Jean-Luc Tissot

Uncooled amorphous silicon technology enhancement for 25-μm pixel pitch achievement

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.

LETI/LIR's amorphous silicon uncooled microbolometer development

Today, a large number of uncooled infrared detector developments are under progress due to the availability of silicon technology that enables realization of low cost 2D IR arrays. LETI/LIR, which has been involved in this field for a few years, has chosen resistive amorphous silicon as thermometer for its uncooled microbolometer development. After a first phase dedicated to acquisition of the most important detector parameters in order to help the modeling and technological development, an IRCMOS laboratory model (256 X 64 with a pitch of 50 micrometer) was realized and characterized. It was shown that NETD of 90 mK at f/1, 25 Hz and 300 K background can be obtained with high thermal insulation (1.2 107 K/W).

Amorphous silicon based uncooled microbolometer IRFPA

LETI LIR has been involved in Amorphous Silicon uncooled microbolometer development for a few years. This paper reports recent progress that have been carried out both in technological and product field. Due to the very particular features of LETI LIR technology, large fill factor, high thermal insulation, associated with small thermal time constant, can be achieved, resulting in a large detector responsivity. In addition, pulsed bias has been introduced showing performance improvement in terms of power consumption, reliability, faster thermal response. A model has been developed which accounts for these improvements. Electro-thermal results obtained from an IRCMOS 256 X 64, 47 micrometers detector sizes, laboratory prototype show that NETD less than 50 mK at f/1 can be obtained even at a high video scanning rate, that is compatible with micro scanning techniques.

LETI/LIR's uncooled microbolometer development

Today, a large number of uncooled infrared detector developments are under progress due to the availability of silicon technology that enables realization of low cost 2D IR arrays. LETI/LIR, which has been involved in this field for a few years, has chosen resistive amorphous silicon as thermometer for its uncooled microbolometer development. After a first phase dedicated to acquisition of the most important detector parameters in order to help the modeling and technological development, an IRCMOS laboratory model (256 X 64 with a pitch of 50 micrometer) was realized and characterized. It was shown that NETD of 70 mK at f/1, 25 Hz and 300 K background can be obtained with high thermal insulation (1.2 107 K/W).

Latest amorphous silicon microbolometer developments at LETI-LIR

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.

Enhanced amorphous silicon technology for 320 x 240 microbolometer arrays with a pitch of 35 um

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.

320x240 uncooled microbolometer 2D array for radiometric and process control applications

Uncooled infrared focal plane arrays are being developed for a wide range of thermal imaging applications. Developments are focused on the improvement of their sensitivity enabling the possibility to manufacture high performance radiometric devices with internal temperature stabilized shield to determine precisely the input infrared flux. We present the characterization of a new radiometric device obtained from 320 x 240 uncooled microbolometer array with f/1.4 aperture. This device is well adapted to radiometric or process control applications and moreover shows a high level of stability due to the internal temperature stabilized shield which prevents the detector from camera internal temperature shift artifacts.

320 x 240 microbolometer uncooled IRFPA development

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.

Uncooled amorphous-silicon technology: high-performance achievement and future trends

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.

Low cost uncooled IRFPA and molded IR lenses for enhanced driver vision

Uncooled infrared focal plane arrays are being developed for a wide range of thermal imaging applications. CEA / LETI developments are focused on the improvement of their sensitivity enabling the possibility to reduce the pixel pitch and the decrease of the system cost by using smaller optics. We present the characterization of a 160 x 120 infrared focal plane array with a pixel pitch of 35 μm. The amorphous silicon based technology is using recent process enhancement developed by CEA / LETI and transferred to ULIS. ULIS developed for this device a low cost package. The readout integrated circuit structure is using an advanced skimming function to enhance the pixel signal exploitation. This device is well adapted to high volume infrared imaging applications where spatial resolution (in term of pixel number) is less important than cost. The electro-optical characterization is presented. Besides, A unique and high precision molding technology has been developed by Umicore IR Glass to produce low cost chalcogenide infrared glass lenses with a high performance level. Spherical, aspherical and asphero-diffractive lenses have been manufactured with very accurate surface precision. The performances are comparable to those of an optic made with aspherical germanium. This new glass named GASIR offers an alternative solution to germanium for thermal imaging, especially for medium and high volumes applications. These two key technologies are well adapted to develop infrared driver vision enhancement (DVE) system for commercial application. A European project named ICAR has been setting up to exploit these advantages. An overview of the project will be given.