Volume acoustic wave filter

Abstract

Body wave acoustic filter. This description relates to a method for manufacturing a body wave acoustic filter, comprising a step of transferring a first structure onto a second structure. The first structure comprises, on an upper face of a first substrate (107), a layer of a piezoelectric material (109) surmounted by a first electrode (113). The second structure comprises, on an upper face of a second substrate (101), an insulating layer (103). The insulating layer (103) comprises a cavity (105) formed from the upper face of the insulating layer (103). The transfer step consists of transferring the first structure, by its upper face, onto the upper face of the second structure, the first electrode (113) being aligned with the cavity (105) in the insulating layer (103). Figure for the abstract: Fig. 4

Description

Title of the invention: Volume acoustic wave filter technical field

[0001] This description relates generally to electronic devices and more particularly to bulk acoustic wave or BAW (from the English "Bulk Acoustic Wave") filters. Previous technique

[0002] Many electronic devices include at least one volume acoustic wave filter. Such filters are, for example, integrated into mobile phones, or smartphones, to prevent the operation of a radio frequency communication reception channel of the phone from being disrupted by interference caused by radio frequency signals emitted by other electronic devices, or by noise from external radio frequency sources.

[0003] Two types of bulk acoustic wave filters have already been proposed: rigidly mounted resonator filters, known as "SMRs" (from the English "Solidly Mounted Resonator"), and thin-film bulk acoustic resonator filters, known as "FBARs" (from the English "Thin-Film Bulk Acoustic Resonator"), also called "membrane" bulk acoustic wave filters. An SMR filter typically comprises a membrane made of an insulating material located on and in contact with a Bragg mirror, and a piezoelectric layer located on the membrane and interposed between lower and upper electrodes. An FBAR filter differs from the SMR filter primarily in that, in the case of the FBAR filter, the Bragg mirror is replaced by an air cavity above which the membrane is suspended. The presence of the air cavity gives the FBAR filter greater efficiency than the SMR filter.The air cavity provides superior acoustic insulation compared to a Bragg mirror with multiple bilayers (approximately fifteen bilayers would provide insulation equivalent to that of an air cavity, which would be very difficult to achieve in practice), resulting in reduced energy losses.

[0004] However, existing acoustic wave filters, particularly existing FBAR filters, suffer from various drawbacks. FBAR filters are especially complex and expensive to manufacture, as current manufacturing processes for such filters require precise control of the flatness of the structure and involve a delicate step of forming the air cavity by removing a sacrificial layer. Furthermore, FBAR filters are affected by heating and other problems. mechanical robustness. As a result, it proves difficult to miniaturize existing FBAR filters.

[0005] There is a need to overcome all or part of the drawbacks of bulk acoustic wave filters, in particular existing FBAR filters and their manufacturing processes. It would be especially desirable to simplify the manufacturing processes of such filters and to be able to produce FBAR filters with superior mechanical strength and thermal performance compared to existing FBAR filters. This would make it easier to miniaturize FBAR filters. Summary of the invention

[0006] For this purpose, an embodiment provides a method for manufacturing a volume acoustic wave filter, comprising a step of transferring a first structure onto a second structure, the first structure comprising, on an upper face of a first substrate, a layer of a piezoelectric material surmounted by a first electrode, the second structure comprising, on an upper face of a second substrate, an insulating layer, the insulating layer comprising a cavity, formed from the upper face of the insulating layer, the step of transferring consisting of transferring the first structure, by its upper face, onto the upper face of the second structure, the first electrode being aligned with the cavity in the insulating layer.

[0007] According to one embodiment, during the transfer step, the first structure comprises, on the upper face of the first electrode, another insulating layer, the insulating layer of the second structure being brought into contact with the other insulating layer of the first structure.

[0008] According to one embodiment, at the end of the transfer step, the first electrode of the first structure does not come into contact with the bottom and the lateral sides of the cavity.

[0009] According to one embodiment, the process comprises, after the transfer step, a step of forming a second electrode on the face of the piezoelectric layer, opposite the cavity, the second electrode being formed at least partly in line with the first electrode.

[0010] According to one embodiment, the process comprises, after the transfer step, a step of forming an opening in the piezoelectric layer, directly above the first electrode.

[0011] According to one embodiment, the process comprises, after the step of forming the opening in the piezoelectric layer, a step of forming a via conductor, in the opening, the via conductor being formed in contact with the first electrode.

[0012] Another embodiment provides for a volume acoustic wave filter comprising: - a substrate; - an insulating layer, formed on an upper face of the substrate, and comprising a cavity, the upper face of which is entirely flush with the upper face of the insulating layer; - a piezoelectric layer on the insulating layer; - a first electrode formed on the lower face of the piezoelectric layer, within the cavity, the piezoelectric layer not being open directly above the cavity.

[0013] According to one embodiment, the cavity is an air or vacuum cavity.

[0014] According to one embodiment, the thickness of the first electrode is less than the depth of the cavity.

[0015] According to one embodiment, the piezoelectric layer is made of lithium niobate.

[0016] According to one embodiment, the filter comprises a second electrode formed on the upper face of the piezoelectric layer, at least partly directly above the first electrode.

[0017] According to one embodiment, the piezoelectric layer and the insulating layer are separated by another insulating layer.

[0018] Another embodiment provides for a method of using the filter as described, comprising the application of a radio frequency signal between the first and second electrodes which tends to make the resonator resonate, the signal being attenuated if the frequency of the signal is different from the resonance frequency of the resonator. Brief description of the drawings

[0019] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0020] Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9A, Fig. 9B and Fig. 10 are each a view of a structure obtained at the end of a step in a manufacturing process for a volume acoustic wave filter according to an embodiment; and

[0021] [Fig. 11] is a cross-sectional view of an electronic device comprising the volume acoustic wave filter of [Fig. 10]. Description of the implementation methods

[0022] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0023] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0024] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0025] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0026] Unless otherwise specified, the expressions "approximately", "roughly", and "on the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0027] Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9A, Fig. 9B and Fig. 10 are each a view of a structure obtained at the end of a step in a manufacturing process of a volume acoustic wave filter according to an embodiment.

[0028] More specifically, the aforementioned figures illustrate the manufacturing process of an example of a volume acoustic wave filter, for example a FBAR type filter.

[0029] Figure 1 illustrates, by way of a cross-sectional view, a starting structure comprising a semiconductor substrate 101, for example a wafer or a piece of wafer made of a semiconductor material. By way of example, the semiconductor substrate 101 is made of silicon. By way of example, the substrate 101 is made of silicon having high resistivity.

[0030] In the example shown, the starting structure further includes an insulating layer 103 covering an upper face 101T of the semiconductor substrate 101. In the illustrated example, the insulating layer 103 is located on and in contact with the entire upper face 101T of the semiconductor substrate 101. The insulating layer 103 has, for example, a thickness in the range of 1.2 pm to 2 pm.

[0031] The insulating layer 103 is, for example, made of a mineral material. By way of example, the insulating layer 103 is made of an oxide or a nitride. The insulating layer 103 is, for example, made of silicon oxide and / or silicon nitride.

[0032] Fig. 2 illustrates, by a cross-sectional view, a structure obtained at the end of a cavity formation step 105 in the insulating layer 103 of the structure illustrated in Fig. 1.

[0033] In the example of [Fig.2], two cavities 105 are formed in the insulating layer 103. In practice, it can be expected that a larger number of cavities 105 are formed in the insulating layer 103. The cavities 105 are formed, for example, from the upper face of the insulating layer 103 into the insulating layer 103.

[0034] By way of example, as shown in [Fig.2], the cavities 105 are through-holes and open onto the upper face 101T of the semiconductor substrate.

[0035] Alternatively, the cavities 105 are non-through and have a depth strictly less than the thickness of the insulating layer 103.

[0036] The cavities 105 are formed for example by etching, for example by reactive ion etching or RIE (from the English "Reactive Ion Etching").

[0037] The cavities 105, for example, have a depth in the range of 0.3 pm to 2 pm.

[0038] In the embodiment of [Fig. 2], the cavities 105 have substantially straight and substantially vertical lateral walls. In this embodiment, the cavities 105 have a substantially rectangular shape in cross-section. By way of example, the cavities 105 have a substantially trapezoidal or rectangular shape in top view. Alternatively, the cavities 105 may have any shape in top view.

[0039] Figure 3 illustrates, by way of a cross-sectional view, another starting structure. The starting structure illustrated in Figure 3 comprises, for example, a support 107. By way of example, the support 107 is, for instance, a wafer or a piece of wafer made of a semiconductor material. By way of example, the support 107 is made of silicon.

[0040] The initial structure illustrated in [Fig. 3] further comprises, on the support 107, a piezoelectric layer 109, i.e., a layer of a piezoelectric material. The piezoelectric layer 109 extends, for example, over the upper surface of the support 107, for example, over the entire upper surface of the support 107. By way of example, the piezoelectric layer 109 is made of a single-crystal material. By way of example, the piezoelectric layer 109 is made of lithium niobate (LiNbO3), lithium titanate (LTO), or scandium-doped aluminum nitride (AIN). By way of example, the piezoelectric layer has a thickness in the range of 50 nm to 250 nm, for example, a thickness on the order of 100 nm.

[0041] By way of example, the piezoelectric layer 109 is fixed to the upper face of the support 107, by a bonding layer 111, the bonding layer 111 being in contact, by its lower face with the upper face of the support 107 and, by its upper face, with the lower face of the piezoelectric layer 109.

[0042] The initial structure illustrated in [Fig. 3] further comprises, on the piezoelectric layer 109, more precisely on the upper surface of the piezoelectric layer 109, electrodes 113. The electrodes 113 are, for example, formed on and in contact with the piezoelectric layer 109. In the embodiment of [Fig. 3], two electrodes 113 are shown. In practice, it can be foreseen that a larger number of electrodes 113 are formed. By way of example, the electrodes 113 are made of a conductive material, for example, a metal or a metal alloy. By way of example, the electrodes 113 are made of molybdenum, tungsten, aluminum, copper, or a mixture of two or more of these materials.

[0043] In the embodiment of [Fig. 3], the initial structure further comprises an insulating layer 115 covering the lateral and upper faces of the electrodes 113. In this example, the insulating layer 115 also covers uncoated portions of the upper face of the piezoelectric layer 109 of the electrodes 113. In other words, the insulating layer 115 extends laterally out of the vertical axis of the electrodes 113. The insulating layer 115 is, for example, more precisely located in contact with the lateral and upper faces of the electrodes 113 and with the uncoated portions of the upper face of the piezoelectric layer 109 of the electrodes 113.

[0044] The insulating layer 115 is, for example, made of the same material as the insulating layer 103 of Figures 1 and 2. By way of example, the insulating layer 115 is made of a mineral material. By way of example, the insulating layer 115 is made of an oxide or a nitride. The insulating layer 115 is, for example, made of silicon oxide and / or silicon nitride. The insulating layer 115 acts, for example, as a passivation layer for the upper surface of the electrodes 113. By way of example, the insulating layer 115 has a thickness in the range of 50 nm to 250 nm, for example, a thickness of approximately 150 nm.

[0045] Figure 4 illustrates, by way of a cross-sectional view, a structure obtained after a step of transferring the structure illustrated in Figure 3 onto the structure illustrated in Figure 2. More specifically, during this step, the structure illustrated in Figure 3 is transferred, by its upper face (in the orientation of Figure 3) onto the upper face of the structure illustrated in Figure 2. Thus, in Figure 4, the portion of the structure originating from the structure illustrated in Figure 3 is shown reversed with respect to its orientation in Figure 3.

[0046] During this step, layers 103 and 115 are brought into contact.

[0047] During this step, each electrode 113 is placed inside a cavity 105. The electrodes 113 formed on the structure of [Fig.3] and the cavities 105 formed on the structure of [Fig.2] are arranged in the same way respectively on the surface of the support 107 and the substrate 101 so that each electrode 113, carried by the support 107, faces a cavity 105 of the substrate 101.

[0048] During this step, the structure illustrated in [Fig.3] is transferred onto the structure illustrated in [Fig.2] by aligning the electrodes 113 with the cavities 105. This transfer step is, for example, assisted by an alignment control technique.

[0049] By way of example, the electrodes 113 have a rectangular shape when viewed from above. Following this step, the lateral sides of the electrodes 113 are not in contact with the lateral sides of the cavities 105 that house them. By way of example, the electrodes 113 are smaller than the cavities 105 when viewed from above. By way of example, the electrodes have a width and length less than the width and length of the cavities 105. By way of example, the electrodes have a width and length within the range of 10 pm to 100 pm.

[0050] At the end of this step, the lower faces of the electrodes 113, in the orientation of [Fig. 4], are not in contact with the bottom of the cavities 105 that house them. The electrodes 113 have, for example, a thickness less than the depth of the cavities 105. By way of example, the cavities 105 have a depth in the range of 80 nm to 200 nm.

[0051] At the end of this step, layer 109 does not have any openings opposite cavity 105.

[0052] By way of example, at the end of this step, the cavity 105 is closed. At the end of this step, the cavities 105 contain only a gas, for example air or the gas present in the equipment in which the transfer step is carried out. Alternatively, at the end of this step, the cavities 105 contain a vacuum or a partial vacuum.

[0053] Fig. 5 illustrates, by a cross-sectional view, a structure obtained after a step of removing the support 107 and the bonding layer 111 of the structure illustrated in Fig. 4.

[0054] By way of example, this step is carried out by mechanical polishing or chemical mechanical polishing (CMP). By way of example, this step is carried out by wet etching.

[0055] At the end of this step, the upper face of the piezoelectric layer 109 is completely uncovered and exposed.

[0056] Fig. 6 illustrates, by a cross-sectional view, a structure obtained at the end of a step of forming openings 117 in the piezoelectric layer 109 of the structure illustrated in Fig. 5.

[0057] More specifically, during this step, the openings 117 are created in the layer 109 from the upper face of the layer 109, in the layer 109. The openings 117 are, for example, through-holes, that is to say, they open onto the upper face of the electrodes 113. As an example, an opening 117 is created opposite each electrode 113.

[0058] Fig. 7 illustrates, by a cross-sectional view, a structure obtained at the end of a step of forming electrodes 119 and vias 121 in the structure illustrated in Fig. 6.

[0059] More particularly, during this step, the vias 121 are formed on the upper face of the layer 109 and in the openings 117 created during the step illustrated in [Fig.6]. More particularly, during this step, the electrodes 119 are also formed opposite the electrodes 113.

[0060] The vias 121 facilitate the re-establishment of contact with the electrodes 113. For example, the vias 121 are made of a conductive material, such as a metal or a metal alloy. For example, the vias 121 are made of molybdenum, tungsten, aluminum, copper, or a mixture of two or more of these materials. The vias 121 have, for example, in cross-sectional view, a T-shape comprising a vertical portion extending, in the openings 117, from the upper surface of the layer 109, through the layer 109 to the upper surface of the electrode 113, and a horizontal portion extending laterally on and in contact with the upper surface of the piezoelectric layer 109 directly above and in the vicinity of the vertical portion of the via 121.

[0061] By way of example, the electrodes 119 are formed in contact with the upper face of the piezoelectric layer 109.

[0062] By way of example, during this step, an electrode 119 is formed opposite each electrode 113 and thus opposite each cavity 105. By way of example, an electrode 119 is formed at least partially directly above a cavity 105. As in the example illustrated in [Fig. 7], the electrode 119 is, for example, entirely located directly above the cavity 105. By way of example, each electrode 119 may extend beyond the vertical dimension of the electrode 113 that it covers. This offset facilitates the re-establishment of contact between the two electrodes 113 and 119.

[0063] Electrodes 119 and 113 are, for example, the upper and lower electrodes of an FBAR acoustic filter, respectively. For example, electrodes 119 are made of a conductive material, such as a metal or a metal alloy. For example, electrodes 119 are made of molybdenum, tungsten, aluminum, copper, or a mixture of two or more of these materials. Electrodes 119 are, for example, made of the same material as electrodes 113.

[0064] By way of example, the electrodes 119 and the vias 121 are formed in a single step. The electrodes 119 and the vias 121 are, for example, formed by the deposition of a single layer in which patterns are defined. When the electrodes 119 and the vias 121 are produced simultaneously, the electrodes 119 and the vias 121 are made of the same material.

[0065] At the end of this step, a portion of the piezoelectric layer 109 is located between electrode 113 and electrode 119. At the end of this step, each portion of layer 109, located between two electrodes 119 and 113, forms, with these electrodes 119 and 113, a resonator R of an acoustic filter.

[0066] Fig. 8 illustrates, by a cross-sectional view, a structure obtained after a step of forming an insulating layer 123 on the upper face of the structure illustrated in Fig. 7.

[0067] More specifically, during this step, layer 123 is formed on the upper face of the structure illustrated in [Fig.7].

[0068] The insulating layer 123 is thus formed on, and for example in contact with, the upper face and the lateral sides of the electrodes 119. In addition, the insulating layer 123 is formed on, and for example in contact with, the upper face and sides of the vias 121. Furthermore, the insulating layer 123 is formed on, and for example in contact with, the upper face of the part not covered by the layer 109.

[0069] By way of example, the insulating layer 123 is made of an oxide, for example silicon oxide. The insulating layer 123 is, for example, made of the same material as the insulating layer 115. The insulating layer 123 acts, for example, as a passivation layer for the upper surface of the structure, in particular for the electrodes 119.

[0070] Figures 9A and 9B illustrate a structure obtained after a step of forming openings 125 in layers 123, 109, and 115 of the structure illustrated in Figure 8. Figure 9A is a cross-sectional view of the structure of Figure 9B along section plane AA, and Figure 9B is a horizontal cross-sectional view of the structure of Figure 9A along horizontal section plane BB of Figure 9A. More specifically, Figure 9B is a view along section plane BB of Figure 9A looking towards the top face of the structure.

[0071] More particularly, during this step, an opening 125 is associated with each cavity 105. The openings 125 extend, for example, from the upper face of layer 123, through layer 123, layer 109, layer 115, to the lower face of layer 115.

[0072] By way of example, as shown in [Fig. 9B], the openings 125 can be offset. The cavities 105 then have an arm extending horizontally into the layer 103, thus allowing each opening 125 to lead into a cavity 105.

[0073] Alternatively, the openings are formed opposite the cavities 105, that is to say that each opening 125 is aligned vertically with a cavity 105. In this example, each opening 125 opens, into the associated cavity 105, through the upper face of the cavity 105.

[0074] The openings 125 allow, for example, the balancing of pressures on either side of the resonator R, formed by the electrodes 113 and 119 and the layer 109.

[0075] The 125 openings are, for example, optional.

[0076] Fig. 10 illustrates, by way of a cross-sectional view, a volume 126 acoustic wave filter obtained at the end of a step of forming a membrane 127 on the upper face of the structure illustrated in figures 9A and 9B.

[0077] More specifically, during this step, a membrane 127 is formed above the resonators R.

[0078] During this step, a sacrificial layer, for example a resin, is first formed on the surface of the structure illustrated in Figures 9A and 9B. The resin layer is, for example, etched and then annealed so that its upper face corresponds to the desired geometry for the membrane 127. At the end of these steps, the resin sacrificial layer corresponds to a pad formed above the resonators R, the upper face of which is rounded.

[0079] During this step, for example, the membrane 127 is formed in a second stage on the upper face of the sacrificial resin layer. The membrane is, for example, made of an insulating material, for example an oxide.

[0080] During this step, for example, in a third step, openings are formed in the membrane 127.

[0081] Finally, the sacrificial resin layer is removed through the openings formed in the membrane 127.

[0082] The membrane 127 allows, for example, a cavity to be defined above the upper face of the resonator R. The membrane 127 allows free oscillation of the resonator R without risk of being constrained or of coming into contact with a layer of the structure at the level of its upper or lower face.

[0083] Fig. 11 is a cross-sectional view of an electronic device comprising the volume 126 acoustic wave filter of Fig. 10.

[0084] By way of example, the volume acoustic wave filter 126 is, within an electronic device, connected to one or more passive elementary electronic components. In the example of [Fig. 1 1], the filter 126 is connected to a capacitor C.

[0085] The capacitor C is for example formed in the insulating layer 103 and comprises two conductive layers, an upper one 131 and a lower one 133 separated by an insulating layer 135. By way of example, the stacking of the piezoelectric layer 109 and the insulating layer 115 extends opposite the capacitor C and is open at the level of a part of the capacitor so as to reveal the upper face of the upper conductive layer 131.

[0086] By way of example, the electrodes of the resonator R are connected to one or the other of the conductive layers of the capacitor C. By way of example, the connection between the resonator and the capacitor is made via conductive tracks, for example formed on the surface of the piezoelectric layer 109, connecting the electrodes 113 and 119 to the capacitor.

[0087] By way of example, the device further comprises, on the surface of the resonator R and the capacitor C, one or more coils B1 and B2. The coils B1 and B2 are, for example, formed in two different metallic layers, one above the other. The coils B1 and B2 are, for example, connected to each other and to the capacitor C via vias. By way of example, coil B1 is connected to the capacitor C via a via 136 and coil B2 is connected to coil B1 via a via 137.

[0088] By way of example, the coils are formed on an insulating layer 139 covering the resonator R and the capacitor C. By way of example, the coils are formed in insulating layers, coil B1 being formed, for example, in an insulating layer 141 and coil B2 being formed, for example, in an insulating layer 143. By way of example, the insulating layer 139 is formed on and in contact with the upper face of the membrane 127 and the upper face of layer 123 and layer 109. By way of example, the insulating layer 141 is formed on and in contact with the insulating layer 139. By way of example, layer 143 is formed on and in contact with the insulating layer 141.

[0089] By way of example, coils B1 and B2 are made of a conductive material, for example a metal, for example copper. By way of example, vias 136 and 137 are made of a conductive material, for example a metal, for example copper.

[0090] By way of example, the device includes a contact re-establishment, for example, opposite the coil B2. The insulating layer 143 is locally open so as to expose a portion of the upper face of the coil B2. By way of example, the aforementioned contact re-establishment is made via a boss 145 formed in contact with the coil B2.

[0091] Although not illustrated in [Fig. 1 1], in order to avoid cluttering the drawing, the boss 145 is, for example, intended to be connected to one or more components or circuits external to the device. For example, the boss 145 is intended to be connected to a radio frequency communication circuit of an electronic device.

[0092] During operation, a radio frequency signal is applied, for example, via the boss 145, between the electrodes 113 and 119 of the filter 126. The radio frequency signal is, for example, an alternating voltage. The application of the radio frequency signal to the electrodes 113 and 119 causes, for example, an alternation of expansion and contraction phases of the insulating layer 109. This tends to make the resonator R of the filter 126 resonate. In a case where the radio frequency signal has a frequency substantially equal to a resonant frequency of the resonator R, the radio frequency signal is not, or is only slightly, attenuated by the filter. On the other hand, in a case where the radio frequency signal has a frequency different from the frequency of Due to the resonance of the filter's resonator R, the radio frequency signal is strongly attenuated by the filter. This makes it possible, for example, to prevent the operation of a radio frequency communication receiving channel of an electronic device from being disrupted by interference caused by radio frequency signals emitted by other electronic devices, or by noise from external radio frequency sources.

[0093] An advantage of the present embodiment is that it allows the formation of the cavity 105 without a sacrificial layer.

[0094] Another advantage of the present embodiment is that it avoids a step of removing the sacrificial layer by etching, which is a particularly delicate step to implement, especially with the use of dangerous gases.

[0095] Many applications are likely to benefit from the advantages provided by the filter, this filter can thus be integrated into various types of components.

[0096] By way of example, the filter 126 can be integrated into a component intended for industrial use. The component can also be used in the Internet of Things or smart home applications. The component can also be used for implementing cloud computing systems, 5G radio frequency communication networks, data centers, and servers. The component may, for example, incorporate wide bandgap materials.

[0097] By way of example, the filter 126 can be integrated into a component intended for use in personal electronics, for example, to increase the volume of information exchanged via radio frequency communication, in 5G communication systems, or more generally in any connected component. The component is, for example, a mobile phone, or smartphone, or part of an Internet of Things network. The component is, for example, connected via 5G, Wi-Fi, or broadband communication. The component includes, for example, high-speed interfaces, for example, with advanced filtering and protection against electrostatic discharge.

[0098] By way of example, the filter 126 can be integrated into a component intended for use in communication equipment, or in computers and peripherals. The component is used, for example, in 5G infrastructures and dedicated data centers. The component includes, for example, silicon carbide diodes, Schottky power transistors, electrostatic discharge protection, and transient voltage suppression diodes. The component can also be used in satellites, including, for example, integrated passive components for radio frequency applications.

[0099] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will appear to the person of the trade.

[0100] In particular, although Figures 4 to 10 take as an example a case in which the filter being formed comprises two resonators, each located above a cavity 105, a person skilled in the art is of course able, from the indications in this description, to transpose this embodiment to any number of resonators located above the same cavity 105 made in a semiconductor substrate.

[0101] Based on the indications in this description, a person skilled in the art is also able to make several filters in the same semiconductor substrate, for example by planning to form several cavities in the same semiconductor substrate and at least one resonator located directly above each cavity.

[0102] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A method for manufacturing a volume acoustic wave filter (126), comprising a step of transferring a first structure onto a second structure, the first structure comprising, on an upper face of a first substrate (107), a layer of a piezoelectric material (109) surmounted by a first electrode (113), the second structure comprising, on an upper face of a second substrate (101), an insulating layer (103), the insulating layer (103) comprising a cavity (105), formed from the upper face of the insulating layer (103), the step of transferring consisting of transferring the first structure, by its upper face, onto the upper face of the second structure, the first electrode (113) being aligned with the cavity (105) in the insulating layer (103).

2. A method according to claim 1, wherein, during the transfer step, the first structure comprises, on the upper face of the first electrode (113), another insulating layer (115), the insulating layer (103) of the second structure being brought into contact with the other insulating layer (115) of the first structure.

3. A method according to claim 1 or 2, wherein, at the end of the transfer step, the first electrode (113) of the first structure does not come into contact with the bottom and the lateral sides of the cavity (105).

4. A method according to any one of claims 1 to 3, comprising, after the transfer step, a step of forming a second electrode (119) on the face of the piezoelectric layer (109), opposite the cavity (105), the second electrode (119) being formed at least partly in line with the first electrode (113).

5. A method according to any one of claims 1 to 4, comprising, after the transfer step, a step of forming an opening (117), in the piezoelectric layer (109), directly above the first electrode (113).

6. A method according to claim 5, comprising, after the step of forming the opening (117) in the piezoelectric layer (109), a step of forming a conductive via (121), in the opening (117), the conductive via (121) being formed in contact with the first electrode (113).

7. A volume acoustic wave filter (126) comprising: - a substrate (101); - an insulating layer (103), formed on an upper face of the substrate (101), and comprising a cavity (105), the upper face of which is entirely flush with the upper face of the insulating layer (103); - a piezoelectric layer (109) on the insulating layer (103); - a first electrode (113) formed on an lower face of the piezoelectric layer (109), in the cavity (105), the piezoelectric layer (109) not being open above the cavity (105).

8. Filter according to claim 7, wherein the cavity (105) is an air or vacuum cavity.

9. Filter according to claim 7 or 8, wherein the thickness of the first electrode (113) is less than the depth of the cavity (105).

10. Filter according to any one of claims 7 to 9, wherein the piezoelectric layer (109) is made of lithium niobate.

11. Filter according to any one of claims 7 to 10, comprising a second electrode (119) formed on the upper face of the piezoelectric layer (109), at least partly in line with the first electrode (113).

12. Filter according to any one of claims 7 to 11, wherein the piezoelectric layer (109) and the insulating layer (103) are separated by another insulating layer (115).

13. A method of using the filter according to claim 12, comprising applying a radio frequency signal between the first (113) and second (119) electrodes which tends to make the resonator (R) resonate, the signal being attenuated if the frequency of the signal is different from the resonance frequency of the resonator (R).

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