Various possibilities have been proposed as the cause of the doped‐ or undoped‐HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal‐to‐monoclinic phase transformation by calculating the amount of the transformed phase using X‐ray diffraction pattern. Johnson–Mehl–Avrami and nucleation‐limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal‐to‐monoclinic phase transformation and enhances the ferroelectric property.

This paper introduces a new atomic layer deposition process for highly conformal, nanocrystalline-as-deposited GeTe–Sb2Te3 pseudobinary film growth at a deposition temperature of 130 °C. The process utilizes Ge­(II)-amidoguanidinate (GeIIN­(CH3)2[(N i Pr)2CN­(CH3)2]), Te­(Si­(CH3)3)2, and Sb­(OC2H5)3 with an NH3 coreagent. The alternative GeTe and Sb2Te3 subcycles produced various film compositions, all consistent with the GeTe–Sb2Te3 tie lines, owing to the stoichiometric reactions between the precursors without involvement of undesirable side reactions. The density of the nanocrystalline Ge2Sb2Te5 (GST225) films was 6.2 g·cm–3, similar to the density of the bulk crystalline material. The crystallization behaviors indicated that the distribution of the constituent elements of the GST225 films was highly uniform at the atomic level, as opposed to the case of the low-temperature (100 °C)-deposited films. The cubic to hexagonal transition at 350 °C upon postannealing produced (0001) hexagonal planes highly aligned along the substrate. The demonstration of the phase change memory device achieved high cycling endurance (>107). Considering that further scaling and optimization of the cell design can improve the electrical performance, the nanocrystalline GST films introduced herein can provide potential utilities in the large-capacity three-dimensional vertical-type phase change memory.

Atomic layer deposition (ALD) of Sb2Te3/GeTe superlattice (SL) film on planar and vertical sidewall areas containing TiN metal and SiO2 insulator is demonstrated. The peculiar chemical affinity of the ALD precursor to the substrate surface and the 2D nature of the Sb2Te3 enable the growth of an in situ crystallized SL film with a preferred orientation. The SL film shows a reduced reset current of ≈1/7 of the randomly oriented Ge2Sb2Te5 alloy. The reset switching is induced by the transition from the SL to the (111)‐oriented face‐centered‐cubic (FCC) Ge2Sb2Te5 alloy and subsequent melt‐quenching‐free amorphization. The in‐plane compressive stress, induced by the SL‐to‐FCC structural transition, enhances the electromigration of Ge along the [111] direction of FCC structure, which enables such a significant improvement. Set operation switches the amorphous to the (111)‐oriented FCC structure.

Atomic layer deposition (ALD) of phase-change materials has been suggested as the most feasible technique for the construction of high-aspect-ratio architectures required for ultrahigh-density phase-change random access memory (PcRAM). The recent advances in the ALD technique have established the foundations for the formation of conformal Ge–Te or Ge–Sb–Te films, but their electrical performance as a phase-change memory device has been rarely reported, especially with prolonged cycles. This study introduced Ge­(II)–amido guanidinate (Ge­(guan)­NMe2 (guan = ( i PrN)2CNMe2, Me = CH3)) as a new ALD Ge precursor that was compatible with the high ALD temperature of up to 170 °C, which was necessary for achieving the high-density and stoichiometric as-deposited GeTe thin films. The films were deposited in an amorphous state. Coinjection of NH3 gas with the Te precursor (Te­(SiMe3)2) was essential to initiate the feasible ALD reaction with the new Ge­(II) precursor. Ab initio calculation proposed plausible exergonic chemical reaction pathways where NH3 actively participated in the dissociation of both −SiMe3 and guanidinate ligands from Te and Ge precursors, respectively. The ALD process showed self-limiting growth behavior and produced highly uniform and conformal morphologies. Low impurity levels (<5%) and a low crystallization temperature (180 °C) were observed for the samples deposited at 170 °C. The prototypical memory device showed a current–voltage curve with a voltage snapback region followed by switching to a low resistance state. Over 104 cycling endurance was achieved for the 170 °C grown GeTe film, whereas inferior endurance (<103) was observed for the low-temperature-grown GeTe.

Recent advances in nanoscale resistive memory devices offer promising opportunities for in-memory computing with their capability of simultaneous information storage and processing. The relationship between current and memory conductance can be utilized to perform matrix-vector multiplication for data-intensive tasks, such as training and inference in machine learning and analysis of continuous data stream. This work implements a mapping algorithm of memory conductance for matrix-vector multiplication using a realistic crossbar model with finite cell-to-cell resistance. An iterative simulation calculates the matrix-specific local junction voltages at each crosspoint, and systematically compensates the voltage drop by multiplying the memory conductance with the ratio between the applied and real junction potential. The calibration factors depend both on the location of the crosspoints and the matrix structure. This modification enabled the compression of Electrocardiographic signals, which was not possible with uncalibrated conductance. The results suggest potential utilities of the calibration scheme in the processing of data generated from mobile sensing or communication devices that requires energy/areal efficiencies.