SPAD Image Sensor Trench Isolation Common Node Edge Breakdown
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Solution Overview
Problem
Existing SPAD image sensors face challenges in achieving high photodetective sensitivity and preventing edge breakdown, which limits their ability to detect low-intensity radiation effectively due to the need for a guard ring that consumes a large area, thereby reducing the fill factor.
Innovation Solution
The design replaces the guard ring with a strategically positioned common node and trench isolation structure, adjusting the position of the common node deep inside the substrate to prevent edge breakdown and enhance the electric field intensity at the photodetective portion, allowing for a smaller pixel area without sacrificing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guard ring is used to prevent edge breakdown, then reliability is improved, but area is consumed and fill factor deteriorates
Solution Approach 1:
The patent removes the guard ring structure from the SPAD device. Instead of using a guard ring to prevent edge breakdown, the invention relies on the intrinsic properties of the SPAD structure and optimized doping profiles to achieve edge breakdown prevention without the additional area-consuming guard ring structure.
Solution Approach 2:
The patent implements localized doping profile optimization in specific regions of the SPAD structure. By adjusting dopant concentrations and distributions in the depletion region and surrounding areas, the device achieves enhanced electric field control and edge breakdown prevention in critical locations without requiring a guard ring across the entire structure.
2Use of energy by moving object
If the common node is positioned deep inside the substrate, then electric field intensity at photodetective portion is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes the depth position of the common node within the substrate and adjusts associated doping parameters to achieve the desired electric field intensity distribution. By carefully controlling the common node depth and doping profiles, the device maximizes photodetective sensitivity while maintaining compatibility with standard CMOS fabrication processes.
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 configuration improves the fill factor and ensures high photodetective sensitivity by effectively managing the electric field, reducing noise, and enabling efficient detection of low-intensity radiation without the need for a guard ring, thus enhancing the overall performance of the SPAD image sensor.
Implementation Method 1
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.
Data Source
AI summary
A single photon avalanche diode (SPAD) image sensor is disclosed. The SPAD image sensor includes: a substrate having a front surface and a back surface; a trench isolation in the substrate, the trench isolation extending from the front surface of the substrate toward the back surface of the substrate, the trench isolation having a first surface and a second surface opposite to the first surface, the first surface being coplanar with the front surface of the substrate, the second surface being distanced from the back surface of the substrate by a distance greater than 0; wherein the substrate includes: a first layer doped with dopants of a first conductivity type, the first layer extending from the back surface of the substrate toward the trench isolation and laterally surrounding at least a portion of sidewalls of the trench isolation.