Both ESA and the EC have identified the need for a supply chain of CMOS imagers for space applications which uses solely European sources. An essential requirement on this supply chain is the platformization of the process modules, in particular when it comes to very specific processing steps, such as those required for the manufacturing of backside illuminated image sensors. This is the goal of the European (EC/FP7/SPACE) funded project EUROCIS. All EUROCIS partners have excellent know-how and track record in the expertise fields required. Imec has been leading the imager chip design and the front side and backside processing. LASSE, as a major player in the laser annealing supplier sector, has been focusing on the optimization of the process related to the backside passivation of the image sensors. TNO, known worldwide as a top developer of instruments for scientific research, including space research and sensors for satellites, has contributed in the domain of optical layers for space instruments and optimized antireflective coatings. Finally, Selex ES, as a world-wide leader for manufacturing instruments with expertise in various space missions and programs, has defined the image sensor specifications and is taking care of the final device characterization. In this paper, an overview of the process flow, the results on test structures and imagers processed using this platform will be presented.
This paper presents a 20 Mfps 32 × 84 pixels CMOS burst-mode imager featuring high frame depth with a passive in-pixel amplifier. Compared to the CCD alternatives, CMOS burst-mode imagers are attractive for their low power consumption and integration of circuitry such as ADCs. Due to storage capacitor size and its noise limitations, CMOS burst-mode imagers usually suffer from a lower frame depth than CCD implementations. In order to capture fast transitions over a longer time span, an in-pixel CDS technique has been adopted to reduce the required memory cells for each frame by half. Moreover, integrated with in-pixel CDS, an in-pixel NMOS-only passive amplifier alleviates the kTC noise requirements of the memory bank allowing the usage of smaller capacitors. Specifically, a dense 108-cell MOS memory bank (10fF/cell) has been implemented inside a 30μm pitch pixel, with an area of 25 × 30μm2 occupied by the memory bank. There is an improvement of about 4x in terms of frame depth per pixel area by applying in-pixel CDS and amplification. With the amplifier’s gain of 3.3, an FD input-referred RMS noise of 1mV is achieved at 20 Mfps operation. While the amplification is done without burning DC current, including the pixel source follower biasing, the full pixel consumes 10μA at 3.3V supply voltage at full speed. The chip has been fabricated in imec’s 130nm CMOS CIS technology.
In this paper we discuss the design of a novel miniaturized image sensor based on the working principle of insect
facet eyes. The main goals are to design an imaging system which captures a large field of view (FOV) and to find
a good trade-off between image resolution and sensitivity. To capture a total FOV of 124°, we split up this FOV
into 25 different zones. Each of these angular zones is imaged by an isolated optical channel on our image sensor.
There is an overlap between the zones to cover the full FOV but the different zones are imaged on separated
regions at the image sensor. Every optical channel in the designed component consists of two lenses that are
tilted with respect to each other and the optical axis. Because of this tilt of the lenses, we are able to minimize
field curvature and distortion in the obtained images at the detector, and have an angular resolution below 1°.
The optical system was implemented and optimized in the ray-tracing program ASAP. The parameters (in one
channel) that are optimized to obtain this large FOV with a good image resolution and sensitivity are the radius
of curvature of the two lenses, their conical factor and their tilt in two directions with respect to the optical axis
of the complete system. The lenses are each placed on a pedestal that connects the lens to a planar substrate.
We also add absorbing tubes that connect the two lenses in one channel to eliminate stray-light between different
optical channels. The obtained image quality of the design is analyzed using our simulation model. This is
determined by different parameters as there are: modulation transfer function, distortion, sensitivity, angular
resolution, energy distribution in each channel and channel overlap. The modulation transfer function shows
us that maximum contrast in the image is reached up to 0.3LP/°, distortion is maximal 21% in one of the 25
different channels, the sensitivity is 0.3% and the resolution is better than 1°.