Concave Reflective Shield for Image Sensor Quantum Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in semiconductor image sensors is to maintain high image quality with decreasing pixel size, particularly for long-wavelength light, where the absorption depth is insufficient, especially in backside illumination technology, leading to reduced quantum efficiency and sensitivity.
Innovation Solution
Incorporating a reflective layer above the photodiode, either flat or concave, to redirect and absorb light that has not been initially absorbed, thereby increasing the absorption depth and quantum efficiency by reflecting non-absorbed photons back onto the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to achieve higher resolution, then image sensor resolution is improved, but absorption depth for long-wavelength light becomes insufficient
Solution Approach 1:
The patent introduces a vertical reflective layer structure above the photodiode to extend the light absorption path in the vertical dimension. This allows photons to be reflected back through the photodiode multiple times, effectively increasing absorption depth without increasing horizontal pixel size, thus resolving the contradiction between high resolution and sufficient absorption depth.
Solution Approach 2:
The reflective layer acts as an intermediary element between incident light and the photodiode. It redirects non-absorbed photons back onto the photodiode surface, enabling multiple absorption opportunities and effectively increasing the absorption depth for long-wavelength light without requiring larger pixel dimensions.
2Measurement precision
If pixel size is decreased to achieve higher resolution, then image sensor resolution is improved, but quantum efficiency decreases
Solution Approach 1:
The reflective layer serves as an intermediary that redirects non-absorbed photons back onto the photodiode, giving them multiple chances to be absorbed. This maintains high quantum efficiency even as pixel size decreases, resolving the contradiction between resolution and quantum efficiency.
Solution Approach 2:
The reflective layer enables continuous interaction between photons and the photodiode by reflecting non-absorbed photons back for additional absorption attempts. This continuous useful action maintains high quantum efficiency despite reduced pixel size, allowing higher resolution without sacrificing detection efficiency.
3Reliability
If flat reflective layer is used to increase absorption depth, then quantum efficiency is improved, but light redirection efficiency is insufficient
Solution Approach 1:
The patent employs a concave reflective layer with a curved surface that focuses reflected light back onto the photodiode surface. This curvature improves light redirection efficiency compared to flat layers, ensuring that reflected photons are more effectively directed back onto the active area, thereby enhancing quantum efficiency while remaining manufacturable.
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 reflective layer effectively doubles or more than doubles the absorption depth for long-wavelength light, enhancing the quantum efficiency and image quality by ensuring that more photons are absorbed, even at smaller pixel sizes.
Implementation Method 1
Incorporating a reflective layer above the photodiode, either flat or concave, to redirect and absorb light that has not been initially absorbed, thereby increasing the absorption depth and quantum efficiency by reflecting non-absorbed photons back onto the photodiode
Data Source
AI summary
A method of forming an image sensor device where the method includes forming a first dielectric layer on a substrate. The method further includes patterning the first dielectric layer to define an area for a reflective shield, where the area defined for the reflective shield is above a photodiode. Additionally, the method includes forming the reflective shield on the substrate by filling the defined area with a high reflectivity material, and the high reflective material comprises a polymer.