Bandpass Filter LED Testing for Precise Micro-LED Binning
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Solution Overview
Problem
Existing LED test systems struggle to accurately and efficiently test small form factor LEDs, particularly micro-LEDs, due to insensitivity to small wavelength shifts and inaccuracies in color matching and binning, especially for narrowband light sources.
Innovation Solution
A system utilizing two color bandpass filters with steep and monotonic cutoffs, separated by a spectral gap, to filter light from LEDs, combined with a clear filter, and a processing device to determine intensity ratios and wavelength, enabling precise LED testing through a look-up table for binning based on predefined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional filters are used in LED test systems, then the system can operate with simple filter structures, but the system lacks sensitivity to small wavelength shifts and produces inaccurate test results for narrowband light sources
Solution Approach 1:
The filter system is segmented into multiple discrete bandpass filters, each optimized for a specific color range (red, green, blue). Each filter is paired with a corresponding reference filter, creating multiple independent measurement channels that collectively provide high-resolution wavelength measurement across the visible spectrum.
Solution Approach 2:
Each bandpass filter is designed with locally optimized characteristics tailored to its specific color range. The filters have steep and monotonic cutoffs tailored to their respective wavelength regions, allowing each filter to provide optimal performance for its designated color while contributing to overall system precision.
2Manufacturing precision
If existing LED test systems use standard filters, then the system structure remains simple, but color matching and binning accuracy deteriorate, especially for micro-LEDs requiring nanometer precision
Solution Approach 1:
The filtering system is divided into multiple discrete bandpass filters, each optimized for a specific color range (red, green, blue). Each filter is paired with a corresponding reference filter, creating multiple independent measurement channels that collectively provide high-resolution wavelength measurement across the visible spectrum.
Solution Approach 2:
The system changes the operational parameters of the filters by using multiple narrowband filters with specifically engineered bandwidths and cutoff characteristics. This allows the system to achieve nanometer-level color matching precision by measuring intensity ratios across multiple filtered channels and using lookup tables to determine precise wavelength and line width values.
3Measurement precision
If the filter bandwidth is made narrow to match LED line width, then measurement precision improves, but the system becomes more sensitive to manufacturing tolerances and alignment variations
Solution Approach 1:
The system uses reference filters with known characteristics to provide feedback for calibration and normalization. By measuring the intensity ratio between the test filter and reference filter pairs, the system compensates for variations in LED output intensity and spectral shape, maintaining stable and reliable measurements even with narrowband filters.
Solution Approach 2:
The system changes the operational parameters of the filters by using multiple narrowband filters with specifically engineered bandwidths and cutoff characteristics. This allows the system to achieve nanometer-level color matching precision by measuring intensity ratios across multiple filtered channels and using lookup tables to determine precise wavelength and line width values.
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 system provides accurate and efficient testing of micro-LEDs by sensitively measuring wavelength and line width, ensuring high precision in color matching and binning, thereby improving the testing process for large numbers of LEDs on a wafer.
Implementation Method 1
A first color bandpass filter is configured to receive part of light from a light source and a second color bandpass filter is configured to receive part of the light from the light source
Implementation Method 2
A camera is configured to capture an image of the light from the light source
Data Source
AI summary
An example system includes a first color bandpass filter to receive part of light from a light source and a second color bandpass filter to receive part of the light from the light source. The first color bandpass filter and the second color bandpass filter each has a cutoff wavelength at a band edge. The first color bandpass filter and the second color bandpass filter each has a band edge within a predefined distance of a nominal wavelength of the light source. The first color bandpass filter and the second color bandpass filter is each configured to output filtered light that is based on received parts of the light. One or more processing devices are configured to perform operations that include determining at least first and second values based on the filtered light.