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.