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 m icrostructures can lead to severe problems especially in the case of g old ball bonds. The required ultrasonic power for gold ball bonds is h igher than for aluminium wedge bonds due to the harder gold wire. We f ind that high ultrasonic power can degrade or even destroy YBa2Cu3O7 m icrostructures, such as microbridges, Josephson junctions and supercon ducting 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 signific antly, leaving the microstructures intact. We investigate the influenc e of the ultrasonic power, bonding time and bonding force on the prope rties of the resulting bond contacts.