A domain wall element based on lithium niobate single crystal thin film and a preparation method thereof
By fabricating domain wall elements based on lithium niobate single-crystal thin films and combining micro-nano fabrication technology with external field control, the problem of weak domain wall current signals in traditional low-temperature measurement technology was solved, achieving high-precision and stable low-temperature sensing effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHONGBEI UNIV
- Filing Date
- 2023-03-07
- Publication Date
- 2026-07-21
AI Technical Summary
Traditional cryogenic measurement techniques are insufficient to meet the high-sensitivity and high-precision temperature measurement requirements of high-tech fields, especially in deep space and aerospace. Furthermore, the domain wall current signal is weak, making it difficult to achieve precise control of the distribution of charge bound to the conductive domain walls.
A domain wall device based on lithium niobate single crystal thin film was fabricated by combining micro-nano fabrication technology with external field control. By ion implantation of a damaged layer on the surface of the lithium niobate single crystal and bonding it with the substrate, conductive domain walls were formed by photolithography and dry etching, thereby achieving precise control of the domain wall current.
It achieves high-precision and stable low-temperature sensing, and the domain wall current measurement is not affected by harsh environments. It has a long life and high reliability and is suitable for high-precision temperature measurement.
Smart Images
Figure CN116281838B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of MEMS device structure fabrication technology, and particularly relates to a domain wall element based on lithium niobate single crystal thin film and its fabrication method. Background Technology
[0002] With the rapid development of space science and low-temperature superconducting technology, traditional low-temperature (1K-300K) measurement techniques are insufficient to meet the current demand for precise temperature measurement, especially in high-tech fields such as deep space, aerospace, and national defense, where even more accurate temperature measurements are required. Therefore, there is an urgent need to develop new, highly sensitive, and stable low-temperature sensing technologies. Researching new physical effects of materials and exploring new low-temperature measurement principles have become the main approaches for researchers to develop novel low-temperature sensors, expand test temperature ranges, and improve test accuracy and stability.
[0003] Ferroelectric materials are a class of materials that exhibit spontaneous polarization within a certain temperature range, and the direction of this spontaneous polarization can be controlled by an applied electric field. When the temperature exceeds the Curie temperature of the ferroelectric material, the material transitions from a ferroelectric phase to a paraelectric phase, losing its ferroelectric properties. A domain refers to a region in a ferroelectric material that has the same spontaneous polarization direction. Domain walls are formed by the reversal of domain polarization under the influence of an external field, and are usually defined as the interface between two domains with different spontaneous polarization directions. Normally, domain walls are non-conductive when α = 0°; when α ≠ 0°, due to the formation of bound charges, the charged domain walls cause a redistribution of free charges, thus exhibiting conductivity, and are also called conductive domain walls; when α = 90°, the conductivity of the charged domain walls is strongest. Experimentally, research on the domain wall conductivity mechanism mainly relies on the variation of domain wall current under a temperature field. Theoretically, phase field simulations are used to calculate the relationship between carrier concentration and mobility near the domain wall and temperature, or first-principles calculations are used to calculate the band structure changes of the domain wall and the surrounding material.
[0004] The biggest drawback of using conductive domain walls in cryogenic sensing lies in the relatively weak domain wall current signal. Currently, this problem is mainly addressed through memory and logic circuits established using domain wall current, but it is difficult to achieve precise control of the charge distribution bound by the conductive domain walls, and the challenge of high-precision measurement of domain wall current remains. Therefore, how to significantly increase the domain wall current in cryogenic environments has become the most pressing key issue to be solved in high-precision temperature measurement at low temperatures. Summary of the Invention
[0005] In view of this, this application provides a domain wall element based on lithium niobate single crystal thin film and its preparation method, which can overcome the problems of traditional thermistors being difficult to measure at ultra-low temperatures in various harsh environments, having low measurement accuracy, and being unable to guarantee service life.
[0006] The specific technical solution of this application is as follows:
[0007] The first aspect of this application provides a method for fabricating domain wall devices based on lithium niobate single-crystal thin films, comprising the following steps:
[0008] Step 1: Ion implant a damaged layer on the surface of a lithium niobate single crystal and bond it directly to the substrate. Then, thin and polish the surface of the lithium niobate single crystal to obtain a lithium niobate single crystal film.
[0009] Step 2: Clean the surface of the lithium niobate single crystal thin film, spin-coated mask layer, etch the pattern by electron beam lithography, and then grow the first hard mask and the second hard mask in sequence.
[0010] Step 3: After etching the pattern using ultraviolet lithography, the first hard mask is regrown;
[0011] Step 4: Use ion etching to remove excess mask layers to obtain domain wall devices based on lithium niobate single crystal thin films.
[0012] Preferably, the ion implantation of the damage layer on the surface of the lithium niobate single crystal and its direct bonding with the substrate specifically involves: the ions being helium ions and the substrate being a silicon substrate.
[0013] Preferably, the substrate is prepared by:
[0014] A silicon dioxide thin film with a thickness of 300-500 nm is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition.
[0015] Preferably, the first hard mask is made of Cr metal, and the second hard mask is made of Pt metal. Preferably, the pattern width of the first hard mask and the second hard mask is 50–250 nm. Preferably, the mask layer used for etching is photoresist, and the thickness of the photoresist is 2–4 μm.
[0016] Preferably, the growth of the second hard mask specifically involves growing a metal layer using magnetron sputtering. Preferably, after growing the first hard mask and before growing the second hard mask, the following process is performed: immersing the lithium niobate single-crystal thin film in acetone.
[0017] A second aspect of this application provides a domain wall element based on a lithium niobate single-crystal thin film, which is prepared by the aforementioned preparation method.
[0018] A third aspect of this application provides a low-temperature sensor, including a domain wall element based on a lithium niobate single-crystal thin film, wherein the domain wall element is prepared by the aforementioned preparation method.
[0019] In summary, this application provides a domain wall element based on a lithium niobate single-crystal thin film and its fabrication method. The method involves ion implantation on the surface of a lithium niobate single crystal, stripping of the damaged layer, and direct bonding with a substrate to obtain a lithium niobate single-crystal thin film. A hard mask is then grown after patterning using photolithography and dry etching with a spin-coated mask layer, ultimately yielding a domain wall element based on the lithium niobate single-crystal thin film. This application employs a combination of micro / nano fabrication technology and external field manipulation to induce domain inversion in the sensitive units of the ferroelectric single-crystal thin film's protruding structure, achieving precise control of the distribution of bound charges on the conductive domain walls. This results in tail-to-tail and head-to-head domain wall currents, effectively solving problems such as excessively large coercive field, small current, and poor electrical contact during lithium niobate single-crystal domain wall current measurement. The resulting product is resistant to various harsh environments, exhibits high measurement accuracy, long service life, and can be repeatedly measured, possessing advantages such as large range, high precision, high stability, and high reliability. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a flowchart illustrating the method for fabricating domain wall elements based on lithium niobate single-crystal thin films in this application embodiment;
[0022] Figure 2 This is a schematic diagram of the fabrication process of lithium niobate single crystal thin film in the embodiments of this application, (a) ion implantation; (b) low-temperature bonding; (c) peeling annealing;
[0023] Figure 3 This is a schematic diagram of the fabrication process of the domain wall device based on a single crystal lithium niobate thin film in the embodiments of this application. (a) Spin coating of photoresist; (b) Electron beam lithography; (c) Evaporation growth of the first hard film layer; (d) Dry etching of single crystal lithium niobate; (e) Magnetron sputtering growth of the first hard film layer; (f) Spin coating of photoresist again; (g) Ultraviolet lithography; (h) Evaporation growth of the first hard film layer; (i) Ion etching of the electrode;
[0024] Figure 4 This is a schematic diagram of the domain wall element based on a lithium niobate single crystal thin film in an embodiment of this application;
[0025] Figure 5 This is a schematic diagram illustrating the domain wall formation principle of the domain wall element based on lithium niobate single crystal thin film in the embodiments of this application;
[0026] Figure 6 This is a simulation diagram of the electric field distribution of the product of Embodiment 1 of this application under different applied voltages;
[0027] Figure 7 This is a linear fitting graph of the domain wall current density measurement of the product of Example 1 of this application at low temperature.
[0028] Figure 8 The domain wall current test IV curve of the product of Example 1 of this application;
[0029] Illustration: 1. Silicon substrate; 2. Silicon dioxide thin film; 3. Lithium niobate single crystal thin film; 4. Mask layer; 5. First hard mask; 6. Second hard mask. Detailed Implementation
[0030] Reference Figure 1 , Figure 1 This is a flowchart illustrating the preparation method of domain wall elements based on lithium niobate single crystal thin films in this application.
[0031] The first aspect of this application provides a method for fabricating domain wall devices based on lithium niobate single crystal thin films, comprising the following steps:
[0032] S1: An ion-implanted damage layer is formed on the surface of a lithium niobate single crystal and directly bonded to the substrate. The surface of the lithium niobate single crystal is then thinned and polished to obtain a lithium niobate single crystal thin film.
[0033] S2: Clean the surface of the lithium niobate single crystal thin film, spin-coated mask layer, etch the pattern by electron beam lithography, and then grow the first hard mask and the second hard mask in sequence.
[0034] S3: The first hard mask is regrown after the pattern is etched by ultraviolet lithography;
[0035] S4: Use ion etching to remove excess mask layers to obtain domain wall devices based on lithium niobate single crystal thin films.
[0036] It should be noted that among known ferroelectric materials, lithium niobate has the highest Curie temperature (1210℃) and the largest spontaneous polarization (0.70℃ / m at room temperature). 2 In lithium niobate single crystals, only 180° domain walls exist, and parallel domain walls and tail-to-tail domain walls are non-conductive, while only head-to-head domain walls are conductive. Based on the principle that the larger the domain wall tilt angle α, the better the domain wall conductivity, the semiconductor thermally excited conductive domain walls formed by ferroelectric domain inversion based on lithium niobate single crystal thin films have their own characteristics. These characteristics include an increase in domain wall resistance as the temperature decreases, and the current change can be used to monitor the temperature, which has broad application prospects, especially in low-temperature sensing technology.
[0037] This application addresses the application requirements of high-precision, high-stability, and high-resistance cryogenic sensing technologies in space science and cryogenic superconducting technology. It explores a nanofabrication process compatible with the ferroelectric domain stability of lithium niobate and MEMS technology. Specifically, it employs a combination of micro / nanofabrication techniques and external field manipulation to induce domain reversal in the sensitive units of the convex structure of the ferroelectric single-crystal thin film, thereby achieving precise control of the distribution of bound charge on the conductive domain walls. The domain wall element based on the lithium niobate single-crystal thin film fabricated in this application utilizes a novel ferroelectric domain wall measurement method. This method systematically analyzes the discontinuous distribution of electron and hole concentrations within the material caused by the bound charge centers on the domain walls, reveals the free charge distribution near the conductive domain walls formed by ferroelectric domain reversal, investigates the changes in carrier concentration and mobility near the domain walls under cryogenic conditions, establishes a thermodynamic model of the domain wall current versus temperature, and reveals the domain wall conductivity type. This method overcomes the technical bottlenecks of conventional c-AFM technology, which suffers from lack of relaxation time and poor electrical contact in measuring domain wall current, fundamentally solving the problem of high-precision measurement of domain wall current. The development of a novel low-temperature sensing thermistor unit based on the domain wall element of lithium niobate single crystal thin film according to the embodiments of this application has important scientific significance and application value for the development of high-precision NTC thermistor low-temperature sensors and their functional upgrade and application promotion in the fields of space science and low-temperature superconductivity.
[0038] It should be noted that in S1, the heterogeneous integration of lithium niobate and the substrate is achieved by ion implantation of lithium niobate, and the single crystal material is thinned by ion thinning and chemical mechanical polishing to achieve the required thickness of the single crystal film, and the surface roughness of the film reaches the atomic level.
[0039] In steps S2 and S3, the lithium niobate film is first cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. Then, a nanoscale protrusion structure is grown on the surface of the lithium niobate single-crystal film using electron beam lithography and ultraviolet lithography, effectively solving problems such as excessive coercivity, low current, and poor electrical contact during domain wall current measurement of lithium niobate single crystals. Subsequently, a metal layer is grown using a hard mask, allowing the electrode pattern to be transferred to the sample surface.
[0040] After removing excess metal in S4, a complete protruding structural unit with electrodes can be obtained, which facilitates subsequent measurement work.
[0041] Reference Figures 2-3 , Figure 2 This is a schematic diagram of the fabrication process of lithium niobate single crystal thin film in the embodiments of this application. Figure 3 This is a schematic diagram of the fabrication process of the domain wall element based on lithium niobate single crystal thin film in the embodiments of this application.
[0042] In this embodiment, a lithium niobate single-crystal thin film 3 is first prepared by sequentially implanting a damaged layer into a lithium niobate single crystal, bonding it to a silicon substrate 1 and a silicon dioxide thin film 2 at low temperature, and then thinning the damaged layer by peeling off, polishing, and annealing. Next, a photoresist mask layer 4 is spin-coated onto the surface of the lithium niobate single-crystal thin film 3, and the pattern is etched using electron beam lithography to grow a first hard film layer 5 by evaporation. After dry etching, a second hard film layer 6 is grown by magnetron sputtering. Then, the photoresist mask layer 4 is spin-coated again, and the first hard film layer 5 is grown again by ultraviolet lithography. Finally, excess metal electrodes are etched using ion etching to obtain a complete domain wall device based on the lithium niobate single-crystal thin film.
[0043] According to an embodiment of this application, the ion implantation of a damaged layer onto the surface of a lithium niobate single crystal and its direct bonding to the substrate specifically involves:
[0044] The ion is a helium ion, and the substrate is a silicon substrate.
[0045] It should be noted that the depth of ion implantation on the surface of lithium niobate single crystals is controlled by the energy of helium ions.
[0046] According to an embodiment of this application, the substrate is prepared by:
[0047] A silicon dioxide thin film with a thickness of 300-500 nm is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition.
[0048] It should be noted that if a bottom electrode is required, metal can be grown on a silicon dioxide thin film.
[0049] According to an embodiment of this application, the first hard mask is metal Cr, and the second hard mask is metal Pt.
[0050] According to an embodiment of this application, the pattern width of the first hard mask and the second hard mask is 50 to 250 nm.
[0051] According to an embodiment of this application, the mask layer used for etching is photoresist, and the thickness of the photoresist is 2 to 4 μm.
[0052] According to an embodiment of this application, the growth of the second hard mask specifically involves growing a metal layer using magnetron sputtering.
[0053] It should be noted that a metal layer is magnetron sputtered to grow in the etched lithium niobate single crystal region to ensure good electrical contact between the metal and the lithium niobate protrusion structural unit.
[0054] According to an embodiment of this application, after growing the first hard mask and before growing the second hard mask, the following process is performed: immersing the lithium niobate single crystal thin film in acetone.
[0055] It should be noted that soaking in acetone helps to remove the photoresist, facilitating subsequent dry etching processes.
[0056] Reference Figures 4-5 , Figure 4 This is a schematic diagram of the domain wall element based on a lithium niobate single crystal thin film in an embodiment of this application. Figure 5 This is a schematic diagram illustrating the domain wall formation principle of the domain wall element based on lithium niobate single crystal thin film in the embodiments of this application.
[0057] The second aspect of this application provides a domain wall element based on a lithium niobate single crystal thin film, which is prepared by the method for preparing the domain wall element based on the lithium niobate single crystal thin film.
[0058] It should be noted that the domain wall element based on lithium niobate single crystal thin film prepared in the embodiments of this application forms tail-to-tail and head-to-head domain wall currents, effectively solving the problems of excessive coercive field, small current and poor electrical contact when measuring the domain wall current of lithium niobate single crystal.
[0059] A third aspect of this application provides a low-temperature sensor, including a domain wall element based on a lithium niobate single crystal thin film, wherein the domain wall element based on the lithium niobate single crystal thin film is prepared by the same method as the domain wall element based on the lithium niobate single crystal thin film.
[0060] It should be noted that when the domain wall element based on lithium niobate single crystal thin film obtained in the embodiments of this application is applied to the preparation of a low-temperature sensor, the resulting low-temperature sensor is a negative temperature coefficient (NTC) thermistor low-temperature sensor. It is not afraid of various harsh environments, has high measurement accuracy, long service life, can be repeatedly measured, and has the advantages of large range, high precision, high stability, and high reliability.
[0061] To make the objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0062] The reagents and raw materials used in the embodiments of this application are all commercially available or self-made.
[0063] Example 1
[0064] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 400 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0065] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 3μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 100nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 100nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the metallic Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. Using a hard mask, metallic Cr (100nm) was further grown to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0066] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0067] The simulation diagram of the electric field distribution of the domain wall device based on lithium niobate single crystal thin film obtained in the embodiments of this application under different applied voltages is shown below. Figure 6 As shown, the linear fitting graph of domain wall current density measurement at low temperature is as follows. Figure 7 As shown, the IV curve of the product domain wall current test is as follows. Figure 8 As shown in the figure, the current value of the product obtained in the embodiments of this application is 1-2.5 μA (structural unit size 50-250 nm), and the current density is 10. 2 -10 4 A / cm 2 This indicates that the domain wall current based on lithium niobate single crystal thin film is linearly related to changes in electric field, temperature, and structural unit size, enabling low-temperature, large-range, and repeatable testing of domain wall current.
[0068] Example 2
[0069] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 500 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0070] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 4μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 200nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 50nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. Using a hard mask, metallic Cr (250nm) was further grown to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0071] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0072] The product obtained in this embodiment was tested and found to have similar performance to the product obtained in Example 1, with no significant difference.
[0073] Example 3
[0074] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 400 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0075] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 3μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 250nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 50nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. A 150nm layer of metallic Cr was then grown using a hard mask to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0076] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0077] The product obtained in this embodiment was tested and found to have similar performance to the product obtained in Example 1, with no significant difference.
[0078] Example 4
[0079] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 400 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0080] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 3μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 150nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 250nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the metallic Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. A 50nm layer of metallic Cr was then grown using a hard mask to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0081] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0082] The product obtained in this embodiment was tested and found to have similar performance to the product obtained in Example 1, with no significant difference.
[0083] Example 5
[0084] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 400 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0085] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 3μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 50nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 150nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the metallic Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. A 200nm layer of metallic Cr was then grown using a hard mask to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0086] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0087] The product obtained in this embodiment was tested and found to have similar performance to the product obtained in Example 1, with no significant difference.
[0088] Example 6
[0089] 1. A damage layer is formed by implanting helium ions to a certain depth on the surface of a lithium niobate single crystal using an ion implantation method. The implantation depth is controlled by the helium ion energy. A 500 nm thick silicon dioxide film is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon substrate and the bulk single crystal are bonded together, and the single crystal material is thinned using chemical mechanical polishing and ion thinning methods to achieve the required thickness of the single crystal film. The surface roughness of the film reaches the atomic scale.
[0090] 2. The lithium niobate thin film was cleaned using a semiconductor RCA cleaning process to ensure a smooth and contamination-free surface. A 2μm thick AZ4620 photoresist was spin-coated onto the single-crystal thin film. Electron beam lithography was then used to obtain the pattern to be etched onto the lithium niobate, followed by development. A 200nm layer of metallic Cr was then grown on the sample as a hard mask. After acetone stripping of the photoresist, dry etching was performed. A 100nm layer of metallic Pt was then magnetron sputtered onto the etched lithium niobate single-crystal region to ensure good electrical contact between the metallic Pt and the lithium niobate bump structure units. Spin-coating of photoresist was then continued for lithography and development. Using a hard mask, metallic Cr (100nm) was further grown to transfer the electrode pattern to the sample surface. Excess metal was removed using dry etching to obtain a complete bump structure unit with electrodes.
[0091] 3. The domain wall current of lithium niobate was scanned and measured using a semiconductor characteristic analyzer and a high-low temperature probe station. The voltage was set to a step-by-step scanning mode, and the start voltage, end voltage, step voltage, and step time were set before the scan was performed. After changing the temperature, the relationship between current and temperature was obtained.
[0092] The product obtained in this embodiment was tested and found to have similar performance to the product obtained in Example 1, with no significant difference.
[0093] In summary, the fabrication method of this application combines micro-nano fabrication technology with external field control to induce domain inversion in the sensitive units of the convex structure of ferroelectric single crystal thin films. This achieves precise control over the distribution of bound charges on the conductive domain walls, forming tail-to-tail and head-to-head domain wall currents. This effectively solves the problems of excessively large coercive field, small current, and poor electrical contact in the measurement of domain wall currents in lithium niobate single crystals. The domain wall elements fabricated in this application are resistant to various harsh environments, have high measurement accuracy, long service life, and can be repeatedly measured. They possess advantages such as large range, high precision, high stability, and high reliability.
[0094] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A method for fabricating domain wall devices based on lithium niobate single-crystal thin films, characterized in that, Includes the following steps: Step 1: Ion implant a damaged layer on the surface of a lithium niobate single crystal and bond it directly to the substrate. Then, thin and polish the surface of the lithium niobate single crystal to obtain a lithium niobate single crystal film. Step 2: Clean the surface of the lithium niobate single crystal film, spin-coated mask layer, etch pattern by electron beam lithography, and then evaporate to grow the first hard mask metal Cr. Immerse the lithium niobate single crystal film in acetone and then dry etch the lithium niobate single crystal film. Use magnetron sputtering to grow the second hard mask metal Pt in the etched lithium niobate single crystal area. Step 3: After etching the pattern using ultraviolet lithography, the first hard mask metal Cr is grown again by evaporation. Step 4: Use ion etching to remove excess mask layers to obtain domain wall devices based on lithium niobate single crystal thin films.
2. The method for preparing domain wall devices based on lithium niobate single-crystal thin films according to claim 1, characterized in that, Specifically, the process of ion implanting a damaged layer onto the surface of a lithium niobate single crystal and directly bonding it to the substrate involves: The ion is a helium ion, and the substrate is a silicon substrate.
3. The method for preparing domain wall elements based on lithium niobate single-crystal thin films according to claim 1, characterized in that, The substrate is prepared by the following method: A silicon dioxide thin film with a thickness of 300-500 nm is grown on a silicon substrate using thermal oxidation or plasma-enhanced chemical vapor deposition.
4. The method for preparing domain wall elements based on lithium niobate single crystal thin films according to claim 1, characterized in that, The pattern widths of the first hard mask and the second hard mask are 50–250 nm.
5. The method for preparing domain wall elements based on lithium niobate single-crystal thin films according to claim 1, characterized in that, The mask layer used for etching is photoresist, and the thickness of the photoresist is 2 to 4 μm.
6. A domain wall element based on a lithium niobate single-crystal thin film, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.
7. A low-temperature sensor, characterized in that, This includes domain wall elements based on lithium niobate single crystal thin films, wherein the domain wall elements based on lithium niobate single crystal thin films are prepared by the preparation method according to any one of claims 1 to 5.