104 / 2021-07-13 15:17:19

The Structure and Yield Strength of Electrodeposited Cobalt Films by Micro-Compression Test

electrodeposition,cobalt,micro-compression test

Mechanical property evaluation of materials to be used as the movable components in actuators is critical to ensure the structure stability of the movable component and eventually the lift-time of the device. Components in miniaturized electronic devices are expected to have small size, and the size could be in micrometer scale or smaller. Mechanical properties of metallic materials, such as cobalt, are known to have the sample size effect, which strengthening is observed following a reduction in the size of the sample used in the mechanical property evaluation, especially when the sample size is reduced to micrometer scale. Therefore, for application in miniaturized electronic devices such as MEMS, the mechanical property evaluation has to be conducted using sample sizes similar to those used in application. Micro-mechanical properties of electrodeposited cobalt films were investigated by micro-compression tests for application in miniaturized magnetic electronic devices. FCC and HCP crystal structures were both present in the electrodeposited cobalt. Nanotwins were also confirmed in the HCP lamellas. The average grain size was ranged from 13.8 to 15.4 nm obtained from the Scherrer equation. Yield strengths of the micro-pillars were ranged from 948 to 1075 MPa, which were about twice that of the bulk cobalt. The high yield strength obtained from the micro-compression test was a result of the fine grain size and the small sample size used in the compression test, which correspond well to the Hall-Petch relationship and the sample size effect, respectively.