Amorphous metal alloy based MEMS for RF applications

A new MEMS process based on amorphous metal alloys has been developed. The alloy in question is sputter-deposited molybdenum–silicon–nitrogen (Mo–Si–N) with atomic composition of 31 at% Mo, 20 at% Si, 45 at% N and 4 at% O and tensile residual stress of 300 MPa. This surface micromechanical process has been used for fabrication of variable capacitors for microwave and millimetre wave applications. The devices have been measured up to 110 GHz. They showed low loss (less than 0.2 dB up to 20 GHz and 1.2 dB up to 110 GHz in their up-state) and good matching. The devices have also been cycled 50 million times with 100 Hz frequency between the up- and down-states without impaired performance.