Volume acoustic wave filter

Abstract

Body wave acoustic filter. This description relates to a body wave acoustic filter (200) formed in and on a semiconductor substrate (101), the filter (200) comprising: – an air cavity (201) embedded in the semiconductor substrate (101); and – at least one resonator (121) formed above the air cavity (201), the resonator (121) comprising an active layer (109) interposed between lower (107) and upper (111) electrodes. Figure for the abbreviation: Fig. 2

Description

Title of the invention: Volume acoustic wave filter technical field

[0001] This description relates generally to electronic devices, more particularly to bulk acoustic wave (BAW) 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 volume acoustic wave filters have already been proposed: so-called "SMR" (Solidly Mounted Resonator) filters, on the one hand, and so-called "FBAR" (Thin-Film Bulk Acoustic Resonator) filters, also called "membrane" volume acoustic wave filters, on the other. 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. Summary of the invention

[0005] There is a need to overcome all or part of the drawbacks of existing volume acoustic wave filters, particularly FBAR filters, and their manufacturing processes. It would be especially desirable to simplify the manufacturing processes for 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.

[0006] To this end, one embodiment provides a volume acoustic wave filter formed in and on a semiconductor substrate, the filter comprising: - an air cavity embedded in the semiconductor substrate; and - at least one resonator formed directly above the air cavity, each resonator comprising an active layer interposed between lower and upper electrodes.

[0007] According to one embodiment, the filter comprises a single resonator formed directly above the air cavity.

[0008] According to one embodiment, the filter comprises exactly first and second resonators formed directly above the air cavity.

[0009] According to one embodiment, the upper electrodes of the first and second resonators have different thicknesses.

[0010] According to one embodiment, the lower electrodes of the first and second resonators form a common electrode.

[0011] According to one embodiment, each upper electrode has, in top view, an asymmetrical shape.

[0012] According to one embodiment, the semiconductor substrate is made of silicon.

[0013] According to one embodiment, each resonator is separated from the air cavity by a part of the semiconductor substrate having a thickness between 300 nm and 1.5 pm.

[0014] One embodiment provides for an electronic device, preferably a mobile phone or smartphone, comprising a radio frequency integrated circuit having at least one filter as described.

[0015] One embodiment provides a method for manufacturing a volume acoustic wave filter, the method comprising the following successive steps: a) providing a semiconductor substrate; b) form an air cavity embedded in the semiconductor substrate; and c) form at least one resonator directly above the air cavity, each resonator comprising an active layer interposed between lower and upper electrodes.

[0016] According to one embodiment, the process further comprises, between steps a) and b), a step of forming a plurality of hollow vias in the semiconductor substrate.

[0017] According to one embodiment, in step b), the air cavity is formed, from the plurality of hollow vias, by annealing the semiconductor substrate under a hydrogen atmosphere. Brief description of the drawings

[0018] 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:

[0019] [Fig.1] is a schematic and partial side and cross-sectional view of an example of a volume acoustic wave filter;

[0020] [Fig.2] is a schematic and partial side and cross-sectional view of an example of a volume acoustic wave filter according to one embodiment;

[0021] [Fig.3A], [Fig.3B], [Fig.3C], [Fig.3D] and [Fig.3E] illustrate, by schematic and partial side and cross-sectional views, structures obtained at the end of successive stages of a manufacturing process of the volume acoustic wave filter of [Fig.2] according to an embodiment;

[0022] [Fig. 4] is a schematic and partial side and cross-sectional view of an example of a volume acoustic wave filter according to one embodiment; and

[0023] [Fig.5] is a schematic and partial top view of an example of a device integrating a volume acoustic wave filter. Description of the implementation methods

[0024] 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.

[0025] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the integration of the volume acoustic wave filters into the various electronic devices capable of implementing such filters has not been detailed, as the described embodiments are compatible with all or most electronic devices incorporating at least one filter, possibly with adaptations within the grasp of a person skilled in the art upon reading this description.

[0026] Unless otherwise specified, when referring to two interconnected elements, this means directly connected without any intermediate elements other than conductors, and when referring to two coupled elements " between them, this means that these two elements can be connected or linked via one or more other elements.

[0027] 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.

[0028] Unless otherwise specified, the expressions "approximately", "about", "substantially", and "in the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0029] In the following description, the terms "insulating" and "conducting" mean, unless otherwise specified, electrically insulating and electrically conductive respectively.

[0030] Unless otherwise specified, the expression "in contact with" means "in mechanical contact with".

[0031] Fig. 1 is a schematic and partial side and cross-sectional view of an example of a volume acoustic wave filter 100. The filter 100 is, for example, more precisely of the "FBAR" type (from the English "thin-film bulk acoustic resonator"), or "membrane" volume acoustic wave filter.

[0032] In the example shown, the filter 100 comprises 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.

[0033] In the example shown, the filter 100 further comprises 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 of between 1.3 and 4 µm. By way of example, the insulating layer 103 is made of an oxide, for example, silicon dioxide. The insulating layer 103 acts, for example, as a passivation layer for the upper face 101T of the semiconductor substrate 101.

[0034] In the illustrated example, the filter 100 further comprises a cavity 105 formed in the insulating layer 103. The cavity 105 has, for example, a height strictly less than the thickness of the insulating layer 103 and lateral dimensions strictly less than those of the insulating layer 103. In this example, the walls of the cavity 105 are formed by the material of the insulating layer 103. The cavity 105 has, for example, a height between 0.3 and 2 µm. By way of example, the cavity 105 is filled with air. In the example shown, the cavity 105 has lateral walls substantially straight and substantially vertical. In this example, cavity 105 has, in cross-sectional view, a substantially rectangular shape.

[0035] In the example shown, the filter 100 further comprises an electrode 107 covering a portion of the upper face of the insulating layer 103. In the illustrated example, the electrode 107 is located on and in contact with a portion of the upper face of the insulating layer 103. The electrode 107 is at least partially located directly above the cavity 105. As in the example illustrated in [Fig. 1], the electrode 107 is, for example, predominantly located directly above the cavity 105. In this example, the electrode 107 further comprises a smaller portion extending laterally out of the direct line with the cavity 105. By way of example, the electrode 107 is made of a conductive material, for example, a metal such as aluminum or a metal alloy.

[0036] In the illustrated example, the filter 100 further comprises another insulating layer 109 covering the lateral and upper faces of the electrode 107. In this example, the insulating layer 109 also covers uncoated portions of the upper face of the insulating layer 103 of the electrode 107. In other words, the insulating layer 109 extends laterally out of the vertical axis of the electrode 107. The insulating layer 109 is, for example, more precisely situated on and in contact with the lateral and upper faces of the electrode 107 and with the uncoated portions of the upper face of the insulating layer 103 of the electrode 107. By way of example, the insulating layer 109 is a piezoelectric layer, that is, a layer made of a piezoelectric material, for example, lithium niobate (Lithium Niobate Oxide - LNO). English), aluminum nitride, etc.

[0037] In the example shown, the filter 100 further comprises another electrode 111 covering a portion of the upper face of the insulating layer 109. In the illustrated example, the electrode 111 is located on and in contact with a portion of the upper face of the insulating layer 109. The electrode 111 is, for example, at least partially located directly above the cavity 105. As in the example illustrated in [Fig. 1], the electrode 111 is, for example, entirely located directly above the cavity 105. In this example, the electrode 111 has lateral dimensions strictly smaller than those of the electrode 107. The electrodes 111 and 107 are, for example, the upper and lower electrodes of the filter 100, respectively. By way of example, the electrode 111 is made of a conductive material, for example, a metal such as aluminum or a metal alloy. Electrode 111, for example, is made of the same material as electrode 107.

[0038] The electrode 111, for example, has an asymmetrical shape when viewed from above.

[0039] In the illustrated example, the filter 100 further comprises another insulating layer 113 covering the lateral and upper faces of the electrode 111. In this example, the insulating layer 113 also covers uncoated portions of the upper face of the insulating layer 109 of the electrode 111. The insulating layer 113 is by For example, a layer located on and in contact with the lateral and upper faces of electrode 111 and with the uncoated portions of the upper face of insulating layer 109 of electrode 111. For example, insulating layer 113 is made of an oxide, for example, silicon dioxide. Insulating layer 113 is, for example, made of the same material as insulating layer 103. Insulating layer 113 acts, for example, as a passivation layer for the upper face of the structure, particularly for electrode 111.

[0040] In the example shown, the filter 100 further comprises contact elements 115 and 117 for the electrodes 107 and 111, respectively. In the example illustrated in [Fig. 1], the contact element 115 is located on and in contact with a portion of the upper face of the electrode 107 situated outside the vertical plane of the cavity 105. The contact element 115 has, for example, in cross-sectional view, a T-shape comprising a vertical portion extending from the upper face of the insulating layer 113, through the insulating layers 113 and 109 to the upper face of the electrode 107, and a horizontal portion extending laterally on and in contact with the upper face of the insulating layer 113 in the vicinity of the vertical portion of the contact element 115.

[0041] Furthermore, in this example, the contact element 117 is located on and in contact with a portion of the upper face of the electrode 111 situated directly above the cavity 105. The contact element 117 has, for example, in cross-sectional view, a T-shape comprising a vertical portion extending from the upper face of the insulating layer 113, through the insulating layer 113 to the upper face of the electrode 111, and a horizontal portion extending laterally on and in contact with the upper face of the insulating layer 113 in the vicinity of the vertical portion of the contact element 117. Each contact element 115, 117 is made of a conductive material, for example, a metal or a metal alloy. By way of example, the contact elements 115 and 117 are made of the same material.

[0042] Although this has not been illustrated in [Fig.1] in order not to overload the drawing, the contact resumption elements 115 and 117 are for example intended to be linked or connected to one or more components or circuits external to the filter 100. As an example, the contact resumption elements 115 and 117 are intended to be connected to a radio frequency communication circuit of an electronic device.

[0043] In the example shown, the filter 100 further includes an opening 119 located directly above the cavity 105. In this example, the opening 119 extends from the upper surface of the insulating layer 113, through the insulating layers 113 and 109 and through a portion of the insulating layer 103 not coated with the electrode 107, and extends vertically between the upper surface of the insulating layer 103 and the upper surface of the cavity 105. In the illustrated example, the cavity 119 forms an orifice opening into cavity 105. The opening 119 is for example a via formed to allow the removal of a sacrificial layer previously formed in the insulating layer 103 in order to create cavity 105. The sacrificial layer is for example made of silicon.

[0044] In the example shown, the filter 100 includes a membrane suspended above the cavity 105 and made up of a part of the insulating layer 103 located above the electrode 111 and interposed between the upper face of the cavity 105 and the upper face of the insulating layer 103. The filter 100 includes, for example, an active zone made up of parts of the electrode 111, the insulating layer 109, the electrode 107 and the insulating layer 103 located above the cavity 105 and above the electrode 111.

[0045] The electrodes 107 and 111 and the part of the insulating layer 109 interposed between the electrodes 107 and 111 are for example part of a resonator 121 of the filter 100. The insulating layer 109 is for example called the active layer of the resonator 121 of the filter 100, because the insulating layer 109 is intended to be excited by a signal applied to the electrodes 107 and 111 arranged on either side of this layer.

[0046] In operation, a radio frequency signal is for example applied, by the contact resumption elements 115 and 117, between the electrodes 107 and 111 of the filter 100. The radio frequency signal is for example an alternating voltage. Applying the radiofrequency signal to electrodes 107 and 111, for example, causes alternating phases of expansion and contraction of the insulating layer 109. This tends to cause the resonator 121 of the filter 100 to resonate and the membrane of the filter 100 to vibrate. When the radiofrequency signal has a frequency approximately equal to a resonant frequency of the membrane of the filter 100, the radiofrequency signal is not, or only slightly, attenuated by the filter 100. Conversely, when the radiofrequency signal has a frequency different from the resonant frequency of the membrane of the filter 100, the radiofrequency signal is strongly attenuated by the filter 100.This makes it possible, for example, to prevent the operation of a radio frequency communication reception 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.

[0047] A drawback of the body-wave acoustic filter 100 is that its active area is separated from the semiconductor substrate 101 by a portion of the insulating layer 103 extending vertically from the lower face of the electrode 107 to the upper face 101T of the semiconductor substrate 101 (the portion of the insulating layer 103 located to the left of the cavity 105, in the orientation of [Fig. 1]). Since the insulating layer 103 is made of a material with low thermal conductivity, typically This lower temperature than that of substrate 101 consequently hinders the dissipation of heat generated by the active zone of filter 100 when the membrane vibrates. This results in undesirable heating of the active zone of filter 100, which tends to degrade its performance.

[0048] Another drawback of the filter 100 lies in the presence of the cavity 105 and the through-hole 119. As a result, the filter 100 exhibits relatively low mechanical robustness. Furthermore, the materials of the semiconductor substrate 101 and the insulating layer 103 have different coefficients of thermal expansion, which also tends to weaken the structure due to temperature variations related to the operation of the filter 100.

[0049] Furthermore, a drawback of the filter 100 lies in the fact that the formation of the cavity 105 by removing a sacrificial layer is a particularly delicate step to implement. Moreover, flatness requirements for the insulating layers 103, 109, and 113 and for the electrodes 107 and 111 complicate the fabrication of the filter 100.

[0050] The aforementioned disadvantages limit the use of volume acoustic wave filters such as the filter 100 previously described in relation to [Fig.1] and hinder the miniaturization of these filters.

[0051] An embodiment allowing at least part of these drawbacks to be overcome is detailed below in relation to [Fig.2].

[0052] Figure 2 is a schematic and partial side and cross-sectional view of an example of a 200 volume acoustic wave filter according to one embodiment. The 200 filter is, for example, more precisely an FBAR filter.

[0053] Filter 200 of [Fig.2] includes elements in common with filter 100 of [Fig.1]. These common elements will not be detailed again below.

[0054] The filter 200 of [Fig.2] differs from the filter 100 of [Fig.1] in that it lacks the cavity 105 formed in the insulating layer 103 and the opening 119. According to one embodiment, the filter 200 comprises an air cavity 201 buried, or embedded, in the semiconductor substrate 101. According to this embodiment, the cavity 201 is entirely contained within the semiconductor substrate 101. The cavity 201 is thus completely closed.

[0055] In the illustrated example, the cavity 201 is entirely bordered by the material of the semiconductor substrate 101. In this example, the cavity 201 is separated from the substantially flat upper face 101T of the semiconductor substrate 101 by a portion of the semiconductor substrate 101. The cavity 201 is, for example, located at a depth of between a few hundred nanometers and a few micrometers below the upper face 101T of the semiconductor substrate 101. In other words, the upper face of the cavity 201 is separated from the upper face of the semiconductor substrate 101 by a portion of the substrate 101 having, for example, a thickness between a few hundred nanometers and a few micrometers. The thickness of the part of the substrate 101 interposed between the upper face of the cavity 201 and the upper face 101T of the substrate 101 is, for example, more precisely between 300 nm and 1.5 pm.

[0056] In the example shown, the cavity 201 includes rounded or curved sides, for example sides having a concave shape. By way of example, each side of the cavity 201 has, in cross-sectional view, the shape of an arc of a circle, for example a semicircle.

[0057] Cavity 201, for example, has a rectangular shape when viewed from above. This example is not limiting, however; cavity 201 may more generally have any shape when viewed from above, for example a polygonal shape other than rectangular — for example square, triangular, hexagonal, etc. — or a rounded shape — for example oval, circular, etc.

[0058] The electrode 107 is at least partially located directly above the cavity 201. As in the example illustrated in [Fig.2], electrode 107 is, for example, predominantly located directly above cavity 201. In this example, electrode 107 also includes a minor part extending laterally out of the direct line of cavity 201.

[0059] Furthermore, the electrode 111 is, for example, at least partially located directly above the cavity 201. As in the example illustrated in [Fig.2], the electrode 111 is, for example, totally located directly above the cavity 201. In this example, the electrode 111 has lateral dimensions strictly smaller than those of the electrode 107.

[0060] In the example illustrated in [Fig.2], the contact resumption element 115 is located on and in contact with a part of the upper face of the electrode 107 located outside the vertical axis of the cavity 201. This makes it possible to avoid, or limit, disturbances of the resonator 121 of the filter 200 compared to a case where the contact resumption element 115 would be in contact with a part of the upper face of the electrode 107 located vertically above the cavity 201.

[0061] In the case of the filter 200, the membrane of the resonator 121 is constituted by a part of the semiconductor substrate 101 interposed between the cavity 201 and the upper face 101T of the substrate 101 and located directly above the electrode 111.

[0062] Although not illustrated in [Fig.2], the filter 200 may further comprise a protective cover for the resonator 121 of the filter 200, for example a cover bearing on the upper face 101T of the semiconductor substrate 101 and inside which are located the electrodes 107 and 111 and the insulating layers 109 and 113 of the filter 200. The fabrication of such a protective cover is within the capabilities of a person skilled in the art, based on the indications in this description.

[0063] Because filter 200, unlike filter 100, lacks the cavity 105 located in the insulating layer 103, the insulating layer 103 of filter 200 has, for example, a thickness much less than that of the insulating layer 103 of filter 100. For example, the insulating layer 103 of filter 200 has a thickness between 0.5 and 1.5 µm, for example, 0.8 µm. This advantageously improves the heat dissipation of the resonator 121 of filter 200 compared to filter 100. Heat dissipation is further facilitated by the rounded shape of the sides of cavity 201.

[0064] Another advantage of filter 200 is that the cavity 201 is located in the semiconductor substrate 101. This gives filter 200 greater mechanical strength than filter 100. The fact that filter 200 lacks the opening 119 further contributes to the improved mechanical strength compared to filter 100.

[0065] Fig. 3A, Fig. 3B, Fig. 3C, Fig. 3D and Fig. 3E illustrate, by schematic and partial side and section views, structures obtained at the end of successive stages of a manufacturing process of the 200 volume acoustic wave filter of Fig. 2 according to an embodiment.

[0066] Fig. 3A illustrates a structure obtained at the end of a step of forming a plurality of hollow vias 301 in the semiconductor substrate 101.

[0067] In the illustrated example, the hollow vias 301 extend from the upper face 101T of the semiconductor substrate 101 to a depth less than the thickness of the substrate 101. In other words, the hollow vias 301 are blind and do not open out on the lower face side of the substrate 101.

[0068] Each hollow via 301, for example, has a substantially square cross-section when viewed from above. This example is not limiting, however, as each via 301 may more generally have any shape when viewed from above, for example, a polygonal shape other than square—for example, rectangular, triangular, hexagonal, etc.—or a rounded shape—for example, oval, circular, etc. By way of example, the hollow vias 301 have substantially identical shapes and dimensions, subject to manufacturing variations. For example, the hollow vias 301 have, in particular, the same depth, subject to manufacturing variations.

[0069] The hollow vias 301 are, for example, arranged in a network according to rows and columns. The rows are, for example, substantially perpendicular to the columns. The network formed by the hollow vias 301 has, for example, within manufacturing variations, a substantially constant pitch, that is to say, a substantially constant center-to-center distance between two neighboring vias 301.

[0070] The hollow vias 301 are, for example, produced by photolithography followed by engraving. For this purpose, a layer of photosensitive resin 303 is, for example, deposited on the side of the upper face 101T of the semiconductor substrate 101. The photosensitive resin layer 303 covers, for example, the entire upper face 101T of the semiconductor substrate 101. In the example shown, the photosensitive resin layer 303 is more precisely located on and in contact with the upper face 101T of the semiconductor substrate 101.

[0071] Through openings are then formed for example in the photosensitive resin layer 303 at the desired locations of the future hollow vias 301, for example by exposing the photosensitive resin layer 303 through a mask and removing exposed parts of the layer 303, in the case of a positive resin, or unexposed parts of the layer 303, in the case of a negative resin.

[0072] Once the openings have been formed in the photosensitive resin layer at the desired locations of the future vias 301, the openings are then extended into the semiconductor substrate 101 by etching, for example by reactive ion etching (“Reactive Ion Etching” - RIE), for example by deep reactive ion etching (“Deep Reactive Ion Etching” - DRIE).

[0073] Fig. 3B illustrates a structure obtained after a subsequent step of removing the photosensitive resin layer 303.

[0074] In the example shown in [Fig.3B], the photosensitive resin layer 303 is completely removed.

[0075] Fig. 3C illustrates a structure obtained after a subsequent annealing step of the semiconductor substrate 101 in which the hollow vias 301 have previously been formed.

[0076] In the illustrated example, annealing leads to the formation of the cavity 201 from the hollow vias 301. Annealing is carried out, for example, at a temperature of approximately 1000 °C, for example, between 1000 °C and 1150 °C. Annealing is also carried out, for example, under a hydrogen atmosphere, in the case where the semiconductor substrate 101 is made of silicon. Annealing under hydrogen allows the silicon atoms of the semiconductor substrate 101 to exhibit greater surface mobility than in the absence of hydrogen.

[0077] Under the action of annealing, the silicon atoms of the semiconductor substrate 101 reorganize themselves so that the structure exhibits minimal surface roughness and surface energy without volume loss. In practice, the hollow vias 301 tend to flare out in their lower part, i.e., near their bottom, and to close in their upper part, i.e., near the upper face 101T of the semiconductor substrate 101. As a result of these phenomena, the hollow vias 301 gradually transform into the cavity 201, as illustrated in [Fig. 3C]. The bottom of the cavity 201 is located, in the semiconductor substrate 101, at a depth strictly less than that of the bottom of the hollow vias 301.

[0078] By way of example, a person skilled in the art may, for carrying out the steps set out above in relation to figures 3A to 3C, take inspiration from what is described in the publication by I. Mizushima et al. entitled "Empty-space-in-silicon technique for fabricating a silicon-on-nothing structure" published in November 2000 in the journal Applied Physics Letters.

[0079] Fig. 3D illustrates a structure obtained after a subsequent step of deposition of the insulating layer 103 on the side of the upper face 101T of the semiconductor substrate 101.

[0080] In the example shown, the insulating layer 103 covers the entire upper face 101T of the semiconductor substrate 101. The insulating layer 103 is, for example, more precisely located on and in contact with the entire upper face 101T of the semiconductor substrate 101.

[0081] Fig. 3E illustrates a structure obtained at the end of a later stage of realization of the resonator 121.

[0082] During this step, the electrode 107, the active layer 109 and the electrode 111 are successively formed, in that order, on the face 101T of the semiconductor substrate 101. The electrode 107 is for example formed by depositing a conductive layer on the upper face of the insulating layer 103 and by structuring, for example by photolithography and then etching, the conductive layer so as to retain only a part of the conductive layer corresponding to the electrode 107.

[0083] The insulating layer 109 is then deposited, for example, over the entire upper face of the structure.

[0084] The electrode 111 is for example then made in a manner similar or identical to the making of the electrode 107, for example by depositing a conductive layer on the upper face of the insulating layer 109 and by structuring, for example photolithography then etching, the conductive layer so as to retain only a part of the conductive layer corresponding to the electrode 111.

[0085] Although not illustrated, the insulating layer 113 is then deposited over the entire upper face of the structure.

[0086] The contact elements 115 and 117 are then formed, for example, by opening the insulating layers 113 and 109 directly above electrode 107, for contact element 115, and by opening the insulating layer 113 directly above electrode 111, for contact element 117. A conductive layer filling the openings is then deposited, for example, over the entire upper surface of the structure and textured, for example by photolithography followed by etching, so as to retain only portions of the conductive layer corresponding to the contact elements 115 and 117. Alternatively, a localized deposit of a conductive material may be provided. Filter 200 is thus obtained, for example.

[0087] Figure 4 is a schematic and partial side and cross-sectional view of an example of A 400-ohm volume acoustic wave filter according to one embodiment. The 400-ohm filter of [Fig. 4] includes elements in common with the 200-ohm filter of [Fig. 2]. These common elements will not be detailed again below.

[0088] The filter 400 of [Fig.4] differs from the filter 200 of [Fig.2] in that the filter 400 comprises two resonators 421A and 421B located above and directly above the cavity 201.

[0089] In the example shown, the filter 400 includes an electrode 407 covering a portion of the upper surface of the insulating layer 103. In the illustrated example, the electrode 407 is located on and in contact with a portion of the upper surface of the insulating layer 103. The electrode 407 is at least partially located directly above the cavity 201. As in the example illustrated in [Fig. 4], the electrode 407 is, for example, predominantly located directly above the cavity 201. In this example, the electrode 407 also includes a smaller portion extending laterally out of the vertical position of the cavity 201. The electrode 407 is, for example, similar or identical to the electrode 107 of the filter 200. By way of example, the electrode 407 is made of a conductive material, for example, a metal such as aluminum or a metal alloy.

[0090] Electrode 407, for example, constitutes a common lower electrode for the two resonators 421A and 421B of filter 400. This simplifies the construction of filter 400. However, this example is not limiting, and a person skilled in the art may, as an alternative, provide that each resonator 421A, 421B of filter 400 has a lower electrode isolated from that of the other resonator 421B, 421A.

[0091] The active layer 109 covers the electrode 407 of the filter 400. In the example shown, the active layer 109 is more precisely located on and in contact with the lateral and upper walls of the electrode 109. Furthermore, in this example, the electrode 407 is common to both resonators 421A and 421B of the filter 400. This simplifies the construction of the filter 400. However, this example is not limiting, and those skilled in the art may, as an alternative, provide that each resonator 421A, 421B of the filter 400 has an active layer distinct from that of the other resonator 421B, 421A.

[0092] In the example shown, each resonator 421A, 421B of the filter 400 further comprises another electrode 41IA, 41IB covering a portion of the upper face of the active layer 109. In the illustrated example, each electrode 41IA, 41IB is located on and in contact with a portion of the upper face of the insulating layer 109. The electrodes 41IA and 41IB are, for example, at least partially located directly above the cavity 201. As in the example illustrated in [Fig. 4], each electrode 41IA, 41IB is, for example, completely located directly above the cavity 201. In this example, each electrode 41IA, 41IB has lateral dimensions that are strictly smaller to those of electrode 407. Electrodes 41 IA and 41 IB, for example, constitute the upper electrodes of filter 400. As an example, each electrode 41 IA, 41 IB is made of a conductive material, for example, a metal such as aluminum or a metal alloy. Electrodes 41 IA and 41 IB are, for example, made of the same material as electrode 407.

[0093] Each electrode 41 IA, 41 IB presents, for example, in top view, an asymmetrical shape.

[0094] According to one embodiment, one of the electrodes 41 IA, 41 IB has a different thickness than the other electrode 41 IB, 41 IA. In the example shown, electrode 41 IA (located on the left, in the orientation of [Fig. 4]) has a thickness less than that of electrode 41 IB (located on the right, in the orientation of [Fig. 4]). However, this example is not limiting, and a person skilled in the art may, as an alternative, provide that electrode 41 IA has a thickness strictly greater than that of electrode 41 IB.

[0095] In the example shown, the filter 400 further includes contact resumption elements 415, 417A and 417B of the electrodes 407, 41 IA and 41 IB, respectively. In the example illustrated in [Fig.4], the contact element 415 is located on and in contact with a part of the upper face of the electrode 407 located outside the vertical plane of the cavity 201. The contact element 415 has, for example, in cross-sectional view, a T-shape comprising a vertical part extending from the upper face of the insulating layer 113, through the insulating layers 113 and 109 to the upper face of the electrode 407 and a horizontal part extending laterally on and in contact with the upper face of the insulating layer 113 in the vicinity of the vertical part of the contact element 415.

[0096] Furthermore, in this example, the contact element 417A, 417B is located on and in contact with a part of the upper face of the electrode 41 IA, 41 IB located above the cavity 201. The contact element 417A, 417B has, for example, in cross-sectional view, a T-shape comprising a vertical part extending from the upper face of the insulating layer 113, through the insulating layer 113 to the upper face of the electrode 41 IA, 41 IB and a horizontal part extending laterally on and in contact with the upper face of the insulating layer 113 in the vicinity of the vertical part of the contact element 417A, 417B. Each contact element 415, 417A, and 417B is made of a conductive material, for example, a metal or a metal alloy. For example, contact elements 417A and 417B are made of the same material as contact element 415.

[0097] Although this has not been illustrated in [Fig. 4] in order to avoid cluttering the drawing, the contact re-establishment elements 415, 417A and 417B are, for example, intended to be linked or connected to one or more components or circuits external to the filter 400. For example, the contact resumption elements 415, 417A and 417B are intended to be connected to a radio frequency communication circuit of an electronic device.

[0098] Providing electrodes 41 IA and 41 IB with different thicknesses allows resonators 421A and 421B to have different resonant frequencies. In this case, filter 400 is, for example, a bandpass filter, for example, a filter that allows signals with a frequency within a band of frequencies substantially delimited by the resonant frequencies of resonators 421A and 421B to pass through. By way of example, the bandwidth of filter 400 is on the order of gigahertz, for example, between 0.5 and 6 GHz.

[0099] The 400 filter has advantages similar to those previously described in relation to [Fig.2] in the case of the 200 filter, particularly in terms of thermal performance and mechanical robustness.

[0100] Fig. 5 is a schematic and partial top view of an example of a device 500 incorporating a volume acoustic wave filter, for example the filter 400 previously described in relation to Fig. 4. In the example shown, the device 500 is a mobile phone, or smartphone.

[0101] In this example, the device 500 includes a processing circuit 501 (PA), for example a microcontroller or a main microprocessor of the device 500. The processing circuit 501 is for example connected to a radio frequency integrated circuit 503 (RFIC) comprising at least one filter of the type of filter 200 or 400, for example a filter 400. The filter 400 is for example integrated into an electronic filtering circuit, not detailed in [Fig. 5]. In the illustrated example, the radio frequency integrated circuit 503 is connected to an antenna 505 (ANT), for example a radio frequency communication antenna of the device 500. Although not detailed in [Fig.5] so as not to clutter the drawing, the radio frequency integrated circuit 503 may further include components and circuits intended to implement impedance matching, amplification, modulation / demodulation, switching, etc. functions.

[0102] The device 500 may further include other elements, for example other electronic components or circuits not detailed in [Fig.5]. These elements have been symbolized, in [Fig.5], by a functional block 507 (FCT).

[0103] Although [Fig.5] illustrates a case in which the filter 400 is integrated into the device 500, this example is not limiting and a person skilled in the art is able to foresee, from the indications in this description, to substitute, in the device 500, the filter 400 with the filter 200 or with a filter having a structure similar to that of the filter 200 or 400.

[0104] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will become apparent to those skilled in the art. In particular, although [Fig. 4] takes as an example a case in which the filter 400 comprises two resonators 421A and 421B located above the cavity 201, those skilled in the art are of course able, from the indications in this description, to transpose the embodiment of [Fig. 4] to any number of resonators located above the same cavity made in a semiconductor substrate.

[0105] 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 buried in the same semiconductor substrate and at least one resonator located directly above each cavity.

[0106] Furthermore, although [Fig. 5] uses the example of integrating the 400 filter into a mobile phone or smartphone, the described embodiments are not limited to this example but apply more generally to any device or system with wireless communication functions, for example in the field of telematics. In particular, the 400 filter or the 200 filter can be integrated into motor vehicles, for example to implement wireless internet access functionalities, vehicle communication with external equipment or systems, autonomous driving, etc.for end-use applications such as fleet management (location, movement, status and behavior of each vehicle) or real-time navigation systems, or to enable objects to communicate with a vehicle (for example within the Internet of Things - IoT), all without interference from systems not accepted in an authorized communication "circle".

[0107] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional specifications given above. In particular, the production of filter 400 is within the reach of a person skilled in the art, based on this description, especially using the manufacturing process for filter 200 described in relation to Figures 3A to 3E.

[0108] Furthermore, the embodiments described are not limited to the particular examples of materials and dimensions mentioned in this description.

Claims

Demands

1. A volume acoustic wave filter (200; 400) formed in and on a semiconductor substrate (101), the filter (200; 400) comprising: - an air cavity (201) buried in the semiconductor substrate (101); and - at least one resonator (121; 421A, 421B) formed above the air cavity (201), each resonator (121; 421A, 421B) comprising an active layer (109) interposed between lower (107; 407) and upper (111; 41IA, 41IB) electrodes.

2. Filter (200) according to claim 1, comprising a single resonator (121) formed above the air cavity (201).

3. Filter (400) according to claim 1, comprising exactly first (421A) and second (421B) resonators formed above the air cavity (201).

4. Filter (400) according to claim 3, wherein the upper electrodes (41 IA, 41 IB) of the first (421A) and second (421B) resonators have different thicknesses.

5. Filter (400) according to claim 3 or 4, wherein the lower electrodes of the first (421A) and second (421B) resonators form a common electrode (407).

6. Filter (200; 400) according to any one of claims 1 to 5, wherein each upper electrode (111; 41 IA, 41 IB) has, in top view, an asymmetric shape.

7. Filter (200; 400) according to any one of claims 1 to 6, wherein the semiconductor substrate (101) is silicon.

8. Filter (200; 400) according to any one of claims 1 to 7, wherein each resonator (121; 421A, 421B) is separated from the air cavity (201) by a portion of the semiconductor substrate (101) having a thickness between 300 nm and 1.5 pm.

9. Electronic device (500), preferably a mobile phone or smartphone, comprising a radio frequency integrated circuit (503) having at least one filter (200; 400) according to any one of claims 1 to 8.

10. Method for manufacturing a (200; 400) volume acoustic wave filter, the method comprising the following successive steps: a) providing a semiconductor substrate (101); b) form an air cavity (201) embedded in the semiconductor substrate (101); and c) form at least one resonator (121; 421A, 421B) above the air cavity (201), each resonator (121; 421A, 421B) comprising an active layer (109) interposed between lower (107; 407) and upper (111; 41IA, 41IB) electrodes.

11. A method according to claim 10, further comprising, between steps a) and b), a step of forming a plurality of hollow vias (301) in the semiconductor substrate (101).

12. A method according to claim 11, wherein, in step b), the air cavity (201) is formed, from the plurality of hollow vias (301), by annealing the semiconductor substrate (101) under a hydrogen atmosphere.

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