1. Field of the Invention
The present invention relates to an X-ray detector and a method of manufacturing the same.
2. Description of the Related Art
X-ray detectors employing thin film transistors have been primarily utilized for diagnosis purposes. An X-ray detector is configured to output an X-ray image or X-ray transmission image in the form of a digital signal. Such an X-ray detector can be generally divided into two types, i.e. direct and indirect X-ray detectors.
In the direct X-ray detector, a photoconductive layer made of amorphous cerium (Ce) or the like is used to convert X-rays directly into electric charges. In the indirect X-ray detector, however, X-rays are converted into visible light by a scintillator and the converted visible light is then converted into electric charges by a photoelectric conversion device such as a photodiode. The direct X-ray detector has superior resolution, but dielectric breakdown may occur since high voltage levels are used in the direct X-ray detector. Accordingly, the reliability of the direct X-ray detector may be degraded. Further, a photoconductive material with a low dark current, high sensitivity, thermal stability and the like cannot be easily used for the direct X-ray detector. On the other hand, in the indirect X-ray detector, a photodiode or the like is used to generate a signal charge instead of using a high voltage as in the direct X-ray detector, thereby dielectric breakdown does not occur. Since basic technologies for a scintillator material, a photodiode or the like have been already established, the indirect X-ray detector can be easily commercialized. Accordingly, the indirect X-ray detector has been widely used.
To enhance the efficiency of a scintillator, the scintillator is formed by depositing a fluorescent material such as cesium iodide (CsI) into columnar single crystal. In a case where the scintillator is deposited directly on a lower substrate, the deposition process is performed at a temperature of 200° C. or more, which may cause a failure of the lower substrate. Accordingly, in an indirect X-ray detector, a scintillator is bonded to a lower substrate on which a thin film transistor, a photoelectric conversion device and the like are formed, and the efficiency of the detector greatly varies depending on the method of bonding the scintillator to the lower substrate. That is, if an air layer is introduced between the scintillator and the lower substrate when they are bonded to each other, reflection takes place at an interface between air and a medium due to a difference in refractive indexes of the air and the medium. Thus, the efficiency of light incident to the photoelectric conversion device is lowered. Meanwhile, if an air layer is partially introduced between the scintillator and the lower substrate, the uniformity of the indirect X-ray detector is degraded.
To prevent the production of such an air layer, in a related art, a reflective film and a scintillator are stacked on a glass substrate to fabricate a scintillator panel, and the scintillator panel is bonded to a lower substrate using an adhesive. However, once a scintillator panel is bonded to a lower substrate using an adhesive, the scintillator panel and the lower substrate cannot be separated to be reused even if defects are found. In particular, in a case where a resin is used as an adhesive, i.e. a liquid thermosetting resin is poured, pressed and cured between the scintillator panel and the lower substrate in order to bond the scintillator panel and the lower substrate together, the bonded scintillator panel and lower substrate cannot be separated when defects are found in the subsequent processes, and thus, the productivity is degraded.