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.
Electrostatic Collection Basin
Charge Accumulation
Specialized regions within an image sensor or analytical instrument isolate and hold liberated charge carriers for subsequent measurement. An electrostatic collection basin employs potential wells created by doped semiconductor structures to prevent the lateral migration of electrons. These structures ensure that the signal remains localized to a specific pixel or detection site.
Well Capacity
Saturation limits are reached when the electrostatic collection basin can no longer hold additional electrons without spilling into adjacent regions. This blooming effect degrades image quality and quantitative accuracy. Full well capacity is specified in electrons per pixel and varies with the physical size of the gate and the applied bias voltage.
Transfer Mechanism
Moving the gathered charge to an output amplifier requires precise timing of clock phases to shift the potential walls. In charge-coupled devices, the electrostatic collection basin moves along a column to the horizontal shift register. Any inefficiency in this transfer leaves residual charge behind, which appears as ghosting or smearing in the final data.
Higher clock voltages can improve transfer efficiency but increase the risk of hot carrier injection. Low noise designs focus on the purity of the silicon interface to minimize traps that snag electrons during the move.
Voltage Reference
Stability of the bias supplies is required to maintain a consistent depth for the well. Fluctuations in the supply voltage change the capacity and lead to non-linear response curves.