Chinese researchers have filled the gap in non-destructive testing technology for micro-LED wafers with their 'soft-and-gentle' approach.

Miniature LEDs are core components in next-generation high-end display technology. Wafers equipped with miniature LEDs must achieve a 100% yield rate; otherwise, it will lead to enormous repair costs for end products. However, the industry has yet to find a good method for non-destructive contact testing of wafers. Recently, Chinese researchers have filled this technological gap using a 'soft overcomes hard' approach.

Traditional wafer yield detection methods, some akin to 'engraving jade with an iron pen,' cause irreversible physical damage to the wafer surface; others can only provide a 'general overview,' resulting in high rates of missed and misidentified defects. The lack of non-destructive yield detection technology has severely hindered mass production of miniature LED end products such as large-area displays and flexible displays.

Recently, the team of Professor Huang Xian from the Key Laboratory of Precision Measurement Technology and Instruments of Tianjin University and the Department of Perceptual Science and Engineering, School of Precision Instruments, has broken through the bottleneck in miniature LED wafer testing, achieving high-throughput non-destructive testing of miniature LED wafers. The research findings were published on the 13th in the international academic journal Nature Electronics.

The image shows a flexible probe contacting an LED wafer, illuminating one LED to emit blue light. (Image provided by the interviewee)

The research team proposed a detection method based on flexible electronics for the first time. The three-dimensional structured flexible probe array constructed by this method, with its 'soft overcomes hard' characteristics, can perform adaptive deformation on the surface morphology of the measured object and gently touch the wafer surface with a 'breathing-level pressure' of 0.9 MPa.

“The probe contact pressure of this technology is only one ten-thousandth that of traditional rigid probes. It not only avoids wafer surface wear but also reduces probe wear. After 1 million contact measurements, the probe remains as good as new,” said Huang Xian.

In addition, the team also developed a measurement system that matches the three-dimensional flexible probe. Through the collaborative work of the probe and the detection system, it provides key tools for efficient process control and good product screening of miniature LED products.

The image shows the flexible probe in the testing system. When the probe contacts the LED wafer, it illuminates one LED to emit blue light. The light intensity and wavelength information can be observed through the coaxial optical path. (Image provided by the interviewee)

“We have achieved a breakthrough from zero to one, filling the technological gap in electroluminescent detection of miniature LEDs and providing a revolutionary technical solution for other complex wafer detection. With the continuous expansion of the probe array scale and detection channels, it may have a wider impact in wafer-level integrated detection, biophotonics, and other fields in the future,” said Huang Xian.

It is reported that this technology has started the product process in Tianjin Kai High-tech Innovation Park. In the future, it will provide domestic miniature LED industry with batch, non-destructive, and low-cost detection solutions, further expanding the application fields of flexible electronics.