Studies on the high-temperature superconductor (HTS)/metal/polymer dielectric interconnect structure for packaging applications

A HTS/metal/low dielectric constant polymer dielectric hybrid interconnect structure was fabricated using high density interconnect (HDI) copper/polyimide processing techniques. Nondegraded superconducting properties, J_c of over 1 MAcm^-2 and T_c of 88 K, were obtained using optimum processing conditions. A 0.6 μm-thick YBCO film was coevaporated on LaAlO₃ substrate, annealed, patterned, and Au contact pads were deposited. A Kapton polyimide film was laminated on HTS parts in an oxygen environment. Using a siloxane polyimide (SPI) base adhesive at 170-210°C or a polyester base adhesive at 150°C vias were drilled on the polymer layer using a 351 nm Ar laser followed by subsequent via cleaning with O₂+CF₄ plasma. To complete test parts Ti/Cu/Ti metallization and patterning with a laser adaptive lithography were followed. It was found that the laminated polymer film on the HTS protected HTS film properties from heating and water exposure. The polyimide laminated HTS film maintains its superconductivity up to 210°C of lamination temperature. The hybrid structure also showed excellent reliability performances: 6% J_c decrease at 150°C/65 h thermal bake, 12% J_c decrease after 100 thermal cycles from -96 to 150°C, and maintain superconductivity in water immersion up to more than 10 h. T_c of samples remained always the same 88 K. Coplanar HTS lines, microstrip HTS/metal lines, and HTS power strip line structures were demonstrated on a 2-in-diameter HTS wafer coupon