CMOS image sensors are generally considered as being particularly suited to the harsh space environment, if they can get their performance up to the CCD levels. Recent developments indicate however that this object can be achieved.
This paper presents the current state of the art in CMOS Active Pixel Sensors (APS) for space applications at Fillfactory and also highlights some commercial and industrial development that can be of interest for the space community.
This paper describes a back-side illuminated 1 Megapixel CMOS image sensor
made in 0.18um CMOS process for EUV detection. The sensor applied a so-call
"dual-transfer" scheme to achieve low noise, high dynamic range. The EUV
sensitivity is achieved with backside illumination use SOI-based solution. The
epitaxial silicon layer is thinned down to less than 3um. The sensor is tested and
characterized at 5nm to 30nm illumination. At 17.4nm targeted wavelength, the
detector external QE (exclude quantum yield factor) reaches almost 60%. The
detector reaches read noise of 1.2 ph- (@17.4nm), i.e. close to performance of EUV
This paper describes a 2.2 Megapixel CMOS image sensor made in 0.18 μm CMOS process for high-speed
machine vision applications. The sensor runs at 340 fps with digital output using 16 LVDS channels at
480MHz. The pixel array counts 2048x1088 pixels with a 5.5um pitch. The unique pixel architecture supports
a true correlated double sampling, thus yields a noise level as low as 13 e- and a pixel parasitic light
sensitivity (PLS) of 1/60 000. The sensitivity of the sensor is measured to be 4.64 Vlux.s and the pixel full well
charge is 18k e-.
Two types of backside illuminated CMOS Active Pixel Detectors--optimized for space-borne imaging--have been
successfully developed: monolithic and hybrid. The monolithic device is made out of CMOS imager wafers postprocessed
to enable backside illumination. The hybrid device consists of a backside thinned and illuminated diode array,
hybridized on top of an unthinned CMOS read-out. Using IMEC's innovative techniques and capabilities, 2-D arrays
with a pitch of 22.5 μm have been realized. Both the hybrid and well as the monolithic APS exhibit high pixel yield, high
quantum efficiency (QE), and low dark current. Cross-talk can be reduced to zero in the hybrid sensors utilizing special
structures: deep-isolating trenches. These trenches physically separate the pixels and curtail cross-talk. The hybrid
imagers are suitable candidates for advanced "smart" sensors envisioned to be realized as multi-layer 3D integrated
systems. The design of both these types of detectors, the key technology steps, the results of the radiometric
characterization as well as the intended future developments will be discussed in this paper.
We present the performance characteristics of a CMOS image sensor, manufactured on wafers with a specially designed multiple epitaxial layer. At the homo-junction between two consecutive epitaxial layers a small potential drop or electric field represents a barrier for electrons diffusing towards the back of the wafer. The multiple epitaxial layer stack results thus in a net drive or confinement of photo-charges towards the surface. As a result there is anisotropical diffusion of charge that are generated deep in the Silicon, e.g. by near infrared (NIR) or X-ray radiation. The spectral response is an order of magnitude higher for than for the same image sensor on "regular" wafers. The anisotropical diffusion results in a limited MTF degradation compared to wafers with a single thick epitaxial layer.
The treatment of atrial tachycardia by radio-frequency ablation is a complex and minimally invasive procedure. In most cases the surgeon uses fluoroscopic imaging to guide catheters into the atria. After recording activation potentials from the electrodes on the catheter, which has to be done for different catheter positions, the physiologist has to fuse both the activation times derived from the potentials with the fluoroscopic images and extract from these a 3D anatomical model of the atrium. This model will provide him with the necessary information to locate the ablation regions.
To alleviate the problem of mentally reconstructing these different sources of information, we propose a virtual environment that has the ability to visualize the electrodes information onto a patient specific model of the atria. This 3D atrium surface model is derived from pre-operatively taken MR-images. Within the system this model is visualized in 3 different ways: two views correspond to the 2 fluoroscopes images, which are shown registred in the background while the third one can be freely manipulated by the physiologist. The system allows to annotate measurements onto the 3D model. Since the heart is not a static organ, tools are provided to modify previous annotations interactively. The information contained in the measurements can than be dispersed across the heart after extrapolation and interpolation and subsequently visualized by color coding the surface model.
Preliminary clinical evaluation on 30 patients indicates that the combined representation of the activation times and the heart model provides a thorough and more accurate insight into the possible causes and solutions to the tachycardia than would be obtained using solely the fluoroscopes images and mental reconstruction.
Unlike other tachycardia visualization software, our approach starts with a patient specific surface model which in itself provides extra insight into the problem. Furthermore it can be used very interactively by the physiologist as a kind of 3D sketchbook where he can enter, delete, ... different measurements, tissue types. Finally, the system can visualize at any stage of the surgery a model containing all information at hand.
In this paper we present a system to represent electrocardiographic information that allows the physiologist to mark measurements which can than be visualized on a patient specific atrium model by color coding. First clinical evaluation indicates that this approach offers a considerable amount of added value.
In this paper we discuss the dark current increase in CMOS Active pixel Sensors (APS) due to total dose and proton induced damage. We describe measurement results on several diodes that were used to investigate the degradation of the pixel photodiode under ionizing radiation. This study resulted in the design of radiation tolerant pixels that have proven to tolerate at least 200 kGy(Si) total dose from a 60Co source. Standard APS sensors show already large degradation after less than 100 Gy(Si) due to a strong surface leakage current increase. Standard CMOS imagers were also evaluated with respect to proton induced damage. Highly energetic protons can displace atoms from their lattice position, giving rise to an increase in mean level of dark current and non-uniformity.
Co60 irradiations have been carried out on test structures for the development of CMOS Active Pixel Sensors that can be used in a radiation environment. The basic mechanisms that may cause failure are presented. Ionization induced damage effects such as field leakage currents and dark current increase are discussed in detail. Two different approaches to overcome these problems are considered and their advantages and disadvantages are compared. Total dose results are presented on a pixel that can tolerate more than 200 kGy(Si) (20 Mrad(Si)) from a Co60 source.