In order to explore AlScN for next-generation piezoelectric RF filters, Fraunhofer researchers started research on AlScN technology five years ago. The researchers have succeeded in producing highly crystalline AlScN layers and thus creating surface acoustic wave (SAW) resonators that meet the increasing demands of industrial users. For the depositing process of the material, which is also promising for other power electronic applications, a modern magnetron sputtering infrastructure has been established at Fraunhofer IAF.
AlScN is regarded as one of the most promising materials to replace the aluminum nitride (AlN) traditionally used in RF filters of mobile phones. By adding Scandium (Sc) to AlN, the electromechanical coupling and the piezoelectric coefficient of the material is increased, thus enabling a more efficient conversion from mechanical to electrical energy. This in turn allows the development of significantly more efficient RF devices. However, the instability of the piezoelectric AlScN crystal phase has so far stood in the way of industrial use of the material.
During the course of the project, Fraunhofer IAF researchers succeeded in depositing highly crystalline AlScN layers with different Sc fractions of up to 41 percent. In the process, a good homogeneity of the layers was achieved over the entire silicon wafer (Si) with a diameter of up to 200 mm, thus meeting the requirements of industrial production. In addition, the project team also succeeded in achieving growth of AlScN on sapphire (Al2O3) substrates defined in all spatial directions by means of magnetron sputter epitaxy (MSE), which is important for future materials research.