X-ray detector built on plastic substrate

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Researchers from Holst Centre and imec have demonstrated the first ever X-ray detector built on a plastic substrate that is capable of medical grade performance.

The proof of concept device delivers high resolution, dynamic images at 25fps and 200ppi with high contrast using medical level X-ray doses. In 2012, the team demonstrated the first complete X-ray detector produced on a thin plastic substrate. An indirect flat panel detector (FPD), it combined a standard scintillator with a novel organic photodiode layer and organic thin-film transistor (TFT) backplane. By using a solution-processed organic semiconductor rather than the usual amorphous silicon, the team reduced process temperatures to be compatible with plastic film substrates. They also eliminated a number of costly lithography steps, opening the door to lower production costs. Now, the same team has reduced the photodiode leakage current (the output from the photodiodes at zero light) by a factor of 10,000, down to 10-7mA/cm2 – bringing it well within the requirements for medical detectors. This improves the signal-to-noise ratio, and hence image quality at low radiation dose. At the same time, oxide transistors are used instead of organic transistors. The charge carrier mobility in the metal-oxide TFTs is 10-50 times higher than with amorphous silicon and organic transistors, enabling faster image acquisition. These advances were integrated into a high-aperture QQVGA (160 x 120pixels) detector plate with a resolution of 200ppi. This plate was integrated with off-board electronics consisting of components that are currently used for medical application, and no modifications needed to be made. "X-ray detectors on plastic could lead to lighter, more robust and less expensive X-ray systems that are easier to move around the hospital," said Holst Centre's Gerwin Gelinck, who led the project. "Two years ago, we were the first to show such devices were technically possible. And now we have shown they can deliver the performance necessary for medical use. "Our next goal is to scale up the technology and produce a full size 30 x 30cm demonstrator module for medical applications."