Model choice affects piezoelectric response to probes

Integrated circuits are ubiquitous, and those incorporating ferroelectric materials have applications in areas as wide-ranging as medical sensing and sonar. Piezoresponse force microscopy is a tool widely used for inspecting the electromechanical properties of ferroelectric materials, such as phase transitions and charge domain sensing. However, wear on the probe during imaging alters the electric field transmitted to the material being scanned.

To determine the effect of the probe on a material during a scan, most engineers use a decoupled model, which assumes the materials are similar to dielectrics, allowing them to ignore the effects of electromechanical coupling. Ming et al. present comparisons of coupled and decoupled models for three probe geometries, highlighting how the model choice affects the piezoelectric response of the material more than the probe geometry.

The authors quantitatively determined the electroelastic fields for three different probe geometries using a fully coupled electromechanical model and compared the results to those of the decoupled model. The geometries — modified point charges, disk-plane, and sphere-plane — were intended to resemble the probe tip in different states of wear.

The results reveal that wearing of the probe spreads the out-of-plane electric fields generated in the material while the electric field of the probe tip decreases with wear. Their calculations show electroelastic fields from the coupled model are more localized than those from the decoupled model.

The authors also determined that the maxima of in-plane and out-of-plane displacements in the piezoelectric materials are nearly independent of model geometry. However, the latter are smaller in the coupled model. Their findings demonstrate the vital importance of the calculation method chosen on the piezoresponses of these ferroelectric materials underneath probe tips.

Source: “The effective point charge of probe tip in piezoresponse force microscopy,” by W. J. Ming, R. K. Zhu, K. Pan, Y. Y. Liu, and C. H. Lei, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5047006 .