4 Final Report - Emits - ESA

4 Final
Report
Column decoder
4 outputs 4 outputs
Column readout circuit
4 stitched 1k x 1k arrays
15 µm pixel pitch
Column readout circuit
4 outputs 4 outputs
Column decoder
Figure 4.3-9: Architecture for the MWIR CMOS hybrid detector
The 2k x 2k array with 15 µm pitch consists in 4 independent 1000x1000 pixels sub-arrays. Each subblock
is read out via 4 video outputs with a 10 Mpixels/s output rate, so the read out period is 25 ms,
much larger than the max. integration time (2.5 msec for Marine application).
The operating temperature of the detector is dictated by the level of dark current, which can reduce
the useful dynamic range and significantly increase the detection noise. A temperature of 130K is a
typical choice for a 3.7 µm MWIR band.
4.3.3.4 TIR focal plane
As for MWIR, the two candidate technologies are TIR HgCdTe and AlGaAs/GaAs QWIP. From a
qualitative point of view, the trade-off between both materials is identical: better sensitivity for HgCdTe
and better yield / uniformity (spatial and spectral) / temporal stability / cosmetics for QWIP. The
situation is however worse for TIR HgCdTe as its metallurgy complexity is strongly increasing with cutoff
wavelength. A 25 µm pixel pitch is considered as the smallest achievable pixel pitch. The targeted
format of 0.8k x 0.8k pixels has a 28 mm diagonal, larger than the HgCdTe state of the art. The
development of the GIFTS array made by BAe in the US has shown that, despite important
technological and financial efforts, it looks hard to produce with acceptable operability a 20 mm
diagonal HgCdTe 2D array with very long cut-off wavelength. On the other hand, 640x480 pixels
QWIP arrays with 25 µm pitch are currently produced by few manufacturers. The HgCdTe problem is
well known by ESA detection experts, particularly in the framework of MTG studies, justifying the two
ways approach proposed by the Agency:
• Improve the weaknesses of HgCdTe, via technological development. This is the object of the
running contract "initial design of thermal infrared detector array for MTG"
• Improve performances of alternative ways. This is the object of the contract "Enhanced
QWIP/Sb-superlattice Array Detector".
About ROIC, the 800x800 pixels format with 25 µm pitch avoids the need for stitching.
An alternative to quantum detectors that could be figured for Fire Monitoring applications (which have
much relaxed noise requirements) is the emerging microbolometer technology.
Page 4-36 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009