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Dark mode will be the new driver for AMOLED panels in smartphone applications

29 August 2019 David Hsieh

With the arrival of Apple iOS 13 and Android Q Beta OS, one of the more interesting—and significant—enhancements from the operating systems was the addition of dark mode as an option for smartphone screens. While some applications previously offered dark mode as an option, the ability now to set up dark mode in the OS can help smartphone users more fully utilize and experience this new display mode.

For the industry, dark mode may help boost the adoption of AMOLED panels in the smartphone display market.

Apple in conferemce

LCDs are a type of liquid-crystal display that use liquid-crystal molecules as the switch that polarizes the light illuminated by the backlight to display the video signals being transmitted. LCDs cannot be illuminated without the backlight unit. In comparison, an organic light-emitting diode (OLED) display is a self-emitting device in which diodes and pixels produce their own light and no external light source is needed. The variation in the way light is produced by each technology translates into fundamental differences between LCD and OLED displays in power consumption and display performance.

For AMOLED, the benefits of dark mode are clearly seen in three display panel aspects: power consumption, contrast ratio, and visual defects.

Benefits explained

In discussing the first factor, power consumption, worth noting is that an LCD panel has two power-consuming mechanisms. The first is the thin-film-transistor (TFT) and liquid-crystal switch array, driven mainly by the power voltage and accounting for 10-30% of the total power consumed by the LCD module. The second is the backlight unit (BLU), also driven by the power voltage but representing a much larger share—70-90%—of the total consumed power.

This means the backlight unit is the single most power-hungry component of the LCD panel. Until recently, the OS in both PCs and smartphones utilized the default light mode, which makes the high brightness of LCDs a necessary feature despite the high power consumption involved. In dark mode, the LCD backlight unit is still on, but power in the TFT and liquid-crystal switch is reduced. Even with this accommodation, however, the overall reduction is minor in LCD power consumption since the LCD backlight, the biggest power hoarder, remains lit.

Power consumption works differently in AMOLED displays, which are self-emitting devices driven by the power current, not by the power voltage. In dark mode background, some OLED display pixels do not need to be illuminated, instead lighting only the display or the on-screen characters on screen. As a result, power consumption will be largely reduced if a black background—in other words, dark mode—is used by a smartphone.

Power consumption will be a critical factor for the coming 5G smartphones, especially because the 5G baseband can consume a lot of power. By cutting back power consumption in the screen, it will be easier to extend the 5G smartphone's standby time.

The second benefit provided by dark mode is in contrast ratio, or the proportion of the darkest black to the brightest white on the screen. While local dimming is now available as a feature in LCD panels to make blacks appear deeper and richer, the backlight required for illumination is still on and cannot be switched off, preventing full blackness in color from being achieved.

In comparison, AMOLED does not have this problem. Using self-lighting pixels capable of switching on and off individually, black colors are deep and rich. And with dark mode enabled, most pixels are shut down, allowing contrast to be maximized to the fullest. AMOLED technology is thus more suitable for high contrast ratio in dark mode.

The third benefit from dark mode relates to visual defects. With the backlight always on in LCDs, visual defects—such as mura, a dot or spot of blue—may be obvious even in dark mode. Taken from the Japanese word unevenness or blemish, mura is more common in LCD, a result from various possibilities, such as impurities in the liquid-crystal matrix. Mura is also a challenge in OLED but for different reasons. With each pixel as its own emitter of light in OLED displays, inconsistency from pixel to pixel is inevitable.

As we analyzed in the Smartphone Display Intelligence Service, AMOLED technology has had difficulty establishing constant, persistent presence in the smartphone display market. The challenges include high costs, the complicated manufacturing process, and the lack of flexibility in production.

In comparison, low-temperature polysilicon (LTPS) TFT-LCD has proven to be very-cost effective and is the mainstream technology used for smartphone displays.

LTPS TFT-LCD also benefits from many new form factors, such as screen notches, hole-punches, and so on. AMOLED displays, in contrast, lack the flexibility needed to produce these new form factors.

In the short term, AMOLED displays cannot compete with LTPS TFT-LCDs in the smartphone form factor. Meanwhile, the foldable OLED display is an attractive form factor that LCDs cannot achieve, but the high cost and the complex production difficulties of the foldable screen hamper its growth.

However, the dark mode capability may yet provide AMOLED the necessary advantage to penetrate the smartphone display market more rapidly compared to the past, especially if only a change in software, not hardware, is involved. If consumers start getting used to dark mode, AMOLED displays will rapidly spread throughout the smartphone display market.

Dark mode makes screen notches and holes unobtrusive

When the OS is black, screen-form factors like notches and holes will not be as obvious. Screen notches and holes are not so much functional parts of the display but instead serve as a receptacle for the front-camera module, infrared (IR) module, and facial recognition module. In dark mode, smartphone users won't notice the existence of a notch or hole because the whole screen will show as a dark background.

Given the lack of flexibility in manufacturing or production, AMOLED display makers have long struggled with both OLED front-end and back-end module processes to integrate the form factor of either the notch or the hole. Furthermore, AMOLED displays sometimes miss opportunities in the market because introducing a new process is much more difficult in OLED than in LCD. But as the screen notch or hole becomes less obvious with refinement of the technology, the pressure borne out of introducing new processes can gradually ease for AMOLED display makers.

Since 2019, the technology for under-the-screen fingerprint and fingerprint on display (FoD) readers has taken off, thanks to the promotion of FoD by Chinese smartphone brands, as we pointed out in an analysis in the Display Dynamics article, Display fingerprint (FoD) solutions for TFT LCD displays. But the introduction of FoD gave AMOLED displays an advantage over LCDs, according to research in the Display Fingerprint Technology & Market Report - 2019, impacting the latter despite their inclusion of new features like a bezel-less screen as well as the more discreet screen notch or hole for a streamlined appearance.

Now with the arrival of the new dark mode and given the ramp-up in capacity of new Chinese OLED display makers, Chinese smartphone brands will have even more reason to switch from LCD to AMOLED display use. These developments will affect the long-term prospects of the LTPS TFT-LCD space while leaving relatively untouched the market for amorphous silicon (a-Si) TFT-LCDs, projected to remain stable as their use continues in the low-end smartphone and feature phone market.

The key to how quickly the market transforms will depend on how fast end-users embrace the dark mode feature for their smartphones.

Rigid OLED vs. flexible OLED in dark mode

Dark mode presents no distinct differences whether the feature is used in rigid OLED displays or in flexible counterparts where the screens can be curved or foldable. Nevertheless, newcomers to the panel-supply industry, especially those in China, are all choosing the flexible form factor as their OLED technology of choice, based on the following considerations:

  • OLED fabs in China are all established through government subsidies, and fabs featuring fresh technology—flexible OLED is newer and more advanced than rigid—are considered to have an edge in obtaining the subsidies.
  • Chinese makers are leaders in LTPS TFT-LCD smartphone display shipments and capacity. But because rigid OLED and LTPS TFT-LCD are both glass-substrate-based, the use of rigid OLED does not impart enough differentiation to stand out in the market
  • The cost-performance ratio of rigid OLED displays is lower than that of flexible OLED displays. The large profits of Samsung Display in its use of flexible displays has driven this point home for Chinese panel suppliers.
  • Apple skipped rigid OLED and went directly to flexible OLED when it released the iPhone X. And the iPhone is always on the forefront of innovation.

Nearly all Chinese OLED display suppliers today train their focus on flexible OLED, leaving the rigid OLED market almost entirely to Samsung Display, as we reported in the AMOLED & Flexible Display Intelligence Service. However, flexible OLED displays are not easy to make, which makes their increasing deployment on high-end smartphone models that much more remarkable.

For Chinese panel manufacturers, the introduction of dark mode widens their chance to compete in the market, even as they continue to struggle with low yield rates, high depreciation costs, and other issues. The situation is especially acute for Chinese OLED display makers, who are said to be producing flexible OLED displays without the flexible form factor, such as 2.5D, to cut costs and narrow the gulf between OLED and LTPS TFT-LCD.

Now with a new OS like dark mode, there are greater advantages given to AMOLED displays compared with LTPS TFT-LCDs, and this might be helpful for Chinese OLED display makers to introduce their OLED panels.

Next year will be a critical time for the smartphone display market, with several factors influencing how the smartphone display space will fare in 2020. These factors include the progress of FoD reader technology in LTPS TFT-LCD panels, the new module capacity and capability of Chinese OLED display makers, whether middle=end smartphone models switch to OLED displays from the existing LTPS TFT-LCD technology, and the ramp-up of new fabs among Chinese flexible OLED display makers.

Into this complex, dynamic mix we can add one more factor: the acceptance of the new dark mode by end-users. It remains to be seen whether the feature will create enough interest to help lift AMOLED to new levels of use and influence in the display panel market.

David Hsieh
is research & analysis director for displays at IHS Markit
Posted 29 August 2019



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