The ATLAS Pixel Detector provides a very high granularity, high precision set of measurements as
close to the
interaction point as possible. The system provides three precision measurements over
the full acceptance, and
mostly determines the impact parameter resolution and the ability of the
Inner Detector
to find short lived particles
such as B-Hadrons.
The pixel system is composed of small modules precisely mounted on a stable mechanical system
that must also provide cooling to operate the silicon detectors near 0oC.
A Pixel sensor is a 16.4 x 60.8 mm wafer of silicon with 46,080 pixels, 50 x 400 microns each.
A Pixel module comprises an un-packaged flip-chip assembly of 16 front-end chips bump bonded
to a sensor substrate.
There are 1744 modules in the Pixel Detector for nearly 80 million channels in a cylinder
1.4m long, 0.5m in diameter centered on the interaction point.
The barrel part of the pixel detector consists of the 3 cylindrical layers with the radial
positions of 50.5 mm, 88.5 mm and 122.5 mm respectively. These three barrel layers are made
of identical staves inclined with azimuthal angle of 20 degrees. There are 22, 38 and 52 staves
in each of these layers respectively. Each stave is composed of 13 pixel modules.
In the module there are 16 front-end (FE) chips and one Module Control Chip (MCC).
One FE chip contains 160 raws and 18 columns of pixel cells, i.e. 2889 pixels per FE chip
or 46080 pixels per module.
There are three disks on each side of the forward regions.
One disk is made of 8 sectors, with 6 modules in each sector. Disk modules are identical
to the barrel modules, except the connecting cables.
The front-end chips are a major heat source (0.8W/cm2) dissipating more than 15kW into the
detector volume. This heat is taken out via integrated cooling channels in the detector support
elements: Staves in the barrel region and Sectors in the forward region.
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