PORTLAND, Ore. — To meet the growing demand for displays using metal-oxide thin-film transistors (TFTs), Applied Materials, of Santa Clara, Calif. -- the world's biggest semiconductor equipment maker -- just announced new models of its plasma enhanced chemical vapor deposition (PECVD) and physical vapor deposition (PVD) systems that are especially geared for producing ultra-high-resolution metal-oxide TFT displays.
The ultra-high-res display industry, from 4K and 8K televisions to notebooks, tablets, and smartphones -- is quickly switching to metal-oxide TFTs, as demonstrated earlier this year at the Consumer Electronics Show, where Sony and Panasonic both exhibited 56-inch 4K organic light emitting diode (OLED) TVs using metal oxide backplanes. Since then, LG has begun shipping 55-inch OLED TVs using metal oxide backplanes. And by 2014, all major display makers -- LCD and LED -- will have begun the switch over to metal oxide TFTs.
Up until a few years ago, almost all liquid crystal displays (LCDs) used transistors made with amorphous silicon. However, as displays evolved to higher densities, LCD manufacturers have had to switch to higher-mobility polysilicon transistors in order to scale to smaller dimensions at low power levels. For instance, the retina display on Apple's iPhone was fabricated with low-temperature polysilicon (LTPS), and many in the smartphone industry have followed suit, including Samsung for its OLED displays.
The LTPS process, however, is relatively expensive, requiring up to nine mask steps, compared with four or five for amorphous silicon, is difficult to scale down further, and consumes more power than metal-oxide transistors, according to Applied Materials' director and chief marketing officer for its display business, Max McDaniel. All this is prompting the the next-generation of high-resolution display makers to move to metal oxide TFTs.
"For high-resolution tablets and notebooks a lot of companies want to use metal-oxide, and especially for mobile devices where battery life is important," said McDaniel in an interview with EE Times. "Metal oxide has been talked about for several years, and there has been some sparse adoption of it for the last year, but now we are on the verge of mass adoption of metal oxide displays for tablets, notebooks, and smartphones in 2014 and beyond."
Metal oxide thin-film transistors (TFTs) are required for ultra-high-resolution displays, using indium-gallium-zinc-oxide (IGZO, yellow) as the channel between source and drain (S/D, gray) deposited below a gate insulator (GI, blue) and all covered with a passivization layer (Pass'n, green), which is protected from the channel with an etch-stop layer (ESL, red).
(Source: Applied Materials)
Running displays with metal oxide transistors allows higher-resolution tablets, notebooks, and smartphones that consume less power, require smaller batteries, and fit in a lighter form factor, according to McDaniel, who claims the most popular type of metal-oxide material for next-generation displays is indium-gallium-zinc-oxide (IGZO).
"Displays using IGZO metal oxide transistors are already in pilot production at many manufacturers. And over the next two years -- sooner rather than later -- you are going to see more and more metal oxide TFT displays in the end market."
Applied Materials should know, since virtually every display maker uses its equipment for at least some steps in the display manufacturing process -- notably for the PECVD steps, with the Applied Materials' PVD (also called sputtering) equipment used by fewer manufacturers with some opting for PVD deposition from Ulvac Technologies Inc.
Applied Materials' latest PVD and PECVD systems aim to enhance its competitive position as supplier to makers of ultra-high-definition (UHD) LCD and OLED displays using metal-oxide TFTs.
Applied Materials' plasma enhanced chemical vapor deposition (PECVD) system, the AKT 55KS, handles generation 8.5 glass sizes for displays up to
2.2 x 2.5 meters.
(Source: Applied Materials)
"Our PECVD product is the AKT 55KS, which handles generation 8.5 glass sizes, which are 2.2 x 2.5 meters or 55,000 square centimeters, hence the 55 in its name. The AKT 55KS excels at being defect-free and at keeping hydrogen, which is poison to metal-oxides, out of the CVD."
Applied Materials is also introducing new models of its PVD systems specifically tailored to manufacturing displays using metal-oxide TFTs.
"Our SKT PiVot 25K and 55K product lines, where DT stands for dual-track, is a compact platform that lets the customer run metal-oxides in a single chamber. We are also offering two versions -- the 25K for generation six glass sizes and a 55K for generation 8.5 glass sizes."
The key differentiator for Applied Materials PVD systems, according to McDaniel, is its use of tubular cathodes of donor material, which rotate during deposition for more even consumption and which allow the reactive gas to be introduced between them, rather than around the edges, resulting in more even deposition.
Applied Materials' SKT PiVot 25K and 55K product lines handle generation six and generation 8.5 display sizes, respectively.
(Source: Applied Materials)
"What our tubular cathodes do is rotate during deposition so that they are evenly consumed, rather than having sections that are consumed more than others," says McDaniel. "You also don't have dead spaces like you do with the planar targets that our competitors use, and you don't have re-deposition onto the target which can generate particles that fall off onto the substrate."
The rotary targets are self-cleaning and provide directional plasma control for fewer defects and better uniformity, compared with planar targets, according to Applied Materials.