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GoldCam Gets a Big New Ford Chip and TI3 Gets Sacked (1Jun92)
(from KPNO, NOAO Newsletter No. 30, 1 June 1992)

In mid-February we replaced the TI 800 x 800 CCD (TI5) in the 2.1-m CCD
spectrometer "GoldCam" with a thinned Ford 3K CCD. Although this new
chip is not perfect, it represents a major improvement in the
capabilities of GoldCam. The new chip has 3072 columns (along the
dispersion) and 1024 rows.  The pixel size is 15 um. The chip was
thinned, packaged, and backside treated by Michael Lesser at Steward
Observatory. The backside treatment consisted of a steam oxide (which
allows the chip to be UV flooded) and a silicon dioxide AR coating.
Shown in the plot below is the DQE of the UV-flooded chip compared to
that of the UV-flooded TI chip which we replaced.

Although the chip is flat, the image quality is satisfactory over only
2200 of the 3072 pixels. Also, the best focus we have been able to
achieve is about 2.7 pixels FWHM. Thus, the gain is about a factor of
two over the TI chip in terms of resolution elements.

As was the case for the TI chip, there are obvious fringes longward of
about 7000 A.  These can be removed with flat fields taken using the
internal projector quartz lamp.

The chip has a number of cosmetic defects. It has one bad column and a
number of traps. These traps can be filled by a uniform signal of about
150 electrons, which raises the effective readout noise from 9.5
electrons to about 15 electrons. The charge transfer is excellent. A
complete writeup on the properties of the new chip and observing
strategies to get around some of its problems is available from the
observing support office. Those of you used to the GoldCam parameters
with the old TI chip may want to note that you will have the same
dispersion (A/pixel) but roughly 2.7 times the spectral coverage (2200
pixels vs. 800) with the new Ford chip.

After replacing the chip in GoldCam, we realized that TI5, the previous
GoldCam detector, is a significantly better chip than TI3, which has
commonly been used in a Universal Dewar at the Coude Feed.  Therefore,
we have replaced TI3 with TI5, giving higher QE (particularly below
4000 A) and better cosmetics.

                        [figure not included]

Todd Boroson, Diane Harmer, Rich Reed

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