A ferroelectric capacitor structure and a method of fabricating the same

Abstract

The application provides a ferroelectric capacitor structure and a preparation method thereof, and the ferroelectric capacitor structure comprises a (001)-oriented oxide single crystal substrate, an epitaxial conductive bottom electrode layer, a CeO x buffer layer, a HfO2-ZrO2 ferroelectric superlattice layer, a top electrode layer and a Pt electrode layer arranged in sequence; the (001)-oriented oxide single crystal substrate comprises SrTiO3; the epitaxial conductive bottom electrode layer comprises La 0.67 Sr 0.33 MnO3. The controllable switching of the HfO2-ZrO2 superlattice orientation is finally realized, and meanwhile, the epitaxial quality of the ferroelectric thin film and the overall electrical reliability of the device are ensured. The application further provides a preparation method of the ferroelectric capacitor structure.

Description

Technical Field

[0001] This invention belongs to the field of ferroelectric thin film material preparation and microelectronic device manufacturing technology, specifically relating to a ferroelectric capacitor structure and its preparation method. Background Technology

[0002] Since the discovery of ferroelectricity in hafnium oxide (HfO2) thin films in 2011, hafnium-based ferroelectric materials have become core candidate materials for next-generation non-volatile ferroelectric memory devices due to their significant advantages, such as high compatibility with complementary metal-oxide-semiconductor (CMOS) processes, maintenance of ferroelectricity at the nanoscale, and environmental friendliness. Among them, the zirconium oxide (ZrO2)-doped HfO2 (HZO) system exhibits excellent ferroelectric properties and electrical reliability. Furthermore, the HfO2 / ZrO2 superlattice structure, due to its periodic layered arrangement, can effectively suppress oxygen vacancy migration and phase transitions, further improving the material's electrical properties, fatigue characteristics, and recovery ability, demonstrating significant application potential in the field of highly integrated ferroelectric memory. Unlike traditional lead-based ferroelectric materials where polarization is dominated by the displacement of central cations, the polarization of hafnium-based ferroelectric materials originates from the significant displacement of oxygen anions along specific crystal directions in the lattice. The macroscopic ferroelectric polarization effect is directly related to the preferred crystal orientation. The material can achieve maximum switchable polarization when the polarization direction is consistent with the direction of the applied electric field. Otherwise, the ferroelectric performance and switching speed will decrease due to the reduction of the effective polarization component. Therefore, precise control of the crystal orientation of hafnium-based ferroelectric thin films is the key to improving device performance.

[0003] In existing technologies, researchers have conducted studies on the orientation control of hafnium-based ferroelectric thin films using stress modulation and interface engineering. Related literature also confirms that layered superlattice structures combined with stress modulation can improve the ferroelectric properties of HZO-type materials while maintaining CMOS compatibility. However, many technical bottlenecks still exist in practical applications. In La... 0.67 Sr 0.33 When HfO2–ZrO2 superlattices are directly deposited on a commonly used epitaxial system such as MnO3 (LSMO) electrode / SrTiO3 (STO) substrate, the crystal orientation of the thin film is easily constrained by the bottom electrode, the substrate lattice and the surface energy, and usually spontaneously forms an out-of-plane orientation

[111] . The polarization vector of this orientation has an angle of about 54.7° with the applied electric field, which directly causes insufficient effective polarization and low residual polarization (Pr). Moreover, the switching process requires a higher electric field and a longer time. At the same time, the existing methods of controlling orientation by stress, annealing and other means are mostly empirical optimizations, lacking replicable structural designs and standardized process flows. The repeatability and portability are poor, making it difficult to meet the needs of industrial applications.

[0004] Cerium oxide (CeO) xDue to its high redox activity, good oxygen ion conductivity, and thermochemical stability, hafnium zirconium oxide (HZO) has been shown to be able to control the crystal structure and oxygen vacancy distribution of its materials. Doping it into HZO can also improve the durability and retention of ferroelectric switches and suppress the increase in stress-induced leakage current during polarization cycling. However, CeO... x Due to its inherent high leakage current, using it directly as a dielectric layer would severely impact the electrical performance of devices. Current technologies only focus on its high-k characteristics and doping modification effects, and have not yet developed it as a buffer layer with controllable thickness, nor have they utilized CeO2. x Systematic research on achieving precise orientation switching of HfO2–ZrO2 superlattice has yet to propose an engineering solution that balances orientation control with device electrical performance. In summary, a novel interface engineering scheme is urgently needed to achieve controllable switching of the polarization orientation from

[111] group to

[100] group while ensuring the epitaxial quality of HfO2–ZrO2 superlattice. Simultaneously, it should address the leakage problem caused by the buffer layer material, ensuring that the ferroelectric polarization axis is highly parallel to the applied electric field. This would significantly improve the residual polarization and switching speed of hafnium-based ferroelectric thin films, meeting the application requirements of next-generation low-power, highly integrated ferroelectric memory devices. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention focuses on utilizing the novel material CeO x The system provides a ferroelectric capacitor structure by intercalation, which solves the problems in the existing hafnium-based ferroelectric thin film preparation technology. In the case of HfO2–ZrO2 ferroelectric superlattice directly deposited on the epitaxial system, the orientation of the HfO2–ZrO2 ferroelectric superlattice is prone to spontaneously forming

[111] group orientation, resulting in an angle between the polarization vector and the applied electric field, insufficient effective polarization and limited switching speed. At the same time, the existing orientation control methods are mostly empirical optimization, with poor repeatability and portability. Furthermore, due to the large leakage current of cerium oxide, it is difficult to balance orientation control and device electrical performance. In addition, there is a lack of specific engineering implementation schemes for buffer layer-driven orientation switching. The system also solves the problem in the existing technology that the strain release and stabilization of structural defects such as intercalated stacking faults and ferroelastic domains are not quantitatively analyzed and utilized in engineering. Finally, the controllable switching of the orientation of HfO2–ZrO2 superlattice is realized, while ensuring the epitaxial quality of the ferroelectric thin film and the overall electrical reliability of the device.

[0006] The present invention also provides a method for preparing a ferroelectric capacitor structure.

[0007] A first aspect of the present invention provides a ferroelectric capacitor structure, comprising: (001) Oriented oxide single crystal substrate, epitaxial conductive bottom electrode layer, CeO x Buffer layer, HfO2–ZrO2 ferroelectric superlattice layer, top electrode layer and Pt electrode layer; The (001) oriented oxide single crystal substrate includes SrTiO3; The epitaxial conductive bottom electrode layer includes La 0.67 Sr 0.33 MnO3.

[0008] The ferroelectric capacitor structure of this invention, through hierarchical precise structural design and specific material combination and adaptation, relies on the structural synergy and complementary material properties between layers to achieve controllable modulation of the crystal orientation of hafnium-based ferroelectric thin films, while simultaneously taking into account the epitaxial quality, ferroelectric performance, and electrical stability of the device. Compared with existing CeO-free capacitors... x The ferroelectric capacitance structure of the buffer layer has the following significant beneficial effects: This structure introduces CeO x The buffer layer serves as the core layer for orientation control, paired with a (001) oriented SrTiO3 single crystal substrate and La 0.67 Sr 0.33 The classic epitaxial system of MnO3 conductive bottom electrode allows for controllable switching of the upper HfO2–ZrO2 ferroelectric superlattice layer from the traditional

[111] group orientation to the

[100] group out-of-plane (001) orientation. This makes the ferroelectric polarization axis highly parallel to the direction of the applied electric field, eliminating the effective polarization component loss caused by the approximately 54.7° angle between the polarization vector and the electric field in the traditional

[111] orientation, and significantly improving the remanent polarization value. Under room temperature conditions, the remanent polarization can be increased from approximately 9 μC / cm. 2 Increased to 12μC / cm 2 This approach ensures the stability of ferroelectric properties over a wide temperature range of 77–298 K, while improving the device's readout window and noise immunity. Ultimately, it achieves precise control over the preferred orientation of ferroelectric thin films, significantly enhancing ferroelectric polarization performance.

[0009] (001) Orientation of SrTiO3 substrate and La 0.67 Sr 0.33 The MnO3 bottom electrodes are epitaxially grown in an approximately cubic cube-on-cube manner with low lattice mismatch, with a lattice mismatch of only about 0.8%, laying the foundation for high-quality epitaxy of subsequent layers; CeO x Buffer layer and La 0.67 Sr 0.33 A specific epitaxial relationship can be formed between MnO3 / SrTiO3, achieving approximately 45° rotation in the in-plane direction to reduce interfacial lattice mismatch, while simultaneously achieving a specific relationship between HfO2–ZrO2 / CeO3. x The interface introduces controllable insertion stacking faults and ferroelastic domains, effectively releasing 4-6% of lattice mismatch strain, ensuring high epitaxial quality of the entire heterojunction structure, and avoiding structural defects and performance degradation caused by lattice mismatch. This optimizes the interface lattice matching degree and guarantees high epitaxial quality.

[0010] CeO x The buffer layer itself possesses excellent oxygen ion conductivity, chemical stability, and thermal stability, and can control the crystal structure and oxygen vacancy distribution of the HfO2–ZrO2 ferroelectric superlattice. This structure, however, can also control the CeO2 content. x Used as a buffer layer rather than a direct dielectric layer, and with precise thickness control, it effectively suppresses CeO while achieving orientation modulation. x The material's large leakage current defect avoids the negative impact of leakage current on the device's electrical performance; at the same time, La 0.67 Sr 0.33 The excellent conductivity of the MnO3 bottom electrode provides a stable conductive path for the device, reducing resistance loss in the electrode layer. This balances orientation control with leakage suppression, improving the electrical reliability of the device.

[0011] The top and bottom electrode layers form a symmetrical electrode structure, effectively improving the polarization uniformity inside the ferroelectric capacitor and reducing performance deviations caused by polarization bias. The outermost Pt electrode layer further enhances the conductivity of the entire device, reduces electrode contact resistance, and also provides protection for the underlying La. 0.67 Sr 0.33 The MnO3 top electrode provides effective protection, preventing oxidation and wear during subsequent processes or use, thus extending the device's lifespan and enhancing its process compatibility and practical application value.

[0012] The structure utilizes SrTiO3 and La 0.67 Sr 0.33 MnO3, HfO2–ZrO2, CeO x Materials such as Pt are highly compatible with complementary metal-oxide-semiconductor (CMOS) processes and can be integrated on existing logic lines. Furthermore, the HfO2–ZrO2 ferroelectric superlattice layer can maintain ferroelectricity at a thickness of a few nanometers, which meets the fabrication requirements of highly integrated non-volatile memory devices. This provides an achievable structural solution for the industrialization of next-generation low-power, high-speed, and highly integrated ferroelectric random access memory, ferroelectric field-effect transistors, and other devices.

[0013] According to some embodiments of the present invention, the (001) oriented oxide single crystal substrate includes SrTiO3, as well as other cubic or near-cubic perovskite structure single crystals.

[0014] The epitaxial conductive bottom electrode layer includes La 0.67 Sr 0.33 MnO3 has good electrical conductivity and low lattice mismatch with SrTiO3.

[0015] CeO xThe buffer layer has a CeOx film epitaxially grown along a specific orientation to simultaneously ensure epitaxial quality and leakage current performance.

[0016] According to some embodiments of the present invention, CeO x The thickness of the buffer layer is 0.5~3nm.

[0017] According to some embodiments of the present invention, the CeO x The thickness of the buffer layer is any value among 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, 1.2nm, 1.5nm, 1.8nm, 2.0nm, 2.2nm, 2.5nm, 2.8nm, and 3.0nm, such as 1.0nm, or any range formed by both, such as 0.5nm to 1.0nm.

[0018] A thickness of 4nm is relatively large, which can easily lead to leakage of the HfO2-ZrO2 film, resulting in the loss of ferroelectric properties.

[0019] CeO x The thickness of the buffer layer is preferably 1 nm.

[0020] HfO2–ZrO2 ferroelectric superlattice layer: An orthorhombic ferroelectric superlattice formed by alternating stacks of HfO2 and ZrO2 layers, with an overall thickness of 6–12 nm, typically around 8 nm. As the thickness increases, CeO2… x The out-of-plane lattice constant increases while the in-plane lattice constant decreases, resulting in a decrease in the stress applied to HfO2–ZrO2 and a gradual decrease in polarization intensity. When it reaches a limit of about 3 nm, the o phase of the HfO2–ZrO2 thin film will be converted into the t phase, thus causing the ferroelectricity to disappear.

[0021] The epitaxial conductive bottom electrode layer includes La 0.67 Sr 0.33 MnO3. The epitaxial conductive bottom electrode layer is preferably made of the same material as the bottom electrode, La. 0.67 Sr 0.33 MnO3 is used to form a symmetrical structure and improve polarization uniformity.

[0022] According to some embodiments of the present invention, the top electrode layer is made of the same La as the bottom electrode layer. 0.67 Sr 0.33 MnO3 material forms a symmetrical electrode structure, which further improves the polarization uniformity inside the ferroelectric capacitor and reduces the performance deviation caused by polarization bias.

[0023] The Pt electrode layer further enhances conductivity while protecting La. 0.67 Sr 0.33 MnO3 top electrode.

[0024] A second aspect of the present invention provides a method for preparing the ferroelectric capacitor structure of the first aspect of the present invention, comprising the following steps: S1: An epitaxial conductive bottom electrode layer is deposited on the surface of the (001) oriented oxide single crystal substrate by pulsed laser; S2: CeO is deposited on the surface of the epitaxial conductive bottom electrode layer formed in step S1. x Buffer layer; S3: In the CeO x On the surface of the buffer layer, a HfO2–ZrO2 ferroelectric superlattice layer is deposited, and a top electrode layer is formed on the surface of the HfO2–ZrO2 ferroelectric superlattice layer by photolithography. S4: The Pt electrode layer is formed on the surface of the top electrode layer by measurement and control sputtering, thus obtaining the ferroelectric capacitor structure.

[0025] According to some embodiments of the present invention, in step S1, an (001) oriented STO single crystal substrate is selected, cleaned with a standard chemical solution, and annealed under a suitable atmosphere to obtain atomically flat steps. In a pulsed laser deposition (PLD) cavity, a KrF excimer laser (wavelength 248 nm) is used as the light source; the cavity oxygen pressure is approximately 13 Pa, the substrate temperature is 750 °C, and the laser energy density is approximately 1.0 J / cm². 2 The repetition frequency was 3 Hz, the deposition thickness was about 17 nm, and after deposition, the temperature was cooled to 650 °C at a rate of about 20 °C / min.

[0026] According to some embodiments of the present invention, in step S2, CeO is deposited at 650°C with an oxygen pressure of approximately 10 Pa. x Thin film; laser energy density and repetition rate are similar to LSMO (approximately 1.0 J / cm²). 2 (3Hz); the thickness of the buffer layer is precisely controlled by the deposition time to keep it within 0.5-1nm, so as to ensure epitaxial quality and orientation control capability, while suppressing excessive leakage current.

[0027] According to some embodiments of the present invention, in step S3, the sample is heated to 750°C at a rate of 20°C / min; the oxygen pressure is the same as that during CeO2 deposition; HfO2 and ZrO2 layers are deposited using alternating or composite targets, and the laser energy density is approximately 1.1 J / cm². 2 The repetition frequency is 3Hz; the thickness of the HfO2 and ZrO2 layers can be from single / double atomic layers to several nanometers, forming a periodic superlattice with a thickness of about 1nm for each layer and a total thickness of about 8nm.

[0028] According to some embodiments of the present invention, in step S3, the top electrode is preferably made of LSMO material, and the deposition parameters are the same as those of the bottom electrode; a top electrode pattern with a diameter of about 30 μm is prepared on the surface of the thin film using photolithography.

[0029] According to some embodiments of the present invention, in step S4, 20 nm of Pt is deposited using a magnetron sputtering process to form a ferroelectric capacitor structure. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the hierarchical structure of the epitaxial heterostructure of a ferroelectric capacitor.

[0031] Figure 2 It is CeO x Contains CeO x Buffer layer and CeO-free x X-ray diffraction pattern of the HfO2–ZrO2 thin film of the buffer layer.

[0032] Figure 3 It is CeO x In-plane reciprocal space mapping diagram and angle matching schematic diagram of the thin film and STO / LSMO substrate.

[0033] Figure 4 It is CeO-free x One of the polarization intensity-electric field intensity characteristic curves of HfO2–ZrO2 superlattice thin films with buffer layer.

[0034] Figure 5 It contains CeO x The second polarization intensity-electric field intensity characteristic curve of HfO2–ZrO2 superlattice thin film of buffer layer.

[0035] Figure 6 With / without CeO x Polarization intensity-voltage comparison curves of HfO2–ZrO2 superlattice thin films in the buffer layer.

[0036] Figure 7 With / without CeO x Leakage current density-voltage comparison curves of HfO2–ZrO2 superlattice thin films with buffer layers.

[0037] Figure 8 With / without CeO x Dielectric constant-voltage comparison curves of HfO2–ZrO2 superlattice thin films with buffer layers.

[0038] Figure 9 CeO of different thicknesses x X-ray diffraction comparison patterns of HfO2–ZrO2 superlattice thin films of buffer layer.

[0039] Figure 10 It is CeO x Reciprocal space mapping and lattice strain analysis diagram of thin films. Detailed Implementation

[0040] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0041] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0043] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0044] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0045] In some embodiments of the present invention, the method for preparing the ferroelectric capacitor structure is as follows: 1. Substrate preparation A (001) oriented STO single crystal substrate was selected, cleaned with a standard chemical solution, and annealed in an appropriate atmosphere to obtain atomically flat steps.

[0046] 2. LSMO bottom electrode deposition In the pulsed laser deposition (PLD) cavity, a KrF excimer laser (wavelength 248nm) was used as the light source; the oxygen pressure in the cavity was about 13Pa, the substrate temperature was 750℃, the laser energy density was about 1.0J / cm², the repetition frequency was 3Hz, the deposition thickness was about 17nm, and after deposition, the temperature was cooled to 650℃ at a rate of about 20℃ / min.

[0047] 3. CeOx Buffer layer deposition and thickness control CeO was deposited at 650°C with an oxygen pressure of approximately 10 Pa. x Thin film; laser energy density and repetition rate are similar to LSMO (approximately 1.0 J / cm²). 2 (3Hz); the thickness of the buffer layer is precisely controlled by the deposition time to keep it within 0.5-1nm, so as to ensure epitaxial quality and orientation control capability, while suppressing excessive leakage current.

[0048] 4. HfO2–ZrO2 superlattice deposition The sample was heated to 750℃ at a rate of 20℃ / min; the oxygen pressure was the same as during CeO2 deposition; HfO2 and ZrO2 layers were deposited using alternating or composite targets, with a laser energy density of approximately 1.1 J / cm². 2 The repetition frequency is 3Hz; the thickness of the HfO2 and ZrO2 layers can be from single / double atomic layers to several nanometers, forming a periodic superlattice with a thickness of about 1nm for each layer and a total thickness of about 8nm.

[0049] 5. Top Electrode Deposition and Device Fabrication The top electrode is preferably made of LSMO material, and the deposition parameters are the same as those of the bottom electrode. A top electrode pattern with a diameter of about 30 μm is prepared on the surface of the thin film using photolithography, and 20 nm of Pt is deposited using magnetron sputtering to form a ferroelectric capacitor structure.

[0050] refer to Figure 1 The diagram shows a hierarchical schematic of the epitaxial heterostructure of a ferroelectric capacitor. Figure 1 In the middle, from bottom to top, they are set sequentially: (001) Oriented oxide single crystal substrate (STO), epitaxial conductive bottom electrode layer (LSMO), CeO x Buffer layer, HfO2–ZrO2 ferroelectric superlattice layer, top electrode layer (LSMO) and Pt electrode layer; (001) The oriented oxide single crystal substrate is SrTiO3; The epitaxial conductive bottom electrode layer is La 0.67 Sr 0.33 MnO3.

[0051] In some embodiments of the present invention, CeO-free products were also prepared. x The preparation method of the HfO2–ZrO2 thin film with buffer layer is the same as that of the CeO2-containing film mentioned above. x The preparation method of the HfO2–ZrO2 thin film of the buffer layer is the same.

[0052] CeO x Contains CeO x The buffer layer of HfO2–ZrO2 film and CeO-free xX-ray diffraction tests were performed on the HfO2–ZrO2 thin film sample with the buffer layer, and the results are as follows: Figure 2 As shown.

[0053] from Figure 2 It can be seen that only CeO x At that time, its characteristic diffraction peak appeared around 33°; with the introduction of CeO x The HfO2–ZrO2 superlattice of the buffer layer exhibits a distinct (002) pattern around 35°. o Phase diffraction peaks; without the introduction of the CeOx buffer layer, the HfO2–ZrO2 superlattice exhibits a significant (111) peak at approximately 30°. o Diffraction peaks. This indicates that the CeO of the present invention... x The buffer layer indeed achieved the switching of polarization phase orientation from group

[111] to group

[100] . The STO substrate is cubic, with its

[100] /

[010] directions forming in-plane basis vectors; the LSMO bottom electrode is epitaxially mounted on the STO in an approximately cubic "cube-on-cube" manner, with a lattice mismatch of about 0.8%, and clear quadruple symmetry peaks are visible in the θ scan; the CeOx buffer layer is mounted on the LSMO / STO using CeO. x The rotational extensional relationship of

[110] / / LSMO / STO

[100] is reduced by rotating at approximately 45° to minimize interface mismatch.

[0054] X-ray diffraction Phi scanning and reciprocal space mapping confirmed that CeOx and STO / LSMO maintain a high degree of epitaxial consistency in both in-plane and out-of-plane directions. The results are as follows: Figure 3 As shown.

[0055] Figure 4 and Figure 5 The diagram illustrates the comparison of ferroelectric properties of HfO2–ZrO2 superlattices with different orientations under the same total thickness.

[0056] At 298 K (room temperature), the (111) oriented superlattice (reference) Figure 4 The maximum polarization Pmax (as shown) is approximately 26 μC / cm. 2 The remanent polarization Pr is approximately 9 μC / cm. 2 (002) Oriented superlattice (reference) Figure 5 The Pmax (as shown) is approximately 27 μC / cm. 2 Pr is approximately 12 μC / cm 2The residual polarization is significantly improved; as the temperature drops from 298K to 77K, 2Pr only decreases slightly, indicating that the structure of the present invention has good ferroelectric stability in a wide temperature range; the physical reason is that: (002) the crystal plane is parallel to the polarization vector and perpendicular to the electrode surface, the spontaneous polarization vector is completely in the same direction as the applied electric field, the ion displacement path is direct, and the switching barrier is low; while (111) the crystal plane has a 54.7° angle with the c-axis, the polarization component is decomposed into parallel and perpendicular components, and additional energy is required to complete the rotation and flip.

[0057] Figure 6 With / without CeO x Polarization intensity-voltage comparison curves of HfO2–ZrO2 superlattice thin films with buffer layers. At the same voltage, the sample with the buffer layer exhibits greater polarization and a smaller coercive field.

[0058] Figure 7 With / without CeO x Leakage current density-voltage comparison curves of HfO2–ZrO2 superlattice thin films with buffer layers. Because the polarization direction is outward, the leakage current density of the sample with the buffer layer is higher than that of the sample without the buffer layer.

[0059] Figure 8 With / without CeO x Dielectric constant-voltage comparison curves of HfO2–ZrO2 superlattice thin films with buffer layers. The sample with the buffer layer has a larger dielectric constant.

[0060] Figure 9 CeO of different thicknesses x X-ray diffraction (XRD) patterns of the HfO2–ZrO2 superlattice thin film with a buffer layer. As the thickness increases, the peak position in the XRD shifts to the left, possibly indicating a transition to the t-phase. Ferroelectric properties deteriorate because the lattice constants of materials like La2O3 and Y2O3 do not match well with the LSMO bottom electrode, and therefore they were not selected.

[0061] The key to the ferroelectric capacitor structure of this invention lies in CeO. x Buffer layer and La 0.67 Sr 0.33 A specific epitaxial relationship is formed between MnO3 / SrTiO3: CeO x

[110] / / La 0.67 Sr 0.33 MnO3 / SrTiO3

[100] undergoes approximately 45° rotation in the in-plane direction to reduce interfacial lattice mismatch; the HfO2–ZrO2 superlattice layer in CeO x The buffer layer preferentially forms a

[100] group epitaxial orientation, i.e., an out-of-plane (001) orientation, whose polarization axis is highly consistent with the electric field direction; HfO2–ZrO2 / CeO xThe interface introduces insertion-type stacking faults and ferroelastic domains to release lattice mismatch strain on the order of 4-6%, ensuring high-quality epitaxy and ferroelectric properties.

[0062] CeO x The (010) interplane spacing d = 2.71 Å.

[0063] CeO x It has a fluorite structure and its lattice constant is a CeOx ≈2×d(010)=5.42Å.

[0064] Figure 10 This is a diagram showing the reciprocal space mapping and lattice strain analysis of the CeOx thin film. (Reference) Figure 10 CeO x The reciprocal space spots of the thin film are aligned in the in-plane direction with the STO / LSMO substrate, indicating that its in-plane lattice constant is strongly constrained by the substrate and is essentially consistent with the substrate (α = 3.905 Å for STO). Therefore, CeO x The layer itself is in a biaxial compressive strain state.

[0065] The measured HfO2–ZrO2 lattice parameters were compared with CeO2. x The corresponding lattice parameters are compared. Calculation formula: Mismatch δ = (a CeOx a HZ ) / a HZ ×100%. ≈(5.42) 5.19) / 5.19≈4.4% Considering that the b-axis and c-axis are slightly shorter, the mismatch will be larger. Therefore, the released lattice mismatch strain is on the order of 4~6%.

[0066] Ferroelectric capacitor structure, utilizing CeO x An epitaxial structure and fabrication method for HfO2–ZrO2 ferroelectric superlattice with preferred orientation switching from group

[111] to group

[100] is described, which makes the polarization axis as parallel as possible to the electric field direction, thereby significantly improving remanent polarization and switching speed. This is achieved by precisely controlling CeO2… x The thickness and epitaxial relationship of the buffer layer in HfO2–ZrO2 / CeO x The interface introduces controllable insertional stacking faults and ferroelastic domain structures to release local strain, reduce interfacial strain energy, and stabilize the orthogonal ferroelectric phase with

[100] orientation. While ensuring high epitaxial quality and orientation control, leakage current and ferroelectric performance are also taken into account, realizing a ferroelectric capacitor or memory cell structure with practical application value, providing a material and structural solution with process feasibility for the next generation of low-power, high-speed, and highly integrated ferroelectric memory devices.

[0067] In HfO2–ZrO2 / CeOx The interface introduces controllable insertion-type stacking faults and ferroelastic domain structures, belonging to the category of localized lattice insertion-type stacking faults. This manifests as the insertion of lattice discontinuities of one or two atomic layers into a normal layered structure. At the stacking fault locations, the originally continuous HfO2–ZrO2 lattice exhibits a one-atom-layer dislocation or insertion, forming a localized lattice distortion to alleviate the stress caused by lattice mismatch at the interface. The stacking faults are distributed only in HfO2–ZrO2 / CeO2. x Interface, while in LSMO / CeO x No similar defects were observed on the interface. The distribution was concentrated in HfO2–ZrO2 / CeO x The interface exhibits a discontinuous and localized distribution. A key characteristic is that stacking faults do not cover the entire interface but rather exist as local strain relaxation centers. This is because stacking faults act as a strain compensation mechanism during the initial nucleation stage, helping to reduce system energy and promote the stability of the 001 orientation.

[0068] It should be noted that, regarding the orientation switching mechanism driven by the CeOx buffer layer, this invention introduces CeOx with a specific epitaxial relationship into the STO / LSMO system. x A buffer layer enables controllable switching of the HfO2–ZrO2 superlattice from group

[111] orientation to group

[100] orientation; CeO x The thickness is controlled within a specific range (e.g., 0.5~3nm, preferably 1nm) to balance epitaxial stress and leakage current, ensuring the stability of the

[100] orientation.

[0069] Regarding specific extensional matching relationships, CeO x CeO is satisfied with STO / LSMO. x

[110] / / STO / LSMO

[100] in-plane and out-of-plane epitaxial relationship; HfO2–ZrO2 orthorhombic superlattice and CeO x The out-of-plane orientation relationship between / LSMO / STO is HfO2–ZrO2(001) / / LSMO / STO(001); the above extensional relationship is confirmed by XRD φ scanning and reciprocal space mapping.

[0070] This invention utilizes the (002) orientation to make the ferroelectric polarization vector highly parallel to the applied electric field, thereby obtaining a higher remanent polarization than the (111) orientation; under the same electric field, the orientation-optimized HfO2–ZrO2 superlattice exhibits a faster polarization switching time (approximately 10). -7 s).

[0071] This invention uses STO as a (001) substrate, LSMO as the top and bottom electrodes, and CeO as the bottom electrode. xThe structure consists of a buffer layer and an HfO2–ZrO2 superlattice as the ferroelectric layer, forming a complete ferroelectric capacitor structure. This structure has both CMOS compatibility and good ferroelectric, dielectric, fatigue and switching performance, making it suitable for applications such as FERAM, ferroelectric logic, and ferroelectric neuromorphic devices.

[0072] It should be emphasized that this invention utilizes CeO x The buffer layer achieves the

[100] /

[001] preferred orientation of the HfO2–ZrO2 superlattice, making the polarization vector highly consistent with the applied electric field; under similar thickness and test conditions, the maximum polarization and residual polarization of the structure of this invention are significantly higher than those of the (111) orientation comparison sample, and maintain good stability in the range of 77~298K; higher P r It helps improve read window and noise immunity, making it ideal for high-reliability non-volatile storage applications.

[0073] Furthermore, this invention not only presents the concept of "introducing a buffer layer," but also specifies a particular material (CeO). x Systematic technical solutions such as epitaxial relationships, thickness windows, and interface defect types are provided; related structures and process parameters can be repeatedly implemented on mature thin film process platforms such as PLD, which is conducive to industrial scale-up and process standardization.

[0074] In summary, by introducing and precisely controlling the CeOx buffer layer, this invention establishes a systematic correlation between stress, defects, orientation, and ferroelectric properties, enabling controllable orientation switching of the HfO2–ZrO2 ferroelectric superlattice from the

[111] group to the

[100] group. It has significant advantages over the best existing technologies in terms of polarization performance and switching speed, and has important application prospects.

[0075] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A ferroelectric capacitor structure, characterized in that, Including the following settings in sequence: (001) Oriented oxide single crystal substrate, epitaxial conductive bottom electrode layer, CeO x Buffer layer, HfO2–ZrO2 ferroelectric superlattice layer, top electrode layer and Pt electrode layer; The (001) oriented oxide single crystal substrate includes SrTiO3; The epitaxial conductive bottom electrode layer includes La 0.67 Sr 0.33 MnO3.

2. The ferroelectric capacitor structure according to claim 1, characterized in that, CeO x The thickness of the buffer layer is 0.5~3nm.

3. The ferroelectric capacitor structure according to claim 1, characterized in that, The HfO2–ZrO2 ferroelectric superlattice layer is an orthorhombic ferroelectric superlattice formed by alternating stacking of HfO2 layers and ZrO2 layers.

4. The ferroelectric capacitor structure according to claim 1, characterized in that, The thickness of the HfO2–ZrO2 ferroelectric superlattice layer is 6~12nm.

5. A method for preparing a ferroelectric capacitor structure as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: An epitaxial conductive bottom electrode layer is deposited on the surface of the (001) oriented oxide single crystal substrate by pulsed laser; S2: CeO is deposited on the surface of the epitaxial conductive bottom electrode layer formed in step S1. x Buffer layer; S3: In the CeO x On the surface of the buffer layer, a HfO2–ZrO2 ferroelectric superlattice layer is deposited, and a top electrode layer is formed on the surface of the HfO2–ZrO2 ferroelectric superlattice layer by photolithography. S4: The Pt electrode layer is formed on the surface of the top electrode layer by measurement and control sputtering, thus obtaining the ferroelectric capacitor structure.

6. The method according to claim 5, characterized in that, In step S1, an epitaxial conductive bottom electrode layer is deposited by pulsed laser, using a KrF excimer laser with a wavelength of 248 nm as the light source.

7. The method according to claim 6, characterized in that, In step S1, an epitaxial conductive bottom electrode layer is deposited using pulsed laser with a laser energy density of 1.0 J / cm². 2 The repetition frequency is 3Hz.

8. The method according to claim 5, characterized in that, In step S2, CeO is deposited. x The temperature of the buffer layer is 650℃.

9. The method according to claim 5, characterized in that, In step S3, an HfO2–ZrO2 ferroelectric superlattice layer is deposited, and the sample from step S2 is heated to 750°C at a rate of 20°C / min.

10. The method according to claim 5, characterized in that, In step S3, an HfO2–ZrO2 ferroelectric superlattice layer is deposited using alternating or composite targets.

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