Wake‐Up Effect in HfO₂‐Based Ferroelectric Films

Abstract

HfO2‐based ferroelectric materials are promising candidates for next‐generation nonvolatile memories. Since the first report on Si‐doped HfO2 ferroelectric thin film in 2011, it has been confirmed that various dopants can induce ferroelectricity in HfO2‐based films, and the “wake‐up” effect in HfO2 films with different dopants deposited by different processes has been studied extensively. Recent developments in the wake‐up effect of doped HfO2‐based films are presented. Aside from the differences between the various ferroelectric materials and their deposition methods, the electrodes used in a ferroelectric capacitor, which determine the nature of the interface between the electrode and the ferroelectric layer, can strongly influence the characteristics of the wake‐up effect. The rate of variation of the remanent polarization shows certain trends with different dopants. Based on the wake‐up mechanisms, many methods to optimize and control this effect are presented in this letter. Until now, the reported mechanism explanations of the wake‐up effect all aimed at one type of specific dopant or deposition technique, but can't systematically interpret why the root causes might be different with different dopants and deposition processes. There is also a lack of in‐depth research on the effects of interfacial layer with respect to different electrode material.

Comprehensive and accurate analysis of the working principle in ferroelectric tunnel junctions using low-frequency noise spectroscopy

“…Such a wake-up is inevitably accompanied by the multidomain nature of the ferroelectric layer. 37–39 After 1000 cycles of wake-up pulse, this HfO x FTJ stack shows excellent properties with a 2 P r value of 35.4 μC cm −2 comparable to other conventional HfO x -based ferroelectrics, 2,3,34 indicating sufficient polarization for FTJ operation.…”

“…This is due to the local non-uniformity of domains and crystallinity in the HfO x thin film. 37–39 As cycling proceeds, the domains participating in the switching process become uniformly polarized in the same direction, and a complete hysteric P – V curve starts to appear, as shown in Fig. 1(e).…”

“…Interestingly, the S I / I 2 of the FTJs in the LRS is approximately two orders larger than that in the HRS, which is the opposite trend to the resistive RAMs (RRAMs) where the S I / I 2 in the HRS is much larger. 39–43 In RRAMs, free electrons fill the trap sites, and the fluctuation of the carrier numbers is reduced in the LRS. 39 For a better understanding, the LFN characteristics of the RRAMs with HfO x as a conductive channel are shown in Fig.…”

Epitaxial Ferroelectric HfO2 Films: Growth, Properties, and Devices

“…However, it has to be noted that wake-up effect is not a property genuine of a phase, [69][70][71] and different mechanisms can produce it. 3,[72][73][74][75] Assumptions of Qi et al, 68 which can be extended to the other authors reporting DFT calculations of ferroelectric HfO2 and other polymorphs, are based on strain states that differ to the experimental data revealed by XRD and STEM. 53,57,64…”

Training the Polarization in Integrated La0.15Bi0.85FeO3‐Based Devices

“…The training field was 600 kV cm −1 and the pulse duration as well as the relaxation time in between two voltage pulses were 100 μs. [ 33,34 ] We find reliable and persistent ferroelectric switching events with a degradation of the polarization of only 10% after 10 7 cycles. The ferroelectric hysteresis loops measured on both BiFeO 3 and La 0.15 Bi 0.85 FeO 3 are shown in Figure 3b and confirm the La‐doping‐induced decrease of the coercive field.…”