Integrated structure including a ferroelectric layer deposited on a substrate and having selective polarization in its thickness, and method of fabrication

Abstract

A ferroelectric layer (Ferro) having a first polarization (P1) in a first volume (V1) and a second polarization (P2) opposite to the first polarization in a second volume (V2) different from the first volume. lay ), wherein the first and second polarizations are oriented perpendicular or oblique to the ferroelectric layer, and the surface of the first volume (V1) is oriented perpendicular to the ferroelectric layer (Ferro lay ) surface (Sup), a first volume (V1) is interposed between the surface of the ferroelectric layer and a second volume (V2), the second volume (V2) having a higher hydrogen concentration (called polarity inversion concentration) than the first volume (V1), the polarity inversion concentration being 10 per cubic centimeter. 19 ~10 22 The structure is a range of hydrogen atoms.

Description

[Technical Field]

[0001] The present invention relates to an integrated structure including a ferroelectric layer deposited on a carrier, and to a method for fabricating the same. Such a structure can be used, for example, to form radio frequency (RF) components, particularly bulk acoustic wave components. [Background technology]

[0002] Several types of applications exist that utilize or are influenced by the polarization properties of ferroelectric materials and the existence of opposing polarization domains. These include surface acoustic wave (SAW) devices or bulk acoustic wave (BAW) devices. The existence of these applications has led to the development of methods for controlling the polarization domains in 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] Although the above-described structures and methods allow for effective control of the polarization domains of the ferroelectric layer on its surface, they remain impractical and do not allow for control of the polarization in the thickness of this layer and its integration on the substrate. Summary of the Invention

[0007] A first object of the present invention is to provide a ferroelectric polarization layer, optionally integrated on a substrate, having polarization regions with opposite perpendicular or oblique orientation relative to the plane of this layer, said regions being distributed in the thickness of the ferroelectric layer, which can be used for applications based on bulk acoustic waves, for example. A second object of the present invention is a manufacturing method for obtaining the above-mentioned integrated ferroelectric layer. A third object of the present invention is a method for locally and controlled reversal of the polarization of any ferroelectric element in its thickness.

[0008] To achieve these objects, a first aspect of the present invention provides a structure comprising a ferroelectric layer having a first polarization in a first volume and a second polarization opposite to the first polarization in a second volume different from the first volume, the first and second polarizations being oriented perpendicular or oblique to the ferroelectric layer, a surface of the first volume forming a plane of the ferroelectric layer, the first volume being interposed between this plane of the ferroelectric layer and the second volume, the second volume having a higher hydrogen concentration, referred to as a polarity inversion concentration, than the first volume, the polarity inversion concentration being greater than 10 per cubic centimeter. 19 ~10 22 This is the range of hydrogen atoms.

[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 is deposited, the polarization of which is perpendicular or oblique to the extension plane of the layer and the extension plane of the substrate, the polarization being modulated by the thickness of the ferroelectric layer. Such a structure facilitates the integration of bulk acoustic functions, for example, 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 structure may further comprise a carrier and a metal layer interposed between the carrier and the ferroelectric layer. The ferroelectric layer may be formed by a single crystal. The ferroelectric layer may comprise lithium niobate or lithium tantalate. 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; enriching a given embedded volume of the ferroelectric element with hydrogen ions by ion implantation of hydrogen ions through a face of the ferroelectric element, wherein the first volume of the ferroelectric element is interposed between the given embedded volume and the face of the ferroelectric element; and annealing the ferroelectric element at a temperature in the range of 500°C to 700°C after the introduction of hydrogen ions so as to switch the first polarization of the ferroelectric element in the given volume to a second polarization having an orientation opposite to the first polarization, wherein the first volume has the first polarization after annealing.

[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 polarization of the ferroelectric element can be controlled by its thickness and can be applied 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 first polarization can be monodomain, perpendicular or oblique to the plane of the ferroelectric element. During the selective enrichment of hydrogen ions, the implant dose of hydrogen ions is 10 per cubic centimeter. 19 ~10 22 The method can be adapted to obtain hydrogen concentrations in the range of 10 ... Hydrogen ion implantation can be implemented at energy levels ranging from 3 keV to 210 keV. 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, and the metal layer may be interposed between the monocrystalline silicon substrate and the ferroelectric substrate. [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] SUMMARY OF THE INVENTION A ferroelectric element having polarization selectively modified in its thickness and a corresponding method of fabrication are presented herein. [Figure 2] 2 illustrates another embodiment of the ferroelectric element of FIG. 1. [Figure 3] A first method for integrating a ferroelectric layer onto a carrier is presented. [Figure 4] A second method for integrating a ferroelectric layer onto a carrier is presented. [Figure 5] 1 is a schematic cross-sectional view of an apparatus according to the present disclosure. [Figure 6] 6 is a first variant of the device of FIG. 5. [Figure 7] 6 is a second variant of the device of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0016] Depth-selective polarization reversal After a series of experiments, applicants realized that it was possible to switch the polarization of the polarization domains by hydrogen implantation followed by annealing. These experimental results were implemented in the fabrication method described below, resulting in a ferroelectric element 10 having polarization-reversed domains at a depth 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 2 show a first embodiment, in which the ferroelectric element 10 is a ferroelectric single crystal itself, ie, independent of any 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 a first single-region polarization P1 perpendicular to upper and lower surfaces Sup and Inf, respectively, which are parallel to direction Z and parallel to the extension plane of the ferroelectric element 10, i.e., the crystal plane along 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 through the top surface Sup at an implantation energy level in the range of 3 keV to 210 keV. + The selective ion implantation of hydrogen enriches the silicon at a selective depth. The depth of the implantation and its extent in the Z direction are controlled by the implantation energy and the dose of the implanted hydrogen ions.

[0022] As shown in section (B) of Figure 1, this step S10 results in the formation of a relatively hydrogen-rich volume V2 (shown by cross-hatching in the figure) in the ferroelectric element 10, directly below the top surface Sup and on a relatively hydrogen-poor volume V1 (white region of the ferroelectric element 10), at a depth that depends on the acceleration energy of the implantation step. Thus, volume V2 is interposed between the unimplanted volume V1 and the top surface Sup of the ferroelectric element 10. The implantation dose is 10 19 ~10 22 atoms / cm 3 The implantation energy is adapted to obtain a hydrogen density in the range of . In order to better define the volume V2, it is possible to carry out several successive implantations at different implantation energy levels and doses, thereby homogenizing the distribution of hydrogen implanted in this volume.

[0023] At this stage, the polarization of the entire ferroelectric element 10 remains unchanged within the injected volume, and the regions of injected volume V2 and non-injected volume V1 still form a single monodomain in which the polarization has only one direction.

[0024] As an example, a 10 14 ~10 15 at / cm 2 A hydrogen ion implantation dose in the range of 10 to 150 nm can be used to create a polarization inversion volume V2 extending over about 50 nm in the thickness direction Z, where the hydrogen concentration in volume V2 is 10 to 150 nm. 19 ~10 22 , preferably 5.10 19 ~2.10 21 at / cm 3 In all cases, the hydrogen-enriched volume V2 has a higher hydrogen concentration (called the polarity reversal concentration) than the first volume V1.

[0025] In this specification, 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, perpendicular to the Z axis, which defines the extension direction of the thickness of the ferroelectric element 10. "Depth" is understood to mean the distance along the Z axis considered from the top surface Sup. Furthermore, modulation of the polarization or hydrogen concentration of the ferroelectric element 10 in its thickness is understood to be a change in the hydrogen concentration or a change in the direction of polarization in the Z direction in the volume of this element, respectively.

[0026] In step S20, the hydrogen-enriched ferroelectric element 10 is annealed at a temperature ranging from 500°C to 800°C, preferably from 500°C to 700°C, and more preferably from 550°C to 600°C. This annealing step induces a first polarization P1 of the ferroelectric element 10 only in the hydrogen-enriched volume V2 to produce a second polarization P2 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 but in the same direction. Defining volume V2 by hydrogen enrichment allows the polarization reversal to be selective, propagating from the top surface Sup throughout volume V2, thus transitioning from a parallel polarization between volumes V1 and V2 to an antiparallel polarization between volumes V1 and V2. 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.

[0027] The hydrogen concentration in volume V2 obtained after step S10 is necessary for the polarization reversal obtained in step S20 and for this reason can be called the polarization reversal concentration.

[0028] Sections (C1) and (C2) of FIG. 2 show alternative embodiments of volume V2 obtained by adjusting the number of implants and their respective energy levels and doses. In section (C1), the implant energy was sufficient to enrich a portion of the ferroelectric element 10 away from surface Sup and reaching the lower surface Inf. Thus, volume V2 extends from the lower surface Inf of the ferroelectric element, while unimplanted volume V1 remains on the upper surface Sup side, resulting in the surface of volume V1 forming the surface (Sup) of the ferroelectric layer. In section (C2), hydrogen enrichment of an appropriate concentration affects the entire volume of the ferroelectric element 10, and polarization reversal is effective throughout the entire crystal thickness, such that volume V1 disappears and is completely replaced by volume V2. These alternative embodiments can be obtained by using a hydrogen ion implantation sequence with appropriate parameters.

[0029] 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, such as a ferroelectric crystal attached to a support, as will become apparent throughout the remainder of this disclosure.

[0030] On-substrate integration - Solution 1 The above-described method of selective polarization inversion by depth of a ferroelectric layer is shown in Figures 1 and 2 as applied to a single ferroelectric crystal used as a ferroelectric element 10. This method of selective polarization inversion by depth can also be applied to an assembly formed by ferroelectric crystals integrated on a substrate, which assembly can then form the ferroelectric element 10 shown in Figures 1 and 2.

[0031] Integration onto a substrate can be performed as described below with reference to FIG. 3 and with particular reference to WO 2020 / 200986 A1, which describes the deposition of a thin single-domain ferroelectric layer onto a substrate.

[0032] FIG. 3 shows a method for manufacturing the integrated structure Struct shown in section (D), which includes forming a ferroelectric layer Ferro attached to a carrier Sprt. lay and a conductive metal layer M1 interposed between these two elements. In this example, the metal layer M1 is formed by the carrier Sprt and the ferroelectric layer Ferro. lay The layer M1 is then in direct contact with the ferroelectric layer Ferro lay The presence of metal layer M1 represents just one option; applications other than that of this example do not require the presence of such a layer.

[0033] Conventionally, the structure Struct can be in the form of a circular wafer having a diameter of 100, 200, 300, or 450 mm, although the invention is not limited to these dimensions or this shape.

[0034] Ferroelectric layer lay The 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.

[0035] 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, for example, 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 easily mobile charges, holes, or electrons, which can affect the correct operation of RF components formed based on the structure. However, the present invention is not limited to carriers with such characteristics.

[0036] The thickness of the metal layer can range from a few nanometers to a few microns, for example, 100 nm or more, and can be formed in a single layer or a combination of layers, typically from metals such as chromium, nickel, aluminum, platinum, titanium, tungsten, gold, etc., or any combination of these elements with each other or with other metallic elements.

[0037] Referring to FIG. 3, the structure Struct can be fabricated by a layer deposition fabrication method, which includes: - providing a support Sprt as shown in section (A), in this case forming a metal layer M1 on its surface; Optionally, a ferroelectric donor substrate, Ferro, as shown in section (B) sub To prepare and - The intermediate structure shown in section (C) inter The first surface of the carrier Sprt and the ferroelectric donor substrate Ferro sub The metal layer M1 is assembled with the carrier Sprt and the ferroelectric substrate Ferro sub and interposing between the donor surface of the - Ferroelectric layer on the support Sprt layand remove the donor substrate Ferro from the intermediate structure to obtain the structure shown in section (D). sub and separating a portion of the

[0038] 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 donor substrate may be formed by a composite substrate formed by a first substrate having thereon a first single-domain polarization P1 perpendicular to the implantation plane Imp, which allows hydrogen ions H + is implanted into the donor substrate with a view to the subsequent separation step. This orientation is conventionally achieved by choosing the growth mode of the crystal and its cleavage plane.

[0039] 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 Ferro sub 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

[0040] 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.

[0041] forming a metal layer M1 on the carrier or donor substrate; sub Following the preparation of these two devices, the metal layer M1 is the support Sprt and the ferroelectric layer Ferro lay The ferroelectric layer faces the carrier Sprt, and the intermediate structure Struct shown in section (C) of FIG. inter The carrier substrate Sprt is attached to the donor substrate Ferro. sub However, the present invention is not limited to such a configuration and different sizes, shapes, and configurations may be employed.

[0042] 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.

[0043] The assembly is carried out by molecular adhesion and / or electrostatic bonding to the donor substrate Ferro, as described for example in patent application FR 2 914 492. sub can include bringing the carrier Sprt into intimate contact with the carrier Sprt.

[0044] As is well known, in the molecular adhesion method, a perfectly clean, flat, and smooth support (Sprt) and a donor substrate (Ferro) are used. subThe exposed surfaces of the two bodies are brought into intimate contact to promote the formation of electrostatic or, for example, van der Waals or covalent molecular bonds. Assembly of the two bodies is then achieved without the use of adhesives.

[0045] 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.

[0046] 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.

[0047] Therefore, this separation step is performed to separate the ferroelectric layer Ferro lay To 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.

[0048] 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.

[0049] Whether the removal of part of the thickness of the donor substrate is done by thinning or by fracturing, the ferroelectric layer Ferro layHowever, 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.

[0050] In particular, the ferroelectric layer Ferro with single-domain polarization lay In order to use the ferroelectric layer, a ferroelectric layer is attached to a substrate. lay The purpose of this is to provide a specific treatment to the ferroelectric layer Ferro lay The goal is to obtain a single-region polarization.

[0051] For example, the ferroelectric layer Ferro lay A preparatory heat treatment can be applied to the thinning step.

[0052] The preparatory heat treatment can correct the crystal defects present in the ferroelectric layer. lay This can also help strengthen the bond between the ferroelectric layer and the carrier Sprt. If the temperature is high enough, it can also cause diffusion of hydrogen contained in the ferroelectric layer and 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. Once the preparatory heat treatment is complete, 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 that can prevent hydrogen outdiffusion.

[0053] 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, 50 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.

[0054] Following the above operations, selective polarization inversion shown in FIGS. 1 and 2 applied to the structure Struct shown in section (D) of FIG. 3 makes it possible to form the structure Struct shown in section (D) of FIG. 4.

[0055] 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

[0056] 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 4.

[0057] Therefore, unless otherwise stated, the donor substrate Ferro sub Solution 1 can be referenced for all steps of the assembly method shown in Figure 4, including the alternative of thinning the donor substrate Ferro instead of fracturing it. subhas 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 reversal according to depth, as shown in Figures 1 and 2, and from the related manufacturing method.

[0058] This solution involves the creation of a ferroelectric layer, Ferro, whose surface polarization is controlled without the use of high energy implants. lay This allows you to obtain

[0059] This solution is to determine whether the volume V1 or the volume V2 is the ferroelectric layer in the structure shown in section (D) of FIG. lay In fact, depending on the depth position of the weakened surface Frgl, the weakened surface can be located (1) in the volume V1 or (2) in the volume V2 (position not shown), as shown in FIG. 4. In the first case, as shown in FIG. 4, the ferroelectric layer Ferro lay Located on the free surface of is volume V1 and therefore polarization P1, and volume V2 is buried below volume V1. In the second case, the ferroelectric layer Ferro lay Located on the free surface of is volume V2 and therefore polarization P2, and volume V1 is buried below volume V2.

[0060] Instead, based on the structure shown in section (D) of Figure 4, a ferroelectric layer Ferro lay Optionally, a chemical mechanical polishing step is applied to the volume V2 until the surface of the ferroelectric layer Ferro is exposed. lay This allows the layer to be thinned to form a free surface.

[0061] Alternative Embodiments The above example shown in Figs. 3 and 4 is a ferroelectric layer consisting of a carrier Sprt and a ferroelectric layer Ferro. lay Optionally, the structure explicitly includes only one metal layer M1 located between the carrier Sprt and the ferroelectric layer Ferro. lay The interface between the metal layer and the substrate may include an additional metal layer or an optional dielectric layer.

[0062] FIG. 5 shows a structure Struct including a second metal layer M2 located on the surface of the ferroelectric layer Ferro lay is interposed between two metal layers M1 and M2. This configuration can be used as part of a bulk acoustic wave device, where the metal layers M1 and M2 are interposed between a ferroelectric layer Ferro lay It functions as an electrode for applying an electric field to the

[0063] 6 shows a structure Struct further comprising a first dielectric layer, such as an oxide layer Ox1, interposed between the substrate Sprt and the first metal layer M1. This is the case, for example, when the metal layer M1 is interposed between the ferroelectric layer Ferro lay A dielectric layer Ox1 is formed on the carrier Sprt, and then a ferroelectric layer Ferro lay may be the result of a method for producing a structure Struct assembled on a carrier Sprt by bringing a metal layer into intimate contact with a dielectric layer, in this case an oxide-metal contact, using a method similar to that described in connection with FIG. 3 .

[0064] 7 shows a structure Struct similar to that of FIG. 6, further including a second dielectric layer, such as an oxide layer Ox2, interposed between the first metal layer M1 and the first dielectric layer Ox1. This is the case, for example, when the metal layer M1 and the second dielectric layer Ox2 are interposed between the dielectric layer Ferro lay The dielectric layer Ox1 is formed on the carrier Sprt, and then the ferroelectric layer Ferro lay may be the result of a method for producing a structure Struct assembled on a carrier Sprt by bringing two dielectric layers Ox1 and Ox2 into intimate contact, in this case a dielectric-dielectric contact, more particularly an oxide-oxide contact in this example, using a method similar to that described in connection with FIG. 3 .

[0065] The two methods described above in connection with Figures 6 and 7 are just two examples, and other methods can be contemplated, resulting in the same result or other alternative embodiments of the structure. Thus, a ferroelectric layer, Ferro, can be formed by forming a stack of layer pairs including a layer of SiO2 and a layer of HfSO2, or a layer of SiO2 and a layer of Mo, or other structures and materials known for forming Bragg mirrors. lay A Bragg mirror can be formed adjacent to, preferably between this layer and the carrier Sprt, for example, under the metal layer M1. The metal layer M2 can have the same composition as the layer M1 or a different composition. The oxide layers Ox1 and Ox2 can be, for example, silicon oxide layers or silicon nitride oxide layers.

[0066] Furthermore, the carrier Sprt can be prepared by adding a dielectric layer which can be formed from a stack of different types of dielectric layers, which 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 vapor deposition using techniques known as PVD (Physical Vapor Deposition) or ALD (Atomic Layer Deposition).

[0067] By assembling the carrier with the ferroelectric layer, hydrogen can be accumulated at the interface between them, forming a gradient of hydrogen concentration, e.g., lay Ferroelectric substrate Ferro sub This allows for multi-domain transformation of the portion of the ferroelectric layer close to this interface during the thermal treatment to separate it from the ferroelectric layer.

[0068] Ferroelectric layer lay The metal layer and any dielectric layer adjacent to the ferroelectric layer Ferro lay The hydrogen concentration in the ferroelectric layer can be guaranteed to be lower than the hydrogen concentration present in the layer Ferroelectric. sepDuring the diffusion induced by the thermal treatment to separate the ferroelectric layers, hydrogen can be absorbed into these adjacent layers, thereby preventing hydrogen from accumulating at the assembly interface and avoiding multi-domain transformation in the part of the ferroelectric layer close to this interface.

[0069] The hydrogen concentration in the metal layer and any dielectric layer can be determined, for example, by the amount of hydrogen in the deposited ferroelectric layer Ferro lay This can be reduced by an annealing step aimed at heating these adjacent layers to a temperature higher than the temperature of the preparatory heat treatment for the outdiffusion step, which will be described later in this specification. This layer can therefore be subjected to an annealing temperature of 600°C, 700°C, or even 800°C or higher. The average hydrogen concentration in the dielectric layer after this outdiffusion step is therefore 5.10 20 at / cm 3 Less than, or advantageously, 10 18 at / cm 3 It may be less than.

[0070] Although the examples presented herein are limited to a continuous volume V2 forming a single layer of reversed polarization across the thickness of the ferroelectric layer, it is possible to create a pair of such volumes V2 extending from two opposing surfaces of the piezoelectric layer, with a volume V1 having unreversed polarization, and thus an opposite volume V1 of the two volumes V2, interposed between these two volumes V2. The two distinct volumes V2 can be formed by performing several successive implantations of hydrogen ions at different acceleration energy levels and, therefore, different implantation depths, thereby defining two volumes V2, each opening onto the surface of the ferroelectric layer and having a thickness that is a function of the associated implantation energy level. In this way, alternating opposite polarizations across the thickness of the ferroelectric layer can be obtained.

[0071] Application Examples Each of the structures shown in Figures 5, 6 and 7 can form a bulk acoustic wave device or can be integrated into such a device to form, for example, a BAW bandpass filter.

[0072] Using digital simulations, it was determined that such a device would have reduced frequency sensitivity to thickness, improved power efficiency, and the energy density of the layer would be distributed throughout the thickness of the ferroelectric layer.

[0073] The drawings herein 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.

[0074] 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 volume (V1) and a second polarization (P2) opposite to the first polarization in a second volume (V2) different from the first volume. lay ) a structure comprising: The first and second polarizations are oriented perpendicular or oblique to the ferroelectric layer, and the surface of the first volume (V1) is lay ) surface (Sup), and the first volume (V1) is interposed between the surface of the ferroelectric layer and the second volume (V2), the second volume (V2) has a higher hydrogen concentration (called the polarity reversal concentration) than the first volume (V1); The polarity reversal concentration is 10 per cubic centimeter 19 ~10 22 is the range of hydrogen atoms, structure.

2. Further comprising a carrier (Sprt) and a metal layer (M1) interposed between the carrier and the ferroelectric layer; The structure of claim 1 .

3. the ferroelectric layer is formed of a single crystal; 3. A structure according to any one of claims 1 to 2.

4. the ferroelectric layer comprises lithium niobate or lithium tantalate; 4. A structure according to any one of claims 1 to 3.

5. the carrier comprises monocrystalline silicon; 3. The structure of claim 2.

6. A method for manufacturing a ferroelectric element (10), comprising the steps of: a ferroelectric element (10, Ferro) with a first polarization (P1) lay ) and - Hydrogen ions (H + ) by ion implantation, a given buried volume (V2) of the ferroelectric element is filled with the hydrogen ions (H + ), wherein a first volume (V1) of the ferroelectric element (10) is interposed between the given embedded volume (V2) and the surface (Sup) of the ferroelectric element; - annealing the ferroelectric element at a temperature in the range of 500°C to 700°C after introducing the hydrogen ions so as to switch the first polarization (P1) of the ferroelectric element in the given volume (V2) to a second polarization (P2) having an orientation opposite to the first polarization (P1), wherein the first volume (V1) has the first polarization (P1) after the annealing; A method comprising:

7. The first polarization (P1) is a monodomain perpendicular or oblique to the plane (Sup) of the ferroelectric element; The method of claim 6.

8. During the selective enrichment of hydrogen ions, hydrogen ions (H + ) is implanted at a dose of 10 per cubic centimeter in the given volume (V2). 19 ~10 22 adapted to obtain a hydrogen concentration in the range of hydrogen atoms, 8. The method according to claim 6 or 7.

9. said ion implantation of hydrogen ions is implemented at an energy level in the range of 3 keV to 210 keV; 9. The method according to any one of claims 6 to 8.

10. The ferroelectric element (10, Ferro lay ) is a lithium niobate layer or a lithium tantalate layer; 10. The method according to any one of claims 6 to 9.

11. 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 11. The method according to any one of claims 6 to 10.

12. The carrier (Sprt) is a single crystal silicon substrate, and the metal layer (M1) is a layer formed by bonding the single crystal silicon substrate and the ferroelectric substrate (Ferro sub ) and The method of claim 11.

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