The Defense Advanced Research Projects Agency (DARPA) has a substantial program to develop a 2200 x 2200 pixel CCD (Charge Coupled Device) mosaic array made up of 400 individual CCD's, 110 x 110 pixels square. This type of image sensor appeared to have application in space and ground-based astronomy. Under this grant a CCD television camera system was built which was capable of operating an array of 4 CCD's to explore the suitability of the CCD's to explore the suitability of the CCD for astronomical applications. Two individual packaged CCD's were received and evaluated. Evaluation of the basic characteristics of the best individual chips was encouraging, but the manufacturer found that their yield in manufacturing this design is two low to supply sufficient CDD's for the DARPA mosaic array. The potential utility of large mosaic arrays in astronomy is still substantial and continued monitoring of the manufacturers progress in the coming year is recommended

Schwarzschild, M.

English

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PRINCETON UNIVERSITY
(NASA-CR-158478) LARGE AREA CCD IMAGE
	 N7S-22981
SENSCRS FOR SPACE ASTRONOMY Final Technical
Report, 1 Nov. 1977 - 28 Feb. 1979
' D rinceton Univ. Observatory) 16 p HC	 inclas
A02/NIF A01	 CSCI 03A G3/89 14750
PRINCETON UNIVERSITY OBSERVATORY
Princeton, New Jersey 08540
7INAL TECHNICAL REPORT
"LARGE AREA CCD IMAGE SENSORS FOR SPACE ASTRONOMY"
NSG 7379
Period: November 1, 1977 to February 28, 1979
Submitted to:
National Aeronautics and Space Administration
HEADQUARTERS, Washington, D.C.
Principal Investigator: '1...^k:.^. SLL
Martin Schwarzschild
April 6, 1979
- i -
TABLE OF CONTENTS
Introduction
Description of the CCD Television Camera
Rockwell CCD
Laboratory Tests of Rockwell CCD's
Summary
-ii -
LIST OF FIGURES
Figure 1 CCD Camera Head Assembly
Figure 2 CCD Camera Head Assembly, Control Electronics and IN  Dewar
Figure 3 Rockwell CCD No. 1, Resolution
Figure 4 Rockwell CCD No. 1, Dark Current
Figure 5 Rockwell CAD No. 1, Vertical Charge Transfer Inefficiency
Figure b Rockwell CCD No. 2, Dark Current Exposure
I
k
- 1 -
FINAL REPORT
"LARGE AREA CCD IMAGE SENSORS FOR SPACE ASTRONOMY"
INTRODUCTION
The Defense Advanced Research Projects Agency (DARPA) has a sub-
stant'al program with Rockwell International to develop a 2200 x 2200
pixel CCD mosaic array made up of 400 individual CCD's, 110 x 110 pixels
square. This type of image sensor appeared to have application in space
and ground-based astronomy.
Under this grant, NSG 7379, Princeton has built a CCD television
camera system capable of operating an array of 4 Rockwell CCD's to
explore the suitability of the Rockwell CCD for astronomical applications.
The equipment we have built is flexible enough in its design to allow
Texas Instruments and RCA type CCD's to also be operated with a minimum of
modification. Rockwell agreed to supply CCD's for this evaluation at no
cost to this grant. Two individually packaged CCD's from Rockwell have
been received and evaluated by Princeton.
While we are very encouraged by our evaluation of the basic charac-
teristics of the best individual Rockwell chips, Rockwell has recently
found that their yield in manufacturing this design is too low to supply
sufficient CCD's for the DARPA mosaic array. We understand that Rockwell
has initiated a design improvement program extending c::-^r the next 9 months
in an effort to increase the yield. There appears to be little likelihood
that Rockwell will be able in the near future to provide Princeton with
the 4 CCD array originally contemplated. The potential utility of large
mosaic arrays in astronomy is still substantial and one should continue
to monitor Rockwell's progress in the coming year.
- 2 -
In addition to the Rockwell CCD evaluation we have operated both
RCA and Texas Instruments CCD's in the CCD camera. The RCA CCD was 3
-phase
with 512 x 320 pixels, similar to the RCA SID-52501. These preliminary
tests of this developmental CCD were encouraging. The Texas Instruments
CCD was their 3-phase, back illuminated 100 x 160 pixel CCD. The system
with this CCD is now operating at the Princeton 36" reflector as the
image sensor following a Fabry-Perot narrow band filter.
DESCRIPTION OF CCD TELEVISION CAMERA
The CCD television camera was designed to operate 4 of the 4 phase,
"P" type Rockwell 110 x 110 pixel CCD's. Its design is flexible enough
to also allow the RCA and Texas Instruments 3 phase CCD's made with N
type silicon.
Figure 1 shows the CCD camera head assembly without its light shield.
The head assembly includes a liquid nitrogen cooled Products for Research
photomultiplier housing that can be cooled to -125% with the CCD installed.
Video am,?lifiers and some of the CCD drive electronics are also located in
this head assembly.
Figure 2 shows the CCD camera head assembly mounted on the telescope
behind the offset guiding assembly and a Fabry-Perot narrow band filter.
- 3 -
0
Preamplifier
CCD Cooling
4
- 4 -
CCD
Head Assembly
11-S^	 CCD Control Electronics
<—
Figure 2
-5-
The CCD electronics control assembly is connected via 6 meter cables
to the head assembly. The CCD electronics control assembly is connected
to the OBSCAM data acquisition system via 67 meter long cables.
The CCD readt)ut rate is 105 pixels per second. The data is digitally
recorded with 12 bit accuracy. Details of the OBSCAM system can be found
in the final report on Contract NAS5-22989	 Details on the CCD camera
design and construction can be obtained by writing to Princeton University
Observatory, Department of Astrophysical Sciences, Princeton, New Jersey 08544.
ROCRWCLL CCD
The Rockwell CCD is front illuminated, has 110 x 110 pixels and the
pixel size is 46 microns square. The CCD is scanned out with four phase
clocking of the electrodes. It differs from other CCD's in that Rockwell
uses "P" type silicon for the bulk material.
The CCD's are laid out so that the CCD spacing in the mosaic has gaps
300 P wide along each row. The space between rows is 2.9 mm such that
the total active area is 60% of the 4" x 4" square area subtended by a
2200 x 2200 pixel array.
Laboratory Tests of Rockwell CCD's
Rockwell CCD No. 1	 (Rockwell No. 30273-SSTSD-12-14-F4)
1) Charge Sensitivity
The charge sensitivity of the on-chip amplifier was measured by projecting
a uniformly illuminated 84 by 78 pixel rectangle onto the CCD. During
readout an electrometer measured the current at the drain of the precharge
field effect transistor on the CCD chip. The chip temperature during the
measurement was -900C. The measured charge sensitivity at the chip output
was 1.8 pV/electron.
- 6 -
2) Full Well Capacity
The maximum well capacity before degradation of resolution was 1.3 x 106
electrons/pixel.
3) Readout Noise
The total readout noise for this chip in our system was 153 electrons/pixel
(peak-to-peak) or approximately 30 electrons/pixel (RMS). The readout rate
is 105 pixels/second.
4) Resolution
Figure 3 shows a single line near midframe in the readout of a resolution
test chart image. The CCD was operating at a temperature of -126 0C. The
chart consisted of squara waves with periods equal in width to 1, 2, and
3 pixels, followed by a 12 pixel white patch which is bisected by a
1 pixel black line, and then a 9 pixel black patch. There is no resolution
of the 1 pixel width pattern (as expected). The 2 pixel width pattern shows
modulation of 15% of the black to white difference, and the 3 pixel width
pattern shows 20% modulation. The actual resolution response of the chip
may be higher than these measurements suggest, fcr the phase of the square
wave pattern with respect to the pixels is uncontrolled, and there was a
window of dubious quality in the optical path. The phase effects can be
computed for the three pixel width pattern, and the corrected modulation
for this pattern is approximately 25Z. This is still a lower limit, however,
because of the problem of the window.
5) Dark Current
Figure 4 shows the dark current variation with chip temperature. The dark
current was measured in areas not affected by blemishes (see following dis-
cussion). The dark current is less than 0.1 electron/pixel/second at -1250C.
The error estimates shown were obtained in the standard way by comparing
several different dark exposures taken at the same temperature.
- 7 -
Figure 3
Rockwell CCD No. 1 resolution.
A: 1 pixel period square wave
B: 2 pixel period square wave
C: 3 pixel period square wave
D: 12 pixels white (bisected by 1 pixel black line)
E: 9 pixels black
F: pattern repeats
0: 30 pixels overscan
- 8 -
1.2
W
-a	 4.0
N.
0.8
N
N 0.6C
4- 0.4U 0.2U
+- 0.0C
G^
-0.2
U --0.4
v - 0.6 E0
C71 - 0.80
--
j
 -4.0
-4.2
-80
	 -90 ^J-400	 -110	 -420
	 -430
Temperature CO
Figure 4
Rockwell CCD No. 1 	 Dark Current
Dark current in portions of chip not affected by defects.
No error estimates are available for last two points.
- 9 -
6) Blemishes
There are three single pixel defects in this chip which are nonthermal in
nature, that is, defects chat do not reduce with cooling. In a 1 hour exposure
each of these defects blooms, fully saturating approximately 20 neighboring
columns.
7) Charge Transfer Efficiency
At room temperature the charge transfer efficiency is good everywhere on
the chip. However, at all cooled temperatures we investigated (-75 
0 
C, -90 0C,
-1050C, -1250C) the list 25 co'imns of the device lose vertical charge
transfer efficiency. The image in these columns is smeared vertically
through the entire column. Figure 5 shows this effect; it =bows A line
in the entirely white area of the test chart image approximately six lines
below the resolution pattern. At the right, the smeared image of the square
wave resolution pattern is seen. If there were no transfer inefficiency,
this portion of the line would be at a uniform white level, as on the left
side of the line.
Rockwell Chip CCD No. 2	 (Rockwell No. 30273-SSTSD-19-2-E1)
This chip has approximately six non-thermal ."Jects of the type discussed
cbove. These defects bloom approximately 10 pixels up and down their respective
columns in a few minutes. At all cooled temperatures there is a horizontal
charge transfer inefficiency when the exposure is less than 10% of full well.
This smears the image horizontAlly, including the blooming charge from the
defects. This combination of effects rapidly fills the entire chip with dark
current. Figure 6 shows the readout of an entire frame of a 15 minute dark
exposure at -126 0C. The horizontal scale in this figure is compressed by a
- 10 -
A	 R	 ^.
Figure S
Rockwell CCD No. 1 vertical charge transfer ineffi-iency
A line in the white area of the resolution chart.
A: white image
B: 1 pixel black line in image
C: image of resolution pattern smeared vertically
C. f .	 Figure 3.
- 11 -
Figure 6
Rockwell CCD
	
No. 2
Full frame of a 15 minute dark exposure at
-126"C.	 Most
of chip contains smeared dark current
	 from nonthernial
defects. Only areas marked are clear (about 28% of area).
In slightly longer exposures these areas would also be
affected.
- 12 -
factor of 100 compared with Figures 3 and 5 ; thus all 100 lines of the image are
shown, arranged end to end. Ideally, the dark current in all the lines should
be low, as in the marked areas. Approximately 72% of the image has been contamina-
ted with excessive dark current. In slightly longer exposures the entire chip
is filled. Hence, this chip is greatly inferior to Chip No. 1 for astronomical
applications.
SLTMRY
We feel that the Rockwell CCD shows considerable promise for astronomical
applications. In the good areas of chip No. 1 (approximately 60Z of the total
chip area) the charge sensitivity, full well capacity, readout noise, resolution,
and dark current characteristics are very good. These portions of this chip
would make an excellent astronomical detector. However,the nonthermal blemishes
and charge transfer inefficiency at low temperature reduce the yield of usable
chips to the point where these problems must be solved by Rockwell before these
chips will become useful devices for astronomy.


Large area CCD image sensors for space astronomy

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