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We propose an accurate and effective method, low-frequency noise (LFN) spectroscopy, to examine the resistive switching mechanism in ferroelectric tunnel junctions (FTJs) based on pure hafnium oxide (HfOx). Contrary to previous studies that primarily focused on the ferroelectric (FE) resistive switching (RS) in HfOx-based FTJs, the results of this study demonstrate that non-FE RS affected by the redistribution of oxygen vacancies also plays a significant role in determining the performance of FTJs. LFN spectroscopy is conducted in different conditions by changing the operating temperature and inducing DC cycling stress. The results reveal that the RS mechanism changes from FE to non-FE RS with increased program bias in all conditions. This change is facilitated by the rise in temperature and the number of DC cycling stress. [ABSTRACT FROM AUTHOR]

It has been reported that the HfOx-based metal–ferroelectric–insulator–semiconductor (MFIS) stack is one of the most feasible structures for memory applications in ferroelectric devices. In addition, in MFIS stacks, the formation of a high-quality thin insulator is considered to be a crucial process, because it determines the device performance and reliability. In this study, the effects of different SiO2 thin interfacial layers (ILs) formed by chemical oxidation and atomic layer deposition (ALD) on the ferroelectricity of HfOx were investigated in MFIS stacks. Notably, the IL formation method affected the crystallization temperature of HfOx ferroelectricity. In particular, the chemical oxide IL sample was sufficiently crystallized only at an RTA temperature greater than 800 °C, whereas the ALD oxide IL sample began to undergo a complete ferroelectric phase transition from a low temperature (600 °C). The x-ray analysis verified that the IL formation method affected the initial film state of the HfOx layer by modulating the Hf-O bonding states, resulting in a different temperature dependence for ferroelectricity formation during the subsequent crystallization annealing stage. Consequently, it was confirmed that stable polarization (2Pr > 30 μC/cm2) could be obtained over a wide temperature range (600–800 °C) through IL material engineering; this could facilitate the integration of HfOx-based ferroelectric devices in terms of the heat budget and the application of ferroelectric devices as commercial devices. [ABSTRACT FROM AUTHOR]

In this Letter, we present reset-voltage-dependent precise tuning operation of TiOx/Al2O3-based memristive devices. For the high resistance state (HRS) with high reset voltage, abrupt set operations are observed with a large variation, while the HRS obtained by low reset voltage provides gradual and uniform switching behaviors. The improvement of gradual switching and the programming accuracy are analyzed regarding cycle-to-cycle as well as device-to-device variations. We believe that these results can be applied to operate TiOx/Al2O3-based memristors in areas requiring highly accurate tuning characteristics. [ABSTRACT FROM AUTHOR]