Investigation of ScAlN for piezoelectric and ferroelectric applications

Sc _x Al _1-x N is a promising material to expand the application range of nitride materials, since scandium increases the piezoelectric constants while retaining the crystalline wurtzite structure. In this work, stationary reactive pulse magnetron sputtering is used for the deposition of functional layers with a scandium content x = 0...0.44. Layer morphology, piezoelectric properties and breakdown voltage are studied XRD measurements reveal that high scandium content yields to a weak wurzite formation. The lattice constant dependent on the parameter x is calculated on the base of XRD data and the curve characteristic agrees with the density functional theory. The highest piezoelectric coefficient d ₃₃ was observed at a scandium content of 36.6 %, it amounts to 27.5 pC/N. Parallel capacitor structures are generated by means of chlorine-basedICP etching and lift-off structuring of the top electrodes. Technological details of the structuring process are presented. The etch rate depends strongly on the scandium content. The permittivity was determined on the base of these test structures. It increases significantly with increasing scandium content. High capacitance values up to 7.4 nF were measured The adequate breakdown voltage of 51 V for scandium concentrations of x = 0.22 or higher suggest a use of such layers for integrated thin film capacitors in addition to well-tried piezoelectric applications.