A. Meuris

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.

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.

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.

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.

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 front-end electronics of the Spectrometer Telescope for Imaging X-Rays (STIX) on the ESA Solar Orbiter satellite

Solar Orbiter is an ESA mission to study the heliosphere in proximity to the Sun, scheduled for launch in January 2017. It carries a suite of ten instruments for comprehensive remote-sensing and in-situ measurements.The Spectrometer Telescope for Imaging X-Rays (STIX), one of the remote sensing instruments, images X-rays between 4 and 150keV using an Fourier technique. The angular resolution is 7 arcsec and the spectral resolution 1keV full-width-half-maximum at 6keV. X-ray detection uses pixelized Cadmium Telluride crystals provided by the Paul Scherrer Institute. The crystals are bonded to read-out hybrids developed by CEA Saclay, called Caliste-SO, incorporating a low-noise, low-power analog front-end ASIC IDeF-X HD. The crystals are cooled to -20°C to obtain very low leakage currents of less than 60pA per pixel, the prerequisite for obtaining the required spectral resolution.This article briefly describes the mission goals and then details the front-end electronics design and main challenges, resulting in part from the allocation limit in mass of 7kg and in power of 4W. Emphasis is placed on the design influence of the cooling requirement within the warm environment of a mission approaching the Sun to within the orbit of Mercury. The design for the long-term in-flight energy calibration is also explained.

IDeF-X SX0: A low power CMOS ASIC for the readout of Cd(Zn)Te detectors

The last member of the IDeF-X ASIC family is presented: IDeF-X SX0 a 32-channel front end ASIC designed for the readout of Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) Detectors. It has been designed in the standard AMS CMOS 0.35 μm process technology. The ASIC has been optimized to reduce the power consumption which is now 600 μW per channel; it is five times lower than the power consumption of the previous IDeF-X ECLAIRs chip [1]. Moreover, the dynamic range of the ASIC can now be extended to more than 1 MeV thanks to the in-channel variable gain stage. When no detector is connected to the chip, the lowest equivalent noise charge (ENC), achieved at a 9 μs peak time, is 72 electrons rms. IDeF-X SX0 has been evaluated by performing spectroscopy measurements at room temperature with a thin CdTe Schottky detector. The energy resolution was found to be 1.6 keV fwhm at 60 keV with an 241Am source. The ASIC has been designed for space applications and it will be used for the readout of 16 × 16 pixels CdTe or CdZnTe pixellated detectors to build a new low power Caliste micro Gamma camera [2].

Performance and qualification of CdTe pixel detectors for the Spectrometer/Telescope for Imaging X-rays

The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on-board the ESA Solar Orbiter spacecraft. STIX is designated to the study of energetic phenomena in solar flares. A Fourier-imaging technique using tungsten grid collimators in front of CdTe pixel detectors is employed, covering the 4 to 150 keV energy range with a full-width-half maximum resolution around 1 keV at low energies. Acrorad CdTe detectors of 1 mm thickness with a planar aluminum Schottky contact are used as basis for a subsequent patterning process into eight large pixels, four small pixels, and a guard ring. The patterning is done by means of microfabrication technologies. The area of the patterned sensor is 10×10 mm2. Test equipment has been developed for selecting the detectors with best performance prior to integration with the read-out system, and for qualification purposes. The set-up allows pixel-based dark current measurements at low temperatures. Pixel dark currents below 60 pA are needed to avoid excess noise in the read-out ASIC. The best pixels show dark currents below 10 pA at 300 V bias and −20 °C. Spectroscopic measurements with 133Ba sources confirm the good performance. This paper briefly explains the mission context of the CdTe detectors and then gives details of the production and testing procedures. Typical results are shown, with emphasis on performance degradation studies from displacement damage by proton irradiation. This is expected to be the dominant degradation mechanism for this application.

The High Energy Detector of Simbol‐X

The High Energy Detector (HED) is one of the three detection units on board the Simbol‐X detector spacecraft. It is placed below the Low Energy Detector so as to collect focused photons in the energy range from 8 to 80 keV. It consists of a mosaic of 64 independent cameras, divided in 8 sectors. Each elementary detection unit, called Caliste, is the hybridization of a 256‐pixel Cadmium Telluride (CdTe) detector with full custom front‐end electronics into a unique component. The status of the HED design will be reported. The promising results obtained from the first micro‐camera prototypes called Caliste 64 and Caliste 256 will be presented to illustrate the expected performance of the instrument.

Caliste 64: detection unit of a spectro imager array for a hard x-ray space telescope

In the frame of the hard X-ray Simbol-X observatory, a joint CNES-ASI space mission to be flown in 2014, a prototype of miniature Cd(Zn)Te camera equipped with 64 pixels has been designed. The device, called Caliste 64, is a spectro-imager with high resolution event timetagging capability. Caliste 64 integrates a Cd(Zn)Te semiconductor detector with segmented electrode and its front-end electronics made of 64 independent analog readout channels. This 1 × 1 × 2 cm3 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, perpendicular to the detection plane. We achieved good noise performances, with a mean Equivalent Noise Charge of ~65 electrons rms over the 64 channels. For the first prototypes, we chose Pt//CdTe//Al/Ti/Au Schottky detectors because of their very low dark current and excellent spectroscopic performances. Recently a Caliste 64 prototype has been also equipped with a 2 mm thick Au//CdZnTe//Au detector. This paper presents the performances of these four prototypes and demonstrates spectral performances better than 1 keV fwhm at 59.54 keV when the samples are moderately cooled down to -10°C.