SPAD Conductive Trenches for Biasing and Photon Detection
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Solution Overview
Problem
Current semiconductor devices, such as Single-Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs), face challenges in providing bias voltage to highly-doped layers in arrays, requiring low resistance, small size, and low process complexity, while maintaining high detection efficiency and minimizing slow signal components due to carrier diffusion.
Innovation Solution
The implementation of conductive trenches etched down to the p+ layer, filled with doped polysilicon and metal, provides a low resistivity path and enhances photon detection efficiency through multiple reflections, allowing for both front-side and back-side illumination configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional biasing structures are used for highly-doped layers in SPAD arrays, then the device can be manufactured with standard processes, but the resistance is high and the device size becomes large
Solution Approach 1:
The conductive trench structure embeds multiple functional layers within a compact vertical architecture. The metal layer is nested within the trench, surrounded by dielectric material, creating a compact biasing structure that delivers voltage efficiently without expanding the device footprint horizontally.
Solution Approach 2:
The biasing structure transitions from a planar layout to a three-dimensional trench structure. By etching vertical trenches and filling them with conductive materials, the patent creates low-resistance paths in the vertical dimension, reducing the need for large horizontal area while maintaining effective bias voltage delivery to highly-doped layers.
2Reliability
If conductive trenches are etched and filled with doped polysilicon and metal, then low resistivity path is achieved, but the manufacturing process complexity increases
Solution Approach 1:
The conductive path is segmented into multiple functional layers: doped polysilicon layer for initial conduction, metal layer for enhanced conductivity, and dielectric material for isolation. This segmentation allows each layer to be optimized independently while collectively achieving low resistivity through the trench structure.
Solution Approach 2:
The trench structure employs composite materials combining doped polysilicon, metal, and dielectric materials. This composite approach leverages the advantages of each material - polysilicon for integration with CMOS, metal for low resistance, and dielectric for electrical isolation - achieving superior electrical performance while managing process complexity through systematic material combination.
3Reliability
If the active depleted layer thickness is increased to improve photon detection, then detection efficiency improves, but slow signal components due to carrier diffusion increase
Solution Approach 1:
The patent implements different doping concentrations and depletion characteristics in different regions of the active layer. By creating locally optimized depletion zones with appropriate thickness and doping profiles, the structure achieves efficient photon absorption while maintaining fast carrier collection speeds through controlled electric field distribution.
Solution Approach 2:
The invention optimizes the active depleted layer parameters including thickness, doping concentration, and electric field strength. By carefully adjusting these parameters, the patent achieves the optimal balance between detection efficiency (requiring sufficient depletion depth for photon absorption) and signal speed (requiring thin layers to minimize carrier diffusion time).
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 solution enables efficient biasing of highly-doped layers with low resistivity and process complexity, improving detection efficiency and reducing slow signal components, particularly suitable for near-infrared light detection in applications like Lidar systems.
Implementation Method 1
conductive trenches etched down to the p+ layer, filled with doped polysilicon and metal, provides a low resistivity path
Implementation Method 2
Single-photon avalanche diodes (SPADs) are light silicon sensors able to detect single photons
Implementation Method 3
They are often configured to work in Geiger mode (e.g., biased above the breakdown voltage) so that each photon impacting the device creates a controlled avalanche
Implementation Method 4
enhances photon detection efficiency through multiple reflections
Data Source
AI summary
A semiconductor device, sensor, and array of SPAD cubes are described. One example of the disclosed semiconductor device includes an array of single-photon avalanche diodes, each single-photon avalanche diode including an undepleted anode region, an undepleted cathode region, an active depleted region positioned between the anode region and cathode region, and at least one conductive trench extending between the anode region and cathode region. In some examples, the at least one conductive trench surrounds the active depleted region and reflects light back into the active depleted region such that one or more photons can be absorbed within the active depleted region even though an absorption coefficient of the light is greater than a thickness of the active depleted region.