Basic mechanisms and ground-test data for radiation effects in solid-state imagers are reviewed, with a special emphasis on proton-induced effects on silicon charge-coupled devices (CCDs). For the proton fluxes encountered in the space environment, both transient ionization and displacement damage effects arise from single-particle interactions. In the former case, individual proton tracks will be seen; in the latter, dark-current spikes (or hot pixels) and trapping states that cause degradation in charge-transfer efficiency will be observed. Proton-induced displacement damage effects on dark current and charge transfer are considered in detail, and the practical implications for shielding, device hardening, and ground testing are discussed.

Proton effects in charge-coupled devices

A review of radiation-induced displacement damage effects in semiconductor devices is presented, with emphasis placed on silicon technology. The history of displacement damage studies is summarized, and damage production mechanisms are discussed. Properties of defect clusters and isolated defects are addressed. Displacement damage effects in materials and devices are considered, including effects produced in silicon particle detectors, visible imaging arrays, and solar cells. Additional topics examined include NIEL scaling, carrier concentration changes, random telegraph signals, radiation hardness assurance, and simulation methods for displacement damage. Areas needing further study are noted.

Displacement Damage Effects in Irradiated Semiconductor Devices

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

The probability/incident proton for creation of a defect in a charge-coupled device (CCD) which shows dark current random telegraph signal (RTS) behavior has been measured for energies of 1.5, 10 and 46 MeV. The probability was found to be proportional to the non-ionizing energy loss (NIEL) for elastic collisions. Plots of RTS probability versus mean dark current indicate a correlation with the amount of field enhanced emission. If a pixel already has a defect showing field enhanced emission, it is more likely to show RTS effects. The amplitudes themselves are not correlated with the degree of field enhanced emission. An alternative to the bulk metastable defect model is proposed, based on the reorientation of the phosphorus-vacancy center in a high electric field.

Further measurements of random telegraph signals in proton irradiated CCDs

In this paper, we compare Monte Carlo and analytic calculations of displacement damage resulting from inelastic proton reactions in Si. These comparisons include the nonionizing energy loss rate, the mean recoil damage energy spectra, and their associated variance. In the limit of bulk material, both approaches are in good agreement. Sensitive volumes shrink and incident proton energies increase, the ranges of the spallation recoil fragments approach the smallest dimension of the microvolume, and the pixel-to-pixel damage variance increases rapidly. In this regime, a Monte Carlo approach is used to describe the damage energy distribution. Indeed, we show that such simulations predict the 63 MeV proton-induced dark current histograms more accurately than present analytic methods. The Monte Carlo code is also used to explore ground test fidelity issues for devices with small sensitive volumes. >

A comparison of Monte Carlo and analytic treatments of displacement damage in Si microvolumes

We have completed a Series of CO60 and 8 and 25 MeV proton irradiations of wafer test structures and complete CCD detectors in order to study the changes in threshold voltage, dark current and charge transfer inefficiency (err) of CCD devices with very fast frame readout rates and large pixel geometries. Significant threshold voltage shifts for floating difhsion some followex amplifiers were observed. Changes in dark current were observed for both accumulation mode and depletion mode openition. Some evidence of source follower amplifier breakdown was seen following proton irradiation. Causes are unresolved. CTI changes of less than 0.01% were observed from the proton irradiation.

Experimental Evaluation Of High Speed Ccd Imager Radiation Effects Using Co60 And Proton Radiation

Computer simulations of the non-ionizing energy loss deposited in sensitive volumes as a result of proton-induced spallation reactions agree with analytic models for large sensitive volumes exposed to high fluence. They predict unique features for small volumes and low-fluence exposures which are observed in exposures of large arrays of CCD pixels. Calculations of the number of spallation reactions per pixel correlate with the recently reported relative frequency of switching dark-current states. >

T.-H. Lee

Papers

Experimental Evaluation Of High Speed Ccd Imager Radiation Effects Using Co60 And Proton Radiation

Dark current induced in large CCD arrays by proton-induced elastic reactions and single to multiple-event spallation reactions