Opportunities and Challenges in Mobile Displays
May 24,2016, Society for Information Display, San Francisco—Hiroyuki Oshima from Japan Display presented a wide-ranging talk on displays, focusing on the next generation of mobile devices. This display category is primed with opportunities, yet faced with many technical challenges to achieve those opportunities.
Displays have evolved from the early CRTs to flat panels, first as plasma then moving through arduous technical issues to active-matrix LCD, and now starting to move to OLED. The changing nature of the displays affected the markets for downstream products. Flat panel displays first appeared on portable PCs due to their size, weight, and form factor to enable laptop devices.
From PCs, the technologies bifurcated. One path was for larger displays for TVs and other fixed installations, while the other path addressed the mobile spaces. Together, the markets for active matrix LCD and OLED displays comprise a $140 B market.
The ability to make small, light, low-power displays is a key enabler for innovation in the mobile spaces. The mobile devices are driving new apps like IoT, big data, and new transmission protocols and carrier technologies like 5-G. For all of these emerging areas, the market growth depends on changes in technologies.
The underlying core technologies for all mobile displays have to address the critical factors of visual performance, form factor, power consumption for the display as a system, and touch interfaces. The most promising technologies currently under development are low-temperature poly-silicon (LTPS) for the backplane, in-plane switching (IPS) for the front plane LCD, in-cell sensors, and an overall systems view of the display and drivers.
LTPS is considered the backplane technology of choice since the material has a higher electron mobility than the existing amorphous silicon. The higher mobility allows for better dynamic range, higher refresh frequency for the high-resolution functions, and lower refresh frequency for lower power operation. In addition, the materials do not have to be on a planar surface which permits curved and non-rectangular displays.
The IPS improves viewing angles and other visual parameters. The in-cell touch sensor integrates the touch point with the pixel, virtually eliminating parallax errors while enabling pressure sensing. The technology also helps to reduce manufacturing complexity and display weight by reducing the components in the display stack.
Other efforts are focusing on the visual aspects of the display. The addition of white emitters to the RBG mix improves the overall brightness, something highly desired in mobile displays in outdoor settings. Consumer demands and technology trends call for better resolution, more pixels per inch, and other visual enhancements. These changes will enable handheld and automotive displays to better meet future needs.
We expect to see many changes in the next 4-5 years including increased system integration and displays on flexible substrates. The input sensing functions will move from touch to multi-factor touch that can distinguish between fingers and stylus. Touch functions will gain capabilities to detect hovering and proximity to enable more functions on the display. The added functionality will engender novel apps.
The emergence of flexible substrates will offer a new range of design options for devices with displays. The application of OLED on plastic will let designers work with curved, flexible, and foldable displays. These new functions will require extensive changes in many technologies and in the manufacturing equipment to become viable.
At this time, the industry considers LCD to have better parameters than OLED except for the ability to be on flexible substrates. As a result, expectations are that OLED will overtake LCD in mobile displays in the 2018 timeframe. In the future, expect to see all displays to have improved performance specifications like better viewing angle and lower power. Even so, there will still be a gap between the real world and a display.
As displays evolve from an output device to an interface component, the technologies need to become more human friendly. In addition to the existing functions of touch, we should see other functions associated with the display, including biometric sensing for security and environmental sensors like ambient light to automatically change brightness. The biggest challenge is to integrate the input and output functions into a single device.