Speaker
Description
During the LHC Long Shutdown 3, the ALICE Collaboration will replace the innermost three layers of the existing ALICE silicon tracker, ITS2. The upgraded inner tracker will consist of cylindrical, wafer-scale monolithic silicon sensors using a 65 nm CMOS imaging process. To evaluate the performance of the technology, test structures were fabricated on a multilayer reticle (MLR1). One such structure, the analogue pixel test structure with an operational amplifier (APTS-OPAMP), was developed to investigate the achievable time resolution of this technology.
The APTS-OPAMP chip features a 4 × 4 pixel matrix with a pixel pitch of 10 µm × 10 µm on an approximately 10 µm thick epitaxial layer with a small collection electrode. Each pixel is connected to a dedicated fast operational amplifier located outside the matrix, which buffers the signal output from the pixel front end to the analogue output pad. Characterisations of a non-irradiated sensor have demonstrated a time resolution as low as 63 ps.
To assess the impact of radiation on the time resolution of the 65 nm CMOS imaging process for use in ITS3 and future applications, the APTS-OPAMP was irradiated with neutrons up to fluences of $10^{14}$ and $10^{15}$ 1 MeV n$_\text{eq}$/cm$^2$. This contribution presents the latest performance results, focusing on time resolution and efficiency. It includes measurements from both laboratory and beam tests, with particular emphasis on the APTS-OPAMP performance in the most recent test beam campaign, showing an efficiency of approximately 99% and an overall time resolution comparable to that of a non-irradiated sensor.
