Pixel Array Air Gap Reflectors for BSI Quantum Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Back side illumination (BSI) image sensors face reduced quantum efficiency due to photons refracting, diffusing, or scattering through the bottom surface of photodiodes, which decreases the absorption of incident light.
Innovation Solution
Incorporating air gap reflection structures, such as holes or trenches, under the photodiodes to reflect photons back into the photodiode, increasing the absorption of incident light by lowering the critical angle for total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If BSI image sensor fabrication is used, then manufacturing cost and integration are improved, but quantum efficiency is reduced due to photon refraction and scattering through the bottom surface
Solution Approach 1:
The patent converts the harmful refraction and scattering of photons through the bottom surface into a beneficial effect by introducing air gap reflection structures. These structures cause total internal reflection of photons that would otherwise be lost, turning the problematic optical path into a useful mechanism for increasing photon absorption and quantum efficiency
Solution Approach 2:
The air gap reflection structures serve as an intermediary element between the photodiode bottom surface and the substrate. This intermediary layer with different refractive index creates the conditions for total internal reflection, mediating the optical interaction to improve photon capture without changing the fundamental BSI architecture
2Reliability
If air gap reflection structures are added under photodiodes, then quantum efficiency is improved by reflecting photons back, but device complexity increases
Solution Approach 1:
The patent changes the refractive index parameter by introducing air gaps (refractive index ≈1.0) between the photodiode and substrate. This parameter change creates the optical conditions for total internal reflection, improving quantum efficiency through a fundamental physical property modification rather than complex structural additions
3Reliability
If air gap reflection structures are incorporated, then photon absorption is increased, but manufacturing precision requirements increase
Solution Approach 1:
The air gap reflection structures utilize the natural refractive index difference between air and semiconductor materials to achieve total internal reflection. The structure serves itself by leveraging fundamental optical principles rather than requiring precisely engineered reflective surfaces or complex coatings, reducing manufacturing precision requirements
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 approach enhances the quantum efficiency of the pixel sensor by increasing the number of photons absorbed and reducing resistive-capacitive (RC) delay.
Implementation Method 1
reflect photons back into the photodiode, increasing the absorption of incident light by lowering the critical angle for total internal reflection
Data Source
AI summary
A pixel array may include air gap reflection structures under a photodiode of a pixel sensor to reflect photons that would otherwise partially refract or scatter through a bottom surface of a photodiode. The air gap reflection structures may reflect photons upward toward the photodiode so that the photons may be absorbed by the photodiode. This may increase the quantity of photons absorbed by the photodiode, which may increase the quantum efficiency of the pixel sensor and the pixel array.