Substrate-mounted integrated structures including ferroelectric layers with selective reversal polarization in thickness and methods of making same

Abstract

The structure comprises a ferroelectric layer having a first polarization (P1) in a first volume (V1) and a second polarization (P2) opposite the first polarization in a second volume (V2) different from the first volume, the first polarization and the second polarization being oriented perpendicular or oblique to the ferroelectric layer, wherein a surface of the first volume (V1) forms a face (Sup) of the ferroelectric layer and the first volume (V1) is interposed between the face of the ferroelectric layer and the second volume (V2), the second volume (V2) having a higher hydrogen concentration, referred to as a polarity reversal concentration, than the first volume (V1), and the polarity reversal concentration ranges from 1019 to 1022 hydrogen atoms per cubic centimeter.

Description

Technical Field

[0001] The present invention relates to an integrated structure comprising a ferroelectric layer attached to a carrier and to a method for manufacturing the structure. Such a structure can be used, for example, to form radio frequency (RF) components, in particular bulk elastic wave components. Background Art

[0002] There are several types of applications that utilize the polarization properties of ferroelectric materials and the presence or influence of polarization domains that are opposite to each other. These applications 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 of ferroelectric layers.

[0003] The article entitled "Seeing Is Believing-In-Depth Analysis by Co-Imaging of Periodically-Poled X-Cut Lithium Niobate Thin Films" (Sven Reitzig et al., published in the journal Crystals, November 2021, page 288) describes a lithium niobate layer integrated on a silicon substrate by means of a silicon dioxide layer, and the polarization of the layer parallel to its plane of extension is controlled by applying a voltage between electrodes periodically arranged on the free surface of the layer. It should be noted that in such a structure comprising only electrodes on the only free face of the crystal, in the absence of embedded electrodes, controlling the polarization perpendicular to the substrate by means of an electric field would require a voltage, which would risk causing breakdown of the silicon dioxide layer.

[0004] Document EP 0592226 A1 describes an optical frequency conversion device obtained by periodically juxtaposing parallel strips of opposite polarization on the face of a ferroelectric substrate, the substrate having a spontaneous polarization perpendicular to the plane of extension of the substrate (i.e., perpendicular to the face). The polarization reversal of the strips is achieved 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 face of the ferroelectric crystal by applying an electric field along juxtaposed periodic strips, with the aid of gel electrodes placed on one face of the ferroelectric crystal and on the face opposite the crystal.

[0006] The above structures and methods, although allowing efficient control of the polarization domains of the ferroelectric layer at its surface, are still impractical and do not allow control of the polarization through the thickness of the layer and its integration on a carrier. Summary of the Invention

[0007] A first object of the present invention is to provide a ferroelectric polarization layer, optionally in the form of an integrated layer on a substrate, the ferroelectric polarization layer having polarization domains with opposite and perpendicular or inclined orientations relative to the plane of the layer, wherein the domains are distributed over the thickness of the ferroelectric layer, wherein the ferroelectric layer can be used, for example, for applications based on bulk acoustic waves. 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 over its thickness.

[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 volume and a second polarization opposite to the first polarization in a second volume different from the first volume, wherein the first polarization and the second polarization are oriented perpendicular to or obliquely to the ferroelectric layer, a surface of the first volume forms a face of the ferroelectric layer and the first volume is interposed between the face of the ferroelectric layer and the second volume, the second volume having a higher hydrogen concentration than the first volume, referred to as the polarity reversal concentration, and the polarity reversal concentration is in the range of 10 0 ... 19 hydrogen atoms to 10 22 hydrogen atoms.

[0009] The advantage of the structure according to the invention is that it provides an integrated structure comprising a substrate to which is attached a ferroelectric layer having a perpendicular or tilted polarization relative to the plane of extension of the layer and the substrate, wherein the polarization is modulated over the thickness of the ferroelectric layer. Such a structure facilitates the integration of, for example, bulk acoustic functions while maintaining low cost.

[0010] Additional non-limiting features according to the first aspect of the invention, considered alone or in any technically feasible combination:

[0011] - the structure may further comprise a carrier and a metal layer interposed between the carrier and the ferroelectric layer;

[0012] - The ferroelectric layer can be formed from a single crystal;

[0013] - the ferroelectric layer may comprise lithium niobate or lithium tantalate;

[0014] - The carrier may comprise single-crystalline silicon.

[0015] A second aspect of the present invention relates to a method for manufacturing a structure having a locally controlled polarization, the method comprising the following steps: providing a ferroelectric element having a first polarization; enriching a given embedding volume of the ferroelectric element with hydrogen ions by ion implantation of hydrogen ions through a surface of the ferroelectric element, wherein the first volume of the ferroelectric element is interposed between the given embedding volume of the ferroelectric element and the surface; and annealing the ferroelectric element at a temperature of 500°C to 700°C after the introduction of the 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.

[0016] The advantage of the method according to the invention is that it is simple, flexible and can be easily integrated into a wider range of manufacturing methods based on known and mature manufacturing technologies from the semiconductor industry. In addition, it allows the polarization of the ferroelectric element to be controlled over its thickness and is suitable for integration into thin layers on a substrate.

[0017] Additional non-limiting features according to the second aspect of the invention, considered alone or in any technically feasible combination:

[0018] - the first polarization may be mono-domain, perpendicular or tilted relative to the plane of the ferroelectric element;

[0019] - During the selective enrichment of hydrogen ions, the hydrogen ion implantation dose can be adjusted to obtain a range of 10 per cubic centimeter. 19 hydrogen atoms to 10 22 The hydrogen concentration of hydrogen atoms;

[0020] - hydrogen ion implantation can be performed at energy levels ranging between 3 keV and 210 keV;

[0021] - the ferroelectric element may be a lithium niobate or lithium tantalate layer;

[0022] - the method may further comprise assembling the ferroelectric substrate and the carrier, and then separating or thinning the ferroelectric substrate so as to define the ferroelectric element; and

[0023] The carrier may be a single crystal silicon substrate, and the metal layer may be interposed between the single crystal silicon substrate and the ferroelectric substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Additional features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings, in which:

[0025] [ Figure 1 ] Figure 1 A ferroelectric element with selectively modified polarization in thickness and a corresponding manufacturing method according to the present description are shown;

[0026] [ Figure 2 ] Figure 2 Shown Figure 1 Alternative embodiments of the ferroelectric element;

[0027] [ Figure 3 ] Figure 3 A first method for integrating a ferroelectric layer on a carrier is shown;

[0028] [ Figure 4 ] Figure 4 A second method for integrating a ferroelectric layer on a carrier is shown;

[0029] [ Figure 5 ] Figure 5 is a schematic cross-sectional view of a device according to the present specification;

[0030] [ Figure 6 ] Figure 6 yes Figure 5 A first variant of the device; and

[0031] [ Figure 7 ] Figure 7 yes Figure 5 A second variant of the device. DETAILED DESCRIPTION

[0032] Selective polarization reversal via depth

[0033] After a series of experiments, the applicant has realized that the polarization of the polarization domains can be switched by hydrogen implantation followed by annealing. These experimental results are implemented in the manufacturing method described below, resulting in a ferroelectric element 10 with reversed polarization domains at a depth chosen by the practitioner.

[0034] The ferroelectric element 10 may thus be a ferroelectric single crystal, which may be in the form of a ferroelectric single crystal layer, which ferroelectric crystal or the ferroelectric single crystal layer may be attached to a carrier Sprt within the structure Struct, such as Figure 3 The ferroelectric layer shown in the cross section (D) lay .

[0035] Figure 1 and Figure 2 A first embodiment is shown, in which the ferroelectric element 10 is a ferroelectric single crystal itself, ie independent of any carrier.

[0036] Figure 1Section (A) shows a cross section of the ferroelectric element 10 in the plane ZX, which has two opposite faces Sup and Inf perpendicular to the direction Z and has a first single domain polarization P1 parallel to the direction Z and perpendicular to the upper Sup face and the lower Inf face, each of which is parallel to the extension plane of the ferroelectric element 10, that is, the crystal face with the largest size.

[0037] For illustrative purposes, this embodiment uses an example of polarization perpendicular to the extension plane of the ferroelectric element 10. However, the present invention is also applicable to the case where the polarization is not perpendicular to the extension plane of the ferroelectric element 10, but is tilted thereto. The "perpendicular" feature refers to a tilt of 90° with an accuracy of within 10° relative to the extension plane of the ferroelectric element, and the "tilted" or "obliquely" feature refers to a tilt of at least 5° away from the extension plane of the ferroelectric element. Therefore, a direction with a tilt in the range of 5° to 80°, or 30° to 70°, or even 35° to 60° can be considered to be tilted. For example, a LiTaO350RY layer and a LiTaO342RY layer have polarizations tilted by 50° and 42°, respectively, relative to the extension plane of the layer, and therefore have tilted polarization relative to the extension plane of the layer.

[0038] In step S10, hydrogen ions H are injected through the upper surface Sup at an implantation energy level ranging between 3 keV and 210 keV. + By selective ion implantation, hydrogen is enriched at a selective depth in the ferroelectric element 10. The implantation depth and its extent in the direction Z are controlled by the implantation energy and dose of the implanted hydrogen ions.

[0039] like Figure 1 As shown in the cross section (B) of the ferroelectric element 10, this step S10 results in the formation of a relatively hydrogen-rich volume V2 (indicated by the cross-hatching in the figure) in the ferroelectric element 10, which is directly below the upper surface Sup and above the relatively hydrogen-poor volume V1 (white area of ​​the ferroelectric element 10), and has a depth that depends on the acceleration energy of the implantation step. Therefore, the volume V2 is interposed between the non-implanted volume V1 and the upper surface Sup of the ferroelectric element 10. The implantation dose is adapted to the implantation energy so as to obtain in the volume V2 a volume in the range of 10 19 atoms / cm 3 with 10 22 atoms / cm 3 Several consecutive implantations may be performed with different implantation energy levels and doses in order to better define volume V2 and to homogenize the distribution of the hydrogen implanted in this volume.

[0040] At this stage, the polarization of the entire ferroelectric element 10 remains unchanged in the implanted volume, wherein the regions of the implanted volume V2 and the non-implanted volume V1 still form a single monodomain in which the polarization has only one orientation.

[0041] For example, the range accelerated by a voltage of 6 kV is 10 14 atoms / cm 2 to 10 15 atoms / cm 2 The dose of implanted hydrogen ions can be used to form a polarization reversal volume V2 extending about 50 nm in the thickness direction Z, in which the hydrogen concentration ranges from 10 19 atoms / cm 3 with 10 22 atoms / cm 3 between 5×10 19 atoms / cm 3 With 2×10 21 atoms / cm 3 In all cases, the hydrogen-rich volume V2 has a higher hydrogen concentration, referred to as the polarity reversal concentration, than the first volume V1.

[0042] In this document, the YX plane and the ZX plane are defined by the X, Y, and Z axes of an orthogonal reference system, where the YX plane is defined by the Y and X axes of the reference system, and the ZX plane is defined by the Z and X axes of the reference system. The surfaces Sup and Inf of the ferroelectric element 10 extend parallel to the YX plane and perpendicular to the Z axis, which defines the direction of extension of the thickness of the ferroelectric element 10. "Depth" is understood to mean the distance along the Z axis from the upper surface Sup. Furthermore, a modulation of the polarization or hydrogen concentration of the ferroelectric element 10 across its thickness is understood to mean a change in the hydrogen concentration or a change in the polarization direction within the volume of the element in the direction Z.

[0043] In step S20, the selectively hydrogen-enriched ferroelectric element 10 is annealed at a temperature ranging from 500° C. to 800° C., preferably from 500° C. to 700° C., 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 V2, so as to produce a second polarization P2 having the same alignment direction as the first polarization P1, but in the opposite direction thereof, as shown in the cross section (C0). Antiparallel polarization is defined as polarization aligned in parallel directions but in opposite directions. Conversely, parallel polarization is defined as polarization aligned in parallel directions but in the same direction. Delimiting the volume V2 by hydrogen enrichment allows the polarization reversal to be selective, propagating from the upper surface Sup to the entire volume V2, and thus transforming from a parallel polarization between the volumes V1 and V2 to an antiparallel polarization between the volumes V1 and V2. Annealing is preferably performed in an oxygen atmosphere to reduce outdiffusion of oxygen from the ferroelectric layer, but may also be performed, for example, in a nitrogen or air atmosphere at atmospheric pressure and for a duration ranging between 100 seconds and 10 hours.

[0044] The hydrogen concentration in the volume V2 obtained after step S10 is necessary for the polarization reversal obtained in step S20 and for this reason may be referred to as a polarization reversal concentration.

[0045] Figure 2 Cross sections (C1) and (C2) show alternative embodiments of the volume V2 obtained by adjusting the number of implantations and their corresponding energy levels and doses. In cross section (C1), the implantation energy is sufficient to enrich a portion of the ferroelectric element 10 that is spaced apart from the surface Sup and reaches the lower surface Inf. Thus, the volume V2 extends from the lower surface Inf of the ferroelectric element, while leaving a non-implanted volume V1 on the side of the upper surface Sup, so that the surface of the volume V1 forms the face (Sup) of the ferroelectric layer. In cross section (C2), hydrogen enrichment with a suitable concentration has affected the entire volume of the ferroelectric element 10, and the polarization reversal is effective over the entire thickness of the crystal, so that the volume V1 disappears and is completely replaced by the volume V2. These alternative embodiments can be obtained by using a hydrogen ion implantation sequence with suitable parameters.

[0046] As already mentioned, this first embodiment is illustrative and is not limited to controlling the polarization of a single ferroelectric crystal, but is also applicable to more complex structures, such as a ferroelectric crystal attached to a support, as will become apparent in the remainder of this disclosure.

[0047] Integration on substrate - Solution 1

[0048] exist Figure 1 and Figure 2 The above-described method for selective polarization reversal by depth in a ferroelectric layer is shown in FIG, whereby the method is applied to a single ferroelectric crystal used as a ferroelectric element 10. This method for selective reversal by depth can also be applied to an assembly formed of ferroelectric crystals integrated on a substrate, which assembly can then form Figure 1 and Figure 2 The ferroelectric element 10 is shown.

[0049] Please refer to the following Figure 3 And the integration on the substrate is performed as described with reference to publication WO 2020 / 200986 A1, which specifically describes attaching a single-domain ferroelectric thin layer to a substrate.

[0050] Figure 3 A method for manufacturing an integrated structure Struct shown in cross section (D) is shown, comprising a ferroelectric layer Ferro attached to a carrier Sprt. lay , wherein the conductive metal layer M1 is interposed between the two elements. In this example, the metal layer M1 is connected to the carrier Sprt and the ferroelectric layer Ferro layThe layer M1 can then be used as a direct contact to the ferroelectric layer Ferro lay Embedded electrodes applying the electric field. The presence of the metal layer M1 represents only an option and applications other than that of this example do not require the presence of such a layer.

[0051] Typically, the structure Struct may be in the form of a circular wafer having a diameter of 100 mm, 200 mm, 300 mm or even 450 mm, but the invention is in no way limited to these sizes or this shape.

[0052] Ferroelectric layer lay Made of single crystal ferroelectric material, such as lithium tantalate LiTaO3 or lithium niobate LiNbO3, or even made of materials such as LiAlO3, BaTiO3, PbZrTiO3, KNbO3, BaZrO3, CaTiO3, PbTiO3 or KTaO3. These materials also have piezoelectric properties. Generally speaking, the thickness of the ferroelectric layer can range between 10 nanometers and 10 microns, depending on the envisaged application of the structure Struct and the expected performance capabilities of the component, but the present invention does not exclude the use of different thicknesses, which still depends on the envisaged application. As a reminder, ferroelectric materials are materials that have an electric polarization in their natural state, which can be reversed by applying an external electric field greater than the coercive field of the material. As shown in this document, the ferroelectric layer preferably has a first single domain polarization P1, that is, all dipole moments are aligned parallel to each other in a given direction. In this case, the given direction is a direction perpendicular to the plane of the ferroelectric layer, that is, perpendicular to the free surface of the layer, or even perpendicular to the surface plane of the layer.

[0053] For reasons of availability and cost, for its part, the carrier Sprt is preferably selected from silicon. It can be a carrier made of a substrate based on solid single crystal silicon, but the present invention is not limited to this carrier, and more generally, the carrier can be made of any material, such as silicon, or even electrically insulating materials such as sapphire or glass. When formed from a solid substrate, the thickness of the carrier Sprt is typically several hundred microns. In single crystal silicon, the carrier Sprt is conductive, but preferably has a high resistivity of greater than 1,000 ohms. This limits the density of any charges, holes or electrons that can move easily, which may affect the correct operation of the RF components formed based on the structure Struct. However, the present invention is not limited to carriers with such characteristics.

[0054] The thickness of the metal layer can range between a few nanometers and a few micrometers, for example, more than 100 nm. The metal layer can generally be formed of a metal such as chromium, nickel, aluminum, platinum, titanium, tungsten, gold, or any combination of these elements with each other or with other metal elements in a single layer or a combination of layers.

[0055] refer to Figure 3The structure Struct can be produced by a layer attachment manufacturing method, the method comprising:

[0056] - preparing a support Sprt shown in section (A), in this case forming a metal layer M1 on its surface;

[0057] - Optionally prepare the ferroelectric donor substrate Ferro shown in cross section (B) sub ;

[0058] - Assemble the first side of the carrier Sprt and the ferroelectric donor substrate Ferro sub to form the intermediate structure Struct shown in the cross section (C) inter , wherein the metal layer M1 is inserted between the carrier Sprt and the ferroelectric substrate Ferro sub between the donor surfaces; and

[0059] -Put the donor substrate Ferro sub A portion of the structure is separated from the intermediate structure to define the ferroelectric layer Ferro on the carrier Sprt lay And the structure Struct shown in the cross section (D) is obtained.

[0060] The donor substrate Ferro shown in cross section (B) sub It is composed of ferroelectric layer lay Thus, as an example, the donor substrate may be formed by a solid substrate of lithium tantalate or lithium niobate, or even by a composite substrate formed by a first substrate on which rests a ferroelectric material of a certain thickness (at least equal to the thickness of the layer of Ferro lay The donor substrate preferably has a first single domain polarization P1 perpendicular to the implantation plane Imp, through which the hydrogen ions H + will be implanted into the donor substrate for the subsequent separation step.This orientation is usually achieved by selecting the growth mode of the crystal and its cutting plane.

[0061] Ferroelectric layer lay Smart Cut available TM Technology from ferroelectric donor substrate Ferro sub In this case, the donor substrate must be prepared by introducing a light substance such as hydrogen or helium into the donor substrate. This introduction may correspond to hydrogen implantation, i.e., to the donor substrate Ferro sub The flat surface Imp is bombarded with hydrogen ions. As is well known and shown in the cross section (B), the injected hydrogen ions H + Aims to form a ferroelectric layer defining the ferroelectric material to be transferred layThe embrittlement plane Frgl is located on the surface Imp and another part Ferro forming the rest of the substrate sep on one side and will be connected to the ferroelectric layer in subsequent steps. lay Separation.

[0062] The type and dose of the implanted substance as well as the implantation energy are determined by the thickness of the layer to be transferred and the donor substrate Ferro sub In the case of a donor substrate made of LiTaO3, it is possible to implant a substrate in the range of 10 at an energy level between 30 keV and 300 keV. 16 atoms / cm 2 With 5×10 17 atoms / cm 2 The hydrogen dose is between 200nm and 2,000nm thick to define the ferroelectric layer. lay .

[0063] After the carrier Sprt and donor substrate Ferro were prepared sub Afterwards, it includes forming a metal layer M1 on a carrier or donor substrate, and assembling the two elements by contacting them so that the metal layer M1 is interposed between the carrier Sprt and the ferroelectric layer Ferro lay between which the ferroelectric layer faces the carrier Sprt, so as to obtain Figure 4 The intermediate structure shown in the cross section (C) inter The carrier substrate Sprt may have the same sub Same size and shape, but the present invention is not limited to this configuration and different sizes, shapes and configurations may be employed.

[0064] Before assembly, it is conceivable to prepare the faces of the substrates to be assembled by means of cleaning, brushing, drying, polishing or plasma activation steps.

[0065] The assembly may comprise bonding the donor substrate Ferro by molecular adhesion and / or electrostatic bonding as described in French patent application published under number 2914492. sub In close contact with the carrier Sprt.

[0066] It is known that during the molecular attachment process, a completely clean, flat and smooth support Sprt and donor substrate Ferro sub The exposed surfaces of the substrate are brought into close contact to promote electrostatic bonding or the formation of molecular bonds such as van der Waals or covalent types. The assembly of the two bodies is then achieved without the use of an adhesive.

[0067] Assembly may include applying a low temperature heat treatment (eg, in the range between 50°C and 300°C, typically 100°C) in order to correct any crystal defects present in the ferroelectric layer and to increase the bonding energy sufficiently to enable an optional subsequent thinning step.

[0068] In this embodiment, by applying Smart Cut TM The step of separating a portion of the donor substrate is performed using a technique according to which the ferroelectric layer is formed. lay The layer is delimited by a brittle plane Frgl. After the assembly step, the layer is separated from the donor substrate by breaking in the vicinity of the brittle plane Frgl and is thus attached to the carrier Sprt.

[0069] Thus, the separation step may comprise subjecting the intermediate structure Struct to a temperature in the range of about 80°C to 300°C. inter Applying a heat treatment to separate a portion of the donor substrate from the ferroelectric layer ay Separation and transfer to a carrier substrate Sprt. As an alternative or in addition to the thermal treatment, this step may consist in applying a sheet flow or jet of a gaseous or liquid fluid, or any other mechanical force, to the embrittlement plane Frgl.

[0070] As an implementation of the above Smart Cut TM Alternatively, the step of separating a portion of the donor substrate may be performed by separating the ferroelectric donor substrate Ferro sub The chemical mechanical thinning step is replaced by

[0071] Regardless of whether the removal of part of the thickness of the donor substrate is achieved by thinning or breaking, any type of finishing treatment may be applied to the structure Struct thus formed in order to make the ferroelectric layer Ferro lay Meeting specifications for thickness, thickness uniformity, roughness, crystallographic quality, or any other type of specification.

[0072] Specifically, considering the use of a ferroelectric layer Ferro having a single domain polarization lay , can be attached to the ferroelectric layer Ferro lay Specific treatments are applied, all of which aim to obtain a ferroelectric layer lay single domain polarization.

[0073] For example, the ferroelectric layer Ferro lay A preparatory heat treatment is applied, followed by a thinning step.

[0074] This preparatory heat treatment allows to correct any crystallographic defects present in the ferroelectric layer. In addition, it also helps to enhance the ferroelectric layer layand the bonding between the carrier Sprt. If the temperature is high enough, it also has the effect of causing the diffusion of hydrogen contained in the ferroelectric layer and the multi-domain transition of the surface portion of the ferroelectric layer. The thickness of the surface portion may be about 50 nm or less and may extend over the entire range of the ferroelectric layer. Upon completion of the preparatory heat treatment, the ferroelectric layer has a relatively constant hydrogen concentration over its entire thickness. In the case of LiTaO3, the preparatory heat treatment is designed to bring the ferroelectric layer to a temperature in the range of 300°C and the Curie temperature of the ferroelectric material (and preferably greater than or equal to 450°C, 500°C or 550°C in order to promote hydrogen diffusion) and last for a duration in the range of 30 minutes to 10 hours. The heat treatment is preferably carried out by exposing the free surface of the dielectric layer to an oxidizing or neutral gas atmosphere, i.e., without covering the surface of the thin layer with a protective layer that prevents hydrogen from diffusing outward.

[0075] After the preparatory heat treatment, the ferroelectric layer is thinned. This thinning may correspond to polishing the ferroelectric layer using, for example, mechanical, chemical mechanical thinning and / or chemical etching techniques. lay This allows the preparation of free surfaces such that they exhibit a limited roughness, for example less than 0.5 nm RMS 5×5 μm by atomic force measurement (AFM), and allows the removal of the ferroelectric layer Ferro lay Generally speaking, in order to realize the multi-domain surface part of the ferroelectric layer lay The target thickness was 50 nm to 300 nm, and in all cases the thickness was greater than that of the multi-domain surface portion. Thus, a single-domain thin layer with the desired surface finish, crystalline quality, and polarization quality was formed.

[0076] After the above operations, apply to Figure 3 The structure Struct shown in the cross section (D) is as follows Figure 1 and Figure 2 The selective polarization reversal shown allows the formation of Figure 4 The structure shown in the cross section (D).

[0077] Integration on carrier - Solution 2

[0078] Solution 1 shows a method for assembling a donor substrate Ferro preferably having a first single domain polarization P1 with a flat face perpendicular to the substrate. sub Subsequently, selective polarization reversal can be applied to the ferroelectric layer of the obtained structure Struct lay , so as to realize two perpendicular polarizations in opposite directions in the ferroelectric layer.

[0079] This section discloses an alternative solution 2 to solution 1, wherein, instead of applying the selective polarization reversal after assembly, the selective polarization reversal is applied to the donor ferroelectric substrate before assembly, e.g. Figure 4 shown.

[0080] Therefore, unless otherwise stated, Figure 4 All steps of the assembly method shown can be referred to Solution 1, including thinning the donor substrate Ferro sub Instead of breaking the substrate, the alternative is to break the substrate. However, in this solution 2, the donor substrate Ferro sub With two oppositely directed perpendicular polarizations P1 and P2. Such a substrate can be formed, for example, by Figures 1 to 2 The illustrated selective polarization reversal through depth is obtained from a single domain polarized substrate, and from the associated fabrication methods.

[0081] This solution allows obtaining ferroelectric layers with controlled surface polarization without having to use high energy implantation. lay .

[0082] This solution is also used to determine which of volumes V1 and V2 will be located Figure 4 The ferroelectric layer in the structure shown in the cross section (D) lay In fact, depending on the depth position of the embrittlement plane Frgl, it can be located in (1) volume V1 (such as Figure 4 In the first case, the volume V1 and therefore the polarization P1 will be located in the ferroelectric layer Ferro lay on the free surface of , where volume V2 is embedded below volume V1, as Figure 4 In the second case, the volume V2 and therefore the polarization P2 will be located in the ferroelectric layer Ferro lay The free surface of , where volume V1 is embedded below volume V2.

[0083] Alternatively, based on Figure 4 The structure shown in the cross section (D) is applied to the ferroelectric layer Ferro lay The chemical mechanical polishing step allows the layer to be thinned, optionally until the volume V2 is exposed, so that the surface of the ferroelectric layer Ferro lay The free side.

[0084] Alternative Implementation

[0085] Above Figure 3 and Figure 4 The example shown in FIG. 1 explicitly includes a ferroelectric layer located between the carrier Sprt and the ferroelectric layer Ferro layOptionally, the structure may include a metal layer M1 between the carrier Sprt and the ferroelectric layer Ferro lay An additional metal layer or optional dielectric layer at the interface between.

[0086] Figure 5 The structure Struct includes a second metal layer M2 located on the surface of the ferroelectric layer, wherein the ferroelectric layer Ferro lay 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 act as a conductor to the ferroelectric layer. lay Electrodes that apply the electric field.

[0087] Figure 6 The structure Struct is shown to further comprise a first dielectric layer, such as an oxide layer Ox1, interposed between the substrate Sprt and the first metal layer M1. This may be, for example, the result of a method for manufacturing the structure Struct in which the metal layer M1 is formed on the ferroelectric layer Ferro lay On the carrier Sprt, a dielectric layer Ox1 is formed, and then by using Figure 3 A similar method to that described above allows the metal layer to be brought into close contact with the dielectric layer, in this case using an oxide-metal contact, and the ferroelectric layer Ferro lay Assembled on the vector Sprt.

[0088] Figure 7 Shows something like Figure 6 The structure Struct further includes a second dielectric layer, such as an oxide layer Ox2, interposed between the first metal layer M1 and the first dielectric layer Ox1. This may be, for example, the result of a method for manufacturing the structure Struct in which the metal layer M1 and the second dielectric layer Ox2 are formed continuously and in this order on the dielectric layer Ferro. lay On the carrier Sprt, a dielectric layer Ox1 is formed, and then by using Figure 3 The method similar to the one described above brings the two dielectric layers Ox1 and Ox2 into close contact, in this case using a dielectric-dielectric contact, and more specifically in this example using an oxide-oxide contact, and the ferroelectric layer Ferro lay Assembled on the vector Sprt.

[0089] Above about Figure 6 and Figure 7The two methods described are only two examples, and other methods can be envisaged to obtain the same result or other alternative embodiments of the structure Struct. Thus, by forming a stack comprising a layer pair of SiO2 layers and HfSO2 layers or SiO2 layers and Mo layers or other structures and materials known for forming Bragg mirrors, a ferroelectric layer can be formed adjacent to the ferroelectric layer Ferro lay A Bragg mirror is formed, preferably between this layer and the carrier Sprt, for example below the metal layer M1. The metal layer M2 may have the same composition as the layer M1, or may have a different composition. The oxide layers Ox1 and Ox2 may be, for example, silicon oxide or silicon nitride oxide layers.

[0090] In addition, the carrier Sprt can be prepared by adding a dielectric layer that can be formed by a stack of different types of dielectric layers. The dielectric layer can be produced directly on the carrier Sprt using various techniques known in the art, such as thermal oxidation or nitridation treatment, chemical deposition (using a technique known as LPCVD (low pressure chemical vapor deposition), PECVD (plasma enhanced chemical vapor deposition)) or even PVD (physical vapor deposition) or ALD (atomic layer deposition).

[0091] Assembling the carrier with the ferroelectric layer allows hydrogen to accumulate at the interface between them, thereby forming a hydrogen concentration gradient, allowing, for example, the ferroelectric layer to be assembled. lay Ferroelectric substrate sub During the separate thermal treatment, a multi-domain transition occurs in the portion of the ferroelectric layer near the interface.

[0092] It can ensure the ferroelectric layer lay The adjacent metal layer and optional dielectric layer have a higher lay The lower hydrogen concentration in the presence of the hydrogen concentration makes the separation layer Ferro sep During the diffusion caused by the heat treatment of the ferroelectric layer, any excess hydrogen in the ferroelectric layer can be absorbed into the adjacent layers. This prevents hydrogen from accumulating at the assembly interface and avoids the occurrence of multi-domain transitions in the portion of the ferroelectric layer close to the interface.

[0093] The hydrogen concentration in the metal layer and the optional dielectric layer can be reduced, for example, by means of an annealing step aimed at heating these adjacent layers to a temperature above that of the attached ferroelectric layer. lay The temperature of the preparatory heat treatment, which will be described later in this specification, can thus be brought to an annealing temperature of 600°C, 700°C or even 800°C or higher. After this outdiffusion step, the average hydrogen concentration in the dielectric layer can thus be less than 5×10 20 atoms / cm 3 , or advantageously less than 1018 atoms / cm 3 .

[0094] While the examples presented herein are limited to forming a continuous volume V2 of a single layer of reversed polarization within the thickness of the ferroelectric layer, it is possible to create a pair of such volumes V2, each extending from two opposing surfaces of the piezoelectric layer, with a volume V1 having a non-reversed polarization and, therefore, a polarization opposite to that of the two volumes V2, interposed between the two volumes V2. The two different volumes V2 can be formed by performing several consecutive implantations of hydrogen ions with different acceleration energy levels and, therefore, different implantation depths, so as to define two volumes V2, each opening on the surface of the ferroelectric layer and having a thickness that varies according to the associated implantation energy level. In this way, alternating opposite polarizations can be obtained throughout the thickness of the ferroelectric layer.

[0095] Application Examples

[0096] Figure 5 、 Figure 6 and Figure 7 Each of the structures shown in can form a bulk acoustic wave device, or can be integrated into such a device, thereby forming, for example, a BAW bandpass filter.

[0097] Numerical simulations were used to determine that such a device would have reduced frequency sensitivity relative to thickness and improved power efficiency, where the energy density in the layer is distributed across the thickness of the ferroelectric layer.

[0098] In this document, the drawings are not necessarily drawn to scale. Some features and some components may be shown exaggerated relative to other components or in somewhat schematic form, and some details of conventional elements may not be shown for the sake of clarity and conciseness.

[0099] Of course, the invention is not limited to the embodiments described and alternative embodiments can be applied thereto without departing from the scope of the invention as defined by the claims.

Claims

1. A structure comprising a ferroelectric layer lay ), the ferroelectric layer 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, characterized in that The first polarization and the second polarization are perpendicular to or inclined to the ferroelectric layer, and the surface of the first volume (V1) forms the ferroelectric layer (Ferro lay ) and said first volume (V1) is interposed between this face of said ferroelectric layer and said second volume (V2), wherein the second volume (V2) has a higher hydrogen concentration, referred to as the polarity reversal concentration, than the first volume (V1), and The polarity reversal concentration is in the range of 10 per cubic centimeter. 19 hydrogen atoms to 10 22 hydrogen atoms. 2 . The structure according to claim 1 , further comprising a carrier (Sprt) and a metal layer ( M1 ) interposed between the carrier and the ferroelectric layer. 3 . The structure according to claim 1 , wherein the ferroelectric layer is formed of a single crystal.

4. The structure of any one of claims 1 to 3, wherein the ferroelectric layer comprises lithium niobate or lithium tantalate. The structure of claim 2 , wherein the carrier comprises single crystal silicon.

6. A method for manufacturing a ferroelectric element (10), said method comprising the steps of: - providing a ferroelectric element (10, Ferro lay ); - by hydrogen ions (H) passing through the surface (Sup) of the ferroelectric element + ) ion implantation, so that the given embedding volume (V2) of the ferroelectric element is enriched with the hydrogen ions (H + ), wherein the first volume (V1) of the ferroelectric element (10) is interposed between the given embedding volume (V2) of the ferroelectric element and the surface (Sup); and -After introducing the hydrogen ions, annealing the ferroelectric element at a temperature of 500°C to 700°C 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.

7. Method according to claim 6, wherein the first polarization (P1) is monodomain, perpendicular or tilted with respect to a plane (Sup) of the ferroelectric element.

8. The method according to claim 6 or 7, wherein during the selective enrichment of hydrogen ions, the hydrogen ions (H + ) in order to obtain in said given volume (V2) a dose in the range of 10 per cubic centimeter. 19 hydrogen atoms to 10 22 The hydrogen concentration of hydrogen atoms.

9. The method according to any one of claims 6 to 8, wherein the ion implantation of hydrogen ions is performed at an energy level of 3 keV to 210 keV.

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

11. The method according to any one of claims 6 to 10, further comprising assembling a ferroelectric substrate sub ) and a carrier (Sprt), and then separating or thinning the ferroelectric substrate to define the ferroelectric element (Ferro lay ).

12. The method according to claim 11, wherein the carrier (Sprt) is a single crystal silicon substrate, and the metal layer (M1) is interposed between the single crystal silicon substrate and the ferroelectric substrate (Ferro sub )between.

Images