Fatigue and retention in the growth window of ferroelectric Hf0.5Zr0.5O2 thin films

Abstract

The growth window of epitaxial Hf0.5Zr0.5O2 is established taking into account the main ferroelectric properties that films have to present simultaneously: high remanent polarization, low fatigue, and long retention. Defects in the film and imprint field depend on deposition temperature and oxygen pressure, with an impact on fatigue and retention, respectively. Fatigue increases with substrate temperature and pressure, and retention is short if low temperature is used. The growth window of epitaxial stabilization of ferroelectric Hf0.5Zr0.5O2 is narrower when all major ferroelectric properties (remanence, endurance, and retention) are considered, but deposition temperature and pressure ranges are still sufficiently wide.

Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)

“…HZO was deposited at optimal growth conditions: laser frequency 2 Hz, dynamic oxygen pressure of 0.1 mbar, and substrate temperature (heater block temperature) of 800 °C. 10,20 Films were cooled at the end of the deposition under 0.2 mbar oxygen pressure. Platinum circular top electrodes, of diameter 20 μm and thickness 20 nm, were deposited ex-situ at room temperature by sputtering through stencil masks.…”

An Overview of Ferroelectric Hafnia and Epitaxial Growth

“…In addition, the imprint field relies greatly on oxygen concentration, increasing from a negligible value at 0.01 mbar to %400 kV cm À1 at 0.1 mbar. [87] It is apparent that both the phase stability and ferroelectric characteristic depend on oxygen concentrations. Oxygen vacancy concentration would influence the relative free energy of different crystalline phases, change the grain size, and serve as preferred defective nucleation sites, thus the ferroelectric phase formation in hafnia is also affected.…”

“…Other ferroelectric characteristics such as endurance and coercive voltage were also reported to be affected by deposition temperature. In the study by Lyu et al, [ 87 ] retention was better in films grown at higher temperatures (825 °C) than that at lower temperatures (650 °C), and the coercive voltage increases with deposition temperature from 1.9 to 2.9 V. The imprint field was almost constant for films grown at 650 and 825 °C, around 400 kV cm −1 . [ 87 ]…”

Engineering Ferroelectric Hf0.5Zr0.5O2 Thin Films by Epitaxial Stress

“…10 The resulting films are polycrystalline and contain paraelectric tetragonal and monoclinic phases besides the ferroelectric orthorhombic phase. 1,2,[11][12] The ferroelectric phase has been also grown epitaxially on a few substrates, including yttria-stabilized zirconia, [13][14][15][16] LaAlO3, 17 SrTiO3, [18][19][20][21] and buffered Si. 22 The research on epitaxial stabilization is just emerging in comparison with that on polycrystalline doped HfO2 films.…”