Back-Side 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 requires increased thickness for improved absorption, leading to manufacturing difficulties, increased cost, and reduced accuracy in applications like lidar, while anti-reflection methods are ineffective at varying angles and wavelengths.
Innovation Solution
A back-side illuminated SPAD with a light-trapping structure and anti-reflection structure, including inverted pyramid structures and diffraction grating, is designed to extend the optical path and improve light absorption without increasing thickness, combined with a deep trench isolation structure to reduce crosstalk and enhance filling factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the SPAD is increased to improve light absorption efficiency, then the light absorption efficiency is improved, but the manufacturing difficulty increases and cost increases
Solution Approach 1:
The patent introduces light-trapping structures (such as textured surfaces, gratings, or reflective layers) that transform the light propagation from a simple vertical path to a multi-dimensional path with increased optical length. This allows achieving high light absorption efficiency without increasing the physical thickness of the SPAD, thus avoiding manufacturing difficulties associated with thick substrates.
Solution Approach 2:
The patent employs curved or non-planar light-trapping structures (such as spherical bumps, pyramidal textures, or sinusoidal gratings) on the SPAD surface. These curved structures extend the optical path length and enhance light coupling into the active region, improving absorption efficiency without requiring increased thickness, thereby maintaining ease of manufacture.
2Reliability
If the thickness of the SPAD is increased to improve light absorption efficiency, then the light absorption efficiency is improved, but the device complexity increases
Solution Approach 1:
By introducing light-trapping structures that operate in the optical dimension rather than the structural dimension, the patent achieves enhanced light absorption without adding structural complexity to the SPAD device. The light-trapping structures are integrated into the existing device architecture rather than requiring additional complex components.
3Reliability
If conventional anti-reflection methods are used, then the light absorption is improved at normal incidence, but the effectiveness decreases at varying angles and wavelengths
Solution Approach 1:
The patent employs light-trapping structures (such as broadband anti-reflection coatings, textured surfaces, or resonant gratings) that provide enhanced light absorption across a wide range of angles and wavelengths simultaneously. These structures create multiple optical paths and interfere constructively over broad spectral and angular ranges, making the SPAD effective for various imaging conditions without requiring angle-specific or wavelength-specific optimization.
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 solution significantly enhances light absorption efficiency across a wide wavelength range, improves imaging resolution, and reduces manufacturing complexity and cost, while maintaining high accuracy and tolerance to processing deviations and environmental changes.
Implementation Method 1
a light-trapping structure is disposed in the back-side illuminated single-photon avalanche diode
Implementation Method 2
a light-trapping structure is disposed in the back-side illuminated single-photon avalanche diode
Implementation Method 3
an anti-reflection structure is disposed on an upper surface of the back-side illuminated single-photon avalanche diode
Implementation Method 4
the film structure includes at least two types of films having different refractive indices
Implementation Method 5
the light-trapping structure and/or the anti-reflection structure are inverted pyramid structures
Implementation Method 6
the deep trench isolation structure performs back and forth reflections on an incoming light ray
Data Source
AI summary
A single-photon avalanche diode and a manufacturing method thereof, a detector array, and an image sensor are disclosed. The back-side illuminated single-photon avalanche diode is disposed with a light-trapping structure and a sidewall reflection wall. 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. The manufacturing method of a back-side illuminated single-photon avalanche diode achieves the manufacturing of the back-side illuminated single-photon avalanche diode. For the photoelectric detector array and the image sensor including the back-side illuminated single-photon avalanche diode, since they have the back side illumination single-photon avalanche diode, light absorption efficiencies of the photoelectric detector array and the image sensor are effectively improved.