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Multiplexed readout is a requirement for the successful deployment of large-scale cryogenic detector arrays in applications ranging from x-ray microanalysis to sub-millimeter astronomy. We report on the development of a time-division SQUID multiplexer (SQUID MUX) to read out one column of a 32 × 32 transition-edge sensor (TES) array. The new SQUID MUX has three stages. Individual TES pixels inductively couple to first-stage SQUID's, which are summed and coupled to a second-stage SQUID via a superconducting transformer. The first- and second-stage SQUID's are integrated on the same chip and are operated at the working temperature of the detectors of about 100 mK. The second stage SQUID is read out by a SQUID series array at 4K. Compared to former designs, the new SQUID MUX features a balanced input configuration to reduce crosstalk between read-out channels. In this paper we discuss the SQUID MUX design and analyze the noise and bandwidth performance of the SQUID multiplexer. Multiplexing of test input signals utilizing digital feedback electronics is demonstrated. [ABSTRACT FROM AUTHOR]

Frequency domain multiplexing (FDM) is an attractive option for the readout of imaging arrays of microcalorimeters. The most straightforward implementation of FDM is based on alternating voltage (AC) biasing of the individual microcalorimeters. It is clear that for future applications the performance in terms of energy resolution and count rate capability is crucial. We discuss the consequences of AC bias for the performance of a microcalorimeter, and make a direct experimental comparison between the performance of a TES based microcalorimeter AC and DC bias. Modeling, as well as experiments, show that the performance of the device is very similar in terms of energy resolution and pulse shapes (100 µs effective time constant). The measured energy resolution at 5.89 kev photon energy is 6.3 eV for AC bias at 46 kHz and 5.5 eV for DC bias. [ABSTRACT FROM AUTHOR]

Evaluates sensor geometries of voltage-biased x-ray microcalorimeters with a phase-transition thermometer. Sources of thermal fluctuation noise; Measured energy resolution; Thermal geometry of the sensor.

Studies the intermediate frequency bandwidth of Nb diffusion-cooled superconducting hot-electron bolometer mixers for different bias voltages. Effects of voltage increases on bandwidth; Intrinsic thermal time constant of the mixer; Effect of electrothermal feedback through the intermediate frequency circuit.

We present the first high quality Nb/Al-based tunnel junctions, fabricated with a superconducting interface onto single crystal substrates of Nb and Ta. Current-voltage measurements down to 1.4 K show a subgap current which is dominated by thermal excitation of quasiparticles, no ohmic or superconducting leakages could be observed. The fabrication process and development steps, such as preparation of ultra-smooth crystal surfaces are described. [ABSTRACT FROM PUBLISHER]

Nb-based superconducting tunnel junctions are being developed as high energy resolution X-ray detectors. Unfortunately, loss of excess quasiparticles at the edges, combined with lateral diffusion, results in an inhomogeneous response. To study this degradation of energy resolution, we manufactured detectors with a Ta trap in the top or bottom electrode away from the tunneling barrier. Excess quasiparticles in this so-called killed electrode will be trapped effectively and thus removed from the tunneling process. The X-ray spectra of the active electrode can be fitted with a model based on classical diffusion of quasiparticles. On junctions with a killed bottom electrode also Low Temperature Scanning Electron Microscopy (LTSEM) measurements have been performed. The X-ray spectra and the LTSEM scans are consistent with each other and with the model. The energy resolution of the junctions presented here is limited by loss of quasiparticles at the edges. [ABSTRACT FROM PUBLISHER]