Micro-LED Update
Producing displays is a complex task and as the display industry finds new technologies that can push the industry forward, it also must find ways to make those technologies economically feasible or they will never find their way into commercial mass production. Micro-LEDs are one such technology that shows particular promise as a longer-term display technology, as a self-emitting, high-brightness display modality that can compete on a technical basis with existing LCD and OLED displays that predominate the consumer electronics world. The problem is however that Micro-LED displays are difficult to produce and in the display space, difficult usually means expensive, and without the ability for display companies to see a pathway toward reducing Micro-LED production costs to a competitive level, they will never develop past the point of being a niche product.
One of the biggest production issues facing Micro-LEDs is numbers. As in other self-emitting displays, there is a pixel for each ‘point’ on the screen, and at what is now becoming a baseline for displays, 4K resolution requires 8,294,400 pixels per display. In a large display, such as a TV, the pixels can be placed relatively far apart, but as screen size decreases pixels need to be closer together and while OLED materials can be placed directly on a substrate using metal masks and OVP deposition tools or solution-based processing, LEDs are grown on silicon or sapphire and must be moved from the native wafer to a display substrate. To make matters worse, each pixel mentioned above, is comprised of three sub-pixels (red, green, and blue), which multiplies the number of pixels showed in the table below by 3.
OLED deposition tools require RGB emitter materials to be deposited separately, which adds to the processing time, while blue and green LEDs can be grown on the same wafer, with red on another wafer. However, while OLED substrate can be moved through the deposition process, each Micro-LED must be moved from its production wafer to the display substrate. OLED sub-pixels have size restrictions based on the properties of mask materials but Micro-LEDs can be as small as 2um to 3um, about the size of a red blood cell, which makes them a bit difficult to pickup or move from the wafer to the substrate, so as the display gets smaller, even with the lower resolutions shown toward the bottom of the table, the Micro-LEDs also must get smaller to squeeze them into the smaller space.
We have spent much time over the last few years examining Mini-LED (>100um) and Micro-LED transfer techniques, but we note that while transfer time and cost is certainly a bottleneck in the development of Micro-LED displays, we note that under each sub-pixel there is a TFT (thin-film transistor) circuit that tells the sub-pixel when to go on and off and how bright to be in order to create the millions of color mixes promised by display manufacturers. This circuitry is produced using typical semiconductor photolithography techniques and in OLED displays the TFT takes up a portion of each subpixel, creating what is called an aperture for the OLED light to escape. Hence, the larger the sub-pixel, the TFT takes up less space, creating a bigger aperture, and the sub-pixel can be brighter. However as the display gets smaller, such as in smartphones or AR/VR displays, the TFT remains the same size and the aperture gets smaller and the brightness is reduced.
Micro-LED displays have the same characteristics in that they are self-emitting, but as noted, the complexities of moving over 24m single digit micron sized LEDs with damage can be daunting, but in order for them to work, they have to be moved to a substrate where the TFT circuitry will align with each Micro-LED sub-pixel. Logic holds that ideally one would want to create the TFT circuitry on the same wafer that the Micro-LEDs are grown on, eliminating the complex and expensive transfer step, but the temperatures needed for TFT creation are near 300°C,which would damage the Micro-LEDs, so the expensive process of transfer and attaching these incredibly small LEDs to a substrate with TFT already present.
According to a Manchester, UK company, SmartKem (SMTK), they have developed inks used to produce TFT circuits that can be processed at ~80°C, low enough that no damage to the Micro-LEDs would occur and allowing the TFTs to be built directly on the Micro-LEDs, without having to transfer them to a separate substrate. If this process is as successful as the company indicates, it would sidestep the transfer issue and many of the problems associated with their movement, particularly transfer speed and damage, and the company says it can also benefit OLED displays, assumedly allowing for faster total OLED stack creation. The company claims that the process can be scaled from 10ppi to 2,500ppi, although we believe while the technology has passed the ‘proof of concept’ phase, it will take some time before the commercial scalability can be proven. That said, if such a technology can be applied toward Micro-LED production it would represent a big step forward to meaningful commercialization of Micro-LED display technology, and while there are still many other bridges to cross before Micro-LEDs can compete against more established display technologies, any process that can eliminate a major commercialization bottleneck is a positive one.
One of the biggest production issues facing Micro-LEDs is numbers. As in other self-emitting displays, there is a pixel for each ‘point’ on the screen, and at what is now becoming a baseline for displays, 4K resolution requires 8,294,400 pixels per display. In a large display, such as a TV, the pixels can be placed relatively far apart, but as screen size decreases pixels need to be closer together and while OLED materials can be placed directly on a substrate using metal masks and OVP deposition tools or solution-based processing, LEDs are grown on silicon or sapphire and must be moved from the native wafer to a display substrate. To make matters worse, each pixel mentioned above, is comprised of three sub-pixels (red, green, and blue), which multiplies the number of pixels showed in the table below by 3.
OLED deposition tools require RGB emitter materials to be deposited separately, which adds to the processing time, while blue and green LEDs can be grown on the same wafer, with red on another wafer. However, while OLED substrate can be moved through the deposition process, each Micro-LED must be moved from its production wafer to the display substrate. OLED sub-pixels have size restrictions based on the properties of mask materials but Micro-LEDs can be as small as 2um to 3um, about the size of a red blood cell, which makes them a bit difficult to pickup or move from the wafer to the substrate, so as the display gets smaller, even with the lower resolutions shown toward the bottom of the table, the Micro-LEDs also must get smaller to squeeze them into the smaller space.
We have spent much time over the last few years examining Mini-LED (>100um) and Micro-LED transfer techniques, but we note that while transfer time and cost is certainly a bottleneck in the development of Micro-LED displays, we note that under each sub-pixel there is a TFT (thin-film transistor) circuit that tells the sub-pixel when to go on and off and how bright to be in order to create the millions of color mixes promised by display manufacturers. This circuitry is produced using typical semiconductor photolithography techniques and in OLED displays the TFT takes up a portion of each subpixel, creating what is called an aperture for the OLED light to escape. Hence, the larger the sub-pixel, the TFT takes up less space, creating a bigger aperture, and the sub-pixel can be brighter. However as the display gets smaller, such as in smartphones or AR/VR displays, the TFT remains the same size and the aperture gets smaller and the brightness is reduced.
Micro-LED displays have the same characteristics in that they are self-emitting, but as noted, the complexities of moving over 24m single digit micron sized LEDs with damage can be daunting, but in order for them to work, they have to be moved to a substrate where the TFT circuitry will align with each Micro-LED sub-pixel. Logic holds that ideally one would want to create the TFT circuitry on the same wafer that the Micro-LEDs are grown on, eliminating the complex and expensive transfer step, but the temperatures needed for TFT creation are near 300°C,which would damage the Micro-LEDs, so the expensive process of transfer and attaching these incredibly small LEDs to a substrate with TFT already present.
According to a Manchester, UK company, SmartKem (SMTK), they have developed inks used to produce TFT circuits that can be processed at ~80°C, low enough that no damage to the Micro-LEDs would occur and allowing the TFTs to be built directly on the Micro-LEDs, without having to transfer them to a separate substrate. If this process is as successful as the company indicates, it would sidestep the transfer issue and many of the problems associated with their movement, particularly transfer speed and damage, and the company says it can also benefit OLED displays, assumedly allowing for faster total OLED stack creation. The company claims that the process can be scaled from 10ppi to 2,500ppi, although we believe while the technology has passed the ‘proof of concept’ phase, it will take some time before the commercial scalability can be proven. That said, if such a technology can be applied toward Micro-LED production it would represent a big step forward to meaningful commercialization of Micro-LED display technology, and while there are still many other bridges to cross before Micro-LEDs can compete against more established display technologies, any process that can eliminate a major commercialization bottleneck is a positive one.
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