The Scanning-Beam Digital X-ray (SBDX) system promises low- dose cardiac fluoroscopy and angiography with excellent image quality. The system demands a detector capable of high count rates and excellent detection efficiency. Cadmium zinc telluride (CdZnTe) is well suited to these requirements. The SBDX detector comprises sixteen 3-mm-thick, 13.5 mm X 13.5 mm tiles arranged in a 4 X 4 array. Each tile has 144 imaging elements. Thus, the entire detector measures 54.0 mm X 54.0 mm and includes 2,304 imaging elements on a 1.125 mm pitch. Because the SBDX system has a geometric magnification of 3.3, the imaging-element size is consistent with a system spatial-resolution of 2.2 lp/mm. The 3-mm thickness is chosen to guarantee a stopping efficiency of more than 90% at 120 kVp. Each detector tile is flip-chip mounted to a custom- designed integrated circuit (IC) using indium bump bonding techniques. Fabricated in a 1.2-micrometer CMOS process, the IC includes high-speed photon-counting circuitry that operates at rates up to 5 X 106 counts/s(DOT)mm2. The circuitry is designed both to maximize the achievable count- rate and to minimize false double counts due to charge sharing between elements. Testing confirms that the detector performs with minimum cross talk between elements at count rates in excess of 2 X 106 counts/s(DOT)mm2. Measurements of the detective quantum efficiency (DQE) are presented. The relationship between material properties and detector performance is also discussed. The circuit design and device fabrication techniques are applicable to a variety of imaging applications.