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Home > Advanced Imaging Magazine > February 2003

Advanced Imaging Magazine

X-ray Technology Bets on the Blue Chips

FEATURE

X-ray Technology Bets on the Blue Chips

CCDs are available for most applications, each with its own unique requirements. With new applications appearing almost daily, CCD makers must find improved processes and designs to make their imagers better fit customers' needs...

by Keith Wetzel

February 2003

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Figure 1: CCD Sensor Functional Diagram-Many imaging apps require a large format full-frame transfer style CCD image sensor. Fewer clocks are required for true two-phase sensors, compared to three and four-phase. (Photo: William Des Jardin, et al.)

Figure 2: Details of Pixel Design-The transparent gate process replaces the second polysilicon gate with indium-tin-oxide and improves the spectral response. (Photo: William Des Jardin, et al.)

Figure 3: CCD Sensors in Astronomy-Long exposures with blue camera lens filters obtain correct color balance for full-color photos, but exposure times can be reduced with Blue Plus CCDs because of increased sensitivity at this wavelength. (Photo: Kodak)

Figure 4: CCD Sensors in Biology-Fluorescent dyes monitor calcium activity in cells for DNA sequencing, excited with UV lights to make them visible. Blue Plus CCDs are highly sensitive to detecting the faint signals emitted, and exposure times are low. (Photo: Kodak)

Swissray Digital Optical Detector

Figure 5: Swissray Digital Optical Detector-This digital optical design detector (above) uses mirror optics to focus four high-res CCD cameras on a cesium iodide scintillator screen. Each full-frame CCD with 100% fill factor captures the image of one scintillator quadrant with 10% overlap. The final image (below) composites the four images without a seam or dead zone. (Photo: Rex Harmon, SwissRay International)

Critical parameters common to all CCD chips include resolution, dynamic range, quantum efficiency (QE), responsivity (sensitivity), readout speed, and dark current. Some parameters, however, are more critical for certain applications than for others. For example, CCD chips for astronomy require a large dynamic range, high S/N ratio and low dark current over a wide color spectrum. This is necessary in order to detect a faint star as well as a bright cluster without saturating the photosensitive pixels.

Medical diagnostics CCDs, on the other hand, receive images from an X-ray scintillation plate that emits predominantly green and blue light. The CCD should have the highest QE and sensitivity in this band and a sufficient resolution in order to find the smallest pathogen possible in the X-ray image.

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