Mixed N-P Type Photodiode Array for Image Sensor Crosstalk Reduction
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Solution Overview
Problem
Conventional image sensors with uniform photodiodes suffer from blooming and cross-talk effects due to the generation of charge carriers of the same type, which can lead to reduced optical sensitivity and quantum efficiency.
Innovation Solution
The design incorporates both N-type and P-type photodiodes arranged in a specific pattern to minimize electrical influences between adjacent pixels, forming potential barriers that prevent charge carriers from affecting neighboring photodiodes, thereby reducing blooming and cross-talk effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform photodiodes are used in conventional image sensors, then the structure is simple and manufacturing is easier, but blooming and cross-talk effects occur due to charge carriers of the same type affecting neighboring pixels
Solution Approach 1:
The patent applies local quality by creating different types of photodiodes (N-type and P-type) in different regions of the pixel array. Specifically, first photodiodes are N-type and second photodiodes are P-type, with adjacent photodiodes having different types. This local differentiation prevents charge carriers from the same type from affecting neighboring pixels, thereby reducing blooming and cross-talk effects while maintaining manufacturing feasibility through systematic doping patterns.
2Object-affected harmful factors
If N-type and P-type photodiodes are mixed in adjacent pixels, then blooming and cross-talk effects are reduced, but device complexity increases
Solution Approach 1:
The patent segments the pixel array into distinct regions with different photodiode types. The image sensor divides the array into first photodiodes (N-type) and second photodiodes (P-type), with each type forming a coherent segment. This segmentation approach systematically organizes the complexity by creating regular patterns of alternating types, making the device manageable while effectively preventing charge carrier interference between adjacent pixels.
3Object-affected harmful factors
If trench isolation regions are used to prevent charge carrier interference, then blooming and cross-talk effects are reduced, but pixel density decreases and resolution is limited
Solution Approach 1:
The patent changes the fundamental parameter of photodiode type (N-type vs P-type) rather than using physical isolation structures. By altering the doping type parameter, the invention creates natural electrical barriers between adjacent pixels through potential barriers formed at the interfaces of different types. This parameter-based approach eliminates the need for trench isolation regions, allowing higher pixel density and improved resolution while still preventing charge carrier interference.
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 arrangement enhances optical sensitivity and quantum efficiency while allowing for a higher pixel density without the need for trench isolation regions, thereby improving the resolution and reducing dark current characteristics.
Implementation Method 1
a photosensing element such as a photodiode that converts received light at the unit pixel into charges
Data Source
AI summary
An image sensor is provided. The image sensor may include first to fourth unit pixels. The first unit pixel includes a first photodiode, a first transfer gate, and a first floating diffusion region, and the second unit pixel includes a second photodiode, a second transfer gate, and a second floating diffusion region, and the third unit pixel includes a third photodiode, a third transfer gate, and a third floating diffusion region, and the fourth unit pixel includes a fourth photodiode, a fourth transfer gate, and a fourth floating diffusion region. The first photodiode and the third photodiode may be N-type photodiodes. The second photodiode and the fourth photodiode may be P-type photodiodes.