Interplay between ferroelectric and resistive switching in doped crystalline HfO2

Abstract

Hafnium oxide is widely used for resistive switching devices, and recently it has been discovered that ferroelectricity can be established in (un-)doped hafnium oxide as well. Previous studies showed that both switching mechanisms are influenced by oxygen vacancies. For resistive switching, typically amorphous oxide layers with an asymmetric electrode configuration are used to create a gradient of oxygen vacancies. On the other hand, ferroelectric switching is performed by having symmetric electrodes and requires crystalline structures. The coexistence of both effects has recently been demonstrated. In this work, a detailed analysis of the reversible interplay of both switching mechanisms within a single capacitor cell is investigated. First, ferroelectric switching cycles were applied in order to drive the sample into the fatigued stage characterized by increased concentration of oxygen vacancies in the oxide layer. Afterwards, a forming step that is typical for the resistive switching devices was utilized to achieve a soft breakdown. In the next step, twofold alternation between the high and low resistance state is applied to demonstrate the resistive switching behavior of the device. Having the sample in the high resistance state with a ruptured filament, ferroelectric switching behavior is again shown within the same stack. Interestingly, the same endurance as before was observed without a hard breakdown of the device. Therefore, an effective sequence of ferroelectric—resistive—ferroelectric switching is realized. Additionally, the dependence of the forming, set, and reset voltage on the ferroelectric cycling stage (pristine, woken-up and fatigued) is analyzed giving insight into the physical device operation.

Unraveling Ferroelectric Polarization and Ionic Contributions to Electroresistance in Epitaxial Hf0.5Zr0.5O2 Tunnel Junctions

“…The close correspondence of polarization and ER in Figure a,c strongly suggests that ER is due to polarization‐controlled tunnel transport across the HZO barrier if voltages up to V W ≤ ±4.5 V are used. Ferroelectric switching and ER coexists at larger V W , but these are not consequence one from the other, as reported in polycrystalline HfO 2 thin films …”

“…Recently, ER in tunnel junctions involving ferroelectric HfO 2 barriers have been reported . However, available data do not allow indisputably to conclude if the observed ER is directly governed by polarization‐related effects or it results from electric‐field induced charge motion as commonly observed in non‐ferroelectric HfO 2 barriers . For instance, Wei et al reported current–voltage curves ( I – V ) of 2 nm HZO barriers and argued that data can be described using the Brinkman model, indicating direct tunnel transport across the barrier .…”

Blocking of Conducting Channels Widens Window for Ferroelectric Resistive Switching in Interface‐Engineered Hf0.5Zr0.5O2 Tunnel Devices

“…As mentioned, the growth of (111)-HZO textured on (001) cubic substrates implies the existence of twined HZO crystals, [42] which can be observed in the enlarged view in Figure 6b. Before closing, it should be mentioned that recently Max et al [23,38] reported an earlier attempt to introduce an AlO x layer in ferroelectric HZO devices. A nanometric AlO x layer was grown on symmetric metal-HZO-metal polycrystalline structures, in order to break the symmetry of the junction and to exploit the tunnel transport through the AlO x barrier.…”

Nanoparticle Dynamics in Oxide‐Based Memristive Devices

“…Both ferroelectric and resistive switching have been reported in HfO x , and both effects appear to be influenced by oxygen vacancies. While resistive switching is typically observed in amorphous HfO x , and ferroelectric switching is reported for crystalline HfO x , a recent study demonstrated a reversible combination of resistive and ferroelectric switching in a single poly‐crystalline Sr‐doped cell …”

“…While resistive switching is typically observed in amorphous HfO x , and ferroelectric switching is reported for crystalline HfO x , a recent study demonstrated a reversible combination of resistive and ferroelectric switching in a single poly-crystalline Sr-doped cell. [35] When replacing the metal-insulator-metal structure of classical VCM cells by flexible nanocomposites and colloidal suspensions, based on, e.g., ZnO, resistive switching becomes more complex. These switches have been recently categorized as interfacial coupling mechanism (ICM) devices: [36] Experimental results indicate here that, in those devices, local metal adatom doping of ZnO nanowires is important for conductance changing even for low metal concentrations.…”