Stacked Image Sensor With Optical Shield For Dynamic Range
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Solution Overview
Problem
Conventional image sensors often have limited dynamic range, making them inadequate for capturing images under varying light conditions, particularly in automotive and security applications where high dynamic range is essential.
Innovation Solution
A stacked image sensor design featuring a combination of photodiodes with varying semiconductor material thickness and an optical shield, along with a front and backside illuminated configuration, to enhance sensitivity and dynamic range by optimizing light absorption across different light intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single photodiode layer is used, then the device structure is simple, but the dynamic range is limited
Solution Approach 1:
The image sensor is divided into multiple photodiode layers stacked vertically, with each layer capturing a specific portion of the light spectrum. This segmentation allows different layers to handle different light intensities, thereby expanding the overall dynamic range while maintaining manageable complexity through modular design
Solution Approach 2:
The patent transitions from a planar single-layer structure to a three-dimensional stacked architecture. By adding the vertical dimension with multiple photodiode layers, the sensor captures light at different depths and intensities simultaneously, dramatically increasing dynamic range without proportionally increasing lateral complexity
2Measurement precision
If photodiodes with varying semiconductor material thickness are used, then light absorption sensitivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
Each photodiode layer is designed with locally optimized semiconductor thickness tailored to its specific function. The first photodiode layer has a first thickness optimized for capturing certain light intensities, while the second photodiode layer has a second thickness optimized for other intensities. This local quality approach maximizes light absorption sensitivity for each layer's specific role in the dynamic range capture
Solution Approach 2:
The patent systematically varies the semiconductor material thickness parameter across different photodiode layers to optimize light absorption characteristics. By changing this physical parameter locally for each layer, the design achieves superior light sensitivity and dynamic range performance while the variation itself becomes a controlled design parameter rather than a manufacturing challenge
3Reliability
If optical shield is added between photodiode layers, then cross-talk between layers is reduced, but device complexity increases
Solution Approach 1:
Optical shields are strategically placed between specific photodiode layers to extract and block stray light that would otherwise cause cross-talk. This selective extraction of harmful optical paths improves signal accuracy without requiring shields throughout the entire stack, maintaining a balance between performance and structural simplicity
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 provides a higher dynamic range than individual image sensors, enabling effective image capture across a broader range of light conditions, including both low and high light scenarios with improved sensitivity and reduced saturation.
Implementation Method 1
Photosensitive elements included in the image sensor, such as photodiodes, generate image charge upon absorption of the image light
Implementation Method 2
The thickness of semiconductor material proximate to a first photodiode is less than a thickness of semiconductor material proximate to a second photodiode
Data Source
AI summary
A stacked image sensor includes a first plurality of photodiodes, including a first photodiode and a second photodiode, disposed in a first semiconductor material. A thickness of the first semiconductor material proximate to the first photodiode is less than the thickness of the first semiconductor material proximate to the second photodiode. A second plurality of photodiodes is disposed in a second semiconductor material. The second plurality of photodiodes is optically aligned with the first plurality of photodiodes. An interconnect layer is disposed between the first semiconductor material and the second semiconductor material. The interconnect layer includes an optical shield disposed between the second photodiode and a third photodiode included in the second plurality of photodiodes. The optical shield prevents a first portion of image light from reaching the third photodiode.