SPAD Array Crosstalk Reduction via Deep Groove Isolation
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Solution Overview
Problem
Current single-photon avalanche diode (SPAD) arrays suffer from optical crosstalk, where crosstalk photons excite SPAD units without incident photons, leading to increased measurement errors and incorrect signal calculations.
Innovation Solution
The proposed solution involves a single photon avalanche diode array design that includes at least two SPAD units, micro lenses for focusing incident light, front metal wiring layers, a back metal grid, dielectric layers to reduce reflection, deep groove separation columns to isolate adjacent SPAD units, and a metal filling structure to suppress self-excited photons from entering adjacent units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a back metal grid is used to connect SPAD units to external electrodes, then electrical connectivity is improved, but self-excited photons can enter adjacent SPAD units through grid gaps causing optical crosstalk
Solution Approach 1:
A dielectric layer is introduced as an intermediary substance between the back metal grid and the SPAD units. This dielectric layer fills the gaps in the metal grid structure, preventing self-excited photons from traveling through the grid gaps to adjacent SPAD units, while still allowing electrical connectivity to be maintained through the grid structure.
Solution Approach 2:
The back metal grid is designed with a grid pattern that inherently contains gaps or pores. These gaps are then filled with dielectric material to create a composite structure that maintains electrical connectivity through the metal paths while blocking optical crosstalk through the dielectric-filled gaps.
2Object-affected harmful factors
If deep groove separation columns are added to separate adjacent SPAD units, then optical crosstalk is reduced, but device complexity increases
Solution Approach 1:
The device structure is segmented into distinct regions by introducing deep groove separation columns between adjacent SPAD units. These columns physically divide the device into isolated segments, preventing optical crosstalk between units while maintaining the overall array structure. The segmentation is achieved through vertical grooves that extend into the substrate.
Solution Approach 2:
The separation structure extends in the vertical dimension (depth) rather than only in the horizontal plane. By creating deep grooves that extend vertically into the substrate, the solution addresses optical crosstalk through a three-dimensional approach, adding depth as an additional dimension for isolation rather than relying solely on horizontal spacing.
3Measurement precision
If micro lenses are used to focus incident light onto SPAD units, then detection sensitivity is improved, but reflection of incident light increases
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the micro lens and the SPAD unit. This dielectric layer serves as an anti-reflection coating that reduces the reflection of incident light at the interface, allowing more light to be transmitted to the SPAD unit while the micro lens continues to focus the light effectively.
Solution Approach 2:
The optical parameters at the interface between the micro lens and the SPAD unit are changed by introducing a dielectric layer with specific refractive index properties. This changes the reflection and transmission characteristics of the interface, reducing reflection losses and improving light coupling efficiency while maintaining the focusing capability of the micro lens.
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 reduces the probability of photon crosstalk and optical crosstalk by isolating self-excited photons, thereby improving the accuracy of signal detection and reducing measurement errors.
Implementation Method 1
at least two micro lenses, corresponding to the at least two SPAD units respectively, and the micro lenses are used to focus incident light onto the corresponding SPAD units
Implementation Method 2
a first dielectric layer disposed between the micro lens and the SPAD unit and used to reduce reflection of the incident light
Implementation Method 3
Single photon avalanche diode (SPAD) arrays have been widely used in laser detection and ranging systems (LiDAR)... due to their high sensitivity detection capability for intensities as low as single photons
Implementation Method 4
a deep groove separation column provided between adjacent SPAD units and used to separate the adjacent SPAD units
Implementation Method 5
a metal filling structure arranged between the deep groove separation column and the back metal grid and used to suppress self-excited photons generated by the SPAD units excited by the incident light from entering adjacent SPAD units through a grid gap
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A single-photon avalanche diode array, a receiving sensor and a LiDAR are provided, wherein at least two SPAD units are arranged in an array, a micro lens converges the incident light onto the corresponding SPAD unit, a back metal grid connects the SPAD unit with the corresponding external electrode, a first dielectric layer is arranged between the micro lens and the SPAD unit, a second dielectric layer is arranged between the SPAD unit and a front metal wiring layer, and the front metal wiring layer is electrically connected to the corresponding SPAD unit through a contact metal wire. By arranging deep groove separation columns between adjacent SPAD units, thereby reducing the probability of photon crosstalk and reducing the optical crosstalk of the device.