Foldable displays are the hot new technology on the block, with Royole’s FlexPai2 and Samsung’s Galaxy Fold hitting the market in the last couple of years. These phones are based on active-matrix organic light-emitting diode (AMOLED) screen technology, which offers transparent, high-resolution displays in a flexible film.

The FlexPai2 from Royole.

The FlexPai2 from Royole. Image used courtesy of Royole

Currently, rumors are circulating about a foldable eight-inch iPhone by 2023, based on comments from Apple Analyst Ming-Chi Kuo. Although Apple is notoriously hush-hush about unpolished releases of their technology, they have been receiving patents for years based on folding technology.

It would be hard to argue against the fact that Apple only releases polished technology. In that light, is AMOLED folding technology ready for an Apple product, or are there other display technologies on the horizon that could be a contender for the new iPhone?

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AMOLED Foldable Displays Pass the Test

Royole’s new 3rd generation Cicada Wing flexible display has undergone extensive materials testing for layer peeling and strain relief. Additionally, the film has been through environmental testing for maximum bends (200,000+), twisting, stretching, and drops. This thorough testing conclusively demonstrates that AMOLED display technology is ready for mass commercialization from a physical durability standpoint.

Since OLEDs are mechanically ready, the question remains about overcoming the high cost for organic materials and fabrication procedures that limit electron mobility.

Perhaps the new innovation, micro-LEDs (or µLED), could provide similar mechanical features and superior electrical characteristics?

Are µLEDs the Display Technology of the Future?

Can the dominant display technology in 2021, AMOLED, compete with upcoming µLEDs for the crown in the next decade?

According to research published in Nature by Huang et al., µLED technology has some serious advantages over AMOLED. However, the drawbacks are preventing mass fabrication and the adoption of the technology.

Taking a look at the configurations of the three display technologies, you can get an idea of the display film’s physical construction, thickness, and complexity.

Layers & configurations: LCD, OLED, µLED.

Layers & configurations: LCD, OLED, µLED. Image used courtesy of Topway Technology

Beyond the physical configuration, it is necessary to explore some of the trade-offs before getting excited about the future of your next commercial display.

Benefits of µLEDs When Compared to AMOLED

Several parameters are critical for evaluating the differences in these two technologies.  These parameters include:

  • Efficiency,
  • Luminance Output,
  • Ambient Contrast Ratio (ACR),
  • High Dynamic Range (HDR), and
  • Response Time

According to the research by Huang et al., and depending on the driver characteristics, µLED can overtake AMOLED technologies quickly in maximum luminance, ACR, HDR, and response time.

Relative efficiency with respect to chip size demonstrates the power advantages of color conversion (CC) µLED films.

Relative efficiency with respect to chip size demonstrates the power advantages of color conversion (CC) µLED films. Image courtesy of Huang et al 

In addition to these parameters, AMOLED technologies suffer from two major weaknesses that affect their durability, including screen “burn-in” and a shorter lifespan for organic materials which produce blue wavelengths.

So far, µLEDs seem appealing, but what are the drawbacks?

µLEDs Power Efficiencies Could Slow Mobile Adoption

There are two drawbacks, from an electrical standpoint, that present problems for µLED technology.

micro leds vs oleds whats the future for foldable displays 3 hyperedge embed image

Figure a) external quantum efficiency (EQE) versus luminance; OLED  (dashed lines) and µLED (solid lines). Figure b) normalized EQE / Vf (dashed) vs current for µLED. Image courtesy of Huang et al 

Although µLEDs have a significantly higher peak potential luminance (solid lines figure [a]), the external quantum efficiency (EQE) varies considerably over the operating luminance range. Secondly, unless using a color conversion configuration for all blue light, green and red µLED can be less efficient than OLED.

Comparatively, OLED technologies (dashed line figure [a]) have a flat response up to nearly 1000 cd/m2.

There are two primary modulations used to drive LEDs, pulse amplitude modulation (PAM) and pulse width modulation (PWM). The research found that PWM can be a superior drive technology for µLEDs, improving their relative efficiency over PAM, with an increase of 30%, 91%, and 28% in efficiency (circles vs. triangles in figure [b]).

Seeing the Future in Foldable Displays

It isn’t easy to know how these new technologies, foldable displays, and µLEDs, will be commercialized in the future. Foldable displays are undergoing rigorous environmental testing, and there is a market demand for high-quality, highly flexible, long-lasting display films.

After diving into new research, it does seem that µLED could take the lead over AMOLED in the coming years once efficiencies and fabrication processes improve.

Finally, Apple’s projected release of an eight-inch folding iPhone could be the technology event that blurs the distinction between tablet and cellphone.


Interested in learning more about µLEDs and flexible display advancements? Read more down below.

The Roadmap Ahead for Micro-LEDs is Anything But Small

Designing Stretchable Devices and Displays with Transparent Electrodes

Developing Bendable and Entirely Flexible Electronics with A New Class of Films

This post was first published on: All About Circuits

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