Proceedings Article | 12 July 2023
KEYWORDS: Image sensors, High dynamic range imaging, Astronomical imaging, Semiconducting wafers, Design and modelling, CMOS sensors, Camera shutters, Assembly equipment, High dynamic range image sensors, Capacitors
ELFIS2 is the second generation of the European Low Flux Image Sensor (ELFIS), developed by Caeleste, manufactured at LFoundry and tested by Airbus on behalf of the European Space agency. As the High flux program was aborted, it was decided to continue ELFIS as a High Dynamic Range (HDR) sensor, enabling the simultaneous integration and readout of the same charge packet on a large and a small conversion capacitance. It is combined with charge domain global shutter, so that motion artefacts, typical for multi-exposure or dual photodiode architectures are completely eliminated. The ELFIS core pixel uses the Global Shutter technology pixel, developed at LFoundry, allowing charge domain Integrate-While-Read operation and on-chip CDS. In order to handle photocharge packets that exceed the full well of the core pixel, there are two low gain overflow capacitors, used alternatingly for signal integration and read-out. Whereas ELFIS1 was a fixed size device, ELFIS2 is designed for stitching. The stitch block of 512*1024 pixels can realize every n*m multiple of 1/2k by 1k pixels, as long as it fits on the wafer. The Initial prototype presented has a 2k*2k format. 4k*4k, 8k*8K, etc. can be realized with the same mask set, as well as elongated (hyperspectral) sensors up to 512*10 k pixels. As each stitch segment has its own output amplifiers, the ultimate frame rate is only determined by the number of rows to be read. Frame rate can be increased by applying row random addressing, which are especially versatile in hyperspectral applications. The initial functional tests of ELFIS2 are promising: without further optimization the noise spec of less than 5 e-rms is reached with a HDR full well of 160 ke- ; the core Global Shutter high gain full well is 10 ke- , resulting in a smooth photon shot noise limited behavior from the high gain noise floor till the low gain saturation. The full functional testing and circuit optimization is now starting and will be finished at the moment of this presentation. Also, radiation pre-qualification is planned. Due to the good SEE results obtained in another Rad-Hard by Design (RHbD) in the same technology we are also confident that the SEE will have a LET < 63 MeV/mg/cm2 for both SEL and SEU.
