Metal oxide backplanes gain commercial ground

The IDTechEx market research report 'Metal Oxide TFT Backplanes for Displays 2014-2024: Technologies, Forecasts, Players' estimates that 7km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a $16bn market at the display module level. The LCD display market will add an extra demand of at least 1km sqr per year in 2024 for metal oxide backplanes.

A strong value proposition

The metal oxide backplane technology has many clear advantages, offering high field-effect mobility and spatial uniformity. This is beneficial for large-sized OLED displays, which are current driven. It is also good for HD displays as the high mobility enables increasing the aperture ratio. The ON/OFF ratio is high (also the leakage current is low) meaning that device power consumption is low. The manufacturing process is based on sputtering, which is a well-known process in the industry, therefore not requiring drastic modification to existing installed processes. The wide bandgap nature of the semiconductor also suggests that devices can be transparent, paving the way towards transparent displays although we note that instability issues under visible illumination persist.

This technology therefore compares favourably with many competing solutions. While it is neither as fast nor as stable as LTPS, it is more scalable. It is not as low cost as amorphous silicon (depreciated assets and large accumulated production experience) but is faster and more stable. It is perhaps not as intrinsically flexible as organic and carbon nanotube TFTs, but it is already more mature, stable and amenable to large-scale production.

Technology limitations

The technology is however not without its limitations. The production yield has been low, largely due to a lack of accumulated production experience in the industry. The window of optimal processing conditions is narrow, making manufacturing more challenging that initially assumed. The device stability (e.g. threshold voltage stability) has remained a persistent challenge, although the devices are now far better as the channel composition, the dielectric/challenge and the passivation layer deposition processes are all further optimised.

Plastic and flexible displays are emerging. The first commercial examples are bent or curved mobile phones that are rigid but on a plastic (i.e. polymide) substrate. All types of backplane technologies can be utilised here as the processing takes place over a carrier glass and polyimide substrate itself can also tolerate high processing conditions.

IDTechEx believes that this is the fourth wave of OLED displays after small-sized displays, mobile/tablets and TVs. Indeed, we forecast that the units of rigid plastic displays will be 8m in 2014, 70m in 2018 and 170m in 2024; while the units of flexible plastic displays will be 37m in 2018 and 148m 2024.

Prototypes of flexible displays with metal oxide backplanes have also been demonstrated although there is still a paucity of data on measuring the reliability of these backplanes under extreme or multiple bending cycles. The common strategy today is to carefully control device thinness so that the backplane lies in the neutral plane when bent, thus not experiencing large mechanical stresses. This approach is non-ideal for truly flexible and even rollable devices. Indeed, the technology choice for truly flexible and even rollable devices is still not fully settled and no clear winner has emerged.

Dynamics of the OLED TV market

The dynamics of the large-sized OLED TV market are interesting. LG has invested in a white OLED technology with IGZO backplane that is easier to scale, while Samsung's technology is more competitive at smaller display size. This has meant that many are now seeking to use quantum-dot layers as a way to upgrade large-sized LCD displays to OLED-quality displays. This is a threat to large-sized OLED and therefore also to IGZO planes, although we are still at the early stage and the best quantum-dot products on the market still contain cadmium, a toxic material.

'Metal Oxide TFT Backplanes for Displays 2014-2024: Technologies, Forecasts, Players'

The market for metal oxide backplanes is at the beginning of its growth phase. IDTechEx draws upon its technical and market expertise to make sense of this complex space. IDTechEx analysts have hands-on experience of fabricating, characterising and modelling metal oxide TFTs and have developed a detailed body of market and technology knowledge around displays with strong emphasis on OLED displays including plastic and flexible versions.