MiniCACTUS-V2: A DMAPS Prototype for Timing in High Energy Physics

by Yujing Gan (IFAE)

Wednesday Jul 23, 2025, 9:00 AM → 12:00 PM Europe/Madrid

IFAE Seminar Room (In-person)

Thesis supervisors: Sebastian Grinstein, Raimon Casanova and Guangming Huang

Thesis committee: David Gascon, Abraham Antonio Gallas Torreira, Imma Riu, Jingbo Ye (online)

Abstract: The Large Hadron Collider (LHC) at CERN will be upgraded to the High-Luminosity LHC (HL-LHC) by 2030, increasing collision rates by a factor of 5–7. To handle this, the ATLAS detector will replace its Inner Detector with an all-silicon Inner Tracker (ITk). However, high pile-up in the forward region remains challenging, so ATLAS will add the High Granularity Timing Detector (HGTD) to provide precise time measurements (~30–50 ps) and reduce pile-up effects. The HGTD uses LGAD sensors, which offer excellent timing but require costly bump-bonding.

Monolithic Active Pixel Sensors (MAPS), especially their fully depleted version (DMAPS), integrate sensor and readout on the same chip, simplifying assembly and improving timing and radiation tolerance. To explore DMAPS for timing, the CACTUS and MiniCACTUS prototypes were developed. The first version suffered from degraded resolution due to power coupling; the MiniCACTUS improved this by redesigning the readout architecture. It achieved ~65 ps resolution but had a readout time too long for ATLAS needs.

The new MiniCACTUS-V2 aims for <25 ns readout time while keeping excellent timing resolution. This work proposes a new circuit design approach using more realistic input signal models, validated with simulations, and optimizes transistor parameters using the foundry’s database and custom scripts. A cascode preamplifier with gain-boosting achieves high gain and low noise with low power.

Tests of MiniCACTUS-V2 show good breakdown voltages and time resolutions: 63 ps for CSA2 and 80 ps for VPA readouts, both with <25 ns readout time. These results show that DMAPS can be a viable timing solution for future high-energy physics upgrades like the ATLAS HGTD.