Coupling bulge testing and nanoindention to characterize materials properties of bulk micromachined structures

Abstract

Nanoindentation and the continuous stiffness method was used to obtain the elastic modulus of Pb(ZrxTi1−x)O3 (X:1−XPZT) thin films that can be utilized in high aspect ratio structures. PZT films were deposited onto bulk micromachined silicon wafers by sol–gel deposition and two annealing treatments. Conventional annealing produced films that had an elastic modulus of 80 GPa for both the 52:48 and 40:60 PZT, while a 52:48 PZT deposited using rapid thermal annealing demonstrated a modulus of 70 GPa. These moduli allowed accurate stress measurements of both the composite membranes by bulge testing and also the individual PZT layers by X-ray diffraction. The residual tensile stress in the PZT film ranged from 190 to 400 MPa. Residual stresses were shown to affect both the strain to failure and the resonance frequency of the membrane generators. The applied strain to failure decreased with increasing residual stress. A tungsten underlayer was added to reduce the composite residual stress and increase the compliance, lowering the resonant frequency from 23 to 18 kHz.