Flexible OLED Displays: Overcoming the Final Barriers to Mass Commercialization with High-Yield Manufacturing Processes

January 12, 2017

Technology experts have been tracking and forecasting the flexible OLED display market for years now, assessing the technology’s promise and potential for disrupting the consumer electronics market, and eagerly watching OEMs’ public demonstrations of early prototype flexible displays. And yet many of us would be surprised to learn that flexible OLED display technology has already arrived to the commercial marketplace – it may be in your pocket or strapped to your wrist right now.

Granted, the curved displays featured in Samsung Galaxy Edge smartphones and Apple Watches aren’t designed to be bendable by the end consumer. In the future, flexible OLED displays may be bendable, foldable, or even rollable, but today they are encapsulated in rigid protective glass and give us only a glimpse of what flexible OLED displays are capable of. Flexible OLED displays will differentiate a brand-new class of electronic devices and open a massive market opportunity for consumer electronics providers. Obvious target applications include smartphones, tablets, wearables and maybe also TVs, but new applications continue to emerge.

So what’s slowing the adoption of flexible OLED displays in the mass market? Certainly, it’s not a lack of ambitious product designers racing to exploit this technology and get to market ahead of their competitors with flashy new flexible devices. The real reason why this technology has yet to be commoditized is because flexible OLED displays are extremely difficult to manufacture at scale.

With flexible OLED displays, there is increased manufacturing complexity which will negatively impact yield during early production stages, further adding to the technology’s initially higher expenses. It is a result of manufacturers grappling with a myriad of new variables – new materials, new design layers, and new processes – that end up driving up cost and impacting yield. And as is so often the case, yield rate is the deciding factor when it comes to calculating OEMs’ investment risks and profitability projections associated with nascent technology.

Manufacturing challenges abound

Whereas rigid LCD displays have benefitted from some 30 years of ongoing manufacturing process refinement, mass manufacturing of OLED displays only began in earnest in the last five years or so, and even more recently for flexible-based OLED. And again, these early displays are not the variety designed to be flexed by the end consumer. Glass-encapsulated displays – be they rigid or flexible – are fundamentally more durable, and offer a built-in protective layer for the underlying circuitry, so they are naturally easier to produce.

Flexible OLED displays designed for consumer bendability leverage flexible polyimide substrates that are vulnerable to scratches, bubbles, and dust, etc., and they require thin film encapsulation to seal the display from contamination, particularly moisture. These encapsulating layers must be durable and yet pliant enough to be flexed and folded. In parallel, the per-pixel circuitry in OLED displays is considerably denser than with LCDs, and the pixels themselves are getting smaller to enable higher resolution displays.

Fortunately, these manufacturing challenges can be overcome with advanced automated optical inspection (AOI) and automated repair systems that that can identify and repair at high speeds and with high precision displays with manufacturing defects. This in turn can help boost yield rates toward the thresholds required for commercial viability.

By leveraging AOI and repair systems with sub-micron precision and multi-modal capabilities, it’s now possible to detect, identify and repair defects among multiple layers of transparent materials, from the polyimide substrate to the thin film encapsulation. The ability to illuminate materials from different angles and light wavelengths enables defects to be identified anywhere in the layer stack. And unlike legacy AOI systems that may require multiple scans to inspect materials, newer-generation systems can acquire this data in a single high-speed pass. 

On the repair side, ultra-precise, vibration-immune laser control now makes it possible to cut a short-circuited metal line down to one micron. High magnification and optical wavelength variability in turn enable lasers to ablate or drill through a selected layer in the stack without damaging surrounding layers. This is no easy feat, but it’s achievable today.

Flexible OLED displays position the consumer electronics market for a huge leap forward in design agility, commercial differentiation and revenue growth. Today we’ve only scratched the surface of its potential, but continued advancements in AOI, test and repair technologies that maximize yield are pushing us closer and closer to realizing the full promise of this game-changing technology.
 

Author: Shulik Leshem, VP of Marketing, Flat Panel Display (FPD) Division, Orbotech

Published by: EBN

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