Test beam characterization of 3-D silicon pixel detectors

Three-dimensional (3-D) silicon detectors are characterized by cylindrical electrodes perpendicular to the surface and penetrate into the bulk material in contrast to standard Si detectors with planar electrodes on the top and bottom. This geometry renders them particularly interesting to be used in environments where standard silicon detectors have limitations, such as, for example, the radiation environment expected in an upgrade to the Large Hadron Collider at CERN. For the first time, several 3-D sensors were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip and readout electronics. Devices with different electrode configurations have been characterized in a 100 GeV pion beam at the CERN SPS. Here, we report results on unirradiated devices with three 3D electrodes per 50 $\,\times \,$400 $\mu {\rm m}^{2}$ pixel area. Full charge collection is obtained already with comparatively low bias voltages around 10 V. Spatial resolution with binary readout is obtained as expected from the cell dimensions. Efficiencies of 95.9%$ \pm$0.1% for tracks incident parallel to the electrodes and of 99.9%$ \pm$0.1% for tracks incident at 15 $^{\circ} $ are measured. The homogeneity and charge sharing of the efficiency over the pixel area are measured.