Sputtering

Imagine highly energetic particles (ions or atoms) hitting a metal surface. What happens? The penetration and multiple collisions in the target inevitably lead to the release of a lot of target atoms. The physicists call it sputtering. It´s just like hitting a bulk of billard balls when you open a pool game. The balls get in motion and start spreading all over the table. In our case the spread is out of the surface.

Deposition

Now, we want the target atoms ("balls") to be deposited on a metal substrate. In our case the substrate is aluminium and the target material is Titanium. Actually, we do not want to deposit titanium as it is but titanium dioxide (TiO₂). This compound has an extraordinary ability to kill bacterias when exposed to light (a so called photocatalytic compound) and that is excactly what we AMAS people want! The TiO₂ is produced by making the sputtered target atoms react with O₂ molecules in the chamber.

How to do it

How do we get these things to happen in real life? Well, here´s our receipt, We need ...

1. A vacuum chamber, such that our process isn´t influenced by a lot of different gas

molecules, which are present in atmospheric air.

2. An inert gas (like Argon). "Inert" because we do not want them to chemically react neither with the target (titanium) nor the substrate (aluminium)  nor with any residual gases in the chamber. The argon atoms play the role as sputter projectiles.

3. Sputter projectiles. The argon atoms are of no use if they can´t be accelerated. For this to happen, we need argon ions. One way is to bombard the gas with energetic electrons. In this way we get Ar⁺ ions. Put them in an electric field and whatch them go! If we make the titanium target a cathode (minus), the ions will accelerate to the surface and induce sputtering.

4. Energetic electrons. When applying the voltage some fast electrons are created, but due to the sputtering we get a lot more of them. That´s exactly, what we want. They´re called

secondary electrons and they leave the target with high energy and bombard the argon atoms thereby  creating new argon ions and electrons. Under the right conditions the generation of electrons and ions will be a self-sustainable process and a steady swarm of electrons and ions will be present in the chamber. This ionic gas is called "plasma" (the bluish cloud in the chamber below).

 Now, we´re close to finish. We hope You´ll still hang on.

5. Long electron trajectories. The longer an electron travels in the chamber the higher the probability for a collision with an argon atom to happen. As we want a high sputter rate, we want a lot of argon ions, which again depends on the number of electrons and their travelling path. Can we make the path longer? Yes, we can. Let the electron move in a constant magnetic field around the cathode. It will start spinning vertically to the field lines. A spinning electron certainly has a longer path than the one following a linear path.

HiPIMS: A new deposition technology

When we apply a constant voltage (typically 3-500 V) to the cathode the technology is called: Reactive Magnetron Sputtering. A new variant of this method is:

High Power Impulse Magnetron Sputtering (in short HiPIMS)

Here, high power pulses are applied to the target (typically 800-2000V). As a consequence a flux of fast Ti⁺ ions are created, which take part in the deposition on the aluminium. In “ordinary“ sputtering only about 1% of the deposited metal species are ions whereas in HiPIMS up to 80% are ionized. The ionized metal ions give new possibilities of controlling and manipulating the final coating properties.

Our partner at the Teknologisk Institut, Tribologicenteret in Århus

has facilities to test and produce HiPIMS generated coatings. 

Have a look at their site >>

HiPIMS is one of several examples of Physical Vapour Deposition techniques. We will do a lot of both research an development of the HiPIMS in order to produce anti bacterial alumunium surfaces for use in European industries.

If You prefer a detailed scientific description of HiPIMS, we suggest the following reference:

Arutiun P. Ehiasarian: "Fundamentals and applications of HIPIMS", Plasma Surface Engineering Research and its Practical Applications, 2008: 35-85,

ISBN: 978-81-308-0257-2.