O. Gevin

IDeF-X ECLAIRs: A CMOS ASIC for the Readout of CdTe and CdZnTe Detectors for High Resolution Spectroscopy

The very last member of the IDeF-X ASIC family is presented: IDeF-X ECLAIRs is a 32-channel front end ASIC designed for the readout of Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) Detectors. Thanks to its noise performance (Equivalent Noise Charge floor of 33 e- rms) and to its radiation hardened design (Single Event Latchup Linear Energy Transfer threshold of 56 MeV.cm2.mg-1), the chip is well suited for soft X-rays energy discrimination and high energy resolution, ldquospace proof,rdquo hard X-ray spectroscopy. We measured an energy low threshold of less than 4 keV with a 10 pF input capacitor and a minimal reachable sensitivity of the Equivalent Noise Charge (ENC) to input capacitance of less than 7 e-/pF obtained with a 6 mus peak time. IDeF-X ECLAIRs will be used for the readout of 6400 CdTe Schottky monopixel detectors of the 2D coded mask imaging telescope ECLAIRs aboard the SVOM satellite. IDeF-X ECLAIRs (or IDeF-X V2) has also been designed for the readout of a pixelated CdTe detector in the miniature spectro-imager prototype Caliste 256 that is currently foreseen for the high energy detector module of the Simbol-X mission.

IDeF-X V1.0: performances of a new CMOS multi channel analogue readout ASIC for Cd(Zn)Te detectors

The evolution of the CdTe detector properties (leakage current, capacitance, and geometry) requires a continuous improvement of the electronic frond-end in terms of geometry, noise, and power consumption. This is why our group is working on a new modular spectro-imaging system based on CdTe detectors coupled to dedicated full custom readout ASICs, named IDeF-X for imaging detector front-end. We present the most recent version of IDeF-X which is a sixteen-channel analogue readout chip for hard X-ray spectroscopy. It has been processed with the standard AMS 0.35 /spl mu/m CMOS technology. Each channel consists of a charge sensitive preamplifier, a pole zero cancellation stage, a variable peaking time filter and an output buffer. IDeF-X is designed to be DC coupled to detectors having a low dark current at room temperature and is optimized for input capacitance ranging from 2 to 5 pF.

CALISTE 64, an innovative CdTe hard X-Ray micro-camera

In the frame of the hard X-ray simbol-X observatory, a joint CNES-ASI space mission to be flown in 2013, a prototype of miniature camera equipped with 64 pixels has been designed. The device, called CALISTE 64, is a spectro- imager with high resolution event time-tagging capability. CALISTE 64 integrates a CdTe semiconductor detector with segmented electrode and its front-end electronics made of 64 independent analogue readout channels. This 10times10times18 mm3 camera, able to detect photons in the range from 2 keV up to 250 keV, is an elementary detection unit juxtaposable on its four sides. Consequently, large detector array can be made assembling a mosaic of CALISTE 64 units. Electronics readout module is achieved by stacking four IDeF-X V1.1 ASICs in a 3D-module, perpendicular to the detection plane. We achieved good noise performances, with an equivalent noise charge better than 60 electrons rms in average. We choose CdTe detectors equipped with aluminum Schottky barrier contacts because of their very low dark current and excellent spectroscopic performances. The first integrated CALISTE 64 camera was realized and tested. The device operates properly and all the 64 pixels show good spectra. When the crystal is cooled down to -10degC and biased at -400 V, the resulting sum spectrum shows a spectral resolution of 697 eV FWHM at 13.9 keV and 808 eV FWHM at 59.54 keV. This paper presents the CALISTE 64 design and preliminary performance test results.

IDeF-X HD: A low power multi-gain CMOS ASIC for the readout of Cd(Zn)Te detectors

SINCE few years, our group is developing a family of ASICs for space applications, named IDeF-X for Imaging Detector Front-end [l]-[4]. IDeF-X HD is the new member of the IDeF-X family. It has been optimized for the readout of 16 × 16 pixels CdTe or CdZnTe pixelated detectors to build a new low power Caliste 256 module [5]. This micro gamma-camera will be the elementary unit of the MAC SI (Modular Assembly of Caliste Spectro Imager) camera: A 2048-pixels 8 cm2 gamma camera designed with 8 identical Caliste modules.

Caliste 64, an Innovative CdTe Hard X-Ray Micro-Camera

A prototype 64 pixel miniature camera has been designed and tested for the Simbol-X hard X-ray observatory to be flown on the joint CNES-ASI space mission in 2014. This device is called Caliste 64. It is a high performance spectro-imager with event time-tagging capability, able to detect photons between 2 keV and 250 keV. Caliste 64 is the assembly of a 1 or 2 mm thick CdTe detector mounted on top of a readout module. CdTe detectors equipped with aluminum Schottky barrier contacts are used because of their very low dark current and excellent spectroscopic performance. Front-end electronics is a stack of four IDeF-X Vl.l ASICs, arranged perpendicular to the detection plane, to read out each pixel independently. The whole camera fits in a 10 times 10 times 20 mm3 volume and is juxtaposable on its four sides. This allows the device to be used as an elementary unit in a larger array of Caliste 64 cameras. Noise performance resulted in an ENC better than 60 electrons rms in average. The first prototype camera is tested at -10degC with a bias of -400 V. The spectrum summed across the 64 pixels results in a resolution of 697 eV FWHM at 13.9 keV and 808 eV FWHM at 59.54 keV.

IDeF-X ASIC for Cd(Zn)Te spectro-imaging systems

Progress in the fields of Cd(Zn)Te detector development, microelectronics, and interconnection technologies open the way for a new generation of instruments for physics and astrophysics applications in the energy range from 1 to 1000 keV. Cd(Zn)Te based instruments operating in the range between -20 and 20/spl deg/C will offer high spatial resolution (pixel size ranging from 300/spl times/300 /spl mu/m/sup 2/ to few mm/sup 2/), high spectral response, and high detection efficiency. To reach these goals, reliable, highly integrated, low-noise, and low-power consumption electronics is mandatory. Our group is currently developing a new full custom ASIC detector front-end named IDeF-X, for modular spectro-imaging systems based on the use of Cd(Zn)Te detectors. We present here the first version of IDeF-X that consists of a set of ten low-noise charge sensitive preamplifiers (CSA). It has been manufactured using the AMS 0.35 /spl mu/m CMOS technology. The CSAs are designed to be DC coupled to detectors having low dark current at room temperature. We have optimized the various preamplifiers to match detector capacitances in the range from 0.5 to 30 pF.

Caliste HD: A new fine pitch Cd(Zn)Te imaging spectrometer from 2 keV up to 1 MeV

Caliste HD is the last member of the Caliste family of Cd(Zn)Te micro-cameras for space applications. This hybrid component is made of the assembly of one 16 × 16 pixel Cd(Zn)Te detector and eight analog front-end ASIC named IDeF-X HD equipped with 32 spectroscopic channels. The pixels are 625 µm pitch and are surrounded by a 20 µm wide guard ring. The new generation of ASIC has the advantage of having a power consumption 4 times lower as the previous version (0.2 W for the full device) and offers the possibility to extend the dynamic range from 250 keV to 1 MeV. The technology is fully compliant with operation in space (tolerant to radiation, thermal and mechanical constraints). This paper presents the preliminary spectroscopic results obtained with the samples produced so far. At −16°C the sum spectrum built with all single events of the 1 mm-thick Al Schottky detector show an energy resolution of 0.82 keV FWHM at 14 keV and 0.92 keV FWHM at 60 keV. A good uniformity in gain and in noise is measured over the 256 pixels; the low level-threshold is lower than 2 keV for all pixels.

The focal plane of the Simbol-X space mission

The Simbol-X mission, currently undergoing a joint CNES-ASI phase A, is essentially a classical X-ray telescope having an exceptional large focal length obtained by formation flying technics. One satellite houses the Wolter I optics to focus, for the first time in space, X-rays above ~10 keV, onto the focal plane in the second satellite. This leads to improved angular resolution and sensitivity which are two orders of magnitude better than those obtained so far with non-focusing techniques. Tailored to the 12 arcmin field of view and ~15 arcsec angular resolution of the optics, the ~8x8 cm2 detection area of the spectro-imager has ~ 500x500 μm2 pixels, and covers the full energy range of Simbol-X, from ~0.5 to ~80 keV, with a good energy resolution at both low and high energy. Its design leads to a very low residual background in order to reach the required sensitivity. The focal plane ensemble is made of two superposed spectro-imaging detectors: a DEPFET-SDD active pixel sensor on top of an array of pixelated Cd(Zn)Te crystals, surrounded by an appropriate combination of active and passive shielding. Besides the overall concept and structure of the focal plane including the anti-coincidence and shielding, this paper also emphasizes the promising results obtained with the active pixel sensors and the Cd(Zn)Te crystals combined with their custom IDeF-X ASICs.

Micro hard-X ray camera: From Caliste 64 to Caliste 256

Caliste project aims at hybridizing 1 cm2 Cd(Zn)Te detectors with low noise front-end electronics, in a single component standing in a 1 × 1 × 2 cm3 volume. The micro-camera is a spectro-imager for X and gamma rays detection, with time-tagging capability. Hybridization consists in stacking full custom ASICs perpendicular to the detection surface. The first prototype Caliste 64 integrates a detector of 8 × 8 pixels of 1 mm pitch. Fabrication and characterizations of nine cameras samples validate the design and the hybridization concept. Spectroscopic tests result in a mean energy resolution of ∼0.7 keV FWHM at 14 keV and ∼0.85 keV FWHM at 60 keV with 1 mm-thick Al Schottky CdTe detectors biased at −400V and cooled down to −15°C. The new prototype called Caliste 256 integrates 16 × 16 pixels of 580 8m pitch in the same volume as Caliste 64. Electrical tests with the first sample fabricated without detector result in a mean equivalent noise charge of 64 el. rms (9.6 μs, no leakage current). Caliste devices are 4-side buttable and can be used as elementary detection units of a large hard X-ray focal plane, as for the 64 cm2 high energy detector of the Simbol-X astronomical space mission.

The x-/gamma-ray camera ECLAIRs for the gamma-ray burst mission SVOM

We present ECLAIRs, the Gamma-ray burst (GRB) trigger camera to fly on-board the Chinese-French mission SVOM. ECLAIRs is a wide-field (~ 2 sr) coded mask camera with a mask transparency of 40% and a 1024 cm2 detection plane coupled to a data processing unit, so-called UGTS, which is in charge of locating GRBs in near real time thanks to image and rate triggers. We present the instrument science requirements and how the design of ECLAIRs has been optimized to increase its sensitivity to high-redshift GRBs and low-luminosity GRBs in the local Universe, by having a low-energy threshold of 4 keV. The total spectral coverage ranges from 4 to 150 keV. ECLAIRs is expected to detect ~ 200 GRBs of all types during the nominal 3 year mission lifetime. To reach a 4 keV low-energy threshold, the ECLAIRs detection plane is paved with 6400 4 × 4 mm2 and 1 mm-thick Schottky CdTe detectors. The detectors are grouped by 32, in 8×4 matrices read by a low-noise ASIC, forming elementary modules called XRDPIX. In this paper, we also present our current efforts to investigate the performance of these modules with their front-end electronics when illuminated by charged particles and/or photons using radioactive sources. All measurements are made in different instrument configurations in vacuum and with a nominal in-flight detector temperature of −20°C. This work will enable us to choose the in-flight configuration that will make the best compromise between the science performance and the in-flight operability of ECLAIRs. We will show some highlights of this work.