Philippe Chorier

From visible to infrared: a new detector approach

Sofradir infrared detectors manufacturing is based on the use of a Mercury Cadmium Telluride (MCT) technology hybridized with silicon readout circuit covering a bandwidth from 0.8 to 14 μm thanks to the ability of MCT material to be tuned in terms of cut-off wavelength. Most of the time, infrared detectors are used to answer applications operating between 0.8 μm and 15 μm. New emerging applications express a need for detectors covering a larger waveband and in particular detectors with waveband sensitivity from the visible spectrum up to infrared spectrum. Some of these applications are for example hyperspectral applications where a panchromatic channel is generally associated to an infrared channel. For these applications, the availability of a detector covering these two channels can greatly simplify the instrument architecture. Other potential applications can be spectroscopic applications in visible range needing an extension of the sensitivity of the sensor in near infrared spectrum which cannot be answered with high performances by classical silicon sensors because of the loss of sensitivity between 0.8 μm and 1 μm. Physically, MCT material is able to operate in the visible range and has a potential to offer a high quantum efficiency and large field factor thanks to the hybrid structure. In addition, Sofradir N on P ion implantation process as well as Sofradir hybridization process offer specific advantages to develop high performances detectors sensitive both in visible and infrared spectra. This kind of detector can be an interesting alternative to answer applications needing a large waveband detector. In this paper, Sofradir approach to develop a new kind of detectors sensitive from visible to infrared spectra is presented. Potential applications and the interest of these new Sofradir detectors are discussed versus these needs. Finally, the last results and performances of these detectors are presented.

SOFRADIR infrared detector products: the past and the future

Sofradir has developed second and third generation InfraRed (IR) detectors sensitive in different wavebands covering the 1 to 16 micrometers spectral range. The main material used for cooled IR detector is HgCdTe and Sofradir extends its product range using QWIP for 8-9 micrometers large staring arrays and microbolometers based on amorphous silicon (Si:(alpha) ) thermometer material for uncooled technology. Array characteristics and performances are presented (including new results) and the maturity of technologies and products are discussed for present as well as for short term production activities.

Infrared ROIC for very low flux and very low noise applications

Sofradir is involved in the manufacturing of detectors which cover a large range of wavelengths in the infrared domain from SWIR up to VLWIR for different kind of applications. Thus, different types of ROIC architectures are needed to cover these various kind of applications and operating conditions. As a major player of the infrared market, Sofradir has developed numerous ROIC with architectures enabling to answer most of the infrared applications in tactical, commercial and space domains. Sofradir is now able to present a new detector (384x288 with a 15 μm pitch) especially designed for very low flux applications in the SWIR domain (as astronomy for example). This new ROIC has been developed with CNES support and includes a SFD (Source Follower per Detectors) input stage enabling to achieve a high gain as well as a low readout noise and a vey low power consumption. In this paper, we will describe the architecture and functionalities of this new detector. Then, electro-optical characterizations and results will be described. Finally, main applications of this kind of detectors will be presented.

Very long wavelength infrared detection with p-on-n LPE HgCdTe

Developments made last years at CEA-LETI on p-on-n planar HgCdTe (MCT) photodiodes technology on long-, midand short-wavelength led to the manufacture of focal plane arrays (FPA) demonstrators with high performances. This technology has been successfully transferred to SOFRADIR for industrial production. Improvements have been done on both technology and process to index very long-wavelength spectral band. MCT base layer has been grown by liquid phase epitaxy (LPE) on lattice matched CdZnTe. The n-type doping is achieved during epitaxy by Indium incorporation, as In is naturally active as a donor in MCT. Planar p-on-n photodiodes were manufactured by Arsenic doping. As incorporation is achieved by ion-implantation and activation is done by post-implantation annealing under Hg overpressure. Multiples process settings were tested to find optimized conditions in order to obtain the best detector performances. Cutoff wavelength increase from LWIR at 9.2 μm at 77K was done in two steps, by adjusting technology process to get firstly 12.3 μm cutoff and then 15 μm at 77K. The second step was funded by french National Space Studies Center (CNES) to evaluate p-on-n IRFPAs performances for very long-wavelength detection for space applications such as IASI-NG. Electro-optical characterizations were performed both on test arrays and FPAs. Results show excellent operabilities (over 99.9% with ±0.5×mean value criterion) in responsivity and NETD, and current shot noise limited photodetectors. R0A figure of merit is very high and at the state of the art.

High-performance HgCdTe SWIR detector development at SOFRADIR

HgCdTe (MCT) infrared detectors offer the possibility to tune the material cut-off wavelength between 1 μm and 14 μm in order to adapt the detector detection waveband to the application need. At the same time the detector operating temperature can be tuned as well as the cut-off wavelength between 77 K and more than 230 K in order to offer high performance. Within this range of wavelengths, the SWIR sub- band (1 μm to 3 μm) presents a growing interest for military, commercial and space applications such as non destructive test, spectrometry, SWIR hyperspectral instruments for space applications, ... In addition to the interest of the waveband, these detectors present the advantage of a combination of high performance with the use of thermoelectrical cooler (TEC). Thus, in order to answer the market need for this type of application, Sofradir has developed infrared detectors in the SWIR waveband based on an adaptation of its MCT material to the required waveband and using low noise readout circuits adapted to operate with low photonic current. This paper presents Sofradir MCT detectors results in this waveband including possible trade-offs between the detector performances and operating temperature in function of the application. Then, the SWIR detectors developments and production at Sofradir are presented. In particular, a 320x256 SWIR focal plane array packaged with a TEC and its performances are shown and a particular attention will be paid to the development in progress of a large SWIR focal plane array with high performances between 150 K and 180 K for space application. Finally, trends for future developments in SWIR waveband at Sofradir will be presented.

Sofradir detectors for hyperspectral applications from visible up to VLWIR

Sofradir is involved in the manufacturing of the detector for PRISMA mission. Thanks to this experience, Sofradir has extended its Visible-Near infrared technology, called VISIR. This technology has the huge advantage to enable detection in both visible range and SWIR detection range (0.4μm up to 2.5μm). This 1000x256 array has been especially developed and dedicated for hyperspectral application. MCT Technologies at Sofradir covers also MWIR and LWIR infrared ranges for many years. Detectors for space applications have been already developed and validated and are currently running. For example, 1000x256 or 500x256 arrays 30 μm pitch (called Saturn or Neptune detectors) have already been validated in terms of irradiation behavior, thermal cycling, and ageing. Sofradir is now able to present a large MWIR or LWIR 1016x440 array with a 25μpixel pitch. This detector is also dedicated to hyperspectral application. Thus, with this new detector, Sofradir covers infrared ranges from Visible to VLWIR. After a brief reminding of the current VISIR focal plane array [1], and latest results from this detector, we will present in this paper the 1016x440 new array. The architecture and functionalities of this 1016x440 array will be presented and also the proposed packaging for this detector. Then, main general required performances and previous electro-optical characterizations will be also described.

Development of an SWIR multispectral detector for GMES/Sentinel-2

Within the European Global Monitoring for Environment and Security (GMES) program, the Sentinel-2 mission will provide multi-spectral observations of the Earth surface. The Multi-Spectral Instrument (MSI) developed by Astrium, on board the Sentinel-2 satellite, includes a SWIR channel. Sofradir is in charge of the development, qualification and manufacturing of the infrared detector basis of this SWIR channel. This development relies on Sofradir heritage in terms of design and production of infrared detectors for space applications, and is based on the building blocks validated by Sofradir in the frame of ESA breadboarding program for SWIR hyper-spectral detector development. Whats more, the detector relies on the use of a high reliability 15 μm pitch hybrid Mercury Cadmium Telluride (MCT) technology. Each Sentinel-2 SWIR detector (12 detectors/instrument x 2 satellites) is comprised of an MCT elementary detector including 3 detection lines with a length of 1298 pixels with 15 μm pitch for detection in the 1.3-2.3 μm range, and is integrated into a compact sealed package filled with helium. This device will be used in the 170-200K range. This paper describes the design of the Sentinel-2 SWIR detector. It also presents the performances and the first tests carried out on representative models.

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.

High-performance HgCdTe SWIR detectors for hyperspectral instruments

In the frame of the development of infrared sensors for space applications, Sofradir and the European Space Agency (ESA) have undertaken detector breadboarding activities dedicated for short wave band infrared (SWIR) hyperspectral imagers to be implemented on future earth observation satellites. Based on previous breadboarding activities, a development of a 1000 X 256 SWIR focal plane array has been launched. This focal plane array has a format of 1000 X 256 with a pitch of 30 micrometers . It operates in the 1 to 2.5 micrometers waveband at an operating temperature compatible with passive cooling largely used in satellites. The retina of the detector is based on a photovoltaic HgCdTe array hybridized to a full custom silicon CMOS readout circuit. The readout circuit is versatile so that it answers several system requirements for hyperspectral applications. In this paper, major trade-offs regarding detector design and performances are presented with a particular emphasis on the capability of the retina in terms of noise and dynamic range. Then, the SWIR focal plane array performances are described including different applications requirements needs analysis.

High-performance infrared detectors at Sofradir

The performance of an InfraRed (IR) system is based on a high spatial resolution and on a high thermal resolution. An increase in spatial resolution means an increase in number of pixels, a decrease in detector pitch and an increase in the detector pixel MTF. Regarding thermal resolution increase, it will be achieved mainly by an increase in the maximum quantity of charges which can be stored in the silicon read-out circuits for 2D staring arrays. At present, only cooled detectors answer this need of high performance detectors, such as 2D arrays with TV format resolution and high NETD. In this paper these trends regarding high performance are discussed and recent IRFPA results at Sofradir are presented. Finally, a comparison with uncooled detectors, also processed at Sofradir, is presented, to outline the remaining gap between both types of detectors.