Backside Illuminated NIR Pixels with Buried Reflector
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing image sensors have limited infrared imaging capability due to low absorption of near-infrared light in silicon substrates, leading to pixel crosstalk and lower image sharpness when capturing NIR images.
Innovation Solution
The use of backside illuminated near infrared image pixels formed in a graded n-type epitaxial substrate with deep trench isolation and a buried metal reflector to enhance photon absorption and reduce crosstalk, allowing for improved charge collection and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If typical image pixels are formed in a silicon substrate, then visible light imaging is achieved, but near-infrared light absorption is limited leading to pixel crosstalk
Solution Approach 1:
The patent inverts the traditional front-side illumination approach by implementing backside illumination. The substrate is thinned and processed from the backside, allowing NIR photons to enter directly through the backside surface without passing through front-side structures. This inversion enables much deeper photon penetration and absorption in the silicon substrate, significantly improving NIR imaging capability while reducing pixel crosstalk through proper isolation structure design.
Solution Approach 2:
The patent extends the light absorption path by utilizing the depth dimension of the substrate. By thinning the substrate from 50-100 micrometers to 10-20 micrometers and processing from the backside, NIR photons can penetrate deeper into the substrate along the vertical dimension, increasing absorption probability. The isolation structures extend vertically to contain carrier generation within specific pixel regions, addressing crosstalk in the depth dimension.
2Use of energy by moving object
If NIR photons penetrate deeper into silicon substrate, then more NIR light is absorbed, but pixel crosstalk increases resulting in lower image sharpness
Solution Approach 1:
The patent segments the substrate into isolated pixel regions using deep trench isolation structures. These trenches, filled with dielectric material or air gaps, physically separate adjacent pixels vertically and laterally. This segmentation prevents carrier diffusion between pixels even when NIR photons penetrate deeply, maintaining image sharpness while allowing enhanced NIR absorption within each isolated pixel region.
Solution Approach 2:
The patent introduces intermediary isolation structures (deep trenches filled with dielectric material or air gaps) between pixels. These intermediary elements act as barriers to carrier diffusion while being transparent or non-absorbing to NIR photons. The isolation structures mediate between the need for deep photon penetration and the need to prevent crosstalk, allowing both objectives to be achieved simultaneously.
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 configuration significantly enhances the absorption of near-infrared light, reducing pixel crosstalk and improving image sharpness, enabling more effective capture of infrared images.
Implementation Method 1
Each pixel typically includes a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals
Implementation Method 2
The use of backside illuminated near infrared image pixels formed in a graded n-type epitaxial substrate with deep trench isolation and a buried metal reflector to enhance photon absorption
Implementation Method 3
The use of backside illuminated near infrared image pixels formed in a graded n-type epitaxial substrate with deep trench isolation and a buried metal reflector to enhance photon absorption
Data Source
AI summary
An imaging system may include an image sensor having backside illuminated near infrared image sensor pixels. Each pixel may be formed in a graded epitaxial substrate layer such as a graded n-type epitaxial layer. Each pixel may be separated from an adjacent pixel by an isolation trench formed in the graded epitaxial layer. The isolation trench may be a continuous isolation trench or may be formed from a combined front side isolation trench and backside isolation trench that are separated by a wall structure. A buried front side reflector may be provided that reflects light such as infrared light that has passed through a pixel back into the pixel, thereby effectively doubling the silicon absorption depth of the pixels.