Critical current density and resistivity measurements for long patterned lines in Tl2Ba2CaCu2O8 thin films

Abstract

Epitaxial Tl₂Ba₂CaCu₂O₈ films of thickness 0.65±0.05 μm and T_c of 105±1 K were prepared on (100) LaAlO₃ through a two‐step post‐deposition thallination process and patterned by standard photolithographic techniques and ion beam milling. Using the voltage per unit length criteria E_c=1.0 μV/cm, transport critical current density J_c in zero applied field for a 1.8‐m‐long, 12±1‐μm‐wide meander line separated by 8±1 μm spaces was measured to be 1.04×10⁷ A/cm² at 20 K, 1.82×10⁶ A/cm² at 80 K, and 1.02×10⁵ A/cm² at 100 K. The uniformity in J_c was measured for eight line segments of about 11.7 cm length, yielding variations in J_c of 1.44–3.02×10⁶ A/cm² at 80 K. J_c values independent of linewidth were also measured for three 0.7‐cm‐long lines with widths of 7, 27, and 52 μm. For design of electronic circuits, resistivity may be a more useful design parameter than J_c, and detailed measurements of resistivity ρ as a function of current density J were carried out. At low temperatures (T/T_cJ, and J_c is well defined. At high temperatures (T/T_c≳0.7), ρ is less strongly dependent on J near J_c. At 90 K, where J_c=7.6×10⁵ A/cm², ρ remained less than 10⁻¹⁰ Ω cm (3000× less than oxygen free high conductivity copper at 90 K) even for J=1.4×10⁶ A/cm². The results suggest the potential for the use of patterned Tl₂Ba₂CaCu₂O₈ films in high J_c electronic applications such as chip‐to‐chip interconnects operating at temperatures below 90 K.