Giant Piezoelectricity of Deformed Aluminum Nitride Stabilized through Noble Gas Interstitials for Energy Efficient Resonators
Advanced Electronic Materials
Aluminum nitride (AlN) is a material for a wide range of microwave-frequency electronics devices, because of its piezoelectric properties and high chemical stability. To improve the performance of AlN-based devices, such as acoustic wave filters and energy harvesters, an increased piezoelectric modulus is desirable. Here, an increase of the piezoelectric modulus d33 of this material is achieved by ion implantation of noble gases. For a fluence of 3 × 1016 at cm−2 Ar+, a 30% increase of d33 of AlN is obtained. The improvement is attributed to noble gas atoms implanted into interstitial sites of the wurtzite structure, causing a strong deformation of wurtzite AlN. Density functional theory calculations reveal the formation of deformed, metastable AlN with a 350% increase of the longitudinal piezoelectric coefficient. The ion implantation conditions to prepare AlN with a high piezoelectric coefficient are discussed and verified by X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscopy. Heavier elements, larger fluences, and an implantation angle not aligned to the wurtzite crystal are preferred since those conditions generate tetrahedrally coordinated interstitials. In contrast, the opposite conditions lead to octahedrally coordinated interstitials prior to relaxation, which activates the silent B1high phonon vibration and results in a reduced piezoelectric coefficient.
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Australian Research Council