Stacked Pinned Photodiode Pixel Cell for Dual-Wavelength Imaging
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Solution Overview
Problem
Current image sensors face challenges in performing both 2D and 3D imaging efficiently, as they require separate pixel cells for visible and infrared light, leading to lower spatial resolutions and increased power consumption, and complications in merging 2D and 3D image data due to non-collocated pixel cells.
Innovation Solution
An image sensor with an array of pixel cells featuring a stack structure of two pinned photodiodes, one for visible light and one for infrared light, allowing both modes of imaging to be performed within the same exposure period, with capacitors to convert charges into voltages and a control circuit to manage charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate pixel cells are used for visible and infrared light sensing, then the sensitivity for each wavelength range is improved, but the spatial resolution is reduced and power consumption increases
Solution Approach 1:
The patent combines multiple photodiodes (visible light photodiode and infrared photodiode) into a single pixel cell structure, allowing both wavelength ranges to be sensed at the same spatial location. This merging eliminates the need for separate pixel cells for different light types, thereby maintaining high spatial resolution while preserving sensitivity for both visible and infrared sensing.
Solution Approach 2:
The pixel cell is designed with multi-functional capability to sense both visible light and infrared light simultaneously through different photodiodes within the same cell. This universal design allows a single pixel cell to perform multiple sensing functions, avoiding the need for separate specialized pixel cells and thus maintaining spatial resolution while enabling dual-wavelength sensitivity.
2Reliability
If separate pixel cells are used for visible and infrared light sensing, then the sensitivity for each wavelength range is improved, but the power consumption increases
Solution Approach 1:
The patent merges multiple photodiodes into a single integrated pixel cell structure, reducing the total number of independent sensing elements required. This integration reduces the overall power consumption associated with operating separate pixel cells for visible and infrared sensing, while maintaining the sensitivity benefits of having dedicated photodiodes for each wavelength range within the same cell.
3Reliability
If separate pixel cells are used for visible and infrared light sensing, then the sensitivity for each wavelength range is improved, but the correspondence between 2D and 3D images deteriorates due to non-collocated pixel cells
Solution Approach 1:
The patent merges visible light and infrared sensing capabilities into the same pixel cell location, ensuring that 2D visible light imaging and 3D infrared depth sensing are collocated. This spatial coincidence maintains perfect correspondence between the two image types, eliminating misalignment issues that arise from using separate non-collocated pixel cells for different wavelength ranges.
4Device complexity
If a single photodiode is used in each pixel cell, then the device complexity is reduced, but the ability to perform both 2D and 3D imaging simultaneously is lost
Solution Approach 1:
The pixel cell is designed with multi-functional capability by incorporating multiple photodiodes that can operate in different modes. The same pixel cell structure can perform 2D imaging using visible light photodiodes and 3D depth sensing using infrared photodiodes, either simultaneously or in alternating modes, providing adaptability without requiring fundamentally different hardware configurations.
Solution Approach 2:
The patent implements dynamic control of photodiode operation modes, allowing the system to switch between or combine 2D and 3D imaging modes as needed. The control circuit can dynamically activate specific photodiodes based on the desired imaging mode, enabling flexible adaptation between different sensing requirements while using the same physical pixel cell structure.
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 enables improved spatial resolution, reduced power consumption, and enhanced correspondence between 2D and 3D images by using the same set of pixel cells for both modes of imaging, improving sensitivity and performance in low-light environments.
Implementation Method 1
A typical pixel in an image sensor includes a photodiode to sense incident light by converting photons into charge (e.g., electrons or holes)
Implementation Method 2
The pixel may further include a capacitor (e.g., a floating diffusion) to collect the charge from the photodiode and to convert the charge to a voltage
Data Source
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AI summary
Methods and systems for image sensing are provided. In one example, an apparatus comprises a semiconductor substrate comprising a light incident surface to receive light, a first pinned photodiode, and a second pinned photodiode, the first pinned photodiode and the second pinned photodiode forming a stack structure in the semiconductor substrate along an axis perpendicular to the light incident surface, the stack structure enabling the first pinned photodiode and the second pinned photodiode to, respectively, convert a first component of the light and a second component of the light to first charge and second charge. The apparatus further comprises one or more capacitors formed in the semiconductor substrate and configured to generate a first voltage and a second voltage based on, respectively, the first charge and the second charge.