Multi-Spectral Pixel Optics for Low-Light Signal and Cross-Talk Control
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Solution Overview
Problem
Image sensors face challenges in efficiently absorbing light, leading to low absorption efficiency and a degraded signal-to-noise ratio, especially when detecting low-intensity light, due to the inefficiency of photodiodes in converting photons to charge.
Innovation Solution
The image sensor incorporates a multi-spectral pixel cell design with a semiconductor substrate featuring first and second photodiodes, each with a dedicated optical structure that steers and refracts or diffracts light components based on their wavelengths, increasing the propagation path for in-band light and reducing out-of-band light absorption, using microlenses and filter layers to enhance absorption efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photodiodes are used to convert photons to charge, then light detection is enabled, but absorption efficiency is low and signal-to-noise ratio is degraded
Solution Approach 1:
The patent employs curved or sloped light transmission surfaces in the optical structures (e.g., protrusion structures with inclined surfaces) to increase the propagation path of light within the photodiode. This curvature-based design extends the distance light travels through the photosensitive material, improving absorption efficiency without requiring a larger photodiode area, thereby enhancing signal-to-noise ratio while maintaining compact pixel cell dimensions.
Solution Approach 2:
The patent introduces vertical protrusion structures that extend upward from the photodiode surface, creating a three-dimensional optical path. By adding this vertical dimension to light propagation, the effective absorption path length is increased without expanding the horizontal pixel area, thus improving absorption efficiency and signal quality while maintaining high spatial resolution.
2Adaptability or versatility
If multiple photodiodes are positioned adjacent to each other for multi-spectral detection, then spectral discrimination is enabled, but cross-talk between different spectral components increases
Solution Approach 1:
The patent divides the optical path for each photodiode by introducing dedicated optical structures (protrusion structures with light transmission surfaces) positioned over each photodiode. These segmented optical structures guide and confine light to specific photodiodes based on wavelength, reducing cross-talk between adjacent photodiodes while maintaining multi-spectral detection capability. Each optical structure acts as an independent light management unit for its associated photodiode.
Solution Approach 2:
The patent applies wavelength-specific optical properties to different optical structures, where each optical structure is optimized for a particular wavelength range. The protrusion structures have tailored geometries and materials that selectively transmit, refract, or reflect specific spectral components to their intended photodiodes, enabling spectral discrimination while minimizing cross-talk through localized optical optimization.
3Loss of energy
If optical structures are added to increase light propagation path, then absorption efficiency is improved, but device complexity increases
Solution Approach 1:
The patent integrates the optical structures (protrusion structures with light transmission surfaces) directly into the pixel cell fabrication process, combining multiple functions into unified structures. The optical elements are formed as part of the semiconductor device architecture rather than being separate components, reducing overall device complexity while achieving enhanced light absorption through increased propagation paths within the integrated structures.
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 design improves the absorption efficiency of in-band light components, reducing noise and enhancing the signal-to-noise ratio, thereby improving the performance of the image sensor in capturing low-intensity light and reducing cross-talk between different spectral components.
Implementation Method 1
The first optical structure is configured to: receive the first component of the light at a first angle with respect to the second axis, and steer the first component of the light at a second angle with respect to the second axis towards the first photodiode
Implementation Method 2
The second optical structure is configured to: receive the second component of the light at a third angle with respect to the second axis, and steer the second component of the light at a fourth angle with respect to the second axis towards the second photodiode
Implementation Method 3
the first photodiode being configured to convert a first component of light to a first charge
Implementation Method 4
the second photodiode being configured to convert a second component of the light to a second charge
Implementation Method 5
an optical element positioned over the first optical structure and the second optical structure along the second axis to receive the light and to project the light towards the first optical structure and the second optical structure
Data Source
AI summary
In some examples, an apparatus comprises: a first photodiode to sense a first component of light associated with a first wavelength, and a second photodiode configured to sense a second component of the light associated with a second wavelength, the first component and the second component being associated with, respectively, a first wavelength and a second wavelength. The apparatus further comprises a first optical structure and a second optical structure positioned over, respectively, the first photodiode and the second photodiode. The first optical structure is configured to increase a propagation path of the first component of the light within the first photodiode and has a first optical property based on the first wavelength. The second optical structure is configured to increase a propagation path of the second component of the light within the second photodiode, and has a second optical property based on the second wavelength.