Photodetector Matrix Focusing Structures for Sensitivity
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Solution Overview
Problem
Photodetection devices with pixel matrices face challenges in maximizing sensitivity due to the geometry of photodiodes, where the absorption region extends within a central volume, limiting cross-talk and detection efficiency.
Innovation Solution
Incorporating focussing elements composed of refractive structures, such as truncated pyramids with specific angles and optical indices, to concentrate light radiation onto the absorption regions of photodiodes, thereby improving the capture efficiency and sensitivity by redirecting light to peripheral absorption areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the absorption region extends entirely within a volume surrounding a central region of the pixel, then cross-talk between photodiodes is reduced, but sensitivity and capture efficiency deteriorate
Solution Approach 1:
The patent introduces a vertical dimension by placing microlens arrays above the pixel matrix. These microlenses extend the light collection path in the vertical direction, focusing incident light onto the peripheral absorption regions. This dimensional addition allows light to be captured from above and directed to the absorption regions without requiring the absorption regions to occupy the central pixel area, thus maintaining low cross-talk while improving sensitivity
Solution Approach 2:
The microlens arrays serve as intermediary optical elements between the incident light and the photodiode absorption regions. These microlenses redirect and focus light paths, enabling light that would otherwise miss the peripheral absorption regions to be concentrated onto them. This intermediary structure resolves the contradiction by providing a mechanism to achieve both low cross-talk (through peripheral absorption) and high sensitivity (through focused light collection)
2Object-generated harmful factors
If the absorption region is positioned in a peripheral volume surrounding the central region, then cross-talk is minimized, but light capture efficiency worsens
Solution Approach 1:
By adding the vertical dimension with microlens structures, the patent enables light to be captured from the upper surface and focused downward onto the peripheral absorption regions. This allows the absorption regions to remain in peripheral positions (maintaining low cross-talk) while still receiving concentrated light energy (improving capture efficiency)
Solution Approach 2:
The microlens arrays perform preliminary light focusing and redirection before light reaches the photodiode absorption regions. By pre-concentrating light paths onto the peripheral absorption areas, the system achieves high capture efficiency without requiring the absorption regions to be centrally located, thus maintaining low cross-talk between adjacent pixels
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 enhances the capture efficiency of photodiodes by concentrating light energy within the absorption regions, ensuring that all incident photons can generate charge carriers, even when the central region is occupied by doped zones, thus improving the overall sensitivity of the photodetection device.
Implementation Method 1
Each of the angles φi at the base of the first pyramids and the second pyramids satisfies the following relation: sin(φi) ≤ n0/n1 × sin(θ) in which n0 is the optical index of a medium surrounding the refractive structures on the side opposite the photodiodes, and n1 is an optical index of said refractive structures
Data Source
AI summary
A photodetection device including a pixel matrix, each of the pixels including a photodiode, the absorption region of which extends entirely or almost entirely inside a volume surrounding a central region of the pixel; and a focusing element. An assembly of focusing elements is composed of refractive structures, each formed by a first truncated pyramid with a recess in the shape of a second inverted pyramid. The angles φi at the base of the pyramids satisfy the following relation:2*φi-sin-1(n0n1sin(φi))<π2wherein n0 is the optical index of a medium surrounding the refractive structures on the side opposite the photodiodes, and n1 is an optical index of the refractive structures.