Method for manufacturing surface elastic wave device

Abstract

The present invention relates to a method for manufacturing an elastic wave device configured to operate at a frequency of less than 1 GHz and formed on a POI substrate, the forming of the POI substrate comprising the following steps: a) a step of implanting a substance in a LiTaO3 substrate (210) to form a useful layer (150); and b) a step of transferring the useful layer onto the front face of a support substrate (110); the method further includes forming an intermediate stack between the front side and the useful layer, and the intermediate stack includes, starting from the front side, a first layer (120) including silicon dioxide, a second layer (130) including silicon nitride, aluminum oxide, or aluminum nitride, and a third layer (140) including silicon dioxide or amorphous silicon.

Description

Technical Field

[0001] The present invention relates to the field of surface elastic wave devices, and more particularly to a method for manufacturing a surface elastic wave device, wherein the surface elastic wave device is formed by a POI substrate including a piezoelectric material layer. Background Art

[0002] Surface acoustic wave filters (SAW filters or surface acoustic wave filters), which were originally manufactured on a solid substrate of single-crystal piezoelectric material (hereinafter referred to as a "solid substrate"), now use a piezoelectric substrate on an insulator (hereinafter referred to as a "POI"). The latter specifically includes a piezoelectric material layer, a dielectric material layer and a supporting substrate from the front side to the back side.

[0003] Unlike solid substrates, these POI substrates are able to meet certain requirements regarding the temperature sensitivity of guided surface elastic modes in the piezoelectric material layer.

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

[0005] Generally speaking, the surface elastic mode propagating on the POI substrate from which the surface elastic wave device is formed has a relatively low temperature coefficient of frequency (CTF or in English terminology "temperature coefficient of frequency" ("TCF"), in particular less than 10 ppm.K -1 , the frequency range is 1.4GHz to 2.4GHz.

[0006] The POI substrate can be manufactured by using a process known in the microelectronics field called "SmartCut TM ” process, particularly for the manufacture of silicon-on-insulator substrates.

[0007] In this regard, the document [1] cited at the end of the specification proposes the use of SmartCut TM process, the piezoelectric material layer, and more specifically LiNbO 3 (hereinafter referred to as "LNO") onto a silicon substrate.

[0008] The document [2] cited at the end of the specification also discloses the use of LiTaO 3 The POI substrate of the layer is used for manufacturing a surface elastic wave filter. The surface elastic wave filter described in this document includes a lithium tantalate film on a mirror layer, and the mirror layer is formed of low acoustic impedance layers and high acoustic impedance layers alternately on a silicon substrate.

[0009] It is also considered to insert a so-called trapping layer between the supporting substrate and the layer of dielectric material, which is made of polysilicon for example and is intended to limit the mean free path of the charges at the interface of the stack and the possible crosstalk within the filter formed by the associated POI substrate.

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

[0011] So you can use SmartCut TM The POI substrate formed by the process is usually used to design a surface elastic wave filter operating at a resonance / anti-resonance frequency greater than 1 GHz.

[0012] Nowadays, people are interested in forming surface elastic wave filters that are formed on POI substrates and operate at resonant / antiresonant frequencies less than 1 GHz. However, in order to control the frequency temperature coefficient of the surface elastic mode propagating on the POI substrate to a reasonable value (e.g., less than 10 ppm.K -1 ), it may be necessary to adjust the thickness of the piezoelectric material layer and / or the dielectric material layer. More specifically, it may be necessary to reduce the thickness of the dielectric material layer and / or increase the thickness of the piezoelectric material layer.

[0013] In this regard, SmartCut TM The process has the versatility needed to adjust the thickness of these layers.

[0014] However, thin dielectric material layers, especially those with a thickness of less than 300 nm or even less than 200 nm, are no longer effective barriers to prevent the diffusion of certain species that may form piezoelectric material layers. For example, dielectric material layers with a thickness of less than 300 nm will cause lithium to diffuse from LaTiO 3 In particular, diffusion into the dielectric material (e.g., SiO 2 ) layer causes RF losses.

[0015] Furthermore, it is undesirable to consider piezoelectric material layers that are too thick, in particular thicker than 500 nm. TM These thicknesses require taking into account the relatively high energy required to implant the solid piezoelectric material substrate (donor substrate) when forming the POI substrate, which can result in damage that is generally unacceptable for forming a surface elastic wave filter.

[0016] Therefore, an object of the present invention is to provide a method for manufacturing a surface elastic wave device, wherein the surface elastic wave device operates at a frequency less than 1 GHz, using SmartCut TM process, and wherein diffusion of the species remains restricted during performance of the method. Summary of the invention

[0017] The object of the present invention is achieved by a method for manufacturing an elastic wave device, wherein the elastic wave device is configured to operate at a frequency less than 1 GHz and is formed on a POI substrate, wherein forming the POI substrate comprises the following steps:

[0018] a) In the case of LaTiO 3 a step of implanting a substance into the donor substrate of the present invention, the implantation of said substance being intended to form a layer called embrittlement zone in the volume of the donor substrate and delimiting a useful layer together with a face called main face of said donor substrate;

[0019] b) a step of transferring the useful layer onto the front side of the support substrate, the transfer step comprising, in sequence, assembling the useful layer with a face of the support substrate, called the front side, and carrying out a heat treatment aimed at inducing a fracture wave along the weakening in order to transfer the useful layer onto the front side;

[0020] The method also includes forming an intermediate stack, which is located between the front side and the useful layer, and the intermediate stack includes a first layer, a second layer and a third layer starting from the front side, the first layer includes silicon dioxide, the second layer includes silicon nitride, aluminum oxide or aluminum nitride, and the third layer includes silicon dioxide or amorphous silicon.

[0021] According to one embodiment, the POI substrate further includes a layer called a trapping layer, which is located between the intermediate stack and the front side, and the trapping layer is suitable for limiting the mean free path of the electric carriers at the interface formed between the intermediate stack and the trapping layer relative to the mean free path of the electric carriers at the interface formed between the intermediate stack and the supporting substrate.

[0022] According to one embodiment, the trapping layer includes a defect density greater than a predetermined defect density, the predetermined defect density being a defect density at 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 following materials: amorphous silicon, polycrystalline silicon.

[0024] According to one embodiment, forming the stack comprises forming a third layer on the main face before performing the implanting step a).

[0025] According to one embodiment, forming the stack includes forming the first layer and the second layer on the front side, such that when performing step b), assembling includes contacting the second layer and the third layer.

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

[0027] According to one embodiment, the method comprises a preliminary step carried out before step a) and during which the donor substrate is subjected to a gas-phase oxygen treatment in order to limit or even reduce thermoelectric effects that may appear in the donor substrate and therefore in the useful layer when the donor substrate is subjected to an increase in temperature.

[0028] According to one embodiment, the donor substrate comprises lithium tantalate doped with iron, the iron doping being between 0.001% and 0.05%, advantageously between 0.002% and 0.01%, by weight.

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

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

[0031] According to one embodiment, the supporting substrate comprises at least one of the following elements: a silicon substrate with a 110 orientation, a quartz substrate with a (YXt) / θ / 90° orientation, wherein 0 is between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0032] According to one embodiment, the LiTaO 3 material has an orientation (YX) / θ, wherein θ is between 10° and 52°, advantageously between 15° and 30°. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other features and advantages of the present invention will be explained in the following detailed description with reference to the accompanying drawings, in which:

[0034] [ Figure 1 ] is a schematic diagram of a surface elastic wave resonator in accordance with the principle of the present invention on a cross-sectional plane perpendicular to the main surface of the supporting substrate of the POI substrate;

[0035] [ Figure 2 ] is the TCF of the surface shear fundamental elastic mode propagating under the periodic electrode array of the POI substrate 1Graph representation of the variation of the coefficient (vertical axis, in ppm / K) with the frequency (horizontal axis, in MHz) for a so-called standard POI substrate, which comprises, in order from the front side: a 600 nm thick lithium tantalate layer (according to the IEEE Std-176 piezoelectricity standard, the lithium tantalate layer has a (YX1) / 42° cut), a 500 nm thick silicon dioxide layer, a 1 μm polysilicon layer and a 100 type silicon substrate;

[0036] [ Figure 3 ] is the TCF of the surface elastic mode propagating under the periodic electrode array of the POI substrate 1 Graphical representation of the coefficient (vertical axis, in ppm / K) as a function of frequency (horizontal axis, in MHz), in particular, curves C and D represent the TCF associated with a POI substrate comprising a support substrate made of silicon 1 coefficients, the support substrate is respectively of 110 type or (XYt) / 45° or (YXt) / 45° type according to standard IEEE Std-176;

[0037] [ Figure 4 ] shows the TCF of the surface shear fundamental elastic mode propagating on the POI substrate 1 (vertical axis, unit: ppm / K) with LiTaO 3 Variation of the cutting angle θ (horizontal axis, unit is angle °) of the layer. The considered POI substrate includes a support substrate made of silicon and a 350 nm thick LiTaO 3 SiO between layers 2 layer;

[0038] [ Figure 5 ] is displayed in the Figure 4 The electromechanical coupling (vertical axis, in %) of the surface shear fundamental elastic mode propagating on the POI substrate described in the related literature varies with the LiTaO 3 Changes in the cutting angle θ of the layer (horizontal axis, in degrees);

[0039] [ Figure 6 ] is a schematic diagram of a surface elastic wave resonator in accordance with the principle of the present invention on a cross-sectional plane perpendicular to the main surface of the supporting substrate of the POI substrate;

[0040] [ Figure 7 ] graphically (based on 3D representation) shows the LiTaO surface acoustic wave device formed by the above POI substrate 3 The phase velocity of waves that can propagate in layer 5. This phase velocity, represented by vφ (vertical axis, in m / s), is plotted as a function of the device operating frequency (A axis, in MHz) and the SiO 2Function of the thickness of layer 6 (B axis, in nm);

[0041] [ Figure 8 ] graphically (based on a 3D representation) represents the electromechanical coupling factor of the surface shear fundamental elastic mode propagating on the above POI substrate, expressed as k s 2 The electromechanical coupling factor (vertical axis, unit: %) represented by the operating frequency (A axis, unit: MHz) of the infinite periodic transducer formed on the POI substrate and the SiO 2 Function of the thickness of layer 6 (B axis, in nm);

[0042] [ Fig. 9 ] Graphically (based on 3D representation) represents the TCF of the surface shear fundamental elastic mode propagating in the above POI substrate 1 Coefficient. TCF 1 The TCF 1 The coefficient (vertical axis, in ppm / K) is expressed as a function of the transducer operating frequency (A axis, in MHz) and SiO 2 Function of the thickness of layer 6 (B axis, in nm);

[0043] [ Fig.10 ] graphically (based on a 3D representation) shows the electromechanical coupling factor of the surface shear fundamental elastic mode propagating in the above-mentioned POI substrate whose LiTaO 3 The thickness of layer 5 is equal to 700 nm. s 2 The electromechanical coupling factor (vertical axis, in %) represented by the operating frequency (A axis, in MHz) of the transducer formed on the POI substrate and the SiO 2 Function of the thickness of layer 6 (B axis, in nm);

[0044] [ Fig.11 ] Graphically (based on 3D representation) represents the TCF of the surface shear fundamental elastic mode propagating on the above POI substrate 1 coefficient, the POI substrate LiTaO 3 The thickness of the layer is equal to 700nm. 1 The TCF 1 The coefficient (vertical axis, in ppm / K) is expressed as a function of the transducer operating frequency (A axis, in MHz) and SiO 2 Function of the layer thickness (B axis, in nm);

[0045] [ Fig.12] graphically (based on a 3D representation) shows the electromechanical coupling factor of the surface shear fundamental elastic mode propagating on the above-mentioned POI substrate, the LiTaO 3 The thickness of the layer is equal to 800nm. s 2 The electromechanical coupling factor (vertical axis, in %) is expressed as a function of the operating frequency (A axis, in MHz) of the transducer formed on the POI substrate and the SiO 2 Function of the layer thickness (B axis, in nm);

[0046] [ Fig.13 ] graphically (based on 3D representation) shows the TCF of the surface shear fundamental elastic mode propagating on the above POI substrate 1 coefficient, the POI substrate LiTaO 3 The thickness of the layer is equal to 700nm. 1 The TCF 1 The coefficient (vertical axis, in %) is expressed as a function of the transducer operating frequency (A axis, in MHz) and SiO 2 Function of the thickness of layer 6 (B axis, in nm);

[0047] [ Fig.14 ] is a graphical representation of the fundamental shear mode phase velocity (vertical axis, in m / s) versus frequency (horizontal axis, in MHz) and the shear fundamental mode propagating in a POI substrate comprising 600 nm of LiTaO 3 (YX1) 42° layer, 100nm additional layer, 400nm dielectric layer and silicon support substrate, the additional layer can include diamond carbon, GaN, ZnO, LiNbO 3 ;

[0048] [ Fig.15 ] is a graphical representation of the fundamental shear mode phase velocity (vertical axis, in m / s) versus frequency (horizontal axis, in MHz) and the shear fundamental mode propagating in a POI substrate comprising 600 nm of LiTaO 3 (YX1) 42° layer, 100nm additional layer, 400nm dielectric layer and silicon support substrate, additional layer may include: SiN, polysilicon, AlN, Al 2 O 3 ;

[0049] [ Fig.16 ] is a schematic diagram of a surface elastic wave device in accordance with the principle of the present invention on a cross-sectional plane perpendicular to the front side of a supporting substrate;

[0050] [ Fig.17] is a schematic diagram of step a) of the method according to the present invention;

[0051] [ Fig.18 ] is a schematic diagram of forming a first layer and a second layer on a supporting substrate;

[0052] [ Fig.19 ] is a schematic diagram of the assembly of the second and third layers;

[0053] [ Fig. 20 ] is a schematic diagram of the fracture along the brittle zone. DETAILED DESCRIPTION

[0054] In order to simplify the following description, the same reference numerals are used for the same elements or elements performing the same functions in different embodiments disclosed in the present invention and the prior art.

[0055] The present invention relates to a surface elastic wave device formed by a POI substrate. In this regard, document FR3127660 describes a surface elastic wave device and its operating principle.

[0056] According to the present invention, the surface elastic wave device can be selected from: a filter, a resonator or a sensor. However, it should be understood that the present invention is not limited in these aspects and that those skilled in the art can apply its principles to any type of surface elastic wave device formed by a POI substrate.

[0057] In particular, the present invention relates to a surface elastic wave device generated on a POI substrate. In particular, the POI substrate comprises a piezoelectric material layer, a dielectric material layer and a supporting substrate from the front side to the back side.

[0058] In this regard, the support substrate includes at least one selected from the following elements:

[0059] Silicon substrates with a (110) type orientation, quartz substrates with a (YXt) / θ / 90° orientation, wherein θ is between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0060] In addition, the device according to the present invention includes at least one electroacoustic transducer formed on and / or in a piezoelectric material layer. For example, but not limiting the scope of the present invention, a surface elastic wave device includes at least one input electroacoustic transducer and at least one output electroacoustic transducer, which are formed on or in a piezoelectric material layer. At least one electroacoustic transducer according to the present invention may be equipped with a Bragg reflector with electrodes. The electrodes may be arranged periodically, and in particular their repetition period is close to the repetition period of these electrodes of the at least one transducer located on either side of the transducer. The structure may include at least one free surface spacer inside it. The resonator formed in this way is used as an impedance element of a filter combined with one or more identical units, which include at least one resonator as described above.

[0061] It should be understood that the orientation of a substrate or a layer must be related to its crystal orientation as defined in the standard IEEE 1949 Std-176.

[0062] Furthermore, it will be appreciated that angular deviations relative to the crystal orientation are acceptable. In particular, whatever the crystal orientation considered, it is generally accepted that the latter is specified to be within 10°, advantageously within 5°, around said orientation.

[0063] [ Figure 1 ] is a schematic diagram of a surface acoustic wave device 1 (particularly, in this [ Figure 1 ], the device is a resonator).

[0064] Specifically, the surface acoustic wave device 1 includes a POI substrate 2 .

[0065] In this respect, the POI substrate 2 comprises, from the front side 3 to the back side 4 , a piezoelectric material layer 5 , a first dielectric material layer 6 and a support substrate 7 .

[0066] For example, the surface acoustic wave device 1 has a center frequency f 0 and a bandpass filter with a bandwidth Δf, which can be expressed as a fraction of the center frequency, typically between 0.1% and 10%, wherein the POI substrate is provided with a lithium tantalate LiTaO 3 Considering the piezoelectric layer 5 based on LiNbO 3 The piezoelectric layer 5 allows pushing the upper limit of this fraction back to 15% or higher by choosing the crystal orientation of said layer so as to maximize the electromechanical coupling of the mode thus employed.

[0067] According to one embodiment, the surface elastic wave device 1 includes at least one electroacoustic transducer, for example, as [ Figure 1 ] as shown, 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 consists of at least one unit, which is provided with at least one surface elastic wave resonator, which forms a quadrupole with an input port and an output port. These are acoustic coupling filters known to those skilled in the art, and are called LCRF (longitudinal coupled resonator filter), DMS (dual mode SAW) filter or SCAW (surface cavity acoustic wave) filter in English. When multiple units with a single transducer or multiple transducers connected together to form a dipole are arranged in cascade only by electrical connection, 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 obtained from the output port of the filter. However, it should be noted that the terms "input" and "output" are completely arbitrary and the surface elastic wave device 1, in particular the filter, can be used by applying / sampling an electromagnetic signal on either of the two ports.

[0069] Generally speaking, the input 8 and output 9 electro-acoustic transducers and the resonators used as impedance elements in the unit filter of the cascade arrangement correspond to those known in the art, some features of which will be reviewed below.

[0070] Each transducer 8 and 9 comprises two interdigitated comb electrodes. These transducers 8 and 9 are each formed by an array of metal fingers, which are alternately connected to two buses, between which a potential difference is applied / sampled. Thus, with this device, surface elastic waves can be directly generated / detected in the piezoelectric material layer 5. The input electroacoustic transducer 8 and the output electroacoustic transducer 9 are typically configured to be identical. However, the present invention is not limited to this aspect, and a person 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. In practice, the transfer function of these filters can advantageously be modulated by the interpenetration of the comb electrodes along the propagation direction of the wave. For components of this type, the transducer is able to operate outside the Bragg conditions. These filters are considered to have a finite impulse response. A person skilled in the art can also use a transducer operating under Bragg conditions, advantageously adding a reflector at each end of the filter to return the energy in phase to the structure under consideration, thereby producing a filter with an infinite impulse response. The above-mentioned impedance element filters also correspond to infinite impulse response filters, since they consist of resonant elements.

[0072] The metal of the electrode is usually based on aluminum, for example pure aluminum or an aluminum alloy, such as aluminum doped with Cu, Si or Ti. However, another material can be used, for example, by using a smaller relative electrode thickness than required for aluminum to establish a higher reflection coefficient, in order to achieve similar characteristics. In this regard, preferred electrode materials are copper (Cu), molybdenum (Mo), nickel (Ni), platinum (Pt) or gold (Au), which have an adhesion layer, such as titanium (Ti) or tantalum (Ta) or chromium (Cr), zirconium (Zr), palladium (Pd), iridium (Ir), tungsten (W) and the like. The electrode can also consist of the two materials mentioned above in order to optimize the operation of the transducer through its functions of acoustic reflection, electromechanical coupling and in particular ohmic losses.

[0073] The period p of the electrodes is usually selected so that p=λ / 2, where λ is the frequency of the elastic wave in the piezoelectric material layer 5 at the synchronous frequency f of the transducer. s The wavelength of propagation is given by is the phase velocity of the mode used. The transducer then operates under the Bragg conditions already mentioned above. Other configurations are possible, more generally the period p can be expressed as p=λ / (nb_elec), where nb_elec is the number of fingers (electrodes) per wavelength. These parameters are given by the relation λ=V / f s , where V represents the phase velocity of the elastic wave under the transducer. The velocity of an elastic wave on a free surface or under an electroacoustic transducer depends in particular on the properties of the material in which the wave propagates. The latter is generally known or can be obtained by a person skilled in the art by using elastic constants, piezoelectric constants and dielectric constants and density in a suitable model listed in the literature.

[0074] In the case of a bandpass filter, in particular a bandpass filter with a given frequency and bandwidth, it is possible to consider using a transducer whose synchronization frequency is selected to meet the above requirements. The methods for implementing this selection or these selections are known to those skilled in the art and are therefore not described.

[0075] The metallization width of the electrode (denoted a) is typically selected so that the ratio a / p is about 0.5. This aspect does not limit the scope of the invention, and those skilled in the art may consider other ratios that may be more favorable for a given mode / material combination. The number of finger pairs per transducer is typically selected to be about 20 or 100, which is not limiting. In general, increasing the number of finger pairs makes it possible to increase the suppression of frequencies outside the bandwidth and reduce the spectral range of the admittance or impedance response of the transducer near its synchronization frequency.

[0076] The surface elastic wave device 1 may also include two external reflectors 10 and 11 arranged on both sides of the pair of input electroacoustic transducer 8 and output electroacoustic transducer 9. As is well known, these reflectors 10 and 11 are capable of limiting the maximum elastic energy between the input electroacoustic transducer 8 and the output electroacoustic transducer 9. To this end, these reflectors are designed to have a very high reflection coefficient, as close to 1 as possible (i.e., total reflection of the incident energy), which is achieved specifically by selecting the thickness of the reflector electrodes and the number of these electrodes, typically in the case of a POI substrate for shear waves, each reflector has several dozen electrodes. However, it should be noted that these two external reflectors are not essential to the present invention, and a fully functional device in accordance with the present invention may not have them.

[0077] The object of the present invention is to propose a device, such as a surface acoustic wave filter 1 (but the invention is not limited to this aspect only), for which the temperature sensitivity remains limited at frequencies below 1 GHz.

[0078] In this regard, the temperature behavior of SAW filters is usually correctly expressed by the following relationship:

[0079] Δf / f=TCF 1 ×(TT 0 )+TCF 2 ×(TT 0 ) 2

[0080] The temperature sensitivity requirement means that TCF must be 1 The coefficient is kept below a threshold within the operating frequency range of the surface acoustic wave device. More specifically, the TCF 1 Values ​​of the coefficient less than 20 ppm / K, advantageously less than 15 ppm / K, even more advantageously less than 10 ppm / K are advantageous.

[0081] The inventors were able to observe that POI substrates known in the prior art show a relatively high temperature sensitivity when used to manufacture surface elastic wave devices operating at frequencies less than 1 GHz, and more specifically between 400 MHz and 1 GHz.

[0082] It should be understood that all the graphical representations described in the rest of the description of the invention are the results of numerical simulations based on the model (analysis is carried out based on Green's functions of the substrate and numerical methods such as finite elements and boundary elements), taking into account the characteristics of the transducer studied. The details related to these simulations are not given in the following description. However, a person skilled in the art will find in the document [3] cited at the end of the description the theoretical elements that allow reproducing these simulations.

[0083] For example,[ Figure 2] (curve A) shows the coefficient TCF of the surface shear fundamental elastic mode propagating on the POI substrate known in the prior art 1 In particular, the substrate comprises the following layers from the front side to the back side:

[0084] -LiTaO with a thickness of 600 μm 3 Layer with (XYl) / 42° section

[0085] -SiO with a thickness of 500nm 2 layer

[0086] -100 type silicon substrate, thickness equal to 650μm (in calculating TCF 1 When the coefficients vary, the silicon substrate is assumed to be semi-infinite).

[0087] exist Figure 2 The TCF of the fundamental surface shear elastic mode propagating on the POI substrate surface is known in the art. 1 The coefficient remains below 15ppm / K when the operating frequency is above 1.3GHz, but when the frequency is below 1GHz, its value can reach above 20ppm / K and even 25ppm / K.

[0088] In order to overcome this problem, the inventors studied the influence of the crystal orientation of the silicon substrate 7 .

[0089] In particular, when the 100-type silicon substrate was replaced by the 110-type silicon substrate, the inventors were able to clearly observe that the TCF 1 Considering the silicon substrate 110 leads to a decrease in the electromechanical coupling coefficient of the considered mode, in particular a decrease of 1%.

[0090] Considering that the support substrate made of silicon 110 can reduce the TCF at frequencies below 1 GHz, especially between 400 MHz and 1 GHz 1 coefficient.

[0091] More specifically, according to the invention, a supporting substrate made of silicon of type 110 (or (XYw) / 45° as specified by IEEE Std-176) or IEEE Std-176 (XYt) / 45° may also be considered.

[0092] in this regard,[ Figure 3 ] shows the TCF in a graph 1 The evolution of the coefficients as a function of the fundamental elastic mode frequencies of surface shear guided on different POI substrates. Each POI substrate consists of LiTa0 3 The piezoelectric material layer is made of 700nm thick and SiO 2The thickness of the dielectric material layer is 350 nm. In addition, curve C is obtained from a POI substrate consisting of a 110 type silicon support substrate, while curve D is obtained from a POI substrate comprising an IEEE Std-176 type silicon support substrate (XYt) / 45° or (YXt) / 45°.

[0093] In both cases, TCF 1 The coefficient remains below 13 ppm / K, while the electromechanical coupling of the considered surface elastic modes is hardly affected compared to what is observed in the prior art for surface shear fundamental elastic modes guided by POI substrates.

[0094] The inventors indicate that a support substrate made of quartz may also be considered, with an orientation of (YX / t) / θ / 90°, θ being between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

[0095] Alternatively or additionally, to reduce TCF 1 The coefficients may also be adjusted for the stack formed on the support substrate 7. In particular, the first dielectric material layer 6 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] Similarly, LaTiO 3 or LiNbO 3 The thickness of the manufactured piezoelectric material layer 5 is 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 TCF 1 To illustrate the influence of the crystallographic orientation of the piezoelectric material layer, it is proposed to consider the surface modes guided by a POI substrate consisting of 700 nm thick LiTaO with a crystallographic orientation of (YZl) / θ (θ between 0° and 30°) from the front to the back. 3 layer, SiO with a thickness of 350nm 2 layer, and a supporting substrate made of silicon.

[0098] More specifically, Figure 4 ]and[ Figure 5 ] show the TCF 1 coefficients and the changes in the electromechanical coupling associated with the surface shear fundamental elastic mode guided by the above POI substrate, as well as the LiTaO 3 Thus, for values ​​of 0 between 10° and 35°, advantageously between 15° and 30°, TCF1 The coefficient is kept below 15ppm / K and the electromechanical coefficient is greater than 10%.

[0099] According to a supplementary or alternative aspect of the above content, the POI substrate according to the present invention may further include a second layer 12, which is located between the piezoelectric material layer 5 and the first dielectric material layer 6 ([ Figure 6 ]). The frequency temperature coefficient of the second layer 12 is advantageously opposite in sign to the frequency temperature coefficient of the dielectric material layer 5. The latter aspect compensates for the effect of the dielectric layer 6 on the TCF 1 The influence of coefficient.

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

[0101] Additional layers may include dielectric materials and / or semiconductor or piezoelectric materials.

[0102] According to the present invention, when the dielectric layer 6 (for example, made of SiO 2 When the positive frequency temperature coefficient is associated with the relevant second layer 12 (for example, made of SiN, Al 2 O 3 or AIN) has a negative frequency temperature coefficient.

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

[0104] Considering that the second layer 12 can also reduce the TCF of the fundamental shear elastic mode guided on the POI 1 If the layer contains silicon nitride (SiN), this reduction can reach 5 ppm / K or even higher, depending on the thickness of the layer.

[0105] Adding an additional TCF layer production step with opposite sign to the dielectric material layer can reduce / increase the thickness of the piezoelectric / dielectric layer, respectively, to achieve a given TCF, thereby achieving a higher value for the SmartCut TM The process transfers the piezoelectric layer without damaging it or causing lithium diffusion in the supporting substrate. There is a risk of lithium diffusion when performing annealing to strengthen the bonding interface or out-diffusion implantation of hydrogen, which can cause p-domain inversion.

[0106] It is needless to say that the silicon nitride considered in the present invention is not necessarily stoichiometric.

[0107] The inventors have also noticed that providing the second layer 12 below the first dielectric material layer 6 does not affect the TCF of the surface elastic mode propagating in the POI substrate. 1 The coefficient has a significant impact.

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

[0109] The use of the second layer 12 may advantageously allow for the use of a dielectric layer 6 of greater thickness.

[0110] In addition, the second layer 12 made of SiN and the second layer 13 made of SiO 2 The first dielectric material layer 6 produced can be formed in the same process step, in particular in a pressure enhanced chemical vapor deposition frame (PECVD).

[0111] To illustrate the use of the second layer 12, the inventors estimated its TCF for the surface shear fundamental elastic mode guided on the POI substrate: 1 The simulations employ Green's function analysis to represent the diffusion behavior of the modes on the layered substrate.

[0112] The POI substrates considered in this analysis include, from their front side to their back side:

[0113] - LiTaO oriented along the (YX1) / 42° cross section of the crystal 3 Layer 5, thickness equal to 600 nm;

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

[0115] - SiO with a thickness that can assume one of the values ​​between 300 nm and 600 nm 2 Layer 6

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

[0117] The POI substrate may also include a polysilicon trapping layer, the thickness of which is about 1 μm, typically between 400 nm and 2 μm.

[0118] The inventors were able to evaluate the possible 3 Phase velocity of waves propagating in layer 5, electromechanical coupling coefficient, and TCF of the surface shear fundamental elastic mode guided on the above POI substrate 1 coefficient.

[0119] These evaluation results are shown in [ Figure 7 ]、[ Figure 8 ]and[ Fig. 9 ].

[0120] In particular, Figure 7] graphically shows (based on a 3D representation) that the surface shear-guided fundamental elastic mode described above on a POI substrate may be a function of LiTaO 3 The phase velocity of the wave propagating in layer 5. The phase velocity of this mode, denoted by v φ (vertical axis, unit: m / s), plotted as filter operating frequency (A axis, unit: MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0121] [ Figure 8 ] shows a schematic diagram (3D) of the electromechanical coupling coefficient of the surface shear fundamental elastic mode guided on the above POI substrate. s 2 (vertical axis, unit %) is plotted as the mode operating frequency (A axis, unit MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0122] [ Fig. 9 ] shows the TCF of the surface shear fundamental elastic mode guided on the above POI substrate 1 Schematic diagram of coefficients (3D). TCF 1 The coefficient (vertical axis, in ppm / K) is plotted as a function of the mode operating frequency (A axis, in MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0123] according to[ Fig. 9 ], for frequencies between 600 MHz and 2 GHz and SiO with a thickness less than or equal to 350 nm 2 , the TCF of the considered surface elastic mode 1 Less than 10 ppm / K. Compared with the methods used to make filters known in the art, TCF 1 The coefficient is relatively low, thanks to the use of the SiN layer 12. However, as [ Figure 7 ]and[ Figure 8 ] As shown in FIG. 1 , the use of the second layer 12 results in an increase in the phase velocity and a 1% decrease in the electromechanical coupling coefficient compared to the waveguide surface shear elastic wave known in the prior art (ie, without a SiN layer).

[0124] All the elements described in this invention lead to TCF 1 Adjustment of coefficients. In fact, a technical goal of the present invention is to limit or control the influence of temperature on the operation of a surface elastic wave device formed by a POI substrate.

[0125] The method of adjustment is exemplified by considering a surface elastic wave device formed of a POI substrate, which includes, from the front side to the back side thereof:

[0126] -LiTaO oriented at (YX1) / 42° 3 Layer 5;

[0127] - a SiN layer 12 with a thickness equal to 100 nm;

[0128] - SiO with a thickness that can assume one of the values ​​between 300 nm and 600 nm 2 Layer 6

[0129] - The trapping layer comprises polysilicon and has a thickness of about 1 μm.

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

[0131] The evaluation results are shown in [ Fig.10 ]、[ Fig.11 ]、[ Fig.12 ]and[ Fig.13 ].

[0132] [ Fig.10 ] graphically shows (based on a 3D representation) the electromechanical coupling coefficient of the surface shear fundamental elastic mode guided on the above POI substrate, where LiTaO 3 The thickness of layer 5 is equal to 700 nm. The electromechanical coupling coefficient, denoted as k s 2 (vertical axis, unit %), plotted as mode operating frequency (A axis, unit MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0133] [ Fig.11 ] graphically shows (from a 3D representation) the TCF of the surface shear fundamental elastic mode guided on the above POI substrate 1 Coefficient, its LiTaO 3 The thickness of layer 5 is equal to 700 nm. TCF 1 Coefficient, denoted as TCF 1 (vertical axis, ppm / K), plotted as mode operating frequency (A axis, MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0134] [ Fig.12 ] graphically shows (based on a 3D representation) the electromechanical coupling coefficient of the surface shear fundamental elastic mode guided on the above POI substrate, where LiTaO 3 The thickness of layer 5 is equal to 800 nm. The electromechanical coupling coefficient, denoted as k s 2 (vertical axis, unit %), plotted as mode operating frequency (A axis, unit MHz) and SiO 2Function of layer 6 thickness (B axis, in nm).

[0135] [ Fig.13 ] Graphically (based on 3D representation) represents the TCF of the surface shear fundamental elastic mode guided on the above POI substrate 1 Coefficient, where LiTaO 3 Layer 5 thickness equals 800 nm (asterisk corresponds to k s 2 Maximum TCF 1 The operating point with the smallest coefficient). TCF 1 Coefficient, denoted as TCF 1 (vertical axis, ppm / K), plotted as mode operating frequency (A axis, MHz) and SiO 2 Function of layer 6 thickness (B axis, in nm).

[0136] For SiO with a thickness less than 400 nm 2 Layer 6 and 700nm thick LiTaO 3 For example, the second SiN layer 12 can make the electromechanical coupling coefficient of the mode with a frequency between 800 MHz and 1600 MHz greater than 10% ([ Fig.10 ]), TCF 1r The coefficient is close to 10ppm / K ([ Fig.11 ]).

[0137] Similarly, for SiO with a thickness less than 400 nm 2 Layer 6 and thickness equal to 800nm ​​LiTaO 3 The same second SiN layer 12 can make the electromechanical coupling coefficient of the mode between 800 MHz and 1600 MHz greater than 11% ([ Fig.12 ]), TCF 1r The coefficient is close to less than 10ppm / K ([ Fig.13 ]).

[0138] According to its operating frequency, especially the parameter TCF that characterizes the surface elastic mode 1 The entire description is limited to parameters related to the fundamental shear mode. However, those skilled in the art will appreciate that surface elastic wave devices utilizing related modes also have resonant and antiresonant frequencies, which themselves are determined by their own TCF. 1 Coefficient characterization. TCF characterizing resonance 1 The coefficient is very low or even zero, which will affect the TCF that characterizes the anti-resonance of the relevant equipment. 1The coefficient has a negative impact, especially in the case of single-spin shearing of lithium niobate and lithium tantalate, where it is well known that for the same mode, especially the shear mode, the TCFs of the resonance and antiresonance are different from each other.

[0139] Therefore, the present invention also proposes to optimize the parameters characterizing the POI substrate in order to better understand the TCFs related to the resonance and anti-resonance of the devices formed on said substrate, respectively. 1 More specifically, the present invention proposes to adjust the TCF associated with the resonance 1 Coefficient (hereinafter referred to as TCF 1r ) and TCF related to antiresonance 1 Coefficient (hereinafter referred to as TFC 1AR ). In particular, the present invention proposes to use TCF 1r Adjust the coefficient to a value below 15ppm / K and set the TFC 1AR The coefficient is adjusted to a value between -4ppm / K and 0ppm / K. Similarly, the present invention proposes to adjust TCF 1R Adjust the coefficient to a lower value between 5ppm / K and 10ppm / K and set the TFC 1AR The term is adjusted to a value between -10ppm / K and -5ppm / K.

[0140] These objectives can be achieved by simulating the evolution of the various terms and coefficients mentioned above, thereby determining the material layers and their respective thicknesses.

[0141] The inventors have also studied other materials besides SiN for forming the second layer 12 .

[0142] More specifically, the second layer 12 may include at least one selected from the following materials: SiC, Al 2 O 3 , AlN, diamond carbon, GaN, LiNbO 3 、ZnO.

[0143] Fig.14 is a graph of the fundamental shear mode phase velocity (vertical axis, unit: m / s) versus frequency (horizontal axis, unit: MHz). The POI substrate includes 600nm LiTaO 3 (YX1) 42° layer, 100nm additional layer, 400nm dielectric layer and silicon support substrate, the additional layer may include diamond carbon, GaN, ZnO, LiNbO 3 .

[0144] Fig.15 is a graph of the fundamental shear mode phase velocity (vertical axis, unit: m / s) versus frequency (horizontal axis, unit: MHz). The POI substrate includes 600nm LiTaO 3(YX1) 42° layer, 100nm additional layer, 400nm dielectric layer and silicon support substrate, the additional layer may include SiN, polysilicon, AlN, Al 2 O 3 .

[0145] In addition to diamond carbon, the same behavior is observed at low frequencies when the phase velocity of the mode approaches the shear wave velocity of silicon. At a given frequency, reducing the mode velocity is equivalent to increasing the wavelength of the mode in question, thereby reducing the impact of the POI substrate composite structure.

[0146] Based on these observations and appropriate mathematical treatment (considering the derivative of the phase velocity with respect to frequency), it can be concluded that LiNbO 3 It is the most ideal material to minimize the sensitivity of modes to frequency in the range of 800MHz to 1200MHz.

[0147] The second layer 12 is made of diamond carbon, which seems to be more advantageous for frequencies below 800 MHz.

[0148] In SiO 2 Dielectric layer 6 and LiTaO 3 Between the piezoelectric layers 5, a 100nm thick LiNbO 3 Additional layers can be added to the TCF 1 The coefficient drops below 10 ppm / K, independent of the crystal orientation of the piezoelectric layer.

[0149] As mentioned above, the present invention covers a number of aspects, which can be considered independently or in combination to optimize (reduce) TCF as long as the operating frequency of the device, especially the surface elastic wave filter, is below 1 GHz. 1 The coefficient is such that its value is lower than 20 ppm / K, advantageously lower than 15 ppm / K, even more advantageously lower than 10 ppm / K.

[0150] Advantageously, the POI substrate further comprises a trapping layer between the dielectric material layer and the supporting substrate, the trapping layer being adapted to limit the mean free path of electric carriers at the interface formed between the dielectric material layer and the trapping layer and the mean free path of electric carriers on the interface formed between the dielectric material layer and the supporting substrate.

[0151] In this respect, the trapping layer may consist of polysilicon, with a thickness advantageously comprised between 400 nm and 2000 nm.

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

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

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

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

[0156] a) implanting substances into a donor substrate made of piezoelectric material, the purpose of which is to form a layer called an embrittlement zone in the volume of the donor substrate and to delineate a useful layer on a face called a main face of said donor substrate;

[0157] b) a step of transferring the useful layer to the front side of the support substrate, the transfer step comprising in turn assembling the useful layer with a face of the support substrate (called the front side) and carrying out a heat treatment in order to induce a fracture wave along the embrittled zone, thereby transferring the useful layer to the front side;

[0158] The method further comprises forming an intermediate stack 101 between the front side and the useful layer, the intermediate stack comprising, starting from the front side, 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] therefore,[ Fig.16 ] is a schematic diagram of a POI substrate 100 that can be obtained according to the manufacturing process of the present invention. In particular, the POI substrate includes a supporting 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 constitute an intermediate stack 101) and a useful layer 150 in sequence.

[0160] In this regard, the first layer 120 may include SiO2, the second layer 130 may include silicon nitride (SiN), and the third layer 140 may include SiO 2 .

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

[0162] The trapping layer 160 is located between the intermediate stack 101 and the front side 110a of the support substrate 110. In particular, the trapping layer 160 is adapted to limit the mean free path of electric carriers on the interface formed between the intermediate stack and the support substrate, relative to the mean free path of electric carriers on the interface formed between the intermediate stack and the support substrate.

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

[0164] [ Fig.17 ] is a diagram of step a). In particular, step a) comprises implanting a substance through a face, referred to as the main face 200 of a donor substrate 210, the donor substrate comprising a piezoelectric material.

[0165] In particular, step a) is performed in such a way that a layer, referred to as embrittled zone 211 , is formed in the volume of donor substrate 210 and delimits useful layer 150 with main face 200 of said donor substrate.

[0166] Without stipulating, it is understood that the embrittled region 211 forms a layer substantially parallel to the main surface 200 .

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

[0168] For example, when performing step a), the skilled person may consider implanting hydrogen ions or helium ions.

[0169] Advantageously, step a) may be preceded by a preliminary step during which the piezoelectric material is subjected to a gas-phase oxygen treatment in order to limit or even reduce thermoelectric effects that may appear in the donor substrate and therefore in the useful layer when the donor substrate is subjected to increased temperature.

[0170] The method may further comprise forming a layer of dielectric material on the donor substrate or the support substrate, in particular by PECVD.

[0171] The process may also include forming additional layers, for example, on the dielectric layer if the dielectric layer is first formed on the support substrate.

[0172] Advantageously, the donor substrate 210 may include lithium tantalate doped with iron, with the iron doping ranging between 0.001% and 0.05%, and advantageously between 0.002% and 0.01% by weight.

[0173] Advantageously, the formation of the intermediate stack 101 may include forming a third layer 140 on the main surface before performing step a). The third layer 140 may be formed by PECVD.

[0174] Advantageously, the thickness of the third layer is between 10 nm and 100 nm.

[0175] When the third layer includes SiO 2 When , the above thickness usually corresponds to a thickness less than λ / 20 and ideally less than λ / 50, where λ is the acoustic wavelength equal to twice the mechanical half-life of the interdigital transducer operating at the Bragg frequency.

[0176] Likewise, the formation of the intermediate stack may include forming a first layer 120 on the front side 110 of the support substrate 110, and then forming a second layer 130 ([ Fig.18 ]).

[0177] Advantageously, the thickness of the first layer is between 100 nm and 1000 nm, advantageously between 300 nm and 800 nm, and the thickness of the second layer is 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, LaTiO 3 The thickness of the piezoelectric layer made of SiN can be between 500 nm and 800 nm, the thickness of the second layer made of SiN can be between 100 nm and 200 nm, and the thickness of the second layer made of SiO 2 The thickness of the first layer produced is between 300 nm and 600 nm.

[0179] The formation of the third layer 140 on the one hand and the first layer 120 and the second layer 130 on the other hand are followed by a step b) of transferring the useful layer 150 to the front side of the supporting substrate, the transfer step comprising sequentially assembling the useful layers with one face of the supporting substrate 110 (referred to as the front side 110a), and heat treatment aimed at inducing a fracture wave along the embrittlement zone and thereby transferring the useful layer 150 to the front side 110a.

[0180] Advantageously, assembling may include contacting the second layer 130 and the third layer 140 ([ Fig.19 ]).

[0181] Therefore, according to the present invention, the third layer is an adhesion layer formed at least partially on the donor substrate, more specifically on the main face of the donor substrate.

[0182] This last aspect therefore allows a thermal treatment to be carried out before assembly in order to outdiffuse hydrogen that may be present in the second layer. In fact, the second layer (comprising SiN) is obtained by vapor deposition of a mixture of silane with NH3 and / or N2. The second layer therefore comprises hydrogen, which must be removed in order to avoid its migration to the piezoelectric layer at the end of step b). Therefore, forming the second layer on the front side of the support substrate allows a thermal treatment to be carried out only on the support substrate, the first layer and the second layer. This last aspect makes it possible to limit the thermal history of the piezoelectric material and to maintain its characteristics (in particular to limit the risk of domain inversion). Taking into account that the third layer is at least partially formed on the main face of the donor substrate, this makes it possible to consider the latter as a bonding layer. In other words, this aspect limits the thermal history of the piezoelectric material and limits the risk of domain inversion.

[0183] Third SiO2 The thickness of the layer is between 10 nm (full range) and 50 nm.

[0184] Alternatively, ADB bonding can be performed using a third layer made of amorphous silicon with a thickness of a few nanometers.

[0185] The assembly is advantageously a molecular bonding.

[0186] [ Fig. 20 ] shows a heat treatment which aims to induce a fracture wave along the embrittled zone in order to transfer the useful layer 150 to the front side to form [ Fig.16 ]The POI substrate shown.

[0187] The method may further include forming a trapping layer 160 on the support substrate 110 before forming the first layer 120. In other words, the first layer 120 is formed by covering the trapping layer.

[0188] Of course, the invention is not limited to the embodiments described and implementation variations may be proposed without departing from the scope of the invention as defined in the claims.

[0189] References

[0190] [1] T.Pastureaud et al., “High-Frequency Surface Acoustic Waves Excited onThin-Oriented LiNbO 3 Single-Crystal Loyers Transferred Onto Silicon”, IEEE Trans. on UFFC, Vol. 54, No. 4, pp. 870-876, 2007;

[0191] [2] US2014 / 0152146 A1;

[0192] [3] S.Ballandras et al., "Simulations of surface acoustic wave devices built on stratified media using a mixed finite element / boundary intégralformulation", Journal of Applied Physics, Volume 95, Issue 12, Pages 7731-7741, 2004.

Claims

1. A method for manufacturing an elastic wave device, wherein the elastic wave device is configured to operate at a frequency less than 1 GHz and is formed on a POI substrate, wherein forming the POI substrate comprises the following steps: a) a step of implanting a substance into a donor substrate comprising LiTaO 3 , the implantation of said substance being intended to form a layer called embrittlement zone in the volume of said donor substrate and delimiting a useful layer together with a face called main face of said donor substrate; b) a step of transferring the useful layer to the front side of a supporting substrate, the transfer step comprising in sequence assembling the useful layer with a face of the supporting substrate called the front side, and a heat treatment intended to induce a fracture wave along the embrittlement zone so as to transfer the useful layer to the front side; the method also comprises forming an intermediate stack, the intermediate stack being located between the front side and the useful layer, and the intermediate stack comprising, starting from the front side, a first layer comprising silicon dioxide, a second layer comprising silicon nitride, aluminum oxide or aluminum nitride, and the third layer comprising silicon dioxide or amorphous silicon.

2. The manufacturing method according to claim 1, wherein: The intermediate stack further includes a third layer such that the second layer is located between the first layer and the third layer, the third layer including silicon dioxide or amorphous silicon.

3. The manufacturing method according to claim 2, wherein: The POI substrate also includes a layer called a trapping layer, which is inserted between the intermediate stack and the front side, and the trapping layer is suitable for limiting the mean free path of the electric carriers at the interface formed between the intermediate stack and the trapping layer relative to the mean free path of the electric carriers at the interface formed between the intermediate stack and the supporting substrate.

4. The manufacturing method according to claim 3, wherein: The trapping layer includes a defect density greater than a predetermined defect density, wherein the predetermined defect density refers to a defect density at which the resistivity of the trapping layer is greater than or equal to 10 Kilo-ohm at a temperature between -20°C and 120°C.

5. The manufacturing method according to claim 4, wherein: The capture layer includes at least one of the following materials: amorphous silicon and polycrystalline silicon.

6. The manufacturing method according to any one of claims 2 to 5, wherein: Forming the stack includes forming the third layer on the main surface before performing the implanting step a).

7. The manufacturing method according to claim 6, wherein: Forming the stack includes forming the first layer and the second layer on the front side, such that when performing step b), assembling includes contacting the second layer and the third layer.

8. The manufacturing method according to any one of claims 2 to 7, wherein: The third layer has a thickness between 10 nm and 100 nm.

9. The manufacturing method according to any one of claims 1 to 8, wherein: The method comprises a preliminary step carried out before step a) and during which the donor substrate is subjected to a gas-phase oxygen treatment in order to limit or even reduce thermoelectric effects that may appear in the donor substrate and therefore in the useful layer when the donor substrate is subjected to an increase in temperature.

10. The manufacturing method according to any one of claims 1 to 9, wherein: The donor substrate comprises lithium tantalate doped with iron, the iron doping being between 0.001% and 0.05%, advantageously between 0.002% and 0.01%, by weight.

11. The manufacturing method according to any one of claims 1 to 10, wherein: The thickness of the first layer is between 100 nm and 1000 nm, advantageously between 300 nm and 600 nm, and the thickness of the second layer is between 100 nm and 200 nm.

12. The manufacturing method according to any one of claims 1 to 11, wherein: The method comprises forming at least one electroacoustic transducer, the at least one electroacoustic transducer being formed on and / or in the useful layer.

13. The manufacturing method according to any one of claims 1 to 12, wherein: The support substrate comprises at least one selected from the following elements: a silicon substrate with orientation 110, a quartz substrate with orientation (YX / t) / θ / 90°, wherein θ is between -20° and 60°, advantageously between -10° and 30°, for example equal to 5°.

14. The manufacturing method according to any one of claims 1 to 13, wherein: The LiTaO 3 material has a (YX) / θ orientation, wherein θ is between 10° and 52°, advantageously between 15° and 30°.

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