Image Sensor Absorption Enhancement Layer for High Wavelength Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face challenges with low sensitivity to high wavelength radiation, particularly outdoors due to noise from solar irradiance and a large energy bandgap of monocrystalline silicon, leading to poor quantum efficiency for wavelengths above 900 nanometers.
Innovation Solution
An image sensor with an absorption enhancement semiconductor layer having a lower energy bandgap than the front-side semiconductor layer, stacked between the front-side and back-side semiconductor layers, enhances radiation absorption by increasing the absorption coefficient, allowing for high quantum efficiency even at high wavelengths without increasing substrate thickness or incurring high costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If monocrystalline silicon is used as the semiconductor material, then the manufacturing cost is low and the device structure is simple, but the energy bandgap is large leading to poor sensitivity to high wavelength radiation
Solution Approach 1:
The patent employs a composite semiconductor structure consisting of a first semiconductor layer (monocrystalline silicon for low cost), a second semiconductor layer (germanium or silicon germanium for high absorption coefficient), and a third semiconductor layer (monocrystalline silicon for charge collection). This composite structure combines the advantages of different materials to achieve both cost-effectiveness and high quantum efficiency for high wavelength radiation detection.
2Reliability
If the substrate thickness is increased to improve radiation absorption, then the quantum efficiency for high wavelengths improves, but the die size increases and manufacturing cost increases
Solution Approach 1:
The patent applies local quality by creating a specialized second semiconductor layer with high absorption coefficient specifically positioned between the front and back surfaces. This localized enhancement of absorption properties in a thin intermediate layer achieves high quantum efficiency without requiring uniform thickening of the entire substrate, thus maintaining compact die size.
Solution Approach 2:
Instead of increasing absorption by extending in one dimension (thickness), the patent introduces a new dimensional approach by stacking multiple semiconductor layers with different optical properties. The second semiconductor layer provides enhanced absorption in a thin form factor, achieving high quantum efficiency without proportionally increasing the overall device thickness or die size.
3Reliability
If the substrate thickness is increased to improve radiation absorption, then the quantum efficiency for high wavelengths improves, but the manufacturing cost increases
Solution Approach 1:
The patent uses a composite semiconductor structure where a thin second semiconductor layer of germanium or silicon germanium is integrated between monocrystalline silicon layers. This composite approach achieves high quantum efficiency for high wavelength radiation without requiring expensive thick substrate processing, thereby maintaining cost-effectiveness while improving performance.
4Reliability
If a semiconductor layer with lower energy bandgap is introduced to enhance absorption, then the quantum efficiency for high wavelengths improves, but the device structure becomes more complex
Solution Approach 1:
The patent segments the semiconductor structure into three distinct functional layers: a first layer for charge collection, a second layer for enhanced absorption, and a third layer for additional charge collection. This segmentation allows each layer to be optimized for its specific function while maintaining a relatively simple overall structure that can be integrated into existing CMOS fabrication processes.
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
The solution enables the CMOS image sensor to effectively absorb and detect high wavelength radiation, including wavelengths up to 1375 nanometers, while maintaining low costs and minimizing die size and crosstalk.
Implementation Method 1
the absorption enhancement semiconductor layer has an energy bandgap less than that of the front-side semiconductor layer... enhances radiation absorption by increasing the absorption coefficient
Data Source
AI summary
An image sensor with an absorption enhancement semiconductor layer is provided. In some embodiments, the image sensor comprises a front-side semiconductor layer, an absorption enhancement semiconductor layer, and a back-side semiconductor layer that are stacked. The absorption enhancement semiconductor layer is stacked between the front-side and back-side semiconductor layers. The absorption enhancement semiconductor layer has an energy bandgap less than that of the front-side semiconductor layer. Further, the image sensor comprises a plurality of protrusions and a photodetector. The protrusions are defined by the back-side semiconductor layer, and the photodetector is defined by the front-side semiconductor layer, the absorption enhancement semiconductor layer, and the back-side semiconductor layer.