Integrating Silicon detector with segmentation for scanning transmission X-ray microscopy

Abstract

Scanning transmission X-ray microscopes require detectors with high quantum efficiency and wide dynamic range. While large area detectors provide absorption contrast, the addition of spatial segmentation adds phase contrast imaging capabilities. We describe a charge integrating Silicon detector for use at energies from 200–1000 eV. The detector uses patterned rectifying junctions on high-resistivity n-type Silicon, with separate current readout for each segment. The detector has been subdivided into eight regions arranged in a circular geometry according to the beam profile in a scanning X-ray microscope. The uncooled chip is fully depleted by a positive bias voltage applied at the ohmic contact on the back side. X-rays are collected on the radiation-hard back side with very high efficiency ( > 75 % for 250 eV X-rays), and compact, low-noise electronics integrate the current from the detector segments. The RMS noise of the combined system is about 500 electrons/channel for a 1 ms integration time, which is equivalent to about five photons per channel at 360 eV X-ray energy.