Method for manufacturing an elastic surface wave device

Abstract

The invention relates to a method for manufacturing an elastic wave device configured to operate at a frequency lower than 1 GHz, and formed on a POI substrate, the formation of the POI substrate comprising the following steps: - a) a step of implanting species in a LiTaO3 substrate (210) so as to form a useful layer (150); and - b) a step of transferring the useful layer onto a front face of a support substrate (110); the method further comprising the formation of an intermediate stack, positioned between the front face and the useful layer, and which comprises, starting from the front face, a first layer (120), a second layer (130) and a third layer (140), the first layer comprising silicon dioxide, the second layer comprising silicon nitride, alumina or aluminium nitride, and the third layer comprising silicon dioxide or amorphous silicon.

Description

METHOD FOR MANUFACTURING AN ELASTIC SURFACE WAVE DEVICE FIELD OF THE INVENTION

[0001] The present invention relates to the field of surface elastic wave devices. More particularly, the present invention relates to a method of manufacturing a surface elastic wave device formed from a POI substrate that comprises a layer of piezoelectric material. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Initially manufactured on solid substrates of monocrystalline piezoelectric materials (hereinafter "solid substrate"), surface elastic wave filters ("SAW filter" or "Surface Acoustic Wave filter", according to Anglo-Saxon terminology) now use piezoelectric substrates on insulators (hereinafter "POI"). These include, in particular, from a front face to a rear face, a layer of piezoelectric material, a layer of dielectric material and a support substrate.

[0003] These POI substrates, unlike bulk substrates, make it possible to meet certain requirements in terms of temperature sensitivity of the surface elastic modes guided in the piezoelectric material layer.

[0004] In particular, the support substrate acts as a stiffener and helps limit thermal expansion and influence the thermoelastic behavior of the piezoelectric material layer.

[0005] Thus, in general, a surface elastic mode propagating on a POI substrate, from which a surface elastic wave device is formed, has a relatively low temperature coefficient of frequency (CTF or “TCF” for “Temperature coefficient of Frequency” according to Anglo-Saxon terminology), and in particular less than 10 ppm.K -1 , in a frequency range extending from 1.4 GHz to 2.4 GHz.

[0006] The manufacture of POI substrates can implement a process known as “SmartCut™” well known in the field of microelectronics, particularly for the manufacture of silicon-on-insulator substrates.

[0007] In this regard, document [1] cited at the end of the description proposes transferring a layer of piezoelectric material, and more particularly of LiNbO3 (hereinafter “LNO”), onto a silicon substrate using the SmartCut™ process.

[0008] Document [2] cited at the end of the description also discloses the implementation of a POI substrate using a LiTaO3 layer for the manufacture of a surface elastic wave filter. The surface elastic wave filter described in this document comprises a lithium tantalate film on a mirror layer formed from alternating low acoustic impedance layers and high acoustic impedance layers on a silicon substrate.

[0009] It was also considered to interpose a so-called trapping layer, for example made of polycrystalline silicon, between the support substrate and the layer of dielectric material, and intended to limit the mean free path of the charges at the interfaces of the stack as well as the crosstalk likely to occur within a filter formed from the POI substrate considered.

[0010] The advantages of the SmartCut™ process for forming a POI substrate are well known. In particular, the SmartCut™ process allows the removal of a layer of piezoelectric material, of controlled thickness, from a solid substrate of piezoelectric material called the donor substrate. Furthermore, after recycling, the donor substrate can be used again for the formation of other POI substrates. This last aspect makes the SmartCut™ process competitive.

[0011] POI substrates, thus capable of being formed using the SmartCut™ process, are generally implemented for the design of surface elastic wave filters operating at resonance / anti-resonance frequencies above 1 GHz.

[0012] There is currently interest in forming surface elastic wave filters formed on POI substrates and operating at resonance / anti-resonance frequencies below 1 GHz. However, in order to contain the temperature coefficient of the frequency of a surface elastic mode propagating on a POI substrate to reasonable values ​​(e.g. below 10 ppm.K -1 ), it may be necessary to adapt the thicknesses of the layer of piezoelectric material and / or the layer of dielectric material. More particularly, it may be required to reduce the thickness of the layer of dielectric material and / or to increase the thickness of the layer of piezoelectric material.

[0013] In this regard, the SmartCut™ process offers the versatility needed to adapt the thicknesses of these layers.

[0014] However, a thin layer of dielectric material, and in particular one with a thickness of less than 300 nm or even less than 200 nm, is no longer an effective barrier against the diffusion of certain species likely to form the layer of piezoelectric material. For example, a layer of dielectric material with a thickness of less than 300 nm will allow lithium to diffuse from a layer of piezoelectric material comprising LaTiO3. In particular, the lithium having thus diffused into the layer of dielectric material (for example SiO2) is a source of radiofrequency losses.

[0015] Also, it is not desirable to consider a layer of piezoelectric material with too great a thickness, and in particular greater than 500 nm. Indeed, these thicknesses require, when implementing the SmartCut™ process for the formation of the POI substrate, to consider relatively high implantation energies in the bulk substrate of piezoelectric material (the donor substrate), which, consequently, generate damage that is often prohibitive for the formation of surface elastic wave filters.

[0016] An aim of the present invention is therefore to propose a method for manufacturing a surface elastic wave device, operating at frequencies below 1 GHz, implementing a SmartCut™ method and for which the diffusion of species during the execution of said method remains limited. BRIEF DESCRIPTION OF THE INVENTION

[0017] The object of the present invention is achieved by a method of manufacturing an elastic wave device configured to operate at a frequency below 1 GHz, and formed on a POI substrate, the formation of the POI substrate comprising the following steps:

[0018] a) a step of implanting species in a donor substrate, comprising LaTiO3, the implantation of species being intended to form a layer, called a weakening zone in the volume of the donor substrate, and delimiting with one face, called the main face, of said donor substrate, a useful layer;

[0019] b) a step of transferring the useful layer onto a front face of a support substrate, the transfer step comprising in order an assembly of the useful layer with a face, called the front face, of the support substrate, and a heat treatment intended to initiate a fracture wave along the embrittlement in order to transfer the useful layer onto the front face;

[0020] the method further comprising the formation of an intermediate stack, interposed between the front face and the useful layer, and which comprises from the front face, a first layer, a second layer and a third layer, the first layer comprising silicon dioxide, the second layer comprising silicon nitride, alumina or aluminum nitride, and the third layer comprising silicon dioxide or amorphous silicon.

[0021] According to one embodiment, the formation of the POI substrate also comprises a layer, called a trapping layer, interposed between the intermediate stack and the front face, the trapping layer being adapted to limit the mean free path of electrical carriers at the interface formed between the intermediate stack and said trapping layer with respect to the mean free path of electrical carriers at an interface formed between the intermediate stack and the support substrate.

[0022] According to one embodiment, the trapping layer comprises a defect density greater than a predetermined defect density, the predetermined defect density being a defect density for which the resistivity of the trapping layer is greater than or equal to 10 Kilo-ohm for temperatures between -20°C and 120°C.

[0023] According to one embodiment, the trapping layer comprises at least one of the materials included among: amorphous silicon, polycrystalline silicon.

[0024] According to one embodiment, the formation of the stack comprises the formation of the third layer on the main face before the execution of the implantation step a).

[0025] According to one embodiment, the formation of the stack comprises the formation of the first layer and the second layer on the front face so that the assembly, when performing step b), comprises bringing the second layer and the third layer into contact.

[0026] According to one embodiment, the third layer has a thickness between 10 nm and 100 nm.

[0027] According to one embodiment, said method comprises a preliminary step, carried out before step a), and during which the donor substrate is subjected to a vapor phase oxygen treatment so as to limit, or even reduce, the effects of pyroelectricity likely to appear in the donor substrate, and consequently in the useful layer, when it is subjected to an increase in temperature.

[0028] According to one embodiment, the donor substrate comprises iron-doped lithium tantalate, the iron doping being between 0.001% and 0.05%, advantageously between 0.002% and 0.01%, in mass percentage.

[0029] According to one embodiment, the first layer has a thickness of between 100 nm and 1000 nm, advantageously between 300 nm and 800 nm, and the second layer has a thickness of between 20 nm and 300 nm.

[0030] According to one embodiment, said method comprises the formation of at least one electroacoustic transducer formed on and / or in the useful layer.

[0031] According to one embodiment, the support substrate comprises at least one of the elements chosen from: a silicon substrate having the 110 orientation, a quartz substrate having an orientation (YXt) / θ / 90° with θ between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0032] According to one embodiment, the LiTaO3 material has an orientation (YX) / θ with θ between 10° and 52°, advantageously between 15° and 30°.

[0033] Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

[0034] Laest is a schematic representation of a surface elastic wave resonator according to a section plane perpendicular to a main face of the support substrate of the POI substrate in accordance with the principles of the present invention;

[0035] This is a graphical representation of the evolution of the TCF1 coefficient (vertical axis, in ppm / K), of the fundamental elastic mode of surface shear propagating under a periodic electrode array of a POI substrate, as a function of the frequency (horizontal axis, in MHz), the so-called standard POI substrate which comprises in order, from the front face, a layer of lithium tantalate of cut (YXl) / 42° defined according to the IEEE Std-176 standard on piezoelectricity of 600 nm thickness, a layer of silicon dioxide of 500 nm thickness, a layer of polysilicon of 1 µm, and a type 100 silicon substrate;

[0036] This is a graphical representation of the evolution of the TCF1 coefficient (vertical axis, in ppm / K), of a surface elastic mode propagating under a periodic electrode array of a POI substrate, as a function of the frequency (horizontal axis, in MHz), in particular curve C and curve D represent the TCF1 coefficient associated with a POI substrate which comprises a support substrate made of silicon, respectively, of the 110 type or of the (XYt) / 45° or (YXt) / 45° type according to the IEEE Std-176 standard;

[0037] La represents the variation of the TCF1 (vertical axis in ppm / K) of the fundamental elastic mode of surface shear propagating on a POI substrate and as a function of the cutting angle θ (horizontal axis, in ° of angle) of the LiTaO3 layer, the POI substrate considered comprising a support substrate made of silicon, and a layer of SiO2 350 nm thick and intercalated between the support substrate and the LiTaO3 layer;

[0038] La represents the variation of the electromechanical coupling (vertical axis, in %) of the fundamental elastic mode of surface shear propagating on a POI substrate described in relation to laet as a function of the cutting angle θ (horizontal axis, in °) of the LiTaO3 layer;

[0039] Laest is a schematic representation of a surface elastic wave resonator according to a section plane perpendicular to a main face of the support substrate of the POI substrate in accordance with the principles of the present invention;

[0040] graphically represents (according to a 3D representation) the phase velocity of the waves likely to propagate in the layer 5 of LiTaO3 of a surface elastic wave device formed from the POI substrate described above, the phase velocity, noted vϕ (vertical axis, in m / s), is represented as a function of the operating frequency of the device (axis A in MHz) and the thickness of the layer 6 of SiO2 (axis B in nm);

[0041] Larepresente, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear propagating on a POI substrate described above, the electromechanical coupling factor, noted k s 2 (vertical axis, in %), is represented as a function of the operating frequency of an infinite periodic transducer formed on said POI substrate (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm);

[0042] It represents, graphically (according to a 3D representation), the coefficient TCF1 of the fundamental elastic mode of surface shear propagating in a POI substrate described above, the coefficient TCF1, noted TCF1 (vertical axis, in ppm / K), is represented as a function of the operating frequency of the transducer (axis A in MHz) and the thickness of the layer 6 of SiO2 (axis B in nm);

[0043] Larepresents, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear propagating in the POI substrate described above and whose thickness of the layer 5 of LiTaO3 is equal to 700 nm, the electromechanical coupling factor, noted k s 2 (vertical axis, in %), is represented as a function of the operating frequency of the transducer formed on said POI substrate (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0044] It represents, graphically (according to a 3D representation), the coefficient TCF1 of the fundamental elastic mode of surface shear propagating on a POI substrate described above and whose thickness of the LiTaO3 layer is equal to 700 nm, the coefficient TCF1, noted TCF1 (vertical axis, in ppm / K), is represented as a function of the operating frequency of the transducer (axis A in MHz) and the thickness of the SiO2 layer (axis B in nm).

[0045] Larepresents, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear propagating on the POI substrate described above and whose thickness of the LiTaO3 layer is equal to 800 nm, the electromechanical coupling factor, noted k s 2(vertical axis, in %), is represented as a function of the operating frequency of the transducer formed on the POI substrate (axis A in MHz) and the thickness of the SiO2 layer (axis B in nm);

[0046] It represents, graphically (according to a 3D representation), the coefficient TCF1 of the fundamental elastic mode of surface shear propagating on a POI substrate described above and whose thickness of the LiTaO3 layer is equal to 700 nm, the coefficient TCF1, noted TCF1 (vertical axis, in ppm / K), is represented as a function of the operating frequency of the transducer (axis A in MHz) and the thickness of the layer 6 of SiO2 (axis B in nm);

[0047] This is a graphical representation of the evolution of the phase velocity of the fundamental shear mode (vertical axis, in m / s) as a function of the frequency (horizontal axis in MHz) and propagating in a POI substrate which comprises a 600 nm LiTaO3(YXl)42° layer, an additional 100 nm layer, a 400 nm dielectric layer, and a Silicon support substrate, the additional layer possibly comprising Diamond Carbon, GaN, ZnO, LiNbO3;

[0048] This is a graphical representation of the evolution of the phase velocity of the fundamental shear mode (vertical axis, in m / s) as a function of the frequency (horizontal axis in MHz), and propagating in a POI substrate which comprises a 600 nm layer of LiTaO3(YXl)42°, an additional 100 nm layer, a 400 nm dielectric layer, and a silicon support substrate, the additional layer possibly comprising: SiN, poly Si, AlN, Al2O3;

[0049] This is a schematic representation of a surface elastic wave device according to a section plane perpendicular to a front face of the support substrate in accordance with the principles of the present invention;

[0050] This is a schematic representation of step a) of the method according to the present invention;

[0051] This is a schematic representation of the formation of the first layer and the second layer on the support substrate;

[0052] This is a schematic representation of the assembly of the second layer with the third layer;

[0053] This is a schematic representation of the fracture along the weakening zone.

[0054] DETAILED DESCRIPTION OF THE INVENTION

[0055] For the sake of simplification of the description to come, the same references are used for identical elements or elements ensuring the same function in the different modes of implementation described of the invention and in the state of the art.

[0056] The present invention relates to a surface elastic wave device formed from a POI substrate. In this regard, document FR3127660 describes a surface elastic wave device and its operating principle.

[0057] According to the present invention, the surface elastic wave device can be, as desired: a filter, a resonator, a sensor. It is however understood that the present invention is not limited to these aspects, and those skilled in the art will be able to adapt the principles thereof to any type of surface elastic wave device formed from a POI substrate.

[0058] In particular, the present invention relates to a surface elastic wave device produced on a POI substrate. In particular, the POI substrate comprises, from a front face to a rear face, a layer of piezoelectric material, a layer of dielectric material and a support substrate.

[0059] In this regard, the support substrate comprises at least one of the elements chosen from: a silicon substrate having an orientation of the (110) type, a quartz substrate having an orientation (YXt) / θ / 90° with θ between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0060] Furthermore, the device according to the present invention comprises, formed on and / or in the layer of piezoelectric material, at least one electroacoustic transducer. For example, and without however limiting the scope of the present invention, the surface elastic wave device comprises at least one input electroacoustic transducer and at least one output electroacoustic transducer formed on or in the layer of piezoelectric material. The at least one electroacoustic transducer according to the present invention may be equipped with Bragg mirrors with electrodes. Said electrodes may be arranged periodically, and in particular have a repetition period close to that of electrodes of the at least one transducer, located on either side of the transducer. The structure may include at least one free surface interval therein.The resonator thus formed is used as the impedance element of a filter combining one or more identical cells incorporating at least one resonator as described above.

[0061] It is understood that the orientation of a substrate or layer must be associated with its crystal orientation, defined according to IEEE 1949 Std-176.

[0062] It is further understood that an angular deviation from a crystalline orientation may be allowed. In particular, whatever the crystalline orientation considered, it will generally be accepted that the latter is specified to within 10°, advantageously to within 5°, around said orientation.

[0063] This is a schematic illustration of a surface elastic wave device 1 (notably in this, the device is a resonator).

[0064] In particular, the surface elastic wave device 1 comprises a POI substrate 2.

[0065] The POI substrate 2 comprises, in this regard, from a front face 3 to a rear face 4, a layer of piezoelectric material 5, a first layer 6 of dielectric material and a support substrate 7.

[0066] As an example, the surface elastic wave device 1 is a bandpass filter which has a central frequency f0 and a bandwidth Δf which can be expressed as a fraction of this central frequency, typically between 0.1% and 10% with a POI substrate provided with a piezoelectric layer 5 made of lithium tantalate LiTaO3. The consideration of a piezoelectric layer 5 based on LiNbO3 makes it possible to push the upper limit of this fraction to 15% and more by choosing the crystalline orientation of said layer so as to maximize the electromechanical coupling of the mode thus exploited.

[0067] According to one embodiment, the surface elastic wave device 1 comprises at least one electroacoustic transducer, for example, and as illustrated in, at least one input electroacoustic transducer 8 and at least one output electroacoustic transducer 9.

[0068] According to another embodiment, the surface elastic wave filter is composed of at least one cell provided with at least one surface elastic wave resonator forming a quadrupole with an input port and an output port. These are then acoustic coupling filters known to those skilled in the art under the English names LCRF (Longitudinally Coupled Resonator Filter), DMS (Double Mode SAW) filters or SCAW (Surface Cavity Acoustic Wave) filters. When several cells provided with a single transducer or several transducers connected together to form a dipole are arranged in cascade by electrical connection only, the resulting filter is generally referred to as an impedance element filter. In operation, the electromagnetic signal to be filtered is applied to the input port of the filter and the filtered electromagnetic signal is taken from the output port of the filter.It should be noted, however, that the designation "input" and "output" is completely arbitrary and that the device, and in particular the filter, with surface elastic waves 1 can be operated by applying / taking an electromagnetic signal indifferently on one or the other of the two ports.

[0069] In a very general manner, the input electroacoustic transducer 8 and the output electroacoustic transducer 9, as well as the resonators used as impedance elements in the filters with cells arranged in cascades, conform to those known from the state of the art, some characteristics of which are recalled below.

[0070] Each transducer 8 and 9 comprises two interdigitated comb electrodes. Such transducers 8 and 9 are each formed of a network of metal fingers which are alternately connected to two buses between which an electrical potential difference is applied / taken. With this device, it is thus possible to directly generate / detect an elastic surface wave in the layer of piezoelectric material 5. The input electroacoustic transducer 8 and the output electroacoustic transducer 9 are generally configured to be identical. However, the invention is not limited to this aspect; those skilled in the art may consider two different transducers.

[0071] The filters that can be formed in this way are generally referred to as transverse filters. Indeed, their transfer function can advantageously be modulated by the interpenetration of the comb-shaped electrodes along the direction of propagation of the wave. For this type of component, the transducers are capable of operating outside the Bragg condition. These filters are known to have a finite impulse response. Those skilled in the art can also implement transducers operating under the Bragg condition to which mirrors are advantageously added at each end of the filter to return the energy in phase into the structure considered, thus giving rise to filters with an infinite impulse response. The impedance element filters mentioned above also correspond to filters with an infinite impulse response insofar as they are made up of resonant elements.

[0072] The electrode metal is typically aluminum-based, for example pure aluminum or an aluminum alloy such as aluminum doped with Cu, Si, or Ti. However, it is possible to use another material, for example to establish a higher reflection coefficient for a smaller relative electrode thickness than is necessary with aluminum to achieve similar characteristics. In this respect, preferred electrode materials are copper (Cu), molybdenum (Mo), nickel (Ni), platinum (Pt), or gold (Au) with an adhesion layer such as titanium (Ti) or tantalum (Ta) or chromium (Cr), zirconium (Zr), palladium (Pd), iridium (Ir), tungsten (W), etc. The electrodes can also be composed of two materials among those designated above in order to optimize the operation of the transducer via its functions of acoustic reflection, electromechanical coupling and losses, in particular ohmic.

[0073] The period p of the electrodes is generally chosen such that p = λ / 2, λ being the wavelength of the elastic wave which propagates in the layer of piezoelectric material 5 at the synchronism frequency f s of the transducer given by f s =V φ / λ, V φ representing the phase velocity of the mode being used. The transducer then operates under the Bragg condition already mentioned above. Other configurations are possible, and more generally the period p can be written as p = λ / (nb_elec), with nb_elec the number of fingers (electrodes) per wavelength. These parameters are linked by the relation λ= V / f s, in which V represents the phase velocity of the elastic wave under the transducer. The velocity of the elastic wave on the free surface or under an electroacoustic transducer depends in particular on the nature of the material in which the wave propagates. The latter is generally known or accessible to the person skilled in the art by specifically using the elastic, piezoelectric and dielectric constants as well as the density tabulated in the literature in suitable models.

[0074] In the case of the bandpass filter, in particular of given frequency and bandwidth, it may be considered to implement transducers whose synchronism frequencies are chosen to meet the aforementioned requirements. The methods for implementing this or these choices are known to those skilled in the art and are therefore not described.

[0075] The metallization width of the electrodes, denoted a, is generally chosen so that the ratio a / p is of the order of 0.5. This aspect is not such as to limit the scope of the present invention, and those skilled in the art may consider other ratios which may prove more advantageous for a given mode / material pair. The number of pairs of fingers of each transducer is usually chosen to be of the order of 20 or 100 without being restrictive. Generally speaking, increasing the number of pairs of fingers makes it possible to increase the rejection of frequencies outside the bandwidth and reduces the spectral extent of the admittance or impedance response of the transducer around its synchronization frequency.

[0076] The surface elastic wave device 1 may also comprise two external mirrors 10 and 11 arranged on either side of the pair of input 8 and output 9 electroacoustic transducers. As is well known, these mirrors 10 and 11 make it possible to confine a maximum of the elastic energy between the two input 8 and output 9 electroacoustic transducers. As such, they are designed to have a very high reflection coefficient, as close as possible to 1 (total reflection of the incident energy), by choosing the thickness of the electrodes of the mirrors and the number of these electrodes, typically a few tens per mirror in the case of a POI substrate for a shear wave. It should be noted, however, that these two external mirrors are in no way essential to the invention, and that a device in accordance with the invention and fully functional may be without them.

[0077] The present invention aims to propose a device, for example a filter (without however limiting the invention to this single aspect), with surface elastic waves 1 for which the temperature sensitivity remains limited for frequencies below 1 GHz.

[0078] In this respect, the temperature behavior of a surface elastic wave filter is generally correctly represented by the following relationship:

[0079]

[0080] Temperature sensitivity requirements require that the TCF1 coefficient be controlled below a threshold value over the operating frequency range of the surface elastic wave device. More particularly, it is advantageous to maintain the TCF1 coefficient at a value below 20 ppm / K, advantageously below 15 ppm / K, even more advantageously below 10 ppm / K.

[0081] The inventors were able to observe that the POI substrates known from the state of the art exhibit a relatively high temperature sensitivity when they are used for the manufacture of surface elastic wave devices operating at frequencies below 1 GHz, and more particularly between 400 MHz and 1 GHz.

[0082] It is understood that all of the graphical representations described in the remainder of the statement of the present invention are the result of numerical simulations based on models (implementing an analysis based on Green functions of the substrates and numerical methods such as finite elements and boundary elements) taking into account the characteristics of the transducers studied. The details relating to these simulations are not presented in the statement which follows. However, those skilled in the art will find in document [3], cited at the end of the description, the theoretical elements allowing them to be reproduced.

[0083] As an example, curve A illustrates the variation of the coefficient TCF1 of the fundamental elastic mode of surface shear propagating on a POI substrate known from the state of the art. In particular, this substrate comprises, from a front face to a rear face, the following layers:

[0084] - a layer of LiTaO3 of cut (XYl) / 42° with a thickness equal to 600 μm

[0085] - a layer of SiO2 with a thickness equal to 500 nm

[0086] - a silicon substrate of type 100 and a thickness equal to 650 µm (the silicon substrate is assumed to be semi-infinite in the calculation of the variation of the TCF1 coefficient).

[0087] On this, the coefficient TCF1 of the fundamental elastic mode of surface shear propagating on the POI substrate known from the state of the art remains lower than 15 ppm / K for operating frequencies above 1.3 GHz, but can reach values ​​higher than 20 ppm / K, or even 25 ppm / K, as soon as the frequency is lower than 1 GHz.

[0088] To overcome this problem, the inventors were able to study the effect of the crystalline orientation of the silicon substrate 7.

[0089] In particular, the inventors were able to clearly observe a reduction in the TCF1 coefficient when the 100 type silicon substrate is replaced by a 110 silicon substrate. Considering a 110 silicon substrate induces a reduction, and more particularly a reduction of 1%, in the electromechanical coupling factor of the mode considered.

[0090] Considering a support substrate made of 110 silicon makes it possible to reduce the TCF1 coefficient for frequencies below 1 GHz, and in particular between 400 MHz and 1 GHz.

[0091] More particularly, according to the present invention, it is also possible to consider a support substrate made of silicon of the 110 type (or (XYw) / 45° cut according to the IEEE Std-176 standard) or even of the IEEE Std-176 (XYt) / 45° type.

[0092] In this respect, the graphical illustration illustrates the evolution of the TCF1 coefficient as a function of the frequency of fundamental elastic modes of surface shear each guided on a different POI substrate. Each POI substrate considered comprises a layer of piezoelectric material made of LiTaO3 and with a thickness equal to 700 nm, and a layer of dielectric material made of SiO2 and with a thickness equal to 350 nm. Furthermore, curve C is obtained for a POI substrate which comprises a silicon support substrate of the 110 type while curve D is obtained for a POI substrate which comprises a silicon support substrate of the IEEE Std-176 (XYt) / 45° or (YXt) / 45° type.

[0093] In both cases, the TCF1 coefficient remains below 13 ppm / K while the electromechanical coupling of the surface elastic mode considered is little affected compared to that observed when the fundamental surface shear elastic mode is guided by a POI substrate known from the state of the art.

[0094] The inventors note that it is also possible to consider a support substrate made of quartz having an orientation (YX / t) / θ / 90° with θ between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0095] Alternatively or additionally, and with the aim of reducing the TCF1 coefficient, it is possible to adapt the stack formed on the support substrate 7. In particular, the first layer 6 of dielectric material comprises silicon dioxide and has a thickness greater than 300 nm, advantageously between 300 nm and 600 nm, even more advantageously between 300 nm and 400 nm.

[0096] Equivalently, it is possible to consider a layer of piezoelectric material 5 made of LaTiO3 or LiNbO3 and with a thickness of between 300 nm and 1000 nm, advantageously less than 800 nm, even more advantageously less than 700 nm.

[0097] The inventors also studied the effect of the crystal orientation of the piezoelectric material layer on the amplitude of the TCF1 coefficient. In order to illustrate the effect of the crystal orientation of the piezoelectric material layer, it is proposed to consider a surface mode guided by a POI substrate which comprises, from its front face to its back face, a layer of LiTaO3 which has a thickness of 700 nm and a crystal orientation (YZl) / θ (with θ between 0° and 30°), a layer of SiO2 which has a thickness of 350 nm and a support substrate made of silicon.

[0098] More particularly, la and la represent the variation, respectively, of the TCF1 coefficient and of the electromechanical coupling associated with the fundamental elastic mode of surface shear guided by a POI substrate described above and as a function of the angle θ of the LiTaO3 layer. Thus, for values ​​of θ between 10° and 35°, advantageously between 15° and 30°, the TCF1 coefficient remains lower than 15 ppm / K and the electromechanical coefficient is greater than 10%.

[0099] According to a complementary or alternative aspect to the above, the POI substrate according to the present invention may further comprise a second layer 12 interposed between the layer of piezoelectric material 5 and the first layer 6 of dielectric material (). The second layer 12 is advantageously associated with a temperature coefficient of the frequency of sign opposite to that with which the layer of dielectric material 5 is associated. This latter aspect makes it possible to compensate for the effect associated with the layer of dielectric 6 on the coefficient TCF1.

[0100] It is understood, according to the present invention, that a temperature coefficient of the frequency associated with a layer of a given material corresponds to the temperature coefficient of the frequency of a surface elastic mode propagating on said layer. It is also understood that, in the present case, two temperature coefficients of the frequency are compared for frequencies below 1 GHz.

[0101] The additional layer may comprise a dielectric material and / or a semiconducting or even piezoelectric material.

[0102] According to the present invention, since the dielectric layer 6, for example made of SiO2, is associated with a positive temperature coefficient of the frequency, that with which the second layer 12 is associated, for example made of SiN, Al2O3 or AlN, is negative.

[0103] Furthermore, in order not to disturb the properties of the fundamental acoustic shear modes guided by the stack of material forming the POI substrate, the additional layer may have, for frequencies below 1 GHz, an acoustic impedance greater than or equal to that of the first layer 6 of dielectric material.

[0104] Consideration of the second layer 12 also makes it possible to reduce the TCF1 coefficient of a fundamental elastic mode of guided shear on POI. Since the layer comprises silicon nitride (SiN), this reduction can reach 5 ppm / K or even more depending on the thickness of said layer.

[0105] The addition of a step of producing an additional TCF layer of opposite sign to that of the dielectric material layer makes it possible to respectively reduce / increase the thickness of the piezoelectric layer / dielectric layer to achieve a given TCF, and thus transfer the piezoelectric layer by a SmartCut™ process without damaging it and without inducing lithium diffusion into the support substrate. The risk of lithium diffusion occurs at the time of annealing to strengthen the bonding interface or to exodiffuse the implantation hydrogen (likely to invert µ-domains).

[0106] It is understood, but not necessary to specify, that the silicon nitride considered in the present invention is not necessarily stoichiometric.

[0107] The inventors have further noted that the positioning of the second layer 12 under the first layer 6 of dielectric material does not produce a notable effect on the coefficient TCF1 of a surface elastic mode propagating in the POI substrate.

[0108] Advantageously, the second layer 12 has a thickness of between 20 nm and 300 nm.

[0109] The implementation of the second layer 12 advantageously makes it possible to consider a dielectric layer 6 of greater thickness.

[0110] Furthermore, a second layer 12 made of SiN and a first layer 6 of dielectric material made of SiO2 can be formed during the same process step, and in particular in a pressure-enhanced chemical vapor deposition (PECVD) frame.

[0111] As an illustration of the implementation of the second layer 12, the inventors estimated its effect on the TCF1 coefficient of the fundamental elastic mode of guided surface shear on the POI substrate. This simulation implements an analysis based on Green functions representing the dispersive behavior of the modes on laminated substrates.

[0112] The POI substrate considered in this analysis includes, from its front face to its rear face:

[0113] - A layer 5 of LiTaO3 oriented according to the (YXl) / 42° cut of this crystal and with a thickness equal to 600 nm;

[0114] - A layer 12 of SiN with a thickness equal to 100 nm

[0115] - A layer 6 of SiO2 having a thickness capable of taking one of the values ​​between 300 nm and 600 nm

[0116] - A support substrate 7 made of silicon.

[0117] The POI substrate may also include a trapping layer made of polycrystalline silicon and having a thickness of the order of 1 µm and more generally between 400 nm and 2 µm.

[0118] The inventors were able to evaluate the phase velocity of the waves likely to propagate in layer 5 of LiTaO3, the electromechanical coupling factor as well as the TCF1 coefficient of the fundamental elastic mode of surface shear guided on the POI substrate described above.

[0119] The results of these evaluations are shown in, and.

[0120] In particular, it represents, graphically (according to a 3D representation), the phase velocity of the waves likely to propagate in the layer 5 of LiTaO3 of the fundamental elastic mode of surface shear guided on the POI substrate described above. The phase velocity of this mode, noted v ϕ (vertical axis, in m / s), is represented as a function of the operating frequency of the filter (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0121] Larepresents, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear guided on the POI substrate described above. The electromechanical coupling factor, denoted k s 2 (vertical axis, in %), is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0122] It graphically represents (in a 3D representation) the TCF1 coefficient of the fundamental elastic mode of guided surface shear on the POI substrate described above. The TCF1 coefficient (vertical axis, in ppm / K) is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0123] According to the, the TCF1 of the surface elastic mode considered is less than 10 ppm / K for frequencies between 600 MHz and 2 GHz and for SiO2 thicknesses less than or equal to 350 nm. This relatively low value of the TCF1 coefficient, with respect to the modes used for the manufacture of filters known from the state of the art, is attributable to the implementation of the SiN layer 12. However, as illustrated in the and the, the implementation of the second layer 12 induces an increase in the phase velocity and a reduction in the electromechanical coupling factor of the order of 1% with respect to a guided elastic surface shear wave known from the state of the art, i.e. devoid of the SiN layer.

[0124] All of the elements described in the statement of the present invention make it possible to achieve an adjustment of the TCF1 coefficient. Indeed, in accordance with the technical objective that the present invention proposes to resolve, it is a question of limiting, or controlling, the effect of temperature on the operation of a surface elastic wave device formed from a POI substrate.

[0125] An adjustment is illustrated as an example by considering a surface elastic wave device formed from the POI substrate which comprises from its front face to its back face:

[0126] - A layer 5 of LiTaO3 oriented at an angle (YXl) / 42°;

[0127] - A layer 12 of SiN having a thickness equal to 100 nm;

[0128] - A layer 6 of SiO2 having a thickness capable of taking one of the values ​​between 300 nm and 600 nm

[0129] - A trapping layer made of polycrystalline silicon and having a thickness of the order of 1 µm;

[0130] - A support substrate 7 made of silicon.

[0131] The results of these evaluations are shown in, in, in and in.

[0132] Larepresents, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear guided on the POI substrate described above and whose thickness of the layer 5 of LiTaO3 is equal to 700 nm. The electromechanical coupling factor, noted k s 2 (vertical axis, in %), is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0133] It graphically represents (in a 3D representation) the coefficient TCF1 of the fundamental elastic mode of surface shear guided on the POI substrate described above and whose thickness of the layer 5 of LiTaO3 is equal to 700 nm. The coefficient TCF1, noted TCF1 (vertical axis, in ppm / K), is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the layer 6 of SiO2 (axis B in nm).

[0134] Larepresents, graphically (according to a 3D representation), the electromechanical coupling factor of the fundamental elastic mode of surface shear guided on the POI substrate described above and whose thickness of the layer 5 of LiTaO3 is equal to 800 nm. The electromechanical coupling factor, noted k s 2 (vertical axis, in %), is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0135] It represents, graphically (according to a 3D representation), the coefficient TCF1 of the fundamental elastic mode of surface shear guided on the POI substrate described above and whose thickness of the layer 5 of LiTaO3 is equal to 800 nm (The star corresponds to an operating point for which k s 2 is maximum while the TCF1 coefficient is minimum). The TCF1 coefficient, noted TCF1 (vertical axis, in ppm / K), is represented as a function of the operating frequency of the mode (axis A in MHz) and the thickness of the SiO2 layer 6 (axis B in nm).

[0136] The implementation of the second layer 12 of SiN, allows, for a layer 6 of SiO2 with a thickness of less than 400 nm and a layer of LiTaO3 with a thickness equal to 700 nm, to obtain an electromechanical coupling factor of the mode greater than 10% () for frequencies between 800 MHz and 1600 MHz, and a TCF coefficient 1r close to 10 ppm / K ().

[0137] Equivalently, the same second layer 12 of SiN, allows, for a layer 6 of SiO2 with a thickness less than 400 nm and a layer of LiTaO3 with a thickness equal to 800 nm, to obtain an electromechanical coupling factor of the mode greater than 11% () for frequencies between 800 MHz and 1600 MHz, and a TCF coefficient 1r close to less than 10 ppm / K ().

[0138] The entire description is limited to the parameters relating to the fundamental shear mode according to its operating frequency, and more particularly to the control of the TCF1 parameter characterizing the surface elastic mode considered. However, a person skilled in the art will understand that a surface elastic wave device based on the exploitation of the mode of interest also has a resonance frequency and an anti-resonance frequency, itself characterized by its own TCF1 coefficient. A very low, or even zero, TCF1 coefficient characterizing the resonance can have a negative impact on the TCF1 coefficient characterizing the anti-resonance of the device considered, in particular in the case of single-rotation cuts of lithium niobate and tantalate known to have, for the same mode and particularly for the shear modes of the TCFs, resonance and anti-resonance that are different from each other.

[0139] The present invention therefore also proposes an optimization of the parameters characterizing the POI substrate in order to better appreciate the coefficients TCF1relating, respectively, to the resonance and to the anti-resonance of a device formed on said substrate. More particularly, the present invention proposes to adjust the coefficient TCF1relating to the resonance (hereinafter TCF 1r ) and the coefficient TCF1 relating to anti-resonance (hereinafter TFC 1AR ). In particular, the present invention proposes to adjust the TCF coefficient 1r at values ​​below 15 ppm / K and the TFC coefficient 1AR to values ​​between –4 ppm / K and 0 ppm / K. Equivalently, the present invention proposes to adjust the TCF coefficient 1R at lower values ​​between 5 ppm / K and 10 ppm / K and the term TFC 1AR at values ​​between –10 ppm / K and -5 ppm / K.

[0140] These objectives can be achieved in particular by implementing simulations of the evolution of the different terms and coefficients described above in order to define the material layers and their respective thicknesses.

[0141] The inventors also studied materials other than SiN to form the second layer 12.

[0142] More particularly, the second layer 12 may comprise at least one of the materials chosen from: SiC, Al2O3, AlN, Diamond carbon, GaN, LiNbO3, ZnO.

[0143] This is a graphical representation of the evolution of the phase velocity of the fundamental shear mode (vertical axis, in m / s) as a function of frequency (horizontal axis in MHz) on a POI substrate which comprises a 600 nm LiTaO3(YXl)42° layer, a 100 nm additional layer, a 400 nm dielectric layer, and a Silicon support substrate, the additional layer possibly comprising Diamond Carbon, GaN, ZnO, LiNbO3.

[0144] This is a graphical representation of the evolution of the phase velocity of the fundamental shear mode (vertical axis, in m / s) as a function of frequency (horizontal axis in MHz) on a POI substrate which comprises a 600 nm LiTaO3(YXl)42° layer, a 100 nm additional layer, a 400 nm dielectric layer, and a Silicon support substrate, the additional layer possibly comprising SiN, poly-Si, AlN, Al2O3.

[0145] Thus, with the exception of diamond carbon, the same behavior is observed when the mode phase velocity tends towards the shear wave velocity in silicon at low frequencies. Decreasing said mode velocity is equivalent to increasing the wavelength of the mode considered for a given frequency, and thus reduces the influence of the composite structure of the POI substrate.

[0146] From these observations and an appropriate mathematical treatment (the consideration of the derivative of the phase velocity with respect to the frequency), it emerges that LiNbO3 is the most favorable material to minimize the modal sensitivity to the frequency in the range 800-1200 MHz.

[0147] A second layer 12 made of Diamond Carbon appears advantageous for frequencies below 800 MHz.

[0148] The implementation of an additional layer of LiNbO3, with a thickness of 100 nm, placed between a dielectric layer 6 made of SiO2 and a piezoelectric layer 5 made of LiTaO3, makes it possible to reduce the TCF1 coefficient to a value lower than 10 ppm / K, regardless of the crystalline orientation of the piezoelectric layer.

[0149] The present invention as described above covers a plurality of aspects which can be considered independently or in combination in order to optimize (reduce) the TCF1 coefficient to values ​​below 20 ppm / K, advantageously below 15 ppm / K, even more advantageously below 10 ppm / K, provided that the operating frequency of the device and in particular of the surface elastic wave filter is below 1 GHz.

[0150] Advantageously, the POI substrate also comprises a trapping layer interposed between the layer of dielectric material and the support substrate, the trapping layer being adapted to limit the mean free path of electric carriers at the interface formed between the layer of dielectric material and the trapping layer with respect to the mean free path of electric carriers at an interface formed between the layer of dielectric material and the support substrate.

[0151] In this regard, the trapping layer may comprise polycrystalline silicon and advantageously has a thickness of between 400 nm and 2000 nm.

[0152] The invention also relates to a method of manufacturing the surface elastic wave device.

[0153] Said method notably comprises forming the surface elastic wave device from a POI substrate. The method advantageously comprises forming the POI substrate.

[0154] A method of manufacturing an elastic wave device configured to operate at a frequency below 1 GHz, and formed on a POI substrate.

[0155] The formation of the POI substrate advantageously includes the following steps:

[0156] a) a step of implanting species in a donor substrate, made of a piezoelectric material, the implantation of species being intended to form a layer, called a weakening zone in the volume of the donor substrate, and delimiting with one face, called the main face, of said donor substrate, a useful layer;

[0157] b) a step of transferring the useful layer onto a front face of a support substrate, the transfer step comprising in order an assembly of the useful layer with a face, called the front face, of the support substrate, and a heat treatment intended to initiate a fracture wave along the weakening zone in order to transfer the useful layer onto the front face;

[0158] The method further comprises the formation of an intermediate stack 101, interposed between the front face and the useful layer, and which comprises, from the front face, a first layer, a second layer and a third layer, the first layer and the third layer comprising silicon dioxide, and the second layer comprising silicon nitride.

[0159] Thus, this is an illustration of a POI substrate 100 that can be obtained by carrying out the manufacturing method according to the present invention. In particular, the POI substrate comprises, in order, a support substrate 110, a first layer 120, a second layer 130, a third layer 140 (the first layer 120, the second layer 130 and the third layer 140 forming an intermediate stack 101) and a useful layer 150.

[0160] In this regard, the first layer 120 may comprise SiO2, the second layer 130 may comprise silicon nitride (SiN), and the third layer 140 may comprise SiO2.

[0161] Advantageously, the POI substrate 100 may also comprise a trapping layer 160. In particular, the trapping layer 160 may comprise amorphous silicon and / or polycrystalline silicon.

[0162] The trapping layer 160 is interposed between the intermediate stack 101 and a front face 110a of the support substrate 110. In particular, the trapping layer 160 is adapted to limit the mean free path of electrical carriers at the interface formed between the intermediate stack and said trapping layer with respect to the mean free path of electrical carriers at an interface formed between the intermediate stack and the support substrate.

[0163] Advantageously, the support substrate comprises at least one of the elements chosen from: a silicon substrate having the 110 orientation, a quartz substrate having an orientation (YX / t) / θ / 90° with θ between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0164] This is an illustration of step a). In particular, step a) comprises the implantation of species by a face, called the main face 200 of a donor substrate 210 which comprises a piezoelectric material.

[0165] In particular, step a) is carried out so as to form a layer, called a weakening zone 211 in the volume of the donor substrate 210, and delimiting with the main face 200 of said donor substrate, the useful layer 150.

[0166] It is understood, without it being necessary to specify it, that the weakening zone 211 forms a layer essentially parallel to the main face 200.

[0167] It is also understood that the thickness of the useful layer 150 depends on the conditions of implantation of the species and their nature.

[0168] For example, a person skilled in the art, for carrying out step a), may consider the implantation of hydrogen or helium ions.

[0169] Advantageously, step a) may be preceded by a preliminary step, during which the piezoelectric material is subjected to an oxygen vapor treatment so as to limit, or even reduce, the pyroelectric effects likely to appear in the donor substrate, and consequently in the useful layer, when it is subjected to an increase in temperature.

[0170] The method may also include forming the layer of dielectric material on either the donor substrate or the support substrate, such as by PECVD.

[0171] The method may also comprise forming the additional layer, for example on the dielectric layer if the latter is first formed on the support substrate.

[0172] Advantageously, the donor substrate 210 may comprise iron-doped lithium tantalate, the iron doping being between 0.001% and 0.05%, advantageously between 0.002% and 0.01%, in mass percentage.

[0173] Advantageously, the formation of the intermediate stack 101 may comprise the formation of the third layer 140 on the main face before the execution of the implantation step a). The third layer 140 may be formed by PECVD.

[0174] Advantageously, the third layer has a thickness between 10 nm and 100 nm.

[0175] Since the third layer comprises SiO2, the aforementioned thicknesses typically correspond to one of the thicknesses less than λ / 20 and ideally less than λ / 50 where λ is the acoustic wavelength equal to twice the mechanical period of an inter-digitated transducer operating at the Bragg frequency.

[0176] Equivalently, the formation of the intermediate stack may comprise the formation of the first layer 120 on a front face 110 of a support substrate 110, then the formation of the second layer 130 covering the first layer 120 ().

[0177] Advantageously, the first layer has a thickness of between 100 nm and 1000 nm, advantageously between 300 nm and 800 nm, and the second layer has a thickness of between 20 nm and 300 nm.

[0178] The ratio of the thickness of the second layer to the thickness of the first layer will advantageously be between 1:4 and 1:3. For example, the thickness of the piezoelectric layer made of LaTiO3 may be between 500 nm and 800 nm, the second layer, made of SiN, may have a thickness between 100 nm and 200 nm, and the first layer, made of SiO2, may have a thickness between 300 and 600 nm.

[0179] The formations of the third layer 140 on the one hand, and of the first layer 120 and of the second layer 130 on the other hand are followed by a step b) of transferring the useful layer 150 onto a front face of a support substrate, the transferring step comprising in order an assembly of the useful layer with a face, called the front face 110a, of the support substrate 110, and a heat treatment intended to initiate a fracture wave along the weakening zone in order to transfer the useful layer 150 onto the front face 110a.

[0180] Advantageously, the assembly may comprise bringing the second layer 130 and the third layer 140 () into contact.

[0181] Thus, according to the present invention, the third layer is an adhesion layer formed at least in part on the donor substrate and more particularly on the main face of said donor substrate.

[0182] This latter aspect thus allows the execution, before assembly, of a heat treatment for exodiffusion of the hydrogen likely to be present in the second layer. Indeed, the second layer, which comprises SiN, is obtained by gas phase deposition of a mixture of silane with NH3 and / or N2. Consequently, said second layer comprises hydrogen which should be eliminated in order to prevent its migration towards the piezoelectric layer at the end of step b). Thus, the formation of the second layer on the front face of the support substrate makes it possible to execute a heat treatment only on the support substrate, on the first layer and on the second layer. This latter aspect makes it possible to limit the thermal history of the piezoelectric material and to preserve its properties (in particular to limit the risks of domain inversion).Considering the third layer formed, at least partly on the main face of the donor substrate, allows the latter to be considered as a bonding layer. In other words, this aspect limits the thermal history of the piezoelectric material and limits the risks of domain inversion.

[0183] The thickness of the third SiO2 layer is between 10nm (covering the entire surface) and 50nm.

[0184] Alternatively, it is possible to make an ADB bond with a third layer made of amorphous silicon with a thickness of a few nm.

[0185] The assembly is advantageously a molecular collage.

[0186] Illustrates a heat treatment intended to initiate a fracture wave along the weakening zone in order to transfer the useful layer 150 onto the front face in order to form the POI substrate shown in the.

[0187] The method may also include forming the trapping layer 160 on the support substrate 110 prior to forming the first layer 120. In other words, the first layer 120 is formed overlying the trapping layer.

[0188] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims. REFERENCES

[0189] [1] T. Pastureaud, et al., “High-Frequency Surface Acoustic Waves Excited on Thin-Oriented LiNbO3Single-Crystal Layers Transferred Onto Silicon”, IEEE Trans. on UFFC, vol. 54, no. 4, pp.870-876, 2007;

[0190] [2] US 2014 / 0152146 A1;

[0191] [3] S. Ballandras, et al., “Simulations of surface acoustic wave devices built on stratified media using a mixed finite element / boundary integral formulation”, Journal of Applied Physics, Vol. 95, n  12, pp. 7731-7741, 2004.

Claims

Method for manufacturing an elastic wave device configured to operate at a frequency below 1 GHz, and formed on a POI substrate, the formation of the POI substrate comprising the following steps: a) a step of implantation of species in a donor substrate, comprising LiTaO3, the implantation of species being intended to form a layer, called the embrittlement zone in the volume of the donor substrate, and delimiting with a face, called the main face, of said donor substrate, a useful layer; b) a step of transferring the useful layer onto a front face of a support substrate, the transfer step comprising in order an assembly of the useful layer with a face, called the front face, of the support substrate, and a heat treatment intended to initiate a fracture wave along the embrittlement zone in order to transfer the useful layer onto the front face;the process further comprising the formation of an intermediate stack, interposed between the front face and the useful layer, and comprising, from the front face, a first layer, a second layer and a third layer, the first layer comprising silicon dioxide, the second layer comprising silicon nitride, alumina or aluminium nitride, and the third layer comprising silicon dioxide or amorphous silicon.; A manufacturing method according to claim 1, wherein the intermediate stack also comprises a third layer such that the second layer is intercalated between the first layer and the third layer, said third layer comprising silicon dioxide or amorphous silicon. A manufacturing method according to claim 2, wherein the formation of the POI substrate also comprises a layer, called a trapping layer, interposed between the intermediate stack and the front face, the trapping layer being adapted to limit the mean free path of electric carriers at the interface formed between the intermediate stack and said trapping layer with respect to the mean free path of electric carriers at an interface formed between the intermediate stack and the support substrate. A manufacturing method according to claim 3, wherein the trapping layer comprises a defect density greater than a predetermined defect density, the predetermined defect density being a defect density for which the resistivity of the trapping layer is greater than or equal to 10 Kilo-ohm for temperatures between -20°C and 120°C. A manufacturing process according to claim 4, wherein the trapping layer comprises at least one of the materials included among: amorphous silicon, polycrystalline silicon. Manufacturing method according to any one of claims 2 to 5, wherein the stack formation includes the formation of the third layer on the main face before the execution of step a) of implantation. Manufacturing method according to claim 6, wherein the stack formation includes the formation of the first layer and the second layer on the front face such that the assembly, during the execution of step b), includes the contacting of the second layer and the third layer. A manufacturing method according to any one of claims 2 to 7, wherein the third layer has a thickness between 10 nm and 100 nm. A manufacturing process according to any one of claims 1 to 8, wherein said process includes a preliminary step, carried out before step a), and during which the donor substrate is subjected to vapor phase oxygen treatment so as to limit, or even reduce, the pyroelectric effects that may appear in the donor substrate, and consequently in the useful layer, when it is subjected to a temperature rise. A manufacturing process according to any one of claims 1 to 9, wherein the donor substrate comprises iron-doped lithium tantalate, the iron doping being between 0.001% and 0.05%, advantageously between 0.002% and 0.01%, by mass percentage. A manufacturing method according to any one of claims 1 to 10, wherein the first layer has a thickness between 100 nm and 1000 nm, advantageously between 300 nm and 600 nm, and the second layer has a thickness between 100 nm and 200 nm. A manufacturing method according to any one of claims 1 to 11, wherein said method comprises the formation of at least one electroacoustic transducer formed on and / or in the useful layer. A manufacturing method according to any one of claims 1 to 12, wherein the support substrate comprises at least one of the elements selected from: a silicon substrate having the 110 orientation, a quartz substrate having an (YX / t) / θ / 90° orientation with θ between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°. Manufacturing method according to any one of claims 1 to 13, wherein the LiTaO3 material has an (YX) / θ orientation with θ between 10° and 52°, advantageously between 15° and 30°.

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