Thermosonic bond contacts with gold wire to YBa2Cu3O7 microstructures

A reliable method for making contacts to YBa2Cu3O7 microstructures is ultrasonic bonding. However, the application of bonding to YBa2Cu3O7 microstructures can lead to severe problems especially in the case of gold ball bonds. The required ultrasonic power for gold ball bonds is higher than for aluminium wedge bonds due to the harder gold wire. We find that high ultrasonic power can degrade or even destroy YBa2Cu3O7 microstructures, such as microbridges, Josephson junctions and superconducting interference devices (DC SQUIDS). This problem can be overcome by using thermosonic bonding at a sample temperature of 150 degrees C. With heating the necessary ultrasonic energy can be reduced significantly, leaving the microstructures intact. We investigate the influence of the ultrasonic power, bonding time and bonding force on the properties of the resulting bond contacts. (author)