Growth and Characterization of Ferroelectric Lanthanum-Doped Hafnia

University essay from Lunds universitet/Fasta tillståndets fysik; Lunds universitet/Fysiska institutionen

Abstract: Hafnia-based ferroelectrics show great promise as future nonvolatile memory devices, however, their issues regarding device inconsistency across their lifetime, coupled with the relatively short total lifetime, makes these devices only theoretical as of now. In this thesis, an ALD deposition recipe for lanthanum oxide deposition was created. Using this recipe, lanthanum-doped hafnia thin films were manufactured and characterized. Although several issues emerged which limited the ALD-step of the process, ferroelectric devices were created and characterized. The devices have a coercive field between 0.9 and 1.2 MV/cm with remanent polarizations of up to 20 µC/cm2. Endurance measurements showed no sign of fatigue even after 10 million cycles - indicating a relatively long lifetime of the devices. This long lifetime is accompanied by a very long wake-up, which could be due to the issues with the ALD recipe. A comparison between Rapid Thermal Annealing (RTA) and Flash Lamp Annealing (FLA) as the selected annealing method was made. Although the results indicate no ferroelectricity in the samples annealed in the FLA, no conclusion can be drawn as to whether this is due to the FLA process or underlying problems with the oxide on the samples.

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