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%0 Thesis
%A Zhou, Yiming
%T Crystallization mechanism and switching kinetics of In<sub>3</sub>SbTe<sub>2</sub> based phase change materials
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2025-06007
%P 1 Online-Ressource : Illustrationen
%D 2025
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, RWTH Aachen University, 2025
%X Phase change materials (PCMs) can be switched between their high-resistive amorphous phase and low-resistive crystalline phase. The prominent property contrast of PCMs exists not only in their electrical resistance but also in their switching kinetics. While both phases of PCMs demonstrate stability for more than a decade at ambient temperatures, they can be reversibly switched within nanoseconds at elevated temperatures through electrical pulses. Such high non-linearity in temperature dependent stability and high resistance contrast enables PCM-based non-volatile data storage known as phase change memory. As the first commercialized technology for storage class memory (e.g. 3D XPoint), their large-scale deployment in practical applications has highlighted key optimization targets for novel PCMs. Among all performance metrics, the switching kinetics, especially the crystallization kinetics defines the competitiveness of PCMs. Two major parts have been accomplished in this work. Since the electrical switching of PCMs requires both device dimensions below the 100 nm scale and electrical pulse generating and sensing system on the nanosecond scale, a characterization platform has been established, including developing the fabrication process for confined PCM devices (30-100 nm critical dimensions) and a semi-automatic probing system from scratch. To achieve accurate measurements of crystallization kinetics, the endurance of the device was engineered up to 108 cycles, enabling detailed study of switching process. The protocol of the kinetics measurement employed a two-step write-verify strategy which minimized the artifact of cycle-to-cycle variability. With this protocol, the switching kinetics of prototype PCM Ge2Sb2Te5 reveals a strong similarity between the optical crystallization speed from the different location of an amorphous film and the electrical crystallization speed from a single device from cycle-to-cycle. Therefore, the characterization platform presented great potential for the investigation of crystallization kinetics. Second, this work systematically investigates the crystallization kinetics of In3SbTe2 -based PCMs. The investigation of the crystallization behavior of In3SbTe2 thin film through structure characterization and microstructural analysis revealed a spherulitic growth mechanism in In3SbTe2, traced to the excessive tetrahedral indium motif that exists in amorphous In3SbTe2 depending on its density. While spherulitic growth is a relatively slow crystallization mechanism due to the limited diffusion, reducing device thickness to 50 nm suppressed growth-front nucleation, boosting switching speeds of intrinsic In3SbTe2 to 18 ns, which is 5 times faster than the state-of-the-art In3SbTe2 with tailored doping. Also, SnTe was introduced into In3SbTe2 to reduce tetrahedral motifs in the amorphous phase, though phase separation challenges persist despite both components have the same rock-salt structure and low lattice mismatch. Using comprehensive advanced transient electrical response characterization and statistical analysis of stochastic switching, we demonstrate that nucleation is not only an initiating process but also an accelerating factor in the SET operation of SnTe-doped In3SbTe2 -devices. At voltages slightly above the threshold voltage, stochastic nucleation and subsequent crystal growth serve as the switching mechanism in device. The measured minimum nucleation time is as low as 2 ns, although it happens randomly. Fitting with a Gompertz function provides statistical calculations of nucleation probability and yields a typical nucleation time of 8 ns for 30
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2025-06007
%U https://publications.rwth-aachen.de/record/1014292