阅读说明：本技术 一种周期极化薄膜基板及其制备方法 (Periodically polarized film substrate and preparation method thereof ) 是由 王金翠 张秀全 朱厚彬 李真宇 张涛 于 2020-04-03 设计创作，主要内容包括：本申请提供了一种周期极化薄膜基板及其制备方法,所述周期极化薄膜基板包括依次层压的衬底(1)、缓冲层(2)和压电单晶层(3),其中,压电单晶层(3)包括至少两层压电单晶子层(31),相邻压电单晶子层(31)的极化方向相反,通过键合而得,本申请提供的制备方法通过在缓冲层上直接键合多层压电单晶子层从而形成周期极化薄膜基板,该方法在常温下即可进行,工艺难度低,所制得的周期极化薄膜基板的极化周期及周期数量可灵活控制；有效避免由高压造成的击穿风险以及由表面镀电极而造成的表面质量的变差问题,通过设置缓冲层防止光泄露至衬底中,从而降低信号损耗,基于该基板制得的PPLN具有完全贯穿的垂直电畴壁。(The periodic polarization film substrate comprises a substrate (1), a buffer layer (2) and a piezoelectric monocrystal layer (3) which are sequentially laminated, wherein the piezoelectric monocrystal layer (3) comprises at least two piezoelectric monocrystal sub-layers (31), the polarization directions of the adjacent piezoelectric monocrystal sub-layers (31) are opposite, and the periodic polarization film substrate is obtained through bonding.)

1. The periodically poled film substrate is characterized by comprising a substrate (1), a buffer layer (2) and a piezoelectric monocrystal layer (3) which are sequentially laminated, wherein the piezoelectric monocrystal layer (3) comprises at least two piezoelectric monocrystal sub-layers (31) with the same tangential direction, the polarization directions of the adjacent piezoelectric monocrystal sub-layers (31) are opposite, and the two adjacent piezoelectric monocrystal sub-layers (31) are obtained by bonding.

2. A periodically poled thin film substrate according to claim 1, characterized in that the buffer layer (2) comprises at least one buffer sublayer (21), each buffer sublayer (21) having a refractive index smaller than the refractive index of the piezoelectric single crystal layer (3).

3. A periodically poled thin film substrate according to claim 2, characterized in that a plurality of buffer sublayers (21) are laminated to each other.

4. A periodically poled thin film substrate according to any of claims 1 to 3, characterized in that the refractive indices of two adjacent buffer sublayers (21) are different.

5. A periodically poled thin film substrate according to any of claims 1 to 4, characterized in that the thickness of each of the piezoelectric monocrystalline sub-layers (31) is 10-2000 nm.

6. The periodically poled thin film substrate according to any one of claims 1 to 5, wherein the material for preparing the piezoelectric single crystal layer (3) comprises single crystal lithium niobate, magnesium-doped single crystal lithium niobate, and single crystal lithium tantalate.

7. The periodically poled thin film substrate of claim 1, wherein the periodically poled thin film substrate is prepared by a method comprising:

step 1, preparing a buffer layer on a substrate;

and 2, alternately bonding piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

8. The periodically poled thin film substrate of claim 7, wherein step 2 specifically comprises:

step 2-1, bonding a first piezoelectric single crystal wafer on the buffer layer, and trimming the thickness of the first piezoelectric single crystal wafer to be a target thickness to form a first piezoelectric single crystal sublayer;

step 2-2, continuously bonding a second piezoelectric single crystal wafer on the upper surface of the first piezoelectric single crystal sublayer obtained in the step 2-1, and trimming the thickness of the second piezoelectric single crystal wafer to be the target thickness to form a second piezoelectric single crystal sublayer;

and 2-3, continuously bonding the piezoelectric single crystal sub-layers to the ith piezoelectric single crystal sub-layer on the upper surface of the second piezoelectric single crystal sub-layer according to the method in the step 2-2, wherein i is 1, 2, 3, … …, n, n represents the number of the piezoelectric single crystal sub-layers in the periodically poled thin film substrate, and the total thickness of the first piezoelectric single crystal sub-layer to the ith piezoelectric single crystal sub-layer is the target total thickness.

9. A method of preparing a periodically poled thin film substrate according to any one of claims 1 to 8, comprising:

step 1', preparing a buffer layer on a substrate;

and 2', bonding a plurality of piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

Technical Field

The application belongs to the field of functional semiconductor materials, and particularly relates to a periodic polarization thin film substrate and a preparation method thereof.

Background

Periodically Poled lithium niobate (Periodically Poled L N, PP L N) based on quasi-phase matching technology has been widely applied to the optical parametric processes such as frequency doubling/difference frequency and optical parametric oscillation, THz wave generation and the like by utilizing the maximum nonlinear coefficient d33(25.2pm/V) of lithium niobate, and in addition, has a wide application prospect in the field of optical communication, especially in the aspects of wavelength conversion and all-optical switching.

In lithium niobate, a specific direction from positive to negative is formed due to the shift in the position of lithium ions (positive) and niobium ions (positive) with respect to oxygen ions (negative), which is along the Z-axis of the lithium niobate crystal, i.e., the + Z-axis direction or the-Z-axis direction.

At present, the laser induced applied electric field polarization method is the most commonly used method for preparing PP L N, and is characterized in that a metal electrode with a periodic structure is firstly deposited or sputtered on the + z surface or the-z surface of a single-domain (polarization reversal) lithium niobate crystal, a uniform electrode is manufactured on the other surface of the lithium niobate crystal, then an applied electric field opposite to the spontaneous polarization direction of the crystal is applied to the lithium niobate crystal, when the applied electric field exceeds the coercive field (21KV/mm) of the crystal, the spontaneous polarization direction is reversed, however, the edges of the material with and without polarization reversal are difficult to be aligned or not in a straight line, and therefore, the electric domain wall for manufacturing PP L N is not vertical usually.

In addition, in order to realize a smaller periodic polarization structure, the photolithography technology in the microelectronic industry is needed to be utilized, interferometric feedback control is used to limit the position error of the periodic structure of the electrode within a small range, however, the lithium niobate with the same component has a higher coercive field, when a high electric field is applied to perform polarization reversal, the lithium niobate crystal is in danger of being broken down, the breakdown is a phenomenon that the dielectric loses the insulation property under high voltage, one part of the breakdown phenomenon can be recovered, and the other part can not be recovered. Once the lithium niobate crystal is broken down, not only does the polarization process stop immediately, but the lithium niobate sample is also likely to break.

Further, since the coercive field of lithium niobate crystal is high, and the applied voltage is required to be larger when the total thickness of the sample is larger, and the applied voltage is larger, the risk of sample breakdown is higher, therefore, PP L N prepared by using the laser-induced applied electric field polarization method generally has severe limitation on the total thickness, and it is difficult to prepare PP L N having special requirements on thickness, and especially, for lithium niobate with a cycle thickness of nanometer level, the preparation difficulty is increased geometrically.

Also, if light of different incident angles is transmitted simultaneously (i.e., light of different modes is transmitted) in the piezoelectric thin film layer, light of a small incident angle is easily refracted from the piezoelectric thin film layer having a large refractive index into the substrate layer having a small refractive index, resulting in an increase in loss of light transmission.

Disclosure of Invention

In order to solve at least one of the above problems, for example, the difficulty of manufacturing PP L N by using the prior art method is high, the electrical domain wall of manufactured PP L N has bending deformation and is difficult to approach to vertical, the cycle length is difficult to reach nanometer level, the total cycle length of PP L N is limited, and the signal loss of PP L N in the optical transmission process is large, the present application provides a periodically poled thin film substrate manufactured by stacking through a bonding method, wherein the thickness of each layer of single crystal piezoelectric sub-layer is as low as nanometer level, and the cycle length and the cycle number of the periodically poled thin film can be manufactured as required by controlling the thickness of each layer of single crystal piezoelectric sub-layer and the number of layers of single crystal piezoelectric sub-layers, so that the periodically poled thin film substrate provided by the present application can obtain a periodically poled thin film having a completely penetrated vertical electrical domain wall, the cycle length is nanometer level, and the total cycle length can be specifically set as required.

The periodically poled thin film substrate comprises a substrate 1, a buffer layer 2 and a piezoelectric single crystal layer 3 which are sequentially laminated, wherein the piezoelectric single crystal layer 3 comprises at least two piezoelectric single crystal sub-layers 31 with the same tangential direction, the poling directions of the adjacent piezoelectric single crystal sub-layers 31 are opposite, and the adjacent two piezoelectric single crystal sub-layers 31 are obtained by bonding.

In an implementable manner, the buffer layer 2 comprises at least one buffer sublayer 21, each buffer sublayer 21 having a refractive index less than the refractive index of the piezoelectric single crystal layer 3.

In one implementation, multiple buffer sublayers 21 are stacked on top of each other.

Further, the refractive indices of the two adjacent buffer sublayers 21 are different.

Optionally, the material for preparing the buffer layer 2 includes silicon oxide and/or silicon nitride.

In a realizable manner, each of the piezoelectric monocrystalline sublayers 31 has a thickness ranging from 10nm to 2000 nm.

Optionally, the thickness of each piezoelectric monocrystal sublayer 31 is equal.

In an implementable manner, the material for preparing the piezoelectric single crystal layer 3 includes single crystal lithium niobate, magnesium-doped single crystal lithium niobate, and single crystal lithium tantalate.

In one implementable form, the periodically poled thin film substrate is prepared by a method comprising:

step 1, preparing a buffer layer on a substrate;

and 2, alternately bonding piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

Optionally, before bonding each piezoelectric single crystal layer, detecting the polarization direction of each piezoelectric single crystal layer, and making a positioning mark on the edge of the piezoelectric single crystal layer.

Further, after each piezoelectric monocrystal sub-layer is bonded and before the next piezoelectric monocrystal sub-layer is bonded, polishing is conducted on the upper surface of the piezoelectric monocrystal sub-layer at the current layer, and the roughness of the upper surface of the piezoelectric monocrystal sub-layer is smaller than the preset roughness.

In one implementation, the buffer layer is prepared on the substrate in step 1 by thermal oxidation, bonding and deposition.

Optionally, step 1 specifically includes: and sequentially depositing a plurality of buffer sublayers on the substrate, wherein the refractive index of each buffer sublayer is smaller than that of the piezoelectric single crystal layer.

Further, the refractive indices of adjacent buffer sublayers are different.

In an implementable manner, step 2 comprises in particular:

step 2-1, bonding a first piezoelectric single crystal wafer on the buffer layer, and trimming the thickness of the first piezoelectric single crystal wafer to be a target thickness to form a first piezoelectric single crystal sublayer;

step 2-2, continuously bonding a second piezoelectric single crystal wafer on the upper surface of the first piezoelectric single crystal sublayer obtained in the step 2-1, and trimming the thickness of the second piezoelectric single crystal wafer to be the target thickness to form a second piezoelectric single crystal sublayer;

and 2-3, continuously bonding the piezoelectric single crystal sub-layers to the ith piezoelectric single crystal sub-layer on the upper surface of the second piezoelectric single crystal sub-layer according to the method in the step 2-2, wherein the total thickness of the first piezoelectric single crystal sub-layer to the ith piezoelectric single crystal sub-layer is the target total thickness.

In an implementable manner, step 2 may be followed by:

and 3, cutting the product prepared in the step 2 along the height direction of the lamination.

Optionally, the thickness of the film obtained by cutting in step 3 is a preset thickness.

It is also an object of the present application to provide a method of preparing the periodically poled thin film substrate as described above, the method comprising:

step 1', preparing a buffer layer on a substrate;

and 2', bonding a plurality of piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

Optionally, before bonding each piezoelectric single crystal layer, detecting the polarization direction of each piezoelectric single crystal layer, and making a positioning mark on the edge of the piezoelectric single crystal layer.

In one implementation, the buffer layer is prepared on the substrate in step 1 by thermal oxidation, bonding and deposition.

Optionally, step 1 specifically includes: and sequentially depositing a plurality of buffer sublayers on the substrate, wherein the refractive index of each buffer sublayer is smaller than that of the piezoelectric single crystal layer.

Further, the refractive indices of adjacent buffer sublayers are different.

In an implementable manner, step 2' comprises in particular:

step 2' -1, bonding a first piezoelectric single crystal wafer on the buffer layer, and trimming the thickness of the first piezoelectric single crystal wafer to be a target thickness to form a first piezoelectric single crystal sublayer;

step 2 '-2, continuously bonding a second piezoelectric single crystal wafer on the upper surface of the first piezoelectric single crystal sublayer obtained in the step 2' -1, and trimming the thickness of the second piezoelectric single crystal wafer to be the target thickness to form a second piezoelectric single crystal sublayer;

and 2 '-3, continuously bonding the piezoelectric single crystal sub-layers to the ith piezoelectric single crystal sub-layer on the upper surface of the second piezoelectric single crystal sub-layer according to the method in the step 2' -2, wherein i is 1, 2, 3, … …, n, n represents the number of the piezoelectric single crystal sub-layers in the periodically poled thin film substrate, and the total thickness of the first piezoelectric single crystal sub-layer to the ith piezoelectric single crystal sub-layer is the target total thickness.

In an implementable manner, the + X faces of the single crystal piezoelectric layers are oriented in the same direction.

In an implementable manner, step 2' may be followed by:

and 3', cutting the product prepared in the step 2 along the height direction of the lamination.

Optionally, the thickness of the film obtained by cutting in step 3' is a preset thickness.

Compared with the prior art, in the periodically poled thin film substrate provided by the application, the thickness of each layer of piezoelectric single crystal sub-layer is in a nanometer scale, the thickness of each layer of piezoelectric single crystal sub-layer is equal, the PP L N prepared based on the substrate has a completely penetrated vertical electrical domain wall which is difficult to obtain by adopting a method in the prior art, the surface quality of the PP L N is excellent, the thickness of the PP L N is flexible and controllable, the total period length can be greatly improved, any target thickness, target period length and target total period length can be achieved, namely, the total period length of the PP L N prepared by the method provided by the application is not limited any more, further, the clear aperture of a bulk device prepared based on the PP L N can be effectively increased, and the periodically poled thin film substrate is provided with a buffer layer which can prevent light leakage into a substrate, so that signal loss is reduced.

The preparation method provided by the application is characterized in that a piezoelectric monocrystal wafer is directly bonded on a buffer layer to prepare a plurality of piezoelectric monocrystal sub-layers so as to form a periodically polarized film substrate, the interfaces of the piezoelectric monocrystal sub-layers are smooth and parallel, PP L N with a completely vertical electric domain wall can be obtained, the method provided by the application can be carried out at normal temperature, the process difficulty is low, the polarization period and the period number of the prepared periodically polarized film substrate can be flexibly controlled, the preparation process provided by the application does not involve voltage and other processing processes, the breakdown risk caused by high voltage is effectively avoided, the influence of a surface electrode and a coercive electric field is avoided in the preparation process, and further, the method provided by the application does not involve the surface electrode plating photoetching process step, so that the problem of surface quality deterioration caused by surface electrode plating can be avoided.

Drawings

FIG. 1 is a schematic cross-sectional view of a periodically poled thin film substrate provided in the present application;

FIG. 2 is a schematic cross-sectional view of another example of a periodically poled thin film substrate according to the present application.

Description of the reference numerals

1-substrate, 2-buffer layer, 21-buffer sublayer, 3-piezoelectric monocrystal layer and 31-piezoelectric monocrystal sublayer.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with certain aspects of the invention, as detailed in the appended claims.

The periodic polarization thin film substrate and the method for manufacturing the same provided by the present application are described in detail by specific examples below.

Fig. 1 shows a schematic cross-sectional structure of a periodically poled thin film substrate provided by the present application, and as shown in fig. 1, the periodically poled thin film substrate includes a substrate 1, a buffer layer 2 and a piezoelectric single crystal layer 3 laminated in this order.

In this example, the substrate may be single crystal silicon, quartz, sapphire, lithium niobate, or the like, or other substrate materials that may be used to make PP L N, currently, substrate materials typically include dimensions of 3 inches, 4 inches, 6 inches, and 8 inches.

In this example, the periodic thickness of the prepared PP L N was small, and the total thickness of the resulting PP L N thin film substrate was also small at the nanometer level, and thus, a substrate support was used.

In the present example, the material used for preparing the piezoelectric single crystal layer 1 is a uniaxially polarizable piezoelectric material including single crystal lithium niobate, magnesium-doped single crystal lithium niobate, or single crystal lithium tantalate.

As shown in fig. 1, the piezoelectric single crystal layer 3 includes at least two piezoelectric single crystal sub-layers, and it is understood that fig. 1 only schematically illustrates a cross-sectional structure of a periodically poled thin film substrate including a plurality of piezoelectric single crystal sub-layers, and the number of piezoelectric single crystal sub-layers in the periodically poled thin film substrate is not limited thereto.

Further, the polarization directions of the adjacent piezoelectric single crystal sub-layers 31 are opposite, in this example, the polarization directions of the adjacent two piezoelectric single crystal sub-layers 31 may be a + Z direction and a-Z direction, may also be a + X direction and a-X direction, or a + Y direction and a-Y direction, and the piezoelectric performance of the currently used piezoelectric single crystal material in the + Z direction and the-Z direction is more outstanding, so this example illustrates the scheme of the present application by taking the polarization directions of the adjacent two piezoelectric single crystal sub-layers 31 as a + Z direction and a-Z direction, and taking the tangential direction as an X cut or a Y cut as an example, that is, in this example, the adjacent two piezoelectric single crystal sub-layers 31 are alternately stacked according to the polarization directions of the + Z direction and the-Z direction, and specifically, the included angle of the + Z direction of the adjacent two piezoelectric single crystal layers is 180 °.

It is understood that the polarization directions of the two adjacent piezoelectric monocrystal sub-layers can be specifically set for different piezoelectric monocrystal materials.

In this example, the directions of the cross sections of the piezoelectric monocrystal sub-layers 31 are the same, i.e. for example, the + X direction of the first piezoelectric monocrystal layer is upward, and the + X direction of the rest of the piezoelectric monocrystal layers is also upward, so as to ensure that the obtained periodically poled thin film substrate has excellent and stable performance.

In this example, the number of the piezoelectric single crystal sub-layers in the periodically poled thin film substrate is n, where n can be specifically set according to the requirements of downstream users, and it can be understood that n is a natural number.

As shown in fig. 1, the manufactured periodically poled thin film substrate may be cut along a cross-sectional direction, that is, cut along a stacking height direction of the piezoelectric single crystal sub-layers, to obtain a sheet-shaped periodically poled thin film, where each sheet of periodically poled thin film includes the piezoelectric single crystal sub-layers that are sequentially stacked together, and a downstream device manufacturer may cut the periodically poled thin film again according to a required size and shape.

In this example, the two adjacent piezoelectric monocrystal sub-layers 31 are obtained by bonding, and the bonding mode may be normal temperature bonding, where the normal temperature bonding includes direct bonding or plasma bonding, for example, the bonding surfaces of the two adjacent piezoelectric monocrystal sub-layers are respectively activated, and then the activated surfaces of the two piezoelectric monocrystal sub-layers are pressed together to complete the bonding of the two adjacent piezoelectric monocrystal sub-layers.

According to the method, the multilayer piezoelectric single crystal sublayers are prepared on the substrate in a laminating bonding mode, the limitation of the size of a piezoelectric single crystal material on the size of PP L N is broken through, the restriction of a high-voltage electric field is eliminated, the interfaces among the piezoelectric single crystal sublayers are clear and regular, and the periodically polarized film prepared on the basis of the periodically polarized film substrate has a vertical electric domain wall.

Optionally, the thickness of each piezoelectric single crystal sublayer 31 is 10nm to 2000nm, and optionally, the thickness of each piezoelectric single crystal sublayer 31 is equal, so that each layer in PP L N prepared based on the periodically poled thin film optical substrate is uniformly and periodically distributed, so as to facilitate the use of PP L N.

In this example, the number of periods of the piezoelectric monocrystal sub-layers is 1 or more, and in this application, a group of two adjacent piezoelectric monocrystal sub-layers is referred to as one period.

In this example, the size of the piezoelectric single crystal layer can be specifically selected according to the requirements of downstream customers, for example, the size of the substrate can be 3 inches, 4 inches, 6 inches or 8 inches, and the size of the substrate is adapted to the size of the piezoelectric single crystal layer.

In this example, the buffer layer 2 includes at least one buffer sub-layer 21, for example, as shown in fig. 1, the buffer layer of the periodically poled thin film substrate includes only one buffer sub-layer, and for example, as shown in fig. 2, a cross-sectional view of another example of the periodically poled thin film substrate of the present application is shown, and as shown in fig. 2, the buffer layer 2 includes a plurality of stacked buffer sub-layers 21.

In this example, the refractive index of each buffer sublayer 21 is smaller than that of the piezoelectric single crystal layer 3, so that light leaked from the piezoelectric single crystal layer can be reflected into the piezoelectric single crystal layer by the buffer layer, thereby reducing the loss of optical signals, wherein the refractive index of the buffer sublayers 21 of two adjacent layers may be the same or different.

In an achievable manner, the refractive index of each buffer sublayer 21 may be periodically distributed according to a predetermined rule, for example, a buffer sublayer group is formed by a plurality of adjacent buffer sublayers, as shown in fig. 2, two buffer sublayers form a buffer sublayer group, and the refractive index of the upper buffer sublayer in each buffer sublayer group is greater than the refractive index of the lower buffer sublayer; for another example, three buffer sublayers form a buffer sublayer group, in each of which the refractive index of the upper buffer sublayer is greater than that of the middle buffer sublayer, and the refractive index of the middle buffer sublayer is greater than that of the lower buffer sublayer, and in this application, the side close to the substrate 1 is referred to as "lower", and the side close to the piezoelectric single crystal layer 3 is referred to as "upper".

In another realizable manner, the refractive index of each buffer sublayer 21 decreases from layer to layer in the top-down direction, so that light leaking from the piezoelectric single crystal layer into the buffer sublayer can be reflected by the lower buffer sublayer to the upper buffer sublayer until the piezoelectric single crystal layer, thereby reducing the loss of the optical signal.

In another realizable approach, the refractive indices of the buffer sublayers are randomly distributed.

In this example, the material from which the buffer layer 2 is made may include silicon oxide and/or silicon nitride.

In one implementable manner, the periodically poled thin film substrate is prepared by a method comprising steps 1 and 2:

step 1, preparing a buffer layer on a substrate.

In this example, a plurality of buffer sublayers may be sequentially prepared on the substrate to form the buffer layer, wherein each buffer sublayer has a refractive index smaller than that of the piezoelectric single crystal layer.

In this step, the buffer layer is prepared by means including thermal oxidation, bonding, and deposition.

In an implementation manner, taking a monocrystalline silicon substrate as an example, the thermal oxidation manner specifically includes: and preparing a silicon dioxide layer on the process surface of the monocrystalline silicon substrate by adopting a thermal oxidation method, wherein the thickness of the silicon dioxide layer can be 2 microns.

In another implementation, still taking a single crystal silicon substrate as an example, the deposition specifically includes: and alternately depositing a silicon dioxide layer and a silicon nitride layer on the monocrystalline silicon substrate, wherein the thicknesses of the silicon dioxide layer and the silicon nitride layer are equal.

It is understood that in another implementation manner, the deposition manner may further include depositing only one silicon nitride layer on the single-crystal silicon substrate, or depositing multiple buffer sub-layers, where the structure of the buffer sub-layer is as described in the foregoing buffer layer, and is not described herein again.

In another implementation, the bonding may be any one of the methods for bonding piezoelectric single crystal materials in the prior art.

And 2, alternately bonding piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

Specifically, the step may include:

and 2-1, bonding a first piezoelectric single crystal wafer on the buffer layer, and trimming the thickness of the first piezoelectric single crystal wafer to be the target thickness to form a first piezoelectric single crystal sublayer.

In this example, the terms "first", "second", etc. are used only for distinguishing different elements having the same concept for convenience of description and not for importance of features, and for convenience of description, in conjunction with fig. 1, the lowermost piezoelectric single crystal layer may be referred to as a first piezoelectric single crystal wafer, and sequentially upward, as a second piezoelectric single crystal wafer, through an nth piezoelectric single crystal wafer, respectively.

In this example, the first piezoelectric single crystal wafer may be bonded on the substrate by using a normal temperature bonding process in the prior art, for example, the bonding surfaces of the substrate and the first piezoelectric single crystal wafer may be respectively activated, and then the two bonding surfaces are bonded together, so as to complete bonding of the first piezoelectric single crystal wafer on the substrate.

In this example, after bonding the first piezoelectric single crystal wafer on the substrate, the thickness of the first piezoelectric single crystal wafer may be trimmed to a target thickness, which may be specifically set according to the requirements of downstream customers, for example, the target thickness may be 10nm to 2000 nm.

In this example, the bonding may be a normal temperature bonding, which may be a high vacuum bonding or a plasma bonding.

In one embodiment, the bonding may specifically include:

firstly, ions are implanted into the first piezoelectric single crystal wafer from the-X surface, wherein the implanted ions comprise H⁺、He⁺Plasma, the ion implantation energy is 50 KeV-1000 KeV, for example, 200KeV, and the ion implantation dose is (1 × 10)¹⁶～1×10¹⁷)ions/cm²For example, 4 × 10¹⁶ions/cm². And forming a three-layer structure of a thin film layer, a separation layer and a residual material layer on the first wafer. The applicant finds that the thin film layers with different thicknesses can be obtained as required by performing ion implantation according to the implantation energy, so that the polarization period thickness can be effectively controlled, and on the other hand, the probability of complete separation of the thin film can be increased by performing ion implantation according to the implantation dosage.

And secondly, bonding the thin film layer on the-X surface of the first piezoelectric single crystal wafer after ion implantation with a buffer layer to form a bonded body, placing the bonded body into heating equipment, preserving heat at high temperature until a residual material layer is separated from the bonded body, and forming a lithium niobate single crystal film with the + X surface facing upwards on the single crystal silicon substrate, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 100-600 ℃, and the heat preservation time is 1 minute-48 hours.

In this example, the method of trimming the thickness of the first piezoelectric single crystal wafer includes an ion implantation process, wherein the implanted ions include H⁺、He⁺Plasma, the energy of ion implantation is 50 KeV-1000 KeV, for example, 200KeV, and the dose of ion implantation is (1 × 10)¹⁶-1×10¹⁷)ions/cm²For example, 4 × 10¹⁶ions/cm²。

And 2-2, continuously bonding a second piezoelectric single crystal wafer on the upper surface of the first piezoelectric single crystal sublayer obtained in the step 2-1, and trimming the thickness of the second piezoelectric single crystal wafer to be the target thickness to form a second piezoelectric single crystal sublayer.

In this example, since the piezoelectric single crystal substrate is currently provided with a large cut edge in the industry for convenient positioning, the large cut edge is generally perpendicular to the + Z direction based on the piezoelectric material in the prior art, that is, the direction perpendicular to the large cut edge and pointing to the large cut edge on the piezoelectric single crystal substrate is the + Z direction. Based on this, in the present example, the + Z/-Z direction can be determined by a large cut edge on the piezoelectric single crystal substrate in the process of laminating the respective piezoelectric single crystal sublayers.

Further, in order to make the + Z directions of the two adjacent piezoelectric monocrystal sublayers opposite, the large cut edges of the two adjacent piezoelectric monocrystal sublayers can be centered on two sides of the center of the piezoelectric monocrystal sublayer, and the large cut edges are parallel to each other. In specific operation, the Z axis, namely the large cut edge, of two adjacent piezoelectric monocrystal sublayers can be turned to 180 ℃, so that the + Z directions of the two adjacent piezoelectric monocrystal sublayers are opposite.

It is understood that in another example of the present application, the polarization directions of two adjacent piezoelectric single crystal sub-layers may be opposite in other manners, for example, the + Z/-Z direction of the piezoelectric single crystal sub-layer may be detected by using an existing detection means, and a position mark is made at a corresponding position, and then an operation is performed according to the position mark, so that the polarization directions of the adjacent piezoelectric single crystal sub-layers are opposite.

The applicant finds that the piezoelectric properties of the two piezoelectric single crystal layers with respect to the tangential direction are different, so that the tangential direction of the two adjacent piezoelectric single crystal sub-layers is the same, and the included angle of the + Z direction of the two adjacent piezoelectric single crystal sub-layers is 180 degrees. For example, the + X direction of the first piezoelectric monocrystal sub-layer is upward, and the + X direction of the rest piezoelectric monocrystal sub-layers is also upward, so as to ensure that the manufactured periodically polarized thin film substrate has excellent and stable performance.

In this example, after the thickness of the first piezoelectric single crystal sublayer is trimmed and before the second piezoelectric single crystal sublayer is bonded, the upper surface of the first piezoelectric single crystal sublayer may be polished so that the roughness of the upper surface of the thickness-trimmed first piezoelectric single crystal sublayer is less than or equal to a predetermined roughness, so as to bond the first piezoelectric single crystal sublayer and the second piezoelectric single crystal sublayer.

In this example, the method of polishing the surface of the first piezoelectric monocrystal sublayer may be any one of the methods of polishing the surface of the piezoelectric monocrystal material in the prior art.

In this step, the bonding includes high vacuum bonding or plasma bonding.

In an implementation manner, the directly bonding is, similarly to step 2-1, respectively performing activation processing on bonding surfaces of the first piezoelectric single crystal sublayer and the second piezoelectric single crystal wafer, and then pressing the two bonding surfaces, thereby completing bonding of the second piezoelectric single crystal wafer on the first piezoelectric single crystal sublayer.

After bonding is completed, the thickness of the second piezoelectric single crystal wafer is trimmed to be the target thickness, and the method for trimming the thickness of the second piezoelectric single crystal wafer comprises an ion implantation method, wherein implanted ions comprise H⁺、He⁺Plasma, the energy of ion implantation is 50 KeV-1000 KeV, for example, 200KeV, and the dose of ion implantation is (1 × 10)¹⁶～1×10¹⁷)ions/cm²For example, 4 × 10¹⁶ions/cm²Preferably, the parameters for trimming the thickness of the second piezoelectric single crystal wafer are the same as the parameters for trimming the thickness of the first piezoelectric single crystal wafer.

In another implementation manner, the film transfer bonding is to bond a second piezoelectric monocrystal wafer on another substrate, trim the thickness of the second piezoelectric monocrystal wafer to a target thickness to form a second piezoelectric monocrystal film, bond the second piezoelectric monocrystal film to the first piezoelectric monocrystal sublayer, and remove any one substrate.

The method for trimming the thickness of the second piezoelectric single crystal wafer can also be an ion implantation method, wherein the implanted ions comprise H⁺、He⁺Plasma, the energy of ion implantation is 50 KeV-1000 KeV, for example, 200KeV, and the dose of ion implantation is (1 × 10)¹⁶～1×10¹⁷)ions/cm²For example, 4 × 10¹⁶ions/cm²Preferably, the parameters for trimming the thickness of the second piezoelectric monocrystal wafer and the trimming of the first piezoelectric monocrystal waferThe parameters used for the thickness of the wafer are the same; the second piezoelectric monocrystal film is bonded to the first piezoelectric monocrystal sub-layer by normal temperature bonding, including direct bonding and plasma bonding, for example, the bonding surfaces of the first piezoelectric monocrystal sub-layer and the second piezoelectric monocrystal film are respectively activated and then pressed.

In this example, the method of removing the substrate on the second piezoelectric single crystal film side may employ any one of the methods of removing a substrate in the related art, for example, a chemical dissolution method or the like.

And 2-3, continuously bonding the piezoelectric single crystal sub-layers to the ith piezoelectric single crystal sub-layer on the upper surface of the second piezoelectric single crystal sub-layer according to the method in the step 2-2, wherein i is 1, 2, 3, … …, n, n represents the number of the piezoelectric single crystal sub-layers in the periodically poled thin film substrate, and the total thickness of the first piezoelectric single crystal sub-layer to the ith piezoelectric single crystal sub-layer is the target total thickness.

Optionally, all the piezoelectric single crystal sublayers 31 have equal thickness, so that the layers in the PP L N prepared based on the periodically poled thin film substrate have uniform periodic distribution, thereby facilitating the use of PP L N.

In this example, the total thickness of the periodically poled thin film substrate may be greater than 300 μm, and the number of cycles of PP L N is not particularly limited, thereby breaking through the limitation of the size of the piezoelectric single crystal wafer to the size of PP L N and the number of cycles in the conventional preparation scheme, and fundamentally solving the requirement of large size and multi-cycle PP L N.

In addition, the PP L N provided by the application has nearly completely vertical electric domain walls, and a device manufactured based on the PP L N can effectively control signal loss in an optical transmission process.

The method provided by the embodiment avoids using a high-voltage electric field, thereby eliminating the risk of the piezoelectric single crystal layer being broken down by the high-voltage electric field, and also eliminating the limitation of the PP L N thickness and the total cycle length of the PP L N prepared by an electric field polarization method.

In this example, the manner of the overlay bonding may be a normal temperature bonding method, such as direct bonding or plasma bonding, and further, may be the same as the bonding manner used in step 2-2.

Optionally, the tangential directions of the single crystal piezoelectric sub-layers in the single crystal piezoelectric layer are the same, so that the prepared periodically polarized thin film substrate has excellent and stable performance.

Optionally, before bonding each piezoelectric single crystal layer, detecting the polarization direction of each piezoelectric single crystal layer, and making a positioning mark on the edge of the piezoelectric single crystal layer.

Further, after each piezoelectric monocrystal sub-layer is bonded and before the next piezoelectric monocrystal sub-layer is bonded, polishing is conducted on the upper surface of the piezoelectric monocrystal sub-layer at the current layer, and the roughness of the upper surface of the piezoelectric monocrystal sub-layer is smaller than the preset roughness.

In an implementable manner, step 2 may be followed by:

and 3, cutting the product prepared in the step 2 along the height direction of the lamination, wherein the thickness of the film obtained by cutting is the preset thickness.

The present applicant found that PP L N obtained by stacking and bonding the resulting periodically poled thin film substrates by lamination has a vertical domain wall that penetrates completely, and the periodically poled thin film substrates have a buffer layer, which can effectively prevent an optical signal from leaking into the substrate, thereby reducing loss.

It is also an object of the present application to provide a method of preparing the periodically poled thin film substrate as described above, the method comprising:

step 1', preparing a buffer layer on a substrate;

and 2', bonding a plurality of piezoelectric monocrystal sub-layers on the buffer layer, wherein the polarization directions of two adjacent piezoelectric monocrystal sub-layers are opposite.

In this example, bonding the multilayer piezoelectric single crystal sub-layer on the buffer layer may further include:

and 3', cutting the prepared product along the height direction of the lamination.

Optionally, the thickness of the film obtained by cutting is a preset thickness, so as to obtain the periodically polarized film.

The method provided by the present application is the same as the method disclosed in the periodically poled thin film substrate, and specific implementation manners of steps 1 'to 3' can refer to steps 1 to 3, which are not described herein again.