Hybrid structures for surface acoustic wave devices and related manufacturing methods

Abstract

The invention relates to a hybrid structure (10) for a surface acoustic wave device, comprising: a useful layer (1) of piezoelectric material, the useful layer (1) being bonded to a support substrate (2) having a lower thermal expansion coefficient than the useful layer (1); and an intermediate layer (3) being arranged between the useful layer (1) and the support substrate (2). The intermediate layer is a sintered composite layer (3) formed from powders of at least a first material and a second material, the second material being different from the first material.

Description

Technical Field

[0001] The present invention relates to the field of surface acoustic wave devices, and more particularly to a hybrid structure suitable for manufacturing surface acoustic wave devices. Background Art

[0002] The structure of an acoustic resonator such as a surface acoustic wave (SAW) device uses one or more interdigital transducers produced on a piezoelectric substrate to convert electrical signals into acoustic waves and vice versa. Such SAW devices or resonators are often used in filter applications. Radio frequency (RF) SAW technology provides excellent performance (such as high isolation and low insertion loss). For this reason, RF SAW technology is used for RF duplexers in wireless communication applications.

[0003] Improvements in the performance of RF SAW devices are achieved, inter alia, by obtaining a frequency response that is stable with respect to temperature. The dependence of the operating frequency of a SAW device on temperature or the temperature coefficient of frequency (TCF) depends on the variation of the spacing between the interdigital electrodes of the transducer, which is usually due to the relatively high coefficient of thermal expansion (CTE) of the piezoelectric substrate used, on the one hand, and on the other hand, since an expansion or contraction of the piezoelectric substrate is accompanied by an increase or decrease in the velocity of the surface acoustic waves, the TCF depends on the velocity temperature coefficient. In order to minimize the temperature coefficient of frequency (TCF), one objective is therefore to minimize the expansion / contraction of the piezoelectric substrate, especially in the surface area for the propagation of the acoustic waves.

[0004] The article “Recent development of temperature compensated SAW devices” by K. Hashimoto, M. Kadota et al., IEEE Ultrason. Symp. 2011, pp. 79-86, 2011, outlines methods commonly used to overcome the problem of the dependence of the frequency response of SAW devices on temperature.

[0005] One advantageous approach is to use a hybrid substrate (e.g., a hybrid substrate consisting of a piezoelectric material layer located on a silicon substrate). The low CTE of silicon can limit the expansion / contraction of the piezoelectric layer with respect to temperature. In the case of a piezoelectric layer of lithium tantalate (LiTaO3), the above-mentioned article points out that a ratio of the thickness of LiTaO3 to the thickness of the silicon substrate of 10 can appropriately increase the temperature coefficient of frequency (TCF). One of the disadvantages of this method is the presence of parasitic acoustic waves (referred to as "stray acoustic modes" in the article "Characterization of bonded wafer for RF filters with reduced TCF" Proc. 2005 IEEE International Ultrasonics Symposium, Sept 19-21, 2005, pp. 926-929 by BP Abbott et al.), which have a negative impact on the frequency characteristics of the resonator produced on the hybrid substrate. These parasitic resonances are particularly related to parasitic reflections of the main acoustic wave (which mainly propagates in the surface area of ​​the LiTaO3 layer) on the underlying interface (especially including the interface between LiTaO3 and silicon). One solution to reduce these parasitic resonances is to increase the thickness of the LiTaO3 layer; since this also requires an increase in the thickness of the Si substrate in order to maintain the improvement in TCF, the overall thickness of the hybrid substrate is no longer compatible with the requirements for reducing the thickness of the final assembly, in particular to meet the needs of the mobile phone market. Another solution proposed by K. Hashimoto et al. (the above article) is to roughen the lower surface of the LiTaO3 layer (at the bonding interface with the substrate) in order to limit the reflection of the acoustic waves on this lower interface.

[0006] Purpose of the Invention

[0007] An object of the present invention is to provide an alternative solution to the solutions of the prior art.An object of the present invention is in particular to provide a hybrid structure which enables the said parasitic acoustic waves to be reduced and / or eliminated. Summary of the invention

[0008] The present invention relates to a hybrid structure for a surface acoustic wave device, the hybrid structure comprising: a working layer of piezoelectric material, the working layer being assembled with a supporting substrate, the thermal expansion coefficient of the supporting substrate being lower than the thermal expansion coefficient of the working layer; and an intermediate layer, the intermediate layer being located between the working layer and the supporting substrate. The hybrid structure is remarkable in that the intermediate layer is a sintered composite layer formed of powders of at least a first material and a second material, the second material being different from the first material.

[0009] Advantageous features according to the invention, obtained individually or in combination:

[0010] ·The acoustic impedance of the first material is similar to the acoustic impedance of the working layer; the ratio of the acoustic impedance of the working layer to the acoustic impedance of the second material is greater than 2; and the average size of the particles of the powders of the first material and the second material is greater than or equal to one quarter of the wavelength of the acoustic signal intended to propagate at the surface of the surface acoustic wave device.

[0011] The first material and the second material are selected to form an acoustic impedance matching layer between the working layer and the supporting substrate; the average size of the particles of the powders of the first material and the second material is less than one quarter of the wavelength of the acoustic signal intended to propagate at the surface of the surface acoustic wave device.

[0012] The support substrate comprises a material selected from silicon, glass, silicon dioxide, sapphire, aluminum oxide, and aluminum nitride.

[0013] The working layer comprises a piezoelectric material selected from lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, and zinc oxide (ZnO).

[0014] The first material and the second material are selected from silicon oxide, silicon nitride, silicon, silicon carbide, aluminum oxide, germanium, sapphire, and zirconium.

[0015] The composite layer has a thickness ranging from several hundred nanometers to several tens of micrometers.

[0016] The present invention also relates to a method for manufacturing a hybrid structure for a surface acoustic wave device, the method comprising the following steps:

[0017] i) providing a working layer of piezoelectric material and a supporting substrate, wherein the supporting substrate has a lower thermal expansion coefficient than the working layer;

[0018] ii) depositing on the first side of the working layer and / or on the first side of the support substrate a layer formed from a powder mixture of at least a first material and a second material, the second material being different from the first material;

[0019] iii) sintering the layer formed from the powder mixture to obtain a sintered composite layer firmly attached to the first face of the working layer and / or the first face of the supporting substrate;

[0020] iv) assembling the working layer and the supporting substrate so that the composite layer is located between the working layer and the supporting substrate.

[0021] Advantageous features according to the invention, obtained individually or in combination:

[0022] • Before depositing the layer formed from the powder mixture according to step ii), the first side of the working layer and / or the first side of the supporting substrate comprises a protective layer.

[0023] The protective layer is formed of at least one material selected from silicon nitride, silicon oxynitride, silicon oxide, and aluminum oxide.

[0024] The powder mixture is in the form of a viscous paste and the deposition of the layer formed from the mixture in step ii) is carried out by spin coating.

[0025] - A low-temperature heat treatment is performed after deposition of the layer formed from the powder mixture in order to drive off at least one liquid component of the viscous paste.

[0026] • Depositing a bonding layer on the sintered composite layer prior to assembly step iv).

[0027] The working layer provided in step i) is a piezoelectric material donor substrate.

[0028] The manufacturing method comprises step v): thinning the donor substrate to a desired thickness of the working layer for manufacturing the acoustic wave device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0030] Figure 1 A hybrid structure according to the present invention is presented;

[0031] Table 1a presents a list of suitable materials for forming a sintered composite layer of a hybrid structure according to the present invention;

[0032] Table 1b presents a list of materials used to form the working layers of the hybrid structure according to the invention;

[0033] Figure 2a and Figure 2b A hybrid structure according to the present invention is presented;

[0034] Figure 3 A hybrid structure according to the present invention is presented, comprising a SAW device;

[0035] Figures 4a to 4e A method for producing a hybrid structure according to the invention is presented. DETAILED DESCRIPTION

[0036] In the descriptive part, the same reference numerals as in the drawings may be used for elements of the same nature. The drawings are schematic representations and are not drawn to scale for the sake of readability. In particular, the thickness of the layer along the z-axis is not proportional to the lateral dimensions along the x-axis and the y-axis.

[0037] The present invention relates to a hybrid structure 10 suitable for manufacturing a surface acoustic wave (SAW) device. The hybrid structure 10 is particularly suitable for manufacturing devices having a frequency ranging from tens of MHz to tens of GHz.

[0038] like Figure 1 As shown, the hybrid structure 10 according to the present invention includes a working layer 1 of a piezoelectric material, the working layer 1 having a first surface 1a and a second surface 1b. Since the working layer 1 will be used for the subsequent production of a surface acoustic wave device, the working layer 1 is named as such. For example, the working layer 1 of the hybrid structure 10 can be composed of a material selected from the following group: lithium tantalate LiTaO3 (LTO in Table 1b), lithium niobate LiNbO3 (LNO in Table 1b), aluminum nitride AlN (Table 1b), zinc oxide (ZnO).

[0039] The hybrid structure 10 also includes a Figure 1 The intermediate layer is a sintered composite layer 3 formed from powders of at least two different materials. A sintered layer is understood to mean a layer resulting from the consolidation of a powder mixture: this consolidation is obtained by inputting thermal energy and optionally mechanical energy, but without melting at least one of the powdered materials of the mixture. The sintering properties of the composite layer can therefore be detected by structural analysis of the layer, for example by scanning electron microscopy. The particles or grains of the material powders appear to be welded together, and the density of the composite layer depends on the degree of compaction of the mixture during the input of energy for consolidation.

[0040] The particles of the powders of the various materials forming the sintered composite layer 3 have sizes that follow a typical Gaussian distribution. In the remainder of the specification, the average size of the particles will be similar to the equivalent average diameter of the particles of a given material. The average size of the particles can typically vary between tens of nanometers and several micrometers.

[0041] The sintered composite layer 3 may be formed in particular from at least a first material and a second material selected from silicon oxide, silicon nitride, silicon, silicon carbide, aluminum oxide, germanium, sapphire, zirconium, some properties of which are shown in Table 1.

[0042] The sintered composite layer 3 may optionally include three or more different materials.

[0043] Depending on the embodiment, the sintered composite layer 3 has a thickness between a few hundred nanometers and a few micrometers.

[0044] Finally, the hybrid structure 10 comprises a support substrate 2 having a lower thermal expansion coefficient than the working layer 1, located below the composite layer 3 (along the Figure 1 The support substrate 2 can be formed of a material selected from the group consisting of silicon, III-V semiconductors, silicon carbide, glass, and sapphire.

[0045] like Figure 2a and Figure 2b As shown, the hybrid structure 10 preferably includes an additional layer 4, which is located on the first face 1a of the working layer 1 and / or on the first face 2a of the supporting substrate 2, and may be located on the second face 2b of the supporting substrate 2 and on the edge of the substrate 2 ( Figure 2b As will be seen in the description of the method for producing the hybrid structure 10, these additional layers 4 have in particular the function of protecting the supporting substrate 2 and / or the working layer 1 from the diffusion of impurities contained in the sintered composite layer 3 or present during the production of said layer 3.

[0046] The hybrid structure 10 according to the present invention is suitable for manufacturing a surface acoustic wave (SAW) device, wherein the SAW device comprises, in particular, metal electrodes 20 on a working layer 1, between which acoustic signals are propagated (by Figure 3 (Indicated by the white arrow in FIG. 1 ), in the (x, y) plane, the metal electrode 20 is close to the surface of the second face 1 b of the working layer 1 .

[0047] According to a first embodiment of the hybrid structure 10 according to the invention, the sintered composite layer 3 is configured to maximize the diffusion of incident acoustic waves generated by the acoustic signal and to propagate to the composite layer 3 in the volume of the working layer 1 .

[0048] To this end, in the sintered composite layer 3 formed from powders of at least the first material and the second material, the acoustic impedance of the first material is similar to the acoustic impedance of the working layer 1. The term "similar" is understood to mean a maximum deviation of ±20% around the acoustic impedance value of the working layer 1, and the deviation is preferably less than ±15%, or even ±10%. For example, for a working layer 1 made of LiTaO3, the first material may be aluminum oxide, the acoustic impedance of which (40.6×10 6 Pa.s / m) and the acoustic impedance of lithium tantalate (44.8×10 6 Pa.s / m) are roughly the same.

[0049] Furthermore, the ratio of the acoustic impedance of the working layer 1 to the acoustic impedance of the second material of the sintered composite layer 3 is selected to be greater than or equal to 2 in order to ensure that the reflection coefficient is greater than 10%. For example, if the first material is lithium tantalate (44.8×10 6 Pa.s / m), the second material can be SiO2, the acoustic impedance of SiO2 is 13.2×10 6 Pa.s / m, so that a reflection coefficient of about 30% can be obtained at the interface between the particles of the composite layer 3, and reflection (diffusion) occurs in multiple directions.

[0050] Finally, the particle size of the powders of the first material and the second material is greater than or equal to one quarter of the wavelength of the incident sound wave. This feature ensures that the incident sound wave can be affected by the particles. For example, for an incident sound wave with a wavelength of about 6 microns (i.e., a frequency of about 1 GHz), the average size of the particles will be selected to be about 2 microns. Then, the sintered composite layer 3 has a thickness greater than 5 microns, or even greater than 10 microns.

[0051] If an additional layer 4 is present between the working layer 1 and the composite layer 3, the acoustic impedance of this additional layer 4 will have to be close to the acoustic impedance of the working layer 1 in order to limit parasitic reflections between the two layers. For a working layer 1 made of LiTaO3, for example, aluminum oxide can be used, the acoustic impedance of which is (40.6×10 6 Pa.s / m) is close to the acoustic impedance of LiTaO3, which results in a reflection of less than 0.5%.

[0052] The sintered composite layer 3 according to the first embodiment makes it possible to diffuse incident waves in multiple directions and thus greatly limit the components reflected toward the electrode 20 of the surface acoustic wave device.

[0053] According to a second embodiment of the hybrid structure 10 according to the invention, the sintered composite layer 3 is configured to maximize the transmission of incident acoustic waves generated by the acoustic signal and to propagate to the composite layer 3 in the volume of the working layer 1 .

[0054] To this end, in the sintered composite layer 3 formed of powders of at least the first material and the second material, the first material and the second material are selected to form an acoustic impedance matching layer between the working layer 1 and the supporting substrate 2. Forming an acoustic impedance matching layer implies that the average acoustic impedance of the composite layer 3 is approximately equal to the square root of the product of the acoustic impedance of the working layer 1 and the acoustic impedance of the supporting substrate 2:

[0055]

[0056] It should be remembered that the acoustic impedance Z of a material is given by:

[0057] Z=v×ρ

[0058] Here, v is the speed of the sound wave in the material and ρ is the density of the material.

[0059] In the case of the composite layer 3, the volume fractions V1 and V2 of the various materials forming the composite layer 3 are taken into account; therefore, the acoustic impedance of the composite layer 3 (in the case of two materials) can be evaluated according to the following formula:

[0060] Z 复合层 =(v1×V1+v2×V2)×(ρ1×V1+ρ2×V2)

[0061] Wherein, ρ1 and ρ2 are the densities of the first material and the second material respectively, and v1 and v2 are the velocities of the sound wave in the first material and the second material respectively.

[0062] The volume fractions V1 and V2 are defined by the ratios of the various materials in the composite layer 3 .

[0063] For example, the first material may be Al2O3 and the second material may be SiO2, which are present in the composite layer at a ratio of 65% and 35%, respectively. Therefore, the impedance of the composite layer 3 may be about 30×10 6 Pa.s / m.

[0064] Furthermore, according to this second embodiment, the average size of the particles of the powders of the first material and the second material is less than a quarter of the wavelength of the incident acoustic wave. This feature ensures that the incident acoustic wave sees the composite layer as an almost homogeneous medium. For example, for an incident acoustic wave with a wavelength of about 7.5 microns (i.e., a frequency of about 800 MHz), the average size of the particles can be selected to be about 0.5 microns. The sintered composite layer 3 can have a thickness of several microns.

[0065] If an additional layer 4 is present between the working layer 1 and the composite layer 3, the acoustic impedance of this additional layer 4 will have to be close to the acoustic impedance of the working layer 1 in order to limit parasitic reflections between the two layers. For a working layer 1 made of LiTaO3, for example, aluminum oxide can be used, the acoustic impedance of which is (40.6×10 6 Pa.s / m) is close to the acoustic impedance of LiTaO3, which results in a reflection of less than 0.5%.

[0066] If there is an additional layer 4 between the composite layer 3 and the support substrate 2, the acoustic impedance of this additional layer 4 will have to be close to the acoustic impedance of the support substrate 2 in order to limit parasitic reflections at the additional layer / support substrate interface. For a support substrate made of Si, for example silicon nitride can be used, the acoustic impedance of silicon nitride (~22×10 6 Pa.s / m) is close to the acoustic impedance of Si, which results in a reflection of less than 0.5%.

[0067] The sintered composite layer 3 according to the second embodiment can promote the transmission of incident acoustic waves (through acoustic impedance matching) that are usually reflected at the interface of the hybrid structure from the working layer 1 to the substrate 2: thus, parasitic reflections that have a negative impact on the frequency characteristics of the SAW device produced on the hybrid structure 10 can be reduced.

[0068] According to a variation of the various embodiments described for the hybrid structure 10, the sintered composite layer 3 has good dielectric properties (resistivity greater than 1E7 ohms.cm) and a low equivalent dielectric constant (typically less than the dielectric constant of silicon, 11F / m) so as to provide electrical insulation equivalent to a few microns of silicon oxide. Such a sintered composite layer 3 can improve the linearity of surface acoustic wave devices in the radio frequency field, in particular.

[0069] According to another variant of the various described embodiments applicable to the hybrid structure 10, the sintered composite layer 3 has a mobile charge trapping property. This feature can trap and thus counteract the charges that may be present in the upper part of the support substrate 2 due to the presence of fixed charges in one of the upper layers (additional layer 4 or working layer 1). In order to have this trapping feature, one of the materials constituting the particles of the composite layer 3 can be silicon.

[0070] The invention also relates to a method for manufacturing a hybrid structure 10 for a surface acoustic wave device. The method comprises a first step (indicated by i)) of providing a working layer 1 of piezoelectric material. According to an advantageous embodiment, the working layer 1 is in the form of a piezoelectric material donor substrate 1' having a standard thickness and diameter for the microelectronics industry ( Figure 4a ).

[0071] The first step also comprises providing a support substrate 2 having a lower thermal expansion coefficient than that of the donor substrate 1 ′ (ie also lower than that of the working layer 1 ).

[0072] The manufacturing method according to the invention comprises a second step (indicated by ii)) consisting in depositing on the first face 1a of the working layer 1 (or of the donor substrate 1') and / or on the first face 2a of the support substrate 2 a layer 3' formed of a powder mixture of at least a first material and a second material different from the first material. Figure 4b In the example shown, a layer 3' of the powder mixture is deposited on the first face 2a of the support substrate 2. The layer 3' may be deposited on the first face 1a of the working layer 1; the layer 3' may also be deposited on each of the first face 1a of the working layer 1 and the first face 2a of the support substrate 2, respectively.

[0073] Advantageously, the first face 2a of the support substrate 2 comprises a protective layer 4a produced before depositing the layer 3' of powder mixture. The protective layer 4a may even completely encapsulate the support substrate 2 (ie covering the back side 2b of the support substrate 2 and the edges of the support substrate 2).

[0074] Alternatively, if the layer 3 ′ of powder mixture is deposited on the working layer 1 (or donor substrate 1 ′), the protective layer will be deposited at least on the first face 1 a of said working layer 1 (or of the donor substrate 1 ′).

[0075] Preferably, the protective layer 4a is formed of at least one material selected from silicon nitride, silicon oxynitride, silicon oxide and aluminum oxide. The protective layer 4a can be produced by various known chemical deposition techniques. The diffusion of impurities contained in the layer 3' into the support substrate 2 (or the working layer 1) can be avoided or at least limited.

[0076] According to a variant of the first embodiment, the powder mixture is in the form of a viscous paste.

[0077] Such a paste is generally obtained by adding a liquid compound of the solvent type, in particular an alcohol such as ethanol, to a dry powder mixture. Typically, the powders used comprise particles having an average size between a few tens of nanometers and a few micrometers.

[0078] Alternatively, the powder mixture can be mixed into a matrix of the polymer type based on silicon (PDC for polymer derived ceramics) capable of being transformed into a ceramic at high temperature. Note that in the case of a layer 3 ' with a PDC matrix, the sintered composite layer 3 that will subsequently be obtained will include the first and second materials originating from the powder mixture, but also silicon originating from the transformation of the matrix into a ceramic.

[0079] Deposition of the layer 3 ′ formed of said mixture in step ii) is preferably carried out by spin coating (or dip coating) or screen printing through a mask.

[0080] The viscosity of the paste is adjusted by the powder / liquid compound (solvent and / or polymer) ratio.The viscosity of the paste is chosen so as to be able to deposit a layer 3' uniformly with a thickness that can vary from a few hundred nanometers to a few micrometers.

[0081] Deposition of the layer 3 ′ is followed by a heat treatment at low temperature (for example between 150° C. and 400° C.) in order to drive out the solvent from the layer 3 ′ and avoid any subsequent outgassing during the method, in particular after the assembly step (described below).

[0082] According to a variation of the second embodiment, the powder mixture is in dry powder form and is deposited as a layer 3' on the first face 2a of the support substrate 2 (or alternatively on the face 1a of the donor substrate 1'). The forming of this layer 3' can be carried out by compression molding or hot isostatic pressing. In both cases, a compressive stress is applied to the layer 3' to firmly adhere the particles of the mixture powder to each other and to the first face 2a. A special tool is required to keep the powder mixture on the substrate and apply a uniform compressive stress to the entire surface of the substrate.

[0083] The manufacturing method according to the invention comprises a third step (indicated by iii)) consisting in sintering the layer 3' formed of the powder mixture so as to obtain a sintered composite layer 3 firmly attached to the first face 2a of the support substrate 2 ( Figure 4c ).

[0084] Sintering is usually carried out at a high temperature, typically above 1000° C., for a duration that can vary from a few hours to about 24 hours. However, the sintering temperature is kept below the melting point of at least one of the powders contained in the layer 3 ′. Under the action of heat, the particles of the powders are welded together, which forms the cohesion of the resulting composite layer 3. The composite layer 3 is also firmly attached to the first face 2 a of the supporting substrate 2.

[0085] Optionally, sintering can additionally be carried out under mechanical stress, which can further compact the composite layer 3 .

[0086] Thus, the sintered composite layer 3 consists at least of particles of the first material and the second material. Between the particles, depending on the degree of compaction, there may be more or less empty spaces (or gaps containing ceramics obtained from the PDC matrix). Depending on the particle size distribution, the volume fraction of these gaps may reach 50%, and is more preferably kept below 25%, or even below 15%, in particular to ensure good mechanical strength of the composite layer 3. For the sake of simplicity, this gap volume fraction is not taken into account in the above-described embodiment of the hybrid structure 10; the gap can be considered as a third material in addition to the first material and the second material forming the particles.

[0087] The thickness of the layer 3' deposited in step ii) is chosen so as to obtain the desired thickness of the sintered composite layer 3. In practice, depending on the type of layer 3' deposited (in the form of a paste with solvent and / or polymer or in the form of a dry product), the reduction in thickness during the sintering step will be greater or less. The volume of the layer 3' may be reduced by about 10% to 30%.

[0088] The manufacturing method according to the invention comprises a fourth step (indicated by iv)) which comprises assembling the working layer 1 (donor substrate 1') and the support substrate 2 so that the sintered composite layer 3 is located between the working layer 1 and the support substrate 2 ( Figure 4d ).

[0089] Preferably, before the assembly step iv), a bonding layer 4b is deposited on the composite layer 3. For example, a silicon oxide layer can be deposited on the free surface of the composite layer 3. This bonding layer 4b provides, on the one hand, an encapsulation of the sintered composite layer 3, thereby avoiding or at least limiting the risk of contamination between the layers of the hybrid structure 10; on the other hand, the bonding layer 4b may be advantageous for allowing a conventional surface preparation that is not specific to the components of the sintered composite layer 3.

[0090] Preferably, the two surfaces in contact (ie the first face 1a of the working layer 1 (or of the donor substrate 1') and the substrate from Figure 4c The assembly step is performed by using the free surface of the composite layer 3 in the example of FIG. The molecular adhesion principle known in the prior art will not be described in further detail here.

[0091] Alternatively, assembly may be performed by adding a layer of adhesive material or by any other joining technique suitable for the intended application.

[0092] For most assembly methods, it will be necessary for the substrates to be assembled to have a good surface finish (cleanliness, low roughness, etc.).

[0093] The manufacturing method according to the present invention may further include a fifth step (indicated by v) comprising thinning the donor substrate 1' to a desired thickness of the working layer 1 for manufacturing an acoustic wave device ( Figure 4e ). For example, this step may include mechanical grinding followed by dry or chemical mechanical polishing, thereby ensuring a good surface finish of the working layer 1. Various cleaning procedures may be applied during or after the thinning step in order to ensure the quality and cleanliness of the final hybrid structure 10.

[0094] By any other known technology (especially Smart Thinning of the donor substrate 1 ′ is performed using a TU / T process or other technique for producing thin layers to obtain the working layer 1 .

[0095] Of course, the invention is not limited to the embodiments described and examples and variant embodiments may be introduced without departing from the scope of the invention as defined by the claims.

Claims

1. A hybrid structure (10) for a surface acoustic wave device, the hybrid structure (10) comprising: A working layer (1) of piezoelectric material, the working layer (1) being assembled with a supporting substrate (2), the thermal expansion coefficient of the supporting substrate (2) being lower than the thermal expansion coefficient of the working layer (1); and an intermediate layer (3), wherein the intermediate layer (3) is located between the working layer (1) and the supporting substrate (2), wherein the hybrid structure (10) is characterized in that the intermediate layer (3) is a sintered composite layer formed by powders of at least a first material and a second material, wherein the second material is different from the first material, wherein the first material and the second material are selected from at least one of silicon oxide, silicon nitride, silicon, silicon carbide, aluminum oxide, germanium, sapphire and zirconium.

2. The hybrid structure (10) for a surface acoustic wave device according to claim 1, wherein: The acoustic impedance of the first material is similar to the acoustic impedance of the working layer (1), The ratio of the acoustic impedance of the working layer (1) to the acoustic impedance of the second material is greater than 2, The average size of the particles of the powders of the first material and the second material is greater than or equal to one quarter of the wavelength of an acoustic signal intended to propagate at the surface of the surface acoustic wave device.

3. The hybrid structure (10) for a surface acoustic wave device according to claim 1, wherein: The first material and the second material are selected to form an acoustic impedance matching layer between the working layer (1) and the supporting substrate (2), The average size of the particles of the powders of the first material and the second material is smaller than one quarter of the wavelength of an acoustic signal intended to propagate at the surface of the surface acoustic wave device.

4. The hybrid structure (10) for a surface acoustic wave device according to any one of claims 1 to 3, wherein: The support substrate (2) comprises at least one material selected from silicon, glass, silicon dioxide, sapphire, aluminum oxide and aluminum nitride.

5. The hybrid structure (10) for a surface acoustic wave device according to any one of claims 1 to 3, wherein: The working layer (1) comprises at least one piezoelectric material selected from the group consisting of lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz and zinc oxide (ZnO).

6. A method for manufacturing a hybrid structure (10) for a surface acoustic wave device, characterized in that The method comprises the following steps: i) providing a working layer (1) of piezoelectric material and a supporting substrate (2), wherein the thermal expansion coefficient of the supporting substrate (2) is lower than the thermal expansion coefficient of the working layer (1); ii) depositing a layer (3') formed of a powder mixture of at least a first material and a second material on the first side (1a) of the working layer (1) and / or on the first side (2a) of the support substrate (2), the second material being different from the first material, wherein the first material and the second material are selected from at least one of silicon oxide, silicon nitride, silicon, silicon carbide, aluminum oxide, germanium, sapphire and zirconium; iii) sintering the layer (3') formed from the powder mixture to obtain a sintered composite layer (3) firmly attached to the first face (1a) of the working layer (1) and / or the first face (2a) of the supporting substrate (2); iv) assembling the working layer (1) and the supporting substrate (2) so that the sintered composite layer (3) is located between the working layer (1) and the supporting substrate (2).

7. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to claim 6, wherein: Prior to depositing the layer (3') formed from the powder mixture according to step ii), the first face (1a) of the working layer (1) and / or the first face (2a) of the supporting substrate (2) comprises a protective layer (4, 4a).

8. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to claim 7, wherein: The protective layer (4, 4a) is formed of at least one material selected from silicon nitride, silicon oxynitride, silicon oxide and aluminum oxide.

9. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to any one of claims 6 to 8, wherein: The powder mixture is in the form of a viscous paste and the deposition of the layer (3') formed from the mixture in step ii) is carried out by spin coating.

10. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to claim 9, wherein: After depositing said layer (3') formed from said powder mixture, a low temperature heat treatment is carried out in order to drive off at least one liquid component of said viscous paste.

11. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to any one of claims 6 to 8, wherein: Prior to the assembly step iv), a bonding layer (4b) is deposited on the sintered composite layer (3).

12. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to any one of claims 6 to 8, wherein: The working layer (1) provided in step i) is a piezoelectric material donor substrate (1').

13. The method for manufacturing a hybrid structure (10) for a surface acoustic wave device according to claim 12, comprising step v): thinning the donor substrate (1') to a desired thickness of the working layer (1) for manufacturing the acoustic wave device.

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