In-plane domain control method based on lithium niobate single crystal thin film

Abstract

The application discloses a lithium niobate single crystal thin film-based in-plane domain regulation method, which comprises the following steps: arranging a patterned upper electrode on the upper surface of the lithium niobate single crystal thin film, grounding the upper electrode, and using a piezoelectric force microscope to polarize and regulate the in-plane ferroelectric domain of the thin film. The application can effectively reduce the polarization voltage, reduce the lattice damage, inhibit the out-of-plane signal crosstalk, and obtain a high-quality and stable periodic ferroelectric domain structure, and is suitable for optical, electrical and acoustic device preparation.

Description

Technical Field

[0001] This invention relates to semiconductors, and more specifically to an in-plane domain manipulation method based on lithium niobate single-crystal thin films. Background Technology

[0002] Ferroelectric materials are materials that exhibit spontaneous polarization and whose polarization direction can be altered under the influence of an external field. In recent years, the continuous development of thin-film fabrication processes and ferroelectric domain modulation technologies has propelled the significant advancements of ferroelectric materials in acoustics, optics, and electrical fields. Lithium niobate (LiNbO3, LN) crystals belong to the trigonal crystal system, with a coercive field E... c With a Curie temperature of 1210 °C and a Curie resistance of 210 kV / cm, it is the highest known ferroelectric material in terms of Curie temperature. Ferroelectric domain flipping plays a crucial role in fields such as nonlinear optics and domain wall conductivity of lithium niobate. Therefore, how to prepare high-quality, highly stable periodic ferroelectric domains has become an urgent problem to be solved.

[0003] Currently, probe polarization based on piezoelectric force microscopy (PFM) is one of the main methods for ferroelectric domain manipulation. Due to its patterning capabilities and atomic-level operational precision, PFM probe polarization has gained widespread acceptance. However, existing ferroelectric domain engineering technologies face problems such as high energy consumption and severe crystal structure damage, which significantly limit the application prospects of domain engineering devices. Traditional in-plane domain polarization often involves applying silver paste to the sample edge to ground it and form a conductive loop. However, due to the high resistance of lithium niobate single crystal materials and the uneven electric field distribution during polarization, ferroelectric domain manipulation requires higher voltages and longer polarization times, which easily introduces lattice damage, leading to subsequent experimental failures. Therefore, developing low-energy-consumption, low-damage, and high-quality ferroelectric domain manipulation technologies has become a key objective for researchers. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide an in-plane domain control method based on lithium niobate single crystal thin films that can effectively reduce damage caused by PFM probe polarization, reduce out-of-plane signal crosstalk, and obtain high-quality, stable ferroelectric domains. This solves the problem of large out-of-plane signal crosstalk that is unavoidable when in-plane domain flipping occurs during traditional PFM probe polarization.

[0005] Technical solution: The in-plane domain control method based on lithium niobate single crystal thin film of the present invention includes the following steps: (1) A patterned upper electrode is disposed on the upper surface of the lithium niobate single crystal thin film; (2) Ground the upper electrode; (3) The polarization of the in-plane ferroelectric domains of the thin film was controlled using a piezoelectric microscope.

[0006] After polarization modulation is completed, it can be verified by scanning its in-plane and out-of-plane signals. Preferably, the VectorPFM mode is used to scan the in-plane and out-of-plane signals of the ferroelectric domain.

[0007] Preferably, step (1) includes patterning the upper surface of the lithium niobate single crystal film using photolithography, preparing the upper electrode using magnetron sputtering, and cleaning the photoresist on the surface of the lithium niobate single crystal film using a stripping process to realize the patterned electrode.

[0008] Preferably, the lithium niobate single crystal thin film in step (1) is an X-cut lithium niobate single crystal thin film.

[0009] Preferably, the lithium niobate single crystal thin film structure in step (1) consists of, from bottom to top: lithium niobate substrate, silicon dioxide, metal layer, and lithium niobate single crystal thin film.

[0010] Preferably, the substrate is a 500 μm / X-cut lithium niobate substrate, a 0.2 μm - 2 μm silicon dioxide, a 10 nm - 30 nm Cr / 50-200 nm Au / 10 nm - 30 nm Cr, and a 300~700 nm lithium niobate single crystal thin film.

[0011] Preferably, metal alignment marks are prepared on the surface of a lithium niobate single-crystal thin film. The film surface is patterned using photoresist, and the alignment marks are prepared using ultraviolet lithography exposure and development. Specifically, the photoresist spin-coating speed is 2500-3500 r / min, and the spin-coating time is 30-50 s. A developing solution is used, and the development time is 10-50 s. The magnetron sputtered metal is Cr, with a thickness of 50-500 nm. The photoresist is removed using acetone and alcohol. Photoresists are classified as positive or negative. AZnLOF 2020 is a negative photoresist (for exposure area retention), often used with a transparent feature mask to obtain a retained photoresist pattern corresponding to the transparent area. Alternatively, AZ6130 photoresist (for exposure area removal) is also commonly used in this experiment, often used with a light-shielding feature mask to obtain a retained photoresist pattern corresponding to the light-shielding area.

[0012] Preferably, step (2) includes fixing the prepared thin film sample to the metal connecting piece using conductive silver paste; then connecting the patterned upper electrode to the metal connecting piece using wire bonding technology, and connecting the metal connecting piece to the ground of the piezoelectric microscope equipment, thereby grounding the upper electrode. Preferably, the conductive silver paste connects the lithium niobate single crystal thin film to the small iron piece to fix the sample. Before performing probe polarization, the sample needs to be fixed first. Here, the role of the conductive silver paste is to adhere the sample and the small iron piece firmly (brush a thin layer of silver paste on the surface of the small iron piece, place the sample on the silver paste, and let it stand until it solidifies). Since the PFM equipment platform is grounded, the metal layer prepared on the upper surface of the thin film is connected to the small iron piece by wire bonding. As long as the small iron piece is placed on the PFM platform for the experiment, the upper electrode of the thin film is grounded, thereby ensuring the accuracy of the experiment.

[0013] Preferably, the material used for wire bonding is Au with a purity of 99.995% and a diameter of 0.025 mm.

[0014] Preferably, in step (3), the OBD Lateral PFM mode of the piezoelectric microscope is used to control ferroelectric domains.

[0015] Preferably, the Z-axis of the lithium niobate single-crystal thin film should be placed perpendicular to the probe cantilever of the PFM equipment. This design, where the probe cantilever is perpendicular to the crystal axis, is specifically designed for lithium niobate, a uniaxial ferroelectric material, to allow the electric field to better pass through the in-plane direction and achieve in-plane domain flipping.

[0016] Preferably, the PFM polarization uses a Pt / Ir or Au conductive coating on the probe tip; the grayscale image used for PFM polarization is a black and white striped grayscale image; the tip output negative voltage is -80 V to 0 V, and the positive voltage is 0 V to 120 V, where a positive voltage is applied to the white areas and a negative voltage is applied to the black areas in the grayscale image; the polarization flipped domain area is not greater than 30 μm × 30 μm and not less than 1 μm × 1 μm. The -32V voltage is the minimum in-plane domain flipping voltage within a 5 μm × 5 μm region.

[0017] The probes mentioned are commercially available probes, including Nanoworld's ARROW-EFM, Oxford Instruments' MULTI75GB-G probe, and Nanoworld's CDT-NCHR probe. The Nanoworld ARROW-EFM probe has a free resonant frequency of 65-80 kHz (the company-specified value is generally 75 kHz) and an elastic modulus of 2-3 N / m (the company-specified value is generally 2.8 N / m) (specific values ​​depend on experimental measurements). The Oxford Instruments MULTI75GB-G probe has a free resonant frequency of 65-80 kHz (the company-specified value is generally 75 kHz) and an elastic modulus of 2-4 N / m (the company-specified value is generally 3 N / m). Nanoworld's CDT-NCHR probe has a free resonant frequency of 350-450 kHz (the company's standard value is 400 kHz) and an elastic modulus of 75-85 N / m (the company's standard value is 80 N / m).

[0018] Invention Principle: As a uniaxial crystal, lithium niobate's ferroelectric domain flipping typically only occurs along the crystal axis. Conventional probe polarization techniques struggle to achieve effective domain flipping for samples where only in-plane flipping is possible. A relatively large voltage is usually applied to amplify the in-plane component of the overall input signal, thereby facilitating in-plane ferroelectric domain flipping in the X-cut lithium niobate single-crystal thin film. This invention aims to optimize the electric field distribution on the film surface by introducing an upper electrode, increasing the in-plane component of the input voltage and making in-plane ferroelectric domain flipping easier.

[0019] Probe-polarized ferroelectric domain reversal is divided into two types: out-of-plane ferroelectric domain reversal and in-plane ferroelectric domain reversal. Out-of-plane signals generally refer to signals perpendicular to the sample surface; in-plane signals generally refer to signals parallel to the sample surface. Typically, when probe-polarized in-plane domain reversal is performed, out-of-plane signal crosstalk is unavoidable because the probe is pressurized vertically, and the ferroelectric domain reversal is achieved through an in-plane component voltage. Since probe polarization is a sample surface characterization technique, without the induction of an upper electrode, the high bulk resistance (nearly insulating) of lithium niobate single-crystal thin films makes out-of-plane ferroelectric domain reversal extremely energy-intensive. Directly reversing in-plane ferroelectric domains of lithium niobate single-crystal thin films easily leads to high out-of-plane signal crosstalk, high energy consumption, and excessive input voltage damaging the sample surface morphology. Furthermore, without electrode induction during probe voltage application, the electric field direction cannot be controlled, further increasing the difficulty of in-plane ferroelectric domain reversal in X-cut lithium niobate single-crystal thin films.

[0020] The main innovation of this invention lies in the fact that by sputtering an upper electrode onto the surface of an X-cut lithium niobate single crystal thin film and cleverly connecting the upper electrode to the ground terminal of the PFM device through wire bonding and other methods, the electric field direction on the thin film surface can be controlled to increase the in-plane signal component, thereby reducing the voltage required for in-plane ferroelectric domain flipping. This achieves the goals of not damaging the sample surface, reducing crosstalk between out-of-plane signals and in-plane signals, and reducing energy consumption.

[0021] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: By sputtering a metal electrode onto the surface of an X-cut lithium niobate single-crystal thin film and grounding it with a lead wire, the present invention enables better in-plane domain signals during PFM probe polarization, effectively reducing out-of-plane crosstalk. Under the present invention, the in-plane domains of the lithium niobate single-crystal thin film can stably flip, the flipping voltage is reduced, and out-of-plane crosstalk is effectively reduced during flipping. The present invention is suitable for probe polarization in piezoelectric microscopy. The in-plane domains of lithium niobate prepared by the method proposed in this invention have good stability and remain stable for 480 hours. Attached Figure Description

[0022] Figure 1 This is a flowchart of the device fabrication process in Embodiment 1 of the present invention.

[0023] Figure 2 This is a schematic diagram of the fabrication of the upper electrode using photolithography, sputtering, and lift-off processes in Embodiment 1 of the present invention.

[0024] Figure 3 This is a schematic diagram of in-plane polarization domain flipping using a PFM device in Embodiment 1 of the present invention.

[0025] Figure 4 This is a schematic diagram of the lead bonding on the upper surface of the lithium niobate single crystal thin film in Embodiment 1 of the present invention.

[0026] Figure 5 This is a surface morphology diagram of the lithium niobate single crystal thin film in Embodiment 1 of the present invention.

[0027] Figure 6 This is a signal amplitude diagram within the ferroelectric domain inversion plane of the lithium niobate single-crystal thin film in Embodiment 1 of the present invention.

[0028] Figure 7 This is a phase diagram of the signal within the ferroelectric domain inversion plane of the lithium niobate single-crystal thin film in Embodiment 1 of the present invention.

[0029] Figure 8 This is the out-of-plane signal amplitude diagram of the lithium niobate single crystal thin film ferroelectric domain flipping in Embodiment 1 of the present invention.

[0030] Figure 9 This is the out-of-plane signal phase diagram of the ferroelectric domain flipping of the lithium niobate single crystal thin film in Embodiment 1 of the present invention.

[0031] Figure 10 This is the amplitude diagram of the in-plane domain flipping of the lithium niobate single crystal thin film after 0 hours in Embodiment 1 of the present invention.

[0032] Figure 11 This is a phase diagram of the lithium niobate single crystal thin film after 0 hours of in-plane domain flipping in Embodiment 1 of the present invention.

[0033] Figure 12 This is the amplitude diagram of the lithium niobate single crystal thin film after 480 hours of in-plane domain flipping in Embodiment 1 of the present invention.

[0034] Figure 13 This is a phase diagram of the lithium niobate single crystal thin film after 480 hours of in-plane domain flipping in Embodiment 1 of the present invention.

[0035] Figure 14 This is a surface morphology diagram of the lithium niobate single crystal thin film in Comparative Example 1 of the present invention.

[0036] Figure 15 This is a signal amplitude diagram within the ferroelectric domain inversion plane of the lithium niobate single-crystal thin film in Comparative Example 1 of the present invention.

[0037] Figure 16 This is a phase diagram of the signal within the ferroelectric domain inversion plane of the lithium niobate single-crystal thin film in Comparative Example 1 of the present invention.

[0038] Figure 17 This is the out-of-plane signal amplitude diagram of the lithium niobate single crystal thin film ferroelectric domain flipping in Comparative Example 1 of this invention.

[0039] Figure 18 This is the out-of-plane signal phase diagram of the lithium niobate single crystal thin film ferroelectric domain flipping in Comparative Example 1 of this invention. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0041] The in-plane domain control method based on lithium niobate single crystal thin film described in this invention effectively reduces the lattice damage and out-of-plane signal crosstalk caused by PFM probe polarization to the lithium niobate thin film surface by preparing an upper electrode on the surface of the X-cut lithium niobate single crystal thin film and grounding it through lead wire technology.

[0042] Example 1

[0043] like Figure 1 As shown, the method specifically includes: Step 1: Pattern the surface of the lithium niobate single crystal thin film using photolithography; Step 2: Fabricate the upper electrode using magnetron sputtering technology; Step 3: Clean the photoresist on the surface of the lithium niobate single crystal thin film using a stripping process to achieve patterned electrodes; Step 4: Fix the prepared X-cut lithium niobate single crystal thin film sample to the metal bonding sheet using conductive silver paste; Step 5: Connect the patterned upper electrode to the metal connector using wire bonding technology; Step 6: Select the OBD Lateral PFM mode of the piezoelectric microscope to perform ferroelectric domain modulation;

[0044] Step 7: After completing the above steps, select the Vector PFM mode of the piezoelectric microscope to simultaneously scan the in-plane and out-of-plane signals modulated by the ferroelectric domains.

[0045] This invention involves fabricating a patterned top electrode on the surface of a lithium niobate single-crystal thin film using photolithography, sputtering, and lift-off processes. The thin film sample is then fixed to a metal bonding sheet, and the top electrode is connected to the metal bonding sheet using wire bonding technology for connection to the ground terminal of a piezoelectric microscopy (PFM) device. Subsequently, the OBD Lateral PFM mode of the PFM is used for ferroelectric domain manipulation, achieving low crosstalk in-plane domain manipulation of the lithium niobate single-crystal thin film. Finally, the vector PFM mode is used to characterize the in-plane and out-of-plane signals of the fabricated ferroelectric domains. The selected lithium niobate single-crystal thin film is an X-cut lithium niobate single-crystal thin film. The structure of the selected lithium niobate single-crystal thin film, from bottom to top, is: 500 μm / X-cut lithium niobate substrate, 0.2 μm - 2 μm silicon dioxide, 10 nm - 30 nm Cr / 50-200 nm Au / 10 nm - 30 nm Cr, and 300~700 nm lithium niobate single-crystal thin film.

[0046] In step 1, metal alignment marks are prepared on the surface of a lithium niobate single crystal thin film. The thin film surface is positioned and patterned using AZnLOF 2020 photoresist, and the alignment marks are prepared by ultraviolet lithography exposure and development method. The photoresist spin coating speed is 3000 r / min, and the spin coating time is 40 s. ZX-238 developer is used, and the development time is 30 s.

[0047] In step 2, the magnetron sputtered metal is Cr, with a thickness of 100 nm.

[0048] In step 3, the stripping process uses acetone and alcohol to peel off the surface photoresist.

[0049] In step 4, the conductive silver paste is Leitsilber 200 conductive silver paste from TED PELLA, INC.

[0050] In step 5, the wire bonding material used is Au with a purity of 99.995% and a diameter of 0.025 mm. After the upper electrode and the metal connector are connected by wires, the metal connector can be connected to the PFM equipment ground, thereby grounding the upper electrode. In step 6, the Z-axis of the X-cut lithium niobate single crystal film should be placed perpendicular to the PFM equipment probe cantilever. The PFM polarization probe used is the Nanoworld ARROW-EFM probe, with a probe free resonant frequency of 75 kHz, an elastic modulus of 2.8 N / m, and a tip conductive coating of Pt / Ir. ​​The grayscale image used is a black and white striped grayscale image. The tip output voltage is -32 V / 40 V (where negative voltage polarization domain flips), where a positive voltage is applied to the white area and a negative voltage is applied to the black area in the grayscale image. The polarization flipped domain area is 5 μm × 5 μm.

[0051] In step 7, when measuring the in-plane and out-of-plane effects of the flipped domains, a region larger than the area of ​​the polarized ferroelectric domain flipped is generally selected. For example, if the polarized ferroelectric domain flips to 5 μm x 5 μm, then a region of 7 μm x 7 μm is generally selected when scanning its in-plane and out-of-plane signals in order to show the flipping effect of the entire region.

[0052] Example 2

[0053] like Figure 1 As shown, the method specifically includes: Step 1: Pattern the surface of the lithium niobate single crystal thin film using photolithography; Step 2: Fabricate the upper electrode using magnetron sputtering technology; Step 3: Clean the photoresist on the surface of the lithium niobate single crystal thin film using a stripping process to achieve patterned electrodes; Step 4: Fix the prepared X-cut lithium niobate single crystal thin film sample to the metal bonding sheet using conductive silver paste; Step 5: Connect the patterned upper electrode to the metal connector using wire bonding technology; Step 6: Select the OBD Lateral PFM mode of the piezoelectric microscope to perform ferroelectric domain modulation;

[0054] Step 7: After completing the above steps, select the Vector PFM mode of the piezoelectric microscope to simultaneously scan the in-plane and out-of-plane signals modulated by the ferroelectric domains.

[0055] This invention involves fabricating a patterned top electrode on the surface of a lithium niobate single-crystal thin film using photolithography, sputtering, and lift-off processes. The thin film sample is then fixed to a metal bonding sheet, and the top electrode is connected to the metal bonding sheet using wire bonding technology for connection to the ground terminal of a piezoelectric microscopy (PFM) device. Subsequently, the OBD Lateral PFM mode of the PFM is used for ferroelectric domain manipulation, achieving low crosstalk in-plane domain manipulation of the lithium niobate single-crystal thin film. Finally, the vector PFM mode is used to characterize the in-plane and out-of-plane signals of the fabricated ferroelectric domains. The selected lithium niobate single-crystal thin film is an X-cut lithium niobate single-crystal thin film. The structure of the selected lithium niobate single-crystal thin film, from bottom to top, is: 500 μm / X-cut lithium niobate substrate, 0.2 μm - 2 μm silicon dioxide, 10 nm - 30 nm Cr / 50-200 nm Au / 10 nm - 30 nm Cr, and 300~700 nm lithium niobate single-crystal thin film.

[0056] In step 1, metal alignment marks are prepared on the surface of a lithium niobate single crystal thin film. The thin film surface is positioned and patterned using photoresist AZ6130, and the alignment marks are prepared by ultraviolet lithography exposure and development method. The photoresist spin coating speed is 3000 r / min, and the spin coating time is 40 s. AZ400K developer is used, and the development time is 10 s - 50 s.

[0057] In step 2, the magnetron sputtered metal is Cr, with a thickness of 50-500 nm.

[0058] In step 3, the stripping process uses acetone and alcohol to peel off the surface photoresist.

[0059] In step 4, the conductive silver paste is Chemtronics' CW2400 conductive silver paste.

[0060] In step 5, the material used for wire bonding is Au, with a purity of 99.995% and a diameter of 0.025 mm. After the upper electrode and the metal connector are connected by wires, the metal connector can be connected to the ground of the PFM device, thereby grounding the upper electrode.

[0061] In step 6, the Z-axis of the X-cut lithium niobate single crystal thin film should be placed perpendicular to the probe cantilever of the PFM equipment; the PFM polarization probe is the Budget Sensors Multi75GB-G probe, with a probe free resonant frequency of 75 kHz, an elastic modulus of 3 N / m, and a conductive coating of Au at the tip; the grayscale image used is a black and white striped grayscale image; the tip output voltage is -50V / 70V (where negative voltage polarization domain flips), where a positive voltage is applied to the white area and a negative voltage is applied to the black area in the grayscale image; the polarization flipped domain area is 20 μm × 20 μm.

[0062] In step 7, when measuring the in-plane and out-of-plane effects of the flipped domains, a region larger than the area of ​​the polarized ferroelectric domain flipped is generally selected. For example, if the polarized ferroelectric domain flips to 20 μm x 20 μm, then a region of 25 μm x 25 μm is generally selected when scanning its in-plane and out-of-plane signals, so as to show the flipping effect of the entire region.

[0063] According to the appendix Figure 1 The steps shown enable the low-voltage, low-out-of-plane crosstalk in-plane ferroelectric domain modulation described in this invention. (Appendix) Figure 2 This diagram illustrates the photolithography, sputtering, and stripping processes. Electrodes are patterned on the surface of an X-cut lithium niobate single-crystal thin film using photolithography, followed by magnetron sputtering of a metal layer. Finally, excess metal is stripped away using acetone and alcohol, thus fabricating the upper electrode. (See attached diagram.) Figure 3 This is a schematic diagram of probe polarization near the upper electrode using a piezoelectric microscope. (Attached) Figure 4 This diagram illustrates the wire bonding connection between the thin film sample and the ground terminal. The upper electrode guides the voltage signal applied by the probe tip to act more in-plane, thereby reducing the voltage required for polarization and reducing out-of-plane signal crosstalk. After applying -32V / 40V in OBD Lateral PFM mode using a piezoelectric microscope, the process is switched to Vector PFM mode to simultaneously measure both in-plane and out-of-plane signals. (Attached...) Figure 5 The sample surface morphology, based on experimental data, shows a root mean square roughness (RMS) of 186.096 pm. (See attached image.) Figure 6 , 7 The amplitude and phase diagrams of the in-plane signal, measured using Vector PFM mode, are shown below, after applying a tip voltage of -40 V / 20 V (where negative voltage polarization domains flip) and in-plane domain flipping. (See attached diagram.) Figure 8 , 9 The amplitude and phase diagrams of the out-of-plane signal measured in Vector PFM mode after applying tip voltages of -40 V and 20 V (with negative voltage polarization domain flipping) for in-plane domain flipping are shown respectively. Figure 10 , 11The images show the amplitude and phase diagrams within 0 hours after the ferroelectric domains in the probe polarization plane flip. (Attached) Figure 12 , 13 The images show the amplitude and phase diagrams 480 hours after the ferroelectric domains in the probe polarization plane flip.

[0064] Comparative Example 1 Step 1: Fix the prepared X-cut lithium niobate single crystal thin film sample to the metal connecting sheet using conductive silver paste; Step 2: Select the OBD Lateral PFM mode of the piezoelectric microscope to perform ferroelectric domain modulation;

[0065] Step 3: After completing the above steps, select the Vector PFM mode of the piezoelectric microscope to simultaneously scan the in-plane and out-of-plane signals modulated by the ferroelectric domains.

[0066] This comparative example demonstrates in-plane ferroelectric domain modulation on the surface of an X-cut lithium niobate single-crystal thin film without an upper electrode, and scans its in-plane and out-of-plane signals. The selected lithium niobate single-crystal thin film is an X-cut lithium niobate single-crystal thin film. The structure of the selected lithium niobate single-crystal thin film, from bottom to top, is as follows: 500 μm / X-cut lithium niobate substrate, 0.2 μm - 2 μm silicon dioxide, 10 nm - 30 nm Cr / 50-200 nm Au / 10 nm - 30 nm Cr, and 300~700 nm lithium niobate single-crystal thin film.

[0067] In step 1, the conductive silver paste is Leitsilber 200 conductive silver paste from TED PELLA, INC.

[0068] In step 1, after the conductive silver paste connects the lithium niobate film to the metal connector, the metal connector can be connected to the ground of the PFM device to achieve the purpose of probe pressure polarization ferroelectric domain reversal.

[0069] In step 2, the Z-axis of the X-cut lithium niobate single crystal thin film should be placed perpendicular to the probe cantilever of the PFM equipment; the PFM polarization probe is the Nanoworld ARROW-EFM probe, with a probe free resonant frequency of 75 kHz, an elastic modulus of 2.8 N / m, and a tip conductive coating of Pt / Ir; the grayscale image used is a black and white striped grayscale image; the tip output voltage is -32 V / 40 V (where negative voltage polarization domain flips), where a positive voltage is applied to the white area and a negative voltage is applied to the black area in the grayscale image; the polarization flipped domain area is 5 μm × 5 μm.

[0070] In step 3, when measuring the in-plane and out-of-plane effects of the flipped domains, a region larger than the area of ​​the polarized ferroelectric domain flipped is generally selected. For example, if the polarized ferroelectric domain flips to 5 μm x 5 μm, then a region of 7 μm x 7 μm is generally selected when scanning its in-plane and out-of-plane signals, so as to show the flipping effect of the entire region.

[0071] Figure 14 This is a surface morphology diagram of the lithium niobate single crystal thin film in Comparative Example 1. Figure 15 It is the signal amplitude diagram within the ferroelectric domain inversion plane. Figure 16 It is the phase diagram of the signal within the ferroelectric domain inversion plane. Figure 17 It is the out-of-plane signal amplitude diagram of its ferroelectric domain flipping. Figure 18 It is the phase diagram of the out-of-plane signal of its ferroelectric domain flipping.

Claims

1. A method for in-plane domain manipulation based on lithium niobate single-crystal thin films, characterized in that, Includes the following steps: (1) A patterned upper electrode is disposed on the upper surface of the lithium niobate single crystal thin film; (2) Ground the upper electrode; (3) The polarization of the in-plane ferroelectric domains of the thin film was controlled using a piezoelectric microscope.

2. The method according to claim 1, characterized in that, Step (1) includes patterning the upper surface of the lithium niobate single crystal film using photolithography, preparing the upper electrode using magnetron sputtering, and cleaning the photoresist on the surface of the lithium niobate single crystal film using a stripping process to realize the patterned electrode.

3. The method according to claim 1, characterized in that, Step (2) includes fixing the prepared thin film sample to the metal connecting piece using conductive silver paste; then connecting the patterned upper electrode to the metal connecting piece using wire bonding technology, connecting the metal connecting piece to the piezoelectric microscope equipment ground, and then grounding the upper electrode.

4. The method according to claim 1, characterized in that, Step (3) Select the OBD LateralPFM mode of the piezoelectric microscope to perform ferroelectric domain modulation.

5. The method according to claim 1, characterized in that, The lithium niobate single crystal thin film in step (1) is an X-cut lithium niobate single crystal thin film.

6. The method according to claim 1, characterized in that, The lithium niobate single crystal thin film structure in step (1) consists of, from bottom to top: lithium niobate substrate, silicon dioxide, metal layer, and lithium niobate single crystal thin film.

7. The method according to claim 2, characterized in that, Metal alignment marks were fabricated on the surface of a lithium niobate single-crystal thin film. The film surface was patterned using photoresist, and the alignment marks were fabricated using ultraviolet lithography exposure and development. The photoresist spin coating speed was 2500-3500 r / min, and the spin coating time was 30-50 s. The developing solution was used, and the developing time was 10 s-50 s. The magnetron sputtered metal was Cr, with a thickness of 50-500 nm. The photoresist was removed from the surface using acetone and alcohol.

8. The method according to claim 3, characterized in that, The material used for wire bonding is Au.

9. The method according to claim 4, characterized in that, The Z-axis of the lithium niobate single crystal thin film should be placed perpendicular to the probe cantilever of the PFM equipment.

10. The method according to claim 4, characterized in that, The grayscale image used in PFM mode is a striped grayscale image with alternating black and white lines; the negative voltage of the tip output is -80 V ~ 0 V, and the positive voltage is 0 V ~ 120 V, where a positive voltage is applied to the white areas and a negative voltage is applied to the black areas in the grayscale image; the polarization flip domain area is not greater than 30 μm × 30 μm and not less than 1 μm × 1 μm.

Images