In this paper we describe microfabrication developments for a 1024 pixel calorimeter array, to be used in future X-ray spectroscopic space missions. We report on an optimization study of high packing ...factor, mushroom shaped, Cu/Bi absorbers, for which a sputter deposition technique into a new type of photoresist mould has been developed. We have fabricated a prototype 32×32 array where 98 representable pixels are potentially functioning TESs. To gain more control on the detector pixel performance a new procedure was developed to couple absorber and thermometer, utilizing a thin insulating layer. Advances are reported in the fabrication of superconducting LC resonating circuits, needed for frequency domain multiplexed read out. A quality factor
Q
∼4000 @ 2.6 MHz has been measured, which was limited by critical current in the circuit.
It has been recently demonstrated that superconducting transition edge-sensors behave as weak-links due to longitudinally induced superconductivity from the leads with higher
T
c
. In this work we ...study the implication of this behaviour for transition-edge sensors (TES)-based bolometers and microcalorimeter under ac bias. The TESs are read-out at frequencies between 1 and
5
MHz
by a frequency domain multiplexer based on a linearised two-stage SQUID amplifier and high-
Q
lithographically made superconducting
L
C
resonators. In particular, we focus on SRON TiAu TES bolometers with a measured dark noise equivalent power of
3.2
×
10
-
19
W
/
Hz
developed for the short wavelength band for the instrument SAFARI on the SPICA telescope.
The so-called excess noise limits the energy resolution of transition-edge sensor (TES) detectors, and its physical origin has been unclear, with many competing models proposed. Here we present the ...noise and impedance data analysis of a rectangular X-ray Ti/Au TES fabricated at SRON. To account for all the major features in the impedance and noise data simultaneously, we have used a thermal model consisting of three blocks of heat capacities, whereas a two-block model is clearly insufficient. The implication is that, for these detectors, the excess noise is simply thermal fluctuation noise of the internal parts of the device. Equations for the impedance and noise for a three-block model are also given.
In the process to develop the transition edge sensor (TES) bolometer technology for the SAFARI FIR Imaging Spectrometer on the SPICA telescope and for future FIR space telescopes, we have recently ...demonstrated a TiAu TES with a Ta thin film absorber on a thin SiN membrane, which has a dark NEP as low as 4.2 × 10 -19 W/√Hz. It is known that superconductors are sensitive to magnetic fields. Therefore, it is important to know how these extremely sensitive TES detectors are affected by external magnetic fields. This is desirable from an application point of view since the design of the SAFARI instrument demands such knowledge and interesting from a fundamental point of view. In this paper, we will describe a detailed experimental study of the effects of magnetic fields, both parallel and perpendicular to the TiAu plane, on the performance of a TES. We investigated the effect on the current, responsivity, speed, and TES parameters of α (dependence of temperature) and β (dependence of current), around the operating points. In order to achieve this highly sensitive measurement, the temperature stability has been improved and a new coil assembly has been designed. The latter allows accurately applying a parallel magnetic field.
We have demonstrated the operation of a 12-channel Beyer-style SQUID-based time domain multiplexer. It was manufactured using a fabrication process that is cross-compatible between VTT and IPHT-Jena. ...The multiplexer consists of twelve 12-SQUID series arrays, each shunted by a Zappe-style interferometer array acting as a flux-controlled superconducting/normal conducting switch. By keeping all switches but one in the superconducting state, it is possible to select one active readout channel at a time. A flux feedback coil common to all SQUID arrays allows realization of a flux-locked loop. We present characteristics of the multiplexer and measurement data from experiments with a 25-pixel X-ray calorimeter array operated at T < 100 mK in a dilution refrigerator.
Operation of TES-based bolometers in a resistance locked loop (RLL), i.e. keeping the operating resistance constant by means of feedback on the bias voltage, provides a number of attractive ...properties for applications. In combination with frequency domain multiplexing, the technique reduces electrical cross talk, and provides a more detector load independent behaviour with respect to operation under standard voltage bias. This paper shows a quantitative estimation of the large signal properties under the RLL, and shows a comparison with the situation under voltage bias. Furthermore, an unorthodox, low-bandwidth mode of operation will be discussed, from the perspective of the electro-thermal stability in the RLL.
SRON is developing the Frequency Domain Multiplexing (FDM) read-out and the ultra low NEP TES bolometers array for the infra-red spectrometer SAFARI on board of the Japanese space mission SPICA. The ...FDM prototype of the instrument requires critical and complex optimizations. For single pixel characterization under AC bias we are developing a simple FDM system working in the frequency range from 1 to 5 MHz, based on the open loop read-out of a linearized two-stage SQUID amplifier and high
Q
lithographic
LC
resonators. We describe the details of the experimental set-up required to achieve low power loading (<1 fW) and low noise (
) in the TES bolometers. We conclude the paper by comparing the performance of a
TES bolometer measured under DC and AC bias.
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