Characterization of imaging performance of a large-area CMOS active-pixel detector for low-energy X-ray imaging

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2011-10, Vol.652 (1), p.500-503
• Main Authors: Hwy Lim, Chang, Yun, Seungman, Chul Han, Jong, Kim, Ho Kyung, Farrier, Michael G., Graeve Achterkirchen, Thorsten, McDonald, Mike, Cunningham, Ian A.
• Format: Article
• Language: English
• Subjects: Arrays; Cascaded model analysis; CMOS; Detectors; DQE; Fiber-optic faceplate; Imaging; MTF; NPS; Photodiodes; Photons; Pixels; X-rays
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2010.09.081

We report the imaging characteristics of the recently developed large-area complementary metal-oxide-semiconductor (CMOS) active-pixel detector for low-energy digital X-ray imaging applications. The detector consists of a scintillator to convert X-ray into light and a photodiode pixel array made by the CMOS fabrication process to convert light into charge signals. Between two layers, we introduce a fiber-optic faceplate (FOP) to avoid direct absorption of X-ray photons in the photodiode array. A single pixel is composed of a photodiode and three transistors, and the pixel pitch is 96 μm. The imaging characteristics of the detector have been investigated in terms of modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). From the measured results, the MTF at the Nyquist frequency is about 20% and the DQE around zero-spatial frequency is about 40%. Simple cascaded linear-systems analysis has showed that the FOP prevents direct absorption of X-ray photons within the CMOS photodiode array, leading to a lower NPS and consequently improved DQE especially at high spatial frequencies.