Determination of the mechanical properties of thin polyimide films deposited on a GaAs substrate by bulging and nanoindentation tests

In order to characterize the mechanical behavior of thin polyimide films deposited on a GaAs substrate in a membrane configuration, bulging and nanoindentation tests are performed. By these means, Young’s modulus of polyimide films, with thicknesses on the micron scale is found to be equal to 2.8 GPa. These two different techniques, which do not rely on the same assumptions, give results in very good agreement. The tensile residual stress in the membranes due to the fabrication process is a decreasing function of the thickness: 12<σ0<25 MPa. These membranes are already employed as mechanical support for coplanar wave guides up to the millimeter wave range.