SPAD Microcell Array for Wide-Area Single-Photon Detection
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Solution Overview
Problem
Existing single-photon detectors face challenges in achieving a balance between wide photosensitive area and fast time-gating capability, which is essential for applications like Near-Infrared Spectroscopy and Single-Photon LiDAR.
Innovation Solution
A solid-state photodetector is designed with a bi-dimensional array of microcells, each comprising a single-photon avalanche diode (SPAD) and a blind device, allowing for fast time-gating with sub-nanosecond transition times and a wide active area of at least 0.5 mm^2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the photodetector uses a large photosensitive area to maximize light harvesting, then the light collection efficiency is improved, but the time-gating transition speed deteriorates due to increased capacitance
Solution Approach 1:
The photodetector is divided into multiple independent microcells, each with its own SPAD and readout circuitry. This segmentation allows each microcell to maintain fast response characteristics while the aggregate array provides a large photosensitive area. The independent operation of each microcell avoids the capacitance scaling issues that would affect a monolithic large-area detector.
Solution Approach 2:
The patent transitions from a single large-area detector to a two-dimensional array of microcells. This dimensional approach allows the system to achieve large effective photosensitive area through spatial distribution rather than increasing the area of a single detector element, thereby maintaining fast gating performance in each element while achieving high light collection efficiency across the array.
2Measurement precision
If the photodetector uses fast time-gating to reject early photons and improve dynamic range, then the measurement precision is improved, but the device complexity increases due to additional gating circuitry
Solution Approach 1:
The time-gating functionality is merged with the readout circuitry of each microcell. The gating control is integrated into the existing pixel structure, sharing circuit elements and control signals with the detection function. This integration reduces the overall system complexity compared to having separate gating and detection subsystems.
Solution Approach 2:
The readout circuitry in each microcell is designed to perform multiple functions: photon detection, signal amplification, and time-gating control. This multi-functionality eliminates the need for dedicated gating circuitry separate from the readout system, thereby reducing device complexity while maintaining the ability to achieve fast time-gating for improved dynamic range.
3Area of stationary object
If the photodetector array increases the number of microcells to achieve wide coverage, then the photosensitive area is improved, but the manufacturing precision requirements worsen due to increased variability
Solution Approach 1:
Each microcell is designed with locally optimized structures and materials tailored to its specific position and function within the array. This allows for compensation of local variations and ensures that each microcell meets performance specifications despite variations in the overall array. The local quality approach enables high manufacturing yield while achieving large total active area.
Solution Approach 2:
The patent employs parameter changes in the microcell design, such as varying the SPAD breakdown voltage, active area size, or doping concentrations, to compensate for manufacturing variations across the array. By adjusting these parameters locally, the system maintains uniform performance characteristics across all microcells, enabling the fabrication of large-area detectors with acceptable precision requirements.
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 photodetector achieves single-photon sensitivity with a wide photosensitive area and fast time-gating capability, enhancing the dynamic range and reducing noise, thereby improving the performance in applications like TD-NIRS and Single-Photon LiDAR.
Implementation Method 1
a first device (111) which is a photosensitive device and is configured to detect photons impinging on an active area
Implementation Method 2
single-photon avalanche diode (SPAD)
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3b
AI summary
A photodetector is disclosed comprising an array of microcells and an output module configured to collect from each microcell an output signal indicative of a photon detection and to combine the collected output signals in at least one output line. Each microcell comprises a first device and a second device, wherein at least one of devices is a photosensitive device capable of detecting the photon, a time-gating module connected to said at least one photosensitive device and configured to provide a gate signal to the at least one photosensitive device to activate it and a readout module configured to receive, upon arrival of the photon on the at least one activated photosensitive device, a corresponding signal from the at least one activated photosensitive device and, on the basis of the received signal, to provide the output signal to the output module.