Olivier Saint-Pe

Influence of pixel topology on performances of CMOS APS imagers

This paper describes a 128 X 128 pixels prototype array organized as sub-arrays of 32 X 32 pixels each, with 21 micrometers pixel pitch. The sub-arrays, photodiode or photogate based, are implemented using a standard 0.7 micrometers CMOS process. Various topologies of the photosensitive area have been implemented and some of them have an optical metal shield over the so-called non-sensitive area to evaluate the contribution of the active electronic area to the responsivity of the sensor. A synthesis of the measurements carried out by CIMI-SUPAERO and MMS, addressing darkness parameters, noise, photometric and radiometric performances, are presented with emphasis on the photogate type pixels. Results of spot-scan analysis and crosstalk measurements performed on selected topologies are also reported. Several samples were irradiated at different proton doses and their related behavior is discussed. From these results, a new 512 X 512 pixels array has been designed for space applications. The main features of this APS device are presented here.

Design and characterization of CMOS APS imagers with two different technologies

In the paper, we present experimental results from measurements on CMOS PAS imager designed by CIMI-SUPAERO on two different technologies. In both cases, pixels with photoMos and photodiode structures have been designed. The first circuit has been developed using a standard CMOS DLP/DLM 1.2 micrometers process from Austria Micro Systems. The detector array consists of 32 X 32 square pixels with 50 micrometers pixel pitch; fill factor is 75 percent for photodiode and 50 percent for photoMos. The circuit is also including row and column address decoders and the readout circuitry so as to perform on-chip correlated double-delta sampling to reduce column to column fixed pattern noise. Two other chips have been developed with a standard CMOS SLP/DLM process form MIETEC with 0.7 micrometers design rules, which includes a 128 X 128 pixels array, with 21 micrometers pixel pitch and analogue redout circuitry. Among 10 different arrays, no faulty one was observed for both circuits. In this paper, we compare both performances of 32 X 32 pixels and 128 X 128 pixels in terms of dark current, quantum efficiency, conversion gain, dynamic range, linearity and spatial uniformity.

Recent experimental results from a CMOS Active Pixel Image Sensor with Photodiode and Photogate Pixels

An APS test circuit including three 32 by 32 arrays with photodiode and photogate pixels has been developed using a 1.2 micrometer double-layer polysilicon double-layer metal CMOS process. The first experimental results have been published in the Aerosense conference in Orlando (April 1996). In this paper we present the latest experimental results including radiation hardness, quantum efficiency and spot scan pixel sensitivity.

Uncooled focal plane array for thermal observation of the Earth

A medium scale infrared sensor dedicated to applications in agriculture, hydrology, forest fires and environment has been studied within the framework of a European Commission contract. An innovative push broom concept using linear arrays of uncooled microbolometers has been preferred to a traditional scanner concept using cryogenically cooled photoconductor detectors, for its performances and because it does not require any cooling, and is free of micro-vibrations. The instrument offers a resolution of 250 m for a swath width of about 1400 km, and the radiometric resolution is better than 0.5 K in two spectral channels around 11 and 12 micrometer. Focal plane topology and radiometric modeling will be presented in this paper, demonstrating the suitability of microbolometers focal planes for medium resolution radiometric missions on board Low Earth Orbit satellites.

Experimental characterization of CMOS APS imagers designed using two different technologies

This paper presents measurements results performed on CMOS APS imagers implemented on two different technologies. Both PhotoMOS (PM) and PhotoDiode (PD) structures have been designed by the CIMI-SUPAERO group and high APS readout rate measurements have been performed by Matra Marconi Space. Every circuit also includes the pixels address decoders and the readout circuit required to perform on-chip correlated double sampling and double delta sampling. The aim of this paper is to compare performances of those arrays operating at 5 Volts in terms of dark current, quantum efficiency, conversion gain, dynamic range.

HRIS technology development results and their implementation in future hyperspectral imagers

The recent developments within the ESA funded HRIS (high resolution imaging spectrometer) technology program -- aiming at an airborne demonstrator model -- yielded rather successful subsystem developments. HRIS is designed as a true pushbroom hyperspectral imager with comparatively high spatial and spectral resolution, covering the spectral range from 450 to 2350 nm. The main breadboard units, with a space-near design, are essentially: a TMA (three mirro anastigmat, Carl Zeiss) front optics, a dual path spectrometer optics (Officine Galileo) with a novel in-field spectral separation unit, a 2-D SWIR CMT detector array with a dedicated CMOS readout multiplexer (GEC Marconi IR, MATRA MSF for testing), the signal processing electronics (DSS), some calibration elements (DLR + DSS), and the extensive testing of all units. The paper presents the essential results per unit, with possible exception of the front optics (which may not be completed at the conference paper presentation yet), including derived further development efforts. Also, the remaining steps towards an airborne test mission are outlined, together with a brief description of the envisaged high-altitude aircraft. We hope that this paper may also stir some potential users of later airborne HRIS test missions over dedicated target areas. Positive responses would support ESA to pursue the program. The technology units development under the HRIS contract have turned out useful for follow-on instrument developments such as the ESA Explorer mission candidate PRISM (processes research by an imaging space mission). This leads to the conclusion that the achieved development results are a sound basis for future airborne and spaceborne hyperspectral imager developments in Europe. A brief survey of the current PRISM baseline concept is added to the paper.

PRISM (processes research by an imaging spaceborne mission) high-resolution hyperspectral imager for scientific land processes monitoring applications

Dasa (Daimler-Benz Aerospace) currently is in charge of an ESA contract for the PRISM feasibility study, including MATRA MS/France and SIRA/UK. The main PRISM mission objectives are to monitor selected target areas with emphasis on bio-chemical stress analyses which are the subject of changes such as vegetation, in particular deforestation; further areas include glaciers, land/water boundaries, and similar features. The Dasa study team makes use of a similar ESA instrument currently the subject of dedicated subunits technology developments, the HRIS (high resolution imaging spectrometer), also lead by Dasa. Its main features and technology developments are covered in a survey. PRISM is covering most of the HRIS features, i.e., it will have an imaging spectrometer segment for the visible/NIR and the SWIR spectrum (450-2350 nm) as HRIS, but implements four MIR and TIR channels to provide surface temperature data, represented by linear detector arrays (essentially the features of another currently pursued ESA development program designated HRTIR). In a first study phase it also included a novel feature, a wide-angle two-axis pointing system for along- and across-track pointing in order to yield multi-directional reflectance data of dedicated targets, which turned out to be the greatest design driver in the instrument, it was omitted in the later phases. The geometric sampling interval is defined to 50 m (design goal) at 50 km swath. PRISM is currently studied in a feasibility study in a competitive way by two teams, one being lead by Dasa. At the time of the Symposium both studies are completed. The results of the Dasa team are presented. Since PRISM covers most of the HRIS mission it is rather likely that in the case of a successful concept feasibility proof (performance and technology wise), it may later replace the HRIS instrument. It is anticipated that a major part of the technology developments currently performed for HRIS will be utilized -- with some modifications -- for PRISM as well.

Camera of the Infrared Space Observatory

The Infrared Space Observatory (ISO) camera (ISOCAM) is designed to map selected regions of the sky in the spectral region from 2.5 to 17 μm at various spatial and spectral resolutions and at high sensitivity (at >4 μm, <1 mJy/10 s in 200 5). It will make images, within the 3-arcmin field of view of the ISO telescope, with two 32 x 32 IR array detectors: an InSb charge injection device (CID) for the 2.5- to 5.5-μm range and a Si:Ga direct voltage readout for the 4- to 17-μm range. Four different pixel fields of view are available on each channel: 1.5, 3, 6, and 12 arcsec. The spectral range can be selected in each channel by a set of about 10 fixed bandpass filters (resolution from 2 to 100) and continuous variable filters (resolution ≈45); polarization measurements are possible as well. A very wide range of astrophysical problems can be tackled with ISOCAM. We present a brief description of the program planned by the ISOCAM team.

Development of ISOCAM: the camera of the Infrared Space Observatory

ISOCAM, the camera of the Infrared Space Observatory, will image the sky at various angular and spectral resolutions in the wavelength range 2.5 to 17 microns. We recall the main steps of the development, leading to the delivery of the flight model to ESA, and we outline some of the scientific programs to which it will be applied.

French SWIR technology used for astronomy

During the last 30 years, the Space Research Department (DESPA) of Paris Observatory has developed infrared instrumentation for space and ground-based telescopes. First, we present the PbS linear detector of the ISM IR imaging spectrometer of the Phobos mission. Then the CID InSb focal plane of ISOCAM-SW is described. The studies of this CID InSb focal plane allowed us to develop an IR camera for the first astronomical observations using adaptive optics. We also describe the linear array built for the OMEGA imaging spectrometer of the Mars 96 mission. The last chapter is dedicated to the IR spectrometer of the Huygens probe. To conclude, the needs and challenges in the area of mid-band infrared astronomy are discussed.