by Dr.-Ing. Katja Tonisch, Technische Universität Ilmenau
07.11.2019, 17:00 h, TF, Aquarium
Micromechanical resonators show significant promise for many sensor applications such as chemical and biological sensing, electrometry and scanning probe techniques. In these applications, a change in mass, temperature, charge, or any other applied force induces a small shift in the resonance frequency of the oscillator. Typically, resonators require both an actuation and a detection of the resonance frequency. The main advantage of using the (inverse) piezoelectric effect is the possibility to use it in both ways, the inverse effect as actuation and the direct one as detection. The exceptional properties of wide-bandgap III-V nitride semiconductors are promising for such applications. Among the nitrides, Aluminum nitride (AlN) has the largest piezoelectric coefficients and good mechanical strength, which makes AlN a favourite and often used material for electromechanical devices in micro- and nanometer scale. Only recently the ‘nitride universe’ was expanded by the introduction of Scandium. While pristine Scandium nitride is cubic, Scandium aluminium nitride (ScxAl1-xN) maintains the wurtzite structure of AlN up to a Scandium amount of approximately 45%. Especially the enormous increase in its piezoelectric properties while maintaining other advantageous properties like its high thermal stability makes ScxAl1-xN a promising material for novel sensor applications such as magnetoelectric MEMS.
Co-sputtered ScAlN layers are investigated using XRD, XPS, FTIR, Raman spectroscopy and spectral ellipsometry for scandium concentrations from 0 to 50 %. The impact of Sc incorporation regarding residual biaxial strain, bond softening and the change in electrical properties, as well as the impact on electromechanical sensors is discussed based on experimental results.