Brook Lakew

Etching of

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.

{\rm MgB}_{2}

Noise was studied in an MgB2 thin film grown on a SiN substrate, with a superconducting transition temperature, Tc, near 39K. At the mid-point of the transition and at 10Hz a noise spectral density Sv = 0.34nVHz1/2 was measured. The temperature noise, Kn , of the MgB2 film at different frequencies is compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used currently in transition-edge devices. Kn values predict that 2-D arrays of high performance infrared devices can be developed using MgB2.

Thin Films for Transition Edge Superconducting Bolometer Fabrication

An MgB2 thin film was grown on a SiN-Si substrate, with a superconducting transition temperature, Tc, near 39K. At the mid-point of the transition (T= 38.24K) and at 10Hz a noise spectral density SV = 0.34nV/ √Hz was measured. The temperature noise, Kn, of the MgB2 film at different frequencies is compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used currently in transition-edge bolometers. Κn values predict that high performance far-IR thermal detectors (i.e bolometers) can be developed using MgB2 as a thermistor.

Noise in superconducting MgB2 thin film

The performance of a high Tc (~90 K) transition-edge superconducting (TES) bolometer on a monolithic sapphire membrane is presented and discussed. It is compared to the performance of a previous TES bolometer on non-monolithic sapphire substrate. The development and optimization of monolithic sapphire membranes is critical for the fabrication of 1 and 2-D arrays of TES bolometers. Moderately cooled and optimized TES bolometers are expected to be the replacements of choice for thermopiles and other room temperature thermal sensors on far IR instruments on future planetary missions.