Infrared sensors for Earth observation missions
2007
SELEX S&AS is developing a family of infrared sensors for earth observation missions. The spectral bands cover shortwave
infrared (SWIR) channels from around 1μm to long-wave infrared (LWIR) channels up to 15μm.
Our mercury cadmium telluride (MCT) technology has enabled a sensor array design that can satisfy the requirements of
all of the SWIR and medium-wave infrared (MWIR) bands with near-identical arrays. This is made possible by the
combination of a set of existing technologies that together enable a high degree of flexibility in the pixel geometry,
sensitivity, and photocurrent integration capacity.
The solution employs a photodiode array under the control of a readout integrated circuit (ROIC). The ROIC allows
flexible geometries and in-pixel redundancy to maximise operability and reliability, by combining the photocurrent from
a number of photodiodes into a single pixel. Defective or inoperable diodes (or "sub-pixels") can be deselected with
tolerable impact on the overall pixel performance.
The arrays will be fabricated using the "loophole" process in MCT grown by liquid-phase epitaxy (LPE). These arrays
are inherently robust, offer high quantum efficiencies and have been used in previous space programs. The use of
loophole arrays also offers access to SELEX's avalanche photodiode (APD) technology, allowing low-noise, highly
uniform gain at the pixel level where photon flux is very low.
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