Stacked Image Sensor Pixel Structure for Dual-Spectrum Detection
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Solution Overview
Problem
As electronic devices become smaller and feature-dense, there is a need for image sensors that can detect optical signals across multiple spectrum ranges in a limited area without compromising resolution, while minimizing space and optimizing the pixel structure.
Innovation Solution
A semiconductive stack with a specific layered structure, including doped layers and gate structures, is used to create a unit pixel that can detect both short and long wavelength spectra within a single pixel, utilizing epitaxial deposition to minimize damage and enhance doping profile accuracy, allowing for efficient charge transfer and reduced dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single photodiode is used per pixel, then the pixel structure is simple and manufacturing is easy, but the full-well capacity is limited and dynamic range is restricted
Solution Approach 1:
The pixel is divided into multiple photodiodes (first photodiode and second photodiode) within a single pixel structure. Each photodiode captures light independently, and their signals are combined to increase the full-well capacity while maintaining the same pixel size and manufacturing process complexity.
2Quantity of substance
If multiple photodiodes are integrated in a pixel, then the full-well capacity increases, but the pixel aperture area is reduced and light collection efficiency decreases
Solution Approach 1:
The photodiodes are arranged in a stacked configuration across multiple vertical levels (first level and second level) rather than spreading them out horizontally. This vertical stacking allows multiple photodiodes to coexist within the same pixel aperture area, maintaining light collection efficiency while increasing full-well capacity through multi-level integration.
3Quantity of substance
If photodiodes are stacked vertically, then the full-well capacity increases without reducing aperture area, but alignment precision between photodiodes and microlens becomes difficult to control
Solution Approach 1:
A first intermediate layer is introduced between the first photodiode and the second photodiode. This intermediate layer serves as a structural mediator that facilitates precise vertical alignment between the stacked photodiodes and the microlens, ensuring that the light paths remain properly aligned while maintaining the multi-level photodiode configuration for increased full-well capacity.
4Measurement precision
If multiple photodiodes are integrated in a pixel, then the dynamic range improves, but the pixel structure becomes more complex requiring additional gate structures
Solution Approach 1:
The first gate structure and second gate structure serve multiple functions: they act as reset gates for the photodiodes, control the timing of charge transfer, and enable the switching between different readout modes. This multi-functional design increases the dynamic range capability while minimizing the overall structural complexity by avoiding redundant gate elements.
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 approach enables the detection of dual optical spectrums in a single unit pixel, improving sensitivity across multiple spectrum ranges without increasing the pixel area, thus optimizing the use of limited space in image sensors.
Implementation Method 1
The unit pixel includes a first photodiode and a second photodiode formed in the semiconductive stack
Data Source
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AI summary
Disclosure herein relates to a unit pixel structure incorporating multiple photodiodes is disclosed. The unit pixel is formed in a semiconductive stack. The unit pixel includes a sensor well region, a floating diffusion region, a first gate structure and a second gate structure. The first gate structure is disposed over the semiconductive stack and the second gate structure extends into the semiconductive stack.