MoTiC: Development of a Prototype of a Monolithic Particle Tracking Detector with Timing

Abstract

Depleted Monolithic Active Pixel Sensors (DMAPS) are a promising technology for particle tracking detectors in future particle physics experiments. CMOS processes that are tolerant of the high voltages required for full depletion have become available in recent years. This allows for charge collection by drift, which has made DMAPS strong candidates for future pixel detectors. The combination of measurements of spatial coordinates with time of arrival measure- ments promises capabilities to disentangle tracks originating from multiple interaction vertices. In this thesis, a new DMAPS prototype called MoTiC (Monolithic Timing Chip) and the data acquisition system for its operation are presented. There are two chips: MoTiC A incorporates 5120 and MoTiC B 3840 square pixels of 50 µm pitch. While MoTiC A features several different preamplifiers, the sensor geometries are varied in MoTiC B. Groups of 4 pixels share a time-to-digital converter (TDC), consisting of a digital part with coarse resolution and an analog part for interpolation. The chips were designed and fabricated in a modified 110 nm CMOS process. The performance of the chips was evaluated in laboratory measurements and beam tests with an electron beam at DESY. While the TDC has a resolution of below 10 ps in standalone test structures, the TDC in the pixel array was demonstrated to have a resolution of better than 50 ps, measured with calibration signals. The best spatial resolution achieved at an incident angle of 8◦ with samples of 200 µm thickness was 4.8 ± 0.5 µm, while the spatial resolution at vertical incidence was measured to be 6.3 ± 0.4 µm. Hit efficiencies above 99.8 % were achieved with most preamplifiers and sensor geometries. The time resolution of the TDC in the beam was demonstrated to be about 1.2 ns, relying only on the digital part of the TDC. When also using the analog part of the TDC, the time resolution with actual particle hits is expected to be on the order of some hundred picoseconds. Within the thesis, an improved version of MoTiC was developed, eliminating several design flaws in the first version.