SPAD Array Radial Field Design for NIR Detection
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Solution Overview
Problem
Developing arrays of single-photon avalanche diodes (SPADs) in silicon for near-infrared (NIR) radiation detection is challenging due to silicon's low energy absorption coefficient, leading to trade-offs between detection speed, noise, uniformity, and sensitivity.
Innovation Solution
A SPAD array design featuring a silicon substrate with primary and secondary electrodes of specific doping types, arranged to create a radially uniform and peaked electric field within a depletion layer, allowing for efficient photon absorption and charge multiplication without additional doped regions or intrinsic substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a depleted volume is used in addition to an electric field to detect NIR radiation, then detection efficiency is improved, but detection speed decreases and noise increases
Solution Approach 1:
The patent transitions from planar 2D electrode structures to three-dimensional vertically extended electrode structures. The first and second electrodes extend in the third dimension (vertical direction) through the substrate, creating a volumetric detection region that increases photon absorption probability while maintaining fast carrier transport pathways.
Solution Approach 2:
The patent implements non-uniform doping concentrations within the electrode structures. The first electrode has a first doping concentration and the second electrode has a second doping concentration, with the substrate having a third doping concentration. This local variation in doping quality optimizes the electric field distribution to balance carrier multiplication (for efficiency) and carrier drift speed (for detection speed).
2Measurement precision
If additional doped regions are introduced to enhance photon absorption, then detection sensitivity is improved, but noise increases and uniformity deteriorates
Solution Approach 1:
The patent employs a composite doped structure where regions of different doping types and concentrations are integrated. The first electrode (first doping type), second electrode (second doping type), and substrate (third doping concentration) form a composite structure that optimizes both photon absorption and noise suppression through controlled electric field distribution.
Solution Approach 2:
The patent systematically varies doping concentrations as a key parameter: the first electrode has a first doping concentration, the second electrode has a second doping concentration, and the substrate has a third doping concentration. By optimizing these parameter values, the patent enhances detection sensitivity while controlling noise generation from excessive carrier multiplication.
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 design enables effective absorption and amplification of single NIR photons in silicon, maintaining fast carrier transport and reducing noise, while avoiding detrimental effects from additional doped regions, thus enhancing detection efficiency and uniformity.
Implementation Method 1
individual photo-generated charges are multiplied into detectable charge packets through impact ionization in an electric field
Implementation Method 2
A commonly-used technique for single-photon detection is based on solid-state avalanche photodiodes
Implementation Method 3
The semiconductor layers include a first doped layer, a second doped layer, and a third doped layer, each having a different doping type or doping concentration
Data Source
AI summary
Example embodiments relate to single-photon avalanche diode detector (SPAD) arrays. One embodiment includes a SPAD array that includes a silicon substrate, a plurality of primary electrodes, and a plurality of secondary electrodes. Each of the primary electrodes includes a semiconductor material of a first doping type, extends in the silicon substrate in a first direction, and has a rotationally symmetric cross-section in a first plane perpendicular to the first direction. The plurality of secondary electrodes includes a semiconductor material of a second doping type and extends parallel to the primary electrodes in the silicon substrate. Further, the silicon substrate includes a doped upper field redistribution layer, a doped lower field redistribution layer, and a doped depletion layer arranged between the upper field redistribution layer and the lower field redistribution layer. A cross-section of each primary electrode is surrounding by one or more cross-sections of at least one neighboring secondary electrode.