Development of the characterization methods without electrothermal feedback for TES bolometers for CMB measurements

TL;DR

This paper introduces a new characterization method for TES bolometers used in CMB measurements that does not rely on electrothermal feedback, enabling more accurate assessment of thermal properties.

Contribution

The authors developed a complementary evaluation method that directly biases the antenna termination resistor, allowing measurement of Psat and tau0 without electrothermal feedback influence.

Findings

Psat correlates with inverse leg length.

Measured tau0 values are consistent with expected TES parameters.

Method enables fabrication verification and feedback for future TES development.

Abstract

Superconducting Transition-Edge Sensor (TES) bolometers are used for cosmic microwave background (CMB) observations. We used a testbed to evaluate the thermal performance of TES bolometers in regard to the saturation power Psat and intrinsic thermal time constant tau0. We developed an evaluation method that is complementary to methods with electrothermal feedback. In our method, the antenna termination resistor of the bolometer is directly biased with DC or AC electric power to simulate optical power, and the TES is biased with small power, which allows Psat and tau0 to be determined without contribution from the negative electrothermal feedback. We describe the method and results of the measurement using it. We evaluated Psat of five samples by applying DC power and confirmed the overall trend between Psat and the inverse leg length. We evaluated tau0 of the samples by applying DC plus AC power, and the measured value was reasonable in consideration of the expected values of other TES parameters. This evaluation method enables us to verify whether a TES has been fabricated with the designed values and to provide feedback for fabrication for future CMB observations.