Michael Schober, Development Manager in Refractory Metals at Plansee, talks to AZoM about using advanced thin film materials in the touch panel market.
Plansee is well-known as a manufacturer of high-performance materials made from refractory metals. How did you move into the touch panel market?
Within the touch panel market, there are several different manufacturing processes available. The newest one is ‘on-cell and in-cell technology’, which I would say is the future orientation technology. The standard manufacturing technique is known as ‘capacitive touch technology’.
In both of these methods, a nanometre-thick metallic layer provides the function of the touch unit. The actual technology in the capacitive touch unit is known as an on-glass solution sensor.
Plansee supplies sputtering targets to our customers and they produce thin metallic films for these sensors. The process our customers carry out is known as physical vapour deposition, or PVD. They sputter our metal targets onto a glass substrate and they get a metallic thin layer, which is the basis for these sensors.
Is the touch panel fabrication market a new area of business for Plansee?
No, it is not new to Plansee but it opens new opportunities to us as the requirements to touch panels increase steadily. Plansee has been delivering coating materials in different areas for more than 20 years. Examples are hard-coating technologies for tools and components, thin-film solar cells or the LCD display industry.
Plansee has been operating in the display industry since the mid-1980s. Using its experience in the display industry, the touch panel industry was the next logical market for Plansee to move into.
The touch panel industry has grown with the popularity of smartphones, such as the iPhone and the Samsung Galaxy, over the last eight to nine years. That's why the touch panel industry is much younger than the display industry.
The production of a touch panel is much easier compared to a display because the layers are thicker and the structures are bigger, so it's easier for a touch panel producer and also for us as a target maker.
Could you tell our readers which metals in particular Plansee supplies?
Particularly for the touch panel market Plansee provides pure molybdenum as well as, from my point of view, the most important material, an oxide-free molybdenum-niobium alloy, known as moly-niobium. This is an alloy containing molybdenum and niobium, and this I would say is the most important material alloy for touch panel manufacturers in general.
As a material scientist yourself, could you explain the role the properties of the material used to create the sputtering target plays in the finalised touch panel?
The touch panel sensor is made of an ITO sensor. It's an indium tin oxide sensor and to contact the sensor you use metal contact lines. These lines are made of molybdenum or molybdenum alloys due to their electrical conductivity and high corrosion resistance, which is a very important factor. Another really important factor for a high electrical conductivity is the purity.
The purity of the sputtering target is important because the purer the material, the higher the electrical conductivity. Another important factor is the coefficient of thermal expansion. In order to guarantee that there is a perfect match and good film adhesion between glass and the molybdenum, the coefficient of thermal expansion has to be nearly the same for both materials. Molybdenum is perfect for sputtering on a glass substrate.
Another important factor is the density of the sputtering target because the higher the density, the better the sputtering as you get less arcs, and therefore there is less particle generation. Particles are a problem for display or touch panel producers because particles can destroy the whole thin-film area. Plansee has a complete in-house manufacturing process, we can adjust all these parameters and guarantee a perfect match for our customers.
Which sputter target designs are available from Plansee to customers?
Generally, there are two main designs. One design is known as a ‘planar target’, which is a s rectangular plate-like target, and the newer version is known as a ‘rotary target’. We can deliver pure molybdenum or molybdenum-niobium in planar or asrotary versions. Both are possible.
What are the associated benefits of the different shapes which Plansee produces?
Many of our customers have always used planar targets and their facilities are focused on planar targets. The new standard design will be the rotary target, and this will become more and more important.
The reason is that planar targets have a utilization of around 40%, and the rotary targets have a utilization of up to nearly 80%, which means the service lifetime is increased and also, particle generation is lowered for a rotary target. That's why the rotary targets are increasing in popularity.
In which countries around the world are your current touch panel customers located in?
Mainly in Asia – in particular: China, Taiwan, Korea, and Japan. In each country, Plansee has its own representatives and our own experts to ensure best customer care. If touch panel targets have to be bonded (soldered) on a backing plate (i.e. a cooling plate) or in case of rotary targets on backing tube, it is also possible to do it in one of our four bonding shops, which are located close to our Asian customers.
Are there any plans to expand Plansee’s distribution to other areas in the future?
In the field of coating materials, another interesting material for us and also for our customers is a new alloy called molybdenum-tantalum. This is really interesting because it stands out, in particular, with excellent resistance to corrosion.
When you think about moisture and hand sweat for the touch panel industry, it's really important not to have a corrosive material. Molybdenum-tantalum provides excellent protection in this case.
The corrosion resistance is really high so humidity is no problem and also hand sweat is no problem for the finished touch unit itself. So, molybdenum-tantalum could be a new material in this area.
Another advantage of molybdenum-tantalum is that the etching for the contact lines is nearly the same as for pure molybdenum, so the customers have no changes in their production set-up. They can use molybdenum-tantalum, change between molybdenum-tantalum and pure molybdenum just as required.
Another opportunity for us is using the material molybdenum-niobium, which is mainly focused on touch, but we are also introducing it in the standard thin film transistor (TFT) display industry This could also be a future step and because we have our own manufacturing process, we are flexible in size and shape for each material.
Where can our readers find out some information about Plansee?
If they visit www.plansee.com, they’ll find great information about our materials, our alloys and our markets as well as contact persons close to them for all relevant applications.
About Michael Schober
Michael Schober is project manager in development of refractory metals at Plansee SE. In his current role, he is mainly responsible for the development of production processes for new target materials.
Michael Schober holds a PhD degree in material science from the Montanuniversität Leoben, Austria.
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