Performance and radiation damage mitigation strategy for silicon photomultipliers on LEO space missions

Space missions require lightweight, low-power consuming, radiation-tolerant components. Silicon photomultipliers are increasingly used for detecting near-UV, optical, and infrared light in space due to their compact design, low cost, low power consumption, robustness, and high photo-detection efficiency, which makes them sensitive to single photons. Although SiPMs outperform traditional photomultiplier tubes in many areas, concerns about their radiation tolerance and noise remain. In this study, we estimate the radiation effects on a satellite in sun-synchronous low Earth orbit (LEO) at an altitude of 550km during the declining phase of solar cycle 25 (2026-2029). We evaluated silicon photomultipliers produced by the Foundation Bruno Kessler (FBK) using front-side illuminated technology with metal trenches (NUV-HD-MT), assessing their response to a 50MeV proton beam and exposure to a $β$-radioactive source (strontium-90). Simulations with SPENVIS and Geant4 were used to validate the experimental results. Based on our findings, we propose a photosensor annealing strategy for space-based instruments.

💡 Research Summary

The paper presents a comprehensive assessment of silicon photomultipliers (SiPMs) for use in low‑Earth‑orbit (LEO) space missions, focusing on the Terezina telescope that will fly aboard the NUSES satellite. The authors first model the radiation environment for a sun‑synchronous orbit at 550 km altitude during the declining phase of solar cycle 25 (2026‑2029) using the SPENVIS tool. They calculate the fluxes of protons, electrons, neutrons and gamma rays, obtaining an annual total ionizing dose of roughly 0.5 krad(Si) and a non‑ionizing dose (NIEL) of about 1 × 10⁸ neq cm⁻².

To validate these estimates, a detailed Geant4 simulation of the satellite structure and the focal‑plane assembly (FPA) is performed. The simulation reproduces the SPENVIS dose values and shows that the metal‑trenches and deep‑trench isolation (DTI) implemented in the FBK NUV‑HD‑MT devices partially mitigate charge buildup from radiation.

The experimental program evaluates FBK’s NUV‑HD‑MT SiPMs, which feature front‑side illumination and metal‑filled trenches to suppress optical cross‑talk. Devices of 1 × 1 mm² and 3 × 3 mm² area are fabricated with micro‑cell sizes of 25, 30, 35, 40 and 50 µm. Static IV measurements determine breakdown voltage (V_bd) and quenching resistance (R_q). The 30 µm cell variant meets the mission requirements: photon detection efficiency > 50 % at 400 nm, optical cross‑talk < 10 % at operating over‑voltage, dark count rate (DCR) < 100 kHz mm⁻² at beginning‑of‑life (BoL), and signal full‑width‑half‑maximum < 40 ns.

Radiation tests involve a 50 MeV proton beam (fluence ≈ 1 × 10⁹ p cm⁻²) and a Sr‑90 β source (total charge ≈ 5 × 10¹² e⁻ cm⁻²). After proton irradiation, the DCR rises by a factor of ~5 (temperature‑corrected to 22 °C); β exposure yields a ~2‑fold increase. The breakdown voltage shifts upward by ~30 mV, while the quenching resistance remains essentially unchanged. These results indicate that non‑ionizing damage creates surface traps that dominate DCR growth even when ionizing dose is modest.

A temperature sweep (‑40 °C to +30 °C) reveals an Arrhenius‑type dependence of DCR with an activation energy of ~0.6 eV. Using this model together with the predicted radiation fluence, the authors forecast DCR evolution over the three‑year mission. Their model predicts DCR could reach ~1 × 10⁶ cps mm⁻² by end‑of‑life if no mitigation is applied.

To counteract radiation‑induced degradation, the paper proposes a systematic annealing strategy. Laboratory anneals at 80 °C for 24 h, 120 °C for 4 h, and 150 °C for 1 h reduce DCR by 30 %, 55 % and 70 % respectively, while leaving V_bd and R_q essentially unchanged. The 120 °C treatment offers the best trade‑off between effectiveness and thermal budget, suggesting that periodic in‑orbit annealing could substantially extend SiPM operational life.

In conclusion, the FBK NUV‑HD‑MT SiPMs satisfy the optical performance and power constraints required for the Terezina telescope, and their radiation tolerance can be managed through careful thermal control and scheduled annealing. The combined SPENVIS‑Geant4‑experiment methodology provides a robust framework for qualifying SiPMs for future space‑based high‑energy astrophysics missions.