Abstract:The ferroelectricity
in ultrathin HfO2 offers a viable
alternative to ferroelectric memory. A reliable switching behavior
is required for commercial applications; however, many intriguing
features of this material have not been resolved. Herein, we report
an increase in the remnant polarization after electric field cycling,
known as the “wake-up” effect, in terms of the change
in the polarization-switching dynamics of a Si-doped HfO2 thin film. Compared with a pristine specimen, the Si-doped HfO2 thin film exh… Show more
“…It revealed that the sample which was grown at lower undergoes a large wake‐up effect, whereas the sample grown at higher is almost wake‐up free and its pristine 2 P r value is about 97% of the wake‐up state ( Table 1 ). This is only 63% in case of the sample grown at = 5 s. Lee et al [ 19 ] using Monte Carlo simulation demonstrated that the ferroelectric hysteresis of a doped HfO 2 thin film with a lower defect ratio exhibits an increase in both P r and the coercive field E c . Defects can pin the ferroelectric domains and strongly affect the ferroelectric properties of thin films.…”
Section: Resultsmentioning
confidence: 99%
“…A locally distributed inhomogeneous internal field that originated from the spatially unevenly distributed charged defects, such as oxygen vacancies, can be the origin of the internal field in the pristine material. [ 16–21 ] During the electric field cycling process, the oxygen vacancies may diffuse into the bulk regions of the ferroelectric HfO 2 ‐based films, in which case the wake‐up process will occur. Starschich et al [ 21 ] showed that even a DC pulse with an adequate length wakes up the doped HfO 2 capacitors.…”
Wake‐up effect is still an obstacle in the commercialization of hafnia‐based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf0.5Zr0.5O2 (HZO) films is investigated. A nearly wake‐up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken‐up Pr at the pristine state whereas that grown below 5 s ozone pulse time shows a pinched hysteresis loop, that underwent a large wake‐up effect. This behavior is attributed to the increase in oxygen vacancy and carbon concentration in the films deposited at insufficient O3 dosage, which is confirmed by X‐ray photoelectron spectroscopy (XPS). The X‐ray diffraction (XRD) scan shows that the increase in ozone pulse time yields the reduction of tetragonal phase; therefore, the dielectric constant reduces. The I–V measurements reveal the increase in current density as the ozone dosage decreases, which might be due to the generation of oxygen vacancies in the deposited film. Finally, the dynamics of wake‐up effect is investigated, and it appears to be explained well by the Johnson–Mehl–Avrami–Kolmogoroff model, which is based on structural phase transformation.
“…It revealed that the sample which was grown at lower undergoes a large wake‐up effect, whereas the sample grown at higher is almost wake‐up free and its pristine 2 P r value is about 97% of the wake‐up state ( Table 1 ). This is only 63% in case of the sample grown at = 5 s. Lee et al [ 19 ] using Monte Carlo simulation demonstrated that the ferroelectric hysteresis of a doped HfO 2 thin film with a lower defect ratio exhibits an increase in both P r and the coercive field E c . Defects can pin the ferroelectric domains and strongly affect the ferroelectric properties of thin films.…”
Section: Resultsmentioning
confidence: 99%
“…A locally distributed inhomogeneous internal field that originated from the spatially unevenly distributed charged defects, such as oxygen vacancies, can be the origin of the internal field in the pristine material. [ 16–21 ] During the electric field cycling process, the oxygen vacancies may diffuse into the bulk regions of the ferroelectric HfO 2 ‐based films, in which case the wake‐up process will occur. Starschich et al [ 21 ] showed that even a DC pulse with an adequate length wakes up the doped HfO 2 capacitors.…”
Wake‐up effect is still an obstacle in the commercialization of hafnia‐based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf0.5Zr0.5O2 (HZO) films is investigated. A nearly wake‐up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken‐up Pr at the pristine state whereas that grown below 5 s ozone pulse time shows a pinched hysteresis loop, that underwent a large wake‐up effect. This behavior is attributed to the increase in oxygen vacancy and carbon concentration in the films deposited at insufficient O3 dosage, which is confirmed by X‐ray photoelectron spectroscopy (XPS). The X‐ray diffraction (XRD) scan shows that the increase in ozone pulse time yields the reduction of tetragonal phase; therefore, the dielectric constant reduces. The I–V measurements reveal the increase in current density as the ozone dosage decreases, which might be due to the generation of oxygen vacancies in the deposited film. Finally, the dynamics of wake‐up effect is investigated, and it appears to be explained well by the Johnson–Mehl–Avrami–Kolmogoroff model, which is based on structural phase transformation.
“…The HTA film with high oxygen deficiency exhibited a counterintuitively sharper distribution with faster characteristic switching than the LTA film as shown in Fig. 4 c. Intuitively, enhanced film homogeneity with respect to defects and/or the ferroelectric phase results in a sharper distribution with slower ferroelectric characteristic switching time 46 . Figure 4 Ferroelectric switching dynamics of the HfO 2 films.…”
Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. By controlling the annealing conditions, we controlled the oxygen deficiency concentration in the ferroelectric orthorhombic HfO2 phase. Rapid high-temperature (800 °C) annealing of the HfO2 film accelerated the characteristic switching speed compared to low-temperature (600 °C) annealing. Scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) revealed that thermal annealing increased oxygen deficiencies, and first-principles calculations demonstrated a reduction of the energy barrier of the polarization flip with increased oxygen deficiency. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed.
“…In conclusion, diode-like threshold and resistive switching characteristics with current conduction mechanism have been explored using an Al/Ag/Al2O3/TiN structure. Before forming, the thicker Al2O3 layer-based device exhibits diode-like highly uniform threshold switching of >10 4 cycles with high rectifying ratio of >10 4 , at a low CC of 100 nA. After forming, the 5 nm-thick Al2O3 device shows better uniformity and P/E cycle endurance with high on/off ratio.…”
Section: Discussionmentioning
confidence: 99%
“…The challenges faced by conventional flash memories can be overcome by introducing alternative non-volatile memories (NVM) [1]. Lots of emerging NVM devices, such as phase changeable memory (PCM) [2], magnetic random access memory (MRAM) [3], ferroelectric RAM (FeRAM) [4], resistive random access memory (RRAM) [5], conductive bridging random access memory (CBRAM) [6], and so on, are investigated since several decades to fulfill the criteria of nanoscale memory technology. These alternative NVMs have several exciting features, such as (i) physical size reduction, (ii) good endurance characteristics, (iii) longer retention, and (iv) low power consumption [7].…”
Diode-like threshold switching and high on/off ratio characteristics by using an Al/Ag/Al2O3/TiN conductive bridge resistive random access memories (CBRAM) have been obtained. The 5 nm-thick Al2O3 device shows superior memory parameters such as low forming voltage and higher switching uniformity as compared to the 20 nm-thick switching layer, owing to higher electric field across the material. Capacitance-voltage (CV) characteristics are observed for the Ag/Al2O3/TiN devices, suggesting the unipolar/bipolar resistive switching phenomena. Negative capacitance (NC) at low frequency proves inductive behavior of the CBRAM devices due to Ag ion migration into the Al2O3 oxide-electrolyte. Thicker Al2O3 film shows diode-like threshold switching behavior with long consecutive 10,000 cycles. It has been found that a thinner Al2O3 device has a larger on/off ratio of >108 as compared to a thicker one. Program/erase (P/E) cycles, read endurance, and data retention of the thinner Al2O3 oxide-electrolyte shows superior phenomena than the thicker electrolyte. The switching mechanism is also explored.
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