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.
Row Delay Gradient
Timing Variation
Non-uniform signal propagation times across the rows of a pixel matrix generate systematic differences in exposure or readout timing. A measurable row delay gradient occurs because of the distributed resistance and capacitance of the control lines. This spatial variation means that pixels further from the row driver receive their control signals later than those close to it.
Sensor Design
Image sensor architectures require high-speed row addressing to achieve high frame rates. If the row delay gradient is large, it introduces sub-row exposure skew, which degrades the performance of global shutter sensors. Minimizing this effect requires thick metal lines and dual-sided driving of the row control signals.
Array Calibration
Dynamic range and linearity can be affected by the non-uniform shutter timing across the pixel array. Accounting for the row delay gradient is necessary when designing high-speed imaging systems to prevent spatial distortion in the captured images. Designers use compensation matrices in the digital image signal processor to correct for the non-uniform exposure time, which ensures a uniform response across the entire active area of the sensor.
Performance Test
Optical bench testing under uniform illumination identifies the spatial variations caused by these delay differences. Technicians measure the row delay gradient by comparing the response of pixels at opposite ends of the array.