Disclosed are a thin-film transistor array substrate for a high-resolution digital X-ray detector and a high-resolution digital X-ray detector including the same in which a photo-sensitivity is improved by increasing a fill factor, and interference between PIN diodes is minimized, and step coverage of the PIN diode is improved to improve stability of the PIN diode. To those ends, an area of the PIN diode is maximized, and a pixel electrode of the PIN diode is disposed inside the PIN layer. Further, a clad layer made of inorganic material is formed in an edge region and/or a contact hole region of the pixel electrode. Thus, a leakage current resulting from concentrating an electric field on a curved region may be minimized.