X-ray image sensor

Abstract

This invention provides an imaging system for producing images from electromagnetic radiation such as x-rays. The system includes a detector comprised of a radiation-absorbing layer sandwiched between an array of CMOS integrated circuits (which we call pixel circuits) and a surface electrode layer transparent to the radiation. Each of the pixel circuits in the array has a charge collecting electrode. An external voltage applied between the surface electrode layer and the charge collecting electrodes produces an electric field across the thickness of the absorbing layer. Radiation passing through the transparent surface electrode layer is absorbed in the absorbing layer creating electron/hole pairs in the absorbing layer. A portion of the liberated holes (or electrons) migrates under the influence of the electric field toward the charge collecting electrodes, which collect the holes and store them as charges on small capacitors located within each circuit. This process results in a discrete distribution of stored voltages across the array proportional to the distribution of radiation photons incident on the absorbing layer. Circuitry in each pixel provides for the voltage on each pixel capacitor to be recorded via readout circuitry and permits the resetting of the pixel capacitors. Preferred embodiments provide fine resolution with a large number of pixels with dimensions about the size of the thickness of human hair.