MIT/Lincoln Labs CCID20 W7C2 CCD Test Results
This is a standard epi, thinned, backside MIT/Lincoln
Labs 2Kx4K CCD. It is similar to other standard epi CCID20s tested at Lick
but in most respects is just a little bit better than anything else we've
tested to date (Oct. 1, 1997).
A summary report
is available. Noteworthy points in the report include:
- QE. The QE tops out at over
93%, the highest value we've measured for a CCID20 to date. Probably related
to high QE, fringing and brickwall nonuniformity are lower in this device
than most other CCID20s.
- CTE. Near perfect CTE is
achieved using the serial and parallel clocks which generate low spurious
charge. This is typical of Lincoln CCDs.
- Read Noise. Read noise is
around 2 electrons. This is as good as or
better than any thin CCD in the world.
- Low Level Traps. Only 2
traps were detected with charge pumping. This is a very small number.
- Column defects. The only
notable problems with this device are two partially blocked columns (one
of them very short) and one very bright column. The bright column appears
to be caused by a single hot pixel in the first imaging column on the A-amplifier
side of the CCD. By proper parallel clock biasing during integration it
might be possible to reduce the glow from this hot pixel during the integration
interval. This hasn't been tested.
- Dark versus parallel clock voltages.
We did a few preliminary tests to see if dark current could be reduced
by operating in partially inverted mode. Normally we run with parallel
clock voltage rails of +2v and -6v. The tests are so far inconclusive but
they do show that if we integrate in partially inverted mode we may still
need to read out with +2v and -6v to keep spurious charge generation low.
We need to repeat these tests at a higher temperature (around -100C) and
we may find that integrating with partially inverted clocks of +2v and
-8V does indeed reduce dark current generation.
Original postscript files are available from our anonymous
ftp server and these provide better resolution and clarity than is
usually possible on a web page. Check the INDEX
file for a description of what the other files contain. Here are a few
figures to illustrate device highlights:
- QE curve
- This is an exceptionally good QE curve for the CCID20s.
The QE is an average over a fairly large portion of the CCD, so this result
is an average over the brickwall variations.
- Surface plot
- This is a nice flat CCD as the surface plots show.
Here is a surface plot of
the CCD at room temperature. Most of the CCD surface was measured and over
the measured area the peak-to-peak variation was only about 6 µm.
The CCD connector is along the right edge in this view. A postscript
version is available.
This view shows the same data from nearly edge-on to more clearly show
the slight twist. A postscript
version is available.
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