Dennis J. Kountz

High performance superconducting thin films on large area substrates

The first fabrication of 3-in-diameter, thin films of thallium-based superconductors is reported. (Tl/sub 0.5/Pb/sub 0.5/)Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9/ thin films on LaAlO/sub 3/ are found to display the best surface resistance (R/sub s/) properties of any superconductor at higher temperatures and show approximately 50* better performance than copper at 100 K and 10 GHz. A Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin film, processed as a 1.8-m-long, 10- mu m-wide meander line carries about 1*10/sup 7/ A/cm/sup 2/ at 4.2 K and 2*10/sup 6/ A/cm/sup 2/ at 80 K. The thallium-based superconductors are compared to YBa/sub 2/Cu/sub 3/O/sub 7/ with respect to T/sub c/, R/sub s/, and Q.<<ETX>>

Microstructural and electronic properties of highly oriented Tl/sub 0.5/Pb/sub 0.5/Sr/sub 2/Cu/sub 2/O/sub 7/ films on LaAlO/sub 3/

Epitaxial Tl/sub 0.5/Pb/sub 0.5/Sr/sub 2/CaCu/sub 2/O/sub 7/ films produced by RF magnetron sputtering followed by annealing in the presence of thallium oxide vapor have been produced on

Power Handling Capability of Large Area HTS Thin Films at Microwave Frequencies

Measurements of the surface resistance Rs of Tl2Ba2CaCu2O8, (Tl,Pb)Sr2CaCu2O7, and YBa2Cu3O7 thin films prepared on 5 cm (2 inch) diameter LaAlO3 substrates show that these films maintain low surface resistance at microwave frequencies even while carrying high power. A 5.55 GHz TE011 mode resonator has been designed for measurement of Rs at high power. Superconductor films are placed on both sides of a sapphire cylinder and microwave power is coupled into and out of the resonator. The Q-value and S-parameters are measured, from which Rs is calculated. By controlling the temperature and changing the input power, Rs can be determined as a function of both temperature and maximum rf magnetic field amplitude Hmax. For Tl2Ba2CaCu2O8 films at 4.2 K and Hmax = 85 Oe, Rs at 5.55 GHz was 72µΩ YBa2Cu3O7 and (Tl,Pb)Sr2CaCu2O7 films exhibited similarly low Rs at 4.2 K for maximum magnetic fields up to about 20 Oe. At 90 K, the surface resistance for the Tl2Ba2CaCu2O8 films remained below 100µΩ for maximum magnetic fields up to 6 Oe. The results demonstrate the potential for superconducting films for use in high power applications at microwave frequencies.

A Materials System Approach to Optimum Performance in High Temperature Superconducting Thin Films

Leading microwave performance data are reported for epitaxial YBa2Cu3O7, Tl2Ba2CaCu2O8, Tl2Ba2Ca2Cu3O10, Tl0.5.Pb0.5Sr2CaCu2O7, and Tl0.5Pb0.5Sr2Ca2Cu3O9 high temperature superconducting compositions on a variety of substrates. An in situ process for thallium superconductors is reported. No deterioration in superconductor performance was encountered during subsequent photolithography and metallization processing. A 1.8 meter long patterned meander line with 10 μm lines and spaces demonstrated a critical current of 2 x 106 amp/cm2 at 80 K. Contact resistivity between superconductor and silver pads was below the detection limit of 0.1 x 10-8 Ω-cm2 at 77 K.