Alloying aluminum nitride with molybdenum could significantly enhance its electromechanical coupling constant

Aluminum nitride (AlN) has been widely used in bandpass filters for wireless communication applications, but its low electromechanical coupling factor (kt2) limits the bandwidth of the filter based on it. In this work, AlN alloys incorporated with various transition metals are theoretically studied, and Mo-alloy AlN (MoxAl1−xN) is predicted to be more prominent in improving kt2. Furthermore, the influence of Hubbard U correction on the kt2 of MoxAl1−xN is discussed, and the correction is found to show a crucial role at a high x. The magnitude of kt2 is more correlated with the piezoelectric stress constant e33, and both of them depend on the distribution of Mo atoms. The contribution of each atom to piezoelectric performance is described by an effective displacement-response internal-strain parameter Γ33 in this work, which is generally proportional to internal parameter u and response of u to applied strain along the z-axis. The increase of kt2 is ascribed to the Mo-induced larger u and Γ33, but the Mo dimer and line along the z-axis weaken the increase mechanism. To obtain a high kt2, it is better to alloy Mo atoms into more sublayers of AlN and with fewer Mo dimers and lines along the z-axis. The behavior that the Mo atoms distributed evenly in the xy plane is also beneficial. A high kt2 of 37.8% is predicted in a special quasirandom configuration of Mo0.167Al0.833N, which might be the highest value reported to date for the AlN alloys.