Charge-coupled devices (CCDs) have been fabricated on high-resistivity, n-type silicon. The resistivity, on the order of 10 000 /spl Omega//spl middot/cm, allows for depletion depths of several hundred micrometers. Fully depleted, back-illuminated operation is achieved by the application of a bias voltage to an ohmic contact on the wafer back side consisting of a thin in situ doped polycrystalline silicon layer capped by indium tin oxide and silicon dioxide. This thin contact allows for a good short-wavelength response, while the relatively large depleted thickness results in a good near-infrared response.

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Fully depleted, back-illuminated charge-coupled devices fabricated on high-resistivity silicon

Photonic imagers are being increasingly used in space systems, where they are exposed to the space radiation environment. Unique properties of these devices require special considerations for radiation effects. This paper summarizes the evolution of radiation effects understanding in infrared detector technology, charge coupled devices, and active pixel sensors. The paper provides a discussion of key radiation effects developments and a view of the future of the technologies from a radiation effects perspective.

Radiation effects on photonic imagers-a historical perspective

A new type of p-channel CCD constructed on high-resistivity n-type silicon was exposed to 12 MeV protons at doses up to 1x1011 protons/cm2. The charge transfer efficiency was measured as a function of radiation dose and temperature. We previously reported that these CCDs are significantly more tolerant to radiation damage than conventional n-channel devices. In the work reported here, we used pocket pumping techniques and charge transfer efficiency measurements to determine the identity and concentrations of radiation induced traps present in the damaged devices.

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Proton radiation damage in high-resistivity n-type silicon CCDs

Dark current and charge transfer inefficiency (CTI) data are presented for three charge-coupled devices (CCD) device types after 9.5- and 60-MeV proton irradiation. Comparison of the damage at the two energies allows a test of the validity of NIEL scaling. The ratio of the damage at 9.5 MeV to that at 60 MeV was found to be 35% higher for the CTI than for the average bulk dark current, for the devices tested. Both the CTI and the dark current showed significant annealing at 150/spl deg/C, and this has implications for the lattice defects involved. Cobalt-60 data are also discussed.

Comparison of CCD damage due to 10- and 60-MeV protons

We report on a proton radiation damage experiment on P-channel CCD newly developed for an X-ray CCD camera onboard the ASTRO-H satellite. The device was exposed up to 10 9 protons cm −2 at 6.7 MeV. The charge transfer inefficiency (CTI) was measured as a function of radiation dose. In comparison with the CTI currently measured in the CCD camera onboard the Suzaku satellite for 6 years, we confirmed that the new type of P-channel CCD is radiation tolerant enough for space use. We also confirmed that a charge-injection technique and lowering the operating temperature efficiently work to reduce the CTI for our device. A comparison with other P-channel CCD experiments is also discussed.

Proton radiation damage experiment on P-Channel CCD for an X-ray CCD camera onboard the ASTRO-H satellite

P-channel backside illuminated silicon charge-coupled devices (CCDs) were developed and fabricated on high-resistivity n-type silicon. The devices have been exposed up to 1 /spl times/ 10/sup 11/ protons/cm/sup 2/ at 12 MeV. The charge transfer efficiency and dark current were measured as a function of radiation dose. These CCDs were found to be significantly more radiation tolerant than conventional n-channel devices. This could prove to be a major benefit for space missions of long duration.

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A. Wagner

Papers

Proton radiation damage in p-channel CCDs fabricated on high- resistivity silicon