Prof. Pavan Nukala , Indian Institute of Science
Ferroelectric doped HfO2 films
Werner-Hartmann-Bau, Room 205/206 , Nöthnitzer Straße 66 , 01069 Dresden
I’ll briefly start with our in situ TEM work on HZO (r-phase) capacitors sandwiched between LSMO electrodes (Science 2021), where we show that oxygen vacancies and their migration is very much intertwined with polarization switching in these samples. Following this, we investigated the electromechanical response from these samples, in operando, while the samples are undergoing polarization switching, using nanobeam XRD (at MAX IV, Sweden). I’ll discuss how these measurements are performed, and how repeated collection of data and averaging procedures allow us to detect very small lattice parameter changes with a precision <0.01 pm. We were able to measure the d33 values of these samples in the linear piezoelectric regime to be ~0.5 to 0.8 pm/V. Very interestingly however, although we observe second order effects, they are not correlated to the coercive fields of ferroelectric switching. The onset of second order effects is related to leakage in the samples, and hence Joule heating and defect-induced electrostriction, but not ferroelectricity. This uncorrelation of ferroelectric switching with electrostrain response is suggestive of ferroelectricity majorly driven by chemical polarization switching, and not necessarily crystallographic polarization switching (which anyway is very small: 2 µC/cm2).
If time permits, I’ll also spell out our recent efforts in stabilizing wake-up free ferroelectricity on o-phase La:HfO2 samples, and how we have reason to believe that interfacing this system with electrostrictive Gd:CeO2 can enhance both ferroelectric as well as electromechanical properties.
Prof. Pavan Nukala has joined the Indian Institute of Science/Center for nanoscience and engineering in Aug 2020. He is a materials scientist/engineer by training and works in the broad fields of oxides (correlated oxides, ferroelectric and piezoelectric oxides), phase-change memories (chalcogenides) for electronic applications (neuromorphic computation, in particular) and topological insulators. He has expertise in in situ electron microscopy, spectroscopy (EELS) and x-ray diffraction techniques, especially on real working devices. He has been working in the field of hafnia-based ferroelectrics since 2015, first as a Postdoc at University of Groningen/Netherlands.