# Investigating the Impact of Sensor Layout on Radiation Hardness in 25 µm Pitch Hybrid Pixel Detectors for 4th Generation Synchrotron Light Sources

## TL;DR

This paper studies how sensor layout affects radiation resistance in pixel detectors for advanced synchrotron light sources.

## Contribution

The paper introduces new sensor design variations and evaluates their radiation hardness performance in hybrid pixel detectors.

## Key findings

- The default pixel design is suboptimal and benefits from layout changes like full metal coverage of implants.
- Layout changes alone are insufficient for future full-sized sensors requiring higher radiation hardness.
- Annealing dynamics and noise increase due to radiation damage were measured up to 100 kGy.

## Abstract

With the evolution of synchrotron light sources to fourth generation (diffraction-limited storage rings), the brilliance is increased by several orders of magnitude compared to third generation facilities. For example, the Swiss Light Source (SLS) has been upgraded to SLS 2.0, promising a horizontal emittance reduced by a factor of 40, and a brilliance up to two orders of magnitude (three at higher energies). A key challenge arising from the increased flux is the heightened accumulated dose in silicon sensors, which leads to a significant increase in radiation damage. This translates into an increase of both noise and dark current, as well as a reduction in the dynamic range for long exposure times, thus affecting the performance of the detector, in particular, for charge-integrating detectors. We have designed sensors with a 4 × 4 mm2 pixel array featuring 16 design variations of 25 µm pitch pixels with different implant and metal sizes and tested them bump-bonded to MÖNCH 0.3, a charge integrating hybrid pixel detector readout ASIC. Following a first assessment of the functionality and performance of the different pixel designs, the assembly has been irradiated with X-rays. The variation in the tested parameters was characterized at different accumulated doses up to 100 kGy at the sensor entrance window side. The annealing dynamics at room temperature have also been measured. The results show that the default pixel design is currently not optimal and can benefit from layout changes (reduction in the inter-pixel gap area with full metal coverage of the implant). Further studies on the metal coverage over large implants could be conducted. The layout changes are, however, not sufficient for future full-sized sensors, requiring improved radiation hardness and long-term stability, and additional strategies such as focusing on detector cooling and changes in sensor technologies would be required.