Mitigating parasitic contributions in measured piezoresponse for accurate determination of piezoelectric coefficients in Sc-alloyed-AlN thin films using piezoresponse force microscopy

Abstract

We present a methodology to mitigate the effect of the parasitic electrostatic contribution usually present in piezoresponse force microscopy (PFM) measurements for quantitative characterization of polycrystalline piezoelectric thin films using a case study on a set of Al1−xScxN thin films. It involves minimizing the voltage sensitivity of the measured piezoresponse by optimizing the optical lever sensitivity using the laser positioning of the beam-bounce system. Additionally, applying a dc-voltage offset (determined through Kelvin probe force microscopy) during PFM scans and positioning the probe over the interior/edge portion of the specimen are explored to minimize the local and nonlocal-electrostatic tip–sample interaction. The results show that the effective piezoelectric coefficient (d33-eff) of our c axis oriented wurtzite (wz)-Al1.0Sc0.0N thin film is ∼4.9 pm/V. The highest enhancement in the d33-eff value occurred in the wz-Al0.58Sc0.42N thin film. Above x ˃ 0.42, d33-eff reduces due to phase-mixing of the wz-Al1−xScxN phase with the cubic-Sc3AlN phase until piezoelectricity finally disappears at x ≈ 0.51.