Speaker
Description
The development of monolithic silicon sensors with simultaneous high spatial and temporal resolution is being pursued at INFN within the ARCADIA project, with particular interest in applications requiring 4D tracking. The integration of internal gain in fully depleted CMOS sensors has led to the development of CMOS-LGAD devices, combining the fast signal formation of LGADs with monolithic readout electronics. Beam-test measurements of a first prototype, developed during the early R&D for the ALICE3 Time-of-Flight detector, demonstrated a time resolution down to 75 ps, providing a first experimental validation of the concept.
In parallel, INFN has developed Resistive AC-Coupled Silicon Detectors (RSDs), exploiting a continuous resistive electrode and capacitive signal induction to achieve 100% geometrical fill-factor and spatial resolutions at the level of a few percent of the sensor pitch, while retaining LGAD-like timing performance. The combination of these two approaches has motivated the development of CMOS-AC-LGADs, or CMOS-RSDs, integrating the resistive cathode and AC-coupling structure directly within the CMOS sensor.
The first CMOS-AC-LGAD implementation has been investigated through TCAD simulations using the parameters of the standard CMOS process, with the aim of preserving the existing fabrication technology without additional processing steps. The simulated signal formation and charge sharing reproduce the main features observed in hybrid RSDs, including position-dependent signal induction and approximately constant total response across the inter-pad region. Monte Carlo simulations of an 80 μm-pitch device predict a spatial resolution of about 2.3 μm, corresponding to approximately 3% of the pitch.
These results provide the basis for the design of the first CMOS-AC-LGAD prototype. The ongoing work is focused on completing the prediction of the main figures of merit, including timing performance and optimization of the sensor and readout geometry, with the ultimate goal of developing a scalable, low-power monolithic detector for high-resolution 4D tracking.
