Low resistance metal contacts to TlBaCaCuO thin films

Stable low resistance contacts to TlBaCaCuO (2212) films using single layer and trilayer metal contacts were fabricated ex-situ. For single layer contacts, Au contacts were evaporated on either large (unpatterned) or small (patterned) contact pads through a shadow mask or a photoresist mask. Prior to the metal deposition, the air exposed films were cleaned by oxygen plasma. Rapid Thermal Annealing (RTA) was performed on single layer contact samples at 450-600/spl deg/C for 30 seconds. The contact resistivities of the samples were measured using a cryogenic Kelvin probe at 78 K and 300 K. The large contacts showed the best contact resistivity of 1.4/spl times/10/sup -8/ /spl Omega/cm/sup 2/ at 78 K, which is the lowest value ever reported for ex-situ contacts. The films were patterned using chemical etching or ion implantation with a minimum line width of 2 /spl mu/m. Contact resistivity of 1.5/spl times/10/sup -8/ /spl Omega/cm/sup 2/ at 78 K for the small contacts was obtained. Au/Ni/Au (3000/2000/3000 /spl Aring/) trilayer contacts were made by RF sputtering. The contact resistivities of trilayer metal contacts were measured and showed the lowest value of 7.4/spl times/10/sup -7/ /spl Omega/cm/sup 2/ at 78 K. Such low resistance contacts allow a supercurrent of 200 mA or a current density of 3/spl times/10/sup 5/ A/cm/sup 2/ to cross the metal-HTS film interface without dissipating electric power. We have also showed that the contact resistivity values remain the same after several thermal cycling processes.