Application of a Micromechanical Test Structure to the Measurement of Stress in an Electroplated Permalloy Film

Suspended microrotating test structures designed to measure the stress in thin, surface micromachined films have been applied to the production of thick layers of electroplated permalloy (NiFe alloy). This process has particular significance to the production of magnetic MEMS components and devices. It is extremely important to characterise the stress in such materials, especially where these films are to be used on wafers with underlying integrated circuitry as it is well known that the matching of transistors can be affected by mechanical strains induced by interconnect features running above them. A new test chip has been designed and fabricated in order to determine the optimum dimensions for permalloy stress sensor structures.