Dual-Photodiode Image Sensor Barrier Potential Control
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Solution Overview
Problem
Existing image sensors with two photodiodes in a single pixel region face challenges in controlling the barrier area potential for efficient charge movement, leading to signal saturation and reduced performance due to uniform doping and narrow isolation areas.
Innovation Solution
The image sensor employs a method of ion implantation with a tilted beam to selectively dope impurities, forming a barrier area with controlled potential between photodiodes, using device isolation films and a doped layer to manage charge movement and prevent saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If uniform doping is applied to the substrate, then the manufacturing process is simple, but the barrier area potential cannot be controlled leading to signal saturation
Solution Approach 1:
The patent divides the substrate into distinct regions with different doping concentrations: a first doped region adjacent to the first photodiode and a second doped region adjacent to the second photodiode. This segmentation allows independent control of barrier area potential while maintaining manageable manufacturing processes through selective ion implantation in specific zones rather than uniform treatment of the entire substrate.
Solution Approach 2:
The patent implements local quality by creating non-uniform doping distribution where different regions of the substrate have different impurity concentrations. The first and second doped regions are selectively doped with different concentrations to optimize charge movement in specific areas, allowing precise control of barrier area potential without requiring complex global doping processes.
2Productivity
If the isolation area between photodiodes is narrowed to increase pixel density, then the pixel density increases, but the charge movement control becomes difficult leading to signal saturation
Solution Approach 1:
The patent applies local quality by creating selectively doped regions adjacent to each photodiode within the narrowed isolation area. Even though the overall isolation area is reduced to increase pixel density, the local doping quality is enhanced with specific impurity concentrations in the first and second doped regions, enabling precise control of charge movement and prevention of signal saturation despite the compact layout.
Solution Approach 2:
The patent changes the doping concentration parameter in specific local regions to control charge movement. By adjusting the impurity concentration in the first and second doped regions adjacent to different photodiodes, the patent optimizes the barrier area potential to prevent signal saturation while maintaining high pixel density through reduced isolation areas.
3Manufacturing precision
If tilted beam ion implantation is used to control doping concentration, then the barrier area potential is controlled improving performance, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the ion implantation process into distinct steps for different regions. The tilted beam is used to selectively dope the first region adjacent to the first photodiode and the second region adjacent to the second photodiode separately. This segmentation allows precise control of doping concentration in each region while breaking down the complex process into manageable, repeatable manufacturing steps.
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 enhances the image sensor's performance by controlling the doping concentration and potential, reducing signal saturation and improving charge management between photodiodes, leading to improved autofocusing and operational efficiency.
Implementation Method 1
a method of ion implantation with a tilted beam to selectively dope impurities, forming a barrier area with controlled potential between photodiodes
Implementation Method 2
each of the pixel regions may include at least one photodiode (PD) for converting incident light into an electrical signal
Data Source
AI summary
An image sensor includes a substrate having first and second surfaces, pixel regions arranged in a direction parallel to the first surface, first and second photodiodes isolated from each other in each of the pixel regions, a first device isolation film between the pixel regions, a pair of second device isolation films between the first and second photodiodes and extending from the first device isolation film, a doped layer adjacent to the pair of second device isolation films and extending from the second surface to a predetermined depth and spaced apart from the first surface, the doped layer being isolated from the first device isolation film, and a barrier area between the pair of second device isolation films and having a potential greater than a potential of a portion of the substrate adjacent to the barrier area.