Low noise high-Tc superconducting bolometers on silicon nitride membranes for far-infrared detection

Abstract

High-T c GdBa 2 Cu 3 O 7Ϫ␦ superconductor bolometers with operation temperatures near 89 K, large receiving areas of 0.95 mm 2 and very high detectivity have been made. The bolometers are supported by 0.62 m thick silicon nitride membranes. A specially developed silicon-on-nitride layer was used to enable the epitaxial growth of the high-T c superconductor. Using a gold black absorption layer an absorption efficiency for wavelengths between 70 and 200 m of about 83% has been established. The noise of the best devices is fully dominated by the intrinsic phonon noise of the thermal conductance G, and not by the 1/f noise of the superconducting film. The temperature dependence of the noise and the resulting optimum bias temperature have been investigated. In the analysis the often neglected effect of electrothermal feedback has been taken into account. The minimum electrical noise equivalent power ͑NEP͒ of a bolometer with a time constant of 95 ms is 2.9 pW/Hz 1/2 which corresponds with an electrical detectivity D* of 3.4ϫ10 10 cm Hz 1/2 /W. Similar bolometers with ϭ27 ms and NEPϭ3.8 pW/Hz 1/2 were also made. No degradation of the bolometers could be observed after vibration tests, thermal cycling and half a year storage. Measurements of the noise of a Pr doped YBa 2 Cu 3 O 7Ϫ␦ film with T c ϭ40 K show that with such films the performance of air bridge type high-T c bolometers could be improved.

Effect of Substrate Thickness on Responsivity of Free-Membrane Bolometric Detectors

“…5, the normalized frequency-dependent response of the bolometer versus the substrate thickness is depicted for the modulation frequencies of 1, 4, 10, and 50 Hz. For this calculation, the total thermal conductance of the sample is taken to be approximately 10-50 WK [21], [22]. The responsivity is normalized to its value at low thicknesses to show its trend when the thickness is changed.…”

1/f Noise in the superconducting transition of a MgB2 thin film

“…The electrical resistance change modifies the Joule heating, P bias = I bias V [W], giving rise to an Electro-Thermal Feedback (ETF) [5][6][7] into the bolometer that produces an effective thermal conductance G e ¼ Gð1 À L 0 Þ [W/K] and an effective time…”

MgB/sub 2/ superconducting films for bolometer applications

“…In the last years, HTS bolometers with high performance have been realized but the fabrication of high quality HTS films on Si and SiN requires deposition of one or more buffer layers to lattice matching and to avoid diffusion. Moreover, the noise in HTS bolometers is limited by the noise in epitaxial film too [2].…”