Study of the signal response of the MÖNCH 25μm pitch hybrid pixel detector at different photon absorption depths

Abstract

MÖNCH is a 25 μm pitch hybrid silicon pixel detector with a charge integrating analog read-out front-end in each pixel. The small pixel size brings new challenges in bump-bonding, power consumption and chip design. The MÖNCH02 prototype ASIC, manufactured in UMC 110 nm technology with a field of view of 4×4 mm2 and 160×160 pixels, has been characterized in the single photon regime, i.e. with less than one photon acquired per frame on average on a 3×3 pixel cluster. The low noise and small pixel size allow spatial interpolation with high resolution. Understanding charge sharing as a function of the photon absorption depth and sensor bias is a key for optimal processing of single photon data for high resolution imaging. To characterize the charge collection of the detector, the sensor was illuminated with a 20 keV photon beam in edge-on configuration at the SYRMEP beamline of Elettra. By slicing the beam by means of a 5 μm slit and scanning through the 320 μm silicon sensor depth, the charge collection is characterized as a function of the photon absorption depth for different sensor bias voltages.

Single shot x-ray phase contrast imaging using a direct conversion microstrip detector with single photon sensitivity

“…A more effective exploitation of all photons for detecting the phase shift and increase in the maximum spatial resolution can be achieved by enhancing the charge sharing, which is larger at lower energies (with the disadvantage that the radiation dose is increased as well) or can be obtained by an optimization of the detector by using smaller strip pitches, thicker sensors (which also increases the absorption efficiency), or the use of lower bias voltages to the sensors. 32 These last expedients will increase the diffusion time for the charge generated by the photons absorbed closer to the backplane, but will not affect the ones absorbed deeper in the sensor bulk, which are still a considerable amount at the energy used in our experiment. Spatial resolution is also affected by the alignment of the sensor compared to the X-ray beam due to the parallax given by the different depth of absorption of the 16.7 keV photons through the 320 lm silicon sensor ($300 nm per 1 mdeg misalignment).…”

Micrometer-resolution imaging using MÖNCH: towards G2-less grating interferometry

“…This effect is known as charge sharing and is more prominent in smaller pixel pitch detectors. The amount of charge sharing depends on several parameters including the sensor thickness, the sensor bias and the photon energy (Cartier et al, 2014(Cartier et al, , 2015. It has been measured that, for a 320 mm-thick silicon sensor biased with 120 V, the size of the charge cloud is of the order of 17 AE 3 mm in the 10-20 keV energy range (Bergamaschi et al, 2008).…”