Grain-wise piezoelectric response of polycrystalline aluminum nitride thin films: an empirical investigation using piezo force microscopy

Abstract Local mapping of piezoelectric response across grains with different crystal planes is crucial to enhance the level of understanding of the piezoelectric behavior of wurtzite hexagonal (WH) AlN thin films. To investigate this phenomenon, polycrystalline WH-AlN thin films were deposited by pulsed-DC magnetron sputtering using a mixture of argon (Ar) and nitrogen (N 2 ) with varying N 2 content as 5%, 10%, and 20% in the form of the AlN/Ti/Si (100) heterostructure. Piezo force microscopy (PFM) was used to establish a correlation among piezo-response (PR) phase contrast, polarity, and crystal planes constituting the film surface. A phenomenological model is also presented to correlate the distribution of interface sheet charges with polar (0002)-, semi-polar (10 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mover> <mml:mn>1</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:mrow> </mml:math> 1)-, and non-polar (10 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mover> <mml:mn>1</mml:mn> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:mrow> </mml:math> 0)-planes present on the film surface. This interdependence eventually regulates the phase between piezoelectric oscillations and modulation voltage, which is ultimately translated into a grain-wise contrast obtained from PR-phase images.