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

TL;DR

This paper introduces a methodology to reduce parasitic electrostatic effects in piezoresponse force microscopy, enabling more accurate measurement of piezoelectric coefficients in Sc-alloyed-AlN thin films, with specific optimization techniques and case study results.

Contribution

It presents a novel approach combining optical and electrical adjustments to mitigate electrostatic artifacts in PFM measurements of piezoelectric thin films.

Findings

Effective piezoelectric coefficient (d33-eff) measured as 4.9 pm/V for AlN.

Maximum d33-eff observed at x=0.58 in AlScN films.

Piezoelectricity diminishes at x=0.51 due to phase mixing.

Abstract

We present a methodology to mitigate the effect of the parasitic electrostatic contribution usually present in piezoresponse force microscopy (PFM) measurement 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 or edge portion of the specimen are explored to minimize the local and non-local electrostatic tip-sample interaction. The results shows that the effective piezoelectric coefficient (d33-eff) of our c-axis oriented wurtzite (wz)-Al1.0Sc0.0N thin film is 4.9 pm per Volt. The highest enhancement in the d33-eff value occurred in the wz-Al0.58Sc0.42N thin film. Above x = 0.42, the d33-eff reduces due to phase-mixing of the wz-Al1-xScxN phase with cubic-Sc3AlN phase till the piezoelectricity finally disappear at x = 0.51