New sizes, new shapes, new technologies: a huge wave of change in smartphone displays

Nov 15, 2017

By Patrick Worfolk

Once again, the mobile phone display is the engine of change in the mobile phone market. Previous waves of change have brought capacitive touchscreens, high-resolution Full HD displays, and the integration of touch and display controllers. Now, the rate of innovation is accelerating once again, as smartphone manufacturers introduce new aspect ratios, new edge-to-edge infinity display designs with almost no bezel, and new biometric sensing technologies including advanced fingerprint sensing, face recognition, and iris recognition. All this on top of a continuing shift from liquid crystal display (LCD) technology to organic LED (OLED) display technology.

So how are these emerging display technologies and designs likely to evolve in the coming months? And how do suppliers of display and sensor technologies to mobile phone manufacturers need to respond if they are to profit from this evolution?

The ‘unputdownable’ device

The drive to maximize the display area is evident in the infinity display found on Samsung’s flagship Galaxy S8 range, and the recently announced Apple iPhone X. The smartphone has become an all-purpose portable media player. And since 4G/LTE connectivity means that the phone is constantly connected to a broadband internet service, consumers can enjoy an endless stream of broadcast content, social networking interactions and music. Much of the content consumed is pictures or video, and the bigger and the higher-resolution the display, the better these can be rendered.

A bezel-less or edge-to-edge display allows the manufacturer to provide a bigger effective display area without necessarily increasing the overall dimensions of the phone.

At the same time, manufacturers have brought in the first major shift in aspect ratios for at least five years, replacing the common 16:9 aspect ratio with extra-long aspect ratios of 18:9, 19:9 and more. This satisfies the requirements of virtual reality (VR) headsets that use a smartphone as the display device. Here, a minimum 1:1 aspect ratio for each eye provides an optimal viewing experience.

These new display formats create a design problem for the phone manufacturer, however: with no space for a physical home button, how can they provide an easy and secure method of unlocking the phone? The most recent generations of mid-range and high-end phones used a fingerprint sensor as the primary secure unlocking device. The sensor is normally located on the home button in the bezel on the front of the phone.

If the front bezel is removed, what is to be done with the fingerprint sensor?

This is an important question for phone manufacturers. Consumer research shows that it is not uncommon for users to look at their phone 80 or more times a day, which translates to unlocking their phone 80 or more times a day. The fingerprint sensor has emerged as the preferred method for unlocking the display – it is quick, secure and convenient. But it is not the only method, and other technologies including face recognition and iris recognition, may gain favor as a multi-factor supplement to the fingerprint sensor for stronger security.

But if the unlocking operation is to be performed 80 times a day, it has to be so smooth and easy that it causes no irritation to the user. For this reason, shifting the fingerprint sensor to the back of the phone, while convenient from a design point of view, is often unpopular with users. Most users leave the phone display side up when idle. With the fingerprint sensor on the back, they have to pick the phone up and locate their finger on the blind side of the display in order to unlock it.

Is there no solution?

The answer is in the display! When the fingerprint sensor is required, such as for unlocking the phone or to authenticate a mobile payment, a small area of the screen could be briefly highlighted as the sensing area. When not acting as a fingerprint sensor, this area operates as a normal portion of the display screen.

This calls for the implementation of new optical fingerprint sensing technology, and the technology for secure, reliable optical fingerprint sensing exists today. The challenge is to implement it within the very tight space, location and power constraints imposed by mobile phone manufacturers, and to integrate it in the complete display assembly in such a way that it causes no discernable degradation in image quality. This requires an excellent working relationship with the display manufacturers.

New style of Home button

If smartphone manufacturers are to eliminate the bezel at the bottom of the display screen, with the effect of lengthening the display, they will also lose the location of the Home button (if provided). Today, the Home button is typically provided in the form of an electro-mechanical switch – a physical device which requires a fixed location on the phone assembly, separate from the display.

Here, advanced sensing technology can provide a solution: a variable-force sensing device can detect a sustained or measured press on a defined portion of the display screen, even through the tough cover glass of a mobile phone display.

A sensor can therefore be configured to provide a virtual home button whenever the display is in ‘user input’ mode – for instance, when the display detects the proximity of the user’s finger.

Why is Synaptics well-positioned to succeed from these disruptions?

In the above, we have outlined a series of challenges facing the mobile phone display supply ecosystem arising from a profound change in the size, format and design of the display, complicated by a continued migration from LCD to OLED technology.

With change comes opportunity, and the commercial potential is greatest for those companies which can offer attractive and proprietary technology which will help electronics manufacturers maximize consumer appeal.

In the view of Synaptics, the current wave of change plays to the strengths of its portfolio of advanced user-interface technologies. In particular, Synaptics can offer:

  • A clear roadmap for the commercialization of in-display optical fingerprint sensing for mobile phones. Optical fingerprint sensing in industrial and commercial settings is widely used today, but the challenge is to implement it in a display assembly which is only a millimeter thick, and without affecting the display viewing experience. Synaptics expects to reach full production with a top-tier customer with this technology by the end of the 2017 calendar year.
  • Commercial availability today of in-display force sensing, which can be used to implement a virtual home button. The Synaptics in-display force sensor has no negative impact on the display viewing experience.
  • Complete solutions, such as our broad touch controller and display driver integration (TDDI) product portfolio, a result of its long standing engineering relationships with display manufacturers.

Synaptics provides the most advanced capacitive and optical sensing technologies deployed today, as well as superior display-driver performance. As the display takes on ever greater importance as a factor driving consumer preferences, Synaptics stands well-placed to support mobile phone manufacturers in providing an ever-improving user interface, and to excel in these opportunities by providing high-performance components that are of great value to display screen and mobile phone manufacturers.

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