Beating the Diffraction Limit: How a Revolution in Optics is Transforming microLED Inspection

microled high resolution testing

The past few years have seen a dramatic acceleration in microLED development. The industry abounds with new companies focused on a variety of technical challenges. Just this month, CES featured new microLED screens by some of the leading display manufacturers. There is little doubt that microLED is poised to emerge as a leading display technology in the coming years.

One of the most fundamental challenges facing microLEDs, however, is inspection. The microLED pixels that are currently being developed are on the single-micron scale. At this size, sub-pixel defects can be as small as hundreds of nanometers. The ability to identify defects at this scale is critical for the continued development of microLED technology. In order for microLEDs to be a commercially viable display technology, yields must improve dramatically. And the key to improving yields, as always, is effective inspection.

Of course, many inspection technologies already exist in the display market. In fact, most display inspections are based on optical methods, such as AOI (Automated Optical Inspection). However, optics-based inspection technologies are fundamentally inadequate for microLEDs.  Why does this method of inspection, so effective with LCD displays for example, fall short when it comes to microLEDs? The answer relates to a basic principle in optics known as “the diffraction limit”. Practically, optical techniques tend to have a resolution limit of approximately 1 micron. Therefore, as the pixel approaches 1 micron in size, and defects emerge on the nanoscale, less and less sub-pixel information is effectively obtained via standard optical techniques.

Fortunately, there is a technique which facilitates the continued employment of optics for inspection – even for single micron pixels and 100nm defects. In 1984, InZiv Chief Scientist Professor Aaron Lewis, then of Cornell University, demonstrated that a much higher optical resolution can be achieved when light passes through a sub-wavelength diameter aperture. The light illuminates a sample that is placed within its near field, at a distance much less than the wavelength of the light. The result is a resolution as high as 50nm (up to 20x times more powerful!) Lewis’s work offered such a profound contribution to the scientific community, that his student Eric Betzig went on to win the Nobel Prize in Chemistry in 2014 for related work in super-resolution microscopy. 

Now, with the advent of microLEDs and their sub-micron defects, this proprietary optical technique is ideally suited to address the inspection needs of today’s display manufacturers. Not only does InZiv’s inspection technology offer the highest resolution in microLED inspection, it also offers a full range of data – optical, spectral, and structural. EQE, PL and EL mapping, nano-PL and nano-EL measurements, lifetime measurements, and sidewall measurements can all be obtained. With the ability to measure ≤1 micron chips and to identify the smallest defects, InZiv’s OmniPix-ML1000 is quickly emerging as a must-have tool for microLED developers and manufacturers.

As the microLED industry continues to move ahead, InZiv will be there to provide the inspection solutions that are necessary for the unique challenges presented by this exciting display technology.

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