Charge Collection Studies with Pixel Sensor Prototypes for ALICE ITS3

Sammanfattning

During the upcoming LHC Long Shutdown 3 the ALICE experiment will upgrade its 3 Inner Tracking System (ITS2) layers to ITS3. The final design of ITS3 will have silicon sensors of up to 26 cm × 10 cm, thinned to 50 μm and bent into a cylindrical shape. The sensor prototypes developed are MOnolithic Stitched Sensors (MOSS) that are made of 10 Repeated Sensor Units (RSU). A babyMOSS sensor, consisting of a single-RSU, is manufactured to facilitate in-beam sensor characterization. Each babyMOSS has a top and bottom half-unit (HU). The difference between these half units is the pitch of the pixels, with the top HU having a pixel pitch of 22.5 μm and the bottom HU having a pixel pitch of 18 μm. The design of the pixel features a low-doped, deep n-type implant in the pixel to deplete the pixel over its full area. Implants of neighboring pixels are separated by a gap, which enhances charge collection near pixel edges. For a subset of sensors, and only for pixels with a 22.5 μm pitch, the pixel-to-pixel gap width was increased from the baseline of 2.5 μm to 5 μm. This thesis provides a Time over Threshold analysis from a test beam with a babyMOSS telescope performed at the CERN PS and from a Cosmics Telescope constructed with babyMOSS sensors at Lund University. For the test beam, two babyMOSS sensors representing different pixel variants were tested with negatively charged pions of 7 GeV/c. A cooling plate was provided to keep the babyMOSS devices under test at a constant temperature of 27 ◦C. Time over Threshold (ToT) data were collected in the test beam, along with source and pulsing data separately for a complete ToT analysis. Afterwards, the Lund Cosmics Telescope was designed and constructed with 5 babyMOSS planes, 4 tracking planes and 1 Device Under Test, with a looped trigger sequence. Time over Threshold data was collected with and without cosmics along pulsing data for a simplified ToT analysis.