Metal-Ion Synchronized HiPIMS of AlN and AlScN for Piezoelectric Applications

Ionized physical vapor deposition (PVD) techniques, such as High Power Impulse Magnetron Sputtering (HiPIMS), offer unique opportunities to control the microstructure of thin film materials by accelerating ions onto the growing film using substrate-bias potentials. At moderate acceleration potentials, the increase in ad-atom mobility often leads to improved crystalline quality and texture. This, in turn, enables the deposition of high-quality thin films at low deposition temperatures. However, gas-ion incorporation can limit the feasibility of such synthesis approaches for defect-sensitive materials. In recent years, HiPIMS processes with a synchronized pulsed substrate bias have been developed with the goal to selectively manipulate the kinetic energy and momentum transfer of the film-forming species, particularly the metal ions. These processes hold remarkable potential to significantly reduce the defect concentration and stress in HiPIMS-deposited films, potentially unlocking a host of new applications for the technique.<br/>In this presentation, I will showcase our latest work on the development of reactive metal-ion synchronized HiPIMS processes for the growth of piezoelectric AlN and AlScN thin films. It will be shown how highly textured, c-axis oriented AlN and AlScN films can be grown using reactive metal-ion synchronized HiPIMS. Here, even unconventionally moderate substrate bias potentials of up to only -30 V already lead to significant improvements in the films' properties.[1] Most strikingly, the application of a substrate bias facilitates the deposition at oblique deposition angles and on structured substrates, while also significantly reducing the fraction of undesirable misoriented grains. A detailed characterization of the piezoelectric coefficients of the materials show values comparable to the current state-of-the-art. In addition, for AlScN in particular, the phase formation and stress state can be tailored by applying different biasing schemes and combinations of different sputter modes (i.e., HiPIMS or DCMS, or hybrid).[2] Importantly, it will be shown that the applicability of these types of processes can be significantly extended, even on insulating substrate materials.<br/>The goal of this presentation is to demonstrate the tremendous potential of synchronized HiPIMS processes for the deposition of defect-sensitive materials, especially in applications where tailoring microstructure and texture of the thin film materials is important.<br/><br/>[1] J Patidar, A Sharma, S Zhuk, G Lorenzin, C Cancellieri, MF Sarott, M Trassin, K Thorwarth, J Michler, S Siol<br/>Surface and Coatings Technology 468, 129719<br/>[2] J Patidar, K Thorwarth, T Schmitz-Kempen, R Kessels, S Siol<br/>Phys. Rev. Materials (under review), preprint arXiv:2405.00210