Pixel Sensor Metal Grid Openings for High Dynamic Range
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Solution Overview
Problem
Existing CMOS image sensors face challenges in achieving a high dynamic range without degrading dark performance due to irregular pixel arrays with combinations of large and small photodiodes, which also complicate the formation of isolation structures and increase photodiode leakage.
Innovation Solution
The implementation of a pixel array with photodiodes of uniform size but varying sensitivity by patterning a metal grid with different sized openings over photodiodes, allowing for a combination of low-sensitivity, mid-sensitivity, and high-sensitivity photodiodes, which enhances dynamic range and reduces photodiode leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If irregular pixel arrays with combinations of large and small photodiodes are used to achieve high dynamic range, then dynamic range is improved, but dark performance is degraded and photodiode leakage increases
Solution Approach 1:
The patent applies local quality by placing metal openings of different sizes over uniformly sized photodiodes at specific locations within the pixel array. This creates locally differentiated sensitivity (high-sensitivity photodiodes under larger openings, low-sensitivity photodiodes under smaller openings) while maintaining uniform photodiode geometry throughout the array, thereby achieving high dynamic range without the dark performance degradation associated with irregular photodiode arrays.
2Measurement precision
If irregular pixel arrays with combinations of large and small photodiodes are used to achieve high dynamic range, then dynamic range is improved, but formation of isolation structures is complicated
Solution Approach 1:
The patent segments the dynamic range adjustment function into two independent components: uniform photodiodes for consistent electrical characteristics and isolated structure formation, and selectively sized metal openings for sensitivity differentiation. This segmentation simplifies isolation structure formation since all photodiodes are uniformly sized and regularly arranged, while still achieving high dynamic range through the segmented metal opening pattern.
3Measurement precision
If irregular pixel arrays with combinations of large and small photodiodes are used to achieve high dynamic range, then dynamic range is improved, but photodiode leakage increases
Solution Approach 1:
The patent applies local quality by placing metal openings of different sizes over uniformly sized photodiodes at specific locations within the pixel array. This creates locally differentiated sensitivity (high-sensitivity photodiodes under larger openings, low-sensitivity photodiodes under smaller openings) while maintaining uniform photodiode geometry throughout the array, thereby achieving high dynamic range without the dark performance degradation associated with irregular photodiode arrays.
4Reliability
If uniform photodiodes with varying sensitivity are used through metal grid patterning, then photodiode leakage is reduced and dark performance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent uses a standard photodiode design that can be repeatedly copied across the entire pixel array through standard semiconductor fabrication processes. The varying sensitivity is achieved not by varying photodiode geometry but by placing different patterns of metal openings (which can be formed using standard photolithography and etching) over the uniform photodiodes, thereby maintaining ease of manufacture through copying while achieving the desired sensitivity variation.
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 approach achieves a dynamic range of approximately 140 dB or higher while maintaining better dark performance compared to irregular pixel arrays, and simplifies the formation of isolation structures, reducing material and processing costs.
Implementation Method 1
Complementary metal oxide semiconductor (CMOS) image sensors utilize light-sensitive CMOS circuitry to convert light energy into electrical energy. As the photodiode is exposed to light, an electrical charge is induced in the photodiode (referred to as a photocurrent).
Implementation Method 2
forming a metal layer configured to reflect light; a first photodiode associated with a first opening in the metal layer; a second photodiode associated with a second opening in the metal layer, the second opening being smaller than the first opening
Data Source
AI summary
A metal grid of a pixel array may be patterned with different sized openings over photodiodes. As a result, a uniform pixel array of photodiodes with different sensitivities may be formed. For example, the pixel array may include low-sensitivity photodiodes (LSPDs), mid-sensitivity photodiodes (MSPDs), and high-sensitivity photodiodes (HSPDs). The LSPDs, MSPDs, and HSPDs have different capture rates. Therefore, a higher dynamic range is achieved by combining signals from LSPDs, MSPDs, and HSPDs. For example, the pixel array may achieve a dynamic range of approximately 140 decibels or higher due to its increased capacity. Additionally, the pixel array exhibits better dark performance as compared to a pixel array with a combination of large photodiodes (LPDs) and small photodiodes (SPDs). Because each photodiode in the pixel array is approximately a same size, photodiode leakage is reduced as compared with irregular pixel arrays including a combination of LPDs and SPDs.