Demonstration of Ferroelectricity in PLD Grown HfO2-ZrO2 Nanolaminates




Das, Sree Sourav

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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.



Ferroelectricity, Orthorhombic phase, Remnant polarization, Hysteresis loop, Endurance, Wake-up, Leakage current


Das, S. S. (2021). <i>Demonstration of ferroelectricity in PLD grown HfO2-ZrO2 nanolaminates</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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