Avalanche Photodiode Pixel Isolation for Crosstalk Reduction
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Solution Overview
Problem
Existing light receiving devices face challenges in increasing sensitivity while preventing crosstalk between adjacent avalanche photodiodes, which limits the ability to enhance the signal-to-noise ratio effectively.
Innovation Solution
The light receiving device incorporates a silicon substrate with two-dimensionally arranged pixel regions, each containing a photoelectric conversion element with a P+ type Si epitaxial layer surrounding the side and bottom surfaces of an N+ type Si epitaxial layer, along with a quenching resistor and electrode configuration that enhances light sensitivity and reduces crosstalk by optimizing the PN junction area and separation between adjacent elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the aperture ratio is increased to improve light receiving sensitivity, then light receiving sensitivity is improved, but crosstalk between adjacent APDs increases
Solution Approach 1:
The device is divided into multiple pixel regions with individual APDs, each surrounded by isolation structures. The quenching resistors are also segmented and positioned in specific regions to prevent signal interference between adjacent pixels while maintaining independent operation of each APD unit
Solution Approach 2:
Isolation structures including deep trenches and quenching resistors are introduced as intermediary elements between adjacent APDs. These intermediaries physically separate the APDs and absorb or redirect stray photons, preventing crosstalk while allowing each APD to maintain its full aperture for light reception
2Measurement precision
If the APD size is increased to improve light receiving sensitivity, then light receiving sensitivity is improved, but the signal-to-noise ratio deteriorates due to increased crosstalk
Solution Approach 1:
The pixel array is segmented into independent units with clear boundaries. Each APD is isolated by deep trenches and quenching resistors, allowing individual APDs to be sized optimally for sensitivity without compromising the overall signal-to-noise ratio through inter-pixel interference
Solution Approach 2:
The harmful crosstalk component is extracted and removed from the system by introducing isolation structures that physically separate adjacent APDs. This extraction of the harmful interaction allows each APD to operate independently, maintaining both high sensitivity and good signal-to-noise ratio
3Object-generated harmful factors
If deeper isolation structures are introduced to reduce crosstalk, then crosstalk is reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The isolation function is segmented into multiple components: deep trenches for physical separation, quenching resistors for electrical isolation, and positioning structures for geometric control. This segmentation allows each component to be optimized independently while working together to reduce crosstalk effectively
Solution Approach 2:
The deep trench structures serve multiple functions simultaneously: they provide physical isolation between adjacent APDs, act as etch stop layers during manufacturing, and define the boundaries of pixel regions. This multi-functionality reduces the need for additional separate isolation components, simplifying the overall device 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 increases light receiving sensitivity and maintains low crosstalk, thereby improving the signal-to-noise ratio without degrading the performance, as the P+ type Si epitaxial layer effectively surrounds the N+ type Si epitaxial layer, increasing the effective PN junction area and reducing noise.
Implementation Method 1
a photoelectric conversion element (71) provided in the P type Si epitaxial layer (161)
Implementation Method 2
a plurality of pixel regions (21) in which a plurality of photoelectric conversion elements (71) are formed on a silicon substrate (10)
Data Source
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AI summary
A light receiving device includes: first semiconductor layers (161) provided on a first main surface of a semiconductor substrate (10) and having a first conductivity type impurity at a first concentration; an insulating film (130) provided between the first semiconductor layers (161); a photoelectric conversion element (71) provided in the first semiconductor layer (161); a first electrode (42) provided on the insulating film (130); and a second electrode (15) provided on a second main surface opposite the first main surface of the semiconductor substrate (10). The photoelectric conversion element (71) includes a second semiconductor layer (163) provided at a predetermined depth from an upper surface of the first semiconductor layer (161) and having a second conductivity type impurity at a second concentration, and a third semiconductor layer (162) provided within the first semiconductor layer (161) to surround a side surface and a lower surface of the second semiconductor layer (163) and having the first conductivity type impurity at a third concentration higher than the first concentration.