IDTechEx’ insight on touch technologies for flexible displays

June 20, 2019 //By Julien Happich
flexible displays
The technologies seeking to unseat ITO (Indium Tin Oxide) are by now themselves old, at least in the sense that they have been around for a decade and a half, but they now have to compete on flexibility and foldability too if they are to be successful in flexible displays.

Leading Analysts at IDTechEx have been researching the technology and market landscape for the past eight years, but it is only from late 2018 to early 2019 that a series of foldable displays products were announced, some already in the customers’ hands. In its report, “Transparent Conductive Films and Materials 2019-2029: Forecasts, Technologies, Players” IDTechEx notes that every display company is building up the capability to develop and manufacture flexible/foldable displays, all of which will require some type of flexible touch technology.


Film vs on-cell: a story of trade-offs

The analysts saw flexible touch technologies emerge as two distinct approaches: film and on-cell types. In the former case, a flexible film is bonded atop the OLED device. In the latter, the touch layers are deposited and patterned directly on, or perhaps later as part of, the thin film encapsulation (TFE).

The table below provides a comparison of the two approaches. Film-type is the simplest to implement. Crucially, it decouples the production yield of the touch layer from that of the display layer. Furthermore, the films could be manufactured using lower cost assets. The scalability to larger areas will also be simpler and production speeds likely higher as R2R film production techniques can be deployed. Therefore, the film-based approach is a more accessible technology that offers an easier and lower cost roadmap towards larger-area flexible displays.

However, this approach falls short on performance. Material choices are now available which offer high flexibility and foldability. Metal mesh films are likely to be good enough for medium levels of folding. The picture for higher bending degrees becomes hazier, however technology options such as silver nanowires have already demonstrated that they can sustain the technology roadmap towards high bending levels. Clearly, all technology choices require further improvement however current issues are unlikely to be a fundamental showstopper. As such, transparent conductive layer technology choice itself is not a performance bottleneck.

The real limitation of the film-based approach is that it requires an additional substrate plus an additional bonding layer. This increases overall thickness, which in turn lowers flexibility.

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