CN112195520A - Preparation method of lithium niobate film superlattice - Google Patents

Preparation method of lithium niobate film superlattice Download PDF

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CN112195520A
CN112195520A CN202011060218.8A CN202011060218A CN112195520A CN 112195520 A CN112195520 A CN 112195520A CN 202011060218 A CN202011060218 A CN 202011060218A CN 112195520 A CN112195520 A CN 112195520A
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electrode
periodic
preparing
interdigital electrode
interdigital
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CN112195520B (en
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尹志军
崔国新
叶志霖
许志城
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Nanjing Nanzhi Institute Of Advanced Optoelectronic Integration
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Nanjing Nanzhi Institute Of Advanced Optoelectronic Integration
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • C30B33/04—After-treatment of single crystals or homogeneous polycrystalline material with defined structure using electric or magnetic fields or particle radiation
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C30B29/30—Niobates; Vanadates; Tantalates
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/355—Non-linear optics characterised by the materials used
    • G02F1/3551—Crystals

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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The application provides a preparation method of a lithium niobate thin film superlattice, which comprises the following steps: 1) preparing an overlay mark; 2) preparing a periodic interdigital electrode structure on the surface of the x-cut lithium niobate thin film according to the overlay mark; 3) plating metal electrodes on the photoetched interdigital electrode structure; 4) removing the photoresist to obtain a periodic interdigital electrode; 5) connecting an electrode anode on one interdigital electrode, grounding the other interdigital electrode, applying an electric field to invert domains between the interdigital electrodes, and removing the electrodes to obtain a first periodic domain inversion structure; 6) translating the overlay mark to the right by a period distance, and repeating the steps 2) to 5) to obtain a second periodic domain turnover structure; 7) and step 6) is repeatedly executed until the distances among all the obtained domain turnover structures are equal, and the preparation is finished. By adopting the scheme, the periodic electrode is prepared on the surface of the x-cut lithium niobate thin film by adopting multiple times of alignment and multiple times of electric field polarization, and a domain structure with a domain wall vertical to the z axis is prepared.

Description

Preparation method of lithium niobate film superlattice
Technical Field
The application relates to the technical field of semiconductors, in particular to a preparation method of a lithium niobate thin film superlattice.
Background
Lithium niobate (LiNbO)3LN) is a very important nonlinear optical crystal material, and is the first choice material in the field of optical frequency conversion and optical parametric conversion. The lithium niobate superlattice has many advantages, and the maximum nonlinear coefficient of the crystal can be utilized firstly; and secondly, the domain structure is designed very flexibly, so that the requirements under different application scenes can be met. The superlattice structure of the lithium niobate is realized by domain inversion of the lithium niobate crystal, and in the lithium niobate crystal, the spontaneous polarization direction, namely the domain inversion is changed by changing the relative position of Nb atoms and Li atoms in a crystal lattice formed by O atoms, so that the spontaneous polarization direction can be changed by an electric field, and the periodical spontaneous polarization direction change is realized to prepare the lithium niobate superlattice.
At present, the room temperature polarization technology has become the most mature and widely applied technology in the superlattice preparation method. The room temperature polarization is to introduce a conductor processing technology into the preparation of the optical superlattice, design a domain structure to be reversed into a pattern to be made on a photoetching mask, correspondingly convert the pattern into electrodes on the surface of a matrix material through photoetching, film coating, etching and other semiconductor processing technologies, fill insulating media between the electrodes, and apply a high-voltage electric field to reverse the ferroelectric domain according to the designed pattern, thereby obtaining the superlattice structure. The room temperature polarization technology converts the design of nonlinear material function into more flexible planar structure design, and the method can be used for preparing a wafer-level domain structure and can meet the requirement of large-scale application. Therefore, the room temperature polarization technology is also widely applied to the preparation of lithium niobate superlattices.
In the prior art, when a room temperature polarization technology is utilized to prepare the lithium niobate optical superlattice, a periodic electrode is usually prepared on the surface of a z-cut lithium niobate wafer, and then an electric field is applied to prepare the lithium niobate optical superlattice. However, the domain wall of the prepared domain structure can only be parallel to the z-axis direction, and in some special nonlinear optical fields, a superlattice structure with the domain wall of the domain structure perpendicular to the z-axis direction needs to be used, so that the current preparation method cannot meet the requirements.
Disclosure of Invention
The application provides a preparation method of a lithium niobate film superlattice, which aims to solve the problem that domain walls of domain structures prepared in the prior art can only be parallel to the direction of a z axis, and the application of the superlattice structures with the domain walls vertical to the direction of the z axis cannot be prepared.
In a first aspect, an embodiment of the present application provides a method for preparing a superlattice of a lithium niobate thin film, including:
1) preparing an overlay mark for overlay;
2) preparing periodic interdigital electrode structures on the surface of the x-cut lithium niobate thin film by adopting a photoetching method according to the overlay mark, wherein one period is arranged between every two interdigital electrode structures, and the interdigital is vertical to the z-axis of the lithium niobate;
3) plating a layer of metal electrode on the photoetched interdigital electrode structure;
4) removing the photoresist to obtain a periodic interdigital electrode;
5) connecting an electrode anode on one interdigital electrode, grounding the other interdigital electrode, applying an electric field to enable domains between the interdigital electrodes to be inverted, and removing the electrodes to obtain a first periodic domain inversion structure;
6) translating the overlay mark to the right by a period distance, and repeating the steps 2) to 5) to obtain a second periodic domain turnover structure;
7) and step 6) is repeatedly executed until the distances among all the obtained domain turnover structures are equal, and the preparation is finished.
With reference to the first aspect, in one implementation manner, the method for preparing the overlay mark in step 1) includes:
preparing an overlay mark photoresist pattern on a sample wafer by adopting an ultraviolet photoetching method;
plating a layer of metal with the thickness of 30nm-300nm which is difficult to remove on the photoetching structure;
the resist is removed using acetone or nmp solution, leaving the metal mark for the overlay, resulting in an overlay mark.
With reference to the first aspect, in one implementation manner, the photolithography in step 2) is a method of ultraviolet lithography.
With reference to the first aspect, in one implementation, the metal electrode in step 3) is aluminum, nickel, chromium, or titanium.
With reference to the first aspect, in one implementation manner, the method for removing the photoresist in the step 4) is etching removal by using acetone or nmp solution.
With reference to the first aspect, in one implementation manner, the electric field applied in step 5) is 100V to 400V, and is determined according to the period size and the coercive field.
With reference to the first aspect, in one implementation manner, the overlay marks in step 6) are all translated to the right on the basis of the previous time, and the distance of one period of translation is equal to the interval between every two interdigital electrode structures.
With reference to the first aspect, in one implementation, the step 7) is repeated at least 1 time, resulting in a third periodic domain inversion structure.
With reference to the first aspect, in one implementation manner, in step 6), an electric field between a first electrode for preparing the first periodic domain inversion structure and a second electrode for preparing the second periodic domain inversion structure exceeds a coercive field of domain inversion, and an electric field between the second electrode and a third electrode for preparing the third periodic domain inversion structure is lower than the coercive field.
In a second aspect, the present application provides a superlattice for a lithium niobate thin film, which is prepared by the preparation method according to any one of the first aspect.
The embodiment of the application provides a preparation method of a lithium niobate thin film superlattice, which comprises the following steps: 1) preparing an overlay mark for overlay; 2) preparing periodic interdigital electrode structures on the surface of the x-cut lithium niobate thin film by adopting a photoetching method according to the overlay mark, wherein one period is arranged between every two interdigital electrode structures; 3) plating a layer of metal electrode on the photoetched interdigital electrode structure; 4) removing the photoresist to obtain a periodic interdigital electrode; 5) connecting an electrode anode on one interdigital electrode, grounding the other interdigital electrode, applying an electric field to enable domains between the interdigital electrodes to be inverted, and removing the electrodes to obtain a first periodic domain inversion structure; 6) translating the overlay mark to the right by a period distance, and repeating the steps 2) to 5) to obtain a second periodic domain turnover structure; 7) and step 6) is repeatedly executed until the distances among all the obtained domain turnover structures are equal, and the preparation is finished. By adopting the scheme, the periodic electrode is prepared on the surface of the x-cut lithium niobate thin film by adopting a method of multiple times of alignment and multiple times of electric field polarization, a superlattice structure with a domain wall of the domain structure vertical to the z-axis direction is prepared, and the application is widened.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1-1 is a schematic view of a domain structure prepared in the prior art parallel to the z-axis direction;
FIG. 1-2 is a schematic structural diagram of a domain structure to be prepared in the present application perpendicular to a z-axis direction;
FIG. 2 is a top view of an x-cut lithium niobate thin film provided in an embodiment of the present application;
FIGS. 3-1 to 3-7 are schematic process diagrams of a method for preparing a superlattice of a lithium niobate thin film according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of a superlattice of a lithium niobate thin film provided in an embodiment of the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
As can be seen from the description of the background art, the domain structure of the periodic electrode prepared in the prior art can only be parallel to the z-axis direction, as shown in FIG. 1-1, but in some special application fields, a domain structure with the domain structure perpendicular to the z-axis direction is required, as shown in FIG. 1-2, and the general preparation method is difficult to prepare the superlattice structure.
Therefore, in order to solve the above problems, the present application discloses a method for preparing a superlattice for a lithium niobate thin film, the method being performed on the surface of an x-cut lithium niobate thin film, and a top view of the lithium niobate thin film used in the present application is shown in fig. 2. The method of marking electric field polarization by 3 times of alignment is taken as an example in the application, domain inversion is respectively realized in iii and iii areas, and the lithium niobate film superlattice structure is prepared.
Specifically, referring to fig. 3-1 to 3-7, the preparation method includes the following steps:
and 11, preparing an overlay mark for overlay.
Alternatively, the method for preparing the overlay mark may include the steps of:
preparing an overlay mark photoresist pattern on a sample wafer by adopting an ultraviolet photoetching method;
plating a layer of metal with the thickness of 30nm-300nm which is difficult to remove on the photoetching structure;
using acetone or nmp solution (N-methylpyrrolidone, C)5H9NO), removing the photoresist, and leaving the metal mark for alignment to obtain the alignment mark.
Wherein the metal may be gold.
And 12, preparing periodic interdigital electrode structures on the surface of the x-cut lithium niobate thin film by adopting a photoetching method according to the overlay marks, wherein one period is arranged between every two interdigital electrode structures, and the interdigital is vertical to the z axis of the lithium niobate.
The photolithography is a method of ultraviolet lithography.
The method comprises the following steps of preparing a periodic interdigital electrode structure on the surface of an x-cut lithium niobate thin film based on an overlay mark, namely etching the periodic interdigital electrode structure on the surface of the x-cut lithium niobate thin film so as to plate metal on the periodic interdigital electrode structure in the next step, thus obtaining the interdigital electrode structure, wherein a period is arranged between every two interdigital electrodes, and the interdigital is vertical to the z-axis of the lithium niobate.
And step 13, plating a layer of metal electrode on the photoetched interdigital electrode structure.
Optionally, the metal electrode is selected from aluminum, nickel, chromium or titanium.
In the step 13, metal is plated on the periodic interdigital electrode structure to form a metal electrode, and specifically, a vapor deposition or magnetron sputtering mode can be adopted.
And step 14, removing the photoresist to obtain the periodic interdigital electrode.
Alternatively, the photoresist is removed by etching with acetone or nmp solution.
The photoresist on the surface of the x-cut lithium niobate thin film is removed, and a metal electrode is left, wherein the metal electrode is a periodic interdigital electrode, as shown in fig. 3-1, a white area in the figure is the interdigital electrode which is periodically arranged, and the interdigital electrode is vertical to the z-axis direction.
And step 15, connecting an electrode anode on one interdigital electrode, grounding the interdigital electrode on the other interdigital electrode, applying an electric field to enable domains between the interdigital electrodes to be inverted, and then removing the electrode (the first electrode) to obtain a first periodic domain inversion structure.
Optionally, the applied electric field is 100V to 400V, which is determined according to the period size and the coercive field.
The step is to connect the periodic interdigital electrode prepared in the step 14 to a power supply, apply an electric field, specifically, connect an electrode anode on one side of the interdigital electrode, that is, connect an anode (an electrode with + in the figure) on the lower interdigital electrode in fig. 3-2, and connect an interdigital electrode on the other side to the ground, that is, connect a ground (an electrode with-in the figure) on the upper interdigital electrode in fig. 3-2, after applying the electric field, the domain between the interdigital electrodes is inverted, and then remove the electrode, so as to obtain a first periodic domain inversion structure, as shown in fig. 3-3, assuming that the direction before the inversion is the left direction of the z axis, the direction after the inversion is the right direction of the z axis, and it can be seen in the figure that the domain wall of the first periodic domain inversion structure is perpendicular to the direction of the z.
And step 16, translating the overlay mark to the right for a period of distance, and repeating the steps 12-15 to obtain a second periodic domain turnover structure.
Optionally, in this step, the overlay mark is shifted to the right by a distance of one period, each shift of the overlay mark is shifted to the right on the basis of the previous shift, for example, the first shift is a shift to the right by one period at the original position, the second shift is a shift to the right by two periods at the original position, that is, the second shift is a shift to the right by a distance of one period on the basis of the position at the first shift, and the distance of one period of the shift is equal to the interval between every two interdigital electrode structures in step 12.
The method comprises the steps of translating an overlay mark to the right for a period of distance, as shown in fig. 3-4, repeating the steps 12-15 after the overlay mark is translated, namely, preparing a periodic interdigital electrode structure on the surface of an x-cut lithium niobate thin film by using a photoetching method again at the translated position, plating a layer of metal electrode on the again-photoetched interdigital electrode structure, removing the photoresist to obtain a new periodic interdigital electrode, connecting an electrode anode on one interdigital electrode of the new interdigital electrode, grounding the interdigital electrode on the other side, applying an electric field to invert domains between the interdigital electrodes, and removing the electrode (second interdigital electrode) to obtain a second periodic domain inversion structure, as shown in fig. 3-5, wherein a domain wall of the second periodic domain inversion structure is perpendicular to the z-axis direction.
Since the used overlay marks are the same, the shape of the second periodic domain inversion structure prepared in this step is completely the same as the first periodic domain inversion structure obtained in step 15, except that the entire position is shifted to the right by a period of distance.
And step 17, repeatedly executing the step 16 until the obtained intervals among all the domain turnover structures are equal, and finishing the preparation.
Wherein, the step is repeated at least once to obtain a third periodical domain turnover structure.
In this step, step 16 is repeatedly executed, but on the basis of the position of the overlay mark in step 16, the overlay mark is shifted to the right for a period of distance, as shown in fig. 3-6, after the overlay mark is shifted, the aforementioned steps 12-15 are repeated again, that is, the distance is shifted for a period (the original position of the overlay mark is shifted to the right for two periods) on the basis of step 16, a periodic interdigital electrode structure is prepared on the surface of the x-cut lithium niobate thin film by photolithography again, a layer of metal electrode is plated on the interdigital electrode structure which is photo-etched again, the photoresist is removed to obtain a new periodic interdigital electrode, the positive electrode of the electrode is connected to one side of the new interdigital electrode, the interdigital electrode on the other side is grounded, then an electric field is applied to flip the domain between the interdigital electrodes, then the electrode (third electrode) is removed, a third periodic domain inversion structure is obtained as shown in fig. 3-7, where it can be seen that the domain wall of the first periodic domain inversion structure is perpendicular to the z-axis direction.
Since the used overlay marks are the same, the shape of the third periodic domain-inversion structure prepared in this step is identical to the shape of the second periodic domain-inversion structure obtained in step 16, except that the entire position is shifted to the right by a period of distance.
And when the distances (the distance of one period) between all the prepared domain overturning structures are equal, stopping translating the overlay mark, and finishing the preparation.
The preparation method disclosed by the application is characterized in that periodic electrodes are prepared on the surface of an x-cut lithium niobate thin film and an electric field is applied, and as part of the electric field is distributed in the lithium niobate thin film, the polarization direction in the z direction can be changed, a superlattice structure vertical to a domain wall of the domain structure and the z-axis direction is prepared, and a better periodic domain structure can be prepared only by accurately controlling the polarization electric quantity in the preparation process. Therefore, in the preparation method disclosed in the present application, the electric field polarization of a single step can take an excessive amount of electricity until the domain inversion stops because only the domain inversion of the region between the two electrodes is needed.
Optionally, an electric field between a first electrode for preparing the first periodic domain inversion structure and a second electrode for preparing the second periodic domain inversion structure exceeds a coercive field for domain inversion, and an electric field between the second electrode and a third electrode for preparing the third periodic domain inversion structure is lower than the coercive field.
In addition, in the preparation method disclosed above, it is necessary to ensure that the electric field between the first electrode and the second electrode exceeds the coercive field of domain inversion, and the electric field between the second electrode and the third electrode is lower than the coercive field to ensure that the domain structure with the changed polarization direction will not be inverted again, so that the present application adopts a polarization frequency of 3 times or more to realize periodic domain inversion.
On the basis of the preparation method disclosed above, the application also discloses a lithium niobate thin film superlattice prepared by any one of the preparation methods. As shown in fig. 4, the lithium niobate thin film includes, in order from top to bottom: lithium niobate thin film layer 110, silicon dioxide layer 120, substrate layer 130. The superlattice of the lithium niobate thin film is prepared on the lithium niobate thin film layer 110, and details which are not disclosed are referred to the above preparation method, which is not described herein again.
In order to make the process of the present application more clear, specific examples are also disclosed.
Example 1
a) And preparing an alignment mark photoresist pattern on the sample wafer by adopting an ultraviolet photoetching method.
b) And plating a layer of gold with the thickness of 30nm, which is difficult to remove, on the photoetching structure.
c) And removing the photoresist by using acetone, and leaving the metal mark for alignment to obtain the alignment mark.
d) And c) preparing a periodic interdigital electrode structure of the photoresist on the surface of the x-cut lithium niobate thin film by using the overlay mark prepared in the step c) by adopting an ultraviolet lithography method, wherein a period is arranged between every two interdigital electrodes.
e) Plating a layer of metal electrode aluminum on the structure which is well etched in the step d).
f) And removing the photoresist by using acetone to only leave the periodic interdigital electrode structure.
g) And connecting an electrode anode on the lower interdigital electrode, connecting the upper interdigital electrode to the ground, applying an electric field at about 200V to overturn domains between the interdigital electrodes, and removing the electrodes to obtain a first periodic domain overturning structure.
h) And (4) translating the alignment mark to the right by a distance of one period compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
i) And (g) repeating the step (g) to obtain a second periodic domain switching structure.
j) And (4) translating the alignment mark to the right for a distance of two periods compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
k) And (g) repeating the step (g) to obtain a third periodic domain switching structure.
Example 2
a) And preparing an alignment mark photoresist pattern on the sample wafer by adopting an ultraviolet photoetching method.
b) And plating a layer of gold with the thickness of 35nm, which is difficult to remove, on the photoetching structure.
c) The photoresist is removed using nmp solution, leaving the metal mark for the overlay, resulting in an overlay mark.
d) And c) preparing a periodic interdigital electrode structure of the photoresist on the surface of the x-cut lithium niobate thin film by using the overlay mark prepared in the step c) by adopting an ultraviolet lithography method, wherein a period is arranged between every two interdigital electrodes.
e) Plating a layer of metal electrode nickel on the photoetching structure in the step d).
f) And removing the photoresist by using acetone to only leave the periodic interdigital electrode structure.
g) And connecting an electrode anode on the lower interdigital electrode, connecting the upper interdigital electrode to the ground, applying an electric field at about 300V to overturn domains between the interdigital electrodes, and removing the electrodes to obtain a first periodic domain overturning structure.
h) And (4) translating the alignment mark to the right by a distance of one period compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
i) And (g) repeating the step (g) to obtain a second periodic domain switching structure.
j) And (4) translating the alignment mark to the right for a distance of two periods compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
k) And (g) repeating the step (g) to obtain a third periodic domain switching structure.
Example 3
a) And preparing an alignment mark photoresist pattern on the sample wafer by adopting an ultraviolet photoetching method.
b) And plating a layer of gold with the thickness of 35nm, which is difficult to remove, on the photoetching structure.
c) The photoresist is removed using nmp solution, leaving the metal mark for the overlay, resulting in an overlay mark.
d) And c) preparing a periodic interdigital electrode structure of the photoresist on the surface of the x-cut lithium niobate thin film by using the overlay mark prepared in the step c) by adopting an ultraviolet lithography method, wherein a period is arranged between every two interdigital electrodes.
e) Plating a layer of metal electrode chromium on the structure etched in the step d).
f) The photoresist was removed using nmp solution, leaving only the periodic interdigitated electrode structure.
g) And connecting an electrode anode on the lower interdigital electrode, connecting the upper interdigital electrode to the ground, applying an electric field of about 400V to overturn domains between the interdigital electrodes, and removing the electrodes to obtain a first periodic domain overturning structure.
h) And (4) translating the alignment mark to the right by a distance of one period compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
i) And (g) repeating the step (g) to obtain a second periodic domain switching structure.
j) And (4) translating the alignment mark to the right for a distance of two periods compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
k) And (g) repeating the step (g) to obtain a third periodic domain switching structure.
Example 4
a) And preparing an alignment mark photoresist pattern on the sample wafer by adopting an ultraviolet photoetching method.
b) And plating a layer of gold with the thickness of 30nm, which is difficult to remove, on the photoetching structure.
c) The photoresist is removed with acetone, leaving the metal mark for the overlay.
d) And c) preparing a periodic interdigital electrode structure of the photoresist on the surface of the x-cut lithium niobate thin film by using the overlay mark prepared in the step c) by adopting an ultraviolet lithography method, wherein a period is arranged between every two electrodes.
e) Plating a layer of metal electrode aluminum on the structure which is well etched in the step d).
f) And removing the photoresist by using acetone to only leave the periodic interdigital electrode structure.
g) And connecting an electrode anode on the lower interdigital electrode, connecting the upper interdigital electrode to the ground, applying an electric field at about 200V to overturn domains between the interdigital electrodes, and removing the electrodes to obtain a first periodic domain overturning structure.
h) And (4) translating the alignment mark to the right by a distance of one period compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
i) And (g) repeating the step (g) to obtain a second periodic domain switching structure.
j) And (4) translating the alignment mark to the right for a distance of two periods compared with the step (d), repeating the steps (d) to (f) by adopting an alignment technology, and preparing the periodic interdigital electrode again.
k) And (g) repeating the step (g) to obtain a third periodic domain switching structure.
l) translating the overlay mark to the right by a distance of three periods compared with the step (d), repeating the steps (d) to (f) by adopting an overlay technology, and preparing the periodic interdigital electrode again.
m) repeating the step (g) to obtain a fourth periodic domain inversion structure.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.

Claims (10)

1. A method for preparing a superlattice of a lithium niobate thin film is characterized by comprising the following steps:
1) preparing an overlay mark for overlay;
2) preparing periodic interdigital electrode structures on the surface of the x-cut lithium niobate thin film by adopting a photoetching method according to the overlay mark, wherein one period is arranged between every two interdigital electrode structures, and the interdigital is vertical to the z-axis of the lithium niobate;
3) plating a layer of metal electrode on the photoetched interdigital electrode structure;
4) removing the photoresist to obtain a periodic interdigital electrode;
5) connecting an electrode anode on one interdigital electrode, grounding the other interdigital electrode, applying an electric field to enable domains between the interdigital electrodes to be inverted, and removing the electrodes to obtain a first periodic domain inversion structure;
6) translating the overlay mark to the right by a period distance, and repeating the steps 2) to 5) to obtain a second periodic domain turnover structure;
7) and step 6) is repeatedly executed until the distances among all the obtained domain turnover structures are equal, and the preparation is finished.
2. The method for producing according to claim 1, wherein the method for producing the overlay mark in step 1) comprises:
preparing an overlay mark photoresist pattern on a sample wafer by adopting an ultraviolet photoetching method;
plating a layer of metal with the thickness of 30nm-300nm which is difficult to remove on the photoetching structure;
the resist is removed using acetone or nmp solution, leaving the metal mark for the overlay, resulting in an overlay mark.
3. The method according to claim 1, wherein the photolithography in the step 2) is a method of uv lithography.
4. The production method according to claim 1, wherein the metal electrode in step 3) is aluminum, nickel, chromium, or titanium.
5. The method of claim 1, wherein the photoresist is removed in step 4) by etching with acetone or nmp solution.
6. The method according to claim 1, wherein the electric field applied in step 5) is 100V to 400V, which is determined according to the period size and coercive field.
7. The method according to claim 1, wherein the overlay marks in step 6) are all translated to the right on the basis of the previous time, and the distance of one period of translation is equal to the interval between every two interdigital electrode structures.
8. The method according to claim 1, wherein the step 7) is repeated at least 1 time to obtain a third periodic domain inversion structure.
9. The method according to claim 8, wherein in step 6), an electric field between the first electrode for preparing the first periodic domain inversion structure and the second electrode for preparing the second periodic domain inversion structure exceeds a coercive field for domain inversion, and an electric field between the second electrode and the third electrode for preparing the third periodic domain inversion structure is lower than the coercive field.
10. A lithium niobate thin film superlattice, characterized in that it is prepared by the preparation method as claimed in any one of claims 1 to 9.
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