Single Photon Detector Lock-In Thermography for Micron-Scale Defect Localization
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Solution Overview
Problem
Current thermographic inspection methods, such as lock-in thermography, face limitations in accurately localizing defects within devices due to low spatial resolution, especially in the z-axis, and inability to effectively time-tag individual photons for precise defect identification.
Innovation Solution
The use of an array of single low-noise photon detectors operating in Geiger mode, which timestamp each detected photon and correlate it with the excitation stimulus, allowing for the determination of time differences and generation of histograms to identify the origin of thermal hot-spots within devices, thereby enhancing spatial resolution to the micron scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermographic inspection methods are used, then the inspection can be performed with standard equipment, but the spatial resolution is low and defect localization is inaccurate
Solution Approach 1:
The patent changes the operational parameters of the detector system by operating single-photon detectors in Geiger mode at high frequencies (above 100 kHz), which enables precise time-tagging of photons and improves defect localization precision to the micron scale in the z-axis direction
Solution Approach 2:
The patent segments the detection process by using arrays of independent single-photon detectors, each capable of timestamping individual photons. This segmentation allows parallel processing of photon signals from different spatial locations, achieving high-resolution defect localization without requiring a monolithic complex detector system
2Measurement precision
If high-frequency lock-in thermography is implemented, then defect localization precision is improved, but the device complexity increases due to single photon detectors operating in Geiger mode
Solution Approach 1:
The patent replaces conventional thermal camera systems with single-photon detectors operating in Geiger mode. This substitution enables the system to detect and timestamp individual photons, achieving micron-scale spatial resolution and high-frequency operation (above 100 kHz) that conventional mechanical thermal systems cannot achieve
3Loss of information
If conventional detectors are used, then the system is simpler to operate, but the ability to time-tag individual photons is lost, reducing defect identification accuracy
Solution Approach 1:
The patent implements preliminary action by having each single-photon detector in the array continuously timestamp photons as they are detected. This real-time timestamping captures photon timing information before any processing occurs, enabling subsequent correlation of photons with specific excitation cycles and defect identification without losing temporal information
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 approach enables more precise localization of defects by improving the timing fidelity and signal-to-noise ratio, allowing for accurate identification of defects at specific depths within devices, beyond the limitations of prior art systems.
Implementation Method 1
a detector that includes a number (e.g., an array) of single low-noise photon detectors operating in a Geiger mode (e.g., avalanche photodiodes, nanowire detectors, and superconducting single-photon detectors)
Implementation Method 2
a stimulation signal (i.e., power) is applied to a device. Photons resulting from the stimulation
Data Source
AI summary
Systems, methods, and computer readable media to improve the operation of thermographic imaging systems are described. Techniques are disclosed for generating thermograms using single low-noise photon detectors. More particularly, an array of single low-noise photon detectors operating in the Geiger mode may be used to accurately identify the time delay between the application of a periodic power stimulus to a device under test and the generation of photons resulting from that stimulus. In one embodiment an array of single photon detectors may be used to time-tag each detected photon. Thereafter, a high-speed counting circuit can correlate the detected photons to the applied stimulus. When operating at the frequencies possible in the Geiger mode, such measurements permit a higher degree of spatial resolution (e.g., in the x, y and z axes) of thermal hot-spots within the device under test than prior art approaches.