Jul 01, 2020
By Janice Mori
There is little question that OLED displays are the future of mobile. Device makers confirm with the on-going stream of new device introductions that OLED provides superior performance and enhanced optical characteristics compared to the older LCD option.
Synaptics is in the middle of this evolution, enabling the advantages of OLED for top-tier device manufacturers. These benefits include improved image quality, including better contrast, higher brightness, fuller viewing angle, blacker blacks, a wider color range, and much faster refresh rates; lower power consumption; and better durability to operate in a broader temperature range.
As importantly, OLED more readily enables flexible display panels which can bend in your pocket or even fold and have emerged as the favored alternative to rigid displays. Market forecasts predict 40% CAGR over the next three years for flexible OLED displays (which includes the subset of emerging foldable displays). We expect this to be a key growth driver throughout the high-end sector of mobile devices and into the mainstream – and potentially even down into the more price sensitive mid-tier by 2023.
Being in the midst of the shift with our OEM partners, Synaptics gets a front row seat to some pretty cool innovations enabled by OLED display technology. Flexible OLED displays not only provide an enhanced user experience, but also enable new form factors and features. These include borderless ‘infinity’ and waterfall displays, enhanced touch controls to replace physical buttons, face detection to automatically dim the screen when the handset is held to the ear, active pen based input, and foldable screens – all additional ways phone makers will differentiate their devices on top of traditional display performance features such as pixel count and refresh rates.
But in consumer markets with narrow profit margins, OEM product developers and their display suppliers must balance the need for continuous improvement for an improved user experience with cost effective manufacturing and yield processes.
Flexible On-Cell OLED is challenging, the touch metal mesh is integrated with the polarizer into the encapsulation layer and only 80µ from noisy pixels
On-Cell Architecture Lowers Cost but Presents New Challenges
Underlying the shift to flexible OLED displays is manufacturers’ transition to On-Cell architectures. This technique deposits the touch sensor directly on the encapsulation layer of the display, eliminating the need for a separate layer to enable touch. On-Cell improves optical and mechanical performance, allows for a significantly thinner display module stack-up, and reduces system cost by integrating the touch sensor directly in the display. With On-Cell, an embedded metal mesh touch screen allows a brighter OLED display.
But On-Cell also poses major technical challenges including high background capacitance coupled with ongoing display noise which impacts touch performance. Overcoming these increased noise challenges is critical to delivering on the full potential of On-Cell.
Addressing Display Noise and Interference Challenges
Capacitive touch controller chips that enable accurate sensing are evolving to meet the requirements of flexible displays, and On-Cell specifically. Synaptics has earned its market share lead in touch displays by working closely with display manufacturers on a mass production on-cell solution for years, building simulation and testing tools and developing special algorithms addressing the challenges to meet touch accuracy, position, and linearity requirements.
On-Cell OLED is an order of magnitude more challenging to solve than LCD, requiring Synaptics to develop novel display noise removal circuitry to resolve noise issues and deliver the necessary performance in a power-efficient manner. In addressing the background capacitance advanced analog circuitry is also required for removing the background capacitance. Noise avoidance techniques can also be used, including a technique called frequency hopping that senses what frequency range where the noise interference is located at and then jump/hop to another frequency spectrum that is quieter.
At the same time, touch controllers must continue to provide the intuitive user experience developers demand, with better signal to noise to ratios (SNR) and high touch refresh rates (up to 240Hz), as well support emerging premium features such as active stylus-based input, face detection, variable force sensing, edge-to-edge displays and side touch controls that can eliminate physical buttons.
Touch Controller ICs Evolve with Display Innovation
Displays on mobile devices will continue to be an important differentiator for product developers, and evolutions in capacitive touch sensing is a critical aspect of that progress. Specific challenges in the flexible space including performance in noisy environments, enabling better industrial designs, and supporting advanced features like active pen and face detect, require innovative approaches by the underlying controllers. Advanced touch controllers specifically for flexible on-cell OLED displays are needed to support the thinner, brighter displays for a new generation of advanced smartphones.