Low-toxicity chemical solution deposition of ferroelectric Ca:HfO2

Abstract

So far, a few chemical solution routes for the fabrication of ferroelectric HfO2 films have been reported. Most of them employ precursors, solvents or additives that are considered difficult to handle, unstable, toxic, generally unfriendly with the environment and/or unsuitable for large scale industrial processes. In this work, we present a new effective chemical route for the preparation of ferroelectric doped-HfO2 films. The solution is prepared from simple, stable, and available precursors, handled in an open atmosphere and requires no restrictive processing conditions. We used 5 at% Ca as the dopant of HfO2 to induce a maximum remnant polarization of 9.3 and 11.1 μC cm−2 for 54 and 90 nm thick Ca:HfO2 films, respectively. The current-electric field loops show intense and distinctive ferroelectric switching peaks and the corresponding ferroelectric loops show excellent saturation, which speaks of good device quality with low leakage. Crystallization and the wake-up of ferroelectricity in Ca:HfO2 films were achieved by means of rapid thermal annealing at different temperatures and times in an Ar:O2 atmosphere. In comparison to thin films, thicker ones exhibited the highest remnant polarization at shorter annealing times, thus evidencing the need for precise control of thermal processing. The Ca:HfO2 films with a thickness of 50 nm displayed a good balance between leakage and retention, maintaining the ferroelectric response above 105 cycles at 1 kHz. The developed precursor solution is promising for its use in spray-coating and ink-jet printing techniques.