Convex Photodiode Array Structure for Crosstalk Isolation
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Solution Overview
Problem
Conventional photodiode arrays suffer from crosstalk due to charge carrier diffusion, leading to reduced modulation transfer function (MTF) and quantum yield, especially in high-density arrays, and existing solutions like vertical p-n junctions or mesa-shaped photodiodes either fail to effectively isolate photodiodes or compromise quantum yield.
Innovation Solution
The array architecture features photodiodes with convex-shaped absorption regions that are physically separated, each having a coverage region with a higher bandgap energy to enhance radiation concentration and reduce crosstalk, improving quantum yield and MTF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar architecture is used, then manufacturing is simpler, but crosstalk increases due to charge carrier diffusion
Solution Approach 1:
The absorption region is given a convex (curved) shape instead of a flat planar structure. This curvature concentrates the incident radiation at the center of each photodiode and reduces the lateral diffusion path of charge carriers to neighboring photodiodes, thereby reducing crosstalk while maintaining manufacturing feasibility through standard epitaxial growth processes.
2Object-generated harmful factors
If the thickness of the absorption layer is reduced, then crosstalk is reduced, but quantum yield decreases
Solution Approach 1:
The convex shape of the absorption region increases the effective optical path length by curving the radiation path, allowing more interaction between photons and the absorption material without increasing the physical thickness. This maintains quantum yield while the separated absorption regions reduce crosstalk.
Solution Approach 2:
The absorption regions are physically separated from each other, creating isolated detection zones. This segmentation prevents charge carrier diffusion between adjacent photodiodes, reducing crosstalk while each region maintains its own quantum efficiency independently.
3Object-generated harmful factors
If mesa-shaped photodiodes with deep trenches are used, then charge carriers are confined and crosstalk is reduced, but quantum yield decreases and leakage currents increase
Solution Approach 1:
Instead of using deep trenches to confine charge carriers, the invention uses a convex curved shape of the absorption region itself. This provides natural confinement through geometry without the need for deep etching, avoiding the creation of leakage paths and maintaining high quantum yield.
Solution Approach 2:
The absorption regions are naturally segmented by spacing them apart, creating isolated detection zones without requiring deep separating trenches. This reduces crosstalk through physical separation while avoiding the harmful effects of deep etching such as increased leakage currents and reduced quantum yield.
4Illumination intensity
If a microlens array is deposited, then radiation concentration at pixel center is improved, but manufacturing complexity increases and diffraction limits MTF
Solution Approach 1:
The convex shape of the absorption region inherently concentrates radiation at its center through geometric focusing, eliminating the need for additional microlens structures. This achieves radiation concentration while avoiding the manufacturing complexity and diffraction limitations associated with microlens arrays.
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 design effectively isolates photodiodes, reducing crosstalk, increasing quantum yield, and allowing for higher operating temperatures while maintaining a high MTF.
Implementation Method 1
The absorption region is configured to absorb an incident radiation on the photodiode and to enable a diffusion of charge carriers
Implementation Method 2
the geometric shape of the active region of each photodiode enables a better concentration of the radiation at the centre of the pixel
Implementation Method 3
the absorption region is configured to absorb an incident radiation on the photodiode and to enable a diffusion of charge carriers
Data Source
AI summary
An array of at least two photodiodes, wherein each photodiode includes an absorption region and a capture region, the capture region including an electrically conductive pad, the absorption region being in contact with the capture region, the absorption region being configured to absorb an incident radiation on the photodiode and to enable a diffusion of charge carriers, in which each absorption region is separated from the other absorption regions, and wherein the absorption region of each photodiode has a convex shape towards the incident radiation.