Radial Trench SPAD Structure for Low-Crosstalk Small Pixels
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Solution Overview
Problem
Conventional single-photon avalanche diodes (SPADs) face challenges in achieving improved sensitivity, timing resolution, reduced optical and electrical crosstalk, noise, and pixel size, while maintaining enhanced breakdown probability and voltage.
Innovation Solution
The SPADs employ a radial configuration with deep trench anode and cathode structures of opposing polarities, extending into the semiconductor substrate, which induces a radial electric field and reduces crosstalk, noise, and pixel size, utilizing photolithographic processes and dopant-driven fabrication techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planar SPAD structures are used, then manufacturing is simpler, but sensitivity and timing resolution are limited
Solution Approach 1:
The patent transitions from a planar two-dimensional junction to a three-dimensional radial junction structure. The deep trench anode and cathode extend vertically into the substrate, creating a radial electric field configuration that increases the effective interaction volume with incident photons, thereby improving sensitivity and timing resolution without sacrificing manufacturability
Solution Approach 2:
The SPAD structure is segmented into distinct deep trench regions: a first deep trench anode structure and a second deep trench cathode structure, separated by a dielectric material. This segmentation creates isolated radial junctions that reduce optical crosstalk while maintaining individual photon detection capability, resolving the contradiction between improved sensitivity and structural complexity
2Area of moving object
If pixel size is reduced for miniaturization, then device density increases, but breakdown probability and voltage uniformity deteriorate
Solution Approach 1:
By extending the anode and cathode structures vertically into deep trenches rather than spreading them horizontally, the patent achieves miniaturization in the planar footprint while maintaining adequate breakdown probability through increased vertical interaction length. The radial field configuration ensures uniform breakdown characteristics even in reduced pixel dimensions
Solution Approach 2:
The patent nests the first deep trench anode structure within the second deep trench cathode structure (or vice versa), creating a concentric radial configuration. This nested arrangement maximizes the electric field utilization within a compact pixel area, maintaining breakdown probability and voltage uniformity while achieving pixel miniaturization
3Object-generated harmful factors
If deep trench structures are implemented, then optical and electrical crosstalk is reduced, but manufacturing complexity increases
Solution Approach 1:
A dielectric material is introduced as an intermediary between the first deep trench anode structure and the second deep trench cathode structure. This dielectric layer provides electrical isolation and optical isolation, effectively reducing crosstalk between adjacent pixels while allowing the deep trench structures to be manufactured using standard semiconductor fabrication processes
Solution Approach 2:
The patent applies different materials and doping configurations to specific local regions: the anode trench receives p-type doping, the cathode trench receives n-type doping, and the separating region receives dielectric material. This localized differentiation achieves crosstalk reduction through proper material placement rather than complex global structure design, simplifying manufacturing
4Reliability
If radial configuration with deep trenches is used, then fill factor and sensitivity improve, but device complexity increases
Solution Approach 1:
The radial configuration utilizes the vertical dimension by extending trenches deep into the substrate, allowing the active detection region to extend downward rather than outward. This increases the fill factor (ratio of active area to pixel area) without requiring larger lateral dimensions, and the radial symmetry simplifies the overall device architecture despite the three-dimensional structure
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 enhances sensitivity, timing resolution, and fill factor, while maintaining a uniform breakdown probability and reducing optical crosstalk, leading to improved performance and miniaturization capabilities.
Implementation Method 1
The SPADs employ a radial configuration with deep trench anode and cathode structures of opposing polarities, extending into the semiconductor substrate, which induces a radial electric field
Implementation Method 2
In operation, the SPAD is reverse-biased above its breakdown voltage which allows Geiger-mode operation. In a SPAD, the reverse bias is so high that impact ionization occurs which is able to cause an avalanche current to develop. For example, a photo-generated carrier is accelerated by the electric field in the device to a kinetic energy which overcomes the ionization energy of the bulk semiconductor material, knocking out electrons.
Implementation Method 3
A large avalanche of current carriers grows quickly and can be triggered from as few as a single photon-initiated carrier
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to single-photon avalanche diodes and methods of manufacture. The structure includes: a first deep trench structure in a semiconductor substrate having a conductive material and a material of a first polarity; a second deep trench structure in the semiconductor substrate surrounding the first deep trench structure, the second deep trench structure having a conductive material and a material of a second polarity; and contacts to both the first deep trench structure and the second deep trench structure.