SPAD Guard Ring Layout for High Fill Factor and Breakdown Control
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Solution Overview
Problem
Existing single photon avalanche diodes (SPADs) face challenges in achieving high fill factor and efficiency due to limitations in their design and structure, which affect their performance in applications such as image sensors and LiDAR devices.
Innovation Solution
The proposed SPAD design includes a first well with a specific conductivity type, a heavily doped region, a guard ring, and a second region configured to multiply charge carriers. The second region extends onto the boundary between the lower portion of the guard ring and the first well, and has an electric field of 3×10^5 V/cm or more, enhancing charge carrier multiplication and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the second region is extended onto the boundary between the lower portion of the guard ring and the first well, then charge carrier multiplication efficiency is improved, but device complexity increases
Solution Approach 1:
The second region is extended onto the boundary between the lower portion of the guard ring and the first well, utilizing the vertical dimension to create an additional avalanche multiplication zone. This dimensional extension allows charge carriers to undergo multiplication in a three-dimensional space, improving efficiency without requiring additional lateral components that would increase device complexity.
Solution Approach 2:
The second region is configured with a high electric field (3×10^5 V/cm or more) specifically at the boundary between the lower portion of the guard ring and the first well. This localized high electric field creates an optimal environment for charge carrier multiplication precisely where needed, while other regions maintain lower electric fields to prevent premature breakdown, thus improving efficiency without uniformly increasing device complexity throughout the entire structure.
2Productivity
If the electric field in the second region is increased to 3×10^5 V/cm or more, then charge carrier multiplication is enhanced, but premature breakdown phenomena occur
Solution Approach 1:
The patent implements a localized high electric field (3×10^5 V/cm or more) specifically in the second region at the boundary between the lower portion of the guard ring and the first well, while other regions maintain lower electric fields. This spatial differentiation allows charge carrier multiplication to occur efficiently in the high-field zone without causing premature breakdown in other parts of the device, thus resolving the contradiction between multiplication efficiency and breakdown resistance.
Solution Approach 2:
The device is segmented into multiple regions with different electric field characteristics: the second region with high electric field for charge carrier multiplication, and other regions with lower electric fields to prevent breakdown. This segmentation allows each region to perform its specific function optimally, with the high-field region enabling efficient multiplication while low-field regions maintain device reliability and prevent premature breakdown.
3Productivity
If the fill factor is increased, then light absorption efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The second region is extended onto the boundary between the lower portion of the guard ring and the first well, utilizing the vertical dimension to create additional light absorption and charge carrier multiplication space. This dimensional approach increases the effective fill factor and light absorption efficiency without requiring proportionally tighter lateral manufacturing tolerances, as the additional functional volume is achieved through vertical extension rather than lateral expansion.
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 improves the fill factor and light absorption efficiency of SPADs, leading to enhanced performance in image sensors and LiDAR devices by effectively multiplying charge carriers and reducing premature breakdown phenomena.
Implementation Method 1
the additional electron-hole pairs are generated in succession by the impact ionization by such accelerated electrons
Implementation Method 2
This process repeats the process leading to the avalanche multiplication of the photo-generated electrons and holes
Implementation Method 3
The high electric field accelerates the photo-generated electrons quickly toward an anode, and the additional electron-hole pairs are generated in succession by the impact ionization by such accelerated electrons
Implementation Method 4
a heavily doped region provided on the first well, a guard ring surrounding the heavily doped region, and a second region formed between the first well and the heavily doped region and configured to multiply charge carriers
Data Source
AI summary
Disclosed is a single photon avalanche diode comprises a first well having a first conductivity type, a heavily doped region provided on the first well, a guard ring surrounding the heavily doped region, and a second region formed between the first well and the heavily doped region and configured to multiply charge carriers. The heavily doped region and the guard ring have a second conductivity type different from the first conductivity type. The second region extends onto a boundary between a lower portion of the guard ring and the first well.