M. Talvard, V. Revéret, Y. Le-Pennec, Ph. André, A. Arnaud, L. Clerc, C. de Breuck, C. Delisle, E. Doumayrou, L. Duband, D. Dubreuil, L. Dumaye, E. Ercolani, P. Gallais, M. Lortholary, J. Martignac, J. Relland, L. Rodriguez, F. Roussel, F. Schuller, F. Visticot
We present the latest results obtained with the wide-field submillimeter camera ArTeMiS that is operating on APEX since July 2013. This camera is presently equipped with 1870 pixels at 350 μm and 800 pixels at 450 μm simultaneously. ArTéMiS is a PI-camera open to the ESO and Swedish community. It has already taken a part in the 2016-2017 scientific results of APEX. So far, it offers the best performance in terms of mapping speed at 350 and 450 μm in the southern hemisphere.
Major improvements of the APEX telescope have been achieved at the end of 2017, requiring a complete removal of the instruments in the C-Cabin. In the meantime, the ArTeMiS camera has been kept safe at the ALMA Operations Support Facility (OSF) building. We took advantage of this re-installation to improve a bit more the optical coupling of detectors. We present here the present status of the camera.
Since APEX operation is now guaranteed until the end of 2022, our prospects are to install in time new detectors presently developed at CEA/Léti in the frame of R&D developments made for the future SPICA space mission. Those detectors, which have new polarization capabilities, are also presented.
Vincent Revéret, Philippe André, Jean Le Pennec, Michel Talvard, Patrick Agnèse, Agnès Arnaud, Laurent Clerc, Carlos de Breuck, Jean-Charles Cigna, Cyrille Delisle, Eric Doumayrou, Lionel Duband, Didier Dubreuil, Luc Dumaye, Eric Ercolani, Pascal Gallais, Elodie Groult, Thierry Jourdan, Bernadette Leriche, Bruno Maffei, Michel Lortholary, Jérôme Martignac, Wilfried Rabaud, Johan Relland, Louis Rodriguez, Aurélie Vandeneynde, François Visticot
ArTeMiS is a wide-field submillimeter camera operating at three wavelengths simultaneously (200, 350 and 450 μm). A preliminary version of the instrument equipped with the 350 μm focal plane, has been successfully installed and tested on APEX telescope in Chile during the 2013 and 2014 austral winters. This instrument is developed by CEA (Saclay and Grenoble, France), IAS (France) and University of Manchester (UK) in collaboration with ESO. We introduce the mechanical and optical design, as well as the cryogenics and electronics of the ArTéMiS camera. ArTeMiS detectors consist in Si:P:B bolometers arranged in 16×18 sub-arrays operating at 300 mK. These detectors are similar to the ones developed for the Herschel PACS photometer but they are adapted to the high optical load encountered at APEX site. Ultimately, ArTeMiS will contain 4 sub-arrays at 200 μm and 2×8 sub-arrays at 350 and 450 μm. We show preliminary lab measurements like the responsivity of the instrument to hot and cold loads illumination and NEP calculation. Details on the on-sky commissioning runs made in 2013 and 2014 at APEX are shown. We used planets (Mars, Saturn, Uranus) to determine the flat-field and to get the flux calibration. A pointing model was established in the first days of the runs. The average relative pointing accuracy is 3 arcsec. The beam at 350 μm has been estimated to be 8.5 arcsec, which is in good agreement with the beam of the 12 m APEX dish. Several observing modes have been tested, like “On- The-Fly” for beam-maps or large maps, spirals or raster of spirals for compact sources. With this preliminary version of ArTeMiS, we concluded that the mapping speed is already more than 5 times better than the previous 350 μm instrument at APEX. The median NEFD at 350 μm is 600 mJy.s1/2, with best values at 300 mJy.s1/2. The complete instrument with 5760 pixels and optimized settings will be installed during the first half of 2015.
Silicon-based vacuum packaging is a key enabling technology for achieving affordable uncooled Infrared Focal Plane Arrays (IRFPA) required by a promising mass market that shows momentum for some extensive consumer applications, such as automotive driving assistance, smart presence localization and building management. Among the various approaches studied worldwide, CEA, LETI in partnership with ULIS is committed to the development of a unique technology referred to as PLP (Pixel Level Packaging). In this PLP technology, each bolometer pixel is sealed under vacuum using a transparent thin film deposition on wafer. PLP operates as an array of hermetic micro caps above the focal plane, each enclosing a single microbolometer. In continuation of our on-going studies on PLP for regular QVGA IRFPAs, this paper emphasizes on the innate scalability of the technology which was successfully demonstrated through the development of an 80 × 80 pixel IRFPA. The relevance of the technology with regard to the two formats is discussed, considering both performance and cost issues. We show that the suboptimal fill factor inherent to the PLP arrangement is not so critical when considering smaller arrays preferably fitted for consumer applications. The discussion is supported with the electro-optical performance measurements of the PLP-based 80×80 demonstrator.
Terahertz uncooled antenna-coupled microbolometer focal plane arrays are being developed at CEA Leti for real time
THz imaging and sensing. This detector relies on LETI amorphous silicon uncooled infrared bolometer technology that
has been deeply modified to optimize sensitivity in the THz range. The main technological key lock of the pixel structure
is the quarter wavelength cavity that consists in a thick dielectric layer deposited over the metalized CMOS wafer; such
cavity improves significantly the optical coupling efficiency. Copper plugs connect the microbolometer level down to the
CMOS readout circuit (ROIC) upper metal pads through this thick dielectric cavity. This paper explains how we have
improved the copper vias technology and the challenges we have faced to customize the microbolometer while keeping a
monolithically above IC technology fully compatible with standard silicon processes. The results show a very good
operability and reproducibility of the contact through this thick oxide cavity. Due to these good results, we have been
able to characterize a very efficient THz absorption that enables real time imaging with high sensitivity in the 1-3 THz
range.
Fusion of multispectral images has been explored for many years for security and used in a number of commercial products. CEA-Leti and FBK have developed an innovative sensor technology that gathers monolithically on a unique focal plane arrays, pixels sensitive to radiation in three spectral ranges that are terahertz (THz), infrared (IR) and visible. This technology benefits of many assets for volume market: compactness, full CMOS compatibility on 200mm wafers, advanced functions of the CMOS read-out integrated circuit (ROIC), and operation at room temperature. The ROIC houses visible APS diodes while IR and THz detections are carried out by microbolometers collectively processed above the CMOS substrate. Standard IR bolometric microbridges (160x160 pixels) are surrounding antenna-coupled bolometers (32X32 pixels) built on a resonant cavity customized to THz sensing. This paper presents the different technological challenges achieved in this development and first electrical and sensitivity experimental tests.
Silicon based vacuum packaging is a key enabling technology for achieving affordable uncooled Infrared Focal Plane Arrays (IRFPA) as required by the promising mass market for very low cost IR applications, such as automotive driving assistance, energy loss monitoring in buildings, motion sensors… Among the various approaches studied worldwide, the CEA, LETI is developing a unique technology where each bolometer pixel is sealed under vacuum at the wafer level, using an IR transparent thin film deposition. This technology referred to as PLP (Pixel Level Packaging), leads to an array of hermetic micro-caps each containing a single microbolometer. Since the successful demonstration that the PLP technology, when applied on a single microbolometer pixel, can provide the required vacuum < 10-3 mbar, the authors have pushed forward the development of the technology on fully operational QVGA readout circuits CMOS base wafers (320 x 240 pixels). In this outlook, the article reports on the electro optical performance obtained from this preliminary PLP based QVGA demonstrator. Apart from the response, noise and NETD distributions, the paper also puts emphasis on additional key features such as thermal time constant, image quality, and ageing properties.
Recent developments at the Infrared Lab (LIR) of CEA, LETI have been concentrated on the pixel size reduction of uncooled infrared detectors. With the support from French company ULIS, we have successfully demonstrated the technological integration of 12μm pixels on a commercial TV-format read-out circuit (VGA-ROIC) supplied by ULIS. The 12μm pixel has been designed, processed and characterized in CEA, LETI and first results showed exceptional performances. This paper presents the characterization and associated imagery results.
Vacuum packaging is definitely a major cost driver for uncooled IRFPA and a technological breakthrough is still
expected to comply with the very low cost infrared camera market. To address this key issue, CEA-LETI is developing a
Pixel Level Packaging (PLP) technology which basically consists in capping each pixel under vacuum in the direct
continuation of the wafer level bolometer process. Previous CEA-LETI works have yet shown the feasibility of PLP
based microbolometers that exhibit the required thermal insulation and vacuum achievement.
CEA-LETI is still pushing the technology which has been now applied for the first time on a CMOS readout circuit. The
paper will report on the recent progress obtained on PLP technology with particular emphasis on the optical efficiency of
the PLP arrangement compared to the traditional microbolometer packaging. Results including optical performances,
aging studies and compatibility with CMOS readout circuit are extensively presented.
As packaging represents a significant part of uncooled IR detectors price, a collective packaging process would
contribute to enlarge uncooled IRFPA application to very low cost camera market. Since the first proof of the pixel level
packaging for uncooled IRFPA in 2008, CEA-LETI is still strongly involved in the development of an innovative
packaging technology. This one aims at encapsulating each pixel under vacuum in the direct continuity of the bolometer
process. Moreover, a thin film getter has been developed to be integrated in the micropackaging so as to increase the
packaging lifespan. This paper presents the recent development at CEA-LETI of this pixel level packaging technology
including getter integration and vacuum level measurements.
Reducing production costs would contribute to keep on extending applications of uncooled IRFPA to high volume of
low cost camera market where weight, power and cost reduction are of importance. Since the first proof of the pixel level
packaging for uncooled IRFPA in 2008, CEA-LETI, MINATEC is still strongly involved in an innovative packaging
technology. The main point is that no additional technological steps are necessary to integrate the FPA chip under
vacuum as the microbolometer process comprises itself the vacuum integration at the pixel level. Moreover, to keep the
vacuum level around each microbolometer a thin film getter is deposited. This paper presents the recent development at
CEA-LETI, MINATEC of this innovative packaging technology with getter inside.
Uncooled antenna-coupled microbolometer focal plane arrays have been specifically tailored for optimum performance
in the 1-5 Terahertz range. A prototyping batch of 160 × 120 pixel chips has been designed and then processed above 8"
silicon substrates. An actively illuminated system has been experimentally tested where Quantum Cascade Lasers
(QCLs) are associated with the room-temperature operating 2D sensor. Whereas explosives samples were introduced in
the THz beam optical path, the profile of the modified beam has been sensed by a unique pixel translated via an X-Y
stage. These represent the first demonstration essays of explosive identification using our system.
The traditional design of optical systems is severely complicated by the curved shape of the image surface which
has to be recorded on a planar retina. This constraint decreases the image quality; optical elements are then
added to avoid aberrations and lead to increase the dimensions of the system. However, miniaturization could be
achieved, without decreasing resolution and sensibility, by recording the image surface on a curved retina. The
optical advantages of curved sensors have been demonstrated; the simplification leads to scale down the entire
system. Moreover, the hemispherical shape increases the field of view (FOV).
In this paper the advantages of curved focal plane will be detailed through two applications: spectrometry and
large FOV telescopes. In astronomy, large FOV and miniaturization with good resolution can only be achieved
by curving the focal plane; the difficulty is to curve in a hemispherical shape large detectors. The advantages are
highlighted by the European Extremely Large Telescope (E-ELT) project.
Despite this high interest in curved detectors, only few articles are dedicated to this hemispherical shape
technology. Some solutions exist, which mainly consist in structuring the die in sub-devices. We propose a
solution to curve an IR sensor with a fill factor equal to 100%. To do so, we developed a dedicated bonding
process which allows curving silicon using its mechanical properties. A curved uncooled infrared detector has
been performed without mechanical and electrical damage.
In the outlook of the next 12μm pixel node uncooled IR FPA, the Laboratoire InfraRouge (LIR) of the Electronics and
Information Technology Laboratory (LETI) is still pushing forward the amorphous silicon (a-Si) based microbolometer
technology. A promising approach is the development of a lower resistance a-Si pixel, giving such a microbolometer IR
sensor an edge for enhanced bias current capability, resulting in higher sensitivity.
With this goal in sight, the paper reports on a preliminary study that aims at incorporating a germanium ratio in the
standard amorphous silicon film. This approach successfully resulted in a significantly reduced thin film resistance. Both
physical and electrical characteristics of these low resistance a-SiGe thin films are presented. From these basic parameter
measurements, the paper further elaborates on the expected IR performance when such an a-SiGe film is applied to an
uncooled FPA. Finally, we describe how this new generation of low resistance pixel fits perfectly with the maximum
voltage requirement of advanced CMOS processes, which are needed for future smart ROIC and intelligent IR pixel.
The Laboratoire Infrarouge (LIR) of the Laboratoire d'Electronique et de Technologie de l'Information (LETI) has been
involved in the development of microbolometers for over fifteen years. Two generations of technology have been
transferred to ULIS and LETI is still working to improve performances of low cost detectors. Simultaneously,
packaging still represents a significant part of detectors price. Reducing production costs would contribute to keep on
extending applications of uncooled IRFPA to high volume markets like automotive. Therefore LETI is developing an
on-chip packaging technology dedicated to microbolometers.
This paper presents an original microcap structure that enables the use of IR window materials as sealing layers to
maintain the expected vacuum level. The modelling and integration of an IR window suitable for this structure is also
presented. This monolithic packaging technology is performed in a standard collective way, in continuation of
bolometers' technology. The CEA-LETI, MINATEC presents status of these developments concerning this innovating
technology including optical simulations results and SEM views of technical realizations.
The Laboratoire Infrarouge (LIR) of the Laboratoire d'Electronique et de Technologie de l'Information (LETI) has been
involved in the development of microbolometers for over fifteen years. Two generations of technology have been
transferred to ULIS and LETI is still working to improve performances of low cost detectors. Simultaneously,
packaging still represents a significant part of detectors price. Reducing production costs would contribute to keep on
extending applications of uncooled IRFPA to high volume markets like automotive. Therefore LETI develops an onchip
packaging technology dedicated to microbolometers.
The efficiency of a micropackaging technology for microbolometers relies on two major technical specifications. First,
it must include an optical window with a high transmittance for the IR band, so as to maximize the detector absorption.
Secondly, in order to preserve the thermal insulation of the detector, the micropackaging must be hermetically closed to
maintain a vacuum level lower than 10-3mbar.
This paper presents an original microcap structure that enables the use of IR window materials as sealing layers to
maintain the expected vacuum level. The modelling and integration of an IR window suitable for this structure is also
presented. This zero level packaging technology is performed in a standard collective way, in continuation of
bolometers' technology. The CEA-LETI, MINATEC presents status of these developments concerning this innovating
technology including optical simulations results and SEM views of technical realizations.
Thermal imaging market is today more and more attracted by systems with "instant-on" and low power consumption. "TECless" operation of uncooled microbolometer detectors, that is where no Peltier module is needed, is one of the major features required by the market. In order to fulfill this demand, LETI/SLIR is developing and optimizing a new IRCMOS architecture based on a differential reading implemented with current mirrors. This design simultaneously reduces focal plane temperature sensitivity and simplifies the detector driving. An IRCMOS prototype (320 × 240 with a pitch of 25 μm) has been designed, processed, and characterized. This paper presents an overall view of this new design and the latest characterization results of the prototype.
This paper reviews specifications and performances of a 160 x 120 uncooled infrared focal plane array made from
amorphous silicon micro bolometer with a pixel-pitch of 25 μm, integrated in a LCC package. This detector has been
specifically designed for being produced in large volume. The detector has kept all the innovations developed on the
full TV format ROIC (detector configuration by serial link, low power consumption or wide electrical dynamic range... ) and offers an advanced TEC-less focal plane array well adapted to low end thermal imaging cameras. The specific
appeal of this unit lies in the miniaturization of the packaging and its extremely light weight.In the last part of the paper,
we will look more closely at electro-optical performances of this TEC-less product 160 x 120 as well as the other 25 μm
products like the 384 x 288. We will insist on the wide thermal dynamic range and the low consumption achieved
thanks to the mastering of the amorphous silicon technology coupled with the innovation in the ROIC design.
LETI has been involved in IRFPA development since 1978, the design department (LETI/DCIS) has focused its work on new ROIC architecture since many years. The trend is to integrate advanced functions into the CMOS design in the aim of making cost efficient sensors.
The purpose of this paper is to present the latest developments of an Analog to Digital Converter embedded in a 25μm pixel.
The design is driven by several goals. It targets both long integration time and snapshot exposure, 100% of image frame time being available for integration. All pixels are integrating the IR signal at the same time. The IR signal is converted into digital by using a charge packet counter. High density 130nm CMOS allows to use many digital functions such as counting, memory and addressing.
This new structure has been applied to 25μm pitch bolometer sensors with a dedicated 320 x 240 IRCMOS circuit. Due to smart image processing in the CMOS, the bolometer architecture requirements may become very simple and low cost. The room temperature sensitivity and the DC offset are solved directly in the pixel. This FPA targets low NETD (<50mK), a variation of 80 Kelvin for the FPA temperature, 14 bits output at 50/60Hz video rate.
This paper reviews specifications and performances of a 160 x 120 uncooled infrared focal plane array made from
amorphous silicon micro bolometer with a pixel-pitch of 25 μm, integrated in a LCC package and mass production
oriented.
This new 25 μm pixel design benefits from a higher pixel thermal insulation while keeping low thermal time constant.
Furthermore, we developed this new 25 μm version on the basis of the well mastered 35 μm pixel-pitch technology.
Thanks to this new pixel design and by pushing the design rules even further, a high fill factor has been kept, without the
use of a complex, as well as an expensive, two-level structure.
The detector is described in terms of readout integrated circuit (ROIC) architecture, packaging, operability and electro-optical
performances.
A new read out integrated circuit structure has been designed specifically for this detector. High level functions like gain,
image flip and integration time could be operated through a serial link to minimize the number of electrical
interconnections.
In addition, a small LCC package has been developed enabling mass production dedicated to compact hand held or
helmet mounted cameras.
Thermal imaging market is today more and more attracted by systems with "instant-on" and low power consumption.
Therefore the "TECless" operation of uncooled microbolometer detectors, that is where no Peltier module is needed, is
the major step to fulfill the market requirement. In order to fulfill this trend, LETI/SLIR is working on a new IRCMOS
architecture. This new design is based on a differential reading implemented with current mirrors that simultaneously
reduces focal plane temperature sensitivity and simplifies the detector driving. An IRCMOS prototype (320 x 240 with
a pitch of 25 &mgr;m) has been designed, processed, and characterized. This paper presents an overall view of this new
design and the preliminary characterization results got from this focal plane array.
This paper reviews characteristics and performance of the amorphous silicon microbolometers with a pixel-pitch of 25 μm. We first present the advantages of amorphous silicon uncooled microbolometer technology which enables the production of high volume and low cost uncooled IRFPA. The 25 μm pixel architecture profits from the low thermal time constant of 45 μm pixel detector, to design higher thermal insulated pixel. It enables the development of a 25 μm pixel-pitch detector which has high performance despite the pixel pitch reduction. Thanks to this new pixel design and by pushing the design rules even further, high fill factor has been kept, without the use of complex, as well as expensive, two-level structure. IRFPAs are then described in terms of ROIC architecture, packaging, operability and electro-optical performances. New readout integrated circuit structure has been specially developed for this pixel pitch. High level functions like gain, offset correction, image flip and windowing could be operated through a serial link to simplify the electrical interface.
At a 60Hz frame rate, focal planes with less than 50mK (f/1) NETD are now achieved with high stability regarding environmental temperature.
The Laboratoire Infrarouge (LIR) of the Laboratoire d'Electronique, de Technologie et d'Instrumentation (LETI) has been involved in the development of microbolometers for several years. Therefore a first generation of a high performance technology made from amorphous silicon thermometer has been transferred to ULIS in 2000 and a second generation has been transferred in 2003 for being able to manufacture small pixel pitch uncooled IRFPA. LETI is still working to improve uncooled IRFPA and two principal research orientations are currently studied. First LETI improves performances of low cost detectors for both military and civil applications. Secondly LETI develops a very low cost packaging technology for high volume applications like automotive. Since packaging operations represent today the most significant part of detectors price, LETI has studied an original on-chip packaging structure less expensive than wafer level packaging structure. Il means, that after standard collective technology of bolometers, the process continues with microcaps manufacturing over the microbolometer or over the array of microbolometers.
It requires specific technological developments in order to build this micro-caps and the main difficulty consists in closing hermetically micro-events manufactured previously in the caps, while maintaining expected vacuum around the detector. Another difficulty consists in choosing window cap materials and thickness to minimize IR absorption that is crucial for our application.
LETI will present status of its developments of this innovating technology and SEM views from the first lab test device.
The Laboratoire Infrarouge (LIR) of the Laboratoire d’Electronique, de Technologie et d’Instrumentation (LETI) has been involved in the development of microbolometers for several years. Therefore a first generation of a high performance technology made from amorphous silicon thermometer has been transferred to ULIS in 2000 and a second generation has been transferred in 2003 for being able to manufacture small pixel pitch uncooled IRFPA. LETI is still working to improve uncooled IRFPA and two principal research orientations are currently studied. First LETI improves performances of low cost detectors for both military and civil applications. Secondly LETI develops a very low cost packaging technology for high volume applications like automotive. Since packaging operations represent today the most significant part of detectors price, LETI has studied an original on-chip packaging structure less expensive than wafer level packaging structure. Il means, that after standard collective technology of bolometers, the process continues with microcaps manufacturing over the microbolometer or over the array of microbolometers. It requires specific technological developments in order to build this micro-caps and the main difficulty consists in closing hermetically exhausts holes manufactured previously in the caps, while maintaining expected vacuum around the detector. Another difficulty consists in choosing window cap materials and thickness to minimize IR absorption that is crucial for our application.
LETI will present status of its developments of this innovating technology and SEM views from the first lab test device.
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