Michel Vuillermet

Status of MCT focal plane arrays in France

This paper describes the recent developments of Mercury Cadmium Telluride (MCT) infrared technologies in France at Sofradir and CEA-LETI made in the frame of the common laboratory named DEFIR. Among these developments, one can find the crystal growth of high quality and large Cadmium Zinc Telluride (CZT) substrates which is one of the fundamental keys for high quality and affordable detectors. These last years, a great effort was done on this topic and also on MCT epitaxy layer process from Short Waves (SW) to Very Long Waves (VLW). These developments about the quality of the material are needed for the challenge of the High Operating Temperature (HOT). Over these lasts years, the operating temperature of n-on-p MCT detectors was increase of several tens of Kelvin. In addition the development of the p-on-n MCT technology that reduces dark current by a factor ~100 saves about twenty Kelvin more. The next step for the increase in operating temperature will be the complex photodiodes architectures using molecular beam epitaxy layer. The reduction of the pixel pitches is another challenge for infrared technologies for Small Weight and Power (SWAP) detectors. Moreover, this reduction allows the increase in the resolution and consequently in the detection range of the systems. In addition, last results on 3rd generation detectors such as multicolor focal plan arrays, 2D, 3D, low noise and high images rate focal plane array using Avalanche Photodiode (APD) are described.

Advances in detector technologies for visible and infrared wavefront sensing

The purpose of this paper is to give an overview of the state of the art wavefront sensor detectors developments held in Europe for the last decade. The success of the next generation of instruments for 8 to 40-m class telescopes will depend on the ability of Adaptive Optics (AO) systems to provide excellent image quality and stability. This will be achieved by increasing the sampling, wavelength range and correction quality of the wave front error in both spatial and time domains. The modern generation of AO wavefront sensor detectors development started in the late nineties with the CCD50 detector fabricated by e2v technologies under ESO contract for the ESO NACO AO system. With a 128x128 pixels format, this 8 outputs CCD offered a 500 Hz frame rate with a readout noise of 7e-. A major breakthrough has been achieved with the recent development by e2v technologies of the CCD220. This 240x240 pixels 8 outputs EMCCD (CCD with internal multiplication) has been jointly funded by ESO and Europe under the FP6 programme. The CCD220 and the OCAM2 camera that operates the detector are now the most sensitive system in the world for advanced adaptive optics systems, offering less than 0.2 e readout noise at a frame rate of 1500 Hz with negligible dark current. Extremely easy to operate, OCAM2 only needs a 24 V power supply and a modest water cooling circuit. This system, commercialized by First Light Imaging, is extensively described in this paper. An upgrade of OCAM2 is foreseen to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4 synchronized cameras and pyramid wavefront sensing. Since this major success, new developments started in Europe. One is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor necessitates an increase of the pixel format. Two detectors are currently developed by e2v. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. The LGSD is a scaling of the NGSD with 1760x1680 pixels and 3 e readout noise (goal 1e) at 700 Hz (goal 1000 Hz) frame rate. New technologies will be developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for very high QE, full digital outputs with signal digital conversion on chip. In addition, the CMOS technology is extremely robust in a telescope environment. Both detectors will be used on the European ELT but also interest potentially all giant telescopes under development. Additional developments also started for wavefront sensing in the infrared based on a new technological breakthrough using ultra low noise Avalanche Photodiode (APD) arrays within the RAPID project. Developed by the SOFRADIR and CEA/LETI manufacturers, the latter will offer a 320x240 8 outputs 30 microns IR array, sensitive from 0.4 to 3.2 microns, with 2 e readout noise at 1500 Hz frame rate. The high QE response is almost flat over this wavelength range. Advanced packaging with miniature cryostat using liquid nitrogen free pulse tube cryocoolers is currently developed for this programme in order to allow use on this detector in any type of environment. First results of this project are detailed here. These programs are held with several partners, among them are the French astronomical laboratories (LAM, OHP, IPAG), the detector manufacturers (e2v technologies, Sofradir, CEA/LETI) and other partners (ESO, ONERA, IAC, GTC). Funding is: Opticon FP6 and FP7 from European Commission, ESO, CNRS and Université de Provence, Sofradir, ONERA, CEA/LETI and the French FUI (DGCIS).

RAPID, a revolutionary fast optical to NIR camera applied to interferometry

The RAPID camera is an Avalanche Photo Diode array allowing very fast observation from the optical to the infrared with still a low noise per read. The camera born from a large collaboration within the FUI/FOCUS is intensively tested at IPAG (Grenoble) on an interferometric bench and will soon replace the actual camera of the PIONIER interferometer mounted on the visitor focus of the VLTi. We shortly present here the PIONIER instrument design and success to then focus on the RAPID tested performances. We will then resume the performance tests made on sky with the PIONIER. The RAPID camera is the first IR APD matrix ever mounted on an on-sky astronomical instrument. We show here how this fast, low-noise, large-band and sensitive camera improves PIONIER and the optical interferometry in general.

MCT IR detectors in France

This paper describes the status of MCT IR technology in France at Leti and Sofradir. This concerns first evolution of crystal growth of large CZT for substrates, and MCT epilayers grown by LPE and MBE. A focus will be made on extrinsic doping of MCT with Indium and Arsenic for device fabrication. Evolution of detector technology will also be considered for detectors that operate from NIR/SWIR to VLWIR, moving from an n on p vacancy doped technology to a fully extrinsically doped p on n device architecture. Last results on 3rd generation detectors such as multicolor FPAs, HOT detectors and 2D or 3D FPAs that use MCT APD will also be described. Moving to larger FPAs, pixel pitch reduction become mandatory and technology evolution to achieve this goal will be presented .Then, cost reduction achievement through more compact systems that operate at higher temperature and/or integrate optical functions inside the cryostat will also be considered.

Reliability optimization for IR detectors with compact cryo-coolers

IR applications are more and more demanding regarding reliability. It is the case of handheld and lightweight UAV applications. To answer these needs, Sofradir and Thales Cryogenics developed a new product family in order to minimize system weight, cost and to increase detector and cooler reliability. Thales Cryogenics has been working on RM integral Stirling cryocoolers since 1995. Then, as a result of several design improvements, it has been possible to increase significantly the efficiency and the reliability of the RM2-Xi cooler over the last 2 years. The RM2-Xi reliability is measured through life time tests which are run continuously on samples taken out from the mass production. Several new tests profiles have been implemented with different climatic and cooler operation conditions. The results gathered enable an accurate evaluation of the cryocooler reliability in the various mission profiles of the customers applications. Another important performance of an integral cryocooler is efficiency. New mechanical and thermal designs have been implemented. The resulting improvements will be presented and compared with the characteristics of the cryocooler previous version. Based on this new design, Sofradir offers new IR detector products well adapted to handheld and high reliability systems. These new product designs are discussed as well as reliability analysis results.

HOT infrared detectors using MCT technology

Cooled IR technologies are challenged for answering new system needs like the reduction of power consumption. This reduction is requested in new IR system design in particular for cooled IR detection. The goal is to reduce system sizes, to increase system autonomies and reliabilities and globally to reduce system costs. One of the key drivers for cooled systems is the cooler and the operating temperature. As far as operating temperature is concerned, Sofradir and CEALETI LIR put a lot of efforts to increase the operating temperature of IR MCT detectors. The n/p and p/n MCT technologies are improved to operate at high temperature with good performances and particularly with low rate of defective pixels. These detectors operate in the MW blue band, MW and LW. In addition complex structures like nBn structures are developed to go further in the high operating temperature. Results are presented and discussed.

A 320x256 HgCdTe avalanche photodiode focal plane array for passive and active 2D and 3D imaging

CEA-Leti has developed a dual mode infrared array detector for passive (thermal) or active 2D and 3D imaging. Very high sensitivity in 3D mode of operation is achieved by using an HgCdTe avalanche photodiode array with linear gain. The 30 μm pitch detector array is hybridized to a 320x256 pixels Readout Integrated Circuit (ROIC). In passive mode, the 3.6x106 e- well capacity and the low noise of the ROIC allow to reach photon noise limited NETD. For active imaging mode, each pixel measures the time of arrival (3D) and the intensity (2D) of one laser pulse. A sensor based on a detector array with a cut off wavelength of 4.6μm at 80K was fabricated and tested. This paper describes the pixel architecture and presents ranging performances obtained in laboratory conditions. The first 2D and 3D active videos obtained during a field trial of our focal plane array are presented.

The third generation cooled IR detector approach in France

The infrared (IR) detectors produced in France are using up to date and well mastered technologies based on Mercury Cadmium Telluride (HgCdTe-MCT) material. Based on the maturity of these IR detectors and technologies, IR systems have been produced and are more and more used in different applications including military, security, process control, environment monitoring, science and space. The produced IR cameras are the so-called second and second and half generations which are very performing but still have some limitation regarding identification, their ability to operate in all weather conditions, and in terms of compactness and reliability. Therefore researches for moving to the next generation (the third one) of cooled detectors have started to overcome these limitations with the use of bi-color or dual-band as well as to offer more performances. To conduct these researches SOFRADIR and CEA-LETI (LIR) have set up a specific organization, called DEFIR (Design of Excellence for the Future of IR), necessary to increase the efficiency and to reduce the time to production of this new generation. The approach in France regarding the key technologies for the third generation considers the different parameters from the performance to the system cost criteria. Among all the technologies candidates, a new HgCdTe technologies based on molecular beam epitaxy (MBE) have been chosen. Then prototype demonstrations are in progress and confirm the validity of the chosen key technologies.

Space activity at Sofradir and new results for hyperspectral detectors

Sofradir started to work in the field of space applications and especially in the earth observation domain in the beginning of the 1990th. Thanks to the work done with the support of the French Ministry of Defense and the European Space Agency, Sofradir has acquired a large know-how and became a major supplier for European space industry. Sofradir space technologies offer possibilities to develop a large panel of high reliable detectors like long linear arrays or two dimensional arrays covering bandwidth from 0.8 to 15 μm, answering hyperspectral needs, based on qualified Mercury Cadmium Telluride (MCT) technology. Furthermore, Sofradir has a great experience in the field of packaging and offers complete detectors including dewars and coolers. This paper proposes an overview of Sofradir technology capabilities for design of custom space detectors for earth observation or hyperspectral applications, covering the field of detection, hybridisation, readout circuit, focal plane structures, packaging and test. Finally, this paper presents the last results obtained in the development of infrared detectors for hyperspectral instruments.

Main results of Sofradir IRFPAs including IRCCD and IRCMOS detectors

Sofradir has developed many MCT IRFPAs using either the 8 to 12 micron spectral band or the 3 to 5 micron spectral band and using different silicon processor technologies to readout these detector arrays. This paper presents an overview of results coming from different types of arrays, (linear array, TDI array, staring array) using CCD or CMOS readout circuits with different types of signal processors.