Piezoelectric microsystems using AlScN as a transducer material
Micromechanics with piezoelectric transducer principle are gaining importance in almost all target markets for MEMS applications. They are mainly characterized by improved dynamics as well as a higher potential for miniaturization. In this context, a trend towards lead-free transducer materials can be identified, as the frequently used lead zirconate titanate, PZT, is increasingly viewed critically due to its poor environmental compatibility and disposability. Piezoelectric aluminum nitride, AlN, represents a very good alternative here, as it is easy to manufacture, cost-effective, CMOS-compatible and, as a green technology, environmentally compatible to a high degree. In addition, AlN shows no material fatigue or thermal degradation due to its ceramic properties. However, the piezoelectric coefficients of AlN are comparatively low and limit its usability. To improve these on the material side, scandium can be added to the AlN, which can provide an increase of up to ≥ factor 5. The production of suitable sputtering targets for aluminum scandium nitride, AlScN, coatings with increased scandium content is difficult and is currently only offered by a few manufacturers in the Asian region. However, the long transport distances involved lead to oxygen contamination of the targets, which significantly deteriorates the piezoelectric properties of the coatings produced with them. The availability of functional and cost-effective AlSc sputtering targets in the European region is the basis for the industrial application of AlScN technology in the MEMS field in Europe.
The goal of the FastMEMS project is the fabrication of a functional sputtering target for piezoelectric AlScN layers in the MEMS area. In this project, the TU Chemnitz is collaborating with robeko GmbH & Co. KG, a national manufacturer of sputtering targets and evaporator granulates.
The targets are manufactured at the facility of robeko GmbH & Co. KG. The TU Chemnitz has the task to install the manufactured targets in their sputtering equipment and to develop processes for the production of piezoelectric AlScN layers. Different process parameters are to be varied and the properties of the layers, stoichiometry, crystallinity and piezoelectric coefficients, are to be analyzed. The aim of the investigations is to analyze the influences of both the target production process and the AlScN deposition process on the piezoelectric properties of the layers to be produced, in order to ultimately be able to establish a functional target with associated process on the national and European market. Investigations into the use of the AlScN layers in finished MEMS sensors and actuators to analyze the transducer properties with regard to the targeted increase round off the investigations within the FasMEMS project.
MEMS inertial sensors for testing the sensory transducer properties of the AlScN
MEMS micromirrors for testing the actuator transducer properties of the AlScN
