Speaker
Description
Achieving excellent time resolution in small pixel cells is a key challenge for the next generation of silicon detectors. In the high-density collision environment of the HL-LHC, detectors will need to cope with extreme pile-up. To disentangle different collisions and restore the efficiency of track reconstruction algorithms, silicon pixel detectors must provide per-hit time measurements with a resolution on the order of tens of picoseconds, enabling 4D tracking. Silicon sensors with a 3D electrode geometry, where vertical electrodes penetrate into the substrate, offer a promising solution due to their intrinsic radiation hardness and fast charge collection properties.
This work presents a timing performance study of the first 3D silicon sensor read out by a Timepix4 ASIC. The sensor is a p-on-n double-sided 3D device, featuring columns of 10 µm diameter etched from both sides of the wafer to form partially penetrated electrodes. Designed with a 55 µm pixel pitch aligns with the Timepix4 pixel size and populates 256 × 256 pixels of the ASIC matrix.
The analyzed data were collected during testbeam campaigns at the CERN SPS North Area H8 beamline, using the Timepix4 beam telescope. The telescope is composed of eight detector planes: four optimized for the spatial resolution and four for timing measurements. The 3D sensor is placed in the center of the telescope as the detector under test (DUT), where the telescope has a pointing resolution of 2.3 μm. Behind the telescope, two MCP-PMTs with a combined timestamp accuracy of about 12 ps are used as the reference time for the telescope and the DUT characterization.
A detailed timing analysis was carried out, including corrections for the time-walk effect and for frequency variations in the Voltage Controlled Oscillators. To achieve the best time resolution, correction parameters must be determined for different areas within the pixel. After applying these corrections, a (currently best) time resolution on order of 160 ps was achieved for the pixel area between the electrodes. The sensor response was examined under both perpendicular and grazing angle incidence of the tracks, with the latter providing insight into the timing behavior at different depths in the sensor. Various studies of the 3D sensor as function of bias voltage, threshold setting and optimal angle tilt will be presented, and the limitations of the tested 3D sensor will be discussed. These results can be further investigated and interpreted by Two-Photon Absorption (TPA) laser measurements, which offers complementary information on the sensor behavior across different depths.
This study can provide valuable input for the developments for the future LHCb VELO upgrade, where 3D sensors are a prominent candidate for achieving precise timing in a dense collision environment.
| Position | PhD student |
|---|---|
| Affiliation | Nikhef |
| Country | Netherlands |