Enhanced Ferroelectric Properties and Insulator − Metal Transition- Induced Shift of Polarization-Voltage Hysteresis Loop in
VO
x‑ Capped Hf
0.5Zr
0.5O
2Thin Films
Yan Zhang, Zhen Fan,* Dao Wang, Jiali Wang, Zhengmiao Zou, Yushan Li, Qiang Li, Ruiqiang Tao, Deyang Chen, Min Zeng, Xingsen Gao, Jiyan Dai, Guofu Zhou, Xubing Lu,* and Jun-Ming Liu
Cite This:ACS Appl. Mater. Interfaces2020, 12, 40510−40517 Read Online
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sı Supporting InformationABSTRACT: A capping layer is known to be critical for stabilizing the ferroelectric (FE) orthorhombic phase (o-phase) in a HfO2- based thinfilm. Here, vanadium oxide (VOx), a functional oxide exhibiting the insulator−metal transition, is used as a novel type of a capping layer for the Hf0.5Zr0.5O2 (HZO) thin film. It is demonstrated that the VOxcapping layer (VCL) can enhance the FE properties of the HZO thinfilm comprehensively. Specifically, the HZO thinfilm with a VCL shows large remanent polarization (2Pr≈36.9μC/cm2), relatively small coercivefield (Ec≈1.09 MV/
cm), high endurance (up to 109cycles), and long retention (>105 seconds). The enhanced FE properties may be attributed to the VCL-induced stabilization of the FE o-phase and suppression of
oxygen vacancies at the interface. Furthermore, the HZO thinfilm with a VCL exhibits a successive rightward shift of polarization- voltage (P-V) hysteresis loop as the temperature increases. This is well correlated with the insulator−metal transition in a VCL, which can modulate the interfacial built-infield and thus cause theP-Vloop shift. It is therefore demonstrated that a VCL not only enhances the FE properties of HZO thinfilms but also provides a temperature degree of freedom to modulate the FE properties, which may open up a new pathway to develop HfO2-based FE memories with high performance and novel functionalities.
KEYWORDS: Hf0.5Zr0.5O2ferroelectricfilm, VOxcapping layer, endurance, insulator−metal transition, solution process
1. INTRODUCTION
Ferroelectric random access memory (FeRAM) has been long investigated as a promising candidate for next-generation low- power memory and logic devices.1−3FeRAM devices based on traditional ferroelectric (FE) materials, however, still suffer from scaling limitation and poor complementary metal-oxide semiconductor (CMOS) compatibility. Solutions to these scaling and integration issues may lie in the recently emerging HfO2-based FE materials.4−8Ferroelectricity in HfO2-based FE materials originates from a noncentrosymmetric orthorhombic phase (o-phase; space group: Pca21).9−11Theoretically, this o- phase can exhibit a remnant polarization (Pr) as high as 50 μC/cm2.11However, the experimentalPrvalues of HfO2-based FE materials reported in recent years were limited to the range of∼10−20μC/cm2,10−35well below the theoretical value. In addition, the coercive field (Ec) values of HfO2-based FE materials were typically 1−2 MV/cm,10−31about one order of magnitude higher than those of traditional FE materials. The highEcmakes the appliedfield to be high, inevitably increasing the risk of breakdown.36Besides, most of the reported HfO2- based FE materials exhibited the wake-up effect and relatively low endurance (∼105−107 cycles),27−30greatly limiting their
practical applications in FeRAM devices. Therefore, further improving the FE properties, including enhancingPr, reducing Ec, suppressing the wake-up effect, and improving endurance, are of great importance for putting HfO2-based FE materials into practical applications.
To improve the FE properties, capping layers have been widely used when growing HfO2-based FE thinfilms. This is mainly because a capping layer can stabilize the FE o-phase in a HfO2-based thin film by providing the desired mechanical stress. Besides, capping layers also have other functionalities.
For example, metallic capping layers, such as TiN,13−19Ru,13,14 Au,19Ta,19W,19Pt,19,20Pd,21Ni,21,22TaN,23and ITO,24can act as top electrodes. In addition, some oxide capping layers, such as Al2O332,33and ZrO2,35can reduce the leakage current.
Other oxide capping layers, like RuO2,30 can reduce the
Received: June 16, 2020 Accepted: August 12, 2020 Published: August 12, 2020 Downloaded via NANJING UNIV on October 10, 2020 at 10:58:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
number of oxygen vacancies at the interface, thus suppressing the wake-up effect and improving the endurance and retention properties. Therefore, great efforts have been made to explore capping layers, which can not only stabilize the FE o-phase but also possess novel functionalities.
Vanadium oxide (VOx,x= 2−2.5) is a transition metal oxide with many intriguing properties. VOxhas a thermal expansion coefficient of ∼2.1 × 10−5/K,37−39 which is much different from that of the most commonly used bottom electrode material: TiN (∼9.1×10−6/K).40Different thermal expansion coefficients may induce a high in-plane tensile strain to stabilize the FE o-phase. In addition, the energy of the V−O bond (625.0± 19.0 kJ/mol) is lower than that of the Hf−O bond (810.0±13.0 kJ/mol);41,42therefore, VOxmay supply oxygen for HfO2-based materials to suppress the formation of oxygen vacancies at the interface. Moreover, VOxis known for exhibiting the insulator−metal transition, which may provide a temperature degree of freedom to modulate the FE properties of VOx-capped HfO2-based capacitors. Therefore, the use of VOxas a capping layer is of great interest, but it has never been attempted so far.
Herein, we use VOxcapping layers (VCLs) for the growth of Hf0.5Zr0.5O2 (HZO) thin films on TiN-buffered silicon substrates. HZO is a prototype HfO2-based FE material, which possesses a high Pr and a wide process window. We show that VCLs can improve the FE properties of HZO thin films, including enhancingPr, keepingEcrelatively small, and improving endurance and retention properties. Besides, we also demonstrate that the FE properties of the HZO thinfilms with VCLs can be effectively tuned by the temperature due to the insulator−metal transition in VOx.
2. METHODS
2.1. Device Fabrication.The fabrication process of TiN/HZO/
VOx/Cu devices is shown inFigure 1a. TiN bottom electrodes with a thickness of 50 nm were deposited via sputtering on the Si/SiO2
substrates, which were chemically cleaned and dried. HZO thinfilms were grown by atomic layer deposition (ALD) at 280°C on Si/SiO2/ TiN substrates. During the ALD process, Hf[N(CH3)2]4, Zr[N- (CH3)2]4, and O3were used as the Hf-precursor, Zr-precursor, and oxygen source, respectively. After ALD, the HZO thin films were
treated with UV-ozone irradiation for 5 min for cleaning and increasing hydrophilicity. The VOx sol−gel solutions with concen- trations of 1, 1.67, and 2 mg/mL (seeFigure S1) were spin coated on the Si/SiO2/TiN/HZO surface at 6000 rpm for 60 s and then annealed at 270°C for 20 min. Then, the Si/SiO2/TiN/HZO/VOx multilayered films were annealed at 550 °C for 30 s via a rapid thermal annealing (RTA) system. The resulting HZO layers were 20 nm thick.32Finally, Cu top electrodes (∼50 nm) were deposited via thermal evaporation through a shadow mask. Besides the HZOfilms with VCLs, those without VCLs were also prepared for comparison.
In addition, the VOx single layer was specifically fabricated to determine the thickness of the VCL (∼8.1 nm for the VOx layer derived from the 1.67 mg/mL solution; seeFigure S2a).
2.2. Structure Characterization, Element Analysis, and Electrical Measurements.The structures of the HZO films were examined by grazing incidence X-ray diffraction (GIXRD). X-ray reflectivity (XRR) was used to measure the thickness of the VCL. The morphologies and FE properties were characterized by atomic force microscopy (AFM) and piezoresponse force microscopy (PFM), respectively. The leakage current, FE, and dielectric properties were measured with a semiconductor device analyzer (Agilent B1500A), FE tester (Radiant Precision), and impedance analyzer (Agilent E4900A), respectively. X-ray photoelectron spectroscopy (XPS) measurements were performed by using an Escalab 250Xi system with Al Kαsource (1486.6 eV). The XPS spectra of V 2p are shown inFigure S2b, based on which thexin″VOx″is estimated to be∼2.1.
To gain information about oxygen vacancies at the interface, XPS spectra of Hf 4f were measured for the HZO films after properly removing the Cu and VOxcapping layers by ion etching.
3. RESULTS AND DISCUSSION
Figure 1b shows GIXRD patterns measured in the 2θrange of 25−55° for the three HZO thin-film samples with VCLs prepared from 1, 1.67, and 2 mg/mL VOx sol−gel solutions (labeled as “HZO/VOx-1”, “HZO/VOx-1.67”, and “HZO/
VOx-2”, respectively) and two control samples: one without a VCL (labeled as“HZO/0”) and the other without both a VCL and RTA (labeled as “HZO/0-NA”). All the HZO samples except the HZO/0-NA one exhibit polycrystalline structures, suggesting that the annealing at 550°C is a necessary process for the crystallization of HZO. According to the liter- ature,6,11,16,19,32
the peak at ∼30.5° may correspond to the (111) peak from the FE o-phase and/or the (101) peak from Figure 1.(a) Flow chart of the fabrication process of the TiN/HZO/VOx/Cu capacitor. (b) GIXRD patterns of different HZO samples: HZO/
VOx-1, HZO/VOx-1.67, HZO/VOx-2, HZO/0, and HZO/0-NA. (c, d) AFM topography images and (e, f) corresponding PFM phase images in panels (c, e) HZO/0 and panels (d, f) HZO/VOx-1.67 samples (measured on the barefilms). Scale bars in panels (c, d) indicate 0.5μm.“−9 V”
and“+9 V”in panels (e, f) represent the writing voltages.
the t-phase, while the peaks at ∼28.6 and ∼31.7° can be assigned to the (−111) and (111) peaks from the paraelectric monoclinic phase (m-phase). Compared with the HZO/0 sample, the HZO/VOx-1, HZO/VOx-1.67, and HZO/VOx-2 samples exhibit apparently higher peaks from the o- and t- phases but lower peaks from the m-phase, indicating that the VCL can promote the formation of o- and t-phases while suppressing the m-phase formation.
To understand the origins for the VCL-induced stabilization of the o-phase, the morphologies of the HZO/0 and HZO/
VOx-1.67 samples were measured and compared. As shown in Figure 1c,d, the HZO/0 sample shows coarse isolated grains while the HZO/VOx-1.67 sample exhibits a much flatter surface withfiner grains. The root mean square roughness and average grain size (the method to estimate the grain size is described inFigure S3) in the HZO/0 sample are∼1.328 and
∼125.0 nm, respectively, but these values decrease to∼0.720 and ∼64.5 nm in the HZO/VOx-1.67 sample, respectively.
Therefore, the VCL can reduce the grain size, leading to a relatively high surface energy that can be used to stabilize the FE o-phase.34,43 In addition, the different thermal expansion coefficients of the VCL (∼2.1 × 10−5/K) and TiN bottom electrode (∼9.1 ×10−6/K) can induce a high in-plane tensile stress in the HZO thinfilm upon annealing, which can further stabilize the FE o-phase. The reduced grain size and different thermal expansion coefficients caused by the VCL are therefore considered as the two major factors contributing to the stabilization of the FE o-phase.
To further confirm that the VCL can stabilize the FE o- phase, the PFM phase images of the HZO/0 and HZO/VOx- 1.67 samples were measured and compared. As shown in Figure 1e,f, andFigure S4, some regions in the HZO/0 sample cannot be switched while the whole left and right regions in the HZO/VOx-1.67 sample can be uniformly switched. It is therefore indicated that the HZO/VOx-1.67 sample contains a larger amount and a more uniform distribution of the FE o- phase than the HZO/0 sample. This in turn suggests that the VCL can induce the formation of the FE o-phase. However, the VCL seems not to influence the domain orientation of the
HZOfilm in the as-grown state, and the possible reason taking into account the depolarizationfield44has been discussed (see Figure S5and related discussion).
Having confirmed that the VCL can stabilize the FE o-phase, whether the HZO samples with VCLs can exhibit enhanced FE properties is of interest. The polarization-voltage (P-V) hysteresis loops were thus measured after depositing Cu top electrodes on the bare and VOx-capped HZOfilms.Figure 2a shows the typicalP-Vloops measured with a maximum applied voltage (Vmax) of 5 V for the HZO/0, HZO/VOx-1, HZO/
VOx-1.67, and HZO/VOx-2 samples. As expected, all the three samples with VCLs exhibit higher 2Prvalues than the HZO/0 sample. In particular, the HZO/VOx-1.67 sample exhibits the most saturated loop and the highest 2Prvalue of 36.9μC/cm2. This is consistent with the XRD result that the HZO/VOx-1.67 sample exhibits the highest peaks from the o- and t-phases and the lowest peaks from the m-phase (seeFigure 1b).
Using the voltages shown inFigure 2a and the thickness of the HZO film (∼20 nm), the values of Ec and maximum applied field (Emax) of the HZO/VOx-1.67 sample are calculated to be∼1.09 and∼2.5 MV/cm, respectively (note:
because only the thickness of HZO layer is used, the actualEc andEmax values should be even lower).Figure 2a also shows that the P-V loops of the samples with VCLs are more symmetric than that of the HZO/0 sample, probably because inserting a VCL between HZO and Cu modifies the interfacial built-infield (to be explained in detail later).
Figure 2b compares the 2Pr,Ec, andEmaxvalues of the HZO/
VOx-1.67 sample and those of the HZO-based capacitors taken from the literature. Compared with its counterparts, our HZO/
VOx-1.67 sample exhibits almost the highest 2Prand the lowest Ec and Emax, demonstrating that the VCL can significantly improve the FE properties.
Figure 2c presents theVmax-dependent evolution ofPrfor the HZO/0, HZO/VOx-1, HZO/VOx-1.67, and HZO/VOx-2 samples. The HZO/VOx-1.67 sample exhibits the highest Pr at any Vmax. In addition, for all the samples, Pr gradually increases with increasingVmax, probably because the saturation of the switched polarization has not been reached and/or the Figure 2.(a)P-Vhysteresis loops at 300 K of different HZO samples, (b) comparison of FE performance between the HZO/VOx-1.67 sample and previous HZO-based capacitors (note: data are obtained from refs10−35and plotted by the authors). In panel (b), capping layer materials are indicated at the corresponding data points, while the bottom electrode and seed layer materials are represented by the colors of the data points that are illustrated in the right of the panel.“B”and“S”indicate the bottom electrode and the seed layer, respectively. (c)Pras a function ofVmax, (d)P- Vhysteresis loops obtained by the PUND method, and (e)I−Vcharacteristics of different HZO samples.
leakage current is involved. To exclude the influence from the leakage current,P-Vloops were measured by using a positive- up-negative-down (PUND) method. As shown in Figure 2d, the HZO/VOx-1.67 sample still exhibits the highestPr, and the 2Prvalue can reach 30.9μC/cm2, close to that obtained from conventional P-Vloops (Figure 2a). Therefore, VCL-induced Pr enhancement is an indicator of the truly enhanced ferroelectricity rather than the leakage current contribution.
The leakage currents were then directly measured for the samples with and without VCLs, and the results are shown in Figure 2e. It is observed that the samples with VCLs exhibit lower leakage currents than the HZO/0 sample, particularly when the applied voltage is large (>3 V). The reduced leakage current may result from the suppression of oxygen vacancies at the interface by the VCL (to be explained in detail later).
Another observation is that the current peaks exist in the voltage ranges of 1 to 2 V and −1 to −2 V, which can be attributed to the polarization switching-induced negative differential resistance effect.32,45
Endurance and retention are two crucial parameters to evaluate the reliability of a FeRAM device.6−8The endurance measurements were performed by applying repetitive bipolar
±4 V pulses with a triangular shape and a width of 0.001 ms (see inset in Figure 3a). Figure 3a shows the endurance
characteristics of the HZO/0 and HZO/VOx-1.67 samples.
For both samples, no wake-up effect is observed. The HZO/
VOx-1.67 sample exhibits a polarization reduction as small as
∼10.9% after 109 cycles, demonstrating excellent endurance performance. By contrast, noticeable polarization decay is observed in the HZO/0 sample after only 106cycles. Then, the retention measurements were carried out by applying a write pulse (+5 V/1 ms) to align the polarization in one direction and then applying a read pulse (−5 V/1 ms) to measure the retained polarization. The waiting time between the write pulse and the read pulse was varied (see inset inFigure 3b). During the waiting time, polarization relaxation, i.e., retention loss, may occur. This can be well characterized by the reduction of the polarization measured by the read pulse.Figure 3b shows that the polarization loss after 105seconds is only∼4.6% in the HZO/VOx-1.67 sample, while that becomes as large as
∼23.1% in the HZO/0 sample. Moreover, by using linear extrapolation, it is estimated that∼93.0% polarization can be retained after 3× 108seconds (10 years) in the HZO/VOx- 1.67 sample, fulfilling the requirement of nonvolatility. Given the above endurance and retention performance, our HZO thinfilms with VCLs outperform most of the reported HfO2- based FE materials in terms of reliability.11,17,18,28,30
The
significant enhancements in both endurance and retention can be attributed to the VCL-induced suppression of oxygen vacancies at the interface (to be explained in detail later).
Note that the FE properties (including Pr, endurance, and retention) of HZOfilms with thickness other than 20 nm are also observed to be improved by the VCL (seeFigure S6);
therefore, the wide applicability of VCL-induced enhancement of FE properties has been confirmed.
Another thing of interest is to investigate the temperature- dependent FE properties of HZO thin films with VCLs, allowing for the fact that VOxcan exhibit the insulator−metal transition. Hence, theP-Vhysteresis loops in the temperature range of 100−400 K were measured for the HZO/VOx-1.67 sample. As shown inFigure 4a, theP-Vloop successively shifts
rightward along the voltage axis as the temperature increases, and the largest shift occurs in the temperature range of 300− 400 K. The shift of the P-Vloop can be more quantitatively described by the evolution of the center of positive and negative coercive voltages, i.e., (|+Vc|−|−Vc|)/2, as a function of temperature, as depicted in Figure 4b. Additionally, the temperature-dependent capacitance−voltage (C−V) character- istics also exhibit a rightward shift with increasing temperature (Figure S7a), consistent with the behavior of the P-V loops.
After heating to 400 K, the HZO/VOx-1.67 sample was cooled to 300 K. During cooling, the P-V loop shifts leftward and becomes almost the same as that observed at the initial 300 K (Figure S8), demonstrating the reversibility of the temper- ature-dependent P-V loop shift. However, for the HZO/0 sample, theP-Vloop does not shift with varying temperature (Figure 4c). These results reveal that the temperature- dependent P-V loop shift is related to the VCL, where the insulator−metal transition may occur in this temperature range.
To confirm the occurrence of the insulator−metal transition, temperature-dependent current−voltage (I−V) characteristics were measured for the VOxlayer sandwiched between TiN and Figure 3. (a) Endurance and (b) retention characteristics of the
HZO/0 and HZO/VOx-1.67 samples. Insets in panels (a, b) schematically shows the pulses applied in the endurance and retention tests, respectively.
Figure 4.(a)P-Vhysteresis loops of the HZO/VOx-1.67 sample at different temperatures. (b)±Vc and (|+Vc| − |−Vc|)/2 values as a function of temperature for the HZO/VOx-1.67 sample. The (|+Vc|−
|−Vc|)/2 value of the HZO/0 sample is indicated by the dotted line.
(c) P-V hysteresis loops of the HZO/0 sample at different temperatures. (d) Temperature-dependentI-Vcharacteristics of the TiN/VOx(1.67 mg/mL)/Cu capacitor.
Cu electrodes. As shown inFigure 4d, the current does not change much when the temperature is below 300 K, but it increases significantly as the temperature increases from 300 to 400 K. The I−V characteristics in the temperature range of 300−400 K were further analyzed by the curve fitting (Figure S9). The fitting results show that the conduction behavior changes from space-charge-limited conduction (SCLC) to ohmic conduction with increasing temperature,46,47 implying the occurrence of the insulator−metal transition in this temperature range. The above results have shown that both the largest shift of the P-V loop and the insulator−metal transition in the VCL occur in the temperature range of 300− 400 K. Therefore, the successive P-V loop shift can be well correlated with the insulator−metal transition in the VCL.
Based on all the above results, possible mechanisms for VCL-induced enhanced FE properties and successiveP-Vloop shift are analyzed as follows. As has been revealed, the VCL can stabilize the FE o-phase by refining the grain size and providing the in-plane tensile stress, thereby enhancingPr. In addition, the VCL is much more conductive than the HZO layer, as supported by the leakage current in the TiN/VOx/Cu capacitor (∼1.03×10−6A at 1 V; seeFigure 4d) being much larger than that in the TiN/HZO/VOx/Cu capacitor (∼1.44× 10−10A at 1 V; seeFigure 2e andFigure S7b). When applying a voltage to the TiN/HZO/VOx/Cu capacitor, most of the voltage drop should occur across the HZO layer. Therefore,Ec is kept small despite the use of the VCL. As described earlier, the energy of the V−O bond (625.0±19.0 kJ/mol) is lower than those of Hf−O (810.0±13.0 kJ/mol) and Zr−O (766.1
±10.6 kJ/mol) bonds.41,42The VCL may thus provide oxygen for the HZO film to suppress the formation of oxygen vacancies at the interface, as evidenced by the Hf 4f peak of the nonstoichiometric HfO2‑xphase (at∼16.1 eV30,48) being much lower at the HZO/VOx interface than at the HZO/Cu interface (Figure 5a,b). The suppression of oxygen vacancies by the VCL can reduce the leakage current; and it may also improve the endurance and retention performance, because
oxygen vacancy formation and accumulation at the interface during thefield cycling and the retention period are believed to be responsible for the endurance and retention failures, respectively.29,30,49
Finally, let us focus on how the insulator−metal transition in the VCL induces theP-Vloop shift. As schematically shown in Figure 5c−e, TiN is metal with a work function (WF) of 4.2− 4.6 eV50−52 while HZO is assumed to be an n-type semiconductor with a band gap of∼5.1 eV.52,53At the TiN/
HZO interface, a built-in field (Ebi−b) pointing downward is formed. At low temperature, e.g., 300 K, VOx is a semi- conductor with a band gap of ∼0.6 eV and a WF of 5.15 eV.54−56 The band bending at the HZO/VOx interface may lead to a built-infield (Ebi−t) pointing upward. When Ebi−bis slightly larger thanEbi−t, the overall built-infield is small and points downward. This may be the origin for the observation that theP-Vloop of the TiN/HZO/VOx/Cu capacitor at 300 K is relatively symmetric with only a small negative value of (| +Vc|−|−Vc|)/2 (seeFigure 4b). As the temperature increases, VOxexhibits the insulator−metal transition, during which the bandgap of VOx decreases to 0 while its WF increases by
∼0.15 eV.56 Therefore, the band bending at the HZO/VOx interface increases, giving rise to a largerEbi‑t(Figure 5d). As Ebi‑t increases, the overall built-in field changes its direction from downward to upward. This well explains why the P-V loop successively shifts rightward as the temperature increases (Figure 4a). Besides, when the temperature is sufficiently high, e.g., 400 K, VOxis metal-like, making the band bending at the top interface and Ebi‑t in the TiN/HZO/VOx/Cu capacitor similar to those in the TiN/HZO/Cu capacitor (see comparison betweenFigure 5d and e). This can explain why the (|+Vc| − |−Vc|)/2 value of the TiN/HZO/VOx/Cu capacitor at 400 K is close to that of the TiN/HZO/Cu capacitor (Figure 4b).
4. CONCLUSIONS
In summary, HZO thin films with solution-processed VCLs were fabricated and their FE properties were characterized.
GIXRD and PFM results show that the HZO samples with VCLs exhibit a higher fraction of FE o-phase compared with those without VCLs, suggesting that the VCL can stabilize the FE o-phase. The reason for this may be because the VCL can reduce the grain size and provide in-plane tensile stress, both of which benefit the formation of the FE o-phase. Then, enhanced FE properties were observed in the HZO samples with VCLs. Particularly, the HZO/VOx-1.67 sample exhibits a large 2Prvalue of 36.9μC/cm2, a relatively smallEcof∼1.09 MV/cm, and excellent endurance and retention (polarization losses after 109 cycles and 105seconds are only ∼10.9% and
∼4.6%, respectively). While the enhancedPrcan be attributed to the VCL-induced stabilization of the FE o-phase, the relatively smallEcis well due to the fact that the VCL is much more conductive than the HZO layer. The excellent endurance and retention may be explained by the VCL-induced suppression of oxygen vacancies at the interface. More interestingly, a successive rightward shift of P-V loop is observed as the temperature increases, which is well due to the insulator−metal transition occurring in the VCL and the consequent modulation of interfacial built-infield. Our results therefore demonstrate that the VCL can not only enhance the FE properties of HZO thin films but also enable the temperature modulation of the FE properties, which may Figure 5.XPS Hf 4f spectra of the (a) HZO/0 and (b) HZO/VOx-
1.67 samples after removing the Cu and VOx capping layers, respectively. The peak of the HfO2‑xphase in panel (b) is much lower than that in panel (a), suggesting that the number of oxygen vacancies at the HZO/VOx interface is smaller than that at the HZO/Cu interface. Schematic energy band diagrams of the TiN/HZO/VOx/ Cu capacitor at (c) low and (d) high temperatures, and (e) the TiN/
HZO/Cu capacitor.
benefit the development of CMOS-compatible multifunctional memory and logic devices.
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ASSOCIATED CONTENT*sı Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.0c10964.
Schematic synthesis process of the VOxprecursor; XRR curves and XPS spectra of the VOx layer; method to estimate the grain size; PFM phase and amplitude hysteresis loops; domain orientations in the as-grown HZO/0 and HZO/VOs-1.67 samples; FE properties of 10 nm HZOfilms with and without VCLs; temperature- dependentC−VandI−Vcharacteristics;P−Vhysteresis loops in a heating/cooling cycle, and fittings of I−V characteristics (PDF)
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AUTHOR INFORMATION Corresponding AuthorsZhen Fan−Institute for Advanced Materials, South China Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China;
orcid.org/0000-0002-1756-641X; Email:fanzhen@
m.scnu.edu.cn
Xubing Lu−Institute for Advanced Materials, South China Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China;
orcid.org/0000-0002-2552-9571; Email:luxubing@
m.scnu.edu Authors
Yan Zhang−Institute for Advanced Materials, South China Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Dao Wang− Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Jiali Wang−Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Zhengmiao Zou−Institute for Advanced Materials, South
China Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Yushan Li−Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Qiang Li−Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong
Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Ruiqiang Tao−Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China Deyang Chen−Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China;
orcid.org/0000-0002-8370-6409
Min Zeng−Institute for Advanced Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China; orcid.org/0000- 0003-3594-7619
Xingsen Gao−Institute for Advanced Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China; orcid.org/0000- 0002-2725-0785
Jiyan Dai− Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, China
Guofu Zhou−Guangdong Provincial Key Laboratory of Optical Information Materials, South China Academy of Advanced Optoelectronics and National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China; orcid.org/0000-0003-1101- Jun-Ming Liu1947 − Institute for Advanced Materials, South China
Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China; Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 21009, China;
orcid.org/0000-0001-8988-8429 Complete contact information is available at:
https://pubs.acs.org/10.1021/acsami.0c10964
Author Contributions
X. L. and Z. F. designed and supervised this work. Y. Z. carried out the solution synthesis, thin film preparation, device fabrication and electrical measurements. D. W., J. W., Z. Z., R. T., and G. Z. conducted XRD and XRR. Y. L., Q. L., D. C., M. Z., X. G., and J. D. performed AFM and PFM. Y. Z., X. L., and Z. F. wrote the manuscript. All authors read and commented on the manuscript.
Notes
The authors declare no competingfinancial interest.
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ACKNOWLEDGMENTSThis work is supported by National Natural Science Foundation of China (Nos. 51872099 and U1932125), J. Y.
D. acknowledges the support from Hong Kong Research Grant Council (No.15300619). D. Y. C. acknowledges thefinancial Support from Science and Technology Planning Project of Guangdong Province, China (No. 2019A050510036). X. B. L.
and Z. F. acknowledge the supports from the Project for Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2016 and 2018). This work is also supported by Science and Technology Program of Guangzhou (No. 2019050001), Guangdong Provincial Key Laboratory of
Optical Information Materials and Technology (No.
2017B030301007), Natural Science Foundation of Guangdong Province (No. 2020A1515010996), 111 Project, and Innova- tion Project of Graduate School of South China Normal University (No. 2019LKXM011).
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