Pixel Wiring Layout for Low-Noise High-Sensitivity Imaging
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Solution Overview
Problem
Existing imaging devices face challenges in achieving high-quality imaging due to noise in high-sensitivity cells, which affects image quality and dynamic range.
Innovation Solution
The proposed imaging device incorporates a semiconductor substrate with a pixel structure that includes a first cell with high sensitivity and a second cell with lower sensitivity. The pixel structure features an upper wiring layer with specific wire configurations to reduce capacitance and noise, enhancing the conversion gain of the high-sensitivity cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-sensitivity cell with a large-area photodiode is used, then sensitivity is improved, but noise increases and affects image quality
Solution Approach 1:
The pixel is divided into two separate cells: a first cell with a large-area photodiode for high sensitivity and a second cell with a small-area photodiode for low sensitivity. This segmentation allows each cell to serve a specific function, with the first cell capturing more light for improved sensitivity while the second cell providing a reference for noise reduction through differential processing.
Solution Approach 2:
Different regions of the pixel structure are given different properties: the first cell has a large photodiode area optimized for light capture, while the second cell has a small photodiode area optimized for reference signaling. The wiring structure is also locally optimized with different wire distances from the nodes to control capacitance values, creating local quality variations that resolve the noise-sensitivity contradiction.
2Device complexity
If wires are placed close to charge accumulator nodes, then wiring complexity is reduced, but capacitance increases and noise increases
Solution Approach 1:
The wiring structure implements local quality by creating asymmetric wire placements: the first wire connected to the first node is positioned at a greater distance to reduce capacitance and noise in the high-sensitivity cell, while the second wire connected to the second node is positioned at a smaller distance. This local differentiation optimizes each cell's electrical characteristics for its specific function.
Solution Approach 2:
The invention changes the physical parameter of wire-to-node distance to control capacitance values. By adjusting this geometric parameter, the capacitance of the first node is reduced relative to the second node, thereby reducing noise in the high-sensitivity first cell while maintaining functional wiring connectivity.
3Measurement precision
If conversion gain is increased to improve signal quality, then sensitivity is improved, but noise is also amplified
Solution Approach 1:
The second cell provides feedback information about the noise characteristics and conversion gain effects. By comparing the signals from both cells, the system can identify and subtract noise components that are amplified during conversion, thereby improving signal quality while reducing the impact of noise amplification.
Solution Approach 2:
The asymmetric wiring configuration creates different capacitance values for the two cells, which results in different conversion gains. The first cell is designed with lower capacitance for higher conversion gain and sensitivity, while the second cell has higher capacitance for lower conversion gain and reference functionality. This asymmetry allows optimized signal quality in the first cell while the second cell provides noise reference for differential processing.
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 configuration effectively reduces noise in high-sensitivity cells, increases conversion gain, and improves overall image quality, enabling the realization of high-quality imaging devices with enhanced dynamic range.
Implementation Method 1
a first photoelectric converter that converts light into first signal charge
Implementation Method 2
a second photoelectric converter that converts light into second signal charge
Data Source
AI summary
A second cell is less sensitive than a first cell. The first cell includes a first charge accumulator and a first wire. The first charge accumulator accumulates first signal charge and is electrically connected to a first node. The first wire is located within an upper wiring layer and is electrically connected to the first node. The second cell includes a second charge accumulator and a second wire. The second charge accumulator accumulates second signal charge and is electrically connected to a second node. The second wire is located within the upper wiring layer and is electrically connected to the second node. In the upper wiring layer, a shortest distance between the first wire and wires is greater than a shortest distance between the second wire and the wires.