Demolition: miniLED backlight on iPad Pro.
SystemPlus analysts took a closer look at the innovative illumination of the latest iPad Pro, based on the many promising miniLED technology.
After years of waiting, Apple has finally released its first miniLED-based display on the latest iPad Pro. System Plus Consulting has just published a full report on the demolition of the backlight unit along with an analysis of the technology and its costs.
Liquid crystal display (LCD) manufacturers have long used full-array local dimming (FALD) to improve the contrast of their panels. In LCD displays, the depolarization effects in the layers of TFT transistors, liquid crystal cells and color filters cause minimal illumination - therefore, even when the pixel is turned off, a residual amount of light always 'leaks' from the backlight unit (BLU), causing poor image contrast. To improve the characteristics of the LCD display, global or local backlight dimming is used. In the case of local dimming, the display is divided into multiple zones where the backlight can be controlled individually and completely turned off in dark areas of the image as shown in the figure below.
Figure 1: Innovative MOSFET structure from Toshiba with built-in SBD. © Toshiba
Until now, FALDs have only been used in desktop TV sets and PC monitors, but not in the displays of mobile devices such as laptops, tablets or mobile phones. One reason is that by placing the LEDs on the back of the display facing the viewer, the thickness of the device increases. The LED housing itself is then not only relatively thick, but also a sufficient distance is required so that the light from individual chips spreads evenly across the screen, eliminating the so-called 'Hot spots'.
MiniLEDs are coming
MiniLEDs solve this problem by multiplying the number of LED units and thus reducing the spacing between individual light sources, and thus also reducing the thickness of the backlight. Interestingly, they can also significantly increase the number of zones, which should reduce the 'blooming' effect - the halo effect when bright objects, much smaller than individual dimming zones, are displayed against a very dark background.
Ultimately, well-designed miniLED backlights can improve LCD contrast to a level close to OLED performance while maintaining LCD high brightness and long life, eliminating common concerns of 'burn-in'. They can also reduce energy consumption as most zones will be turned off in dark images or their brightness will not be full.
So why is the miniLED backlight not widely used? The answer is cost. More LED units means higher chip cost and more zones means more drivers. One possible way to reduce costs is to make LEDs as small as possible. However, it makes chip manufacturing more complicated, increases susceptibility to defects and reduces productivity. By reducing the spacing between the pads, miniLEDs also make it difficult to mount the matrix on the PCB: the requirements for mounting accuracy, a perfectly flat PCB and the accuracy of lithography become very stringent. So the costs are rising again.
Apple's MiniLED iPad Pro secrets
Designing and manufacturing miniLED BLU is a complex art that must balance technology, performance and cost. The demolition of the iPad Pro miniLED backlight unit carried out by System Plus reveals that the device uses 10,384 miniLED chips, mounted directly on a special PCB, creating 2,596 zones. The MiniLEDs manufactured by Epistar are not as small as you might expect, leading to the relatively high cost of a single chip. In addition, the matrix has some features such as DBR dielectric mirrors which are most commonly used for larger chips used for general lighting or automotive applications.
However, Apple manages to manage the lighting with a small number of custom drivers provided by ST Microelectronics. Both companies appear to have found a good balance between cost and performance by optimizing the number of channels and the multiplexing capabilities of each driver.
While OLEDs were once thought to be a sure winner in many applications, miniLEDs change that belief somewhat, providing LCD manufacturers with the opportunity to reduce performance variations and more fully utilize their huge installed LCD production capacity. For mid-size panels such as tablets and laptops, this offers the opportunity to gain a strong foothold in high-end product segments, while OLED manufacturers are investing heavily in new factories and technologies used in these devices.
However, as is often the case in the display and LED industry, reducing costs will be key to enabling the technology to take more advantage. The demolition of the miniLED System Plus Consulting backlight shows that balancing cost and performance is not as easy as some might think. SPC is also preparing further demolitions of related devices (TVs, monitors), which will allow to obtain a real image of the miniLED BLU technology and estimate the cost-performance ratio.
Of course, with Apple's acquisition of LuxVue in 2014, the company is expanding its microLED technology. As 'MicroLED Displays - Market, Industry and Technology Trends 2021' has been widely discussed, we see a strong development in microLED technology, but many technical challenges and supply chain concerns remain. Many solutions look great on paper, but integrating real-world processes into a mass-production environment is much more difficult. However, Apple has a strong incentive to succeed: MicroLED can offer the company a unique, competitive technology while allowing it to control the microLED display supply chain independent of traditional panel manufacturers.
But for Apple, miniLED is also a strategic decision. The iPad is just the first step - MiniLED is expected to be a key differentiator for Apple's next generation of upcoming MacBooks
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