GGP – magnetron sputtering

The performance of today’s most advanced glazing systems is largely down to microscopically thin coatings that change the properties of the light entering and leaving a building. Greg Clarke, Process Engineer at Pilkington United Kingdom Limited, part of the NSG Group, talks us through the magnetron sputtering process that makes this possible.

Glass plays a key role in regulating the climate inside a building by determining the amount of energy that enters and leaves through windows and any other glazed elements.

In many modern glazing systems, the energy transmission properties are modified by adding very thin layers of material to the surface of the glass. This alters how the glass interacts with light and leads to changes in both its appearance and performance.

These coatings can be used to significantly decrease the amount of energy that buildings consume. They can regulate energy flow by reducing losses, thereby keeping interiors warmer in colder climates. They can also prevent excessive energy from sunlight from entering buildings, which prevents overheating and reduces load on air conditioning systems.

Thin layers of material on the glass can also change the way the surface interacts with water or particles of dirt, giving windows self-cleaning properties.

Complex interactions

Today, advanced multi-layer coatings are often used, with systems being made up of anywhere from one to more than 20 different layers of material.

The performance of coated glass is a result of complex interactions between light, the coating and the glass itself. For a given product, the specific materials that are used, the order in which they are applied and their exact thicknesses are critical. The production methods and formulas that are used to produce such coatings are closely guarded secrets of the glass manufacturers.
But how do manufacturers apply these materials to glass where the thicknesses are over 1,000 times thinner than a sheet of paper? The answer is a process called magnetron sputtering.

So how does it work?

The aim of the sputtering process is to remove material from a one surface, referred to as a target, and deposit it on to another, which in this case is the surface of the glass.

To do this, the uncoated glass passes through a chamber that contains a low pressure plasma. Such plasmas consist of a soup of electrical charged and neutral particles. By applying a negative voltage to the target, positively charged particles, known as ions, from the plasma are attracted to it. The ions collide with the target at high speed causing particles to be ejected from the surface of the target. It is this process that is referred to as sputtering. 

Through the use of magnets behind the target, the efficiency of the process and the quality of the final coating can be improved. The term “Magnetron” relates to how the magnetic and electric fields, as produced by the magnets and the voltage applied to the target, interact with one another.  

The material that is sputtered from the target travels across the chamber and is deposited on the surface of the glass to form a coating layer. The technique is not only capable of creating layers of pure metals. It’s also possible to deposit combinations of metals and gases, such as oxygen or nitrogen, by introducing them into the sputtering chamber. This gives us access to a huge range of possible properties for the each of the layers that we use.

All in the build-up

In order to create the complex multi-layer coatings that feature on products like our low-e Pilkington K Glass™ S, or our Pilkington Suncool™ One solar control glass, every pane passes through a series of sputtering chambers. Each of the chambers deposits a layer of material of a specific thickness, the order of which determines the structure of the coating.

Performing this process efficiently for multiple products requires a large and sophisticated coating line. The coater at our site in St Helens, Merseyside, which produces much of our coated glass, is over 100 meters in length. Depending on what is being made, the glass can take anywhere from 10 minutes to half an hour to travel along the line.

Our coater is celebrating its fourth birthday, having opened in November 2012. In that time it has coated in excess of 20 million sq m of glass – enough to cover almost 3,000 football pitches. This equates to countless buildings delivering improved energy performance and climate control for those who use them.