Thin film coating technology for large area glass

The glass industry has continuously introduced advanced coating technologies over the past 30 years to achieve value-added products, accommodating the growing market need for improved aesthetics and functional comfort.

Within large area glass coating, the architectural, automotive and display markets are the major segments. Common coatings for these applications include AR-stacks (Anti-Reflection), low-emissivity and solar control stacks for the management of heat and TCOs (Transparent Conductive Oxide) for smart windows and displays. Various techniques can be distinguished for the coating of flat glass.

Magnetron sputtering

Magnetron sputtering is a thin film coating technology that is of worldwide economic interest today. In the past ten years this industry has advanced rapidly, and vacuum coating by magnetron sputtering has gained greater economic importance than almost any other flat glass coating technique. Relative ease in scalability to high volumes and its wide variety of available materials and possible complex multi-layer coating stacks for realizing all sorts of applications are key advantages.

Rotatable magnetron sputtering

The original sputtering electrode has come a long way since its invention in the late 1960s. Given its strategic value, many changes and improvements have taken place in recent years in addition to substantial increase in capacity.

Most notably, the development of rotating cylindrical magnetrons and advanced rotating cylindrical sputter targets has permitted manufacturers to address two key challenges: increase coating throughput while maintaining (and improving) layer quality and layer thickness uniformity.

Ultimately, these new products result in a decrease of the total cost of ownership and an increase in the diversity of conditions in which these sputter products can be used.

The success of rotating cylindrical magnetron technology can be explained by three unique benefits:

1. Larger material inventory and higher utilization degree
A cylindrical target may contain more material and has a clearly superior utilization degree (generally more than 75%) in comparison to planar targets. This results in much longer production runs and reduced downtime of the machine, thus increasing the throughput of the coating equipment.

2. Increased deposition rate
Another advantage is the possibility to use higher power densities because the heat load is divided equally over the circumference of the target. As a consequence, deposition speed can be increased.

3. Improved performance in reactive processes
An improved performance during reactive sputtering may be accomplished. Rotating cylindrical magnetrons show drastically reduced arc sensitivity and enhanced anode functionality in AC processes as compared to planar magnetrons. This superior process stability is also beneficial for the deposition speed in reactive processes.

Theory into practice: rotatable technology gains market share

Glass coaters all over the world firmly believe in the substantial added value of upgrading their existing coaters to rotatable technology.

· Given the inherent advantages of rotating cylindrical magnetron sputtering, this technology is broadly applied in diverse conditions such as vertical and horizontal mounting, metallic processes, reactive processes, AC, DC, high power applications, long stand-times and low voltage applications.

· Close partnering with key customers supported the continuous development of new rotatable sputter target materials. Besides alloyed soft metals (ZnAl, ZnSn, ...) also pure soft metals (Zn, Sn, ...), ceramics (Si+, TiOx, ITO, ...) and hard metals (Cu, Ti, Zr, Cr, Al, ...) are used right now.

· Another booster was the development of robust, reliable and user-friendly sputter hardware. The combination of both supported a continuous reduction of the glass coater´s total cost of ownership and is the key for success of this technology.

Moreover the state-of-the art latest glass coaters are designed to enable successful integration of rotatable cathodes.

What will the future bring?

There are numerous growth opportunities for rotatable magnetron sputtering e.g.

· Windows become active participants in its environment. Smart glazing, photovoltaic applications, optical applications,... will need rotatable sputter-coat technology.

· Replacement of lower quality float glass production (China, Russia, India and the Middle East) by high quality float, initiates investments in sputter coating lines, which enlarges the potential market for rotatable sputter technology.

· As flat panels become larger, rotating cylindrical magnetron technology offers a number of important advantages in comparison to planar magnetron sputtering. Bekaert is the first company to field test a full set of rotatable sputtering solutions for the display market, including rotatable ITO targets, compact end blocks and vertical magnetrons. Initial field tests have shown that display coaters using rotatable ITO targets and rotating sputter hardware significantly reduce cost savings per square meter.

Conclusion

We can conclude that the rotatable target technology is one of the rising stars of the global flat glass coating industry.

For glass coating applications (excl. display glass) the installed base consists out of more than 150 coating lines worldwide. On a yearly basis, consumption of rotatable sputter targets covers nowadays for 30 to 40% of their target needs. Five years ago, this amount only counted for 20%.

The impact of introducing this disruptive technology in a booming LCD industry both governed by a striving for better products/quality and by a need to reduce costs, is also expected to be huge. Bekaert aims at launching its ITO rotatable target for various applications shortly.