Over the past two decades, piezoelectric microelectromechanical systems (MEMS) have become attractive in many daily-life applications – such as high frequency and temperature-stable resonators that significantly miniaturises cell phones, piezoelectric sensors and energy harvesting devices. However, suitable non-toxic (lead-free) and cheap piezoelectrics with high piezoelectric response are sought for these devices. In this regard, environment friendly lead-free wurtzite AlN has already shown its huge potential for realizing more complex sensing and mobile communication systems because of compatibility of AlN based devices with complementary metal oxide semiconductor (CMOS). High Curie temperature, low acoustic and dielectric losses, high acoustic wave velocity, and compatibility with established silicon manufacturing process make AlN a perfect candidate for various MENS devices.
High performance RF filters made of AlN based resonators also hold a great promise for mobile phones. However, low electro-mechanical coupling coefficient, which is closely related to the piezoelectric coefficients, is the main drawback of pure AlN material. Therefore, enhancement of this coupling in AlN based materials becomes one of the key challenges for academia as well as industry. Promisingly, very recent experiments have demonstrated a significant enhancement in doped (mainly Sc-doped) AlN.
We propose a systematic theoretical and experimental investigation on AlN based materials to understand the influence of doping and substrate on piezoelectric constants, elastic constants, dielectric constants, lattice constants as a function of doping type and doping concentration. Our main aims of this investigation are two-folds: firstly, to understand the origin of the enhancement in piezoelectric response from the first principles calculations with a view to improving the piezoelectric properties through material doping, proper selection of substrate material and processing conditions; secondly to implement our understanding into new AlN based device realization.