As uncooled microbolometer market grows, there is a need for cost-reduced detectors with the right performance level for the considered market. CMOS devices as transistors or diodes are therefore promising alternatives to standard thermistor materials of microbolometers. In this context CEA LETI developed a 12μm pitch proof of concept of a FDSOI transistor-based microbolometer suspended pixel. The suspended pixel is realized with a 3D integration technological process. This proof of concept aims to validate the technological process by demonstrating pixel capacity to be sensitive to the infrared ux. This work reports details on technological process, electro-optical measurements and discussion on achievable performances.
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.
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 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.
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