CN111025432B - Method for preparing periodic optical superlattice - Google Patents
Method for preparing periodic optical superlattice Download PDFInfo
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- CN111025432B CN111025432B CN201911410876.2A CN201911410876A CN111025432B CN 111025432 B CN111025432 B CN 111025432B CN 201911410876 A CN201911410876 A CN 201911410876A CN 111025432 B CN111025432 B CN 111025432B
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/002—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials
- G02B1/005—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials made of photonic crystals or photonic band gap materials
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- 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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- 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
- G02F1/3558—Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM]
Abstract
The application provides a method for preparing periodic optical superlattice, in the method, ferroelectric crystal is processed to obtain periodic titanium diffusion structure; a periodic target electrode is coated on the non-diffusion area to form a target substrate; and applying an electric field to the target substrate to form the periodic optical superlattice. According to the method, the target electrode is arranged in the non-diffusion area in an alignment mode, the width of the target electrode is smaller than that of the non-diffusion area, when an electric field is applied to the target substrate, the area corresponding to the target electrode is subjected to domain inversion, the titanium diffusion area adjacent to the target electrode can inhibit the transverse expansion of the domains in the area, and therefore the periodic optical superlattice with a small line width can be prepared.
Description
Technical Field
The application relates to the technical field of polarization of iron electrode crystals, in particular to a method for preparing periodic optical superlattice.
Background
Ferroelectrics are a special class of dielectric materials, and include crystals that can spontaneously polarize within a certain temperature range, and the direction of spontaneous polarization can be reversibly changed by an external electric field, such as LiNbO3, KTP, GaP, GaAs, and the like. The microstructure is introduced into the ferroelectric crystal, so that the positive domain and the negative domain of the ferroelectric crystal are orderly arranged according to a certain mode to prepare the optical superlattice, and the optical superlattice is mainly used for laser frequency doubling. Wherein, the microstructure can be periodic or non-periodic; may be one-dimensional or multi-dimensional. At present, the long-term attention and research of researchers at home and abroad is paid to the preparation of the optical superlattice from the ferroelectric crystal by utilizing the periodic polarization process, and the room-temperature electric field polarization process in the periodic polarization process has the advantages of accurate structure control, simple and rapid manufacturing method and the like, and is the most mature technology for development and most extensive application in the preparation method of the optical superlattice.
In the prior art, there are various ways to implement a room temperature electric field polarization process, such as a conventional metal thin film electrode polarization method, a liquid electrode polarization method, and a light-induced assisted liquid electrode polarization method, wherein the conventional metal thin film electrode polarization method is widely used due to the advantage of mass production. The metal film electrode polarization method mainly comprises the following steps: step (1), calculating a polarization period; step (2), designing a required template by using software; step (3), photoetching is carried out on the single-domain crystal by using a designed template to obtain a periodic electrode pattern; step (4), applying voltage on the electrode to perform domain inversion; and (5) removing the thin film electrode, and cutting to obtain the optical superlattice. In the step (5), domain inversion occurs to the ferroelectric crystal under the action of the external electric field, so as to form a stable electric domain structure. Domain inversion process as shown in fig. 1, fig. 1 (a) to 1 (f) are schematic diagrams of different stages of domain inversion, fig. 1 (a) shows nucleation at the edge of the electrode, which is the beginning of the formation of a new domain; FIG. 1 (b) shows the propagation of the tip of the nucleus along the crystallographic axis toward the other face of the crystal, during which the diameter of the nucleus also increases slightly; FIG. 1 (c) shows the propagation of the tip to the other side of the crystal terminating in a very short time (less than 1 microsecond); FIG. 1 (d) shows adjacent domains rapidly joining to form a larger domain; FIG. 1 (e) shows domain wall lateral expansion; fig. 1 (f) shows that the electric domain structure eventually stabilizes.
However, in the conventional metal thin film electrode polarization method, since the photolithography process in step (3) provides a periodic electrode, when a voltage is applied, the electric field in some places inside the ferroelectric crystal is large, the electric field in some places is small, and the larger the electric field difference is, the more obvious the region where the inversion can occur and the region where the inversion cannot occur are. As the electrode period becomes smaller, the difference in electric field between the regions directly connected to the electrode and the regions not connected to the electrode becomes small, and it takes time for the domains to turn to negative, and not all the regions turn together. As shown in fig. 2, fig. 2 (a) is a schematic structural diagram of just occurring domain inversion, and fig. 2 (b) is a schematic structural diagram of constantly performing domain inversion, however, in the domain inversion process, the domain wall of the region that is firstly inverted is likely to be continuously inverted, which causes the region that is not connected to the metal electrode to be continuously inverted, and the region that is adjacent to the metal electrode may not be inverted yet, and at this time, the region that is not connected to the metal electrode is continuously and laterally expanded to the region that is adjacent to the metal electrode, which is likely to cause a domain connection phenomenon due to serious lateral expansion of the domain, as shown in fig. 2 (c), and the occurrence of the domain connection phenomenon makes it difficult to prepare an optical superlattice with a small period.
Disclosure of Invention
The application provides a method for preparing a periodic optical superlattice, which aims to solve the problem of serious domain transverse expansion in the existing optical superlattice preparation process.
The present application provides a method of making a periodic optical superlattice comprising:
processing the ferroelectric crystal to obtain a periodic titanium diffusion structure, wherein a titanium diffusion area is embedded in the surface of the titanium diffusion structure;
a periodic target electrode is arranged on an undispersed area in an overlaying mode, a target substrate is formed, the undispersed area is an area except for titanium diffusion, the undispersed area and the titanium diffusion area are located on the same surface of the ferroelectric crystal, the target electrode is an electrode directly contacting the ferroelectric crystal, and the width of the target electrode is smaller than that of the undispersed area between any two adjacent titanium diffusion areas;
and applying an electric field to the target substrate to form the periodic optical superlattice.
Optionally, processing the ferroelectric crystal to obtain a periodic titanium diffusion structure, includes:
photoetching a layer of periodic first photoresist structure on the surface of a ferroelectric crystal to form a first substrate, wherein the first photoresist structure covers a region needing domain inversion;
plating a layer of metal titanium film on the surface of the first substrate to form a second substrate with a first strip-shaped structure and a second strip-shaped structure which are staggered, wherein the first strip-shaped structure is a structure formed by stacking a first photoresist structure and the metal titanium film, and the second strip-shaped structure is a single metal titanium film;
stripping the first strip-shaped structure on the surface of the second substrate to obtain a third substrate with a periodic metal titanium film on the surface;
and carrying out diffusion treatment on the metal titanium film on the surface of the third substrate to obtain a periodic titanium diffusion structure.
Optionally, the step of forming a target substrate by overlaying a periodic target electrode on the non-diffused region includes:
photoetching a layer of periodic second photoresist structure on the surface of the titanium diffusion structure to form a fourth substrate, wherein the second photoresist structure covers the titanium diffusion area, and the section between the adjacent second photoresist structures is a semi-elliptical structure;
and plating a layer of metal film on the surface of the fourth substrate to form a target substrate with a third strip structure and a fourth strip structure which are staggered, wherein the third strip structure is a structure formed by stacking a second photoresist structure and the metal film, the fourth strip structure is a single metal film, and the fourth strip structure is used as a target electrode.
Optionally, the metal used for the metal film is nickel or chromium.
Optionally, forming a fourth substrate by performing photolithography on a layer of a periodic second photoresist structure on the surface of the titanium diffusion structure, including:
uniformly covering a layer of photoresist on the surface of the titanium diffusion structure;
incompletely drying the titanium diffusion structure covered with the photoresist to obtain a first substrate to be exposed;
performing incomplete exposure on the first substrate to be exposed by using a preset mask, wherein the preset mask comprises a hollow area and a shielding area, the area corresponding to the hollow area is used as an exposure area, and the exposure area corresponds to the non-diffusion area;
and developing the exposure area to obtain a fourth substrate with a second photoresist structure, wherein the interval between the adjacent second photoresist structures is smaller than the width of the hollow area.
Optionally, after the developing process is performed on the exposed area to obtain a fourth substrate having a second photoresist structure, the method further includes: and drying the exposed area after the development treatment.
Optionally, forming a first substrate by photolithography of a periodic first photoresist structure on the surface of the ferroelectric crystal, includes:
uniformly covering a layer of photoresist on the surface of the ferroelectric crystal;
completely drying the ferroelectric crystal covered with the photoresist to obtain a second substrate to be exposed;
completely exposing the second substrate to be exposed by using a preset mask to obtain the substrate to be developed, wherein the hollow area of the preset mask corresponds to the titanium diffusion area;
and carrying out development treatment on the substrate to be developed to obtain a first substrate.
According to the technical scheme, the application provides a method for preparing the periodic optical superlattice, wherein the method comprises the steps of processing a ferroelectric crystal to obtain a periodic titanium diffusion structure; a periodic target electrode is coated on the non-diffusion area to form a target substrate; and applying an electric field to the target substrate to form the periodic optical superlattice. According to the method, the target electrode is arranged in the non-diffusion area in an alignment mode, the width of the target electrode is smaller than that of the non-diffusion area, when an electric field is applied to the target substrate, the area corresponding to the target electrode is subjected to domain inversion, the titanium diffusion area adjacent to the target electrode can inhibit the transverse expansion of the domains in the area, and therefore the periodic optical superlattice with a small line width can be prepared.
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 is a schematic diagram of a domain inversion process provided in the prior art;
FIG. 2 is a schematic diagram of a process in which domain cross-domain expansion is severe and domain linking occurs;
fig. 3 is a schematic flow chart of a method for fabricating a periodic optical superlattice according to an embodiment of the present application;
FIG. 4 is a schematic view of a titanium diffusion process provided in an embodiment of the present application;
FIG. 5 is a schematic diagram of a fourth substrate forming process in an embodiment of the present application;
fig. 6 is a schematic structural diagram of a target substrate according to an embodiment of the present disclosure.
Detailed Description
The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
In the conventional process for preparing the periodic optical superlattice, periodic electrodes are required to be engraved on the surface of a ferroelectric crystal, and then a voltage is applied to the periodic electrodes, so that domain inversion occurs in the ferroelectric crystal. In order to prevent domain connection caused by severe lateral domain expansion, it is usually necessary to provide periodic electrodes with a large line width on the surface of the ferroelectric and to set a relatively large distance between adjacent periodic electrodes when using conventional fabrication processes. However, the performance of the optical superlattice prepared from the periodic electrode with a large line width in practical application is limited, and in order to obtain a periodic optical superlattice with more excellent performance, embodiments of the present application provide a method for preparing a periodic optical superlattice to prepare a periodic optical superlattice with a small line width.
Fig. 3 is a schematic flow chart of a method for fabricating a periodic optical superlattice according to an embodiment of the present disclosure.
As shown in fig. 3, embodiments of the present application provide a method of preparing a periodic optical superlattice, comprising the steps of:
In the examples of the present application, a method for producing a periodic optical superlattice is described by taking a lithium niobate crystal as an example. Referring to the schematic diagram of the titanium diffusion process shown in fig. 4, processing the lithium niobate crystal to obtain a periodic titanium diffusion structure may include the following steps:
step 1011, a first periodic photoresist structure is formed on the surface of the ferroelectric crystal by photolithography, and a first substrate is formed, wherein the first photoresist structure covers the region where domain inversion needs to occur.
In the step, a layer of periodic first photoresist structure is prepared on the + z surface of a piece of double-sided polished z-cut lithium niobate by methods such as ultraviolet lithography, and the first photoresist structure is periodically arranged on the + z surface of the lithium niobate. As shown in fig. 4, a schematic diagram of a first substrate forming process can be performed in the following manner: firstly, uniformly covering a layer of photoresist on the + z surface of lithium niobate; completely drying the ferroelectric crystal covered with the photoresist to obtain a second substrate to be exposed; then, completely exposing the second substrate to be exposed by using a preset mask to obtain the substrate to be developed, wherein the hollow-out area of the preset mask corresponds to the titanium diffusion area; and finally, carrying out development treatment on the substrate to be developed to obtain a first substrate.
In this process, the exposure process can perform a selective photochemical reaction on the ferroelectric crystal coated with the photoresist to react the photoresist in the exposed portion. For the photoresist in the embodiment of the application, the photoresist corresponding to the preset mask hollowed-out area is a light-sensing part, the light-sensing part is dissolved in an organic solvent during development, and the complete exposure means that the photoresist corresponding to the preset mask hollowed-out area is completely dissolved in the organic solvent during development, so that the same graph as the preset mask is formed on the surface of the ferroelectric crystal. In general, it is necessary to bake the first substrate after development at a certain temperature, and remove the developer and residual moisture absorbed by the first substrate during development, thereby enhancing the corrosion resistance of the first substrate.
Step 1012, plating a layer of metal titanium film on the surface of the first substrate to form a second substrate with a first strip-shaped structure and a second strip-shaped structure which are staggered, wherein the first strip-shaped structure is a structure formed by stacking a first photoresist structure and the metal titanium film, and the second strip-shaped structure is a single metal titanium film.
In the step, a layer of metal titanium film is plated on the photoresist structure by methods such as electron beam evaporation, magnetron sputtering and the like, and the thickness of the metal titanium film is about 70 nm. Under the condition that the metal titanium film is uniformly paved on the surface of the first substrate, because the first photoresist structure on the surface of the first substrate is periodic, if the metal titanium film falls on the first photoresist structure, a first strip-shaped structure formed by stacking the first photoresist structure and the metal titanium film is formed; if the metallic titanium film falls on the interval part between the first photoresist structures, the metallic titanium film is contacted with the + z surface of the lithium niobate to form a second strip-shaped structure.
And 1013, stripping the first strip-shaped structure on the surface of the second substrate to obtain a third substrate with a periodic metal titanium film on the surface.
Based on the fact that the part of the first strip-shaped structure, which is in contact with the ferroelectric crystal, is the first photoresist structure, and the characteristic that the photoresist is dissolved in acetone, sodium hydroxide solution or NMP solution is utilized, in an achievable mode, the second substrate is placed in the acetone, sodium hydroxide solution or NMP solution, and ultrasonic cleaning is carried out for about 30s, so that the first strip-shaped structure can be separated from the surface of the second substrate.
And 1014, performing diffusion treatment on the metal titanium film on the surface of the third substrate to obtain a periodic titanium diffusion structure.
In the embodiment of the present application, the third substrate may be placed in a high temperature annealing furnace at 1020 ℃ and subjected to diffusion treatment under the condition of staying for 10 hours, and in addition, other diffusion treatment modes may also be adopted, which is not particularly limited in the present application. After the diffusion treatment, the metal titanium film on the surface of the third substrate can be embedded into the ferroelectric crystal to form a periodic titanium diffusion structure, and the titanium diffusion structure can inhibit the domain inversion of a titanium diffusion region.
Because the periodic optical superlattice with a small line width is prepared by using the room-temperature electric field polarization process, after the periodic titanium diffusion structure is formed, the surface of the titanium diffusion structure needs to be subjected to alignment of the target electrode, and the alignment of the target electrode can be performed by adopting the following steps:
step 1021, photoetching a layer of periodic second photoresist structure on the surface of the titanium diffusion structure to form a fourth substrate, wherein the second photoresist structure covers the titanium diffusion area, and the section between the adjacent second photoresist structures is a semi-elliptical structure.
In the traditional photoetching process, the operations of glue homogenizing, pre-baking, exposure and developing are sequentially carried out on the surface of the titanium diffusion structure, so that a regular zigzag photoresist structure can be formed on the surface of the titanium diffusion structure, but the photoresist structure formed by the method is difficult to prepare the periodic optical superlattice with smaller line width under the influence of diffraction effect and photoetching mask preparation process. In order to prepare a periodic optical superlattice with a smaller line width, in the embodiment of the present application, a drying condition in a pre-drying stage is controlled, so that a titanium diffusion structure after photoresist is not completely dried, and incomplete drying may cause that a solvent in a photoresist cannot be completely evaporated, which may hinder an effect of Light on the photoresist in an exposure stage and affect a solubility of the photoresist in a developing solution, see a schematic diagram shown in fig. 5, where fig. 5 (a) shows that a first substrate to be exposed formed after incomplete drying is exposed under ultraviolet rays, in fig. 5 (a), Sample refers to a processed ferroelectric crystal, photoresist is the photoresist, remainingsolution is the residual solvent, Mask is a preset Mask, and UV Light is ultraviolet Light; fig. 5 (b) shows a fourth substrate having a step-like photoresist structure formed after development. Since the solvent remains in the first substrate to be exposed and affects the exposure effect of the light on the photoresist, the exposure operation performed on the first substrate to be exposed formed by incomplete baking is referred to as incomplete exposure.
In this step, the fourth substrate can be prepared in the following manner by taking advantage of the influence of the insufficient pre-baking on the exposure and development stages:
step 10211, uniformly covering a layer of photoresist on the surface of the titanium diffusion structure.
Step 10212, the titanium diffusion structure covered by the photoresist is incompletely dried to obtain a first substrate to be exposed.
Step 10213, performing incomplete exposure on the first substrate to be exposed by using a preset mask, wherein the preset mask includes a hollow area and a shielding area, the area corresponding to the hollow area is used as an exposure area, and the exposure area corresponds to the non-diffusion area.
Step 10214, developing the exposed area to obtain a fourth substrate having a second photoresist structure, wherein a space between adjacent second photoresist structures is smaller than a width of the hollow area.
In the embodiment of the application, the s1813 photoresist is taken as an example, and the normal photoetching process parameters are glue spreading 3000r/s, glue drying 13min, exposure at 100 ℃ for 5s and development for 17 s. In order to prepare the periodic optical superlattice with a small line width, in an achievable mode, the photoetching process parameters can be 3000r/s of photoresist homogenizing, 8min of photoresist baking, 100 ℃, 4s of exposure and 10s of developing. In practical applications, specific values of the photolithography process parameters need to be determined according to the required line width and the process conditions, and the present application is not limited specifically.
The second photoresist structures are step-shaped, the closer the second photoresist structures are to the middle positions of the intervals between the adjacent second photoresist structures, the lower the steps are, the photoresist at the middle parts of the intervals disappears due to the dissolution of the development stage to form blank areas, and the step-shaped structures enable the width of the blank areas to be smaller, so that a foundation is provided for preparing optical superlattices with smaller line widths.
Because the fourth substrate can absorb the developing solution and the residual moisture during development, after the fourth substrate with the second photoresist structure is obtained by developing the exposure area, the developed exposure area needs to be dried, so that the insulation property of the photoresist is improved, and the line width of the contact area between the photoresist and the ferroelectric crystal is further reduced. Specifically, the fourth substrate may be baked in an oven or a hot plate for about 20 minutes to dry the fourth substrate.
Step 1022, plating a layer of metal film on the surface of the fourth substrate to form a target substrate with a third strip structure and a fourth strip structure arranged in a staggered manner on the surface, where the third strip structure is a structure in which a second photoresist structure and a metal film are stacked, the fourth strip structure is a single metal film, and the fourth strip structure is used as a target electrode.
In the step, a metal film with a thickness of about 200nm is plated on the surface of the fourth substrate by using methods such as electron beam evaporation or magnetron sputtering, and optionally, the metal used for the metal film is nickel or chromium.
Under the condition that the metal film is uniformly paved on the surface of the fourth substrate, if the metal film falls on the surface of the second photoresist structure, the second photoresist structure and the metal film are stacked to form a third strip-shaped structure; if the metal film falls on the blank region, a fourth striped structure is formed. And then, a copper wire is attached to the metal film and sealed by insulating glue. Under the action of applied electric field, the target electrode is directly contacted with the ferroelectric crystal, so that the region directly contacted with the target electrode is firstly subjected to domain inversion. And the photoresist in the third strip-shaped structure has an insulation effect, so that the electric field of a region directly contacted with the third strip-shaped structure is weaker, and in addition, the region directly contacted with the third strip-shaped structure has a titanium diffusion structure which can further inhibit the inversion of the domain of the region.
Fig. 6 is a schematic structural diagram of a target substrate according to an embodiment of the present disclosure. As shown in fig. 6, the lithium niobate substrate is an example provided by the embodiment of the present application, in this example, a metal film is prepared by using chromium (Cr) metal to form a Cr metal film, as can be seen from fig. 6, a cross section between two adjacent second photoresist structures is a semi-elliptical structure, a bottom surface of the semi-elliptical structure is in direct contact with the lithium niobate substrate, and a width of a region in direct contact is smaller than a width of a hollowed-out region of a preset mask.
And 103, applying an electric field to the target substrate to form the periodic optical superlattice.
The embodiment of the application utilizes a metal film electrode polarization method to prepare the optical superlattice, and can be carried out by adopting the following steps:
(1) the target substrate is placed in a circuit for polarization, and a short pulse which is far lower than the coercive field voltage is firstly used for observing whether the electrode on the surface of the target substrate can normally carry out the charging and discharging processes. If so, the voltage is slowly increased again until a polarization current occurs.
(2) And adjusting the width of the polarization pulse, estimating the domain turnover area by recording the electric quantity in the polarization process, and finishing the polarization process in a single polarization pulse by using up a long polarization pulse.
After the lithium niobate or lithium tantalate reaches the coercive field voltage, domain inversion does not occur immediately. But there will be different response delays depending on the shape of the applied pulse. The width of the poling pulse can be controlled so that domain inversion occurs at a smaller poling voltage, thereby suppressing lateral expansion of the domain.
By using the method provided by the embodiment of the application, the optical superlattice for blue light frequency doubling can be prepared, the period of the optical superlattice is about 4 microns, the width is 2 millimeters, the length is 20 millimeters, the input of 890nm pulse light and the output of 445nm blue light can be realized, and the conversion efficiency is 20%.
As can be seen from the above technical solutions, the embodiments of the present application provide a method for preparing a periodic optical superlattice, in which a ferroelectric crystal is processed to obtain a periodic titanium diffusion structure; a periodic target electrode is coated on the non-diffusion area to form a target substrate; and applying an electric field to the target substrate to form the periodic optical superlattice. According to the method, the target electrode is arranged in the non-diffusion area in an alignment mode, the width of the target electrode is smaller than that of the non-diffusion area, when an electric field is applied to the target substrate, the area corresponding to the target electrode is subjected to domain inversion, the titanium diffusion area adjacent to the target electrode can inhibit the transverse expansion of the domains in the area, and therefore the periodic optical superlattice with a small line width can be prepared.
The mechanism of suppressing the lateral expansion of the domains by the titanium diffusion region will be briefly described below.
At about 500 ℃, Ti metal on the surface is rapidly oxidized into TiO2Polycrystal, oxygen ions come from air and lithium niobate crystals at the same time, and the Nb/O ratio on the surface of the crystals is changed; the temperature rises to 600-800 ℃ due to Li2O out-diffusion to generate LiNb on the crystal surface3O8(ii) a When the temperature is further increased to 800-900 ℃, the LiNb on the surface3O8Cannot exist stably, but Ti begins to diffuse into the crystal, and Nb ions form Ti0.56Nb0.35O2(ii) a The temperature is raised to 950 ℃, Ti is totally diffused into the crystal, and Ti is generated on the surface0.56Nb0.35O2A layer; further heating up Ti0.56Nb0.35O2As a diffusion source, Ti therein is further diffused into the crystal to produce TixNbyO2. The titanium diffusion temperature is usually chosen to be 1000-1070 ℃, and Li is present in the crystal at high temperature2The out-diffusion phenomenon of O is independent of the presence of Ti on the surface. Li2O causes the composition of the crystal surface to change, and inhibits the domain inversion of the area.
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 (5)
1. A method of making a periodic optical superlattice, comprising:
processing the ferroelectric crystal to obtain a periodic titanium diffusion structure, wherein a titanium diffusion area is embedded in the surface of the titanium diffusion structure;
a periodic target electrode is arranged on an undispersed area in an overlaying mode, a target substrate is formed, the undispersed area is an area except for titanium diffusion, the undispersed area and the titanium diffusion area are located on the same surface of the ferroelectric crystal, the target electrode is an electrode directly contacting the ferroelectric crystal, and the width of the target electrode is smaller than that of the undispersed area between any two adjacent titanium diffusion areas;
applying an electric field to the target substrate to form a periodic optical superlattice;
wherein, processing the ferroelectric crystal to obtain a periodic titanium diffusion structure comprises:
photoetching a layer of periodic first photoresist structure on the surface of a ferroelectric crystal to form a first substrate, wherein the first photoresist structure covers a region needing domain inversion;
plating a layer of metal titanium film on the surface of the first substrate to form a second substrate with a first strip-shaped structure and a second strip-shaped structure which are staggered, wherein the first strip-shaped structure is a structure formed by stacking a first photoresist structure and the metal titanium film, and the second strip-shaped structure is a single metal titanium film;
stripping the first strip-shaped structure on the surface of the second substrate to obtain a third substrate with a periodic metal titanium film on the surface;
performing diffusion treatment on the metal titanium film on the surface of the third substrate to obtain a periodic titanium diffusion structure;
wherein, the step of forming a target substrate by overlaying a periodic target electrode on the non-diffusion region comprises the following steps:
photoetching a layer of periodic second photoresist structure on the surface of the titanium diffusion structure to form a fourth substrate, wherein the second photoresist structure covers the titanium diffusion area, and the section between the adjacent second photoresist structures is a semi-elliptical structure; the second photoresist structures are step-shaped, and the closer to the middle position of the interval between the adjacent second photoresist structures, the lower the step is; in the photoetching process, carrying out incomplete drying and incomplete exposure on a titanium diffusion structure covered with photoresist, wherein the incomplete exposure is an operation of exposing a first substrate to be exposed formed by utilizing the incomplete drying;
and plating a layer of metal film on the surface of the fourth substrate to form a target substrate with a third strip structure and a fourth strip structure which are staggered, wherein the third strip structure is a structure formed by stacking a second photoresist structure and the metal film, the fourth strip structure is a single metal film, and the fourth strip structure is used as a target electrode.
2. The method of claim 1, wherein the metal used for the metal film is nickel or chromium.
3. The method of claim 1, wherein forming a fourth substrate by photolithography of a periodic second photoresist structure on the surface of the titanium diffusion structure comprises:
uniformly covering a layer of photoresist on the surface of the titanium diffusion structure;
incompletely drying the titanium diffusion structure covered with the photoresist to obtain a first substrate to be exposed;
performing incomplete exposure on the first substrate to be exposed by using a preset mask, wherein the preset mask comprises a hollow area and a shielding area, the area corresponding to the hollow area is used as an exposure area, and the exposure area corresponds to the non-diffusion area;
and developing the exposure area to obtain a fourth substrate with a second photoresist structure, wherein the interval between the adjacent second photoresist structures is smaller than the width of the hollow area.
4. The method according to claim 3, wherein after the developing process is performed on the exposed region to obtain a fourth substrate having a second photoresist structure, further comprising: and drying the exposed area after the development treatment.
5. The method of claim 1, wherein forming the first substrate by photolithography of a periodic first photoresist structure on the surface of the ferroelectric crystal comprises:
uniformly covering a layer of photoresist on the surface of the ferroelectric crystal;
completely drying the ferroelectric crystal covered with the photoresist to obtain a second substrate to be exposed;
completely exposing the second substrate to be exposed by using a preset mask to obtain the substrate to be developed, wherein the hollow area of the preset mask corresponds to the titanium diffusion area;
and carrying out development treatment on the substrate to be developed to obtain a first substrate.
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