O. Limousin

New trends in CdTe and CdZnTe detectors for X- and gamma-ray applications

The CdTe gamma-ray camera IBIS/ISGRI, on board the INTEGRAL satellite launched in October 2002, is currently the largest spectro-imager of this type in the world. The development of this detector, for research in the field of astrophysics, has provided the opportunity to demonstrate the feasibility of massive integration of CdTe nuclear detectors, taking advantage of the CdTe good spectral performances and high modularity. Many other groups in the world work also to further develop detectors using this material in view of improving its spectral performances (crystal quality, electrode geometry and type, electronics and filtering, etc.), the spatial resolution (pixelization of monolithic crystals) and the detection efficiency at high energy (thickness). In this review, I will detail the main directions in which to strive in order to explore these fields in the upcoming years through examples of techniques or applications.

Simbol-X: mission overview

Simbol-X is a hard X-ray mission, operating in the ~ 0.5-80 keV range, proposed as a collaboration between the French and Italian space agencies with participation of German laboratories for a launch in 2013. Relying on two spacecraft in a formation flying configuration, Simbol-X uses for the first time a 20-30 m focal length X-ray mirror to focus X-rays with energy above 10 keV, resulting in over two orders of magnitude improvement in angular resolution and sensitivity in the hard X-ray range with respect to non-focusing techniques. The Simbol-X revolutionary instrumental capabilities will allow us to elucidate outstanding questions in high energy astrophysics such as those related to black-holes accretion physics and census, and to particle acceleration mechanisms, which are the prime science objectives of the mission. After having undergone a thorough assessment study performed by CNES in the context of a selection of a formation flight scientific mission, Simbol-X has been selected for a phase A study to be jointly conducted by CNES and ASI. The mission science objectives, the current status of the instrumentation and mission design are presented in this paper.

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.

A basic component for ISGRI, the CdTe gamma camera on board the INTEGRAL satellite

A basic component, called Polycell, has been developed for the ISGRI (INTEGRAL Soft Gamma Ray Imager) CdTe camera on board the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) satellite. Operating at room temperature, it covers the 20 keV -1 MeV energy range. It features a sub-ensemble of 16 CdTe detectors and their associated front end electronics. This electronics is based on 4-channel analog-digital ASICs. Their analog part features a low noise preamplifier, allowing a threshold below 20 keV and a pulse rise-time measurement which permits a charge loss correction. The digital part ensures the internal acquisition timing sequence as well as the dialogue with external electronics. Two versions of the ISGRI ASIC have been developed in a collaboration of two CEA microelectronics teams from CEA/DTA/LETI/DSYS and CEA/DSM/DAPNIA/SEI, respectively on a standard CMOS AMS process hardened against radiation by lay-out, and on a Silicon On Insulator process (DMILL MHS), the latter being latch-up free. This paper presents the ASIC and polycell architecture as well as experimental results obtained with polycells equipped with AMS ASICs.

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.

SIMBOL-X: a formation flying mission for hard-x-ray astrophysics

SIMBOL-X is a hard X-ray mission, operating in the ~ 0.5-70 keV range, which is proposed by a consortium of European laboratories in response to the 2004 call for ideas of CNES for a scientific mission to be flown on a formation flying demonstrator. Relying on two spacecrafts in a formation flying configuration, SIMBOL-X uses for the first time a ~ 30 m focal length X-ray mirror to focus X-rays with energy above 10 keV, resulting in a two orders of magnitude improvement in angular resolution and sensitivity in the hard X-ray range with respect to non focusing techniques. The SIMBOL-X revolutionary instrumental capabilities will allow to elucidate outstanding questions in high energy astrophysics, related in particular to the physics of accretion onto compact objects, to the acceleration of particles to the highest energies, and to the nature of the Cosmic X-Ray background. The mission, which has gone through a thorough assessment study performed by CNES, is expected to start a competitive phase A in autumn 2005, leading to a flight decision at the end of 2006, for a launch in 2012. The mission science objectives, the current status of the instrumentation and mission design, as well as potential trade-offs are presented in this paper.

The basic component of the ISGRI CdTe γ-ray camera for space telescope IBIS on board the INTEGRAL satellite

Abstract The γ-ray imager telescope IBIS, on board the INTEGRAL satellite, features a coded mask aperture and two detector arrays. The first detector array (ISGRI) is an assembly of 16xa0384 CdTe detectors (4×4 mm 2 large, 2 mm thick) operating at room temperature under 100 V bias. ISGRI covers the lower part (20 keV–1 MeV) of the IBIS energy range (20 keV–10 MeV). The polycell is the basic component of the ISGRI detector array. It is made of 16 CdTe pixels and their front-end electronics. In order to improve the response of the instrument, a charge loss correction based on the charge-drift time is necessary. Therefore, the front-end electronics performs the rise-time measurement in addition to the standard pulse-height measure. On the other hand, the necessarily tight packaging and the limited available power requires the use of ASICs. These 4-channel analog–digital ASICs should be radiation resistant either through the use of a latch up free technology or by applying an appropriate layout design. The optimal operating temperature (around 0°C) is ensured under vacuum conditions by radiative cooling. This paper describes the ISGRI design with particular emphasis on the ASICs and polycells, and reports preliminary performance measurements.