Octagonal SPAD Layout for Faster Timing and Denser Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optoelectronic devices with single photon avalanche diodes (SPADs) face challenges in efficient photon detection due to the geometry of the substrate, leading to longer jitter tails and reduced timing characteristics, as well as limitations in array density due to the placement of diodes and resistors.
Innovation Solution
The design incorporates an octagonal profile for the SPADs with insulating trenches and conductive tracks, forming a resistor on the anode trench, and arranging diodes in an array with distinct and common walls to enhance photon collection and reduce distance to doped regions, while maintaining electrical and optical insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional substrate geometry is used for SPADs, then the device structure is simple, but the timing characteristics deteriorate due to longer jitter tails
Solution Approach 1:
The substrate is segmented into distinct functional regions: an active region containing the SPAD and a separate region for the resistor. This segmentation allows the SPAD to have an optimized geometry for timing characteristics while the resistor is placed in a dedicated area, reducing interference and improving overall device performance.
Solution Approach 2:
The design transitions from a planar layout to a three-dimensional structure by forming the resistor on a raised insulating trench. This vertical dimensionality change allows better separation between the SPAD and resistor, improving timing characteristics by reducing capacitance while maintaining a compact footprint.
2Quantity of substance
If diodes and resistors are placed in a conventional arrangement, then the device layout is simple, but the array density is reduced
Solution Approach 1:
The design merges the SPAD and resistor into a single integrated pixel unit with a shared active region. This consolidation reduces the overall area per pixel compared to separate layouts, thereby increasing array density while maintaining distinct functional zones through the insulating trench.
Solution Approach 2:
By placing the resistor on a raised trench structure rather than in the same plane as the SPAD, the design utilizes vertical space to reduce lateral footprint. This enables higher array density without increasing the planar area occupied by each pixel.
3Object-affected harmful factors
If the resistor is placed close to the SPAD, then the device area is reduced, but the dark count rate increases
Solution Approach 1:
An insulating trench is introduced as an intermediary structure between the SPAD and the resistor. This trench provides both electrical and optical isolation, reducing the dark count rate by preventing charge carrier injection and photon cross-talk, while the compact raised structure minimizes the area penalty.
Solution Approach 2:
The insulating trench segments the device into electrically isolated regions, separating the high-field SPAD region from the resistor region. This segmentation reduces parasitic effects and dark count rate while maintaining a compact overall footprint through efficient spatial arrangement.
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 improves timing characteristics by quicker photon absorption and increases the density of SPAD arrays, reducing the dark count rate and allowing for a higher density of SPADs in the substrate.
Implementation Method 1
A single-photon avalanche diode (SPAD) is a solid-state photodetector within the same family as photodiodes and avalanche photodiodes (APDs), while also being fundamentally linked with basic diode behaviors. As with photodiodes and APDs, a SPAD is based around a semi-conductor p-n junction that can be illuminated with ionizing radiation.
Implementation Method 2
The electric field is high enough that a single charge carrier injected into the depletion layer can trigger a self-sustaining avalanche. The current continues until the avalanche is quenched.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The present disclosure relates to a device comprising a single photon avalanche diode (12) in a portion of a substrate (50), the portion having an octagonal profile.