Backside High-Absorption Image Sensor for Infrared Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors have a low absorption coefficient for high wavelength radiation due to the large energy bandgap of monocrystalline silicon, leading to poor quantum efficiency, and increasing the depth of photodetectors in the semiconductor substrate is difficult and costly, while also increasing crosstalk and die size.
Innovation Solution
A high absorption image sensor is developed with a non-porous semiconductor layer on the front side and a porous semiconductor layer with a periodic structure on the back side, featuring a high absorption layer with a low energy bandgap, which enhances radiation absorption and quantum efficiency without increasing substrate thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the depth of photodetectors in the semiconductor substrate is increased to improve quantum efficiency for high wavelength radiation, then quantum efficiency is improved, but manufacturing difficulty and cost increase, and crosstalk and die size increase
Solution Approach 1:
The patent introduces a porous semiconductor layer with periodic structure on the back side of the substrate. This porous structure increases the effective surface area and light-trapping capability, enabling high quantum efficiency for high wavelength radiation without increasing the physical substrate thickness. The porosity allows photons to interact with the photodetector over a longer path length while maintaining a compact device form factor.
Solution Approach 2:
The patent creates a composite structure combining a non-porous semiconductor layer on the front side with a porous semiconductor layer on the back side. This composite material approach allows the device to benefit from both the structural integrity of non-porous material and the enhanced light absorption of porous material, achieving high quantum efficiency without the drawbacks of simply increasing substrate thickness.
2Loss of energy
If a thick semiconductor substrate is used to enhance radiation absorption, then absorption efficiency is improved, but manufacturing cost and die size increase
Solution Approach 1:
The porous semiconductor layer provides enhanced radiation absorption through its increased surface area and light-trapping periodic structure. This allows thin substrate fabrication that is easier and less costly to manufacture while achieving the same or better absorption efficiency that would require a much thicker substrate, thereby reducing manufacturing cost and die size.
Solution Approach 2:
Instead of increasing absorption efficiency by adding thickness in the vertical dimension, the patent introduces porosity and periodic structures that create additional absorption paths in the lateral dimension. This dimensional transformation allows efficient radiation absorption in a thin substrate, avoiding the cost and complexity associated with thick substrate manufacturing.
3Reliability
If a thick semiconductor substrate is used to improve quantum efficiency, then quantum efficiency is improved, but crosstalk between adjacent pixels increases
Solution Approach 1:
The porous semiconductor layer with periodic structure enhances quantum efficiency through increased light-trapping and absorption paths within a thin substrate. Because the substrate remains thin, the vertical distance for charge carrier diffusion between adjacent pixels is limited, thereby reducing crosstalk while maintaining high quantum efficiency through the enhanced optical interaction provided by the porous 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
The solution achieves high quantum efficiency for high wavelength radiation, such as infrared, while maintaining low cost, die size, and crosstalk, allowing effective sensing without the need for a thick semiconductor substrate.
Implementation Method 1
A high absorption layer lines the periodic structure on the back side of the semiconductor substrate. The high absorption layer is a semiconductor material with an energy bandgap less than that of the non-porous semiconductor layer.
Implementation Method 2
A photodetector is in the semiconductor substrate and the high absorption layer
Data Source
AI summary
An image sensor with high quantum efficiency is provided. In some embodiments, a semiconductor substrate includes a non-porous semiconductor layer along a front side of the semiconductor substrate. A periodic structure is along a back side of the semiconductor substrate. A high absorption layer lines the periodic structure on the back side of the semiconductor substrate. The high absorption layer is a semiconductor material with an energy bandgap less than that of the non-porous semiconductor layer. A photodetector is in the semiconductor substrate and the high absorption layer. A method for manufacturing the image sensor is also provided.