Review on X-ray Detectors Based on Scintillators and CMOS Technology
Jose G. Rocha and Senentxu Lanceros-Mendez
Affiliation: Algoritmi Research Center, University of Minho, Campus de Azurem, 4800-058 Guimaraes, Portugal. and Center of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Keywords: X-rays, scintillators, digital radiography, CMOS imaging, X-ray Detectors, CMOS Technology, visible light, photodetectors, pn junctions, photoconductors, barium platinocyanide screen, radiographic image detector, computerized tomography, nuclear medicine imaging, photon, infrared, ultraviolet, radio waves, electromagnetic radiations, oscillation, wavelength, Planck's constant, momentum, electron-Volt (eV), synchrotron, electron laser, radiotherapy, X-Ray Tube, bremsstrahlung, thermionic emission, high-sped electrons, anode, X-Ray Spectrum, molybdenum anode, kinetic energy, K shell, L or M shells, photoelectric absorption, Compton scattering, electron-positron pairs, coefficient of linear absorption, mass absorption coefficient, relative atomic mass, Compton effect, Photoelectric Effect, elastic collisions, Thomson cross-section, vacuum permittivity, Planck constant, Auger effect, photoionization, binding energy, electron-positron pair, threshold, Coherent or Rayleigh Scattering, Photonuclear Absorption, total attenuation coefficient, Elastic Nuclear Scattering, Inelastic Nuclear Scattering, Delbrück Scattering, annihilation, cesium iodide, mass attenuation coefficient, iodine, atomic number, atomic mass, cesium, RADIATION DETECTORS, amorphous silicon, electron-hole pair, amorphous selenium, HgI2, PbI2, Seebeck coefficients, copper, Sb2Te3, p type, Bi2Te3, n type, Hz, spatial resolution, thallium doped cesium iodide (CsI:Tl), aluminum, photon noise, electronic noise, standard deviation, variance, Poisson, arbitrary angle, homogeneous metallic reflector, Snell law, anti-reflective filter, quarter-wave film, silicon nitride, ZrO2, TiO2, prismatic or parallelepipedic, n+/p-epilayer junction, Si3N4 layer, binomial distribution, Monte Carlo method, surface area, FABRICATION OF A SCINTILLATOR MATRIX, laser, Deep Reactive Ion Etching, photolithographic process, photoresist, inductively coupled plasma (ICP), OmniCoat, SU-8TM, MicroChem, spin-coater, viscosities
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.
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