Jean-Pierre Chatard

Progress in HgCdTe homojunction infrared detectors

Abstract SOFRADIR/LIR HgCdTe homojunction infrared (IR) detector technology has already demonstrated its high maturity level by delivering more than 1000 s and third generation detection dewar assemblies. This specific HgCdTe photovoltaic technology proves high performance including low fixed pattern noise and high yield. This is due to the high impedance photodiode (including the longwave band) obtained thanks to the high-quality HgCdTe material used and the planar homojunction technology based on a very efficient passivation and ion implantation. Furthermore, much progress has been made in reducing IR detector cost and proposing new detector dewar assemblies. The efforts are mostly dedicated to the increase in HgCdTe wafer dimensions and yield for large staring arrays, and to the increase in IR detector operating temperature in order to reduce dewar and cooler assembly cost as well as cooler input power. Thus, Sofradir offers HgCdTe staring arrays operating at full performance at over 90 K for 8–10 μm wave band and at around 130 K for 3–5 μm wave band. Based on existing detector results, the main technological progress is presented. In particular, a 320 × 240 InfRared Focal Plane Array (IRFPA) is presented in 3–5 μm at 130 K and in 8–10 μm with the same performance at 80 and 90 K. Those new staring arrays provide very high thermal sensitivity (less than 10 mK) and low fixed pattern noise. A 5 cm long linear array using a special butting hybridization technique and allowing zero defect at the joints is introduced. It consists of a one 1500 × 1 linear array sensitive in the 3–5 μm wave band. The same format, sensitive in the 8–12 μm wave band, is also presented. Finally, future trends are discussed.

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.

MCT technology challenges for mass production

Second generation infrared (IR) detectors are now mature at the production level. These detectors are mostly based on HgCdTe (MCT) materials technology. The main second generation detectors at the mass production level are the 288 4 long wave length for most of the European forward-looking infrared (FLIR) and the 480 6 long wave length for the U.S. Army SADA applications. As far as the 288 4 is concerned, SOFRADIR has delivered more than 3000 units already and the market is estimated to be 15,000 units at least! The market is also very large for SADA II units and SOFRADIR has produced them since the end of 1999. Thus, SOFRADIR produces large quantities of mercury cadmium telluride (MCT) detectors and has a unique experience for MCT detectors in mass production. MCT materials technology challenges for mass production concern the main following issues: Quality and reproducibility, MCT wafer size increase, array yield level increase, and the collective manufacturing approach. These issues are discussed in detail in this paper as well as future trends.

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.

LW MCT IRFPA cost optimization

Today, Sofradir has delivered more than 2000 LW new generation IR detectors which gives a very important data base for yield and performance analysis. The target of this paper is on one hand to show a performance statistical analysis both globally and over the year which demonstrates the validity of MCT choice and on the other hand to present the impact of the improvement of the process and the adaptation of tooling on the cost.

Long linear MWIR and LWIR HgCdTe arrays for high-resolution imaging

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.

Low-cost amorphous-silicon-based 160x120 uncooled microbolometer 2D array for high-volume 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 reduce the pixel pitch in order to decrease the total system by using smaller optics. We present the characterization of a 160 x 120 infrared focal plane array with apixel pitch of 35 μm. The amorphous silicon technology is the latest one developed by CEA/LETI and transferred to ULIS to manufacture 160 x 120 2D arrays. We developed for this device a low cost package based on existing technologies. 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 process control applications where spatial resolution is less important than device costs. The electro-optical characterization is presented.

1500-element linear MWIR and LWIR HgCdTe arrays for high-resolution imaging

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

High-performance infrared detectors at Sofradir

The performance of an InfraRed (IR) system is based on a high spatial resolution and on a high thermal resolution. An increase in spatial resolution means an increase in number of pixels, a decrease in detector pitch and an increase in the detector pixel MTF. Regarding thermal resolution increase, it will be achieved mainly by an increase in the maximum quantity of charges which can be stored in the silicon read-out circuits for 2D staring arrays. At present, only cooled detectors answer this need of high performance detectors, such as 2D arrays with TV format resolution and high NETD. In this paper these trends regarding high performance are discussed and recent IRFPA results at Sofradir are presented. Finally, a comparison with uncooled detectors, also processed at Sofradir, is presented, to outline the remaining gap between both types of detectors.