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Holst Centre, Imec develop fully-organic imager

Posted: 14 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:x-ray imaging? photodetector? organic imager?

Holst Centre and Imec, in collaboration with Philips Research, have developed a large-area fully-organic photodetector array fabricated on a flexible substrate. Presented at the International Image Sensor Workshop, the imager's sensitivity is suitable for the wavelength range of x-ray imaging applications.

Due to their very high absorption coefficient, organic semiconductors allow extremely thin active layers (10-50nm). Given their low processing temperature, they can be processed on foils. As a result, organic imagers can be more robust and light-weight compared to their traditional counterparts and may be used for conformal coating of randomly shaped substrates. Moreover, the wide variety of organic molecules available ensures that the properties of the active layer can be tuned to applications requiring specific wavelength ranges.

The presented imager is sensitive in the wavelength range between 500 and 600nm, making it compatible with typical scintillators and therefore suitable for x-ray imaging applications. It was fabricated by thermally evaporating an ultrathin (submicron) photosensitive layer of small organic molecules (SubPc/C60) on top of an organic readout circuit.

Organic imager

Fully organic, flexible imager. Source: Imec, Holst Centre and Philips Research.

A semi-transparent top contact enables front-side illumination. The readout backplane was manufactured on six inch foil-laminated wafers. It consists of pentacene-based thin-film transistors (TFTs) in arrays of 32x32 pixels with varying pitch (1mm and 200?m). To prevent degradation of the organic semiconductors in the air, the photodetector array is encapsulated. The imager was characterized under illumination with a calibrated green light-emitting diode (LED), yielding a linearly increasing photocurrent from the incident power of 3 ?W/cm2. Dark current density is below 10-6 A/cm2 at a bias voltage of -2V.

"This latest achievement is a significant step forward in not only finding the optimal materials, but identifying the best ways to process materials into reliable organic circuits and systems with state-of-the-art performance," said Paul Heremans, technology director at the imec/Holst Centre. "Once again, we're proud to demonstrate how imec's top-notch research that leads to relevant industrial solutions, and subsequently brings added value to our partners' businesses."

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