Pixel Cell PINNED Structure Dynamic Range Optimization
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Solution Overview
Problem
Conventional image sensors face limitations in dynamic range and sensitivity due to small pixel sizes, requiring larger chip sizes to maintain resolution, which increases costs and reduces performance.
Innovation Solution
The implementation of a PINNED structure connected with the floating diffusion structure, where the doping concentration and type of the PINNED structure are controlled to achieve nonlinear sensitivity, enhancing the dynamic range and visibility of the image sensor, particularly in low and high illuminance conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pixel size is decreased to reduce chip size and cost, then manufacturing cost decreases, but sensitivity and dynamic range are limited
Solution Approach 1:
The patent introduces a PINNED structure with specific doping characteristics (doping concentration of 10^16 to 10^18 atoms/cm³, which is lower than the floating diffusion structure's 10^19 atoms/cm³) in the pixel region. This creates local variation in electrical properties, enabling the small pixel to achieve nonlinear sensitivity characteristics that improve dynamic range without requiring larger pixel dimensions.
Solution Approach 2:
The patent changes the doping concentration parameter of the PINNED structure to be lower than conventional structures, which directly affects the depletion voltage and creates nonlinear sensitivity. By controlling the doping concentration within a specific range (10^16 to 10^18 atoms/cm³), the patent achieves improved dynamic range while maintaining small pixel size.
2Reliability
If a pixel cell comprising large and small pixels is used to improve dynamic range, then sensitivity performance is improved, but chip size must be increased to maintain resolution
Solution Approach 1:
Instead of using multiple pixels of different sizes, the patent changes the doping concentration parameter of a single pixel's PINNED structure to achieve nonlinear sensitivity. This allows one pixel to perform the function that previously required multiple pixels, thereby improving dynamic range without increasing chip area.
Solution Approach 2:
The patent makes a single pixel structure capable of handling both low illuminance and high illuminance conditions through the nonlinear sensitivity characteristic introduced by the PINNED structure. This multi-functional capability replaces the need for separate large and small pixels, reducing the overall chip size while maintaining comprehensive dynamic range performance.
3Reliability
If the doping concentration of the PINNED structure is controlled to achieve nonlinear sensitivity, then dynamic range is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a broad doping concentration range (10^16 to 10^18 atoms/cm³) for the PINNED structure, which provides flexibility in manufacturing. This range is sufficiently wide to accommodate normal manufacturing variations while still achieving the desired nonlinear sensitivity effect, thereby balancing performance improvement with manufacturing feasibility.
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 allows for improved dynamic range and sensitivity control, preventing over-exposure and enhancing dark state visibility, thus achieving a wider dynamic range without increasing chip size, thereby improving cost performance.
Implementation Method 1
by controlling the doping concentration of the floating diffusion structure, the first diffusion region and the second diffusion region, the depletion voltage of the PINNED structure is made lower than the reset voltage of the floating diffusion structure
Implementation Method 2
a pixel cell comprises a photodiode 103, a pass transistor 107, a floating diffusion structure 104 and a PINNED structure 105
Data Source
Figure 1
Figure 2~3
Figure 4~5b
AI summary
A pixel cell, a method for manufacturing the same and an image sensor comprising the same are provided. The pixel cell comprises: a substrate (101); a photodiode (103), a pass transistor (107) and a floating diffusion structure (104) respectively formed on the substrate (101), in which the pass transistor (107) is formed between the photodiode (103) and the floating diffusion structure (104); and a PINNED structure (105), formed on the substrate (101) and connected with the floating diffusion structure (104), in which a reset voltage of the floating diffusion structure (104) is higher than a depletion voltage of the PINNED structure (105).