The ALICE silicon pixel detector (SPD) comprises the two innermost layers of the ALICE inner tracker system. The SPD includes 120 detector modules (half-staves) each consisting of 10 ALICE pixel chips bump bonded to two silicon sensors and one multi-chip read-out module. Each pixel chip contains 8192 active cells, so that the total number of pixel cells in the SPD is ≈ 10 7 . The on-detector read-out is based on a multi-chip-module containing 4 ASICs and an optical transceiver module. The

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... aints on material budget and detector module dimensions are very demanding. I. SPD LAYOUT AND PARAMETERS The ALICE silicon pixel detector (SPD) consists of two barrel layers at radii of 3.9 cm and 7.6 cm, respectively and has an active length of 28.3 cm. The basic detector module is the half-stave, in which the sensitive elements are two silicon sensors bump-bonded to 5 read-out ASICs each, see fig. 1 . A multilayer aluminum flexible flat cable provides power to the pixel chips and connects signal lines to a multi-chip read-out module (MCM). Each pixel chip contains a matrix of 8192 cells. The SPD contains 9.83 x 10 6 pixel cells. A half-stave has the physical dimensions of 240 mm x 15 mm x 2 mm. Each layer of the SPD has a material budget of 1 % of radiation length X 0 . The distance of the half-staves in the inner layer to the ALICE beam pipe is 4 mm only.