Low cost flexible displays poised for growth

At present, most displays are either the key feature of the device, such as televisions or smartphones, or a prominent fixture in a high value product (e.g., car interiors). Most displays are thus relatively high value components requiring relatively high resolutions and a lifetime of at least a few years.

However, as a greater proportion of devices become functional, opportunities for low-cost displays with different key performance indicators are likely to increase dramatically.

Application opportunities

Smart packaging is arguably the low cost display application with the greatest scope for growth. Displays can be integrated into both shelf-level and item-level packaging, with the former likely to emerge first since the lower volumes enable higher unit costs.

At present, electroluminescent displays are sometimes incorporated into limited edition production runs for marketing processes, but these are not regarded as an effective long term solution due to their high power requirements.

Another application for low cost displays is small consumer goods. This has long been the case for some premium items such as electric shavers, with small displays that show the remaining charge, for example.

However, as displays get cheaper and electronic functionality/wireless capability is integrated into more devices, this could be expanded to an ever-growing range of devices and appliances. Indeed, it might not be long before bank and travel cards contain a low-cost display to show your balance and/or recent transactions.

Wearable technology is another promising application for low cost displays. While OLED displays are widely used smart watches, they are generally too expensive at present to incorporate into clothing and skin patches for medical/fitness/therapeutic applications.

The key attributes for displays in clothing and skin patches are durability, flexibility, and low power consumption. This example demonstrates that for many emerging display applications, the traditional key performance indicators of resolution, color gamut and refresh rate are no longer especially important.

Electrophoretic displays

The most promising low-power display technologies are those that employ a bi-stable material that requires power only to change color rather than to maintain it. Electrophoretic Displays (EPDs) are the best-known example, which have long been used for e-readers. However, they are somewhat falling out of favor for this application as consumers prefer the full-colour images available on a tablet.

However, EPDs still hold promise for applications in which a straightforward non-emissive display is entirely adequate and low power consumption is a priority. The most notable technical development in this space is the recent launch of full-colour electrophoretic displays by Plastic Logic. This display is flexible, active-matrix driven with 240 x 146 pixels capable of displaying 4 colours plus black and white, and is being targeted at smartcards, wearable technology such as e-textiles, and shelf labels.

Figure 1: Novel applications for electrophoretic displays. Photography courtesy of Plastic Logic

Electrochromic displays

Another, arguably simpler low power and low cost technology is electrochromic displays. By applying a small voltage across the active material, its oxidation state and thus colour will change. This process is again bi-stable, meaning that a continuous power supply is not required. However, the colour will gradually fade as the system returns to thermodynamic equilibrium, requiring a voltage to be briefly applied to return to the required colour.

Ynvisible are the main players in the electrochromic display space; they are targeting both smart-packaging and medical applications such as skin patches with indicators. IDTechEx forecast electrochromic displays to exhibit the fastest growth, but electrophoretic displays to continue to dominate the market.

Figure 2: Market forecasts for electroluminescent, electrochromic and electrophoretic displays. Source: IDTechEx Report 'Flexible, Printed OLED Displays 2020-2030: Forecasts, Markets, Technologies'

Alternative approaches

For applications that require low-cost emissive displays, neither electrophoretic or electrochromic displays are applicable. An emerging approach here is mounting conventional (or mini) inorganic LEDs on flexible substrates with conductive traces applied by either printing conductive ink or etching/ablating.

Although these approaches cannot compete on resolution with conventional OLED or LCD displays, their low cost per area and flexibility makes them suitable for large-area displays such as marketing and architectural lighting/display features.

A related low-cost display technology is printable LEDs, in which mini-inorganic LEDs are suspended in liquid and can thus be printed using conventional graphics printers. The LEDs themselves lie between two layers of conductive ink with an intermediate dielectric layer and can be addressed in segments if required. Again, these are targeted primarily at smart packaging and wearable medical/therapeutic applications.

A comprehensive overview

Overall, IDTechEx believe that the market for low cost displays is set to greatly expand over the next decade as increasing numbers of devices gain electronic functionality. The differing requirements of these applications, most importantly low power consumption and flexibility, will lead to increased adoption of alternatives to conventional LCD and OLED displays.