Review on X-ray Detectors Based on Scintillators and CMOS Technology

Abstract

This article describes the theoretical basis, design and implementation of X-ray microdetectors based on scintillating materials and CMOS technology. The working principle of such microdetectors consists in the absorption of X-rays by scintillators, which produce visible light. The visible light is then detected and converted into electric signals by means of photodetectors. In order to understand such detectors, several issues related to its implementation are presented in this article, namely: Production of X-rays and interaction between them and matter-the first step necessary to the detection of X-rays is that they must be absorbed by some material, in this case by a scintillator; Radiation detectors-there are several types of detectors, namely: pn junctions, photoconductors, based on thermal effects and scintillators; Fabrication of scintillator arrays-after the X-ray radiation is absorbed by a scintillator, this material emits visible light whose intensity is proportional to the total energy of the absorbed X-rays; Optical interfaces between scintillators and photodetectors-the visible light generated by scintillators must arrive to the photodetectors, so, it is necessary to have an interface between the scintillators and the photodetectors that ideally does not introduce losses; Photodetectors and interface electronics-the visible light is absorbed by the photodetectors and converted into electrical signals, which are finally converted into digital images by means of interface electronics. The article presents some promising patents on X-ray detectors based on scintillators and CMOS technology.

Large area CMOS active pixel sensor x‐ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization

“…T 0 (E) is approximately 0.95 assuming that a thin protection film of Al (<100 µm) is used. 36 g 1 reflects the mean number of absorbed x-rays per incident x-ray quanta. In general, QDE is scintillator thickness dependent, i.e., a thicker CsI:Tl layer produces a higher QDE.…”

Development and Validation of an X-ray Imaging Detector for Digital Radiography at Low Resolution

“…X-rays interact with the object through a process such as photoelectric effect, Rayleigh and/or Compton dispersion. These physical processes are implicitly included in the socalled mass attenuation coefficient of the various materials that constitute the sample [7][8][9]10].…”

Noise power spectrum of the fixed pattern noise in digital radiography detectors

“…The noise properties of radiography image detectors can be characterized according to several different noise sources, such as the photon noise, the electronic noise, and the fixed pattern noise. [1][2][3][4][5][6] The noise energy spectrum versus the spatial frequency can be understood as the noise power spectrum (NPS) measured from uniform exposure images. 7-10 From a normalized NPS (NNPS) by the image expectation, we can evaluate the imaging performance of the detector in terms of noise.…”

“…31 To obtain a uniform surface with low surface roughness and eliminate irregularities, the top surface is polished. 6,39 Hence, developing detectors, which show quite low fixed pattern noises, is of importance. Here, we can observe and analyze the energy of the fixed pattern noise from the NNPS of the nonuniform gain.…”