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

The random telegraph signal (RTS) behavior of the dark current has been studied in a radiation-hardened CMOS active pixel sensor (APS). Several devices have been irradiated with protons of different energies and up to different fluences. The influence of the proton energy, fluence, and operating temperature on the amplitude, time constants, and occurrence of the RTS is investigated. Mechanisms for this behavior are discussed and several suggestions are made for possible defect types.

Random telegraph signals in a radiation-hardened CMOS active pixel sensor

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.

T.L. Miller

Papers

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