Characterisation of a PERCIVAL monolithic active pixel prototype using synchrotron radiation

Abstract

A: PERCIVAL ("Pixelated Energy Resolving CMOS Imager, Versatile And Large") is a monolithic active pixel sensor (MAPS) based on CMOS technology. Is being developed by DESY, RAL/STFC, Elettra, DLS, and PAL to address the various requirements of detectors at synchrotron radiation sources and Free Electron Lasers (FELs) in the soft X-ray regime. These requirements include high frame rates and FELs base-rate compatibility, large dynamic range, single-photon counting capability with low probability of false positives, high quantum efficiency (QE), and (multi-)megapixel arrangements with good spatial resolution. Small-scale back-sideilluminated (BSI) prototype systems are undergoing detailed testing with X-rays and optical photons, in preparation of submission of a larger sensor.A first BSI processed prototype was tested in 2014 and a preliminary result -first detection of 350eV photons with some pixel types of PERCIVAL -reported at this meeting a year ago.Subsequent more detailed analysis revealed a very low QE and pointed to contamination as a possible cause. In the past year, BSI-processed chips on two more wafers were tested and their response to soft X-ray evaluated. We report here the improved charge collection efficiency (CCE) of different PERCIVAL pixel types for 400eV soft X-rays together with Airy patterns, response to a flat field, and noise performance for such a newly BSI-processed prototype sensor.

On the Charge Collection Efficiency of the PERCIVAL Detector

“…The results are shown in figure 1. As a comparison, the CCE at 400 eV previously measured at I-10 beam-line at DLS, and already reported in [4], is also shown.…”

“…It basically accounts for the number of electrons measured with the TSs in a particular illumination situation, per unit time. See also [4] for a detailed description. This number is then compared to the number of electrons expected to be created under the same photon flux conditions.…”

“…Moreover, at FELs, handling repetition rates of up to 120 Hz while imaging every pulse's diffraction pattern individually is mandatory. These and other requirements have already been described in more detail in [4].…”

PERCIVAL: possible applications in X-ray micro-tomography

“…• Exposure modes, FEL: all photons in < 300 fs, synchrotron: quasi-continuous Some P2M sensors in the Front Side Illuminated (FSI) configuration are being under tests and preliminary results have already been reported in [3,4]. Moreover, the characterization of several smaller sized test prototypes, which had been built to evaluate the performance of the chosen architecture, has been reported in [5,6]. In addition two wafers have been processed for soft X-ray compatibility and back side-illumination (BSI) compatible chips have been bonded to detector heads.…”

The Percival 2-Megapixel monolithic active pixel imager

“…Three generations of pixel-and-ADC prototypes, and one prototype verifying digital data handling, have been fabricated and tested [2][3][4][5][6][7] in preparation for this first large-scale sensor.…”