Al/Au and Cu/Au bilayer‐metal contacts to YBa2Cu3O7−x thin films

Electrical contact resistivities of both Al and Cu single layer contacts as well as Cu/Au and Al/Au bilayer metal contacts to YBa2Cu3O7−x (YBCO) thin film have been studied. It was found that aluminum and copper make poor electrical contacts to YBCO due to interface reactions. These contacts have large contact resistivity (10−1–1 Ω cm2), orders of magnitude higher than that of a gold/YBCO contact (10−6 Ω cm2). When an ultrathin Au interlayer (10–30 A) was inserted between an Al or Cu overlayer and a YBCO film, interface reaction was greatly reduced. The contact resistivities of Al/Au and Cu/Au bilayer‐metal contacts dropped by five orders of magnitude when Au interlayer thickness was increased from 0 to 10 A. With the gold interlayer thickness of 15 A, the Al/Au and Cu/Au bilayer‐metal contacts reached a minimum contact resistivity, approaching that of a thick single‐layer Au metal contact.