CMOS Image Sensor Blooming Node Charge Diversion
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Solution Overview
Problem
CMOS image sensors experience blooming due to excess light exposure, leading to inaccurate image data and color inaccuracies, as charge spills from overexposed pixels to adjacent ones, affecting white balance and color accuracy.
Innovation Solution
Incorporating a blooming node with a lower doping concentration connected to a voltage source, which creates a pathway for excess charge to be diverted from photodiodes, preventing them from exceeding saturation and reducing pixel blooming without increasing dark current or hot pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode collects sufficient charge to reach saturation, then the light detection capability is maximized, but excess charge spills into adjacent pixels causing blooming and color inaccuracies
Solution Approach 1:
The patent divides the charge collection system into separate regions: a first well for collecting signal charge from the photodiode and a second well for collecting overflow charge. This segmentation prevents excess charge from spilling into adjacent pixels while maintaining full well capacity for light detection, thereby resolving the blooming problem without sacrificing measurement precision.
Solution Approach 2:
The patent introduces an intermediate structure (the second well coupled to the first well) that acts as a buffer for excess charge. This intermediary region captures overflow charge before it can spread to adjacent pixels, eliminating the blooming effect while allowing the first well to operate at full capacity for accurate light detection.
2Quantity of substance
If the photodiode full well capacity is increased to handle more light, then dynamic range is improved, but the pixel area and device complexity increase
Solution Approach 1:
The patent extends the charge collection capability into a vertical dimension by implementing multiple wells (first well and second well) stacked or coupled together. This three-dimensional charge storage architecture increases the effective full well capacity without proportionally increasing the lateral pixel area, thereby improving dynamic range while maintaining compact pixel dimensions.
Solution Approach 2:
The patent nests the second well within or coupled to the first well structure, creating a hierarchical charge storage system. The smaller second well is positioned to receive overflow from the larger first well, efficiently utilizing space to increase total charge capacity without significantly expanding the pixel footprint.
3Measurement precision
If color filters are used to improve color accuracy, then wavelength selectivity is improved, but certain wavelengths dominate and cause excessive charge generation and blooming
Solution Approach 1:
The patent applies different properties to different regions: the first well is optimized for collecting signal charge with specific spectral response, while the second well is designed to collect overflow charge from all wavelengths. This local differentiation allows color filters to maintain their wavelength selectivity for accurate color detection while the dual-well structure handles excessive charge generation from dominant wavelengths without blooming.
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
Effectively prevents blooming by managing excess charge, maintaining accurate color representation and reducing pixel defects, thereby enhancing image quality.
Implementation Method 1
The photodiode or other light detector may capture light which may then be used to create an image of a scene or object
Implementation Method 2
a blooming node in communication with the bridge region and a voltage source. The second doping concentration is less than the first doping concentration and when light sensitive element collects sufficient charge to reach the first saturation value, additional charge received by the light sensitive element travels to the blooming node via the bridge region
Data Source
AI summary
An image sensor for an electronic device. The image sensor includes a first light sensitive element for collecting charge and having a first saturation value and a well surrounding at least a portion of the first light sensitive element and having a first doping concentration. The image sensor further includes a bridge region defined in the well and in communication with the first light sensitive element and having a second doping concentration and a blooming node in communication with the bridge region and a voltage source. The second doping concentration is less than the first doping concentration and when light sensitive element collects sufficient charge to reach the first saturation value, additional charge received by the light sensitive element travels to the blooming node via the bridge region.