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Descrizione
Single photon counting and charge integrating hybrid pixel detectors are an established standard for photon science applications at hard X-ray energies between $\sim\,$2 keV and 20 keV. Their capabilities for high frame rates and dynamic range, large area coverage, high signal-to-noise ratio and spatial resolution also make them attractive for applications at soft X-ray energies (< 2keV). However, using hybrid detectors for soft X-ray detection has been difficult so far. This is mainly due to the low quantum efficiency of standard silicon sensors at soft X-ray energies and the noise of the readout electronics.
At PSI, we have been developing inverse Low Gain Avalanche Diode (iLGAD) sensors for soft X-ray detection in collaboration with FBK. These sensors feature an optimized thin entrance window, enabling a quantum efficiency at soft X-ray energies comparable to standard CCD and CMOS image sensors (i.e., 62% at 250 eV). The internal signal amplification in the iLGAD sensor improves the signal-to-noise ratio at low photon energies and enables single photon resolution down to $\sim\,$200 eV
We present the development of iLGAD-based hybrid detectors for soft X-ray photon science at PSI and illustrate the capabilities and current limitations of the technology. We discuss in depth characterization results of a prototype consisting of an iLGAD sensor bump bonded to the charge integrating 75 µm pixel JUNGFRAU chip. Cooled to -22°C, this system achieves an effective equivalent noise charge of ≤ 5.5 electrons r.m.s. at a 5 μs integration time. Single photon resolution at 200 eV with a signal-to-noise ratio better than 5 becomes feasible by cooling further to -50°C. Based on these results, we give an outlook on future improvements and show a first look on applications of iLGAD hybrid detectors for soft X-ray experiments.
