DEPFET beam test results — Pixel properties studied at micron level resolution

Fully depleted DEPFET active pixel sensors designed for ILC vertex detector were tested at CERN SPS using beams of pions and electrons with energies between 40 and 120 GeV. The sensors tested were 450 μm thick prototypes with pixel size between 20 and 32 μm. The paper presents a brief overview of measurement and analysis, followed by a selection of results focused on detailed in-pixel variation of resolution, cluster size and charge collection. Reliable determination of detectors' intrinsic resolutions was reached by numerical separation the contributions of multiple scattering, telescope precision and intrinsic resolutions to tracking residuals. The intrinsic resolutions obtained are around 1 μm and were determined with typical accuracy of 0.1 μm, as confirmed by simulation studies. For the material presented in this paper, the resolutions serve as a useful analysis tool. Special effect studies included edge distortions, gain variation and η distributions. Some interesting effects arising from the layout of the readout structures are described.