Stacked Image Sensor Pixel Pads With Coupling Prevention Line
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Solution Overview
Problem
Stack-type image sensors face issues with coupling capacitance between pixel pads and metal wiring layers, leading to white spot defects and deterioration in electrical characteristics, which are challenging to address due to limited design freedom in fine pixel structures.
Innovation Solution
Incorporating a coupling prevention line around pixel pads and electrically connecting it to the source region of the source-follower transistor to reduce or prevent coupling capacitance, thereby improving image clarity and conversion gain through the Miller effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pixel size is reduced to increase integration, then resolution and signal processing speed improve, but coupling capacitance between pixel pads and metal wiring layers increases causing white spot defects
Solution Approach 1:
A coupling prevention line is introduced as an intermediary conductive structure between the pixel pad and metal wiring layers. This line is electrically connected to the source region of the source-follower transistor and positioned to shield the pixel pad from the metal wiring layer, thereby reducing coupling capacitance while maintaining the reduced pixel size design
Solution Approach 2:
The coupling prevention line is designed to preemptively counteract the harmful coupling capacitance effect before it can degrade image quality. By establishing this protective conductive structure in advance during the manufacturing process, the patent prevents white spot defects from occurring in the first place
2Measurement precision
If pixel size is reduced to increase integration, then resolution improves, but design freedom in fine pixel structures is limited
Solution Approach 1:
The coupling prevention line extends in the vertical direction (z-axis) across multiple layers, utilizing the third dimension to solve the coupling capacitance problem without consuming additional planar area in the x-y plane. This allows the pixel structure to maintain high resolution while incorporating the protective structure
3Ease of manufacture
If coupling capacitance is not prevented, then manufacturing is simpler, but white spot defects and deterioration in electrical characteristics occur
Solution Approach 1:
The coupling prevention line is merged with the existing metal wiring layer structure and is electrically connected to the source region of the source-follower transistor. This integration allows the coupling prevention function to be achieved without adding completely separate manufacturing processes, thereby maintaining manufacturing simplicity while improving reliability
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
The solution effectively shields the pixel pads and metal wiring layers, reducing coupling capacitance and enhancing image quality by restricting unwanted electrical interactions, thus improving the overall performance of the image sensor.
Implementation Method 1
coupling capacitance between the pixel pad and the metal wiring layer
Implementation Method 2
a photodiode receiving incident light and converting the light into an electrical signal
Data Source
AI summary
Provided is an image sensor including a first structure and a second structure stacked in a vertical direction, wherein the first structure includes a first pixel region, a photoelectric conversion unit in the first pixel region, a floating diffusion region in the first pixel region, a first interlayer insulating layer on the floating diffusion region, and a first pixel pad electrically connected to the floating diffusion region, and the second structure includes a second pixel region, a source-follower transistor in the second pixel region, a second interlayer insulating layer on the source-follower transistor, and a second pixel pad electrically connected to a gate of the source-follower transistor, and the image sensor includes a coupling prevention line arranged around the first and second pixel pads and electrically connected to the source region of the source-follower transistor.