Improvement of SrTiO/sub 3/ thin film surface polished by chemical mechanical planarization for HTS multilayer device

Abstract

In order to improve the superconducting and insulation properties of the HTS multilayer structure, .we have introduced Chemical Mechanical Planarization (CMP) into the fabrication process. While the surface roughness of the upper SrTiO,(STO) film due to the precipitates on the base YBa,Cu,O, (YBCO) film was decreased less than 1/10 by CMP and those of the edge angle of the patterned base films was reduced from 90 t o less than 1 degree, the as-polished surface crystallinity was amorphous as observed by RHEED. For improvement of the crystallinity, the surface was annealed to show pattern with clear streaky spots. The top YBCO stripline in the crossover structures had a T, of 89 K and J, of more than 1.0 X 1O6A/cm2 ,at 77 K. The insulation resistivity between two YBCO layers at 77 K was 7 X 1 0 8 Q c m .

Experimental investigations on super-smooth polishing of strontium titanate based ceramics substrates

“…X-ray diffraction pattern showed that the surface roughness reduced from Ra 52.1 nm to Ra 4.6 nm after experiencing chemical mechanical polishing. Takashima et al (1999) improved the superconductivity and insulation characteristic of all layers utilising the chemical mechanical polishing. The surface roughness of upper layer SrTiO 3 reduced to 10% of the original value and the deflection of the base film decreased from 90º to less than 1°.…”

Enhancement of high-TCsuperconducting thin film devices by nanoscale polishing

“…There have been different attempts to solve this problem; e.g. Takashima et al [6] used a polishing method, too. However, they polished the insulating film instead of the superconducting layer.…”

Noise properties of high-Tc superconducting flux transformers fabricated using chemical-mechanical polishing

“…14 The chemical-mechanical polishing (CMP) method was suggested for fabrication of high-T c multilayer structures as an alternative approach. 15,16 CMP has several benefits when compared to previous techniques. CMP does not require hazardous chemicals like Br-ethanol.…”

“…17,18 It has further been shown that edge slope angles of less than 1 can be obtained using CMP, meaning crossovers with very high critical current densities (2 Â 10 6 A/cm 2 ) are within reach. 15 Takashima et al fabricated a CMP-based multilayer YBa 2 Cu 3 O 7-x /SrTiO3/YBa 2 Cu 3 O 7-x (YBCO/STO/ YBCO) SQUID magnetometer, but their device was limited to a single-turn input coil. 19 CMP-processed multilayer high-T c superconducting flux transformers with multiturn coils have yet to be experimentally realized.…”