Voltage-biased superconducting transition-edge bolometer with strong electrothermal feedback operated at 370 mK

Abstract

We present an experimental study of a composite voltage-biased superconducting bolometer ͑VSB͒. The tested VSB consists of a Ti-film superconducting thermometer ͑T c ϳ 375 mK͒ on a Si substrate suspended by NbTi superconducting leads. A resistor attached to the substrate provides calibrated heat input into the bolometer. The current through the bolometer is measured with a superconducting quantum interference device ammeter. Strong negative electrothermal feedback fixes the bolometer temperature at T c and reduces the measured response time from 2.6 s to 13 ms. As predicted, the measured current responsivity of the bolometer is equal to the inverse of the bias voltage. A noise equivalent power of 5 ϫ 10 Ϫ17 W͌͞Hz was measured for a thermal conductance G ϳ 4.7 ϫ 10 Ϫ10 W͞K, which is consistent with the expected thermal noise. Excess noise was observed for bias conditions for which the electrothermal feedback strength was close to maximum.

THz radiation sensors

“…For intermediate values of P, the electrothermal feed− back keeps the total power input P + V 2 /R and, thus, the tem− perature as constant. For a thermal circuit with a single pole response, the current responsivity is [7,156] …”

Future Developments in Low Temperature Detectors for CMB and Submm Astronomy

“…Absorber-coupled transition-edge sensors (TESs) [27,28,29] have demonstrated background-limited performance for ground-based imaging in the APEX-SZ [30], SPT, and ACT [31] receivers. The first two employ spiderweb designs by the Berkeley group while the latter uses GSFC-manufactured pop-up absorbers with TESs [32].…”

Superconducting detectors and mixers for millimeter and submillimeter astrophysics

“…The response of the bolometer current to a change in the optical power is called the current responsivity . For a thermal circuit with a single pole response [82] ( 1) where is the loop gain, is a measure of the steepness of the superconducting transition, is the differential thermal conductance and is the effective time constant. For a typical loop gain 10 , the low-frequency responsivity becomes , and depends only on the bias voltage and is independent of the signal power and the heat sink temperature.…”

“…The current noise of the bolometer with no optical input can be written as a quadrature sum of contributions from thermal fluctuation noise, Johnson noise, and SQUID noise referred to the SQUID input [82]. At frequencies below , thermal fluctuation noise usually dominates.…”