For the innermost layers of the foreseen upgrade to the ATLAS tracker, charge trapping will be the main limitation in terms of the sensor lifetime. A possible solution to the degradation of the charge collection efficiency (CCE) could be the use of 3D detectors. In 3D detectors the electrodes are processed not just at the surface of the sensor, but they extend partly or completely through the silicon bulk. The distance between the columnar electrodes of 3D detectors can be adjusted to the expected fluence range. We designed and constructed prototype modules comprising ATLAS SCT front-end electronics and 3D single-type column (stc) p-type strip detectors with different strip isolation techniques and different substrate materials. With a strip length of 18.4 mm these sensors could be a radiation hard option for the innermost short strip region of the inner detector in the upgraded ATLAS experiment. We characterised these 3D stc p-type sensors in terms of their noise behaviour and hence their effective capacitance as a function of applied bias voltage at a read-out speed of 40 MHz which is also anticipated for sLHC. Employing an IR laser and automated x–y stages with micrometer resolution we characterised the sensors regarding the CCE in dependence of the bias voltage and the IR laser position relative to the sensors before irradiation.
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