Parasitic Light Sensitivity Limits in Stacked Backside Illuminated Global Shutter Image Sensors
Stacked BSI global shutter sensor parasitic light sensitivity depends on silicon depth, metal shield alignment, and active illumination wavelength.
Memory Node
Intermediate Storage
Global shutter image sensors temporarily hold photo-generated charge within each pixel matrix element to enable simultaneous exposure across all rows without rolling motion artifacts. An in-pixel storage element designated as a memory node retains analog electron packets between optical exposure completion and serial readout. Photodiodes transfer their accumulated charge into this node immediately after exposure, freeing the optical collector to begin the next exposure frame.
Physical Characteristic
Subsurface implantation forms potential wells optimized for complete charge retention and minimal dark current generation. Maintaining integrity within the memory node requires isolation from ambient illumination and adjacent silicon structures. Parasitic light leak into the storage region causes image contamination, introducing shading artifacts in bright scene regions.
Designers utilize physical light shields and optimized p-n junctions to isolate the storage volume from substrate diffusion currents.
Evaluation Method
Metrological evaluation measures charge transfer efficiency into and out of the storage element under varying timing schemes. Test equipment applies short light pulses while sweeping readout delay times to calculate leakage rates and dark current accumulation within the storage well. Comparative measurement determines parasitic light sensitivity by measuring signal increase in unexposed pixels during prolonged readout periods.
Data logging validates charge preservation across specified operational temperature windows.
Architecture Limit
Pixel area allocation limits total storage capacity.