The way of patterning of Tl-based superconducting thin films
The aim of the work was to find fast and effective way for the patterning of the thin superconducting films based on thallium using wet etching. So far, some bi- and tri-carboxylic acids as succinic, oxalic, malonic, citric, adipic or tartaric acid were used successfully for the wet etching of the thin superconducting Tl- based films. However, the etching rate is very low (0.3 – 0.6 nm / s). Ethylenediaminetetraacetic acid (H4EDTA) and its sodium salts can be used too with etching rate about 1 nm / s, but it is necessary to maintain the pH of the solution and nitrogen bubbling during etching process. The main drawbacks of these methods consist in forming a low etching rate and selective etching. The above mentioned problems can be solved by the use of etchant based on potassium iodide. The invention is used for the preparation of thin film structures of superconductors based on Tl using photolithography and wet etching. An aqueous potassium iodide solution, hydrochloric acid, and ascorbic acid is used as an etchant. The etching process is fast enough (about 15 nm / s), do not remain residues on the surface of the substrate, and there is no degradation of the superconducting properties.
SEM images of Tl-based superconducting structure prepared by photolitography and wet etching using KI based etchting solution.
The results obtained are the subject of patent application no. PP 5030-2013, entitled The way of patterning of thin superconducting films based on thallium.
Sojková, M., Štrbik, V., Španková, M., and Chromik, Š.: Patterning of Tl-based superconducting films using new etching solution. Applied Surface Sci 312 (2014) 208-211.