It is designed operated in MULTI-PINNED PHASE (MPP) mode, in order to substantially decrease dark current (typically)
from 30 e–/pixel.s standard mode to 0.5 e–/pixel.s MPP mode at – 40°C) Compared to standard technology, MPP allows,
at constant performance, either to increase exposure time, or to operate at higher temperature.
Dark current is due to thermal generation in the substrate of the CCD. The different generation sources are :
– surface states at the Si-SiO2 interface, which is the main contribution,
– generation and diffusion in bulk,
– generation in depleted region.
If the gates are polarized with an adequately negative bias, holes appear at the Si-SiO2 interface and fill the interface states,
suppressing their dark current contribution. As a result, only the minor bulk contribution remains.
This effect is applied in MPP mode. During exposure time, all the clocks of image zone are biased at a negative voltage,
resulting in potential inversion in the substrate and holes creation. To achieve it, two design changes were necessary, compared
to standard product :
– suppression of protection diodes of the image zone clocks. It is important to note that MPP devices are consequently
more sensitive to electrostatic discharge,
– addition of an implant beneath one gate of each pixel (ΦP3) in order to have discrete potential wells when the same bias
is applied to all the clocks.
MPP technology is very efficient for radiation hardening. Damages created at the Si-SiO2 interface are inhibited by holes,
and only bulk damage effects are observed after irradiation.
HIGH DETECTIVITY CONFIGURATION
The best way to obtain the highest detectivity from a given CCD is :
– to increase exposure period for sensitivity improvement,
– to decrease data rate in order to limit the readout noise,
– to operate at low temperature (dark signal suppression).
In addition, this device comprises a second readout register and three additional outputs (one at each corner). Nevertheless,
these features are not useful for high frequency applications. They have been designed for low data rate uses ; as a con-
sequence, the CCD is tested only in the described configuration, and extra pins must be properly biased in order to avoid
spurious effects.
GEOMETRICAL CHARACTERISTICS
The image is made up of a single field of 512 lines plus 4 extra lines. The video line is composed of 512 useful pixels, and
552 elements in total (see timing diagrams).
19
m
m
A
f
P4
f
P1
f
P2
19
m
m
f
P3
f
P4
Poly Si gates
A'
Channel stop
0
1 Stage
f
P3
f
P4
f
P1
f
P2
Si O2
Poly Si
x
Substrate
Signal charges
V
f
Figure 2a :
Front view of a photoelement.
Figure 2b :
Cross-sectional view (AA’) of a photoelement and
Figure 2b :
potential profile during integration.
Figure 2c :
Configuration of the gates.
2/16
TH 7895M-(H)
ABSOLUTE MAXIMUM RATINGS
Storage temperature ................................................................................................................................................ – 55°C to + 150°C
Operating temperature............................................................................................................................................... – 40°C to + 85°C
Maximum applied voltages :
– pin : H3 ................................................................................................................................................................... – 0.3 V to + 20 V
– pins : D2, C4, J3, F4, C1, J4, C2....................................................................................................................... – 0.3 V to + 18 V
– pins : A3, B1, B2, B4, C3, D1, E1, F4, G4, H1, H2, K2, K3, K4 .................................................................. – 0.3 V to + 15 V
– pins : A2, H4 ................................................................................................................................................................... 0 V (ground)
– pins : A1, A4, B3, D4, E4, F1, G1, J1, J2, K1 .................................................................................................... – 12 V to + 3 V
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