Demonstration of Ferroelectricity in PLD Grown HfO2-ZrO2 Nanolaminates
Date
2021-05
Authors
Das, Sree Sourav
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Abstract
Ferroelectricity was demonstrated for Pulsed Laser Deposition (PLD) of HfO<sub>2</sub>-ZrO<sub>2</sub> bilayer thin films grown on TiN bottom electrodes on SiO<sub>2</sub>/Si as a function of deposition conditions and individual HfO<sub>2</sub>-ZrO<sub>2</sub> layer thicknesses. Thicknesses of individual layers in HfO<sub>2</sub>-ZrO<sub>2</sub> bilayer system were varied from 5 nm to 15 nm, deposition temperature was varied from room temperature to 750°C and partial oxygen pressure was varied from 10<sup>-6</sup> torr to 0.124 mtorr. The films deposited at higher temperature, higher pressure and have higher thicknesses showed better ferroelectric response with 12 μC/cm<sup>2</sup> remnant polarization and 10<sup>-7</sup> A leakage current (at 8 V) with endurance greater than 10<sup>11</sup> cycles indicative of an orthorhombic crystal phase. On the other hand, films deposited at lower temperatures and pressures did not exhibit ferroelectric behavior. These films were determined to have a monoclinic structure, lower grain size and higher leakage current. The effects of ZrO<sub>2</sub> layer were also demonstrated by changing the sequence in the structure and it was found that ZrO<sub>2</sub> as the top layer provided better mechanical confinement for stabilizing the orthorhombic phase. Finally, the effect of the interfacial layer between HfO<sub>2</sub>-ZrO<sub>2</sub> nanolaminates was investigated by depth profile analysis and a bilayer structure was proposed with proper process conditions and layer thicknesses that could potentially exhibit higher remnant polarization and strong endurance against fatigue for memory applications.
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Keywords
Ferroelectricity, Orthorhombic phase, Remnant polarization, Hysteresis loop, Endurance, Wake-up, Leakage current
Citation
Das, S. S. (2021). <i>Demonstration of ferroelectricity in PLD grown HfO2-ZrO2 nanolaminates</i> (Unpublished thesis). Texas State University, San Marcos, Texas.