SPAD Trench Isolation and Light Scattering for Crosstalk Control
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Solution Overview
Problem
Conventional image sensors face limitations in determining object distance and have lower than desired image quality and resolution, which can be improved by incorporating single-photon avalanche diodes (SPADs) for enhanced light sensitivity and depth sensing capabilities.
Innovation Solution
The implementation of SPADs in imaging systems, including passive and active quenching circuitry, readout circuitry for photon counting and time-of-flight measurement, and the use of silicon photomultipliers to increase dynamic range and resolution, along with light scattering structures and isolation structures to enhance light absorption and prevent crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional image sensors are used, then manufacturing is simpler, but image quality and resolution are lower than desired
Solution Approach 1:
The sensor is divided into multiple pixel types within the same array: first pixels with first photodiodes for standard imaging, and second pixels with second photodiodes for enhanced sensitivity. This segmentation allows different regions to serve different functions, improving overall image quality while maintaining a manageable device structure through systematic organization of diverse pixel elements.
2Measurement precision
If single-photon avalanche diodes are used to improve light sensitivity, then detection capability increases, but device complexity increases
Solution Approach 1:
Multiple functional elements are merged into a single integrated sensor array: standard photodiodes for imaging, SPAD photodiodes for single-photon detection, shared readout circuitry, and combined data processing pathways. This merging approach enables the system to achieve high light sensitivity through SPADs while avoiding excessive complexity by consolidating functions rather than implementing separate independent systems.
3Adaptability or versatility
If multiple photodiode types are used in the same array, then functionality is improved, but crosstalk between pixels increases
Solution Approach 1:
Different photodiode types are strategically positioned within the array with specific spatial relationships: first photodiodes in first regions, second photodiodes in second regions, with isolation structures placed between them. This local differentiation and strategic positioning allows the system to maintain diverse detection capabilities while minimizing crosstalk by creating localized zones with optimized properties and using isolation structures at critical interfaces between different pixel types.
4Measurement precision
If semiconductor substrate thickness is increased to maintain sensitivity, then detection performance improves, but manufacturing complexity increases
Solution Approach 1:
Instead of increasing substrate thickness to maintain sensitivity, the invention changes other critical parameters: using SPAD photodiodes with optimized depletion regions, implementing specific isolation structure depths and configurations, and adjusting well depths and doping profiles. These parameter optimizations allow the system to maintain high detection sensitivity with a standard substrate thickness, avoiding the manufacturing complexity associated with thick substrates while preserving excellent light detection capability.
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 approach enables effective detection of low light levels, improved image quality, and accurate depth sensing, increasing the dynamic range and resolution of imaging systems while maintaining sensitivity without increasing semiconductor substrate thickness.
Implementation Method 1
single-photon avalanche diodes (SPADs) for single photon detection
Implementation Method 2
light scattering structures and isolation structures to enhance light absorption
Implementation Method 3
outer isolation structure that absorbs light and an inner front side deep trench isolation (FDTI) structure that reflects light
Implementation Method 4
inner front side deep trench isolation (FDTI) structure that reflects light
Data Source
AI summary
An imaging device may include single-photon avalanche diodes (SPADs). To improve the sensitivity and signal-to-noise ratio of the SPADs, light scattering structures may be formed in the semiconductor substrate to increase the path length of incident light through the semiconductor substrate. To mitigate crosstalk, multiple rings of isolation structures may be formed around the SPAD. An outer deep trench isolation structure may include a metal filler such as tungsten and may be configured to absorb light. The outer deep trench isolation structure therefore prevents crosstalk between adjacent SPADs. Additionally, one or more inner deep trench isolation structures may be included. The inner deep trench isolation structures may include a low-index filler to reflect light and keep incident light in the active area of the SPAD.