Change is Coming to Smartphone Displays

Apr 04, 2017

By Kevin Barber


In the ruthlessly competitive smartphone market, the choice of display technology is one of the more important decisions that a manufacturer will make. Advances in touchscreen features and capabilities have in the past contributed to clear shifts in market share from one device to another. Handset manufacturers create marketing campaigns aimed at bringing consumers’ attention to the key visual and design differences central to their new model’s display and the displays of competing products.

There is always a question about how much consumers are willing to pay for incremental improvements in the viewing experience, or for a fractionally thinner form factor enabled by a new display, but edge-to-edge or infinity displays look poised to gain traction. The best evidence of this today is coming from the market for high-end smartphones, where OLED (organic light-emitting diode) display technology, pioneered by Samsung Display, is offering an alternative to proven, high-yield LCD (Liquid Crystal Display) technology.

While gadget enthusiasts readily recognize that a new OLED display offers, in some respects, a superior viewing experience to that of an LCD screen, the reality is that both OLED and LCD technologies in handheld form factors have reached an extraordinarily high level of quality. In terms of resolution, color gamut, contrast and brightness, today’s mobile phone displays – whether OLED or LCD – provide a stunning viewing experience.

Since OLED is the “new and improved” technology, it might be tempting to assume that it is on course to usurp LCD in almost all smartphones with the passage of time. But, in fact, each technology offers a mix of advantages and disadvantages, and more likely outcome is the continued use of both technologies for many years to come.

As the leading provider of touch controllers, display driver integrated circuits (DDICs), and touch and display driver integration (TDDI), Synaptics’ industry experience positions the company well to assess the upcoming market and technology trends for smartphone displays and display drivers.

OLED: a promising technology

The mix of benefits and drawbacks for OLED encompasses both the user’s viewing experience and the handset manufacturer’s operations, particularly involving system design and production.

From a purely visual perspective, OLED displays offer distinct benefits. The Organic LEDs offer a larger color gamut and a faster refresh rate, resulting in reduced motion artifacts and displays that “pop”. OLED displays are emissive, meaning they don’t require a backlight. Individual pixels can be turned on and off, resulting in high contrast with deeper, darker blacks and fully saturated color. By comparison, in an LCD panel the pixels are like windows. A backlight behind the window lights up the pixels. When a pixel is required to be dark, its “shutter” closes to block the backlight, but some light can still leak through.

Flexibility in industrial design is another important advantage of OLED technology. Removing the separate backlight and applying TFE (Thin Film Encapsulation) technology allows companies to produce curved displays, such as those found on some models of the Galaxy smartphone. The new and distinctive appearance of these phones is made even more appealing because the OLED panel is thinner and lighter than an LCD panel of the same surface area.

OLED displays are not without their drawbacks, however, as manufacturing cost and power consumption when the screen is brightly lit are still issues. Furthermore, the longevity of the panels is still a concern. An OLED display’s blue pixels degrade faster when the display is bright than the red and green pixels, which means that the viewing experience can worsen over the lifetime of the panel. Also, their organic materials are sensitive to moisture and oxygen, and require complex technology to ensure trouble-free operation over the lifetime of the phone. OLED displays at higher resolutions are still more expensive than LCDs due in part to the relatively low yields during manufacturing and assembly. Yields are improving, especially for flexible displays, but today they remain a premium priced product.

LCD: a proven technology

Advances in LCD technology have led to substantial improvements in viewing angle, resolution, and contrast, enabling LCDs to remain the display of choice for a majority of high-end smartphones. Price is always a factor when making design choices that must balance market appeal with integrated features and profitability, and the performance of well-priced high-quality LCDs has made it an optimum choice for mainstream phones as well.

Another factor where LCD has the advantage is the need for smartphone manufacturers to manage their supply chains very carefully to maintain volume production runs of many millions of units per month. The LCD panel market is proven, enjoys stable high yields at the highest resolutions, and is supported by a well-populated ecosystem of display manufacturers and component suppliers, including the requisite display driver integrated circuits (DDICs). By contrast, today Samsung Display is the only high volume supplier of mobile OLED panels, and most of its output goes to its sister company that manufactures smartphones.

Over time, the smartphone market will mature and bring up additional high-volume OLED panel manufacturers. Competition always drives innovation and cost, and various manufacturers of LCD panels already have plans to install manufacturing capacity for OLED panels in order to diversify their offering. Before the end of this decade, the OLED supply chain is expected to have scaled up sufficiently to meet the volume demands for all leading smartphone brands. At the same time, larger size and flexible-foldable designs will create new markets, as yield and supply improve.

Today, owing to this limited supply chain and associated cost premium, OLED displays have been introduced at the top end of the model range, especially in flagship smartphones, such as the Samsung Galaxy S. Most other smartphone manufacturers are expected to offer an OLED-based model beginning in 2017. Wider adoption of OLED technology in mid-range smartphones is unlikely to take place before 2019. So despite the increased investments in OLED manufacturing, LCD panels are likely to maintain their strong market position well into the next decade (see Figure 1).

Figure 1: Forecast of unit volumes for handsets using each of the three main display technologies

Related changes in display driver technology

Every display panel requires a DDIC or TDDI, which is a device that converts the data signals from the phone’s processor into the outputs needed to control each of the panel’s millions of pixels. For this reason, a DDIC or TDDI must be specifically designed and configured for each different model and type of display panel, whether LCD or OLED. 

Because every manufacturers’ display requirements are different, it is essential for their engineering teams to work closely with the IC vendor engineering teams to achieve a successful integration for optimal industrial design and best performance. This requires close cooperation all along the supply chain—from the display, backlight, and IC vendors through the device manufacturers.

In addition to integrating the display with the display driver, it is also beneficial to integrate the display’s other major functions: touch navigation and user interface. Incorporating the touchscreen controller into the DDIC is known by the acronym TDDI (Touch and Display Driver Integration).

TDDI offers important benefits to both the manufacturers and users of smartphones. By replacing two chips – a touchscreen controller IC and a DDIC – with a single chip integrating both functions, manufacturers are able to reduce the size, complexity, and cost of the display assembly, and to simplify their supply chains and production processes. TDDI even enables manufacturers to design a better and brighter display, including those with narrower borders because there is no need for external routing on the sides or top of the display panel. These narrower borders allow the bezel-less designs that are needed to produce full-size, edge-to-edge “infinity” displays.

As flagship designs push towards ever larger, brighter, better displays against the constraints of comfortable industrial design the edges of the phone must give. This leaves little room for extra buttons, sensors, and integration becomes critical. The move away from rigid display materials will be first, towards flexible display packaging and plastic backplanes, which even LCD manufacturers are working on. The question is only how quickly the industry ramps manufacturing capabilities. Ultimately, your mobile device may be truly foldable, but manufacturers will want to bring these features to mid-range devices as well.

Smartphone manufacturers are enjoying the cost-saving, additional features, and performance benefits of TDDI today for phones that use an LCD panel. The same benefits can be expected for phones with flexible OLED panels, but this will take time because both OLED display manufacturers and TDDI vendors will first need to learn from the implementation of discrete DDICs and touchscreen controllers in OLED displays. Then, the current manufacturing and integration challenges facing mobile OLED displays will be overcome, making this innovative technology available for the broadest selection of models from a growing range of phone manufacturers.

Summary

LCD is currently the mainstream technology for smartphone displays, with a broad, mature supply chain and with panels that are used in low-end smartphones all the way up to flagship products.  Companies like Synaptics are providing display manufacturers with the latest display and touch capabilities via high-performance DDIC and, increasingly, TDDI solutions. OLED provides benefits over LCD due to the fact that OLED panels do not require a backlight and can be flexible. While OLED displays are now common in flagship models from Samsung and others, the OLED supply chain will need to grow and mature further for OLED to gain traction in mainstream phones. Whether display panels are LCD or OLED, Synaptics - as the industry leader in touch controllers, DDICs, and TDDI - is well positioned to bring continued innovation and display driver products to the global smartphone market.