Etching of ${\rm MgB}_{2}$ Thin Films for Transition Edge Superconducting Bolometer Fabrication

Membrane-structured superconducting MgB₂ thin films are potential candidates for the development of moderately cooled bolometers sensitive to far infra-red radiation. On the path to developing such devices, we present a comparison of three etching techniques for MgB₂ thin films namely, chlorine plasma etch, aqueous hydrochloric acid etch and an aqueous nitric acid etch. Out of the three etch techniques, the aqueous 50% nitric acid solution etch, using standard photolithography, proved to have a high MgB₂ etch rate (> 51 nm/s), with better sidewall delineation and selectivity to the underlying SiN-film-coated Si substrate, moreover the etched film structure showed good superconductivity transition characteristics, namely, a superconducting critical transition at 38.57 plusmn 0.6 K, a transition width of 0.09 K and a RRR of 2.22.