Thermal boundary resistance of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ multilayer strip

The present work deals with measurements of the thermal resistance at the boundary between a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(YBCO) thin film and its substrate. Above the film's critical temperature (T/sub c/) the YBCO strips were heated by Joule effect. We used a method based on the third harmonic generation of the voltage across the strips. At high frequency of the heating current, the deduced thermal resistance is dominated by the boundary effect. We used that method to evaluate the possible enhancement of the thermal insulation between the upper layer (YBCO thicker film) and the MgO substrate when ten 2/spl times/8 nm thick YBCO/STO bi-layers are deposited between them. The strips were 600 /spl mu/m long and 40 /spl mu/m wide. The thermal resistance was measured at various frequencies and temperatures above T/sub c/, both for a single layer taken as a reference sample and for a multilayer sample. Below T/sub c/, we used optical heating of the strips to evaluate the insulation effect obtained with multilayered sample. The ratio of thermal conductances was close to 11, thus demonstrating the insulation enhancement obtained with the multilayered structure. The effect could lead to antenna-coupled microbolometers with improved performances.