Integrated structure including a ferroelectric layer with selective polarization attached to a substrate and method of fabrication

Abstract

A ferroelectric layer (Ferro) having a first polarization (P1) in a first zone and a second polarization (P2) opposite to the first polarization in a second zone (V) different from the first zone. lay ), wherein the first and second polarizations are oriented perpendicular or oblique to the ferroelectric layer, the second polarization zone has a higher hydrogen concentration than the first polarization zone, and the structure further includes a carrier (Sprt) and a dielectric layer (Diel) interposed between the carrier and the ferroelectric layer.

Description

[Technical Field]

[0001] The present invention relates to an integrated structure comprising a ferroelectric layer attached to a carrier by a dielectric layer, and to a method for fabricating the structure. Such a structure can be used to form nonlinear optical or radio frequency (RF) components, in particular surface acoustic wave components. [Background technology]

[0002] Several types of applications utilize or are influenced by the polarization properties of ferroelectric materials and the existence of opposing polarization regions. These include, for example, nonlinear optics, with devices called frequency doublers, in which periodically poled ferroelectric crystals can generate electromagnetic waves with twice the frequency of the frequency sent to the device's input. Surface acoustic wave (SAW) devices may also be mentioned. The existence of these applications has led to the development of methods for controlling the polarization regions of ferroelectric layers.

[0003] The paper "Seeing Is Believing" by Sven Reitzig et al. (Crystals 2021, 11, 288) describes a lithium niobate layer integrated on a silicon substrate with a silica layer, and describes controlling the polarization of this layer parallel to the plane of its extension by applying a voltage between electrodes periodically arranged on the free surface of this layer. It should be noted that in structures with electrodes only on the free surface of the crystal, controlling the polarization perpendicular to the substrate by an electric field, in the absence of embedded electrodes, requires a voltage that risks breaking down the silica layer.

[0004] EP 0 592 226 A1 describes an optical frequency converter obtained by periodically juxtaposing parallel strips of reversed polarization on the surface of a ferroelectric substrate having a spontaneous polarization perpendicular to the extension plane of the substrate, i.e. perpendicular to this plane. The polarization reversal of the strips is obtained by proton exchange through a mask.

[0005] Document WO 2005 / 052682 A1 describes the local reversal of the polarization of a ferroelectric crystal having a spontaneous polarization perpendicular to one of its faces by applying an electric field along juxtaposed periodic strips by means of gel electrodes placed on this face and on the opposite face of the crystal.

[0006] While the above-described structures and methods can effectively control the polarization domains of a ferroelectric layer, they remain impractical and do not allow for effective and safe control of polarization perpendicular to the plane of the ferroelectric crystal, much less control of a ferroelectric layer integrated on a carrier. Summary of the Invention

[0007] The first object of the present invention is to provide a ferroelectric layer in integrated form on a substrate, with polarization regions having opposite perpendicular or oblique orientation relative to the plane of the layer, which can be used for applications based on nonlinear optics or bulk acoustic waves, for example. The second object of the present invention is a manufacturing method for obtaining the integrated ferroelectric layer described above. The third object of the present invention is a method for localized and controlled reversal of the polarization of any ferroelectric element.

[0008] To achieve these objects, a first aspect of the present invention is a structure comprising a ferroelectric layer having a first polarization in a first zone and a second polarization opposite to the first polarization in a second zone different from the first zone, the first and second polarizations being oriented perpendicular or oblique to the ferroelectric layer, the second polarization zone having a higher hydrogen concentration than the first polarization zone, the structure further comprising a carrier and a dielectric layer interposed between the carrier and the ferroelectric layer.

[0009] The advantage of the structure according to the invention is that it provides an integrated structure comprising a substrate on which a ferroelectric layer having at least two different polarizations, perpendicular or oblique to the extension plane of the layer and the substrate, is deposited. Such a structure facilitates the integration of nonlinear optical or surface acoustic functions while keeping costs low.

[0010] According to additional non-limiting features of the first aspect of the present invention, considered individually or according to any technically feasible combination: - The hydrogen density in the second zone (V) is 10 19 ~10 22 atoms / cm 3 The range may be: The first zone and the second zone may define a periodic pattern. The ferroelectric layer may be formed by a single crystal. The ferroelectric layer may comprise lithium niobate or lithium tantalate. The dielectric layer may comprise silicon oxide. The carrier may comprise monocrystalline silicon.

[0011] A second aspect of the present invention relates to a method of fabricating a structure with locally controlled polarization, the method comprising: providing a ferroelectric element having a first polarization; selectively enriching the ferroelectric element with hydrogen ions through a face of the ferroelectric element; and annealing the ferroelectric element at a temperature between 400°C and 700°C after introducing the hydrogen ions so as to switch the polarization of the ferroelectric layer within a volume defined by the selective introduction of the hydrogen ions.

[0012] The method according to the invention is advantageous in that it is simple, flexible and can be easily integrated into wider manufacturing methods based on known and proven manufacturing techniques from the semiconductor industry. Furthermore, the invention allows for local control of the polarization of ferroelectric elements where a single surface is accessible, and is therefore applicable to thin layers integrated on a substrate.

[0013] According to additional non-limiting features of the second aspect of the present invention, considered individually or according to any technically feasible combination: - The polarization can be monodomain, perpendicular or oblique to the plane of the ferroelectric element. Selective enrichment of hydrogen ions can be implemented by ion implantation of hydrogen ions through a mask that defines areas of the ferroelectric element that are not to receive hydrogen ions. - Hydrogen ion implantation is at energy levels ranging from 3 keV to 210 keV. The selective introduction of hydrogen ions can be provided by an element intended to form part of a surface acoustic wave device. The ferroelectric element can be a lithium niobate or lithium tantalate layer. The method may further comprise assembling the ferroelectric substrate and the carrier, and then separating or thinning the ferroelectric substrate to define the ferroelectric elements. The carrier may be a monocrystalline silicon substrate, a dielectric layer comprising silicon oxide being interposed between the monocrystalline silicon substrate and the ferroelectric substrate. - Hydrogen ions (H + The dose of selective enrichment by 19 ~10 22 atoms / cm 3 The hydrogen density can be adjusted to obtain a hydrogen density in the range of . [Brief explanation of the drawings]

[0014] Further features and advantages of the present invention will become apparent from the following detailed description of the invention, which proceeds with reference to the accompanying drawings.

[0015] [Figure 1] 1A-1C illustrate a ferroelectric element having selectively altered polarization and corresponding fabrication methods according to the present disclosure. [Figure 2] 2 illustrates another embodiment of the ferroelectric element of FIG. 1. [Figure 3]2 illustrates another embodiment of the ferroelectric element of FIG. 1. [Figure 4] A first method for integrating a ferroelectric layer onto a carrier is presented. [Figure 5] A second method for integrating a ferroelectric layer onto a carrier is presented. [Figure 6] 1 is a schematic plan view of an apparatus according to the present disclosure; [Figure 7] FIG. 7 is a schematic cross-sectional view of the device of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0016] Selective polarization inversion After a series of experiments, applicants realized that it was possible to switch the polarization of the polarization regions by hydrogen implantation followed by annealing. These experimental results are implemented in the fabrication method described below, resulting in a ferroelectric element 10 having polarization regions with a geometry selected by the practitioner.

[0017] The ferroelectric element 10 may be a ferroelectric single crystal itself, or this single crystal may be in the form of a ferroelectric single crystal layer, and this ferroelectric crystal or this ferroelectric single crystal layer is the ferroelectric layer Ferro shown in section (D) of FIG. lay The polymer may be attached to a carrier Sprt within a structure Struct such as:

[0018] 1 and 3 show a first embodiment in which the ferroelectric element 10 is a ferroelectric single crystal itself, ie, not attached to a carrier.

[0019] Section (A) of Figure 1 shows a cross section in plane ZX of a ferroelectric element 10 having two opposing surfaces Sup and Inf perpendicular to direction Z and having a first single-region polarization P1 perpendicular to the upper surface Sup and lower surface Inf parallel to direction Z and parallel to the extension plane of the ferroelectric element 10, i.e., the crystal plane in which its dimension is greatest.

[0020] For illustrative purposes, this embodiment uses the example of polarization perpendicular to the extension plane of the ferroelectric element 10. However, the present invention also applies to situations where the polarization is not perpendicular to the extension plane of the ferroelectric element 10 but oblique to it. A "perpendicular" characteristic refers to a 90° inclination relative to the extension plane of the ferroelectric element to the nearest 10°, while an "oblique" or "obliquely" characteristic refers to a inclination at least 5° away from the extension plane of the ferroelectric element. Thus, a direction having an inclination within the range of 5° to 80°, or 30° to 70°, or even 35° to 60° can be considered oblique. For example, a layer of LiTaO3 50RY and a layer of LiTaO3 42RY have polarization inclined at 50° and 42°, respectively, relative to the extension plane of the layer, and therefore have polarization oblique to the extension plane of the layer.

[0021] In step S10, the ferroelectric element 10 is implanted with hydrogen ions H at an implantation energy level in the range of 3 keV to 210 keV. + The ferroelectric element is selectively enriched with hydrogen by selective ion implantation of hydrogen. As shown in section (B) of Figure 1, selectivity of the implantation can be provided by forming a mask M using conventional lithography methods, which mask is made of a resin, metal, oxide, nitride, or any other material capable of stopping hydrogen ions during implantation, so that the area of ​​the ferroelectric element covered by the mask does not receive hydrogen. In practical applications, the pattern formed by the mask M can be shown, for example, in section (B) as a top view in the YX plane. P ) and may consist of parallel, regularly spaced strips of the same width. After implantation, the mask M is removed in this example.

[0022] This step creates a relatively hydrogen-rich volume V in the ferroelectric element 10, with a surface coverage corresponding to the negative of the pattern of the mask M and a depth that depends on the acceleration energy of the implantation step. Thus, the volume V forms a periodic pattern in a plane parallel to the extension plane of the ferroelectric element 10, i.e., in a direction within the outer surface of the ferroelectric element 10. The implantation dose is 1019 ~10 22 atoms / cm 3 The implantation energy is adjusted to obtain a hydrogen density in the range of . It is also possible to perform multiple successive implantations at different implantation energy levels to better define the volume V and homogenize the distribution of the implanted hydrogen. At this stage, the polarization throughout the ferroelectric element 10 remains unchanged in the implanted zones, and the implanted and unimplanted zones still form a single monodomain in which the polarization has only one orientation.

[0023] As used herein, the YX and ZX planes are defined by the X, Y, and Z axes of an orthogonal reference frame, the YX plane is defined by the Y and X axes of the reference frame, and the ZX plane is defined by the Z and X axes of the reference frame. The surfaces Sup and Inf of the ferroelectric element 10 extend parallel to the YX plane, which is perpendicular to the Z axis, which defines the thickness of the ferroelectric element 10. Furthermore, selective implantation or selective enrichment is understood to mean implantation or enrichment in specific regions of the ferroelectric element 10 selected by the practitioner and defined, in this case, by the pattern of the mask M.

[0024] In step S20, the hydrogen-selectively enriched ferroelectric element 10 is annealed at a temperature ranging from 400°C to 800°C, preferably from 500°C to 700°C, and more preferably from 550°C to 600°C. This annealing step causes a reversal of the first polarization P1 of the ferroelectric element 10 only in the hydrogen-enriched volume V to produce a second polarization P2 specific to the hydrogen-enriched volume V, having the same alignment direction as the first polarization P1 but in the opposite direction, as shown in section (C0). Antiparallel polarization is defined as polarizations aligned in parallel but opposite directions. Conversely, parallel polarization is defined as polarizations aligned in parallel and the same direction. Reversing the polarization only in volume V results in a transition from a configuration of parallel polarization to a configuration of antiparallel polarization between volume V and the rest of the ferroelectric element 10. Preferably, the annealing is carried out in an oxygen atmosphere to reduce out-diffusion of oxygen from the ferroelectric layer, but it can also be carried out, for example, in a nitrogen or air atmosphere at atmospheric pressure for a duration ranging from 100 seconds to 10 hours.

[0025] The volume V defines a second zone having a second, opposite polarization P2, different from the first polarization P1 of the first zone, which is defined by the volume of ferroelectric material contained in the ferroelectric element 10 from which the second zone is removed. The first and second zones are therefore complementary, and the sum of their parts forms the total volume of ferroelectric material contained in the ferroelectric element 10, i.e., the entire ferroelectric crystal, if the ferroelectric element 10 is constructed from such a crystal. The first and second zones may be formed by separate volumes or even a continuous volume, depending on the shape and depth of the selectively implanted regions. During the fabrication process, the second zone is enriched with hydrogen such that the hydrogen concentration in the second zone is higher than that in the first zone.

[0026] Section (C0 P) shows, in a top view in the YX plane at the completion of step S20, the polarization state of the ferroelectric element 10 in the vicinity of the top surface Sup, with regions of opposite polarization having a geometry defined by the volume V obtained following selective hydrogen enrichment by the mask M.

[0027] Sections (C1) and (C2) of Figure 2 show the geometries of volume V that can be obtained by increasing the injection energy level and making it higher than the geometry shown in section (C0). In particular, in section (C2), the polarization reversal is effective throughout the entire thickness of the crystal, which is achieved by a sufficiently high injection energy level, depending on the distance between the planes Sup and Inf.

[0028] FIG. 3 shows an alternative embodiment of the method in step S10, sections (C0) and (C0 P ) and the corresponding cross-sectional view (C3) and plan view (C3 P ) where the mask M is not removed after hydrogen injection, and step S20 is applied while the mask is still present. Polarization reversal in the hydrogen-selectively enriched zone typically occurs in step S20. This alternative embodiment can be used, for example, when it is desirable to precisely align an electrode with the reverse polarization zone. In this case, the hydrogen-enriched zone is self-aligned with the electrode used as a mask for selective hydrogen enrichment.

[0029] The selective polarization reversal method described above is implemented by acting on only one face of the ferroelectric element. This feature therefore offers the possibility of controlling the polarization of ferroelectric elements whose back face is inaccessible or too far from the front face, ensuring great flexibility in the application of the method and its applicability to various geometries.

[0030] As already mentioned, this first embodiment is exemplary and is not limited to controlling the polarization of a single ferroelectric crystal, but can also be applied to more complex structures, as will become apparent throughout the remainder of this disclosure.

[0031] Integration on a carrier - Solution 1 The above-described method for selective polarization inversion is shown in Figures 1-3 as applied to a single ferroelectric crystal used as a ferroelectric element 10. This method for selective inversion can also be applied to an assembly formed by ferroelectric crystals integrated on a substrate, which assembly can form the ferroelectric element 10 shown in Figures 1-3.

[0032] Integration onto a substrate can be performed as described below with reference to FIG. 4 and with particular reference to WO 2020 / 200986 A1, which describes depositing a thin single-domain ferroelectric layer onto a substrate.

[0033] FIG. 4 shows a ferroelectric layer Ferro attached to a carrier Sprt by a dielectric layer Diel. lay The method for fabricating the integrated structure Struct shown in section (D) includes the layer Diel, which is a carrier Sprt and a ferroelectric layer Ferro. lay I am in direct contact with each of them.

[0034] Conventionally, the structure Struct may be in the form of a circular wafer, the diameter of which may be 100, 200, 300 or even 450 mm, although the invention is in no way limited to these dimensions or to this shape.

[0035] Ferroelectric layer layThe ferroelectric layer is composed of a single-crystal ferroelectric material, such as lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), or materials such as LiAlO3, BaTiO3, PbZrTiO3, KNbO3, BaZrO3, CaTiO3, PbTiO3, or KTaO3. These materials also have piezoelectric properties. Generally, the thickness of the ferroelectric layer can range from 10 nanometers to 10 microns, depending on the intended application of the structure and the expected performance capabilities of the component, although the present invention does not preclude the use of different thicknesses depending on the intended application. As a reminder, a ferroelectric material is a material that possesses an electric polarization in its natural state, and that polarization can be reversed by applying an external electric field greater than the material's coercive field. As described herein, the ferroelectric layer preferably has a first, single-domain polarization P1, i.e., all dipole moments are aligned parallel to one another in a given direction. In this case, the given direction is the direction perpendicular to the plane of the ferroelectric layer, ie the direction perpendicular to the free face of this layer or the direction perpendicular to the surface of this layer.

[0036] For reasons of availability and cost, the carrier Sprt is preferably selected, as a part thereof, from silicon. It can be a carrier composed of a solid monocrystalline silicon base substrate, but the present invention is not limited to this carrier. More generally, it can be composed of any material, such as silicon or even an electrically insulating material such as sapphire or glass. When formed from a solid substrate, the carrier Sprt typically has a thickness of several hundred microns. In monocrystalline silicon, the carrier Sprt is conductive, but preferably has a high resistivity of over 1,000 ohms. This limits the density of any easily mobile charges, holes, or electrons, which could affect the correct operation of RF components formed based on the structure. However, the present invention is not limited to carriers with such characteristics.

[0037] Optionally, the carrier Sprt may be provided with a charge trapping layer, which is a non-monocrystalline layer containing structural defects such as dislocations, grain boundaries, amorphous regions, gaps, inclusions, and pores. These structural defects, for example, imperfect or pendant chemical bond sites, form traps for charges that could otherwise flow through the material. Therefore, conduction in the trapping layer is prevented, resulting in high resistivity. In particular, when formed on a resistive carrier, its thickness may be in the range of 0.1 to 3 μm. However, thicknesses below or above this range are entirely feasible, depending on the expected performance level of the structure. Advantageously, and for reasons of ease of implementation, this trapping layer is formed by a layer of polycrystalline silicon. It may also include a layer of a silicon-carbon alloy or be formed entirely of a silicon-carbon alloy. If present, this trapping layer is located on the side of the dielectric layer Diel. Depending on the type of application envisioned, other dielectric or conductive layers with functionality deemed useful by the implementer may also be present adjacent to the dielectric layer Diel.

[0038] The thickness of the dielectric layer Diel can range from a few nanometers to several microns, e.g., 5 microns or more. It is typically made of an amorphous material such as silicon oxide, silicon oxynitride, or silicon nitride-silicon dioxide. It can also be an oxide such as Ta2O5, ZrO2, HfO, or Al2O3.

[0039] Referring to FIG. 4, the structure Struct can be fabricated by a layer deposition fabrication method, which includes: - providing a carrier Sprt as shown in section (A); Optionally, a ferroelectric donor substrate, Ferro, as shown in section (B) sub To prepare the following: - As shown in section (C), the intermediate structure inter The first surface of the carrier Sprt is bonded to the ferroelectric donor substrate Ferro via the dielectric layer Diel to form a sub and assembling the surfaces of - Ferroelectric layer on the support Sprt lay and remove the donor substrate Ferro from the intermediate structure to obtain the structure shown in section (D). sub and separating a portion of the

[0040] The carrier Sprt can be prepared by adding a dielectric layer Diel, as shown in section (A). This dielectric layer can be formed, for example, by a stack of different types of dielectric layers selected from the materials mentioned above. The dielectric layer Diel can be produced directly on the carrier Sprt using various techniques known in the prior art, such as thermal oxidation or nitridation processes, LPCVD (low pressure chemical vapor deposition), PECVD (plasma enhanced chemical vapor deposition), or even chemical deposition using techniques known as PVD (physical vapor deposition) or ALD (atomic layer deposition).

[0041] The donor substrate Ferro shown in section (B) sub is the ferroelectric layer Ferro lay The donor substrate is a substrate that consists of a ferroelectric material or that includes a surface thickness of this material. Thus, by way of example, the donor substrate may be a solid substrate of lithium tantalate or lithium niobate, or even a substrate that includes a thickness of lithium tantalate or lithium niobate (at least Ferro lay The composite substrate can be formed by a first substrate having a thickness (equal to the thickness of the donor layer) on top of it. Preferably, the donor substrate has a first single-domain polarization P1 perpendicular to the implantation plane Imp, where hydrogen ions are implanted into the donor substrate. This orientation is conventionally achieved by selecting the growth mode of the crystal and its cutting plane.

[0042] Ferroelectric layer lay uses Smart Cut™ technology to fabricate ferroelectric donor substrates called Ferro sub In this case, the donor substrate must be prepared by introducing light species such as hydrogen or helium into the donor substrate. This introduction is called hydrogen implantation, i.e., the transfer of the donor substrate from Ferrosub As is known per se and as shown in section (B), the implanted hydrogen ions H + The ferroelectric layer Ferro of the ferroelectric material to be transferred is located on the side of the surface Imp. lay The remaining part of the substrate is then formed, and the ferroelectric layer is then deposited in a subsequent step. lay Another part separated from Ferro sep and a weakened surface Frgl that defines the

[0043] The type and dose of implanted species and the implant energy depend on the thickness of the layer to be transferred and the donor substrate Ferro sub In the case of a donor substrate made of LiTaO3, a ferroelectric layer of about 200-2,000 nm thick is selected as a function of the physicochemical properties of the substrate. lay To define 16 ~5.10 17 at / cm 2 It is possible to choose to implant a hydrogen dose in the range of 0.1 to 1.0.

[0044] Carrier Sprt and donor substrate Ferro sub Following the preparation of these two elements, the intermediate structure Struct is shown in section (C) of Figure 4. inter The carrier substrate Sprt is assembled by contacting the free surface of the dielectric layer with the implantation surface Imp of the donor substrate so as to obtain sub However, the present invention is not limited to such a configuration and different sizes and shapes may be employed.

[0045] Prior to assembly, it is possible to consider preparing the surface of the substrate to be assembled by cleaning, brushing, drying, polishing or plasma activation steps.

[0046] Assemble the donor substrate Ferro by molecular adhesion and / or electrostatic bonding. sub One function of the dielectric layer Diel formed on the carrier Sprt is to facilitate assembly. Instead, preferably, the dielectric layer Diel is formed on the donor substrate Ferro before the formation of the weakened surface Frgl. sub A dielectric layer Diel can be formed on the injection surface Imp of the carrier and donor substrate. It is also possible for the dielectric layer Diel to be formed in two parts, one on each of the carrier and donor substrates.

[0047] As is well known, the molecular adhesion method involves the bonding of a carrier (Sprt) and a donor substrate (Ferro). sub The exposed surfaces of the two bodies (one and / or the other covered with a dielectric layer to form the dielectric layer Diel) are perfectly clean, flat, and smooth and are brought into close contact to promote the development of molecular bonds, e.g., van der Waals bonds or covalent bonds, and the assembly of the two bodies is achieved without the use of adhesives.

[0048] Assembly can include applying a low temperature heat treatment (e.g., in the range of 50-300 °C, typically 100 °C) to correct any crystalline defects present in the ferroelectric layer and increase the binding energy sufficiently to allow for any subsequent thinning steps.

[0049] In this embodiment, the step of separating the part of the donor substrate is performed by applying the Smart Cut™ technology, according to which the ferroelectric layer Ferro lay The layer intended to form is defined by a weakened plane Frgl. After the assembly step, this layer is separated from the donor substrate by a fracture near the weakened plane Frgl and is therefore attached to the carrier Sprt.

[0050] Therefore, this separation step is performed to separate the ferroelectric layer Ferro layTo separate a part of the donor substrate from the substrate and transfer it to the carrier substrate, the intermediate structure is formed at a temperature range of about 80°C to 300°C. inter Alternatively or in addition to the heat treatment, this step can include applying a blade, a jet of gas or liquid fluid, or any other mechanical force to the weakened surface Frgl.

[0051] Instead of implementing the Smart Cut™ method described above, the step of separating a portion of the donor substrate can be performed by separating the ferroelectric donor substrate Ferro sub may be replaced by a chemical-mechanical thinning step.

[0052] Whether the removal of part of the thickness of the donor substrate is done by thinning or by fracturing, the ferroelectric layer Ferro lay However, any type of finishing treatment can be applied to the structure thus formed to enable it to comply with specifications regarding thickness, thickness uniformity, roughness, crystalline quality, or other types of specifications.

[0053] In particular, the ferroelectric layer Ferro with single-domain polarization lay The purpose of using this is to ensure the quality of the dielectric layer, and the ferroelectric layer lay A ferroelectric layer Ferro is deposited on a substrate, all with the aim of obtaining a single domain polarization of lay A specific process can be applied to

[0054] In fact, the assembly causes hydrogen to accumulate at the interface between the dielectric and ferroelectric layers, forming a gradient of hydrogen concentration, which leads to a decrease in the hydrogen concentration in the ferroelectric layer. lay Ferroelectric substrate Ferro sub This allows for multi-domain transformation of the portion of the ferroelectric layer in contact with the fabrication layer during the thermal treatment for separation from the fabrication layer.

[0055] Regarding the dielectric layer Diel, it is the ferroelectric layer Ferro layIt is possible to ensure that the ferroelectric layer has a lower hydrogen concentration than that present in the layer Ferroelectric. sep Hydrogen can be absorbed into the dielectric layer during the diffusion caused by the thermal treatment to separate the ferroelectric layers. This prevents hydrogen from accumulating at the assembly interface and avoids multi-domain transformation in the part of the ferroelectric layer close to this interface.

[0056] The hydrogen concentration in the dielectric layer Diel can be determined by, for example, the concentration of the deposited ferroelectric layer Ferro. lay This can be reduced by annealing the dielectric layer Diel to a temperature higher than the temperature of the preparatory heat treatment for the out-diffusion step, as described later in this specification. Thus, the layer can be annealed at temperatures of 600°C, 700°C, or even 800°C or higher. Thus, the average hydrogen concentration in the dielectric layer after this out-diffusion step is 5.10 20 at / cm 3 Less than, or advantageously, 10 18 at / cm 3 It may be less than.

[0057] Ferroelectric layer lay As regards the thickness of the thinned layer, a preparatory heat treatment can be applied to it, followed by a thinning step.

[0058] The preparatory heat treatment can correct the crystal defects present in the ferroelectric layer. layThis helps strengthen the bond between the ferroelectric layer and the carrier Sprt. If the temperature is high enough, it also has the effect of diffusing hydrogen contained in the ferroelectric layer and causing a multi-domain transformation of the surface portion of the ferroelectric layer. The thickness of this surface portion can be on the order of 50 nm or less and extend throughout the entire ferroelectric layer. Upon completion of the preparatory heat treatment, the ferroelectric layer has a relatively constant hydrogen concentration throughout its entire thickness. In the case of LiTaO3, this preparatory heat treatment is designed to bring the ferroelectric layer to a temperature ranging from 300°C to the Curie temperature of the ferroelectric material (preferably 450°C, 500°C, or 550°C or higher to promote hydrogen diffusion) for a duration ranging from 30 minutes to 10 hours. Preferably, this heat treatment is carried out by exposing the free surface of the dielectric layer to an oxidizing or neutral gas atmosphere, i.e., without covering this surface with a protective layer capable of preventing out-diffusion of hydrogen.

[0059] Following the preparatory heat treatment, the ferroelectric layer is thinned. This thinning can be done, for example, using mechanical, chemical-mechanical thinning, and / or chemical etching techniques to thin the ferroelectric layer. lay This allows the free surface to be prepared to exhibit a roughness limited to RMS 5×5 μm of less than 0.5 nm by atomic force measurement (AFM), and the ferroelectric layer Ferro lay Generally, the ferroelectric layer Ferro lay To achieve the target thickness, 100 to 300 nm is removed, and in all cases, the thickness is greater than the thickness of the multi-region surface portion. Thus, a thin single-region layer is formed with the required surface finish, crystalline quality, and polarization quality.

[0060] Selective polarization inversion as shown in FIGS. 1 to 3 applied to the structure shown in section (D) of FIG. 4 makes it possible to form the structure shown in section (D) of FIG.

[0061] Accumulation on a support - Solution 2 Solution 1 preferably consists of a donor substrate Ferro with a first single-domain polarization P1 perpendicular to the planar surface of the substrate. sub Then, to achieve two perpendicular polarizations of opposite directions in this ferroelectric layer, the ferroelectric layer of the resulting structure is fabricated. lay Selective polarization inversion can be applied to

[0062] This section discloses an alternative solution 2 to solution 1 in that instead of applying selective poling after assembly, selective poling is applied to the donor ferroelectric substrate before assembly, as shown in Figure 5.

[0063] Therefore, unless otherwise stated, the donor substrate Ferro sub Solution 1 can be referenced for all steps of the assembly method shown in Figure 5, including the alternative of thinning the donor substrate Ferro instead of fracturing it. sub has two perpendicular polarizations P1 and P2 in opposite directions. Such a substrate can be obtained, for example, from a single-domain polarization substrate by selective polarization inversion, as shown in Figures 1 to 3, and from the related manufacturing method. [Example]

[0064] Surface Acoustic Wave Device As shown in section (D) of Figure 5, by applying the selective polarization inversion method shown in Figures 1 to 3 to obtain a ferroelectric layer attached to a carrier and having two perpendicular polarizations P1 and P2 in opposite directions, for example, a surface acoustic wave device Dev can be fabricated from the ferroelectric layer whose polarization is selectively changed. SAW It is possible to manufacture

[0065] Such a device, as shown in FIG. 7, which shows a plan view of FIG. 7 and a cross-sectional view along the XX′ axis of FIG. 6, is conventionally formed by a ferroelectric layer Ferro layThe device has interdigitated electrodes formed directly on the ferroelectric layer. Using these electrodes El as a mask M, denoted as M / El in FIGS. 6 and 7, is advantageous during the selective introduction of hydrogen into the ferroelectric layer. In fact, this method allows for self-alignment of the inverted polarization volume V with the interdigitated electrodes M / El, resulting in the configuration shown in section (C3) of FIG. 3. For the features and manufacturing method of the device of FIGS. 6 and 7, please refer to the description of the device of FIGS. 1 to 5.

[0066] The material of the electrodes is a ferroelectric layer Ferroelectric in order to obtain a second polarization P2 opposite to the first polarization P1 in the hydrogen-enriched volume V. lay It is worth ensuring that the annealing in step S20 is compatible with the annealing intended to reverse the first polarization P1 of the film.

[0067] In this specification, the drawings are not necessarily to scale: some features and components may be shown enlarged relative to other components, or in somewhat schematic form, and some details of conventional elements may not be shown for clarity and conciseness.

[0068] Naturally, the invention is not limited to the described embodiments, and alternative embodiments can be applied without departing from the scope of the invention as defined by the claims.

Claims

1. A ferroelectric layer (Ferro) having a first polarization (P1) in a first zone and a second polarization (P2) opposite to the first polarization in a second zone (V) different from the first zone. lay ) a structure comprising: The first polarization and the second polarization are oriented perpendicular or oblique to the ferroelectric layer, the second polarization zone (V) has a higher hydrogen concentration than the first polarization zone, and the structure further comprises a carrier (Sprt) and a dielectric layer (Diel) interposed between the carrier and the ferroelectric layer. structure.

2. The hydrogen density in the second zone (V) is 10 19 ~10 22 atoms / cm 3 is in the range of The structure of claim 1 .

3. the first zone and the second zone define a periodic pattern; 3. The structure of claim 1 or 2.

4. the ferroelectric layer is formed of a single crystal; 4. A structure according to any one of claims 1 to 3.

5. the ferroelectric layer comprises lithium niobate or lithium tantalate; 5. A structure according to any one of claims 1 to 4.

6. the dielectric layer comprises silicon oxide; 6. A structure according to any one of claims 1 to 5.

7. the carrier comprises monocrystalline silicon; 7. A structure according to any one of claims 1 to 6.

8. A method for manufacturing a ferroelectric element (10), comprising the steps of: a ferroelectric element (10, Ferro) with a first polarization (P1) lay ) and - The ferroelectric element is charged with hydrogen ions (H + ) selectively enriching the annealing said ferroelectric element at a temperature ranging from 400°C to 700°C after introducing said hydrogen ions so as to switch said polarization (P1) of the ferroelectric layer in the volume (V) defined by the selective introduction of said hydrogen ions; A method comprising:

9. The polarization (P1) is a monodomain perpendicular or oblique to the plane (Sup) of the ferroelectric element; The method of claim 8.

10. said selective enrichment of said hydrogen ions is implemented by ion implantation of said hydrogen ions through a mask (M) defining areas of said ferroelectric element that are not to receive hydrogen ions; 10. The method according to claim 8 or 9.

11. The ion implantation of hydrogen ions is implemented at an energy level ranging from 3 keV to 210 keV.

11. The method according to any one of claims 8 to 10.

12. the selective introduction of the hydrogen ions is provided by an element (M / El) intended to form part of a surface acoustic wave device, 12. The method according to any one of claims 8 to 11.

13. The ferroelectric element (10, Ferro lay ) is a lithium niobate layer or a lithium tantalate layer; 13. The method according to any one of claims 8 to 12.

14. Ferroelectric substrate sub ) and a carrier (Sprt) are assembled, and then the ferroelectric element (Ferro lay separating or thinning the ferroelectric substrate to define a 14. The method according to any one of claims 8 to 13.

15. The carrier (Sprt) is a single crystal silicon substrate, and the dielectric layer (Diel) containing silicon oxide is a layer formed by stacking the single crystal silicon substrate and the ferroelectric substrate (Ferro). sub ) and 15. The method of claim 14.

16. The hydrogen ions (H + The dose of the selective enrichment by the volume (V) is 10 19 ~10 22 atoms / cm 3 adapted to obtain a hydrogen density in the range 16. The method according to any one of claims 8 to 15.

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