Stability of Piezoelectric Al1-xScxN Thin Films
Research output: Contribution to conference › Poster › Scientific
In addition, mass separation by spinodal decomposition has been observed experimentally and theoretically [8,13,16]. This can lead to Al and Sc rich areas and to the formation of c-AlScN in films with even lower Sc-concentrations. The onset of spinodal decomposition at 1 100 K is at ca. 6% Sc-fraction according to thermodynamic simulations. However, epitaxial strain increases the allowed amount of Sc. When w-AlScN is strained on AlN, w-AlScN is stable up to 40%. Decomposition has not been observed in all experimental studies probably due to the nature of sputter deposition. Low growth temperatures limit kinetically the diffusion driven decomposition. However, studies have not evaluated the stability of w-AlScN. Almost all studies have focused on as-deposited sputtered films. As sputtering can result in nonequilibrium films, it is possible that the microstructure of w-AlScN changes to a more stable one due to high temperatures in processing or during use. The possible issue is loss of texture or formation of new phases with no or reduced piezoelectricity.
In this study 1 μm thick AlScN samples with Sc-fraction of 30% are sputtered at 450 °C directly on (100) Si. The samples are annealed for 5 h at 400, 600, 850 and 1000 °C in order to induce and determine the temperature threshold for possible changes. Afterwards the microstructure of the samples is characterized with XRD and possible decomposition products are detected with RGA. SEM and EDX is used to study the morphology and composition of the films before and after annealing. The results show that AlScN thin films are stable in annealing. The XRD results (Fig. 2) confirm that the samples are c-axis oriented w-AlScN and show no changes after annealing. The RGA test showed no significant decomposition. The EDX results did not show any mass separation. However, the SEM micrographs (Fig. 3) show changes in the topography of the film after annealing.
|Publication status||Published - 15 Jan 2018|
|Event||International Workshop on Piezoelectric MEMS - Orlando, United States|
Duration: 15 Jan 2018 → 16 Jan 2018
Conference number: 6
|Workshop||International Workshop on Piezoelectric MEMS|
|Period||15/01/2018 → 16/01/2018|