Improved aqueous etchant for high T c superconductor materials

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Abstract
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.