High Quantum Efficiency Charge-Coupled Device
APPLICATIONS OF TECHNOLOGY:
Low-level light imaging (Astronomical research, Raman Spectroscopy)
- Back illuminated - High near-IR quantum efficiency without fringing - Excellent broadband wavelength response - Fully depleted for improved spatial resolution - Simplified fabrication - Superior radiation hardness
Stephen Holland at Berkeley Lab has developed a p-channel CCD with high quantum efficiency in the blue and near infrared wavelengths by combining a high-resistivity silicon substrate and a backside contact layer that allows for over-depleted operation. Tests on the Berkeley Lab CCD at Lick Observatory, the National Optical Astronomy Observatory, and the Jet Propulsion Laboratory have shown significantly higher quantum efficiencies in the near-IR region when compared to conventional, thinned CCDs. The high quantum efficiency extends to wavelengths of approximately 1 µm.
This technology maintains all the advantages of back illumination in the blue wavelengths, with the additional benefits of simpler fabrication, improved red wavelength quantum efficiency, including the virtual elimination of fringing effects, and improved spatial resolution.
Conventional methods for overcoming poor blue-wavelength performance require CCDs to be thinned to 10-20 µm - thinner than a human hair. This thinning is accomplished through expensive chemical processing. However, longer red and infrared wavelength performance is sacrificed at those thicknesses. In contrast, the Berkeley Lab high quantum efficiency CCDs only need to be thinned to 200-250 µm, which can be achieved using a simple mechanical process. It is also possible to perform the process for back illumination at wafer level for 150 mm diameter wafers.
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