Back-Illuminated SPAD Light Trapping for Higher Absorption
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Solution Overview
Problem
Conventional single-photon avalanche diodes (SPADs) suffer from low light absorption efficiency due to their planar structure, which limits their application in devices like lidar, where increased thickness is difficult to manufacture and reduces detection accuracy, and is sensitive to wavelength and temperature changes.
Innovation Solution
A back-side illuminated SPAD with a light-trapping structure and sidewall reflection walls, combined with an anti-reflection structure on the upper surface, extends the effective optical path and improves absorption efficiency without increasing the silicon layer thickness, and includes a diffraction grating structure to enhance reflection of specific wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the silicon layer thickness is increased to improve light absorption efficiency, then the absorption efficiency improves, but the manufacturing difficulty increases and detection accuracy decreases due to increased jitter time
Solution Approach 1:
The patent transforms the planar light absorption structure into a three-dimensional light-trapping structure with periodic variations. By introducing vertical and lateral dimensional changes through the light-trapping structure, the optical path length is extended without increasing the overall silicon layer thickness, thereby improving light absorption efficiency while maintaining manufacturing feasibility and minimizing jitter time increase.
2Reliability
If the silicon layer thickness is increased to improve light absorption efficiency, then the absorption efficiency improves, but the detection accuracy decreases due to increased jitter time
Solution Approach 1:
The light-trapping structure introduces three-dimensional geometric features that extend the optical path length within the same physical thickness. This dimensional transformation allows photons to interact with the silicon material for a longer effective distance without increasing the actual layer thickness, thereby improving absorption efficiency while minimizing the increase in jitter time and maintaining detection accuracy.
3Ease of manufacture
If a planar structure is used, then the manufacturing is simple, but the light absorption efficiency is low
Solution Approach 1:
The patent introduces periodic three-dimensional structures into the otherwise planar silicon layer. These light-trapping structures create vertical and lateral geometric variations that enhance light absorption through extended optical paths and multiple internal reflections, while the periodic nature of the structure allows for scalable manufacturing using standard semiconductor fabrication techniques.
Solution Approach 2:
The patent modifies the geometric parameters of the silicon layer by introducing periodic structures with specific dimensions, spacing, and depths. By optimizing these geometric parameters, the light absorption efficiency is enhanced while maintaining compatibility with existing manufacturing processes, thus resolving the contradiction between manufacturing simplicity and absorption efficiency.
4Ease of manufacture
If the circuit layer is placed above the detection layer (front-side illuminated), then the manufacturing is straightforward, but the light detection efficiency decreases due to absorption and scattering by metal wires and dielectric materials
Solution Approach 1:
The patent inverts the conventional front-side illuminated structure by placing the circuit layer below the detection layer, creating a back-side illuminated configuration. This inversion allows incident light to directly reach the silicon detection layer without passing through metal interconnects and dielectric materials, thereby eliminating absorption and scattering losses while maintaining manufacturing feasibility through adapted 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
Significantly improves light absorption efficiency across a wide wavelength range, reducing jitter time and manufacturing complexities, while maintaining high yield and cost-effectiveness, and enhancing detection accuracy and resolution in applications like lidar.
Implementation Method 1
incident light is reflected, scattered, and refracted by the light-trapping structure and then dispersed to various angles, and with the addition of the reflection effect of the sidewall reflection wall, the effective optical path of the light in the back-side illuminated single-photon avalanche diode can be extended
Implementation Method 2
incident light is reflected, scattered, and refracted by the light-trapping structure and then dispersed to various angles
Implementation Method 3
an anti-reflection structure on the upper surface, extends the effective optical path and improves absorption efficiency
Implementation Method 4
includes a diffraction grating structure to enhance reflection of specific wavelengths
Data Source
Figure 1~3
Figure 4
Figure 5~6
AI summary
A single-photon avalanche diode and a manufacturing method, a detector array, and an image sensor. The back-illuminated single-photon avalanche diode is provided with a light-trapping structure (1, 9, 20) and a reflecting side wall (206). Incident light is scattered to various angles after being reflected, scattered, and refracted by the light-trapping structure (1, 9, 20), furthermore, due to the reflecting effect of the reflecting side wall (206), the effective optical path length of light in the back-illuminated single-photon avalanche diode can be extended, thereby improving the absorption efficiency of light in the back-illuminated single-photon avalanche diode. A manufacturing method for the back-illuminated single-photon avalanche diode achieves the manufacture of the back-illuminated single-photon avalanche diode. In addition, for a photodetector array and an image sensor which include back-illuminated single-photon avalanche diodes, due to the presence of the back-illuminated single-photon avalanche diodes, the light absorption efficiencies of the photodetector array and the image sensor are effectively improved.