A high Tc superconductor bolometer on a silicon nitride membrane

In this paper, we describe the design, fabrication, and performance of a high-Tc GdBa2Cu3O7-¿ superconductor bolometer positioned on a 2× 2-mm2 1-¿m-thick silicon nitride membrane. The bolometer structure has an effective area of 0.64 mm2 and was grown on a specially developed silicon-on-nitride (SON) layer. This layer was made by direct bonding of silicon nitride to silicon after chemical mechanical polishing. The operation temperature of the bolometer is 85 K. A thermal conductance G=3.3·10-5 W/K with a time constant of 27 ms has been achieved. The electrical noise equivalent power (NEP) at 5 Hz is 3.7·10-2 WHz-1/2, which is very close to the theoretical phonon noise limit of 3.6·10-12 WHz -1/2, meaning that the excess noise of the superconducting film is very low. This bolometer is comparable to other bolometers with respect to high electrical performance. Our investigations are now aimed at decreasing the NEP for 84-¿m radiation by further reduction of G and adding an absorption layer to the detector. This bolometer is intended to be used as a detector in a Fabry-Perot (FP)-based satellite instrument designed for remote sensing of atmospheric hydroxyl

NEW:A mission to explore the warm-hot intergalactic medium

The most recent observations of the cosmic microwave background (e.g., WMAP) show that baryons contribute about 4% to the total density of the Universe. However at redshift ≤ 1, about half of these baryons have not yet been observed. Cosmological simulations predict that these "missing" baryons should be distributed in filaments, have temperatures of 105 to 107 and K overdensities of a few to hundred times the average baryon density, forming the so-called Warm-Hot Intergalactic Medium (WHIM). There is increasing evidence from Chandra and XMM-Newton that the WHIM may indeed exist. However it is clear that to map the morphology of the WHIM and to measure its physical conditions, a completely different class of instruments is required. Measuring the WHIM in emission in the soft X-ray band is a promising option. To detect the relatively weak, extended emission of the WHIM, the instrument should have a large grasp (collecting area times field of view), and an energy resolving power of about 500 at 1 keV is required to separate the emission of these large scale filaments from foreground emission. We discuss a design that includes X-ray mirrors in combination with a large 2D cryogenic detector, which will allow us to map a significant fraction of this gas. Such detector and its read-out based on Frequency Domain Multiplexing, are currently under development at SRON. It seems feasible to build an array of 24 × 24 pixels of TES microcalorimeters with good energy resolution (few eV). This detector will be combined with a mirror design which is based on 2 and 4 reflections and gives a large area (> 500 cm2) over a relatively large field of view. A preliminary study of the mission concept indicates that this can be implemented in a relatively small satellite (total weight 650 kg). While the main goal of this satellite will be to map and study the physical properties of the missing baryons, the instrument's large area and large field of view will also result in major progress in related fields

Development of an array of transition edge sensors for application in X-ray astronomy

We report on the development activities towards a cryogenic array of micro-calorimeters, based on voltage-biased Ti/Au transition edge thermometers. Fabrication issues are discussed along the lines of two fabrication routes. One route utilizes bulk micromachining in [1 1 0] Si wafers, the other route surface micromachining with a sacrificial layer. Prototype 5×5 arrays have been fabricated and we present the first performance data: Two arrays were irradiated with 5.9 keV X-ray irradiation and an energy resolution of 6–7 eV FWHM was obtained. The arrays have been designed and their performance is analyzed with the aid of finite element simulation of the electrothermal behavior of a single pixel and thermal conductivity in the supporting structure