Contribution to the study of structural and ferroelectric properties of HZO thin films
Nowadays the piezoelectric transduction principle is more and more used in several micro-electro-mechanical sensors and actuators (MEMS devices such as pMUT for fingerprint sensors, microphones and loudspeakers, inkjet nozzle, energy harvesting, acoustic resonators, BIOMEMS, etc.). This progression is mainly due to the effort made for the CMOS compatibility of the deposition process of efficient piezoelectric thin films materials. Among the most efficient materials in terms of coupling factor between electrical and mechanical domains, the PZT layers deposited by sol-gel techniques plays up to now an important role. In the framework of the NEED project devoted to sustainable IOT, our goal is to replace the PZT layers by lead-free piezoelectric materials while maintaining the same level of performances. In this context, we will focus on the deposition on HfZrO (HZO) layers by CMOS compatible techniques. At first, this material has been developed for nanoelectronics devices such as ferroelectric memories. More recently, it has been demonstrated that it is a good candidate as transducer. During the PhD thesis, the first challenge to face up is the deposition of HZO layers (up to 100 nm) on transparent electrodes for MEMS applications. These thin films must be uniformly deposited and stress-free in order to ensure the best performances of the MEMS devices. The structural, electrical, optical and electromechanical characterizations will guide the optimization of the ferroelectric and piezoelectric behavior of these layers. Finally, the optimized materials will be integrated in an MEMS device as demonstrator.