Calculation of the Modulation Transfer Function of Hybrid Semiconductor Pixel Detectors for X-ray Imaging

The hybrid structure of solid-state pixel detector has a semiconductor sensor that converts the X-ray photons to electric pulses, and an electronics chip that processes and stores the signals. The signals are transferred from the sensor chip to the electronic chip through metallic bump bonds, one per pixel. Image quality parameters have to be assessed in order to estimate the imaging capabilities of the detector. The modulation transfer function (MTF), which describes the spatial resolution of the imaging system, is calculated for the sensor part of the detector. The sensor responses to a point-like source for both mono-energetic and poly-energetic beams are calculated by means of Monte Carlo simulation, in terms of the charge carrier distribution at the collecting surface of the sensor. MTFs for different X-ray spectra, sensor materials and pixel sizes are calculated and compared.