Stacked CMOS Image Sensor for High Dynamic Range
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Solution Overview
Problem
Conventional image sensors face limitations in high dynamic range operation, experiencing lower resolution, sensitivity, high noise levels, and Moiré artifacts, which affect their performance in capturing images across a wide range of illumination levels.
Innovation Solution
The implementation of a stacked CMOS image sensor array with an upper, middle, and lower chip configuration, utilizing charge overflow integration and storage on pixel capacitors, and a rolling shutter scanning mode to enhance sensitivity, reduce noise, and minimize Moiré effects, while maintaining high resolution and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional image sensors use alternate rows of pixels with different integration times for HDR operation, then high dynamic range is achieved, but resolution, sensitivity, and quantum efficiency deteriorate
Solution Approach 1:
The patent transitions from a planar pixel array to a three-dimensional stacked architecture with multiple photodiode layers vertically arranged. This dimensional change allows simultaneous capture of different light intensity ranges in separate layers, achieving HDR without sacrificing the spatial resolution and sensitivity of individual pixels.
Solution Approach 2:
The pixel array is segmented into multiple photodiode layers, where each layer is dedicated to capturing specific illumination ranges. This segmentation allows independent optimization of each layer for its intended function, with lower layers capturing bright scenes and upper layers capturing dark scenes, thereby maintaining high resolution and sensitivity in each layer while achieving overall HDR capability.
2Measurement precision
If conventional image sensors increase integration time for dark scenes, then sensitivity to low light improves, but Moiré artifacts and noise levels increase
Solution Approach 1:
By adding a vertical dimension with multiple photodiode layers, the patent enables simultaneous capture of different exposure levels. Upper photodiode layers with shorter integration times capture bright scenes with reduced Moiré artifacts, while lower layers with longer integration times capture dark scenes with high sensitivity, thereby achieving low-light sensitivity without the harmful side effects in either layer.
Solution Approach 2:
Different photodiode layers are assigned different integration times and functional characteristics optimized for their specific illumination ranges. Upper layers are optimized for bright scenes with shorter integration times to minimize Moiré artifacts, while lower layers are optimized for dark scenes with longer integration times to maximize sensitivity, allowing each layer to have locally optimized quality for its intended purpose.
3Measurement precision
If conventional image sensors use larger pixel aperture for better light collection, then quantum efficiency improves, but device area and complexity increase
Solution Approach 1:
The patent utilizes the vertical dimension by stacking multiple thin photodiode layers, each with moderate aperture size. The combined light collection capability of multiple layers achieves high quantum efficiency equivalent to or greater than a single large-aperture pixel, while maintaining compact device area since the layers are vertically stacked rather than horizontally expanded.
Solution Approach 2:
The image sensor employs a composite stacked structure with multiple photodiode layers, each contributing to the overall light collection. This composite architecture achieves high quantum efficiency through the cumulative effect of multiple layers with optimized individual apertures, avoiding the need for any single layer to have a large aperture that would increase device area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design results in image sensors with high quantum efficiency, low dark current, and low noise, achieving high dynamic range performance across a large range of illumination levels exceeding 100 dB, with reduced Moiré artifacts and improved aperture efficiency.
Implementation Method 1
Each pixel includes a photosensitive element that receives incident photons (light) and converts the photons into electrical signals
Data Source
AI summary
Electronic devices may include High Dynamic Range (HDR) complementary metal-oxide-semiconductor (CMOS) image sensor arrays that are illuminated from the back side of the substrate and operate in a rolling shutter (RS) scanning mode. An image sensor may include stacked chips to improve image sensor performance. For example, by stacking photodiodes on top of each other and using dichroic dielectric layers in chip-to-chip isolation, sensor sensitivity may be increased, Moiré effect may be reduced, and the overall image sensor performance may be improved. Image sensors may include a charge sensing and charge storing scheme where charge generated by low incident light levels is transferred onto a charge sensing node of an in-pixel inverting feedback amplifier and charge generated by high incident light levels overflows a certain potential barrier built in the pixel, is stored on capacitors, and is sensed by a source follower.