Split-Photodiode Image Sensor With Light Splitter for Low Crosstalk
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Solution Overview
Problem
Current image sensors with a split photodiode structure face challenges in achieving improved image quality and dynamic range due to limitations in light distribution and crosstalk between photodiode regions.
Innovation Solution
The implementation of an image sensor design featuring a substrate with adjacent first and second photodiode regions, a micro-lens, and a light splitter with a refractive index different from the micro-lens, which extends between the photodiode regions to optimize light distribution and reduce crosstalk, along with deep trench isolation and an interconnection layer for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a split photodiode structure is used to improve dynamic range, then the dynamic range is improved, but crosstalk between photodiode regions occurs
Solution Approach 1:
The photodiode is divided into multiple regions (first PD region and second PD region) with different areas, allowing each region to handle different light intensity ranges. The larger first PD region captures more photons for low-light conditions while the smaller second PD region prevents saturation in bright conditions, thereby improving dynamic range without causing crosstalk.
Solution Approach 2:
Different regions of the photodiode are designed with different properties: the first PD region has a larger area for high sensitivity in low-light conditions, while the second PD region has a smaller area to prevent saturation in bright conditions. This local differentiation allows each region to optimize its performance for specific lighting conditions.
2Area of moving object
If photodiode regions are placed adjacent to each other to improve pixel density, then pixel density is improved, but light distribution between regions becomes problematic
Solution Approach 1:
A micro-lens is introduced above the photodiode regions to control light distribution in the vertical dimension. The micro-lens focuses incoming light onto the appropriate PD region, ensuring that light is properly directed to either the first or second PD region based on its origin, thereby maintaining good light distribution despite the adjacent horizontal placement of regions.
3Illumination intensity
If different sized photodiodes are used to improve dynamic range, then dynamic range is improved, but manufacturing precision requirements increase
Solution Approach 1:
The invention specifies a particular area ratio range (0.2 to 0.8) between the first and second PD regions, providing a design parameter that balances dynamic range improvement with manufacturing feasibility. This parameter guidance helps manufacturers achieve the desired performance without requiring extreme precision.
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 image quality by improving light distribution and reducing crosstalk between photodiode regions, leading to improved sensitivity and dynamic range in image sensors.
Implementation Method 1
a light splitter between the substrate and the micro-lens, or on the color filter. The light splitter includes a material having a refractive index different from a refractive index of the color filter
Implementation Method 2
a micro-lens on the substrate and covering the first PD region
Implementation Method 3
The pixels may each include a PD generating charges in response to external light
Data Source
AI summary
An image sensor that includes a substrate including a first photodiode (PD) region and a second PD region adjacent to the first PD region; a first PD having a first area in the first PD region; a second PD in the second PD region, the second PD having a second area smaller than the first area; a micro-lens on the substrate and covering the first PD region; and a light splitter between the substrate and the micro-lens, the light splitter including a material having a refractive index different from a refractive index of the micro-lens. The light splitter extends from the first PD region to the second PD region.