Radiation Sensitivity of Silicon Imaging Sensors on Missions to the Outer Planets

An investigation of radiation damage mechanisms and the magnitude of their effects on the operating characteristics of imaging sensors utilizing a mosaic array of silicon diodes in a television pickup tube is reported. The effects produced by bombardment of bare-silicon-diode arrays or vidicon tubes with 85kV x-rays, Cobalt 60 gamma rays, 1 MeV and 11 MeV electrons, 3 MeV and 142 MeV protons, and reactor neutrons are presented. Results show that the dark (reverse bias) current of a diode array increases less than a factor of 2 if the fluence level is less than 104 rads of gamma radiation or 4 ×1011 1 MeV electrons/cm2. For these same dose levels, the quantum efficiency increases rather than decreases. Continued bombardment in excess of these fluences decreases the quantum efficiency and increases the dark current. Electrons of 11 MeV were more damaging than 1 MeV electrons by a factor of 10 to 20 while protons of 3 MeV more effectively produced dark current increases and quantum efficiency degradation in silicon diode arrays than 1 MeV electrons by a factor of 105 in fluence. Protons of 142 MeV were less effective than 3 MeV protons in producing the same effects by a factor of 102 in fluence. Measurements of these degradation effects at 217 K indicated that the dark current is reduced by a factor of 200 to 500 relative to room-temperature values.