The combination of piezoelectric thin films and microelectromechanical systems (MEMS) is expected to drive the next generation of lower power, more integrated and better performing microdevices and self-powered systems for the Internet-of-Things (IoT). AlN, as a CMOS compatible piezoelectric material, is already in use for a few state-of-the art sensors. However, its piezoelectric constant is significantly lower than that of the ferroelectric lead zirconate titanate (PZT). On the other hand, with group III transition metal alloys, such as ScAlN, the d₃₃ piezoelectric constants of the wurtzite material can be increased by a factor of 5 which makes it competitive with the less CMOS compatible perovskite ferroelectric materials.

The aim of this work is to perform systematic studies on the deposition of III-N thin films using different techniques. The deposition is to be done mainly by a new UHV sputtering system and to be characterized by several experimental methods available in-house. The focus of the studies is the piezoelectricity, which affects strongly the performance of piezo-MEMS based mechanical sensors and energy harvesters developed in the framework of a running research project (Advanced Functional Advanced Functional Materials for Autonomous Sensor Networks).  

The proposed work consists of the following tasks: i) physical characterization of RF sputtered AlN layers; ii) optimization of the process parameters for AlN deposition in the new pulsed-DC sputtering system; iii) optimization of co-sputtering parameters for novel III-N piezoelectric allays (YAlN, ScAlN); iv) optimized depositions for piezo-MEMS vibrational energy harvesters and frequency sensitive sensor arrays. For comparison, the PhD candidate will also test some alternative deposition methods and materials such as plasma assisted atomic layer deposition (ALD) of thin oxides and nitrides as well as sol-gel deposition of PZT coatings.