Some aspects of the Pixel Vertex Detector (PXD) at Belle II

The innermost detector of the Belle II experiment makes use of the DEPFET technology. It will provide an accurate measurement of the track positions in order to reconstruct the decay vertex of the short living particles. This DEPFET technology combines signal detection and amplification in a single silicon pixel structure, so that the position measurement of traversing particles can be achieved with an overall material budget of 0 : 2% radiation length, corresponding to 75 mu m in order to minimize the impact of multiple scattering for low transverse momentum tracking. Moreover, the DEPEFT detector has an excellent signal-to-noise ratio, low power consumption and offers a non-destructive readout. The instantaneous luminosity of 8 x 10(35) cm(-2) s(-1) expected at SuperKEKB causes large background. The close proximity of the pixel detector to the beampipe (only 1 : 4 cm from the interaction point) poses many challenges to the detector technology, in particular to radiation hardness and readout speed. The vertex pixel detector consists of two DEPFET layers at radii 14mm and 22 mm. These are 20 ladders in total corresponding to 8 megapixels (pixel sizes: (55, 60, 70, 85) x 50 mu m(2)). The four-fold readout in rolling shutter mode results in a total readout time of about 20 mu s for an entire frame. The concept of the sensor and the surrounding readout electronics will be presented in detail with focus on the Belle II experiment. 17 institutes from Europe and Asia work together in the DEPFET collaboration to meet these challenges.