Backplane

This is the fifth article in our OLED display backplane series. In the previous article, we examined oxide TFTs (IGZO), the transparent metal-oxide semiconductor that brought ultra-low leakage and large-area uniformity to OLED TVs and monitors. Here, we look at LTPO - the hybrid backplane that puts LTPS and oxide transistors on the same panel to enable variable refresh rates from about 1Hz to 120Hz.

Two materials, one backplane

Despite the name, LTPO - low-temperature polycrystalline oxide - is not a new semiconductor at all. It is a hybrid backplane that places both LTPS and oxide (IGZO) transistors on the same panel and uses each one where it is best. The idea was originally developed by Apple, which filed its foundational patents around 2014, and it has since become the defining backplane of the premium mobile display.

Samsung Display announced its latest M16 OLED material stack, that enables the world's first 2K 165K smartphone AMOLED panel. The first M16 2K 165Hz panel will debut in the upcoming Vivo iQOO 16 gaming smartphone. The M16 stack supports peak brightness of up to 10,000 nits.

Samsung says that it has managed to reduce the power consumption by around 30% compared to its previous-generation smartphone AMOLEDs, even though it has increased the resolution from 1.5K to 2K.

This is the fourth article in our OLED display backplane series. In the previous article, we examined LTPS, the laser-crystallized silicon that finally drove OLED displays. Here, we look at oxide TFTs (IGZO) - a transparent metal-oxide semiconductor with ultra-low leakage and large-area uniformity, the backplane behind big OLED TVs and the new wave of high-resolution IT panels.

Oxide TFTs broke the old choice between cheap-but-slow a-Si and fast-but-unscalable LTPS by using a different kind of material entirely: an amorphous metal-oxide semiconductor. The most famous is IGZO - indium gallium zinc oxide. IGZO itself was first synthesized as a crystalline ceramic material in 1985 by Dr. Noboru Kimizuka from the Tokyo Institute of Technology. In 2004, a team led by Hideo Hosono at the Tokyo Institute of Technology invented the first amorphous IGZO TFTs.

IGZO's mobility, around 10 to 15 cm²/V·s, sits neatly between a-Si's ~1 and LTPS's ~100. That is comfortably enough to drive displays a-Si never could, and it comes packaged with two properties that turned out to be transformative.

This is the third article in our OLED display backplane series. In the first article, we introduced display backplanes and discussed the PMOLED display architecture, and then in the second article we discussed amorphous silicon (a-Si). 

In this article, we examine polycrystalline silicon, understand how it gave OLED the mobility and stability it needed to become the AMOLED backplane of choice - and also look at its scalability limitations.

From amorphous to polycrystalline

LTPS, or Low-Temperature Polycrystalline Silicon, starts from the same amorphous silicon we met in the previous article, then crystallizes it into polysilicon, which is silicon arranged into ordered crystalline grains rather than a disordered film. The "low temperature" matters because the whole thing has to happen on display glass substrate, and stay below roughly 600°C. Normally classic polysilicon requires much higher temperatures.

In recent years, the main focus of the OLED industry was on reducing power consumption. OLED developers introduced several novel technologies, including new backplanes, materials and device architectures, to increase device and system efficiency.

This article looks into the potential pressure that the acceleration of on-device AI (locally running AI engines as opposed cloud-based AI) will have on OLED developers to reduce the power consumption even further, especially within the laptop segment, and adopt novel next-gen technologies.

This is the second article in our OLED display backplane series. In the first article, we introduced display backplanes and discussed the PMOLED display architecture. Here, we examine amorphous silicon and its limitations.

If one backplane technology made the flat-panel era possible, it is amorphous silicon. a-Si TFTs are deposited by plasma-enhanced chemical vapor deposition (PECVD) at low temperature, in a process that is mature, inexpensive and extraordinarily uniform across very large sheets of glass. That is why a-Si scales effortlessly to the biggest substrates in the industry, up to 10.5-Gen, and why it has been used (and still is) in TVs and monitors for decades.

The main weakness of a-Si is its low electron mobility: at roughly 0.5 to 1 cm²/V·s, a-Si is about a hundred times slower than the polysilicon (LTPS) we meet in the next article. For an LCD, that turns out not to matter much. For an OLED, it is one of two reasons the technology never made it to mass production.

LG Display is reportedly launching a new 3 trillion Won ($2 billion USD) investment plan, to upgrade its existing production small-area mobile flexible AMOLED processes and technologies.

LG Display was chosen by Korea's National Growth Fund, and have received a low-interest loan of 1.3 trillion to increase its competitiveness, as the Korean government hopes to strengthen its display industry and fend off Chinese competition. LG Display will reportedly contribute 1.5 of its own capital, and it has also secured a 200 billion Won in a private loan. 

AP Systems announced that it is developing next-generation OLED mass production equipment, as it sees opportunities in the OLED sector to introduce new production technologies.

The first system the company is developing is a new Plasma Atomic Layer Deposition (PeALD) system, used for the deposition of High-Mobility Oxides (HMO) backplanes. HMO is sees as promising candidate for the next-generation OLED backplane of choice.