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The METimage instrument is part of the EPS-SG (EUMETSAT Polar System Second Generation) program. It
will be situated on the MetOp-SG platform which in operation has an objective of collecting data for
meteorology and climate monitoring as well as their forecasting. Teledyne e2v has developed and
characterised the CMOS VISNIR detector flight module part of the METimage instrument.
This paper will focus on the silicon results obtained from the CMOS VISNIR detector flight model. The
detector is a large multi-linear device composed of 7 spectral bands covering a wavelength range from 428
nm to 923 nm (some bands are placed twice and added together to enhance the signal-to-noise
performance). This detector uses a 4T pixel, with a size of 250μm square, presenting challenges to achieve
good charge transfer efficiency with high conversion factor and good linearity for signal levels up to 2M
electrons and with high line rates. Low noise has been achieved using correlated double sampling to
suppress the read-out noise and give a maximum dynamic range that is significantly larger than in standard
commercial devices.
The photodiode occupies a significant fraction of the large pixel area. This makes it possible to meet the
detection efficiency when front illuminated. A thicker than standard epitaxial silicon is used to improve NIR
response. However, the dielectric stack on top of the sensor produces Fabry-Perot étalon effects, which are
problematic for narrow band illumination as this causes the detection efficiency to vary significantly over a
small wavelength range. In order to reduce this effect and to meet the specification, the silicon manufacturing
process has been modified. The flight model will have black coating deposited between each spectral
channel, onto the active silicon regions.
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