Abstract
Accurate property determination of the piezoelectric thin film material
Al(1−x)Sc(x)N is necessary for designing the next generation of radio
frequency resonators in mobile communication, and for testing results
of ab initio calculations. Sound velocity and piezoelectric coupling of
both longitudinal and shear mode are evaluated from a single dual mode
resonator. This assures a compatible set of coefficients. It is observed that
AlScN thin films grew differently on small, isolated bottom electrodes.
The investigated film starts growing with a slightly tilted, c-textured
microstructure, and switches after 200 nm to a polycrystalline film with
irregularly oriented grains having c-axis tilt angles in the range of 35°–70°,
as revealed by transmission electron microscope nanodiffraction mapping.
Based on this information, a finite element model (FEM) is constructed
that properly reproduces the resonance behavior of the resonator. The
relevant elastic and piezoelectric constants are derived by curve fitting and
yield somewhat lower stiffness and higher piezoelectric coefficients than
ab initio calculations published in the literature. The FEM modeling results
show that the upper film part with the abnormally oriented grains is overall
piezoelectric, i.e., the misoriented grains maintain the polarity projected onto
the growth direction from the starting layer.
Al(1−x)Sc(x)N is necessary for designing the next generation of radio
frequency resonators in mobile communication, and for testing results
of ab initio calculations. Sound velocity and piezoelectric coupling of
both longitudinal and shear mode are evaluated from a single dual mode
resonator. This assures a compatible set of coefficients. It is observed that
AlScN thin films grew differently on small, isolated bottom electrodes.
The investigated film starts growing with a slightly tilted, c-textured
microstructure, and switches after 200 nm to a polycrystalline film with
irregularly oriented grains having c-axis tilt angles in the range of 35°–70°,
as revealed by transmission electron microscope nanodiffraction mapping.
Based on this information, a finite element model (FEM) is constructed
that properly reproduces the resonance behavior of the resonator. The
relevant elastic and piezoelectric constants are derived by curve fitting and
yield somewhat lower stiffness and higher piezoelectric coefficients than
ab initio calculations published in the literature. The FEM modeling results
show that the upper film part with the abnormally oriented grains is overall
piezoelectric, i.e., the misoriented grains maintain the polarity projected onto
the growth direction from the starting layer.
| Original language | English |
|---|---|
| Article number | 1800776 |
| Pages (from-to) | 1-9 |
| Journal | Advanced Elecronic Materials |
| Issue number | 1800776 |
| DOIs | |
| Publication status | Published - 13 Mar 2019 |