Giant Piezoelectricity of Deformed Aluminum Nitride Stabilized through Noble Gas Interstitials for Energy Efficient Resonators

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 d(33) of this material is achieved by ion implantation of noble gases. For a fluence of 3 x 10(16) at cm(-2) Ar+, a 30% increase of d(33) 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 B-1(high) phonon vibration and results in a reduced piezoelectric coefficient.

Automated summary

Ion implantation of noble gases is shown to increase the piezoelectric modulus of aluminum nitride (AlN) by up to 30%. This enhancement is attributed to noble gas atoms causing deformation of the wurtzite AlN structure, resulting in a significant increase in the longitudinal piezoelectric coefficient. Optimal ion implantation conditions for achieving a high piezoelectric coefficient involve heavier elements, larger fluences, and non-aligned implantation angles relative to the wurtzite crystal.