Proposing an Accurate and Fast Optical Batch Inspection Method of Mini-/Micro-LEDs

Based on the microscopic hyperspectral imaging technique, an optical batch inspection method has been proposed by the authors to efficiently and precisely obtain the absolute emission spectra of red (R), green (G), and blue (B) Mini-/Micro-light-emitting diodes (Mini-/Micro-LEDs). The RGB Mini-LEDs (with a chip area of $200\,\,\mu \text{m}\,\,\times 100\,\,\mu \text{m}$ ) based array is selected for carrying out this experiment. Via the proposed method, the photometric and colorimetric properties of each Mini-LED pixel could be derived in detail. In this proposed method, an optimized Canny-based algorithm has been used for quickly detecting the effectively emitting area in the collected hyperspectral images, thus saving more time for workers. While compared with the traditional integrating-sphere-based method, the measured data between the proposed method and traditional method are in fairly good consistence, with their maximum deviation of < 3.2%. The external quantum efficiency (EQE) and chromaticity coordinates of each Mini-LED are acquired at the temperature ranging from 300 K to 340 K by the proposed method. Three RGB Micro-LEDs (with a chip area of $10\,\,\mu \text{m}\,\,\times 10\,\,\mu \text{m}$ ) based arrays are also selected for the optical batch detection, and the pseudocolor maps of normalized electroluminescence (EL) intensity for RGB Micro-LEDs are analyzed. Finally, the optical crosstalk of RGB Mini-LEDs is quantitatively defined and analyzed. The optical crosstalk effects are more prominent for red Mini-LEDs than the other two. Results indicate that the proposed method has shown potential applications in the field of Mini-/Micro-LEDs’ batch inspection.