As we have mentioned a number of times in the past, 2021 will be the year of the mini-LED TV. This ‘interim’ technology that sits between older edge-lit LCD TVs and micro-LED TVs, a product that has the potential to one-day replace current display production methodologies. Mini-LED backlight systems give an additional level of control over the contrast (difference between the blackest black and the whitest white) of a display by increasing the number of LEDs that generate light for LCD pixels. LCD pixels themselves do not generate light, only acting as a ‘gate’ to block light or allow it to pass through the pixel. Once the light passes through the LCD pixel, which is made up of three ‘sub-pixels’, it passes to a color filter, which converts each sub-pixel to red, green, or blue.
In understanding the complexity of an image that is shown on the screen, which is redrawn between 60 and 120 times each second, each sub-pixel’s information is a complex digital ‘word’ of 8 or 10 bits of information that tells each pixel how much of each red, green, and blue sub-pixel color should be presented, with 256 shades of each (that’s over 16.7m possible combinations). Here’s where the problem comes in however, as the LED backlight systems that are commonly used in LCD displays do not do exactly what they are told, in that when the pixel is told to ‘close’, or create a dark spot in an image, they do not close completely and some of the LED backlight leaks through, causing what should be a black dot to be a gray dot. Further, when an image contains bright and dark images in close proximity, the light from the ‘bright’ pixels leaks into the ‘dark’ pixels and also makes them gray.
Therefore Ideally each pixel, or even each sub-pixel should have its own LED backlight, but with a 4K display having 8,294,400 pixels (that’s 24.883,200 sub-pixels), not only would that be an enormous number of LEDs, but they would have to be quite small considering there would need to be 41,209 LEDs for every square inch of a 65” TV screen. Typical high-end TVs have a few hundred LED ‘zones’, which are strings of a number of LEDs that operate as one, while mini-LED systems can have thousands, giving far more control over how the pixels and sub-pixels are lit, but even mini-LED systems, which are just beginning to appear in commercial products, have some limitations.
The illustration below shows a grid of 1,600 pixels, just a bit under .2% of a 4K TV screen. Overlaid on that small segment is a mini-LED that provides the light for each of those 1,600 pixels. This would represent a 4K display with a mini-LED backlight with over 5,000 LEDs, a substantial number considering the commercial product that is in the market currently has ~1,000 zones, but it can be seen how the block of pixels is unevenly lit by the LED. In an actual device, there is a light guide, essentially a translucent sheet that spreads the light from each LED to a wider area and reduces the bright point in the center of the LED, but at the same time, this defeats some of the effect of using large numbers of LEDs to get contrast granularity on a pixel by pixel basis.
Mini-LEDs are an interim step toward solutions that allow for image control on a pixel by pixel basis, but the limitations of LCD technology force an increasing number of progressively smaller LEDs to be used over time. The mechanics of processing and constructing higher density mini-LED backlights presents both physical and financial challenges that will allow the mini-LED backlight space to grow, but will eventually lead to more practical systems. What makes mini-LEDs attractive now is that they continue to improve the quality of existing LCD infrastructure, which represents multiple trillions of dollars of investment and a well-developed supply chain.
In understanding the complexity of an image that is shown on the screen, which is redrawn between 60 and 120 times each second, each sub-pixel’s information is a complex digital ‘word’ of 8 or 10 bits of information that tells each pixel how much of each red, green, and blue sub-pixel color should be presented, with 256 shades of each (that’s over 16.7m possible combinations). Here’s where the problem comes in however, as the LED backlight systems that are commonly used in LCD displays do not do exactly what they are told, in that when the pixel is told to ‘close’, or create a dark spot in an image, they do not close completely and some of the LED backlight leaks through, causing what should be a black dot to be a gray dot. Further, when an image contains bright and dark images in close proximity, the light from the ‘bright’ pixels leaks into the ‘dark’ pixels and also makes them gray.
Therefore Ideally each pixel, or even each sub-pixel should have its own LED backlight, but with a 4K display having 8,294,400 pixels (that’s 24.883,200 sub-pixels), not only would that be an enormous number of LEDs, but they would have to be quite small considering there would need to be 41,209 LEDs for every square inch of a 65” TV screen. Typical high-end TVs have a few hundred LED ‘zones’, which are strings of a number of LEDs that operate as one, while mini-LED systems can have thousands, giving far more control over how the pixels and sub-pixels are lit, but even mini-LED systems, which are just beginning to appear in commercial products, have some limitations.
The illustration below shows a grid of 1,600 pixels, just a bit under .2% of a 4K TV screen. Overlaid on that small segment is a mini-LED that provides the light for each of those 1,600 pixels. This would represent a 4K display with a mini-LED backlight with over 5,000 LEDs, a substantial number considering the commercial product that is in the market currently has ~1,000 zones, but it can be seen how the block of pixels is unevenly lit by the LED. In an actual device, there is a light guide, essentially a translucent sheet that spreads the light from each LED to a wider area and reduces the bright point in the center of the LED, but at the same time, this defeats some of the effect of using large numbers of LEDs to get contrast granularity on a pixel by pixel basis.
Mini-LEDs are an interim step toward solutions that allow for image control on a pixel by pixel basis, but the limitations of LCD technology force an increasing number of progressively smaller LEDs to be used over time. The mechanics of processing and constructing higher density mini-LED backlights presents both physical and financial challenges that will allow the mini-LED backlight space to grow, but will eventually lead to more practical systems. What makes mini-LEDs attractive now is that they continue to improve the quality of existing LCD infrastructure, which represents multiple trillions of dollars of investment and a well-developed supply chain.
Mini-LED Segment Mock-up - Source: SCMR LLC
We expect the mini-LED segment to grow for the next few year, with considerable competition developing in 2022 and beyond, as the technology to produce these devices is not radically different from what is used currently. Much of the cost associated with the production of mini-LEDs is based on production bottlenecks at two points in the process. The first being precisely moving these small die from production tape to their correct position on the display substrate. Typical pick and place devices can move between 2,500 and 3,500 chips/hour with moderate accuracy, which is adequate for low LED count backlights, but as the chips get smaller and more numerous, speed and placement accuracy become a big component of overall cost backlight, which ranges from $250 to over $1,000 for 65” TVs depending on the complexity, and can be as much as 20% of the display’s BOM.
Given the number of LEDs in mini-LED backlights, the 2nd bottleneck actually comes at two points in the process. As LEDs are produced on a polished circular substrate and are processed using typical MOCVD tools, a production wafer represents a large number of die. Not every die on the wafer will have the same characteristics, meaning color, intensity, or voltage sensitivity, so they must be classified according to those characteristics, a process known as binning, which puts those LEDs with similar characteristics in bins that determine their use and price. Mini-LED manufacturers have to determine first what bin level they will be using and must maintain that same level for each model, otherwise the backlights will be inconsistent and look and act differently from TV set to set. Once the bin quality (and price) has been determined, the chips are moved to the mini-LED substrate and attached to circuitry, where they must be tested to insure that each performs as expected and that there are no dead LED, either from damage or from poorly connected bonding and connections. If a bad or poor performing LED is found, the unit must be removed from the line and a rework process must be started, which increases cost significantly. At 5 9’s on a 10,000 LED production line, that would be a rework on ~10% of the devices.
There are alternatives, with one already in production and another in development. OLED displays are self-emitting and do not use a backlight to generate an image. There are two types of OLED displays currently in production, the first commonly used in smartphones, and tablets. These displays use red, green, and blue sub-pixels to generate an image, and while the production process is a bit more complex than LCD production, such displays do not need either an LED backlight or a color filter. This cost savings is offset to a degree by the cost of OLED materials, but is a step above the performance of small panel LCD displays. In large OLED displays, the process is different however, as the substrate is coated with OLED materials that when electrically stimulated, generate white light. While each sub-pixel is white, a color filter is overlaid on the display, converting each individually controlled sub-pixel to red, green or blue. The cost saved by not having to precisely place red, green, and blue OLED materials on the substrate is offset somewhat by the cost of the color filter, but the process remains a self-emissive technology that does not use a backlight and has high contrast.
OLED displays do have some drawbacks. They are more expensive to produce than LCD displays, and there is far less OLED infrastructure in the display space relative to LCD. That said, small panel OLED suppliers are beginning to compete with Samsung Display (pvt), the small panel OLED leader, and to a lesser degree trying to compete with LG Display (LPL) the large panel OLED leader. This additional capacity is moving the OLED space from one dominated by South Korean suppliers to a more global supply chain, but such changes not only take capital but expertise, which is something that has to be developed over time, so we expect OLED display technology will remain a growth industry for some time, albeit a more ‘homogenous’ industry than it was. That said, the anti-OLED marketing pitch has to do with the fact that each type of OLED material ages differently, and those differences can cause OLED displays to ‘burn-in’ when a particular image is left on the screen for an extended period of time. This causes the image to appear as a faint but visible ‘ghost’ on the display, however improving OLED materials and image manipulation has been lessening the issue, however it is still a rallying cry for competitive technologies.
We mentioned that there is another alternative to mini-LEDs that is micro-LEDs. While mini-LEDs are used to enhance existing LCD displays, micro-LEDs are more like OLED than they are like LCD, in that they are self-emissive. Micro-LEDs are much smaller LEDs that do not use a backlight or a color filter to generate an image, in a similar fashion to RGB OLED displays. In a micro0LED display, there would be an LED for every sub-pixel, which, as we noted, would mean that there would be almost 25m micro-LEDs in a 4K display. This is a considerable amount more than 10,000 mini-LEDs, which are a bit of a logistical challenge, so a 4K micro-LED display becomes almost 2,500 times such a challenge.
The size of the LEDs necessary to fit that many in such a space would mean far smaller die and therefore a far more difficult task to move those die to a display substrate, and in fact, there are many methods being explored as to how to move such vast numbers of such small chips in a cost effective way, including mechanical stamps that pick up and place thousands of chips at a time, and ‘floating’ the chips in a liquid across the substrate (among others). Again the specter of 5 9’s appears here, but even more so, with a 4K micro-LED display averaging 249 dead pixel for each display, along with an infinitely more difficult rework process. Micro-LED development will continue over the next few years and specialty micro-LED displays will show up sporadically, but they will be prohibitively expensive until solutions for the above are found, so while we expect there will be some consumer confusion between mini-LED displays and micro-LED displays, there is a vast difference between the two.
All in, Mini-LED backlights will proliferate over the next few years and will help to extend the life of LCD display architecture, along with quantum dots, a technology we will cover separately, and will, at least from a marketing point of view, challenge OLED displays to a degree. That said, we expect both to coexist, and while mini-LEDs will see cost decreases based on improvements in process and scale, so will OLED technology, especially given the infrastructure investments made to date in the OLED space. Mini-LED density will have to improve considerably before it can truly compete with the almost infinite contrast that OLED displays provide.
Whether the cost of the higher density mini-LED backlights needed to compete with OLED will be cheaper than OLED at some point is still an open question, although expectations are that such a point could come around 2025 or 2026, as timelines in the display space tend to be longer than early expectations. We expect it could be a bit later and we would be more inclined to believe that micro-LED research will push itself forward from a cost perspective more quickly than mini-LEDs, which are attached to LCD technology. Given that micro-LED displays would need to establish a new supply chain to enter mass production, albeit one based on LED technology, that will also add to the life of existing display technology, so when the headlines read ‘New display technology to replace XYZ (fill in LCD, OLED, etc.)”, take it with a grain of salt.
Given the number of LEDs in mini-LED backlights, the 2nd bottleneck actually comes at two points in the process. As LEDs are produced on a polished circular substrate and are processed using typical MOCVD tools, a production wafer represents a large number of die. Not every die on the wafer will have the same characteristics, meaning color, intensity, or voltage sensitivity, so they must be classified according to those characteristics, a process known as binning, which puts those LEDs with similar characteristics in bins that determine their use and price. Mini-LED manufacturers have to determine first what bin level they will be using and must maintain that same level for each model, otherwise the backlights will be inconsistent and look and act differently from TV set to set. Once the bin quality (and price) has been determined, the chips are moved to the mini-LED substrate and attached to circuitry, where they must be tested to insure that each performs as expected and that there are no dead LED, either from damage or from poorly connected bonding and connections. If a bad or poor performing LED is found, the unit must be removed from the line and a rework process must be started, which increases cost significantly. At 5 9’s on a 10,000 LED production line, that would be a rework on ~10% of the devices.
There are alternatives, with one already in production and another in development. OLED displays are self-emitting and do not use a backlight to generate an image. There are two types of OLED displays currently in production, the first commonly used in smartphones, and tablets. These displays use red, green, and blue sub-pixels to generate an image, and while the production process is a bit more complex than LCD production, such displays do not need either an LED backlight or a color filter. This cost savings is offset to a degree by the cost of OLED materials, but is a step above the performance of small panel LCD displays. In large OLED displays, the process is different however, as the substrate is coated with OLED materials that when electrically stimulated, generate white light. While each sub-pixel is white, a color filter is overlaid on the display, converting each individually controlled sub-pixel to red, green or blue. The cost saved by not having to precisely place red, green, and blue OLED materials on the substrate is offset somewhat by the cost of the color filter, but the process remains a self-emissive technology that does not use a backlight and has high contrast.
OLED displays do have some drawbacks. They are more expensive to produce than LCD displays, and there is far less OLED infrastructure in the display space relative to LCD. That said, small panel OLED suppliers are beginning to compete with Samsung Display (pvt), the small panel OLED leader, and to a lesser degree trying to compete with LG Display (LPL) the large panel OLED leader. This additional capacity is moving the OLED space from one dominated by South Korean suppliers to a more global supply chain, but such changes not only take capital but expertise, which is something that has to be developed over time, so we expect OLED display technology will remain a growth industry for some time, albeit a more ‘homogenous’ industry than it was. That said, the anti-OLED marketing pitch has to do with the fact that each type of OLED material ages differently, and those differences can cause OLED displays to ‘burn-in’ when a particular image is left on the screen for an extended period of time. This causes the image to appear as a faint but visible ‘ghost’ on the display, however improving OLED materials and image manipulation has been lessening the issue, however it is still a rallying cry for competitive technologies.
We mentioned that there is another alternative to mini-LEDs that is micro-LEDs. While mini-LEDs are used to enhance existing LCD displays, micro-LEDs are more like OLED than they are like LCD, in that they are self-emissive. Micro-LEDs are much smaller LEDs that do not use a backlight or a color filter to generate an image, in a similar fashion to RGB OLED displays. In a micro0LED display, there would be an LED for every sub-pixel, which, as we noted, would mean that there would be almost 25m micro-LEDs in a 4K display. This is a considerable amount more than 10,000 mini-LEDs, which are a bit of a logistical challenge, so a 4K micro-LED display becomes almost 2,500 times such a challenge.
The size of the LEDs necessary to fit that many in such a space would mean far smaller die and therefore a far more difficult task to move those die to a display substrate, and in fact, there are many methods being explored as to how to move such vast numbers of such small chips in a cost effective way, including mechanical stamps that pick up and place thousands of chips at a time, and ‘floating’ the chips in a liquid across the substrate (among others). Again the specter of 5 9’s appears here, but even more so, with a 4K micro-LED display averaging 249 dead pixel for each display, along with an infinitely more difficult rework process. Micro-LED development will continue over the next few years and specialty micro-LED displays will show up sporadically, but they will be prohibitively expensive until solutions for the above are found, so while we expect there will be some consumer confusion between mini-LED displays and micro-LED displays, there is a vast difference between the two.
All in, Mini-LED backlights will proliferate over the next few years and will help to extend the life of LCD display architecture, along with quantum dots, a technology we will cover separately, and will, at least from a marketing point of view, challenge OLED displays to a degree. That said, we expect both to coexist, and while mini-LEDs will see cost decreases based on improvements in process and scale, so will OLED technology, especially given the infrastructure investments made to date in the OLED space. Mini-LED density will have to improve considerably before it can truly compete with the almost infinite contrast that OLED displays provide.
Whether the cost of the higher density mini-LED backlights needed to compete with OLED will be cheaper than OLED at some point is still an open question, although expectations are that such a point could come around 2025 or 2026, as timelines in the display space tend to be longer than early expectations. We expect it could be a bit later and we would be more inclined to believe that micro-LED research will push itself forward from a cost perspective more quickly than mini-LEDs, which are attached to LCD technology. Given that micro-LED displays would need to establish a new supply chain to enter mass production, albeit one based on LED technology, that will also add to the life of existing display technology, so when the headlines read ‘New display technology to replace XYZ (fill in LCD, OLED, etc.)”, take it with a grain of salt.
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