Plansee AG’s High Performance Materials division based in Reutte, Austria, has developed two new molybdenum based materials for applications in solar cells and semiconductor wafers. Thanks to its good adhesion to glass and a high electrical conductivity, molybdenum (Mo) is the back contact material in CIGS solar cells. However, when exposed to corrosive atmospheres Mo can be prone to oxidation, and Plansee has found that adding a small amount of tantalum to Mo provides a far superior corrosion resistance compared with the pure Mo metal.
On flexible substrates such as stainless steel foil and polyimide, the new Mo-Ta alloy can function as a corrosion resistant contact and protective layer. It effectively protects the backside of the stainless steel web during the selenization step in the CIGS manufacturing process.
Plansee has also developed a new molybdenum-copper composite material designated Mo-Cu R670 for semiconductor wafer substrates. The company states that the metallic wafer made from the Mo-Cu material ensures optimized heat dissipation in LED chips.
The metallic wafer is bonded to the semiconductor layers at high temperatures. Stresses caused by different coefficients of thermal expansion can lead to cracks in the semiconductor layers. To prevent these defects, the metal wafer ideally possesses the same coefficient of thermal expansion (CTE) as sapphire.
Mo is commonly used for such wafer substrates because it offers good thermal conductivity and is very heat-resistant. However, Mo has a lower coefficient of thermal expansion than sapphire (Al2O3), hence the development of wafer substrates made from the Mo-Cu composite material R670 especially for sapphire-based and high temperature-bonded LED chips. R670 has a thermal conductivity of 170 W/mK and, with 6.7 ppm/K, the same coefficient of thermal expansion as sapphire (Al2O3).
Edited by: Paul Whittaker, Editor ipmd.net, [email protected]