ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The bolometric nature of the optical sensitivity of YBCO (YBa2Cu3O7−δ) thin-film microstrips in the superconducting state is demonstrated. Below the critical temperature Tc the critical current temperature dependence of the device provides a suitable temperature sensor. A theoretical thermal model that gives reliable forecasts for the sensor time constant and sensitivity over the 10–90 K temperature range has been developed. Sensitivity measurements on high-quality YBCO films deposited on MgO are in quite good agreement with the model, showing that the observed signals are entirely bolometric. The effective heat capacity of the sensor is that of the film in the irradiated area. Owing to the high thermal conductivity of MgO, the substrate stays at the heat sink temperature and the main resistance to heat flow is the film/substrate interface. The heat capacity of the irradiated area of the film, strongly coupled to the heat sink through the thermal boundary resistance gives high-speed bolometers behaving as first-order systems. For SrTiO3 or ZrO2 substrates, their lower thermal conductivity would lead to higher time constants and more complicated behaviors. The precise origin of the measured sensor noise has still to be established. On a 0.2×10×15 μm3 microbridge at 85 K (below the critical temperature), a noise equivalent power of 120 pW/(square root of)Hz and a time constant τ of 20 ns were measured; this corresponds to a noise equivalent temperature of 60 nK/(square root of)Hz and a specific detectivity D* of 1.8×106 cm (square root of)Hz/W. A more relevant criterion for comparing optical sensors is the D*/(square root of)τ ratio. In the case presented, this ratio is equal to 1.3×1011 cm/J which is one of the best values published at this time. Such performances should give competitive composite or antenna coupled bolometers compared to existing sensors for wavelengths greater than 20 μm.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.357390
Permalink
