SQUIDs et Méthodes de Multiplexage

École thématiqueLe SQUID (Superconducting QUantum Interference Device) est un élément essentiel du développement du multiplexage cryogénique. Il fonctionne à température cryogénique, bénéficie d'une grande bande passante (~MHz) et d'un très faible bruit (~pA/√Hz). Dans un premier temps, les deux principes analogiques de multiplexage temporel et fréquentiel seront présentés. Dans un deuxième temps, on parlera de l'utilisation du SQUID qui permet de réaliser un multiplexage temporel ou fréquentiel à l'intérieur d'un cryosta

Introduction au Langage C

DEACours/TPs/examen: Introduction au langage C et C+

Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 µm technology

International audienceSome decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse.This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 µm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm2) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters1 (Silicon PhotoMultiplier – SiPM) or high resolution imagers (SPAD imager). The present work investigates SPAD geometry. MOS transistor has been used instead of resistor to adjust the quenching resistance and find optimum value. From this first set of results, a detailed study of the dark count rate (DCR) has been conducted. Our results show a dark count rate increase with the size of the photodiodes and the temperature (at T=22.5 °C, the DCR of a 10 µm-photodiode is 2020 count s−1 while it is 270 count s−1 at T=−40 °C for a overvoltage of 800 mV). A small pixel size is desirable, because the DCR per unit area decreases with the pixel size. We also found that the adjustment of overvoltage is very sensitive and depends on the temperature. The temperature will be adjusted for the subsequent experiments

Dark Count rate measurement in Geiger mode and simulation of a photodiode array, with CMOS 0.35 technology and transistor quenching.

International audienceSome decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD detectors fabricated in a standard CMOS technology feature both single-photon sensitivity, and excellent timing resolution, while guarantying a high integration. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. In this work, we investigate the design of SPAD detectors using the Austriamicrosystems 0.35 μm CMOS Opto technology. A series of different SPADs has been fabricated and benchmarked in order to evaluate a future integration into a SPAD- based image sensor. The main characteristics of each SPAD operating in Geiger-mode are reported: current voltage, breakdown voltage as a function of temperature. From this first set of results, a detailed study of the Dark Count Rate (DCR) has been conducted. Our results show a dark count rate increase with the size of the photodiodes and the temperature (at T=22.5°C, the DCR of a 10μm-photodiode is 2020 count.s-1 while it is 270 count.s-1 at T=- 40°C for a overvoltage of 800mV). We found that the adjustment of overvoltage is very sensitive and depends on the temperature. The temperature will be adjusted for the subsequent experiments. A mathematical model is presented for reproduce the DCR of a single photodiode. We simulated the noise (DCR) of array of 32x32 photo-detectors. Our results show, of course an increase of DCR of 1024, but especially, the probability of having two pulses simultaneously is 0 (without light). By studying these probabilities of occurrence of the pulses, we think we can reduce the DCR of 50% with a statistical method and reduce the crosstalk of 90%. This study is realized in order to prepare the first digital matrices sensor in Geiger mode

QUBIC: The QU Bolometric Interferometer for Cosmology

One of the major challenges of modern cosmology is the detection of B-mode polarization anisotropies in the CMB. These originate from tensor fluctuations of the metric produced during the inflationary phase. Their detection would therefore constitute a major step towards understanding the primordial Universe. The expected level of these anisotropies is however so small that it requires a new generation of instruments with high sensitivity and extremely good control of systematic effects. We propose the QUBIC instrument based on the novel concept of bolometric interferometry, bringing together the sensitivity advantages of bolometric detectors with the systematics effects advantages of interferometry. Methods: The instrument will directly observe the sky through an array of entry horns whose signals will be combined together using an optical combiner. The whole set-up is located inside a cryostat. Polarization modulation will be achieved using a rotating half-wave plate and interference fringes will be imaged on two focal planes (separated by a polarizing grid) tiled with bolometers. We show that QUBIC can be considered as a synthetic imager, exactly similar to a usual imager but with a synthesized beam formed by the array of entry horns. Scanning the sky provides an additional modulation of the signal and improve the sky coverage shape. The usual techniques of map-making and power spectrum estimation can then be applied. We show that the sensitivity of such an instrument is comparable with that of an imager with the same number of horns. We anticipate a low level of beam-related systematics thanks to the fact that the synthesized beam is determined by the location of the primary horns. Other systematics should be under good control thanks to an autocalibration technique, specific to our concept, that will permit the accurate determination of most of the systematics parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic

Large bolometer arrays with superconducting NbSi sensors for future space experiments

International audienceNew techniques in microelectronics allow to build large arrays of bolometers filling the focal plane of submillimeter and millimeter telescopes. The expected sensitivity increase is the key for the next generation of space experiments in this wavelength range. Superconducting bolometers offer currently the best prospects in terms of sensitivity and multiplexed readout. We present here the developments led in France based on NbSi alloy thermometers. The manufacturing process of a 23 pixel array and the test setup are described