High-Resistivity Transition-Edge Sensor Modeling and Expected Performances

International audienceHigh spectral resolution detectors based on low-resistivity transition-edge sensors (TES) are being developed for future X-ray spatial observatories, but difficulties (cryogenics limitations) are to be expected in next generation’s detectors with even more pixels. A new technology, the high-resistivity TES (HRTES), is likely to offer similar performance to existing TES when associated to an active electrothermal feedback, adding the possibility of moving the readout electronics to a 2.5 K stage of the cryocooler. This work aims to investigate HRTES by making a precise model of the device, comparing it to experimental measurements, and deducing its performance potential

High impedance TES with classical readout electronics: a new scheme toward large x-ray matrices

International audienceHigh impedance transition edge sensors (TES) are good candidates to constitute the sensitive part of new X-ray spectroimagers for the spatial X-ray observation, with even greater number of pixels. We test this solution in this context, developing an original scheme of readout that consist in implementing an active electro-thermal feedback, performed by a low noise cryogenic electronics, in order to solve the problematic effects of the electron-phonon decoupling, to ensure the stability of the system, and to increase the dynamic range of the detector. This paper presents the status of our developments, including the characterisation of the sensor, the experimental test of the active electro-thermal feedback, and our very first results of photon detection.© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Optimization and experimental measurements of high impedance niobium-silicon (NbSi) transition edge sensors (TES) for high spectral and spatial resolution x-ray space-borne telescopes

International audiencepace-borne x-ray observations of supernova remnants, galactic clusters, x-ray binaries, and black holes are key elements in determining the structure of the universe. Astronomers require wide field of view with high spatial resolution but also very high spectral resolution to determine the physical conditions (temperatures, element abundances) with great accuracy. Today’s technologies (mostly TESs) obtain very high spectral resolutions to the detriment of power consumption, mostly due to their cold stage SQUID readout electronics. Their high power consumption limits the instrument’s field of view (FoV) by constraining the total number of pixels affordable at the 50 mK focal plane of a satellite cryostat. We use a new alloy technology: the high resistivity NbSi, enabling us to design TES sensors promising high spectral resolution and ultra low power consumption (below 10 pW). Their high impedance allows the use of a transistor readout at a hotter stage of the cryostat. This, in conjunction with the inherent ultra-low power dissipation of the sensors, raises drastically the number of pixels of the detector.In this article, we explore pixel optimization ways based on our electro-thermal model to reach spectral resolution of the order of 1.8 eV. We then use this model to manufacture a new batch of pixels on which we conduct experimental measurements. We measure the transient response, energy linearity and noise spectrum of our pixels with an Iron 55 source as well as an innovative on-chip pulse injection system. A low noise cryogenic amplifier as well as a cryogenic experimental setup have been designed to perform these measurements.© COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

First-ever test and characterization of the AMS standard bulk 0.35 μm CMOS technology at sub-kelvin temperatures

International audienceFrom medical imaging to particle physics passing, among others, by space applications, integrated readout electronics (ICs) in CMOS technologies are often adopted. When a high sensitivity and a low noise level are required, cooling of detectors and readout electronics is the recommended solution. To maintain a constant cooling temperature, they very often operate at nitrogen and helium-4 liquids temperatures, respectively 77 K and 4.2 K. At these temperatures, Spice parameters of MOSFET transistors may be found in the literature. However, their performances at sub-kelvin temperatures remain unknown because of a lack in scientific publications thereupon. CEA Astrophysics division's focal plane arrays-based bolometers are cooled at 0.1 K. The front-end electronics also. However, a CMOS technology was characterized for the first time at sub-kelvin temperatures. It is shown by measured n and p channel transistors' I-V that the AMS 0.35 μm standard bulk CMOS technology, is still performing at 0.1 K. Despite some specific effects on silicon behaviour at cryogenic temperatures, performances are very satisfactory

LWIR quantum efficiency measurements using a calibrated MCT photodiode read by a cryo-HEMT-based amplifier

International audienceWe present a new development for the measurement of the Quantum Efficiency (QE) of a Mercury Cadmium Telluride (HgCdTe or MCT) detector array in the long wave infrared (LWIR) spectral band. To measure the incident photon flux on the detector, CEA-LETI has designed and produced a calibrated MCT photodiode which, under the test setup conditions used for the QE measurement, delivers a total (dark plus photonic) current of 1nA at 60K. The readout of such a low level of current makes a standard room temperature amplifier inconvenient due to the length of the wires between the focal plane (FP) at cold and the outside of the cryostat (>2m in the current cryostat). A much better approach is to use High Electron Mobility Transistors (Cryo-HEMTs), optimized by CNRS/C2N laboratory for ultra-low noise at very low temperatures (<1K). We have developed a Cryo-HEMT-based transimpedance amplifier to readout the photonic current of the calibrated MCT chip. The paper describes the calibrated photodiode, the Cryo-HEMT amplifier and the test setup, and shows the results of the QE measurements of the LWIR detector

BRAHMS: polarimetric bolometer arrays for the SPICA observatory camera (Conference Presentation)

International audienceIn the last decades, a very large effort has been made to measure, with high sensitivity, the intensity and spectral contents of millimetric (mm) and submillimetric (submm) light from the Universe. Today this picture is in the way to be routinely completed by polarization measurements that give access to previously hidden processes, for example the traces of primordial gravitational waves in the case of CMB (mainly mm), or the effect of magnetic field for star formation mechanisms (submm and mm optical ranges). The classical way to measure the light polarization is to split the two components by a polarizer grid and record intensities with two conjugated detection setups. This approach implies the deployment of a complex instrument system, very sensitive to external constraints (vibrations, alinement, thermal expansion…), or internal ones: determine low degrees of polarization implies a large increase in sensitivity when compared with intensity measurements. The need of detector arrays, with in pixel polarization measurement capabilities, has been well understood for years: all the complexity being reported at the focal plane level. Subsequently, the instrument integration, verification and tests procedure is considerately alleviated, specially for space applications.All silicon bolometer arrays using the same micromachining techniques than the Herschel PACS modules are well suited for this type of development. New thermometers doped for 50 mK operations permit to achieve, with a new design, sensitivities close to the aW/√Hz. It is based on all-legs bolometers (ALB), where the absorbing, insulating and thermometric functions are made by the same suspended silicon structure. This ALB structure, with in this case a spiral design, permits to separate the absorption of the two electromagnetic components of the light polarization. Each pixel consists of four bolometer divided in two pairs, each sensitive to one direction of polarization. This permits to combine the bolometer bridges in a fully differential global structure with a Wheatstone bridge arrangement. Total intensity and polarization unbalance are available directly at the detector level, thanks to a cold readout circuit integrated in the detector structure. This combination of functions is achieved by above IC manufacture techniques (IC for Integrated Circuit).All these developments take place in the prospect of the joint JAXA-ESA SPICA project, to equip a 1344 pixels polarimetric and imaging camera covering three spectral bands (100, 200 and 350 µm)