Ultra Low Tensile Stress Electroplated Nickel Layers: A New Application as Membrane Material for Acoustic Devices

For high-end silicon microphones membranes with low tensile stress are needed to achieve a high sensitivity. Common membrane materials such as silicon nitride or poly silicon have higher tensile stress or require a metallization layer for capacitive readouts. Presented here are the fabrication method and initial characterization results of electroplated nickel membranes. This membranes show a very low tensile stress in the range between 15 MPa and 20 MPa with a standard deviation down to 2 MPa as well as a defined thickness from 0,8 mum to 1,2 mum across a 100 mm wafer. This approach is unique in that it uses nickel as the membrane material in the acoustic device with resonance at 16 kHz. The material characterization was done by nanoindentation and the results of the Young´s modulus and Vickers hardness are presented and was compared with the values published in literature.