Micro LEDs are an exciting new technology that offers the potential to revolutionise the display industry. This Samsung 146inch micro LED TV “The Wall” shown at CES 2018 is a great example of the exciting opportunity that micro LED presents. “The Wall” showed amazing contrast and brightness. The micro LED technology is capable of providing the better image quality compared to OLEDs with the added benefits of reduced power consumption and increased lifetime. Samsung is not the only one company investing in the technology. Other major consumer product suppliers such as Apple or Sony are also looking at developing their products further using this technology to use in smartwatches, phones and AR/VR. The list of patents created is growing fast with the technology giving birth to a lot of start-ups.
Image courtesy of The Verge
The micro LED technology still has a few challenges ahead. To meet the high volume production demanded by the consumer market, the fabrication process flow has yet to be optimised. The skills and knowledge from both LED manufactures and display suppliers has to be combined and supported by an innovative assembly and testing line. The assembly has to be capable of mass transferring millions of LED to a control circuit panel at ±1.5µm accuracy with mass inspection capability for early repairs. Additionally, details of the pixel architecture and driver have yet to be defined.
As an inorganic LED structure can only emit monochromatic light, an arrangement of red blue and green LED must be fabricated to get full colour emission. Array of micro LED must be produced at small pitch with a Thin Film Transistor (TFT) plane used to control each pixel. An example of structure is given below. Each pixel within a display is individually driven to create the brightness and sharpness which makes this technology stands out.
The design of the single LED within a pixel is also to be defined. Several options exist such as flipchip technology. Oxford Instruments has many years of experience in supplying LED manufacturers. Some of our solutions includes fine pitch sloped mesa, fine pitch dielectric passivation for reliability and insulating material to stop crosstalk between pixel.
Another approach is the use of nanowires. The Lund University spin out glō have received support in commercializing its product from major investors such as Google who invested 15 million USD for 13% stake. glō creates direct view displays consisting of nanowires based LED. Oxford Instrument Plasma Technology has a long history of working closely with the Compound Semiconductor community. We have worked along Osram to manufacture defect-free high aspect ratio nanorods with a top-down processing approach which is capable of creating wafer-scale, ordered arrays that can be reliably integrated into large-area devices.
Actual display from glō – Image courtesy of glō
GaN Nanorod manufactured using Oxford Instrument Plasma Pro 100 “Fabrication and properties of etched GaN nanorods”, ICNS Volume 9, Issue 3-4, March 2012
Despite challenges set by the disruptive innovation brought by micro LED, the technology should still take off for small display panel application such as wearable. These displays have lower resolution and can be assembled using the wafer bonding approach. The Apple watch is predicted to use micro LED display which would potentially allow for the watch to be thinner and have extended battery lifetime. Other applications such as headband display for virtual or augmented reality are also expected from manufacturers such as Oculus.
Micro LEDs can bring brighter, clearer images with lower power – It is an exciting time ahead for the display industry.
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