Gigapixel Focal Plane Arrays
for UVOIR Space Telescopes
National Aeronautics and
Space Administration
Jet Propulsion Laboratory
California Institute of
Technology
D. Ebbets, M. Blouke, E. Freymiller, S. McArthur, P. Warren
Ball Aerospace and Technology Corp.
and the ATLAST Concept Study Team
Abstract
A large space telescope produces very sharp images near
the wavelengths where it is diffraction-limited. If it also
provides a wide field of view, the focal planes for its imaging
instruments will require a very large number of pixels. The
8m ATLAST telescope will have a FOV of 8 X 8 arc minutes
for its wide field camera, and image quality expected to be
near 30 milli-arc seconds FWHM in the visible. With Nyquist
sampling of 2 pixels per Airy diameter, an FPA of 32K X 32K
pixels is indicated. With 9 micron pixels, the active imaging
area will be about 300 millimeters on a side. Such a focal
plane appears to be feasible with existing CCD technology
but could be enhanced with detector technology
development.
The ATLAST Gigapixel Focal Plane could be
built with very low risk using current CCD
technology
Future Missions will build on the Heritage of
the Ames-JPL-Ball Kepler Focal Plane
There are options for populating the modules
Future possibilities with
technology development:
• CMOS
• APD arrays
Low risk approach using
today’s technology:
• Conventional CCDs
• LLL CCDs
• p-channel CCDs
• The module could consist of a single 8K x 8K CCD, sixty-four
1 K x 1 K devices or any intermediate combination
• 32K x 32K total format, 9 µm pixels
• Gaps between modules < 1 mm
• 300 mm x 300 mm physical size of sensitive area
• Optical FOV 8 arcmin, Nyquist sampled at 550 nm
• Current design assumes flat focal surface
• FPA + FPE power estimated to be < 300 W
• Total system mass estimated to be < 100 kg
• FPA includes electrical, thermal and mechanical interfaces to
the camera with mounting and alignment aids
• Flight performance and environmental qualification tests are
performed on the completed focal plane
• Driving system device requirements are high sensitivity and
low noise
• Selection will made on the basis of the performance of the
devices available
The performance of the detectors will meet
the scientific requirements
[2]
The Kepler focal plane array is a mosaic of
flat 1k x 2k CCDs on a curved Invar substrate.
This ~0.1 Gpixel FPA will be illuminated by a
0.95 m Schmidt telescope [1]
• Science: Uses differential photometry to monitor 100,000
stars for transits of Earth-sized or larger planets
• Sensitivity is 100 parts per 1,000,000
• 42, 1024 x 2200 CCD arrays in the Science Focal Plane
• 4, 550 x 535 CCDs in the Fine Guidance System
• Radius of curvature of FPA Invar structure = 1.4 m
• Pixel Pitch: 27 µm (Science) and 13 µm (FGS)
• Tint = 3 - 8 sec, Tread = 0.5 sec, 2 amps / chip
• Mass: 88 kg including 31 kg of the radiator
• FPA Power: 7W
• System power: 130W
• Cooling to -85 to -90 C with Ethane heat pipes to an
external radiator
• Planned lifetime: 4 years
• Launch planned for May 2009 via Delta 2 Rocket
Heat pipes to external radiator Each module has independent
cool FPA to -100 C.
thermal, structural and
electrical connections.
[3]
• QE will exceed 70% at all required wavelengths [2,3,4,5]
• Dark Current will be approximately 1e-5 e-/pixel/sec
• Read noise will be 0 – 3 e- per read
• Operation modes can include traditional accumulation (1000
seconds between reads) or single photon counting with high
read-out rates
The Gigapixel FPA is a mosaic of 16 modules,
each with 8K x 8K pixels
Technology Development has the potential
to provide improved performance
AR-coatings tuned for desired spectral range
Optimizing QE across entire wavelength range
Lower power operation for LLL CCD
In-pixel gain for CMOS detectors
• All modules are identical
• Each module is electrically independent from all others,
maximizing fault tolerance
• Thorough performance testing and calibration at module
level: QE, read noise, MTF, CTE, dark current, etc.
• Designed for easy assembly, alignment, removal and
replacement into larger FPA structure
• All connections are made through the back of the device,
minimizing the gaps between modules
• Flat modules can be assembled into a curved focal plane
Better noise and dark current properties for CMOS detectors
Development of large area APD arrays
References
1. V. Argabright et al, Proc. SPIE, 7010, 70102L (2008)
2. M. Lesser, V. Iyer, SPIE 3355 0277-786X (1998)
3. M. Fabricius et al, SPIE-IS&T 6068 60680G-1(2006)
4. M. Blouke, Proc SPIE 1439 (Nov 1990)
5. J. Blacksberg et al, IEEE TED, Vol. 55, No. 12 (2008)