X-ray spectral performance of the Sony IMX290 CMOS sensor near Fano limit after a per-pixel gain calibration

TL;DR

This study evaluates the X-ray spectral performance of the Sony IMX290 CMOS sensor, demonstrating near-Fano limit energy resolution after per-pixel gain calibration and confirming its stability over a month-long period.

Contribution

It introduces a method for per-pixel gain calibration of CMOS sensors and shows their capability to achieve near-Fano limit energy resolution in X-ray detection.

Findings

Gain dispersion of 0.4% across 2.1 million pixels

Energy resolution of 123.6 eV at 5.9 keV after calibration

Stable detector performance over 30 days

Abstract

The advent of back-illuminated complementary metal-oxide-semiconductor (CMOS) sensors and their well-known advantages over charge-coupled devices (CCDs) make them an attractive technology for future X-ray missions. However, numerous challenges remain, including improving their depletion depth and identifying effective methods to calculate per-pixel gain conversion. We have tested a commercial Sony IMX290LLR CMOS sensor under X-ray light using an $^{55}$Fe radioactive source and collected X-ray photons for $\sim$15 consecutive days under stable conditions at regulated temperatures of 21{\deg}C and 26{\deg}C. At each temperature, the data set contained enough X-ray photons to produce one spectrum per pixel consisting only of single-pixel events. We determined the gain dispersion of its 2.1 million pixels using the peak fitting and the Energy Calibration by Correlation (ECC) methods. We measured a gain dispersion of 0.4\% at both temperatures and demonstrated the advantage of the ECC method in the case of spectra with low statistics. The energy resolution at 5.9 keV after the per-pixel gain correction is improved by $\gtrsim$10 eV for single-pixel and all event spectra, with single-pixel event energy resolution reaching $123.6\pm 0.2$ eV, close to the Fano limit of silicon sensors at room temperature. Finally, our long data acquisition demonstrated the excellent stability of the detector over more than 30 days under a flux of $10^4$ photons per second.