MIT/Lincoln Labs CCID20 W6C1 CCD Test Results
This is the third standard epi, thinned, backside MIT/Lincoln
Labs 2Kx4K CCD to be characterized in the UCO/Lick detector lab. It is
very similar to other standard epi CCID20s tested at Lick.
A summary report
is available. Noteworthy points in the report include:
- Parallel clocks. If the
parallel clock negative rail is too low, significant spurious charge is
generated. At -6 volts on the negative rail parallel clocking works fine,
with little or no spurious charge.
- Serial Clocks. Proper serial
clock levels must be chosen to maintain low spurious charge. Based on read
noise measurements, +6v and -3v serial rails seems to produce low spurious
charge.
- 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.
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 a pretty typical 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.
- Serial CTE
- Near perfect CTE is achieved by the Lincoln CCD design.
- Surface plot
- There is about 14 micrometers of curvature in this CCD,
as measured with the Lick laser-based surface measurement instrument.
- Brick wall
- This is the pattern which results from the incomplete
backside laser anneal. This device exhibits a rather high amplitude in
the pattern.
- Dark pattern
- This fascinating image was obtained while the CCD was
warming up.
This plot shows the QE measurement
made at a device temperatures of -127°C. We've found that the QE can
be somewhat temperature sensitive, especially in the less sensitive areas
of the brickwall pattern. So this result will change a little with temperature,
with the QE increasing with increasing temperature.
The Lincoln CCID20 design
produces excellent charge transfer efficiency. This plot shows a test of
serial CTE using Fe55 xrays.
Here are two views of the
surface shape measured at room temperature and one view of an optical flat
for comparison.
The second plot shows the same data in a nearly edge-on
view.
This is the optical flat measurement,
plotted with the same Z-axis scale as the two previous CCD surface measurement
plots. The CCD and the flat are scanned across a laser beam using an old
milling machine. The same X and Y travel of the milling machine was used
for both the W6C1 measurements and the optical flat measurements. This
plot shows that about 2 microns of error are introduced by the milling
machine over the range of X and Y motions. This error is small in comparison
to the CCD curvature.
Each of these images shows
a flat-field in the same area of the CCD, but at different wavelengths.
The percents shown are derived by taking a single row cut through the image
and computing a percentage as (MAX-MIN)/MEAN. Obviously this emphasizes
maximum variations. This device is better than W20C1.
This image was
obtained after the dewar liquid nitrogen ran out and the CCD was warming
up. The pattern does not
appear when the CCD is held at a stable temperature. Therefore it should
not represent any problem during normal operation. What the pattern reveals
is the new method of gluing the CCD to the AlN base. I won't give the details
of the method here, but the bright dots show the locations of more rapid
warming and those locations correspond to the locations of epoxy dots which
attach the CCD to the AlN. So if you see this pattern in any of your CCID20
CCD images it probably means the CCD temperature isn't stable- but the
CCD is working normally.
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