Investigation of boron and nitrogen ion beam implantation in gold thin films for ohmic MEMS switch contact improvement

Contact material and more precisely surface properties are a major issue for RF MEMS ohmic switch reliability. Shallow ion implantation of boron and nitrogen on gold thin film is investigated to increase surface hardness with a limited impact on Electrical Contact Resistance (ECR). The implantation energies were chosen to place the concentration peak of the implanted species at a depth of 100 nm. A microstructural analysis shows that the hardness increases with boron concentration due to a solid solution hardening mechanism, whereas in case of nitrogen, for concentration above 1%, the nitrogen precipitates into a nitride phase correlated to a hardness decrease. The ECR is measured using a Nanoindenter XP which experimental setup reproduces MEMS ohmic switch contact (from 100 μN to 1 mN applied loads under 1 mA). A notable result is obtained with a boron dose of 7.37 × 10¹⁶ ions/cm² at 90 keV into gold thin film: 50% hardness increase and 2.6 times higher ECR than pure gold.