Elastic wave device and filter

Abstract

The invention relates to an elastic wave device (100, 200, 400) configured to operate with elastic waves of interest having wavelengths centred on an operating wavelength, the elastic wave device (100, 200, 400) comprising a piezoelectric layer (1), and at least one transducer (21, 23) formed on and / or buried in a first surface (9) of the piezoelectric layer (1), a first reflector (3, 34) and a second reflector (5, 6) arranged on and / or in the first surface (9) of the piezoelectric layer (1), the first reflector (3, 34) and the second reflector (5, 6) being arranged on either side of the transducer (21, 23) and along a propagation direction (7), and the first reflector (3, 34) and the second reflector (5, 6) extending respectively in a first direction (15) and a second direction (17, 18), each of the first and second directions being neither perpendicular nor parallel to the propagation direction (7).

Description

Description Title: Elastic wave device and filter

[0001] The invention relates to an elastic wave device, a filter and a method for manufacturing such an elastic wave device in the field of components for elastic wave-based telecommunications.

[0002] Elastic wave devices, particularly surface wave devices, are used in a wide range of applications, such as filters, sensors, and delay lines. Radio frequency filters, for example, are used in mobile communication devices due to their simple structures with low insertion losses (less than 2 dB) and small size (on the order of a few mm). 2 or even less than 1 mm 2 ) to radio frequencies (100 MHz - 10 GHz).

[0003] These elastic wave devices comprise one or more electromechanical transducers aligned along the direction of elastic wave propagation. These transducers are placed on or embedded in a substrate made of a piezoelectric material. The direct piezoelectric effect then allows the conversion of an elastic wave propagating through the piezoelectric substrate, particularly at its surface, into electrical signals by electrically exciting the transducers. Conversely, an electrical signal can be induced through the transducers to create an elastic wave of interest, particularly a surface wave, propagating through the piezoelectric substrate.

[0004] Some of the elastic waves propagating between the transducers extend beyond the transducers at the ends of the chain formed by the transducers along the propagation direction. This is primarily due to the unwanted transmission and / or reflection of the waves of interest by the transducers at the ends of the chain. These residual elastic waves are reflected off various elements present on or within the piezoelectric substrate, particularly its edges. Thus, parasitic waves interfere with the elastic waves of interest transmitted and captured by the transducers. The electrical signals and the elastic waves of interest are then corrupted and degraded by these reflected parasitic elastic waves.

[0005] The usual solutions propose either to use a layer placed on the edges of the piezoelectric substrate with a material such as benzocyclobutene (BCB) in order to absorb these parasitic elastic waves, or to make a cut of the piezoelectric substrate biased to deflect the residual elastic waves and not reflect them towards the transducers.

[0006] In the first case, additional manufacturing steps and materials are required, significantly increasing the cost and complexity of device fabrication. Furthermore, the material constituting the absorbent layer can contaminate the substrate surface, and the adsorption of unwanted volatile compounds from the absorbent layer onto the surface can degrade the device's electrical response. In the second case, the substrate cutting and handling process is more complex, increasing the device's manufacturing cost, particularly due to the use of specialized equipment. Specifically, the biased cutting of the substrate makes it more difficult to adapt, incorporate, and use the device within a larger structure.

[0007] The object of the invention is to reduce the impact of reflected parasitic elastic waves while avoiding the disadvantages mentioned above.

[0008] The object of the invention is achieved by means of an elastic wave device, in particular a guided surface elastic wave device, more particularly a guided surface shear wave device, or a device with predominantly longitudinal polarization modes. The elastic wave device is configured to operate with predetermined elastic waves of interest whose wavelengths are centered on a central operating wavelength. The elastic wave device comprises a piezoelectric layer, in particular a ferroelectric layer, and at least one electromechanical transducer formed on and / or embedded in a first surface of the piezoelectric layer, and a first and a second reflector configured to at least partially reflect the elastic waves of interest of the elastic wave device. The first and second reflectors are disposed on, in particular directly on, and / or in the first surface of the piezoelectric layer, and The first and second reflectors are arranged on either side of at least one electromechanical transducer and along a central direction of propagation of the elastic waves of interest of the elastic wave device, called the propagation direction. The first and second reflectors extend respectively along a first and a second direction, each not perpendicular and not parallel to the propagation direction.

[0009] The reflectors reduce interference with signals of interest from residual and reflected elastic waves, particularly from the substrate edges, by deflecting them so they do not interfere with at least one of the transducers. The device according to the invention reduces this interference without requiring additional manufacturing steps or angled edges. Furthermore, the reflectors can be integrated within the substrate's perimeter, reducing the device's overall volume and increasing its compactness.

[0010] The piezoelectric layer can be made of a material including LiTaO3, LiNbO3, KNbO3, PZT, PMnPt, PbTiO3 or AIScN. In one embodiment of the invention, a second surface of the piezoelectric layer can be disposed on, in particular directly on, a supporting substrate, the second surface of the piezoelectric layer being opposite the first surface of the piezoelectric layer.

[0011] In one embodiment of the invention, a dielectric layer, particularly a layer of silicon dioxide, SiN, Ta₂O₅, ZrO₂, HfO₂, SiON, polysilicon, or a combination of these materials, can be arranged between the piezoelectric layer and the base substrate. The dielectric layer, preferably having a thickness less than the central operating wavelength and / or a thickness between 0.2 micrometers and 2 micrometers, simplifies the fabrication of the elastic wave device, especially when the device comprises a multilayer structure. Indeed, this layer can be used to bond the piezoelectric layer to the base substrate during a layer transfer process, for example, by bonding, such as molecular bonding, adhesive bonding, or eutectic bonding. The process may be of the SmartCut™ type.The use of silicon dioxide as a dielectric layer further allows for adjustment of the device's temperature stability, due to the opposite signs of the temperature coefficients of the elastic wave velocity of silicon and silicon dioxide. This layer can also be used to facilitate bonding, particularly at the molecular level, notably via hydrogen bonds, between the substrate and the piezoelectric layer. Its thickness can then be reduced to a few tens of nanometers, specifically less than 50 nanometers and, more specifically, less than or equal to 30 nm. A similar effect can be achieved with thallium pentoxide (Ta₂O₅). Thus, the thickness of the dielectric layer also depends on the thickness chosen for the piezoelectric layer and can preferably be selected to reduce or even minimize the effect of temperature on the device.

[0012] In one embodiment of the invention, a trapping layer, in particular a layer of polycrystalline silicon, AIN, polycrystalline SiOCH, SiON, or any complex composition of these materials, can be arranged between the piezoelectric layer and the base substrate or between the dielectric layer and the base substrate. This trapping layer preferably has a thickness between 300 nm (0.3 pm) and 2 pm. The presence of a trapping layer reduces leakage currents. In the case of a SiON layer, this thickness can be reduced to 200 nm, or even 100 nm, depending on the operating frequencies of the elastic wave devices fabricated.

[0013] The transducer may comprise one or more electrodes. In particular, these electrodes may be comb-shaped, with the comb fingers arranged in parallel bands. The comb-shaped electrodes of the transducer may be interdigitated. The fingers of the comb-shaped electrodes extend essentially in a direction perpendicular to the direction of propagation.

[0014] The first and second reflectors can be configured to reflect at least 50%, and more specifically at least 80%, of the elastic waves of interest from the device. The reflectors reflect and deflect, in particular, elastic waves propagating beyond and from at least one transducer, in both directions along the propagation direction. The reflectors also reflect and deflect elastic waves reflected from the edges of the piezoelectric layer.

[0015] In one embodiment of the invention, at least one second electromechanical transducer may be disposed between the first and second reflectors along the propagation direction. In particular, the second transducer may comprise interdigitated comb-shaped electrodes. In such a device, the first transducer may be used for signal input and the second transducer for output.

[0016] In one embodiment of the invention, a first electromechanical mirror can be arranged between the first reflector and the first transducer, and a second electromechanical mirror can be arranged between the second reflector and the second transducer along the propagation axis. The first and second mirrors further confine the elastic waves of interest in the device between the first and second transducers. This also reduces the amplitude of the transmitted and reflected spurious waves.

[0017] In one embodiment of the invention, the elastic wave device may further comprise one or more electrode arrays arranged between the first and second electromechanical transducers. These arrays may be separated from each other by free and / or metallized propagation gaps, preferably with the same distance between two adjacent electrode arrays. This reduces the frequency width of the transition between the device's passband and its rejection band. The rejection band corresponds to all frequencies outside the device's operating passband. Those skilled in the art will know, depending on the situation, how to define the limits of the passband and rejection band. The transition between the passband and rejection band is called the transition band.We speak of the frequency width of the transition band when the attenuation of the transmitted signal goes from the minimum insertion loss of the device to this same value plus 30 dB, 40 dB or 50 dB depending on the device specifications.

[0018] In one embodiment of the invention, the first reflector and the second reflector may respectively comprise a first and a second electrode array extending in the first and second directions, respectively. The electrodes of the first and second electrode arrays may, in particular, be in the form of parallel strips. More specifically, the electrodes of the same array may be short-circuited. The first and second electrode arrays may further form an electromechanical Bragg mirror, in particular having an operating wavelength equal to or close to the central operating wavelength of the device. Increasing the number of electrodes in the first and / or second array increases the reflectance coefficient of the reflectors.In particular, a first electrode array can comprise at least six electrodes, each with a reflection coefficient of 10%, centered on a given frequency. This ensures at least 50% reflection of waves at the given frequency. If each electrode has a reflection coefficient of 15%, four electrodes are sufficient to achieve at least 50% reflection of waves at the given frequency. To increase the reflection coefficient, the thickness of the electrodes can be increased and / or a metallic or dielectric material with a high reflection coefficient can be chosen, such as molybdenum (Mo) or copper (Cu). Specifically, the electrodes can be made of a material with a higher reflection coefficient than the transducers of the device. In particular, the electrodes of the first and / or second array can be made of molybdenum.In one embodiment, the electrodes of the first and / or second array can be made entirely of molybdenum. Made in this way, the electrodes exhibit a high reflection coefficient. Consequently, compared to electrodes made of other materials such as aluminum, copper, or an AlCu alloy, fewer electrodes are required, resulting in a more compact device.

[0019] The electrode arrays form reflectors that can be made at the same time as the other electrodes and electromechanical transducers of the device.

[0020] In one embodiment of the invention, two adjacent electrodes of the first electrode array may be separated by a first period p1, and two adjacent electrodes of the second electrode array may be separated by a second period p2; in particular, the first and second periods may be equal. More specifically, p1 and p2 may be dimensioned such that at least the entire set of elastic waves of interest from the elastic wave device is at least partially reflected by the first and second electrode arrays. Furthermore, p1 and p2 may also be dimensioned so that their reflection function is centered on the central operating wavelength of the device. Two directly adjacent fingers, each belonging to one of the interdigitated comb-shaped electrodes of the transducers, may be separated by a mechanical pitch p0.And, p1 and p2 can also be equal to p0. A person skilled in the art will be able to determine the frequency limits of the set of elastic waves of interest in the device. It is also possible that p1 and p2 are equal.

[0021] Periodic spacing of electrodes within the same electrode array improves the reflection of unwanted waves. This reduces interference with the signals of interest.

[0022] In one embodiment of the invention, the electrodes of the first electrode array of the first reflector and of the second electrode array of the second reflector can be made of Aluminium or Copper or Molybdenum or Palladium or Tantalum or Tungsten or Platinum or Gold or Nickel or a combination of these materials, in particular they can be made of the same material as the first transducer and / or the second transducer.

[0023] These materials increase the electromechanical coupling and the reflector reflection coefficient for spurious waves. This further reduces interference from these waves. Furthermore, the electrodes of the first and second electrode arrays can have thicknesses h1 and h2, and widths a1 and a2, respectively. h1 / A and h2 / A can preferably be between 0.05 and 0.11, particularly for aluminum and its alloys as mentioned above on LiTaO3-based POIs, and more preferably between 0.08 and 0.11, where A is the central operating wavelength of the elastic wave device. a1 / p1 and a2 / p2 can preferably be between 0.4 and 0.6, and more preferably between 0.45 and 0.55. In particular, the electrodes of the first and second electrode array may have the same parameters mentioned above as those of the electrodes of the first and / or second transducer.

[0024] In one embodiment of the invention, the first and second reflectors may comprise at least one groove, in particular a single groove, cut into the piezoelectric layer. The at least one groove may be cut from the first surface of the piezoelectric layer, in particular the at least one groove may extend from the first surface of the piezoelectric layer to a second surface of the piezoelectric layer, the second surface being opposite the first surface.

[0025] The grooves can be used in addition to, or as an alternative to, electrodes in reflectors. Reflection is ensured by the grooves. It is possible to have only one groove. In one embodiment, the first and second reflectors may each comprise only a single groove and no other elements, in particular no electrodes. Furthermore, one reflector may include grooves while the other does not. Similarly, one reflector may include an array of electrodes while the other does not. The first and second reflectors may or may not have the same number of grooves. Notably, a single groove may be sufficient to reflect enough waves.

[0026] In one embodiment of the invention, the first reflector and the second reflector may respectively comprise a first array of grooves, particularly in the form of parallel bands, and a second array of grooves, particularly in the form of parallel bands, wherein two adjacent grooves of the first and second arrays are spaced respectively apart by a first period p1 and a second period p2, in particular the first and second periods may be equal. Furthermore, p1 and p2 may be defined such that at least the set of elastic waves of interest of the elastic wave device is at least partially reflected by the first and second arrays of grooves. Increasing the number of grooves in the first and / or second array increases the reflection coefficient of the reflectors.The groove arrays within the reflectors allow control of the percentage of wave reflection, particularly increasing it. The pitches p1 and p2 of the groove arrays can be equal to the pitches p1 and p2 of the electrode arrays of the first and second reflectors, respectively, or can also be equal to p0. The pitches p1 and p2 of the groove and / or electrode arrays can also be adjusted so that the center frequency of the reflection function of the first and second reflectors coincides with the center frequency of the device, corresponding to the frequency of the wave having the center wavelength of the device. Ideally, the reflection coefficient characterizing said reflection function should correspond to a stopband with a spectral range greater than the frequency width of interest of the device, particularly the filter. If we define the relative width of the device AfR such that Af. R = (f2 ^ fi)with f c = ^ f2+fl the reflection coefficient of the diffusing mirror such that |Æ| = n with fc 2 f s +f e f c > fs+fe^ sac h an tq ue f s = f2+ ôf and f e = fi - 8f, then we show that |Æ| = -Af R + It 2 2 f c The diffusing mirror should be understood as referring to the first and / or second mirror according to the invention. On this basis, we establish that |R| > ^Af R To ensure that few, if any, parasitic modes contribute to the device's bandwidth, Sf must be greater than f2. Consequently, for relative bandwidths less than or equal to 5%, we obtain |R| > -Af R And, for relative bandwidths between 5 and 10%, we obtain |R| > nAf R. For wider relative bands, we propose to guarantee at least |R| > TC . 2 f R -

[0027] In one embodiment of the invention, the grooves of the first and second groove arrays may have depths e1 and e2, and widths a1 and a2, respectively. Furthermore, e1 / A and e2 / A may preferably be between 0.05 and 0.11, and more preferably between 0.08 and 0.11, where A is the central operating wavelength of the elastic wave device. In particular, these values ​​apply to devices fabricated on a piezoelectric-on-insulator (POI) substrate based on LiTaO3 with a crystal orientation defined by (YXI) / 0 according to IEEE Std-176 revision IRE1949, with 0 between 0° and 60°. For devices on POI based on LiNbO3, the desired reflection conditions are similar for crystalline orientations (YXI) / 0 with 0 between 0° and 60° as well as between 100 and 150°.For this second angle range, the electrodes of the diffusing mirror can advantageously be electrically independent of each other, thus corresponding to open-circuit reflection conditions. For all other configurations, whether the piezoelectric layer is made of LiTaO3 or LiNbO3, the diffusing mirror is preferably composed of at least two electrodes connected together to correspond to short-circuit reflection conditions. These different conditions allow for improved reflection effects depending on the properties of the mode being exploited. The values ​​of a1 / p1 and a2 / p2 can preferably be between 0.4 and 0.6, and more preferably between 0.45 and 0.55. When the surface of the piezoelectric material is passivated with a dielectric layer, a1 / p1 and a2 / p2 can preferably be between 0.55 and 0.7.

[0028] Other configurations allow for the excitation of predominantly longitudinal polarization modes (see document EP3776855A1). The principle of the diffusing mirror also applies to this type of configuration, and the preferred connection method for this type of mode on this type of structure is also the short-circuited electrode method.

[0029] In one embodiment, at least one transducer may extend along a direction perpendicular to the propagation direction, called the width direction, from a first line to a second line. A first minimum distance, denoted L1, along the propagation direction and separating a first projection point of the first reflector and the electromechanical element closest to the first reflector may be equal to or greater than the minimum distance, called the width distance and denoted L3, between the first and second lines along the width direction. The first projection point of the first reflector may correspond to the projection of the point of the first reflector closest to the first line onto the first line.A second minimum distance, denoted L2, along the propagation direction and separating a first projection point of the second reflector from the electromechanical element closest to the second reflector, can be equal to or greater than the width distance L3. The first projection point of the second reflector can correspond to the projection of the point of the second reflector closest to the first line onto the first line. The projection point of the first reflector can correspond to a projection onto the second line if the distance L1 is smaller when the point is projected onto the second line compared to when it is projected onto the first line.Similarly, and this indecently from the projection line used for the first reflector, the projection point of the second reflector can correspond to a projection on the second line in the case where the distance L2 is smaller if the point is projected onto the second line compared to if it is projected onto the first line.

[0030] This configuration allows for a more effective reduction of interference from parasitic elastic waves on the signals of interest. Indeed, this configuration reflects and deflects the parasitic waves so that they have little or no impact on at least one transducer, or any other electromechanical element located between the first and second reflectors.

[0031] In one embodiment, the first and second directions can respectively form a first angle 01 and a second angle 02 with the propagation direction. The first angle 01 and the second angle 02 respectively face at least one electromechanical transducer and are both defined in one of the two half-planes formed in the first surface of the piezoelectric layer by the propagation direction. The first angle 01 can be between 1° and (180 - arctan(L3 / L1)) / 2, or between (180 + arctan(L3 / L1)) / 2 and 179°. The second angle 02 can be between 1° and (180 - arctan(L3 / L2)) / 2, or between (180 + arctan(L3 / L2)) / 2 and 179°. In one embodiment, the first angle 01 and second angle 02 can each be between 45° and 89°, in particular between 75° and 89°, or between 91° and 135°, in particular between 91° and 105°.These angle ranges allow the parasitic waves to be deflected so that they are not reflected at all, or very little, towards the electromechanical transducer(s).

[0032] In one embodiment, the second angle 02 of the second reflector may differ from 180° - 01. In this configuration, there is no symmetry between the reflection via the first reflector and the reflection via the second reflector. Thus, constructive interference is avoided. Stray waves are deflected without undesirable effects.

[0033] In one embodiment, the first angle 01 and the second angle 02 can be equal. In this configuration, the first and second reflectors reflect the waves towards the same half-plane of the first surface of the piezoelectric layer formed by the direction of propagation.

[0034] In one embodiment of the invention, the first reflector can extend along the first direction in a first half-plane of the first surface of the piezoelectric layer formed by the propagation direction, and can extend along a third direction in a second half-plane of the first surface of the piezoelectric layer formed by the propagation direction. In particular, the third direction can be the reflection of the first direction across the propagation direction. The second reflector can extend along the second direction in the first half-plane and can extend along a fourth direction in the second half-plane. In particular, the fourth direction can be the reflection of the second direction across the propagation direction. More specifically, the first and second directions can be the same, and the third and fourth directions can be the same.These additional directions allow for a more compact device. Indeed, the reflectors thus occupy a smaller surface area. In one embodiment, the first, second, third, and fourth directions can all be different from one another. This prevents any overlap of the reflected waves. Furthermore, in one embodiment, the two half-planes in which the first, second, third, and fourth directions extend can be defined and formed by a direction parallel to, but different from, the propagation direction. In particular, the parallel direction can correspond to a slight translation of the propagation direction in a direction perpendicular to the propagation direction. This breaks the symmetry with respect to the device's transducers and thus reduces the coherence of the reflected and / or deflected spurious waves.

[0035] The object of the invention is also achieved by means of a filter, in particular an electroacoustic filter, comprising an elastic wave device according to one of the embodiments described above. An operating frequency range of the filter can be defined by the wavelengths of the elastic waves of interest of the elastic wave device centered on a central operating wavelength. This filter makes it possible to benefit from all the advantages associated with an electromechanical filter, with the signals of interest free from the unwanted contribution of reflected or transmitted parasitic elastic waves.

[0036] The object of the invention is also achieved by means of a delay line comprising an elastic wave device according to one of the embodiments described above. This delay line makes it possible to benefit from all the advantages associated with a delay line with signals of interest freed from the unwanted contribution of parasitic reflected or transmitted elastic waves.

[0037] The object of the invention is also achieved through a method of manufacturing an elastic wave device configured to operate with elastic waves of interest whose wavelengths are centered on a central operating wavelength. In particular, the manufactured device is an elastic wave device according to one of the embodiments described above. The manufactured elastic wave device comprises a piezoelectric layer, in particular a ferroelectric layer, and at least one electromechanical transducer, and a first and a second reflector configured to reflect at least partially the elastic waves of interest from the elastic wave device. The method comprises the following steps, in particular performed simultaneously: arranging the at least one electromechanical transducer on, in particular directly on, a first surface of the piezoelectric layer,or bury it at least partially in the first surface of the piezoelectric layer, and arrange a first and a second reflector, each comprising an array of at least one electrode arranged on, in particular directly on, the first surface of the piezoelectric layer, or buried at least partially in the first surface and / or, each comprising an array of at least one groove buried in the first surface of the piezoelectric layer, so that the first and second reflectors are arranged respectively on either side of at least one electromechanical transducer and along a central direction of propagation of the waves of interest of the elastic wave device, called the propagation direction, and so that the first and second reflectors extend respectively along a first and a second direction, each not perpendicular and not parallel to the propagation direction.

[0038] This manufacturing method allows for the simultaneous production of reflectors and transducers. It therefore requires minimal time and reduces manufacturing costs. This method enables the fabrication of reflectors, particularly those incorporating electrodes, using the same processes as those used to manufacture the transducer(s) of the device.

[0039] The invention will be better understood and other advantages will become apparent upon reading the following description, given by way of non-limiting example, and thanks to the attached figures, among which:

[0040] The [Fig. 1] is a diagram illustrating an elastic wave device according to a first embodiment of the invention, in which the second angle 02 of the second reflector is different from the first angle 01 of the first reflector.

[0041] Figure 2A and Figure 2B illustrate the spectrum of a signal of interest from an elastic wave device respectively without reflectors and according to the invention.

[0042] Figure 3 illustrates an elastic wave device according to a second embodiment in which the first angle 01 of the first reflector and the second angle 02 of the second reflector are equal.

[0043] Figure 4 is a diagram illustrating an elastic wave device according to a third embodiment of the invention.

[0044] Figure 5 is a diagram illustrating a method of manufacturing an elastic wave device according to the invention.

[0045] The invention will be described in more detail using advantageous embodiments, by way of example, and with reference to the drawings. The embodiments described are simply possible configurations, such that the individual features as described can be provided independently of one another or can be omitted when implementing the present invention.

[0046] Figure 1 illustrates an elastic wave device 100 according to a first embodiment of the invention. The device 100 comprises a group 19 of electromechanical elements arranged between a first reflector 3 and a second reflector 5, which are arranged on or in a first surface 9 of a piezoelectric layer 1. Elastic waves generated by the device propagate along the propagation direction 7. The propagation direction 7 forms, in the first surface 9 of the piezoelectric layer 1, a first half-plane 11 and a second half-plane 13.

[0047] The first reflector extends along a first direction 15. The second reflector 5 extends along a second direction 17. The first direction 15 and the second direction 17 form, respectively, a first angle 01 and a second angle 02 with the propagation direction 7. The first angle 01 and the second angle 02 face the group 19 of electromechanical elements, respectively. The first angle 01 and the second angle 02 are both defined in one of the two half-planes 11, 13 formed in the first surface 9 of the piezoelectric layer 1 by the propagation direction 7. In the case of Fig. 1, the first angle 01 and the second angle 02 are defined in the second half-plane 13.

[0048] The electromechanical elements of group 19 extend from a first straight line 33 to a second straight line 35 along a direction 37, called the width direction 37, perpendicular to the propagation direction 7. Group 19 includes a first transducer 21 and a second transducer 23.

[0049] The first transducer 21 comprises a first electrode 25 and a second electrode 27. The first and second electrodes 25, 27 of the first transducer 21 are comb-shaped and interdigitate with each other. The first electrode 25 comprises four parallel-band fingers 211, 212, 213, 214. The second electrode 27 comprises three parallel-band fingers 215, 216, 217. The first electrode 25 of the first transducer 21 is electrically connected to an electrical potential 43. The second electrode 27 of the first transducer 21 is electrically connected to an electrical potential 44. The second electrode 27 of the first transducer 21 may be a floating electrode. The four fingers 211, 212, 213, 214 of the first electrode 25 extend essentially along the width direction 37. The three fingers 215, 216, 217 of the second electrode 27 extend essentially along the width direction 37.In the first transducer 21, a distance pO separates two directly adjacent fingers, one belonging to the first electrode 25 and the other to the second electrode 27. For example, finger 211 and finger 217 are separated by the distance pO.

[0050] The second transducer 23 comprises a first electrode 29 and a second electrode 31. The first and second electrodes 29 and 31 of the second transducer 23 are comb-shaped. The first and second electrodes 29 and 31 are interdigitated with each other. The first electrode 29 comprises four parallel-band fingers 231, 232, 233, and 234. The second electrode 23 comprises three parallel-band fingers 235, 236, and 237. The first electrode 29 of the second transducer 23 is electrically connected to an electrical potential 45. The four fingers 231, 232, 233, 234 of the first electrode 29 extend essentially along the width direction 37. The three fingers 235, 236, 237 of the second electrode 31 extend essentially along the width direction 37. The second electrode 31 of the second transducer 23 is electrically connected to an electrical potential 46.The second electrode 31 of the second transducer 23 can be a floating electrode. In the second transducer 23, two directly adjacent fingers, one belonging to the first electrode 29 and the other to the second electrode 31, can also be separated by the distance pO.

[0051] The number of fingers included in the first and second electrodes 25, 29, 27, 31 of the first and second transducers 3, 5 is only an example and should not be restrictive. There may be more or fewer. Depending on the configurations, and more specifically, on the crystal orientations or the nature of the piezoelectric layer, the electrical connection conditions of the electrodes of the first and second arrays will correspond either to an open circuit or a short circuit. In particular, for configurations including LiNbO3 or concerning elliptical polarization waves for (YXI) / 0 cuts with 0 close to 128°, the electrodes of the first and second arrays will preferably be open-circuited, in other words, electrically independent.For all other configurations of interest, particularly those exploiting shear waves, the electrodes of the first array will preferably be short-circuited, and the electrodes of the second array will also preferably be short-circuited.

[0052] Group 19 further comprises a first mirror 39 and a second mirror 41. The first mirror 39 is arranged between the first reflector 3 and the first transducer 21. The first mirror 39 comprises three electrodes 391, 392, 393 in the form of parallel strips. The three electrodes 391, 392, 393 of the first mirror 39 are electrically connected to each other, specifically via a first connecting electrode 394 and a second connecting electrode 395. In other words, the three electrodes 391, 392, 393 of the first mirror 39 are short-circuited. The three fingers 391, 392, 393 of the first mirror 39 extend essentially along the width direction 37.

[0053] The second mirror 41 is positioned between the second reflector 5 and the second transducer 23. The second mirror 41 comprises three electrodes 411, 412, 413 arranged in parallel bands. These three electrodes 411, 412, 413 of the second mirror 41 are electrically connected, specifically via a first connecting electrode 414 and a second connecting electrode 415. In other words, the three electrodes 411, 412, 413 of the second mirror 41 are short-circuited. The three fingers 411, 412, 413 of the second mirror 41 extend essentially along the width direction 37.

[0054] The number of fingers included in the first and second mirrors 39, 41 is only an example and should not be restrictive. There may be more, or fewer.

[0055] Group 19 of electromechanical elements further comprises a first array 47, a second array 49, a third array 51, and a fourth array 53 of electrodes arranged between the first transducer 21 and the second transducer 23. The first electrode array 47 comprises three electrodes 471, 472, and 473 in the form of parallel strips. The three electrodes 471, 472, and 473 of the first electrode array 47 are electrically connected to each other, specifically via a first connecting electrode 474 and a second connecting electrode 475. In other words, the three electrodes 471, 472, and 473 of the first electrode array 47 are short-circuited. The three electrodes 471, 472, 473 of the first electrode array 47 extend essentially along the width direction 37.

[0056] The electrode arrays 47, 49, 51, 53 between the first and second reflectors 3, 5 can in particular be used to modify, in particular filter and / or delay, the elastic waves propagating between the first and second reflectors 3, 5. Their number can be adapted.

[0057] The second electrode array 49 comprises three electrodes 491, 492, 493 arranged in parallel bands. These three electrodes 491, 492, 493 of the second electrode array 49 are electrically connected to each other, specifically via a first connecting electrode 494 and a second connecting electrode 495. In other words, the three electrodes 491, 492, 493 of the second electrode array 49 are short-circuited. The three electrodes 491, 492, 493 of the second electrode array 49 extend essentially along the width direction 37.

[0058] The third electrode array 51 comprises three electrodes 511, 512, 513 arranged in parallel bands. These three electrodes 511, 512, 513 of the third electrode array 51 are electrically connected to each other, specifically via a first disconnecting electrode 514 and a third connecting electrode 515. In other words, the three electrodes 511, 512, 513 of the third electrode array 51 are short-circuited. The three electrodes 511, 512, 513 of the third electrode array 51 extend essentially along the width direction 37.

[0059] The fourth electrode array 53 comprises three electrodes 531, 532, 533 arranged in parallel bands. These three electrodes 531, 532, 533 of the fourth electrode array 53 are electrically connected to each other, specifically via a first connecting electrode 534 and a fourth connecting electrode 535. In other words, the three electrodes 531, 532, 533 of the fourth electrode array 53 are short-circuited. The three electrodes 531, 532, 533 of the fourth electrode array 53 extend essentially along the width direction 37.

[0060] Instead of using electrodes, it is also possible to use groove networks, which can be engraved furrows.

[0061] A minimum distance, called width distance and denoted L3, corresponds to the minimum distance between the first line 33 and the second line 35 along the width direction 37. L3 can also be defined as the acoustic or elastic opening of the device. The intersection of the first reflector 3 with the first line 33 in the second half-plane 13 corresponds to a first projection point 55 of the first reflector 3. This first projection point 55 corresponds to the point on the first reflector 3 closest to the first line 33. A distance L1 along the propagation direction 7 separates the first projection point 55 of the first reflector 3 from the electromechanical element closest to the first reflector 3. In the case of Fig. 1, the electromechanical element closest to the first reflector 3 is the first mirror 39. The minimum distance L1 can be greater than or equal to the width distance L3. With respect to the propagation direction 7, the first reflector 3 extends along the first direction 15 beyond the first line 33 in the second half-plane 13, and beyond the second line 35 in the first half-plane 11.In an alternative embodiment, the first reflector 3 may not extend beyond the first line 33 and / or the second line 35. However, it is still possible for the distance L1 to be less than the width distance L3. In this case, the deflection of spurious waves by the first reflector 3 and the reduction of spurious wave pollution remain high. In particular, L1 can be on the order of a few wavelengths. This allows us to move beyond the near-field regime of the electromechanical elements emitting elastic waves and still benefit from the technical effects and advantages associated with the first reflector 3.

[0062] The intersection of the second reflector 5 with the second line 35 in the first half-plane 11 corresponds to a first projection point 57 of the second reflector 5. This first projection point 57 corresponds to the point on the second reflector 5 closest to the second line 35. A distance L2 along the propagation direction 7 separates the first projection point 57 of the second reflector 5 from the electromechanical element closest to the second reflector 5. In the case of Fig. 1, the electromechanical element closest to the second reflector 5 is the second mirror 41. The minimum distance L2 can be greater than or equal to the width distance L3. With respect to the propagation direction 7, the second reflector 5 extends along the second direction 17 beyond the first line 33 in the second half-plane 13, and beyond the second line 35 in the first half-plane 11.In an alternative embodiment, the second reflector 5 may not extend beyond the first line 33 and / or the second line 35. However, it is still possible for the distance L2 to be less than the width distance L3. In this case, the deflection of spurious waves by the second reflector 5 and the reduction of spurious wave pollution remain high. In particular, L2 can be on the order of a few wavelengths. This allows the system to escape the near-field regime of the electromechanical elements emitting elastic waves while still benefiting from the technical effects and advantages associated with the second reflector 5.

[0063] The first angle 01 of the first reflector 3 can be between 1° and (180 - Arctan(L3 / L1)) / 2 in Fig. 1. The first angle 01 can also be between (180 + Arctan(L3 / L1)) / 2 and 179°. The second angle 02 can be between 1° and (180 - Arctan(L3 / L2)) / 2 in Fig. 3. The second angle 02 can also be between (180 + Arctan(L3 / L2)) / 2 and 179°. The first angle 01 and the second angle 02 can each be between 45° and 89°, in particular between 75° and 89°, or between 91° and 135°, in particular between 91° and 105°.

[0064] Fig. 2A and Fig. 2B represent the spectrum of a signal of interest from an elastic wave device respectively without reflectors and, as required by the present invention, with reflectors, such as device 100.

[0065] In Fig. 2A, the amplitudes of the electrical reflection S11 and the transfer function S21 of a reflectorless elastic wave device are plotted on the y-axis as a function of the frequency represented in MHz on the x-axis. The amplitudes of the electrical reflection S11 and the transfer function S21 are represented by curves 90 and 91, respectively. Fig. 2A highlights a modulation 92 and 93 of the signal of interest, represented by curves 90 and 91, respectively. This modulation is due to pollution from reflected parasitic elastic waves, particularly from the edges of the piezoelectric layer.

[0066] The modulation of 93 and 92 depends on the path length of the parasitic elastic waves. Indeed, depending on the path length of the parasitic elastic waves, a phase shift appears at the transducers between them and the elastic waves of interest. The parasitic waves and the waves of interest interfere at the transducers of the device. This creates both constructive and destructive interference. Since the parasitic waves have a lower amplitude than the waves of interest, the signal resulting from the interference at the transducers has a fundamental shape corresponding to that of the signal of the waves of interest modulated by a sinusoidal function corresponding to the signal of the parasitic waves.The filter bandwidth is classically defined as the set of frequencies for which the magnitude of the transfer function S21 is between the maximum magnitude of the transfer function S21, denoted S21 MAX, and the value S21 MAX - 3 dB. The specification may sometimes be given for the value S21 MAX - 1 dB.

[0067] In Fig. 2B, the amplitudes of the electrical reflection S11 and the transfer function S21 of an elastic wave device according to the invention, thus comprising reflectors such as device 100, are plotted on the ordinate axis as a function of the frequency represented in MHz on the abscissa axis. The amplitudes of the electrical reflection S11 and the transfer function S21 are represented respectively by curves 94 and 95. Fig. 2B highlights a reduction, or even a disappearance, of the modulation 92, 93 of the signal of interest visible in Fig. 2A and due to pollution by parasitic elastic waves reflected, in particular by the edges of the piezoelectric layer.

[0068] The device according to the invention functions as follows.

[0069] Between the first transducer 21 and the second transducer 23, elastic waves are generated and propagate through the piezoelectric layer 1. These elastic waves have, in particular, a central operating wavelength equal to 2 x p0. Specifically, these waves propagate along the propagation direction 7 in a first direction of propagation represented by a first arrow 59, from the first transducer 21 to the second transducer 23. The first direction of propagation (forward direction) and the first arrow 59 may hereafter be considered equivalent and designated by the same reference number 59. These waves also propagate along the propagation direction 7 in a second direction of propagation represented by a second arrow 61. The second direction of propagation (retrograde direction) and the second arrow 61 may hereafter be considered equivalent and designated by the same reference number 61.The second direction of propagation 61, from the second transducer 23 to the first transducer 21, is therefore opposite to the first direction of propagation 59. Elastic waves transmitted and / or reflected undesirably by the first transducer 21 propagate between the first mirror 39 and the first transducer 21, in both the first and second directions of propagation 59, 61. The first mirror 39 further confines the elastic waves between the first and second transducers 21, 23. Some of the elastic waves propagating between the first transducer 21 and the first mirror 39 also leak beyond the first mirror 39, between the first mirror 39 and the first reflector 3, along the direction of propagation 7.

[0070] The first reflector 3 reflects these parasitic elastic waves in a first direction of reflection along a first reflection direction 63. The first direction of reflection is represented by an arrow 65, with which it can subsequently be confused and designated by the same reference number 65. The first direction of reflection 65 is opposite to a first edge 69 of the piezoelectric layer 1. The first edge 69 is orthogonal to the propagation direction 7. Part of the waves propagating towards the first reflector 3 propagate beyond the first reflector 3, between the first reflector 3 and the first edge 69, along the propagation direction 7. These waves are reflected by the first edge 59 and then propagate in the first and second directions of propagation 59, 61. The waves reflected by the first edge 69 are reflected by the first reflector 3 in a second direction of reflection along the first reflection direction 63.The second direction of reflection is represented by an arrow 67 with which it can subsequently be confused and designated by the same reference number 67. The second direction of reflection 67 points towards the first edge 69 of the piezoelectric layer 1.

[0071] Elastic waves transmitted and / or reflected unintentionally by the second transducer 5 propagate between the second mirror 41 and the second transducer 5, in both the first and second directions of propagation 59, 61. The second mirror 41 further confines the elastic waves between the first and second transducers 3, 5. A portion of the elastic waves propagating between the second transducer 5 and the second mirror 41 also propagate beyond the second mirror 41, between the second mirror 41 and the second reflector 5, along the direction of propagation 7.

[0072] The second reflector 5 reflects these parasitic elastic waves in a first direction of reflection along a first direction of reflection 71. The first direction of reflection is represented by an arrow 73, with which it can subsequently be confused and designated by the same reference number 73. The first direction of reflection 73 is opposite a second edge 77 of the piezoelectric layer 1. The second edge 77 is orthogonal to the direction of propagation 7. The second edge 77 is opposite the first edge 69. A portion of the waves propagating towards the second reflector 5 propagate beyond the second reflector 5, between the second reflector 5 and the second edge 77, along the direction of propagation 7. These waves are reflected by the second edge 77 and then propagate in the first and second directions of propagation 59, 61.The waves reflected by the second edge 77 are reflected by the second reflector 5 in a second direction of reflection along the first direction of reflection 71. The second direction of reflection is represented by an arrow 75 with which it can subsequently be confused and designated by the same reference number 75. The second direction of reflection 75 points towards the second edge 77 of the piezoelectric layer 1. In Fig. 1, the parasitic waves propagating from the group 19 of electrodes are reflected by the first and second reflectors 3, 5 respectively in the first and second half-planes 11, 13.

[0073] Figure 3 illustrates an elastic wave device 200 according to a second embodiment in which the first angle 01 of a first reflector 34 and the second angle 02 of a second reflector 6 are equal. Furthermore, the first reflector 34 comprises a first electrode array. And, the second reflector 6 comprises an electrode array. In Fig. 1, device 100 illustrates a first embodiment in which the first angle 01 of the first reflector 3 is different from the second angle 02 of the second reflector 5. Moreover, in Fig. 1, the first and second reflectors 3, 5 each comprise only one electrode.

[0074] In the example in Fig. 3, the first angle 01 and the second angle 02 are equal. However, the first angle 01 and the second angle 02 may not be equal and still be designed so that the first and second reflectors 34, 6 reflect the parasitic waves in the same half-plane, here the first half-plane 11.

[0075] The first electrode array of the first reflector 34 of device 200 comprises three electrodes 4, 9, 12. The second electrode array of the second reflector 6 comprises three electrodes 22, 96, 98. Both the first and second reflectors 34 and 6 may each also comprise a groove array. Alternatively, both reflectors 34 and 6 may comprise only one groove or a groove array, and in particular, no electrodes. Therefore, reference numbers 4, 9, 12 may also refer to grooves in the first groove array of the first reflector 34. Similarly, reference numbers 22, 96, 98 may also refer to grooves in the second groove array of the second reflector 6.

[0076] In device 200 of Fig. 3, the second reflector 6 extends along a second direction 18. The second reflector 6 reflects the parasitic elastic waves propagating in the first direction of propagation 59 into a first direction of reflection 40 along a first direction of reflection 79. Parasitic waves are reflected by the second edge 77 and then propagate in the first and second directions of propagation 59, 61. The waves reflected by the second edge 77 are reflected by the second reflector 6 into a second direction of reflection 42 along the first direction of reflection 79. In Fig. 3, the first and second reflectors 3, 6 of device 200 both reflect the parasitic elastic waves propagating from the group 19 of electromechanical elements towards the first half-plane 11. In Fig.1, the first and second reflectors 3, 5 of device 100 respectively reflect the parasitic elastic waves propagating from the group 19 of electromechanical elements towards the first half-plane 11 and towards the second half-plane 13.

[0077] The intersection of the second reflector 6 with the first line 33 in the second half-plane 13 corresponds to a first projection point 26 of the second reflector 5. The first projection point 26 corresponds to the point on the second reflector 6 closest to the first line 33. A distance L2 along the propagation direction 7 separates the first projection point 26 of the second reflector 6 from the electromechanical element closest to the second reflector 6. In the case of Fig. 3, the electromechanical element closest to the second reflector 6 is the second mirror 41. The minimum distance L2 can be greater than or equal to the width distance L3. With respect to the propagation direction 7, the second reflector 6 extends along the second direction 18 beyond the first line 33 in the second half-plane 13, and beyond the second line 35 in the first half-plane 11.However, it is possible that the distance L1 and / or L2 may be less than the width distance L3. In this case, the deflection of spurious waves by the first and / or second reflector 34, 6 and the reduction of spurious wave pollution remain significant. The distances L1 and L2 are preferably greater than one times the central wavelength of interest of the device; in particular, L1 and L2 are at least five times greater than the central wavelength of interest of the device. This allows the system to move out of the near-field regime. In particular, having a distance L1 and L2 on the order of the acoustic aperture L3 of the device also allows the system to move out of the near-field regime.

[0078] The first and / or second reflector 34, 6 can be rotated slightly, in particular from ±0.5° to ±1°, without the reflection coefficients of the first and / or second reflector 34, 6 being significantly affected.

[0079] Figure 4 is a diagram illustrating an elastic wave device 400 according to a third embodiment of the invention. Compared to devices 100 and 200 of Figures 1 and 3, device 400 comprises a first reflector 81 and a second reflector 83, each extending in two distinct directions.

[0080] The first reflector 81 comprises a first portion 82 and a second portion 84. The first portion 82 extends along a first direction 20 in the first half-plane 11 of the first surface 9 of the piezoelectric layer 1 formed by the propagation direction 7. The second portion 84 of the first reflector 81 of the device 400 extends along a second direction 16 in the second half-plane 13 of the first surface 9 of the piezoelectric layer 1 formed by the propagation direction 7. In particular, in one embodiment of the invention, the second direction 16 may correspond to the symmetrical counterpart of the first direction 20 with respect to the propagation direction 7. The first reflector 81 reflects the parasitic elastic waves propagating from the group 19 of electromechanical elements as follows; the waves propagating in the first half-plane 11 interact with the first portion 82 of the first reflector 81.These waves are reflected along a first direction of reflection 54 and in a first sense of reflection 56. The waves propagating in the second half-plane 13 interact with the second portion 84 of the first reflector 81. These waves are reflected along a second direction of reflection 64 and in a second sense of reflection 66.

[0081] The first reflector 81 reflects the parasitic elastic waves propagating from the first edge 69 of the piezoelectric layer 1 as follows; the waves propagating in the first half-plane 11 interact with the first portion 81 of the first reflector 81. These waves are reflected along the first reflection direction 54 and in a third reflection direction 58. The waves propagating in the second half-plane 13 interact with the second portion 84 of the first reflector 81. These waves are reflected along the second reflection direction 64 and in a fourth reflection direction 68.

[0082] The second reflector 83 comprises a first portion 86 and a second portion 88. The first portion 86 extends along a first direction 30 in the first half-plane 11 of the first surface 9 of the piezoelectric layer 1 formed by the propagation direction 7. The second portion 88 of the second reflector 83 of the device 400 extends along a second direction 32 in the second half-plane 13 of the first surface 9 of the piezoelectric layer 1 formed by the propagation direction 7. In particular, in one embodiment of the invention, the second direction 32 may correspond to the symmetrical counterpart of the first direction 30 with respect to the propagation direction 7. The second reflector 83 reflects the parasitic elastic waves propagating from the group 19 of the electromechanical element as follows; the waves propagating in the first half-plane 11 interact with the first portion 86 of the second reflector 83.These waves are reflected along the first reflection direction 70 and in the first reflection direction 68. The waves propagating in the second half-plane 13 interact with the second portion 88 of the second reflector 83. These waves are reflected along a second reflection direction 72 and in a second reflection direction 76.

[0083] The second reflector 83 reflects the parasitic elastic waves propagating from the second edge 77 of the piezoelectric layer 1 as follows; the waves propagating in the first half-plane 11 interact with the first portion 86 of the second reflector 83. These waves are reflected along the first reflection direction 70 and in a third reflection direction 66. The waves propagating in the second half-plane 13 interact with the second portion 88 of the second reflector 83. These waves are reflected along the second reflection direction 72 and in a fourth reflection direction 74.

[0084] The directions of reflection and the sense of reflection are specific to each of the first reflector 3, 81 and the second reflector 5, 83. In other words, for example, the first direction of reflection 63 of the first reflector 3 of the device 100 is not the first direction of reflection 71 of the second reflector 5 of the device 100. Nevertheless, the first direction of reflection 63 of the first reflector 3 of the device 100 can be parallel to the first direction of reflection of the second reflector 5 of the device 100.

[0085] The configurations proposed in the various embodiments illustrated in Figures 1, 2, and 4 are examples and are not restrictive. For example, the number of electrode arrays 47, 49, 51, and 53 between the first and second transducers 3 and 5 may differ from four. There may be more than four electrode arrays. There may be fewer than four electrode arrays. In particular, there may be only one group of electrodes between the first and second reflectors 3 and 5. More specifically, there may be no group of electrodes between the first and second reflectors 3 and 5. The electrode group(s) 47, 49, 51, and 53 between the first and second transducers 3 and 5 may be used to modify the electromechanical signal, in particular to filter it. Similarly, the number of electrodes included in the same electrode group 47, 49, 51, 53 can be different from three.An electrode group 47, 49, 51, 53 may comprise fewer than three electrodes, in particular a single electrode. An electrode group 47, 49, 51, 53 may comprise more than three electrodes.

[0086] Devices 100, 200, 400 can be used as filters, in particular electroacoustic filters, or as delay lines.

[0087] Figure 5 is a diagram illustrating the steps of a process for manufacturing an elastic wave device, in particular a device according to one embodiment of the invention. The process begins with step 501, during which at least one electromechanical transducer is disposed on, in particular directly on, a first surface of the piezoelectric layer, or embedded at least partially in a first surface of a piezoelectric layer.

[0088] Then in step 503, a first and a second reflector, each comprising an array of at least one electrode, and / or, each comprising an array of at least one groove, are respectively disposed on, in particular directly on the first surface of the piezoelectric layer and / or buried in the first surface of the piezoelectric layer.

[0089] Steps 501 and 503 can be interchanged. Steps 501 and 503 can also be performed simultaneously.

Claims

Demands 1. Elastic wave device (100, 200, 400), in particular guided surface elastic wave device, more particularly guided surface shear wave device, or device with predominantly longitudinal polarization modes, the elastic wave device (100, 200, 400) being configured to operate with predetermined elastic waves of interest whose wavelengths are centered on a central operating wavelength, the elastic wave device (100, 200, 400) comprising: a piezoelectric layer (1), in particular ferroelectric, and at least one electromechanical transducer (21) formed on and / or embedded in a first surface (9) of the piezoelectric layer (1), and a first (3) and a second (5) reflector configured to reflect at least partially the elastic waves of interest from the (100, 200, 400) elastic wave device and to deflect the elastic waves so that they do not interfere with at least one transducer, and the first (3) and second (5) reflectors are arranged on, in particular directly on, and / or in the first surface (9) of the piezoelectric layer (1), and the first (3, 34) and the second (5, 6) reflectors are arranged on either side of at least one electromechanical transducer (21) and along a central propagation direction (7) of the elastic waves of interest of the elastic wave device (100, 200, 400), called the propagation direction (7), and the first (3, 34) and the second (5, 6) reflectors extend respectively along a first (15) and a second (17, 18) direction, each not perpendicular and not parallel to the propagation direction (7), and wherein the first reflector (3, 34) and the second reflector (5, 6) respectively comprise a first array of at least one electrode (4, 9, 12), in particular in the form of a parallel band, more particularly in a short circuit, and a second array of at least one electrode (22, 98, 96), in particular in the form of a parallel band, more particularly in a short circuit, extending respectively along the first (15) and the second (17, 18) direction, and / or the first (3, 34) and second reflectors (5, 6) comprise at least one groove cut (4, 9, 12, 22, 96, 98), in particular a single groove, in the piezoelectric layer (1), and at least one groove (4, 9, 12, 22, 96, 98) is cut from the first surface (9) of the piezoelectric layer (1), in particular at least one groove (4, 9, 12, 22, 96, 98) can extend from the first surface (9) of the piezoelectric layer (1), to a second surface of the piezoelectric layer (1), the second surface being opposite the first surface (9).

2. An elastic wave device (100, 200, 400) according to claim 1, wherein the first reflector (3) and the second reflector (5) are configured to reflect at least 50%, more particularly at least 80%, of the elastic waves of interest of the device (100, 200, 400).

3. An elastic wave device (100, 200, 400) according to claim 1 or 2, wherein at least a second electromechanical transducer (23) is disposed between the first (3, 34) and the second (5, 6) reflector along the propagation direction (7).

4. An elastic wave device (100, 200, 400) according to any one of the preceding claims, wherein a first electromechanical mirror (39) is disposed between the first reflector (3, 34) and the first transducer (21), and, a second electromechanical mirror (41) is disposed between the second reflector (5, 6) and the second transducer (23) along the propagation axis (7).

5. An elastic wave device (100, 200, 400) according to any one of claims 1 to 4, wherein the elastic wave device (100, 200, 400) further comprises one or more arrays (47, 49, 51, 53) of electrodes arranged between the first electromechanical transducer (21) and the second electromechanical transducer (23), the arrays (47, 49, 51, 53) being separated from each other by free and / or metallized propagation gaps, preferably the distances between two neighboring arrays (47, 49, 51, 53) of electrodes are the same.

6. An elastic wave device (100, 200, 400) according to any one of claims 1 to 5, wherein two adjacent electrodes (4, 9, 12) of the first array of at least one electrode (4, 9, 12) are spaced apart by a first period pi, and two adjacent electrodes (22, 98, 96) of the second array of at least one electrode (22, 96, 98) are spaced apart by a second period p2, in particular the first and second periods are equal, more in particular pi and p2 are configured such that at least the set of elastic waves of interest of the elastic wave device (100, 200, 400) is at least partially reflected by the first (34) and the second (6) array of at least one electrode.

7. An elastic wave device (100, 200, 400) according to any one of claims 1 to 6, wherein the electrodes (4, 9, 12) of the first array of at least one electrode (4, 9, 12) of the first reflector (3) and of the second array of at least one electrode (22, 98, 96) of the second reflector (5, 6) are made of Aluminium or Copper or Molybdenum or Palladium or Tantalum or Tungsten or Platinum or Gold or Nickel or a combination of these materials, in particular are made of the same material as the first transducer (21) and / or the second transducer (23).

8. An elastic wave device (100, 200, 400) according to any one of claims 1 to 7, wherein the first reflector (3, 34) and the second reflector (5, 6) respectively comprise a first array of grooves (4, 9, 12), in particular in the form of parallel bands, and a second array of grooves (22, 96, 98), in particular in the form of parallel bands, wherein two adjacent grooves (4, 9, 12) of the first and second arrays of grooves (4, 9, 12, 22, 96, 98) are respectively spaced by a first period pi and a second period p2, in particular the first and second periods are equal, such that at least the set of elastic waves of interest of the elastic wave device is at least partially reflected by the first and second arrays of grooves (4, 9, 12, 22, 96, 98). 12, 22, 96, 98).

9. An elastic wave device (100, 200, 400) according to any one of claims 1 to 8, wherein at least one transducer (21) extends in a direction perpendicular (37) to the propagation direction (7), referred to as the width direction (37), from a first straight line (33) to a second straight line (35), and a first minimum distance, denoted L1, along the propagation direction (7) and separating a first projection point (55) from the first reflector (3, 34) and the electromechanical element (39, 21, 47, 49, 51, 53, 23, 41) nearest to the first reflector (3, 34) is equal to or greater than the minimum distance, referred to as the width distance and denoted L3, between the first straight line (33) and the second straight line (35) along the width direction (37), the first point of projection (55) of the first reflector (3, 34) corresponding to the projection of the point of the first reflector (3, 34) closest to the first line (33) onto the first line (33), and a second minimum distance, denoted L2, according to the direction of propagation (7) and separating a first projection point (26, 57) of the second reflector (5, 6) and the electromechanical element (39, 21, 47, 49, 51, 53, 23, 41) closest to the second reflector (5, 6) is equal to or greater than the width distance L3, the first projection point (26, 57) of the second reflector (5, 6) corresponding to the projection of the point of the second reflector (5, 6) closest to the first line (33) onto the first line (33).

10. An elastic wave device (100, 200, 400) according to claim 9, in which the first (15) and second (17, 18) direction form respectively a first angle 01 and a second angle 02 with the propagation direction (7), the first angle 01 and the second angle 02 respectively face the at least one electromechanical transducer (21), and are both defined in one of the same two half-planes (11, 13) formed in the first surface (9) of the piezoelectric layer (1) by the propagation direction (7), the first angle 01 and second angle 02 are each between 45° and 89°, in particular between 75° and 89°, or between 91° and 135°, in particular between 91° and 105°.

11. An elastic wave device (100, 200, 400) according to claim 10, wherein 02 is different from 180° - 01.

12. An elastic wave device (100, 200, 400) according to claim 10, in which 02 and 01 are equal.

13. An elastic wave device (100, 200, 400) according to claim 1, wherein the first reflector (81) extends along the first direction (20) in a first half-plane (11) of the first surface (9) of the piezoelectric layer (1) formed by the propagation direction (7), and extends along a third direction (16) in a second half-plane (13) of the first surface (9) of the piezoelectric layer (1) formed by the propagation direction (7), in particular, the third direction (16) corresponds to the reflection of the first direction (15, 20) across the propagation direction (7) and the second reflector (83) extends along the second direction (30) in the first half-plane (11), and extends along a fourth direction (32) in the second half-plane (13), in particular the fourth direction (32) corresponds to the symmetric of the second direction (30) with respect to the direction of propagation (7), more in particular the first (20) and the second (30) directions are the same, and, the third (30) and the fourth (32) directions are the same.

14. A filter, in particular an electroacoustic filter, comprising an elastic wave device (100, 200, 400) according to any one of claims 1 to 12, an operating frequency range of the filter is defined by the wavelengths of the elastic waves of interest of the device (100, 200, 400) centered on a central operating wavelength.

15. Method of manufacturing an elastic wave device configured to operate with elastic waves of interest whose wavelengths are centered on a central operating wavelength, in particular an elastic wave device (100, 200, 400) according to any one of claims 1 to 13, the elastic wave device comprising a piezoelectric layer, in particular a ferroelectric layer, and at least one electromechanical transducer, and a first and a second reflector configured to at least partially reflect the elastic waves of interest from the elastic wave device and to deflect the elastic waves so that they do not interfere with the at least one transducer, the method comprising the following steps, in particular simultaneous steps: to dispose at least one electromechanical transducer (501) on, in particular directly on, a first surface of the piezoelectric layer, or to bury it at least partially in the first surface of the piezoelectric layer, and to dispose a first and a second reflector (503) each comprising an array of at least one electrode disposed on, in particular directly on, or in the first surface of the piezoelectric layer, and / or, each comprising an array of at least one groove buried or engraved in the first surface of the piezoelectric layer, in such a way that the first and second reflectors are arranged respectively on either side of at least one electromechanical transducer and along a direction of propagation of the waves of interest of the elastic wave device, called the direction of propagation, and in such a way that the first and second reflectors extend respectively along a first and a second direction each not perpendicular and not parallel to the direction of propagation.

Images