Metal electrodes on high-Tc superconductors

Four types of electrode formation techniques on high Tc superconductors (YBCO) are reported and compared. These techniques are spot welding, ultrasonic soldering, thin film deposition and ultrasonic bonding methods. Spot welding changes the crystal structure of the YBCO surface and gives a nonohmic semiconductive contact. Ultrasonic soldering can form an ohmic contact but its contact resistivity is large. Thin film deposition gives two kinds of contacts according to the metal materials. One group which includes Cu, Sn and In shows nonohmic and semiconductive properties. The other which includes Au, Ag and Pt shows ohmic and metallic properties. The interface between metal and YBCO surface has been analyzed and discussed. Ultrasonic bonding gives us the lowest contact resistivity. Its V-I characteristics show a nonlinearity which is related to the superconductivity of the YBCO below the superconducting transition temperature. The reason for this characteristic is also discussed. The magneto-sensor using the effect of magnetic field on the nonlinear V-I characteristics is proposed. (orig.)