BSI Image Sensor Bragg Mirrors for Photon Recapture
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Solution Overview
Problem
Back side illuminated (BSI) image sensor devices face challenges in converting incident photons to electrical signals efficiently, leading to the need for long exposure times or large footprints under low radiation conditions due to escaped photons not being recaptured.
Innovation Solution
The formation of Bragg mirror micro-structures on radiation-sensing regions increases the optical path of incident radiation, enhancing photon recapture by using a stack of alternating high-refractive index and low-refractive index material layers, which reflects transmitted radiation back for recapture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If BSI image sensor devices are used to detect radiation from the back side of the substrate, then the sensor can sense incident radiation effectively, but photons escape without being recaptured leading to low conversion efficiency
Solution Approach 1:
The patent implements feedback by using Bragg mirror structures to reflect escaped photons back into the radiation-sensing regions. The mirrors are positioned to capture photons that would otherwise escape and redirect them back through the micro-lenses and color filters to the sensing regions, creating a feedback loop that recycles optical energy and improves conversion efficiency.
Solution Approach 2:
The patent introduces a new dimension by adding Bragg mirror structures at the back side of the substrate, creating a reflective path that extends the optical journey of photons. This dimensional addition allows photons to travel back through the existing optical components (micro-lenses and color filters) and sensing regions, effectively increasing the optical path length without expanding the device footprint.
2Reliability
If the sensor uses standard exposure times, then the device operates efficiently, but under low radiation conditions long exposure times are required due to poor photon recapture
Solution Approach 1:
The feedback mechanism through Bragg mirrors recycles photons that would otherwise be lost, effectively increasing the number of photons available for detection during each exposure period. This improves the signal strength in low radiation conditions, allowing for shorter exposure times while maintaining detection reliability.
Solution Approach 2:
The patent enables continuous useful action by ensuring that photons are not lost but continuously recycled through the Bragg mirror feedback path. This continuous recapture process maintains effective photon utilization throughout the exposure period, improving reliability in low radiation conditions without requiring extended exposure times.
3Loss of energy
If the sensor uses larger footprints, then more photons can be captured, but the device size increases which is not desirable
Solution Approach 1:
The patent solves this contradiction by adding a reflective dimension through Bragg mirrors at the back side of the substrate. This creates a feedback path that recycles photons without requiring additional sensor area, maintaining the same device footprint while improving photon capture efficiency through the extended optical path.
Solution Approach 2:
The patent recovers photons that would otherwise be discarded or lost from the system. The Bragg mirror structures capture escaped photons and redirect them back into the sensing regions, effectively recovering optical energy without requiring additional device area or footprint.
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 improves photon recapture and conversion efficiency, reducing the need for extended exposure times and larger footprints, enabling better performance under low radiation conditions.
Implementation Method 1
The formation of Bragg mirror micro-structures on radiation-sensing regions increases the optical path of incident radiation, enhancing photon recapture by using a stack of alternating high-refractive index and low-refractive index material layers, which reflects transmitted radiation back for recapture
Implementation Method 2
using a stack of alternating high-refractive index and low-refractive index material layers, which reflects transmitted radiation back for recapture
Implementation Method 3
These image sensors utilize an array of pixels that absorb (e.g., sense) the incident radiation and convert it into electrical signals
Data Source
AI summary
The present disclosure describes a method for the formation of mirror micro-structures on radiation-sensing regions of image sensor devices. The method includes forming an opening within a front side surface of a substrate; forming a conformal implant layer on bottom and sidewall surfaces of the opening; growing a first epitaxial layer on the bottom and the sidewall surfaces of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, where the second epitaxial layer forms a radiation-sensing region. The method further includes depositing a stack on exposed surfaces of the second epitaxial layer, where the stack includes alternating pairs of a high-refractive index material layer and a low-refractive index material layer.