LETI/LIR has been involved for a few year in the field of uncooled detectors and has chosen amorphous silicon for its microbolometer technology development. Uncooled IR detectors pave the way to reduced weight systems aboard satellites. The silicon compatibility of our thermometer is a key parameter which has enabled a very fast technology development and transfer to industry. This competitive technology is now able to provide a new approach for IR detectors for space applications.
This paper presents the main characteristics of the CEA / LETI technology which is based on a monolithically integrated structure over a fully completed readout circuit from a commercially available 0.5 μm design rules CMOS line. The technology maturity will be illustrated by the results obtained at LETI/LIR and SOFRADIR on a 320 x 240 with a pitch of 45 μm. First improvement on device reliability and characterization results will be presented.
The Laboratoire Infrarouge (LIR) of the Electronics and Information Technology Laboratory (LETI) has been involved
in the development of Uncooled IR technology since 1986. Along these years, more and more technology improvements
have been done at LETI and ULIS for large-scale production and broad commercialisation of advanced devices.
With ULIS support, LETI is still pushing forward the technology, taking advantage of the well-established user-friendly
properties of amorphous silicon. These developments are primarily driven by performance enhancement and cost
reduction.
In this outlook, the paper will first report on the recent improvements we have brought to microbolometer FPAs with
35 μm pixels, resulting in 11 mK NETD measurements. At the same time, 25 μm pixels have been demonstrated for high
performance achievement. LETI is also developing a 1024 x 720, 17 μm pitch IRFPA that aims very challenging NETD
< 40 mK; the paper will give the main concerns we have focused on to achieve this result. Finally, the LETI is preparing
the next generation of very low cost Uncooled IRFPA, thanks to passing on all the microbolometer technology
developments to the LETI 8 inches wafer facility.
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.
The Laboratoire Infrarouge (LIR) of the Electronics and Information Technology Laboratory (LETI) has been involved since 1993 in the development of subsequent bolometer technological process that aims at reducing the pitch of the amorphous silicon based uncooled microbolometer FPAs. These developments are primarily driven by cost reduction and system miniaturisation concerns. In this outlook, the LIR has recently developed a specific amorphous silicon technology for a 25 μm pitch IRFPA achievement.
This new structure still relies on a single level microbridge arrangement and special cares have been taken in order to ensure noise reduction, thermal insulation increase with a special attention to low thermal time constant achievement. This paper presents a complete characterization of an advanced dedicated 320 x 240 IRCMOS circuit that takes advantage of this new 25 μm pitch bolometer process. Apart from NEDT (< 70 mK) histogram, the paper also puts emphasis on parameters that appear more and more as key points in IR system, like the thermal time constant and the residual fixed pattern noise.
A sensor based on selective optical absorption allows monitoring of hazardous engine exhaust emissions such as gaseous hydrocarbons and carbon monoxide. The IR components presented here offer the potential to develop a compact, fast and selective sensor reaching the technical and cost requirements for on-board automotive applications. Optical gas monitoring requires light sources above 3 μm since most of the gas species have their fundamental absorption peaks between 3 and 6 μm. We report here on resonant microcavity light sources emitting at room temperature between 3 and 5 μm. The emitter combines a CdxHg1-xTe light emitting heterostructure and two dielectric multilayered mirrors. It is optically pumped by a commercial III-V laser diode. The principle of the resonant microcavity emitter allows tailoring of the emission wavelength and the line width to fit the absorption band of a specific gas, ensuring a very good selectivity between species. Moreover, this kind of emitter allows fast modulation enabling high detectivity and short response time. We report performances of light sources in the range 3 - 5 μm allowing the detection of hydrocarbons and carbon monoxide. Association of emitters peaking at different characteristic wavelengths with a single broad band detector allows designing of an optical sensor for several gas species. Sensitivity and time response issues have been characterized: detection of less than 50 ppm of CH4 on a 15 cm path has been demonstrated on synthetic gas; analysis of exhaust gases from a vehicle has allowed the resolution of a cylinder time. This optical sensor offers the potential of various on-board automotive applications.
A sensor based on selective optical absorption allows monitoring of hazardous engine exhaust emissions such as gaseous hydrocarbons and carbon monoxide. The IR components presented here offer the potential to develop a compact, fast and selective sensor reaching the technical and cost requirements for on-board automotive applications. Optical gas monitoring requires light sources above 3μm since most of the gas species have their fundamental absorption peaks between 3 and 6 μm. We report here on resonant microcavity light sources emitting at room temperature between 3 and 5μm. The emitter combines a CdxHg1-xTe light emitting heterostructure and two dielectric multilayered mirrors. It is optically pumped by a commercial III-V laser diode. The principle of the resonant microcavity emitter allows tailoring of the emission wavelength and the line width to fit the absorption band of a specific gas, ensuring a very good selectivity between species. Moreover, this kind of emitter allows fast modulation enabling high detectivity and short response time. We report performances of light sources in the range 3-5μm allowing the detection of hydrocarbons and carbon monoxide. Association of emitters peaking at different characteristic wavelengths with a single broad band detector allows designing of an optical sensor for several gas species. Sensitivity and time response issues have been characterized: detection of less than 50ppm of CH4 on a 15cm path has been demonstrated on synthetic gas; analysis of exhaust gases from a vehicle has allowed cylinder to cylinder resolution. This optical sensor offers the potential of various on-board automotive applications.
In this paper we report on the CEA/LETI infrared laboratory activity in both HgCdTe cooled detectors and amorphous silicon uncooled microbolometers. An overview of the recent developments will be given while the future perspectives of these IR technologies will be highlighted in the context of space applications.
The unique realization of a megapixel HgCdTe MWIR focal plane array with a 15μm pitch was completed in 2003. The electro-optical performances at LN temperature of this high resolution IRFPA will be given extensively.
Beside this large 2D array achievement, CEA/LETI is strongly involved in the development of an innovative cooled multispectral technology that requires a specific HgCdTe growing process to achieve a stack of two dual band photodiodes in each pixel. This technology primarily relies on the molecular beam epitaxy (MBE) of a multiple (211)HgCdTe films grown on a lattice matched CdZnTe substrate. The device structure will be discussed as well as the elementary detectors characteristics which have been found to exhibit performances very close to those obtained in single colour detectors. The main electro-optical performances obtained at LN temperature of a two colours 128x128 IRCMOS FPA, 50μm pitch, operating sequentially within the MWIR (3-5μm) will be presented.
The well establish availability of uncooled infrared detectors has opened new perspectives when miniaturization, weight, power and reliability are of paramount importance. Moreover the recent breakthrough of the performance of these sensors leads to new applications where enhanced resolution is required. The article will review the state of the art of CEA/LETI uncooled IR technology through various examples of focal plane arrays and the future trends of this uncooled technology will be considered. The trade-off between thermal resolution and time constant which is a critical parameter for earth observation will be largely discussed.
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.
After the development of an amorphous silicon based uncooled microbolometer technology, LETI and ULIS are now working to facilitate the IR focal plane arrays (IRFPA) integration into equipment in order to address a very large market. Achievement of this goal needs the integration of advanced functions on the focal plane and the decrease of manufacturing cost of IRFPA by decreasing the pixel pitch and simplifying the vacuum package. We present in this paper the new designs for readout circuit and packages which will be used for 320×240 and 160×120 arrays with a pitch of 35μm.
The emergence of uncooled infrared detectors has opened new opportunities for IR imaging both for military and civil applications. Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power. Uncooled infrared sensor technology has advanced rapidly in the past few years. Higher performance sensors, electronics integration at the sensor, and new concepts for signal processing are generating advanced infrared focal plane arrays. This would significantly reduce the cost and accelerate the implementation of sensors for applications such as surveillance or predictive maintenance. We present the uncooled infrared detector operation principle and the development at CEA/LETI from the 256×64 with a pitch of 50 μm to the 320×240 with a pitch of 35 μm.
LETI has been involved in Amorphous Silicon uncooled microbolometer development since 1992. This silicon IR detection is now well mastered and matured so that industrial transfer of LETI technology was performed in 2000 towards Sofradir. Industrial production of 320 μ240 microbolometer array with 45μm pitch is then started., we present the readout circuit architectures designs and its evolution from the 256×64 array to the different version of 320×240 arrays. Electro-optical results obtained from these IRCMOS are presented. NEDT close to 30 mK is now obtained with our standard microbolometer amorphous silicon technology.
The emergence of uncooled infrared detectors has opened new opportunities for IR imaging both for military and civil applications. Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power. Uncooled infrared sensor technology has advanced rapidly in the past few years. Higher performance sensors, electronics integration at the sensor, and new concepts for signal processing are generating advanced infrared focal plane arrays. This would significantly reduce the cost and accelerate the implementation of sensors for applications such as surveillance or predictive maintenance. We present the uncooled infrared detector operation principle and the development at CEA/LETI from the 256 x 64 with a pitch of 50 micrometers to the 320 x 240 with a pitch of 35 micrometers . LETI has been involved in Amorphous Silicon uncooled microbolometer development since 1992. This silicon IR detection is now well mastered and matured so that industrial transfer of LETI technology was performed in 2000 towards Sofradir. Industrial production of 320 x 240 microbolometer array with 45micrometers pitch is then started., we present the readout circuit architectures designs and its evolution from the 256 x 64 array to the different version of 320 x 240 arrays. Electro-optical results obtained from these IRCMOS are presented. NEDT close to 30 mK is now obtained with our standard microbolometer amorphous silicon technology.
The emergence of uncooled infrared detectors has opened new opportunities for IR imaging both for military and civil applications. Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power. Uncooled infrared sensor technology has advanced rapidly in the past few years. Higher performance sensors, electronics integration at the sensor, and new concepts for signal processing are generating advanced infrared focal plane arrays. This would significantly reduce the cost and accelerate the implementation of sensors for applications such as surveillance or predictive maintenance. We present the uncooled infrared detector operation principle and the development at CEA/LETI from the 256 x 64 with a pitch of 50 micrometers to the 320 x 240 with a pitch of 35 micrometers . LETI has been involved in Amorphous Silicon uncooled microbolometer development since 1992. This silicon IR detection is now well mastered and matured so that industrial transfer of LETI technology was performed in 2000 towards Sofradir. Industrial production of 320 x 240 microbolometer array with 45micrometers pitch is then started. After a description of the technology and the methodology for reliability enhancement, we present the readout circuit architectures designs and its evolution from the 256 x 64 array to the different version of 320 x 240 arrays. Electro-optical results obtained from these IRCMOS are presented. NEDT close to 30 mK is now obtained with our standard microbolometer amorphous silicon technology.
LETI LIR has been involved in Amorphous Silicon uncooled microbolometer development for years. This technology is now in production at Sofradir and first delivery have already been done to customers. From our background in modeling and material mastering LETI/LIR concentrate now on performance enhancement. This is a key point for cost reduction due to the fact that signal to noise ratio enhancement will allow us to decrease the pitch. A new approach of packaging is also described in this paper and first results are displayed. A new technological stack of amorphous silicon fully compatible with industrial process is presented. Electro-optical results obtained from an IRCMOS 320 X 240 with 35 μm pitch are presented. NETD close to 35 mK has been obtained with our new embodiment of amorphous silicon microbolometer technology.
LETI LIR has been involved in amorphous silicon uncooled microbolometer development for a few years. This silicon IR detection is now well mastered and matured so that industrial transfer LETI/LIR technology is performed towards Sofradir. Industrial production of 320x240 microbolometer array with 45 micrometers pitch is now started. After a short description of the technology and the readout circuit architecture we focus on device reliability which is the key point for microbolometer application. Methodology for reliability enhancement is described. First results obtained on amorphous silicon reliability are presented. Electro-optical results obtained from an IRCMOS 320x240 with 45 micrometers pitch are presented. NEDT close to 70 mK can be obtained with our standard microbolometer amorphous silicon technology.
High resolution infrared imaging system calls for very long scanning arrays with several thousands of detectors and high performance. This paper presents the technological developments and the electro-optical performance obtained at LETI/SLIR (Infrared Laboratory) on linear HgCdTe (MCT) arrays working in the 3-5, 8-10 and 11-12.5 micrometers spectral ranges. These large arrays have an indirect hybrid architecture composed of butted HgCdTe PV detection circuits and Si readouts hybridized on a mechanically close-matched fanout substrate. Defect free dicing and butting, respecting the detector pitch, is made by accurate and nondamaging techniques.
LETI LIR has been involved in Amorphous Silicon uncooled microbolometer development for a few years. This silicon IR detection is now well mastered and matured so that industrial transfer LETI/LIR technology is performed towards Sofradir. Industrial production of 320 X 240 mirobolometer array with 45 micrometer pitch started. After a short description of the technology and the readout circuit architecture we focus on device reliability which is the key point for microbolometer application. Methodology for reliability enhancement is described. First results obtained on amorphous silicon reliability are presented. Electro-optical results obtained from an IRCMOS 320 X 240 with 45 micrometer pitch are presented. NEDT close to 70 mK can be obtained with our standard microbolometer amorphous silicon technology.
A 640 X 480 snapshot IRCMOS array with 25 micron pitch operating in the 3 - 5 microns range was fabricated and an image demonstrated at the Infrared Laboratory (LIR). The readout circuit with 2 pC charge handling capacity was designed and processed with a 1.2 micrometer design rules standard CMOS technology. Photovoltaic (PV) detectors were achieved by ion implantation in liquid phase epitaxy MCT layers and interconnected by indium bumps on the readout circuit. A description of the component is given and the main electro-optical characteristics are presented. The pixel operability is greater than 99.8% and a NEDT of 15 mK was measured at half dynamics. Excellent imagery has been obtained with this component operating at 77 K and f/2 optics.
High resolution infrared imaging system calls for very long scanning arrays with several thousands of detectors and high performance. This paper presents the recent technological developments and the electro-optical performances obtained at LETI/LIR (infrared laboratory) on 1500 detector linear HgCdTe arrays working in the 3 - 5 and 8 - 10 micrometer spectral ranges. These very large arrays (length approximately equals 50 mm) have an indirect hybrid architecture composed of butted HgCdTe PV detection circuits and Si CMOS readouts hybridized on a mechanically close-matched fanout substrate. Defect free dicing and butting, respecting the detector pitch, is made by accurate and non damaging techniques.
High resolution infrared imaging system calls for very long scanning arrays with several thousands of detectors and high performance. This paper presents the recent technological developments and the electrooptical performances obtained at LETI I LIR (Infrared Laboratory) on 1500 detector linear HgCdTe arrays working in the 3-5 and 8-10 pm spectral ranges. These very large arrays (length 50 mm) have an indirect hybrid architecture composed of butted HgCdTe PV detection circuits and Si CMOS readouts hybridized on a mechanically close-matched fanout substrate. Defect free dicing and butting, respecting the detector pitch, is made by accurate and non damaging techniques. Keywords: Infrared, HgCdTe, linear array, butting, focal plane array
A 256 by 256 IRCMOS array with a 35 micron pitch operating at 88 K and above 10 microns has been developed at LETI/LIR. High performances have been obtained owing on one hand to a reduced dark current detector technology and on the other hand to a new readout circuit architecture which maximizes both charge handling capacity and responsivity. We have measured a NEDT of 13 mK at 88 K for a cutoff wavelength of 10.1 micrometer. A description of the array is given and the main electro-optical characteristics of the component are presented.
Current tendencies in infrared arrays are to decrease the pitch and increase the number of detectors without degrading the electro-optical performances. It is therefore necessary to maximize the charge-handling capacity in the pixel. In this paper, a new architecture particularly-well suited to this kind of application is described. A brief review of classical readout circuits is given. The advantages and drawbacks of these architectures are emphasized. The new architecture is discussed in detail, compared to existing ones and the performance of the new readout circuit evaluated. Results measured on IRCMOS designed with the new architecture are presented.
Recent results obtained at LIR on PV detectors made on LPE layers and interconnected by metallic bumps to CCD silicon circuits are described. Test results are reported on 128 x 128 mosaics with 50 micron pitch detecting in the 3-5 micron wavelength rate at 77 and 200 K operating temperatures. The high quality and homogeneity of the CMT epilayers and the maturity of the photovoltaic and hybrid technology for large-size arrays are demonstrated, and the feasibility of operation at the above temperatures is shown.
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