Improved aqueous etchant for high T c superconductor materials

We have developed an aqueous etchant suitable for producing feature sizes of 1 μm or less in YBa2Cu3O7 and TlBaCaCuO while not degrading high-frequency surface resistance. The 10%–300% increase in surface resistance previously seen in aqueous solutions is largely due to the presence of dissolved CO2; decarbonation of the water by bubbling N2 before and during etching can produce a better than 50% reduction in the surface-resistance degradation. Surface-resistance degradation can be further reduced by selecting the appropriate solution pH for ethylenediaminetetraacetic acid (EDTA)-based etchants. We have minimized increases in surface resistance to less than 5% following etching in decarbonated disodium EDTA solutions for both YBa2Cu3O7 and TlBaCaCuO superconductors. Similar improvements can be expected from decarbonation and pH control of other aqueous processing solutions.