SPAD Image Sensor Vertical Junction Guard Ring
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Solution Overview
Problem
Existing planar SPAD image sensors face challenges with low fill factor, spectral response, and timing jitter due to the large area consumption by guard rings and unpredictable light absorption depths, which limit their detection efficiency and accuracy.
Innovation Solution
A SPAD image sensor with a vertical p-n junction structure and a modified guard ring design, featuring a substrate with p-type epitaxial layers and deep trench isolation, provides a uniform electric field and increased fill factor, enhancing detection efficiency and reducing timing jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a planar SPAD image sensor uses traditional guard ring design, then device reliability is improved, but fill factor deteriorates due to large area consumption
Solution Approach 1:
The patent transitions from a planar guard ring structure to a vertical p-n junction structure with deep trench isolation. This dimensional change allows the guard ring function to be implemented in the depth direction rather than consuming lateral area, thereby maintaining reliability while significantly improving fill factor.
Solution Approach 2:
The patent segments the sensor structure into distinct vertical layers including p-type epitaxial layers, n-type drift region, and deep trench isolation regions. This segmentation allows independent optimization of each component's function, enabling the guard ring to provide reliability without lateral area consumption.
2Ease of manufacture
If planar SPAD image sensor uses traditional structure, then manufacturing simplicity is maintained, but spectral response deteriorates due to unpredictable light absorption depths
Solution Approach 1:
The patent changes the structural parameters by introducing vertical p-n junctions and deep trench isolation at controlled depths. This allows precise control over light absorption depth and electric field distribution, improving spectral response while maintaining manufacturing feasibility through standard semiconductor processing techniques.
Solution Approach 2:
The patent implements local quality variations through differently doped epitaxial layers and strategically positioned deep trench isolation. This creates localized regions with optimized properties for specific functions, improving spectral response without complicating the overall manufacturing process.
3Device complexity
If planar SPAD image sensor is used, then device complexity is reduced, but timing jitter increases due to unpredictable light absorption
Solution Approach 1:
The patent uses vertical p-n junctions to create a controlled electric field in the depth direction. This dimensional change ensures that all photons are accelerated along a predictable path, reducing timing jitter without significantly increasing device complexity.
Solution Approach 2:
The patent creates equipotential regions through the vertical p-n junction structure and deep trench isolation, ensuring uniform electric field distribution. This equipotential design ensures consistent carrier acceleration and reduces timing variations, maintaining relatively simple device architecture.
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 vertical p-n junction structure and modified guard ring design improve the fill factor, spectral response, and timing jitter of the SPAD image sensor, enabling more efficient detection of low-intensity radiation with reduced area consumption and improved accuracy.
Implementation Method 1
provides a uniform electric field and increased fill factor, enhancing detection efficiency and reducing timing jitter
Implementation Method 2
An avalanche process can be triggered when a reverse biased p-n junction receives additional carriers, such as carriers generated by incident radiation. For example, in order to detect radiations with low intensities, the p-n junction is biased above its breakdown voltage, thereby allowing a single photon-generated carrier to trigger an avalanche current that can be detected
Implementation Method 3
allowing a single photon-generated carrier to trigger an avalanche current
Data Source
AI summary
A single photon avalanche diode (SPAT) image sensor is disclosed. The SPAT) image sensor include: a substrate of a first conductivity type, the substrate having a front surface and a back surface; a deep trench isolation (DTI) extending from the front surface toward the back surface of the substrate, the DTI having a first surface and a second surface opposite to the first surface, the first surface being level with the front surface of the substrate; an epitaxial layer of a second conductivity type opposite to the first conductivity type, the epitaxial layer surrounding sidewalls and the second surface of the DTI; and an implant region of the first conductivity type extending from the front surface to the back surface of the substrate. An associated method for fabricating the SPAD image sensor is also disclosed.