Scientists from Texas A&M University, the Massachusetts Institute of Technology and South Korea’s Sungkyunkwan University have analyzed the state of modern light-emitting diodes (LEDs) and described the prospects of micro-LEDs, which are expected to form the basis of next-generation displays in the foreseeable future.
Modern displays have reached the limit of their capabilities. Liquid crystal displays (LCDs) are unable to produce deep blacks, whereas organic light-emitting diodes (OLEDs) have a short lifespan, are sensitive to moisture and have relatively low brightness. In environments where images must remain clear even in bright sunlight, such as during the use of augmented reality glasses, these technologies prove insufficient.
For this reason, international research teams are tirelessly working to develop micro-LEDs – tiny inorganic diodes measuring less than 100 micrometers. These diodes are characterized by high brightness, energy efficiency, resistance to moisture and overheating, and a significantly longer service life compared to OLEDs. Thanks to their unique properties, micro-LEDs are paving the way for new display formats: transparent shop windows and automotive glass, flexible and stretchable panels, and ultra-dense micro-screens for VR and AR devices.
Currently, a major obstacle continues to be posed by the fact that the efficiency of micro-LEDs sharply declines as their crystal size decreases. This is because, with diode dimensions smaller than 20 micrometers, the number of defects on their lateral surfaces increases, leading to energy loss and a decrease in brightness. This is particularly evident in red LEDs based on aluminum, gallium, indium and phosphorus (AlGaInP). The researchers from the U.S. and South Korea have discovered that switching to red diodes based on indium gallium nitride (InGaN) could be an effective solution. These diodes are grown on sapphire substrates similarly to their green and blue counterparts.
An equally complex challenge involves the mass transfer of micro-LED chips onto the substrate. A single 4K display requires approximately 24 million LEDs, and even a minimal defect rate results in thousands of defective pixels that must be identified and replaced. Approaches being looked into include micro-screen printing, laser transfer, liquid self-assembly and monolithic integration. The latter method envisages the vertical layer-by-layer formation of red, green and blue diodes, making it possible to create panels with a record-high density of over 5,000 pixels per inch. These parameters are critical for VR and AR headsets.
The scientists note that the potential of micro-LEDs is extremely high despite the high cost and technological complexity. Prototypes of transparent displays are already available, with LEDs forming a grid with gaps, alongside flexible and stretchable panels based on new design solutions and elastic materials.
