A Microcantilever Platform for Measuring Internal Friction in Thin Films Using Thermoelastic Damping for Calibration

Measuring structural damping due to internal friction (IF) in deposited thin films can generate valuable insights into the effects of size and confinement on the mechanisms of anelasticity and provide useful guidelines for the design of high-Q micro/nanomechanical resonators used in microelectromechanical systems for sensing, communications, and vibration energy harvesting. However, accurate measurement of IF has been a long-standing challenge because of the difficulty associated with calibrating the background damping. In this paper, we present an approach based on a silicon microcantilever platform that resolves these difficulties. This approach is built upon the ability to operate silicon microcantilevers at the fundamental limits of dissipation established by thermoelastic damping (TED) and the ability to compute TED in metal-coated silicon beams without using any free parameters. Using this method, we present the first accurate measurements of IF at room temperature in films of aluminum, silver, and gold with thickness ranging from 50 to 500 nm. Gold films dissipate less energy than either aluminum or silver at the frequencies measured in this paper. In all cases, IF is dominated by defect-induced processes occurring within the bulk of these films and not at the silicon/film interface or at the free surface of the metals.