Evaluation of a Full Field Fluorescence Imager with Synchrotron Radiation

Abstract: The design and evaluation on the NSLS-II beamline of the 3FI application specific integrated circuit (ASIC) bump-bonded to a simply, planar, two-dimensionally segmented silicon sensor is presented. The ASIC was developed for Full-Field Fluorescence spectral X-ray Imaging (3FI). It is a small-scale prototype that features a square array of 32x32 pixels with a pitch of 100 {\mu}m. The ASIC was implemented in a 65 nm CMOS process. Each pixel incorporates a charge-sensitive amplifier, shaping filter, discriminator, peak detector, and sample-and-hold circuit, allowing detection of events and storing signal amplitudes. The system operates in an event-driven readout mode, outputting analog values for threshold-triggered events, allowing high-speed multi-element X-ray fluorescence imaging. At power consumption of 200 {\mu}W per pixel, consisting almost uniquely of power dissipated in analog blocks, 308 eV full width at half maximum (FWHM) energy resolution at 8.04 keV, that corresponds to 30 e- rms equivalent noise charge (ENC) and 138 eV FWHM energy resolution at 3.69 keV (16 e- rms ENC) were obtained, for Cu and Ca K{\alpha} lines, respectively. Each pixel operates independently, and the detector enables in situ trace element microanalysis in biological and environmental research. Its architecture addresses limitations of X-ray Fluorescence Microscopy (XFM), typically requiring mechanical scanning, by offering frame-lees data acquisition, translating to high-throughput operation. The 3FI ASIC is suitable for example for studies of nutrient cycling in the (mycor)rhizosphere, microbial redox processes, and genotype-phenotype correlations in bio-energy crops. Additional performances, such as enhanced spatial resolution can be further improved with coded-aperture and Wolt, extending the use to environmental, biomedical, and material science studies.