Image Sensor Recess Structures for Infrared Light Trapping
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Solution Overview
Problem
Image sensors face a challenge with low Quantum Efficiency (QE) due to the long wavelength of infrared light, which causes significant portions of infrared light to pass through light-sensitive regions without being absorbed effectively.
Innovation Solution
The image sensor design includes a substrate with light-sensitive regions and transfer gates, featuring recess structures on the substrate surface that are covered by light-reflective layers with protrusion structures. These recess structures and light-reflective layers increase the light paths within the light-sensitive regions, enhancing light absorption and QE by reflecting infrared light back into the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the image sensor uses conventional flat structure, then the manufacturing process is simple, but the quantum efficiency is low due to long wavelength infrared light passing through without absorption
Solution Approach 1:
The patent applies curvature by forming recess structures with curved sidewalls and rounded bottoms in the substrate, rather than using flat surfaces. These curved structures increase the optical path length of infrared light passing through the substrate, enhancing absorption probability and quantum efficiency without significantly complicating the manufacturing process
Solution Approach 2:
The patent transitions from a two-dimensional flat substrate surface to a three-dimensional structured surface with recesses and protrusions. This dimensional change creates additional light-trapping opportunities and increases the effective absorption area, improving quantum efficiency while maintaining manufacturing feasibility through standard semiconductor processing techniques
2Reliability
If the image sensor increases light absorption opportunities, then quantum efficiency improves, but the device structure becomes more complex with additional layers and structures
Solution Approach 1:
The substrate itself is structured to provide the light-trapping function through formed recesses, eliminating the need for separate light-trapping layers or complex multi-layer structures. The substrate serves both its structural role and its optical function of enhancing light absorption, thereby improving quantum efficiency without proportionally increasing device complexity
Solution Approach 2:
The patent modifies the physical parameters of the substrate by creating recess structures with specific depths, widths, and spacing. These parameter changes optimize the optical path length and absorption characteristics for infrared wavelengths, improving quantum efficiency through geometric optimization rather than adding complex functional layers
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 significantly improves the Quantum Efficiency of the image sensor by increasing light absorption opportunities, allowing more infrared light to be captured and converted into electrical signals, thereby enhancing the sensor's performance.
Implementation Method 1
the at least one light-reflective layer has a plurality of protrusion structures towards the light-sensitive regions for reflecting incident light to the light-sensitive regions
Implementation Method 2
For converting various photo energy of the light into electrical signals, the image sensor includes pixels having photosensitive diodes
Data Source
AI summary
An image sensor and a method for fabricating the image sensor are provided. In the method for fabricating the image sensor, at first, a substrate having a first surface and a second surface opposite to the first surface is provided. Then, light-sensitive regions are formed in the substrate. Thereafter, transfer gate structures are formed on the first surface of the substrate. Then, the first surface of the substrate is formed to form recess structures on the light-sensitive regions. Thereafter, light-reflective layers are formed to cover the recess structures of the first surface of the substrate, in which the recess structures are filled with protrusion structures of the light-reflective layers. Further, the second surface of the substrate may be etched to form recess structures corresponding to the light-sensitive regions.