Previous Article
Next Article
Table of Contents

The Mini-Mosaic: 16 Million Pixels Coming Your Way (1Sep92)
(from KPNO, NOAO Newsletter No. 31, 1 September 1992)

Anyone who stopped by the NOAO display at the Columbus AAS meeting
knows that we are well on the way to having larger CCDs. Is a 2048 x
2048 CCD too small for you? We are aiming to make CCDs as large as the
photographic plates that we used ten years ago! The first step in this
development is to build a simple mosaic imager. Because CCDs are made
on 4-inch diameter silicon wafers, they will not be made larger than
2.5 x 2.5 inches in the foreseeable future. Thus, the only way to make
bigger ones is to learn how to put them together into a mosaic.

To this end we have begun a project to produce a 2 x 2 array of Loral
Fairchild 2048 x 2048 CCDs. These chips have 15 um pixels which
correspond to 0.28 arcsec at the 4-m prime focus and 0.43 arcsec at the
f/7.5 focus of the 0.9-m telescope. The fields of view are 19 arcmin on
an edge at the 4-m and 29 arcmin on an edge at the 0.9-m. The chips
themselves have already been fabricated from a design developed by John
Geary (SAO). They are two-side buttable; that is, they have nothing (or
very little) around the edge of the imaging area on two sides. This
permits mounting them very close together - our goal is 500 um. We have
contracted with Mike Lesser (Steward Obs.) to thin the chips and mount
them into two 2 x 2 arrays, which we call "mini-mosaics." One of these
will go to CTIO, and one will go to KPNO.

Although we can not yet describe the properties of the imagers in
detail, we have just received an unthinned prototype which we expect to
have running in a few weeks. This will be tested on the 0.9-m this
fall, and we expect delivery of the first thinned mini-mosaic by the
end of 1992. The hope is to make it available at KPNO by the fall 1993
semester. The mini-mosaic fits in a universal dewar so it is, in
theory, usable anywhere that a universal dewar will go. It will be read
out in quadrants, of course, so the readout time will not be any longer
than a single 2048 x 2048 CCD.

If all this goes smoothly, the next step will be to construct a 4 x 4
array of similar chips. We estimate that this will take another two
years. Watch this space for details.

Todd Boroson, Rich Reed

Previous Article
Next Article
Table of Contents