Two-Layer Image Sensor Photoelectric Conversion Structure
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Solution Overview
Problem
Conventional image sensors have limited image quality due to uneven absorption rates across different wavelengths of visible light, primarily high absorption in certain wavelengths like blue, leading to suboptimal digital image representation.
Innovation Solution
A two-layer photoelectric conversion structure is implemented, with a first photoelectric conversion device and a second photoelectric conversion device separated by a photoelectron barrier, along with a reflection film and transparent electrode, to enhance absorption across a wider range of wavelengths, including near-infrared and ultraviolet regions, and utilize MOS transistors to transfer photoelectrons to a floating diffusion region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer photoelectric conversion device is used, then the device structure is simple, but the absorption rate is uneven across different wavelengths leading to limited image quality
Solution Approach 1:
The photoelectric conversion device is divided into two separate layers: a first photoelectric conversion device closer to the light receiving surface and a second photoelectric conversion device farther from the light receiving surface. Each layer can be independently optimized for different wavelength ranges, with the first layer capturing shorter wavelengths (blue, violet) and the second layer capturing longer wavelengths (red, near-infrared), thereby achieving more uniform absorption across the spectrum while maintaining manageable structural complexity
Solution Approach 2:
The patent transitions from a single-layer two-dimensional structure to a three-dimensional multi-layer structure by stacking photoelectric conversion devices at different depths within the substrate. This vertical dimensionality allows light to be converted at multiple depths, with each layer contributing to different wavelength ranges, thereby improving absorption rate consistency without excessive structural complexity
2Manufacturing precision
If a two-layer photoelectric conversion structure is implemented, then absorption rate consistency across wavelengths is improved, but the device structure becomes more complex
Solution Approach 1:
Both the first and second photoelectric conversion devices are integrated within a single substrate and share common structural elements including the light receiving surface, substrate infrastructure, and readout circuitry. This merging approach allows the multi-layer structure to achieve improved absorption rate consistency while avoiding the full complexity of completely separate devices, as many components are shared across both layers
3Area of stationary object
If photoelectric conversion devices are placed close to each other, then the device area is reduced, but electrical isolation between devices becomes difficult to achieve
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the first and second photoelectric conversion devices. This dielectric barrier provides effective electrical isolation, preventing charge carrier diffusion and leakage between the closely spaced devices. The insulating film acts as a mediator that enables the devices to be positioned close together for area efficiency while maintaining the necessary electrical isolation for reliable operation
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 configuration results in a more consistent absorption rate across a broader spectrum, improving image quality by enhancing the detection of various wavelengths, thereby producing vivid colors and better digital image representation.
Implementation Method 1
a photoelectron barrier, which may be an optically transparent electrically insulating material
Implementation Method 2
Each of the plurality of pixels includes a photoelectric conversion element... converts optical signals to digital signals
Implementation Method 3
MOS transistors may be utilized to transfer photoelectrons generated within the first and second photoelectric conversion devices to a floating diffusion region
Implementation Method 4
A reflection film may also be provided on a surface of the substrate extending opposite the light receiving surface
Data Source
AI summary
Image sensors include a second photoelectric conversion device disposed in a lower portion of a substrate and a first photoelectric conversion device extending between the secondary photoelectric conversion device and a light receiving surface of the substrate. Electrical isolation between the first and second photoelectric conversion devices is provided by a photoelectron barrier, which may be an optically transparent electrically insulating material. MOS transistors may be utilized to transfer photoelectrons generated within the first and second photoelectric conversion devices to a floating diffusion region within the image sensor. These transistors may represent one example of means for transferring photoelectrons generated in the first and second photoelectric conversion devices to a floating diffusion region in the substrate, in response to first and second gating signals, respectively. The first and second gating signals may be active during non-overlapping time intervals.