WNi sputtering targets for electrochromic layers.
Plansee supplies tungsten-nickel sputtering targets for manufacturing the electrochromic layers in smart windows. Our customers use a reactive sputtering process to create the WNi oxide layer from this material. Under normal circumstances, this layer is colorless and transparent. When a DC voltage is applied, inserted lithium ions makes the layer turn blue and thus less transparent.
Homogeneity and density: Issues to watch with sputtering targets.
Traditional tungsten-nickel targets are manufactured using a thermal spraying process. The disadvantage of this process is that the nickel is not distributed homogeneously and the material density in sputtering targets is generally below 90%. So what does this mean for the customer?
If the nickel is not distributed uniformly, the result is ferromagnetic regions caused by pockets of pure nickel in the material. These have a negative impact on the sputtering behavior and affect the coloring quality of the electrochromic layer.
And the spraying process restricts the possible thickness of the sputtering target to just 5-6 mm. This means that customers have to replace the sputtering targets frequently. In addition, the porosity of a sprayed target can lead to higher particle formation and thin film defects during sputtering. We manufacture our tungsten-nickel sputtering targets using a powder-metallurgical process. From metal powder to the finished product, we handle every step of the process in our own facilities. A density of more than 99.5 % means that it is possible to manufacture sputtering targets with a thickness up to 18 mm. Users can carry on coating for 2-3 times longer than with sprayed targets and no longer have to replace the target so often.
Our manufacturing process results in a particularly homogeneous and dense microstructure . You can see this in this optical microscopy image of a Plansee WNi sputtering target: Pure tungsten (dark gray) in a matrix of WNi compounds. But you cannot find two things, namely free nickel and porosity.
However you look at it, the nickel is distributed extremely uniformly across the entire target. The overall nickel content fluctuates by no more than +/- 0.5 percent around the required average value.
|The most important properties of our tungsten-nickel sputtering targets|
|Density (at 20 °C)||≥ 99,5|
|Purity||> 99,97 wt % (3N7)|
|Homogeneity of nickel distribution||< +/- 0,5 wt.%|
|Nickel content||25 bis 55 wt.%|
We have already applied for a patent on our manufacturing process for WNi sputtering targets.