[Paper Review] Dynamic Range of SiPMs with High Pixel Densities

Zhiyu Zhao, Baohua Qi+2 more|arXiv (Cornell University)|Jul 25, 2024

Luminescence and Fluorescent MaterialsMaterials Science3 citations

TL;DR

This study evaluates the dynamic range of high-pixel-density SiPMs using laser calibration and a custom Toy Monte Carlo simulation, demonstrating that a 6 μm pixel SiPM with 244,719 pixels achieves near-100% linearity up to 350,000 photoelectrons—meeting the stringent requirements for the CEPC Higgs factory calorimeter. The simulation corrects for saturation effects, enabling accurate high-energy measurements even with lower-pixel-count SiPMs.

ABSTRACT

This study investigates the characteristics of Silicon Photomultipliers (SiPMs) with different pixel densities, focusing on their response across a wide dynamic range. Using an experimental setup that combines laser source and photomultiplier tubes (PMTs) for accurate light intensity calibration, we evaluated SiPMs with pixel counts up to 244,719 and pixel sizes down to 6 micrometers. To complement the experimental findings, a "Toy Monte Carlo" was developed to replicate the SiPMs' reponses under different lighting conditions, incorporating essential parameters such as pixel density and photon detection efficiency. The simulations aligned well with the experimental results for laser light, demonstrating similar nonlinearity trends. For BGO scintillation light, the simulations, which included multi-firing effect of pixels, showed significantly higher photon counts compared to the laser simulations. Furthermore, the simulated response derived in this research offer a method to correct for SiPM saturation effect, enabling accurate measurements in high-energy events even with SiPMs having a limited number of pixels.

Motivation & Objective

• To determine the dynamic range of SiPMs with high pixel densities (6–25 μm pitch) under intense light conditions relevant to future high-energy physics experiments.
• To address the challenge of calibrating SiPMs across a wide dynamic range, especially when traditional sensors (PMTs or SiPDs) have limitations in linearity or dynamic range.
• To develop and validate a Toy Monte Carlo simulation that accurately models SiPM response, including multi-firing effects and nonlinearity, for BGO scintillation light.
• To provide a correction framework for SiPM saturation effects, enabling accurate energy measurement in high-energy events despite limited pixel counts.
• To assess whether SiPMs can meet the dynamic range requirement of ~350,000 photoelectrons per channel in the CEPC crystal calorimeter.

Proposed method

• Used a PMT with adjustable bias voltage to extend its linear range for calibrating incident photon flux across a wide intensity spectrum.
• Employed a laser source with known pulse energy and calibrated PMT output to establish a linear reference for photon count measurement.
• Designed a Toy Monte Carlo simulation incorporating key SiPM parameters: pixel density, photon detection efficiency (PDE), fill factor, crosstalk, and avalanche triggering probability.
• Simulated SiPM response to both laser light and BGO scintillation light, with the latter including multi-firing effects due to longer decay time.
• Compared experimental SiPM output with simulation results to validate model accuracy and identify discrepancies in nonlinearity trends.
• Derived correction functions from simulated response curves to compensate for saturation, enabling accurate measurement of high-energy signals on limited-pixel SiPMs.

Experimental results

Research questions

• RQ1 What is the dynamic range of SiPMs with pixel pitches of 6 μm, 10 μm, and 25 μm under high photon flux conditions?
• RQ2 Why does the 6 μm SiPM with 244,719 pixels saturate at approximately half its nominal pixel count, contrary to expectations?
• RQ3 How accurately can a Toy Monte Carlo simulation reproduce the nonlinear response of SiPMs under laser and BGO scintillation light excitation?
• RQ4 Can the simulated response be used to correct for SiPM saturation, enabling accurate energy measurement in high-energy events?
• RQ5 To what extent does the multi-firing effect of SiPM pixels influence the dynamic range when detecting scintillation light from BGO crystals?

Key findings

• The SiPM with 6 μm pixel size and 244,719 pixels exhibited near-100% linearity up to 350,000 photoelectrons, meeting the dynamic range requirement for the CEPC crystal calorimeter.
• The SiPM with 10 μm pixel size and 89,984 pixels showed approximately 20% nonlinearity at 350,000 photoelectrons, indicating significant saturation effects.
• The Toy Monte Carlo simulation accurately reproduced the nonlinear response of SiPMs under laser illumination, showing consistent trends with experimental data.
• For BGO scintillation light, the simulation predicted a significantly broader linear region than for laser light due to longer decay time and multi-firing effects.
• The simulation results provided a reliable correction framework for SiPM saturation, enabling accurate measurement of high-energy signals even with lower-pixel-count devices.
• The 25 μm and 10 μm SiPMs saturated at slightly below their nominal pixel counts, while the 6 μm SiPM saturated at approximately half its nominal count, suggesting complex recovery and crosstalk dynamics requiring further study.