Multi-Photodiode Pixel Cell for Collocated 2D and 3D Imaging
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Solution Overview
Problem
Image sensors face challenges in achieving collocated 2D and 3D imaging with high spatial resolution due to the need for separate pixel cells for visible and infra-red light detection, leading to increased form-factor and power consumption, and complications in merging 2D and 3D image data, especially when capturing moving objects.
Innovation Solution
The image sensor employs a stacked photodiode structure with a barrier layer and an anti-blooming channel region to allow collocated 2D and 3D imaging by controlling the flow of charges between photodiodes, preventing blooming and enabling simultaneous detection of different light components at the same location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate pixel cells are used for visible and infra-red light detection, then detection capability for different light components is improved, but device complexity and form-factor increase
Solution Approach 1:
The patent combines multiple photodiodes (first photodiode for visible light, second photodiode for infra-red light) into a single pixel cell structure. This merging allows simultaneous detection of different light components at the same spatial location, improving versatility while reducing the overall device form-factor compared to using separate pixel cells for each wavelength range.
Solution Approach 2:
The patent transitions from a planar arrangement of separate pixel cells to a vertical stacked configuration within a single pixel cell. By stacking photodiodes at different depths (different z-dimension positions) within the semiconductor substrate, the patent enables multi-wavelength detection in the same lateral footprint, effectively using the vertical dimension to resolve the contradiction between detection capability and form-factor.
2Measurement precision
If multiple photodiodes are stacked in a single pixel cell, then spatial resolution is improved, but blooming occurs when photodiodes become saturated
Solution Approach 1:
The patent segments the charge collection function by providing separate drain regions (first drain region for the first photodiode, second drain region for the second photodiode) and separate readout circuits for each photodiode. This segmentation allows independent charge drainage paths, preventing charge overflow from one photodiode from affecting another, thereby mitigating blooming while maintaining high spatial resolution through the stacked configuration.
Solution Approach 2:
The patent introduces an intermediary barrier layer between the first photodiode and the second photodiode in the stacked structure. This barrier layer acts as a charge confinement structure that prevents charge carriers from diffusing between adjacent photodiodes, thereby eliminating the blooming effect while allowing both photodiodes to maintain high spatial resolution in their respective detection channels.
3Adaptability or versatility
If separate pixel cells are used for 2D and 3D imaging, then imaging functionality is improved, but power consumption increases
Solution Approach 1:
The patent creates a universal pixel cell structure that can perform both 2D imaging (using the first photodiode for visible light) and 3D imaging (using the second photodiode for infra-red light time-of-flight measurements) within the same physical location. This multi-functionality eliminates the need for separate dedicated pixel cells for each imaging mode, thereby reducing the total number of active components and lowering overall power consumption while maintaining full imaging functionality.
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 solution allows for high-resolution collocated 2D and 3D imaging while mitigating blooming issues, improving spatial resolution and reducing power consumption by enabling simultaneous detection of visible and infra-red light components at the same pixel location.
Implementation Method 1
a first photodiode to generate a first charge in response to a first component of light within a visible light wavelength range
Implementation Method 2
a second photodiode to generate a second charge in response to a second component of light within an infra-red light wavelength range
Implementation Method 3
a barrier layer between the first photodiode and the second photodiode and configured to control flow of the second charge from the second photodiode to the first photodiode
Data Source
AI summary
In one example, an apparatus comprises: a semiconductor substrate including a front side surface, a first photodiode to generate a first charge, a second photodiode to generate a second charge, a barrier layer between the first photodiode and the second photodiode and configured to control flow of the second charge from the second photodiode to the first photodiode, and a drain region to store the first charge and at least a first part of the second charge. The apparatus further comprises a gate on the front side surface over a first channel region between the first photodiode and the drain region to control the flow of the first charge and the at least the first part of the second charge to the drain region, and a second channel region to conduct at least a second part of the second charge away from the barrier layer when the second photodiode saturates.