Flexible Displays: From Conformables to Foldables

Since the development of flat-panel displays, products often had to be designed around the flat display, so it’s easy to forget that glass display component is a major design constraint. In a car, for example, the only remaining flat surface is usually the integrated display—every other surface is curved. Car designers today are looking for non-flat and non-rectangular displays to enable their seamless integration into the vehicle interior.

另一方面，智能扬声器通常具有圆柱形形状，需要环绕式显示器，而其他智能家庭设备将受益于带有孔的弯曲显示屏，以适应其他设计功能。

What Is a Flexible Display?

The termflexible displayis used in a variety of ways. For some, it means displays that are able to be flexed during use; for others it means displays that are flexed in the product housing, such as a curved glass TV. The most common definition of flexible displays is displays manufactured on plastic substrates. That means at some point during the manufacturing process the display was flexible, even if it’s finally laminated onto a rigid cover glass before being integrated into the product housing.

Conformable displaysare flexible during production but should be conformed to or wrapped around surfaces in a fixed curved shape in the final product. These displays offer a degree of design freedom that is not possible with flat glass-based displays.

One example of a conformable display isFlexEnable’sorganic LCD(OLCD) on plastic, which can be wrapped around surfaces with a bend radius down to 10 mm(Fig. 1). OLCDs can also be easily cut to different shapes by laser profiling, enabling non-rectangular displays and displays with holes, otherwise known as shapeable displays.

Shapeable display是一个不流行的术语，它不是指灵活性，而是设计和切割显示为异常（非矩形）形状的能力，无论是否随后它们都被符合，折叠或滚动。

The term可折叠显示is generally used to describe a display that can be tightly bent at 180 degrees on top of itself repeatedly. Foldable displays have been much talked about in the last few years thanks to some phone manufacturers’ efforts to differentiate themselves from the competition by launching innovative smartphone designs.

Rollable displays请参阅可以像报纸一样滚动至少20毫米的曲率半径或更少的显示器。最近，LG推出了65英寸。市场上可滚动有机发光二极管（OLED）电视，价格惊人的价格为87,000美元(Fig. 2).

Foldable和rollable displays制造仍然很困难且昂贵，但是好消息是，大多数产品不需要在使用过程中必须弯曲，折叠或滚动的显示器。例如，诸如汽车内部，智能房屋设备和店内数字标牌之类的应用程序需要显示在产品弯曲表面上。

要考虑的事情

并非所有灵活的播放技术都会满足每个产品需求。Flexible OLED目前是唯一可以启用可折叠电话和可滚动电视的显示技术。但是，与OLCD相比，由于其可靠性较低和制造成本明显更高（尤其是大型显示器），因此它不适合汽车展示。

Let’s take a look at some of the key characteristics that engineers should consider when choosing a display technology.

Design and Ergonomics

The aesthetics of the product are often determined by the display. Flexible displays offer exciting opportunities to product designers, allowing the display to follow the surface contours of the product housing. Moreover, there’s a trend for truly bezel-less designs, which is observed not only in smartphones, but also in notebooks, tablets and even TVs.

Flexible OLED has been used for several years to deliver bezel-less displays in smartphones by partially curving the display around the side of the product. OLCD offers an alternative approach that’s particularly suited to large-area applications such as notebooks—it makes it possible for the display to be borderless by folding the edges away.

In the case of OLCD, it’s also easy to make apertures—physical holes—within the screen itself, enabling seamless integration of the display with other functions. Consumers often make their buying decision based on the aesthetics of a product, and there’s huge potential to change the form of products in ways never previously imagined. Holes can be cut in the display during production without affecting performance, offering straightforward integration of anything from speakers and cameras to watch hands and toggle switches.

Even the most beautiful aesthetics in the world will soon be forgotten if the product is difficult or irritating to use. Flexible displays, if applied well, can improve the product ergonomics. They can allow wearable devices to sit more comfortably around your body, for example, or allow larger infotainment displays to be incorporated into vehicles, making them easier to view without sacrificing space for passengers. And, of course, plastic screens will also make tablets and laptops much lighter to carry.

Performance

Some of the most important factors for the wide adoption of flexible displays into products are their performance and longevity. For flexible displays to replace their rigid glass counterparts, they must achieve the same reliability standards as well as prove that they can perform equally well when they’re conformed and shaped.

The reliability of flexible displays depends strongly on the materials used to make them. While both organic and inorganic materials can be used for making flexible displays, many organic materials have the advantage of being inherently flexible. Over the last few years, the performance of these materials has improved immensely, allowing for their commercial application.

Organic materials are commonly known for their use in OLED displays, but they’re also used as semiconductor materials to make high-performance organic thin-film transistors (OTFTs). OTFTs can be then combined with a well-established and mature liquid-crystal frontplane technology to create OLCDs.

All display types need to go through rigorous reliability testing to prove they’re commercially viable. For example, shock temperature tests of the displays must be done to ensure that they’re suitable for the end product. New testing sequences also need to be developed that are relevant to the specific application and use case. Different tests will be required depending on whether the display needs to withstand a single bend or multiple bends, and the effect of the impact at different locations on a bent display has to be tested, too.

Display lifetime is an important performance consideration for many applications where the display is embedded. For example, home appliances might be expected to last for a decade, but displays used in automotive applications need to last as long as the vehicle.

While OLED is known for its high contrast and resolution, today’s flexible OLED displays struggle to meet the lifetime requirements for automotive applications. This issue is exacerbated by the high level of brightness required in cars, as it directly impacts on the lifetime of OLED pixels.

通过共享传统LCD显示器的许多组件（以及供应链），与玻璃相比，OLCDS在屏幕性能方面没有折衷。它们足够强大，可以应对振动和较大的温度变化，并且可以使室外使用足够明亮，而不会损害寿命，从而使它们非常适合用于车辆以及消费电子产品(Fig. 3).

一体化

灵活显示器的机械整合是对玻璃显示器的新考虑 - 重要的是，显示器坚固且具有弹性，以实现完整的“表面集成显示”而进行的层压或形成过程。相反，同样重要的是，从电气集成的角度来看，显示器看起来像玻璃显示器，使用相同的接口，协议和电压范围，以最大程度地减少现有和新应用程序采用的障碍。OLED和OLCD都使用标准界面进行驾驶。

费用

Currently, flexible OLED displays are expensive to manufacture, which is why they’re generally only seen in high-end products, such as flagship smartphones and smart watches. Costs will, of course, come down over time, but this issue will be exacerbated for larger display sizes, making it difficult to use this technology in mass-market applications such as home appliances, laptops, or TVs for the foreseeable future.

OLCDs have been developed specifically with this issue in mind. Using a display structure similar to traditional glass-based LCDs, the technology allows large display sizes to be made cost-effectively. This makes it feasible to create flexible, conformable displays for use in a wide range of applications, providing huge differentiation and margin opportunities through the supply chain.

The Future

Not all applications will require all display properties described in this article. For example, automotive displays need to be conformable and shapeable, but not really foldable, whereas a foldable tablet or phone could change the user experience and utility of mobile devices.

在未来几年,我们将开始看到flexible displays in nearly all applications where glass displays are used today. In addition, many new uses are possible, but only if displays can be wrapped around existing, non-flat surfaces.