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.
Spatial Smearing
Signal Leakage
Unwanted charge transfer between adjacent pixels during the readout phase of an imaging sensor degrades the spatial resolution of the device. This spatial smearing arises when carriers generated by intense localized light diffuse into neighboring pixel sites before they can be collected or cleared. Charge-coupled devices operating at high transfer speeds are particularly susceptible to this type of degradation.
Sensor Design
Solid-state imaging arrays rely on physical barriers to prevent cross-talk between sensing elements. When analyzing spatial smearing, engineers measure the ratio of leaked signal to the primary signal to determine the isolation performance of the pixel structures. Inadequate barrier doping or thin insulation layers can worsen this leakage, especially in infrared sensing applications.
Image Degradation
High-contrast scenes containing bright highlights suffer from vertical or horizontal streaks that obscure fine detail. Quantifying the spatial smearing allows developers to calibrate the sensor for high-dynamic-range imaging. If the leakage is not corrected, the resulting image loses contrast and suffers from reduced modulation transfer function, which makes the device unsuitable for high-precision surveillance and scientific microscopy.
Mitigation Technique
Standardized testing under high-intensity spot illumination determines the sensor’s susceptibility to this phenomenon. Laboratories measure the spread of the output signal beyond the illuminated region to verify compliance with imaging standards.