Dean Willett Face

5 GHz high-temperature-superconductor resonators with high Q and low power dependence up to 90 K

The authors have fabricated high-temperature superconducting films made of TlBaCaCuO (2212) and YBaCuO

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>>

In situ growth and properties of epitaxial TlBa/sub 2/CaCu/sub 2/O/sub 7/ and TlBa/sub 2/(Ca/sub 1-x/Y/sub x/)Cu/sub 2/O/sub 7/ thin films

Epitaxial TlBa/sub 2/CaCu/sub 2/O/sub 7/ thin films have been grown on single-crystal LaAlO/sub 3/, NdGaO/sub 3/, and CeO/sub 2/ buffered sapphire substrates by in situ off-axis magnetron sputtering in the presence of Tl/sub 2/O vapor. Phase formation in this system has been investigated for substrate temperatures from 490 degrees C to 600 degrees C and deposition pressures from 50 mTorr to 300 mTorr. The effect of Tl/sub 2/O evaporation rate has also been studied. X-ray diffraction shows that films deposited under optimum conditions are highly epitaxial with the c-axis perpendicular to the substrate surface and

High T/sub c/ superconducting coplanar delay line with long delay and low insertion loss

Coplanar delay lines have been fabricated from TlBaCuCuO (2212) and YBaCuO

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.

Superconducting and normal metal multilayers of thallium-lead cuprates

We report the growth of c-axis oriented, epitaxial thin films of (Tl,Pb)Sr/sub 2/CuO/sub 5/ on (100) oriented LaAlO/sub 3/ substrates by off-axis sputter deposition in the presence of thallium oxide vapor. These films display a resistivity which crosses over from metallic to semiconducting behavior at low temperature. In addition, we have shown that multiple layers of superconducting (Tl,Pb)Sr/sub 2/Ca/sub 0.8/Y/sub 0.2/Cu/sub 2/O/sub 7/ (1212) and nonsuperconducting (Tl,Pb)Sr/sub 2/CuO/sub 5/ (1201) can be deposited sequentially without compromise of the superconducting properties of the 1212 layer. Bilayers of both 1212 on 1201 and of 1201 on 1212 have been fabricated. In either case, both materials grow with their c-axis normal to the substrate surface and with their a-axes aligned to each other and to the major axes of the substrate. Technologically interesting trilayer structures of 1212/1201/1212 have also been fabricated. Both 1212 layers are superconducting with transition temperatures of up to 94 and 93 K for the upper and lower layers respectively. We believe that this is an important step towards the development of thallium cuprate-based multilayer technology.<<ETX>>

Single electron tunneling in TlBa2(Ca0.8Y0.2)Cu2O7 thin films at 10K

Tunneling measurements on TlBa2(Ca0.8Y0.2)Cu2O7 taken at low temperatures with a scanning tunneling microscope reveal clear evidence of single electron tunneling behavior. Topographical studies of the film with both scanning tunneling microscopy and atomic force microscopy provide a simple explanation of the source of the ultra small capacitors necessary to explain the single electron tunneling spectra as a natural result of the planar crystal structure of TlBa2(Ca0.8Y0.2)Cu2O7.

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.