Sputtering Technique Ups Coating Efficiency
BRAUNSCHWEIG, Germany, Sept. 3, 2010 — Sputtering is the phenomenon that occurs when energy-rich ions hit a solid object and cause atoms to be released from its surface. Researchers at the Fraunhofer Institute for Thin Film and Surface Technology IST have discovered a special sputtering technique that can greatly increase the efficiency of the coating process, which could be exploited to apply microscopically thin coatings to glass surfaces.
Sputtering is the preferred process for coating large surfaces. The process leads to a bombardment of a chosen material (target) and causes its constituent atoms to be ejected like billiard balls by the impact of the energy-rich ions — generally noble-gas ions. The latter subsequently condense on the surface of the glass or other substrate to form a thin film with specific properties depending on the characteristics of the starting material.
The new coating module enables IST researchers to produce previously unattainable combinations of materials. (Image: Fraunhofer IST)
Different designs are possible for the coating module. The version that consists of two rotating tubes containing strong magnets is referred to as a double magnetron. The magnets increase the sputtering rate, but severely limit the options available to the design engineers.
"We can only sputter materials for which targets are available and can be produced," said Dr. Bernd Szyszka, IST department head. "Moreover, the sputtering process we have been using up to now is inefficient, because only a fraction of the bombarding ions actually contribute to the sputtering effect. More than 95 percent of their energy is lost in the water-cooling system."
The IST experts have overcome this obstacle by placing an additional flat target made of a heavy element such as bismuth behind each target tube. "This significantly increases the sputtering rate," said Szyszka. The ionized noble gas causes bismuth atoms to be released from the flat solid body. These atoms are gradually "implanted" in the tube target.
"The bismuth has enabled us, for example, to significantly improve the deposition of titanium dioxide," said the research team. The quantity of coating material removed from the target is increased. The IST researchers have meanwhile scaled up this effect to industrial level. "Using a simulation program, we were able to optimize the sputtering process in terms of material deposition on the flat and tube targets, even before we had built the new prototype model. We are now able to combine the target materials in any way we desire, without causing unwanted chemical reactions on the surface."
The result is a higher deposition rate and a more homogenous surface coating based on new materials that previously could not be produced. It also takes less time to produce the coating, reducing the energy consumption.
"The new coating technology has allowed us to replace three old magnetrons with two new ones. The system is much cheaper to operate and produces materials with improved properties," said Szyszka.
The researchers will be present at the Glasstec fair in Düsseldorf from Sept. 28 to Oct. 1, presenting a wide range of applications from panoramic car roofs that provide thermal insulation to photovoltaic cells with improved efficiency.
For more information, visit: www.fraunhofer.de
MORE FROM PHOTONICS MEDIA