MCT p-on-n photodiodes manufactured at Lynred and CEA-LETI have demonstrated state of the art performances for HOT applications. On blue and red mid infrared bands on 15μm pixel pitch, respectively 150 and 130K operating temperatures have been obtained, due to diffusion limited dark current and low defectivity. To achieve equivalent results on smaller pixel, the p-on-n technology at DEFIR, joint laboratory between Lynred and CEA-LETI, has been improved. The technological process was modified to ensure a proper diode formation and to efficiently passivate the interface between MCT and encapsulation layers, especially in the vicinity of the space charge region. The manufactured arrays with a 5.3μm cutoff wavelength have been hybridized on a digital output SXGA (1280×1024) direct injection ROIC with a pixel pitch of 7.5 μm. This paper present the measured current, blackbody responsivity and RMS noise on FPAs with F/4 numerical aperture. We will also discuss spectral response, quantum efficiency, shot-noise limited photodiodes and noise histograms shapes and their distribution tails at 130K. The very low number of defective pixel allow to address higher operating temperature and measurements have been performed at 140K and even 150K with very limited performance degradation. Pixel pitch of 5 μm has been characterized on test chips and present I-V curves with low dispersion and long bias plateau. As for larger pixel sizes, these photodiodes are shot-noise limited. Modulation transfer function has been measured by electron beam induced current and presents high value, up to 56%.
SWAPc (Size, Weight And Power-cost) is a strong trend in IR imaging systems. It requires focal plane arrays with smaller pixels, operating at high temperatures. For MW systems, the full spectral band (up to 5μm) shows a strong advantage over the blue band (4.1µm) as it maximizes the number of incoming photons from a room temperature scene. Few years ago, LETI and Lynred have been developing 7.5μm pitch MCT arrays in MW full band. The first version of this technology was based on n/p diodes operating at 110K maximum temperature. Switching to p/n using extrinsic doping allows today an important gain in dark current, enabling operating temperature up to 130K or even higher. This paper will describe our latest results in the design and fabrication of such HOT small pitch arrays, starting with test chip arrays, followed by the full the characterization of 1280×1024 7.5μm pitch arrays. First order figure of merit (dark current, QE…) are of course considered, but second order figure of merit will also be discussed such as noise tails.
Historically LYNRED (created from the merger of SOFRADIR and ULIS in 2019) has used amorphous silicon materials (“a-Si”) as thermistor materials for its uncooled microbolometer products. If a-Si materials present several advantages that made the success of LYNRED’s products (easy to use and integrate in thermal camera), their intrinsic bolometric performances (i.e. TCR and 1/f noise) are still lower than the commonly used oxides thermistors[1] (i.e. VOx[2] and TiOx[3]). In order to stay in a leading position regarding sensor performances without any trade-off, LYNRED, with the support of its historical R&D partner the CEA-LETI, developed new materials. This strategy has led to new cutting edge products. At the end of 2020 a new 17 µm pixel pitch product (Pico640s[4]), with one of the highest sensor performance reported on the market (typical thermal sensitivity of 25 mK (f/1, 300K, 30Hz)), has been introduced in our product portfolio. We also launched our state of the art 12 µm product range with performances equivalent to our current 17µm product range. More generally, these developments open up new opportunities toward smaller pixel pitch. The symposium presentation and the associated article will present how we have increased the "Signal to Noise Ratio" (SNR) of our products while keeping all the elements which have been our hallmark. Special attention will be paid to NETD, stability of product characteristics during operation and manufacturing excellence. All these features were obtained only by hardware (at the pixel level) improvements without the need to use sophisticated algorithms or specific ROIC functions, in the spirit of LYNRED’s FPA products.
CEA has a long history of customizing optoelectronic components for space and astronomy applications. Based on this expertise, we are undertaking the development of cooled silicon bolometers for millimetre-wave (mm-wave) polarization detection in the next generation of space astronomy missions such as SPICA. Silicon bolometer technology has been demonstrated successfully in space conditions through the Herschel mission. There are many benefits of this technology such as the use of a simple and low-power read-out circuit that can be integrated below the detector array in an above-IC (Integrated Circuit) integration scheme. The advanced integration in a large array and the fabrication process based on microelectronics techniques are key challenges for these developments. This work presents the early results on the design, the fabrication and the first characterization of an innovative pixel for mm-wave polarization detection. The aim is to have an adapted absorption around λ=1.5 mm. These bolometers are composed of an absorbing layer and a thermometer, which are thermally insulated from the substrate. To increase the sensitivity, these detectors are working at very low temperature typically between 50 and 100 mK. The suspended thermometer is made of silicon implanted with Phosphorus and Boron species, and we optimized the design to have a high sensitivity with a 3D Variable Range Hopping conduction (Efros law) and a low 1/f noise at low temperature. The heat capacity of the bolometer is optimized by using a meander shape of the thermometer together with superconducting Ti/TiN thin films for the electromagnetic wave absorption. This sensor is implemented on a standard SOI substrate. Measurements of test structures at room temperature, and first results at very low temperature have been performed to evaluate the electrical performances of the fabricated detectors. The mechanical behaviour of released structures, including pixels with a pitch of 1200μm and 600μm, is presented and discussed.
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.
F. Simoens, J. Meilhan, S. Gidon, G. Lasfargues, J. Lalanne Dera, J. L. Ouvrier-Buffet, S. Pocas, W. Rabaud, F. Guellec, B. Dupont, S. Martin, A. C. Simon
CEA-Leti has developed a monolithic large focal plane array bolometric technology optimized for 2D real-time imaging
in the terahertz range. Each pixel consists in a silicon microbolometer coupled to specific antennas and a resonant
quarter-wavelength cavity. First prototypes of imaging arrays have been designed and manufactured for optimized
sensing in the 1-3.5THz range where THz quantum cascade lasers are delivering high optical power. NEP in the order of
1 pW/sqrt(Hz) has been assessed at 2.5 THz.
This paper reports the steps of this development, starting from the pixel level, to an array associated monolithically to its
CMOS ROIC and finally a stand-alone camera. For each step, modeling, technological prototyping and experimental
characterizations are presented.
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.
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.
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 European Space Agency (ESA) has committed to a multi-spacecraft Cornerstone mission to the planet Mercury.
BepiColombo comprises two spacecraft, one of which (The Mercury Planetary Orbiter platform (MPO)) will contain
remote sensing instruments for making measurements of the planet at wavelengths from the far infrared to γ-rays. The
MERcury Thermal Infrared Spectrometer (MERTIS) measures spectral emittance from Mercury in the range from 7 to
14 μm to derive surface mineralogy. It will employ an uncooled IR focal plane array (IRFPA) at the heart of the
spectrometer. Within this framework, the IRFPA has been developed from a 160 × 120 microbolometer array with a
pixel pitch of 35 μm. This sensor is made from amorphous silicon, which yields a short thermal time constant as well as
very low NETD. Specific attention has been paid to the fact that such detector has to operate in space environment. The
paper will present the specific development under progress and the first results obtained to fulfil the MERTIS
requirements in terms of performance, irradiative and mechanical environments.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.