SPAD Layout With Insulating Trench for Low-Jitter Photon Detection
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Solution Overview
Problem
Existing optoelectronic devices comprising single photon avalanche diodes (SPADs) face challenges related to noise and damage due to high electric fields, and there is a need to improve the design to enhance performance and efficiency.
Innovation Solution
The design incorporates a single photon avalanche diode with an octagonal profile surrounded by an insulating wall, featuring an insulating trench in the anode and a conductive track resistor made of polycrystalline silicon, which is strategically positioned to optimize photon detection and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single photon avalanche diode is biased well above its reverse-bias breakdown voltage to enable single-photon detection, then the detection capability is improved, but noise and damage due to high electric fields increase
Solution Approach 1:
The device is segmented into distinct functional regions: an active detection region with the SPAD and a separate resistor region positioned in a different well. This spatial segmentation allows the high electric field region (SPAD) to operate independently from the noise-sensitive regions, reducing the harmful effects of electric field-induced noise while maintaining detection capability.
Solution Approach 2:
An insulating layer is introduced as an intermediary between the SPAD and the resistor. This insulating mediator electrically isolates the two components, preventing noise coupling from the high electric field region to the readout circuitry, thereby reducing noise while preserving the photon detection function.
2Ease of manufacture
If conventional layouts are used for SPAD arrays, then manufacturing is simpler, but timing characteristics and jitter are degraded
Solution Approach 1:
The design transitions from a planar layout to a three-dimensional architecture by placing the resistor in a different well (separated vertically by an insulating layer) from the SPAD. This dimensional separation allows independent optimization of timing characteristics without compromising manufacturing simplicity, as the dual-well structure can be integrated using standard CMOS processes.
3Productivity
If SPAD density is increased to improve array efficiency, then detection efficiency improves, but noise from adjacent diodes increases
Solution Approach 1:
The array is segmented into isolated pixel units, each containing a SPAD and its dedicated resistor in separate wells. This segmentation creates electrical isolation between adjacent pixels, allowing higher density packaging while preventing noise propagation from neighboring diodes through the insulating layers that separate each pixel's well 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 enhances the timing characteristics of photon detection, reduces jitter, and allows for a higher density of SPAD arrays, improving overall performance and efficiency.
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 semiconductor 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
AI summary
A device includes a single photon avalanche diode in a substrate and a resistor. The resistor is provided resting on an insulating trench located in a doped anode region of the single photon avalanche diode.