Photodiode Size Variation and Trench Isolation for Image Sensor Light Uniformity
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Solution Overview
Problem
Image sensors face non-linear light intensity issues due to obliquely incident light, particularly at the edges of the pixel array, leading to reduced light transmission and difficulty in correcting light intensity variations.
Innovation Solution
The image sensor design includes photodiodes of different sizes and trench isolation regions, with specific size configurations in peripheral and corner regions to optimize light reception and correct non-linear light intensity changes, using Deep Trench Isolation (DTI) and diagonal PD isolation regions to improve sensitivity and reduce cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photodiodes of uniform size are used across the pixel array, then manufacturing is simplified, but light sensitivity becomes non-uniform at peripheral regions due to oblique light incidence
Solution Approach 1:
The patent applies local quality by differentiating photodiode sizes based on their position within the pixel array. Central region photodiodes maintain a standard size, while peripheral region photodiodes are enlarged to compensate for reduced light intensity caused by oblique incidence. This localized modification ensures uniform light sensitivity across the entire array without complicating the overall manufacturing process.
Solution Approach 2:
The patent introduces asymmetry in photodiode dimensions specifically at the peripheral regions of the pixel array. By making photodiodes larger at the edges where light intensity is lower, the design creates an asymmetric structure that balances the optical response across different spatial locations, thereby achieving uniform sensitivity despite the non-uniform light distribution.
2Productivity
If photodiodes are closely packed to increase pixel density, then productivity increases, but cross-talk between adjacent photodiodes increases
Solution Approach 1:
The patent introduces isolation regions as intermediary structures between adjacent photodiodes. These isolation regions act as barriers that prevent electrical and optical cross-talk while allowing the photodiodes to remain closely packed. This mediator structure enables high pixel density without sacrificing signal isolation, effectively resolving the contradiction between productivity and harmful cross-talk.
3Measurement precision
If peripheral photodiodes are enlarged to compensate for oblique light incidence, then light sensitivity uniformity improves, but device area increases
Solution Approach 1:
The patent applies local quality by selectively enlarging only the peripheral photodiodes that require compensation for oblique light incidence, while maintaining standard sizes for central photodiodes. This localized approach achieves uniform light sensitivity across the array without unnecessarily increasing the total device area, as the size modification is applied only where needed.
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 design enhances light sensitivity and corrects non-linear light intensity variations across the pixel array, improving image quality and reducing thermal loads by optimizing photodiode sizes and isolation methods.
Implementation Method 1
A unit pixel includes a photodiode and a transmission transistor. The transmission transistor is disposed between the photodiode and a floating diffusion region to transmit a charge generated by the photodiode
Implementation Method 2
The left and right photodiodes in at least one of the one or more of the first unit pixels may have different sizes and may be optically isolated from each other by a first PD isolation region
Data Source
AI summary
Disclosed is an image sensor may include a pixel array having a central region and peripheral regions around the central region, one or more first unit pixels arranged in the peripheral regions. Each of the first unit pixels comprising a pair of left and right photodiodes. The left and right photodiodes in at least one of the one or more of the first unit pixels may have different sizes and are optically isolated from each other by a first PD isolation region.