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Test-beam results from MiniCACTUS-v2: A depleted monolithic CMOS timing sensor prototype

Y. Degerli, R. Aleksan, R. Casanova, Y. Gan, S. Grinstein, F. Guilloux, A. Hanlon, T. Hemperek, J. P. Meyer, J. Pinol, P. Schwemling, E. Vilella

Abstract

MiniCACTUS-v2 is a monolithic sensor prototype designed in LF 150 nm CMOS process for time tagging of individual Minimum Ionizing Particles with an accuracy better than 100 ps. The sensing element is a deep n-well/p-substrate diode without internal amplification. To minimize detector capacitances, the analog front-ends and the discriminators for each pixel have been implemented outside the pixel, at the column level. After fabrication, the sensors have been thinned to 150 microns, 175 microns and 200 microns and then post-processed for backside biasing. The breakdown voltages measured on these sensors are higher than 500 V, ensuring the complete depletion of the charge collection volume. In this paper, we will focus on the time resolution measurements from a test-beam campaign conducted in July 2025 at SPS-CERN. During this period, several pixels from the 3 different sensor thicknesses have been tested at different bias voltages. The best time resolution measured is 48.88 ps on a 0.5 mm x 0.5 mm pixel from a 175 microns-thick sensor at 500 V, with nominal settings for the on-chip analog front-end and discriminator.

Test-beam results from MiniCACTUS-v2: A depleted monolithic CMOS timing sensor prototype

Abstract

MiniCACTUS-v2 is a monolithic sensor prototype designed in LF 150 nm CMOS process for time tagging of individual Minimum Ionizing Particles with an accuracy better than 100 ps. The sensing element is a deep n-well/p-substrate diode without internal amplification. To minimize detector capacitances, the analog front-ends and the discriminators for each pixel have been implemented outside the pixel, at the column level. After fabrication, the sensors have been thinned to 150 microns, 175 microns and 200 microns and then post-processed for backside biasing. The breakdown voltages measured on these sensors are higher than 500 V, ensuring the complete depletion of the charge collection volume. In this paper, we will focus on the time resolution measurements from a test-beam campaign conducted in July 2025 at SPS-CERN. During this period, several pixels from the 3 different sensor thicknesses have been tested at different bias voltages. The best time resolution measured is 48.88 ps on a 0.5 mm x 0.5 mm pixel from a 175 microns-thick sensor at 500 V, with nominal settings for the on-chip analog front-end and discriminator.
Paper Structure (6 sections, 7 figures, 2 tables)

This paper contains 6 sections, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Sensor Description
  3. In-Lab Tests
  4. Test-beam Setup
  5. Data Analysis and Results
  6. Conclusions

Figures (7)

  • Figure 1: Layout of the MiniCACTUS-v2 sensor.
  • Figure 2: I-V curves measured on several 150µ m, 175µ m (left) and 200µ m (right) sensors. All tested sensors can be safely biased up to 500 V.
  • Figure 3: Picture of the test-beam setup showing the the sensor under test, the PCBs, the PMTs, and the scope used for data acquisition.
  • Figure 4: Measured (a) amplitude distribution on the analog monitoring output (AmpOut) with MIPs at 500 V bias voltage, (b) MPV as a function of sensor bias voltage showing very small variation in this range (0.5 mm $\times~$ 1.0 mm pixel from a 175 µm-thick sensor).
  • Figure 5: Measured time difference distributions between the DUT digital output (DigOut) and the 2 PMTs (PMT1 and PMT2) as a function of analog signal amplitude (AmpOut) for TW corrections.
  • ...and 2 more figures