SPAD Array Bragg Mirror Crosstalk Elimination
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Solution Overview
Problem
Conventional single-photon-avalanche diode (SPAD) arrays suffer from electro-optical crosstalk, where parasitic light from one SPAD can deactivate adjacent SPADs, reducing their detection performance due to the need for recharging, which decreases the overall array efficiency.
Innovation Solution
Incorporating a Bragg mirror between adjacent SPADs to prevent the propagation of parasitic light, allowing both SPADs to operate simultaneously without deactivation, while maintaining a high excess bias voltage by reflecting or absorbing the incident parasitic light emitted during avalanches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the excess bias voltage of SPADs is decreased to attenuate crosstalk, then the number of hot carriers generated during avalanche is reduced, but the detection performance of SPADs deteriorates
Solution Approach 1:
A Bragg mirror is introduced as an intermediary component between adjacent SPADs to reflect parasitic light and prevent crosstalk, allowing the excess bias voltage to be maintained at high levels for optimal detection performance without compromising array reliability
Solution Approach 2:
The patent segments the silicon substrate by introducing Bragg mirrors between individual SPADs, creating optical isolation zones that prevent light propagation between adjacent diodes while maintaining electrical connectivity and detection performance
2Measurement precision
If a high reverse bias voltage is applied to generate sufficient electric field for avalanche, then single photon detection capability is improved, but parasitic light emission from hot carriers increases
Solution Approach 1:
The Bragg mirror converts the harmful parasitic light emission into a reflected signal that remains confined to the originating SPAD, allowing high reverse bias voltages to be maintained for excellent single photon detection while the parasitic light is redirected back rather than propagating to adjacent diodes
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 Bragg mirror effectively eliminates crosstalk, enabling all SPADs in the array to operate continuously without recharging, thus maintaining high performance and detection efficiency.
Implementation Method 1
The Bragg mirror is suitable for preventing a propagation of light between these two diodes
Implementation Method 2
At least one Bragg mirror is positioned between the at least two adjacent diodes, respectively
Implementation Method 3
The initiating charge carrier may be generated photoelectrically by a single incident photon striking the region of high field
Implementation Method 4
SPADs are reverse biased beyond their breakdown voltage. A high reverse bias voltage generates a sufficiently high electric field for a single charge carrier introduced into a depletion region of the SPAD to be able to cause an avalanche that is self-sustained via one ionization per impact
Implementation Method 5
During the avalanche in a SPAD, a high number of hot carriers are generated. These hot carriers relax by emitting parasitic light in the red or in the near infrared in all directions
Data Source
AI summary
An integrated circuit is formed in a semiconductor substrate. An array of single-photon-avalanche diodes is formed at a front side of the semiconductor substrate. The array includes first and second diodes that are adjacent to each other. A Bragg mirror is positioned between the first and second diodes. The Bragg mirror is configured to prevent a propagation of light between the first and second diodes.