Doping concentration dependent piezoelectric behavior of Si:HfO2 thin-films

Abstract

Piezoelectric thin films are of current interest in science and industry for highly integrated nano-electro-mechanical-systems and sensor devices. In this study, the dependence of the piezoelectric properties on the doping concentration in Si:HfO2 thin films and their crystallographic origin are investigated. The Si:HfO2 films with a thickness of 20 nm and various Si doping concentrations in the range of 2.7–5.6 cat.% were examined. The relationship between the piezoelectric displacement and remanent polarization is studied during wake-up from the antiferroelectric-like pristine state until the cycled ferroelectric state, which reveals an application-dependent optimal doping concentration. Furthermore, the piezoelectric and ferroelectric properties, as well as the relative permittivity, were measured over wake-up, thus giving a glimpse at the underlying mechanism of the transition from a pristine antiferroelectric-like behavior to a ferroelectric/piezoelectric one, revealing a pre-existing polar phase that is reorienting during wake-up. The studied samples show a strong displacement and polarization dependence on the doping concentration. Hence, the stoichiometry is an excellent parameter for the application-specific adjustment of complementary metal–oxide–semiconductor compatible piezoelectric thin films.

Substrate-dependent differences in ferroelectric behavior and phase diagram of Si-doped hafnium oxide

“…Internal bias fields and domain wall pinning on the other side would require diffusion/drift processes during wake-up, which are not observed [22]. Moreover, internal bias fields, domain wall pinning and a phase transition from the tetragonal phase do not agree with the recently reported displacement measurements, which fit nicely to the expected values for ferroelastic switching [12]. Finally, antiferroelectric orthorhombic phases would not explain the observed reorientation of the polarization axis by 90° [22] and recent density functional theory calculations coupled with X-ray diffraction data does suggest that this is not the dominating mechanism [30].…”

“…The possibility for nand p-type FeFETs [5] enables in addition a larger freedom for novel circuit designs. Moreover, this material system has spurred attention in other applications, like neuromorphic devices [6][7][8], energy harvesting [9,10], sensors and actuators [11,12].…”

Electric field-induced crystallization of ferroelectric hafnium zirconium oxide

“…In addition, transmission Kikuchi diffraction did not observe a significant monoclinic phase fraction prior wake-up and re-orientation of the polarization axis to the out-of-plane orientation post cycling 10 . Combined with the high Curie temperature 14 – 18 and displacement measurements 5 , transitions from non-polar to polar phases are not supported by the experimental results as an origin for AFE-like behavior. However, antipolar orthorhombic phases could still be present alongside ferroelastic-switching 10 .…”

On the Origin of Wake‐Up and Antiferroelectric‐Like Behavior in Ferroelectric Hafnium Oxide

“…A pre‐existing orthorhombic phase has recently been confirmed by displacement measurements as well. [ 43 ] The stabilization of ferroelectric behavior upon field cycling can be attributed to stress relaxation upon cycling, e.g., by formation of defects such as dislocations or changes in the electrical and stress field distribution. A more detailed discussion is given in the Supporting Information.…”