Comparison of proton damage effects in standard and enhanced depletion CMOS Image Sensors

A comparison of the proton radiation effects in CMOS Image Sensors (CIS) manufactured using a 0.18 μm process with standard and enhanced depletion is presented. 3 and 4-transistor (3T and 4T) architecture devices with multiple pixel variants are characterized. All devices investigated are back-illuminated. Devices have been produced on 2 different wafer types with different epitaxial (epi) resistivities and thicknesses to compare the effect of standard and enhanced depletion. Devices with a higher resistivity epi will have greater depletion under the photodiode compared to the same pixel layout on a lower resistivity wafer. Electro-optical sensitivity to proton damage is presented, in particular for dark signal and random telegraph signals. The primary conclusion is that the sensitivity to proton damage is dependent on the volume of depletion in the photodiode, which introduces a trade-off between proton hardness and deeper depletion for a wide spectral response.