Piezoelectric microelectromechanical resonator device and corresponding manufacturing process

Abstract

Various embodiments of the present disclosure relate to a piezoelectric microelectromechanical resonator device and a corresponding manufacturing process. The microelectromechanical resonator device comprises: a body having a first surface and a second surface opposite to each other along a vertical axis and made of a first layer and a second layer, the second layer being arranged on the first layer; a cover having a first surface and a corresponding second surface opposite to each other along a vertical axis and coupled to the body via a bonding element; and a piezoelectric resonator structure formed by a moving element, a piezoelectric material region, and a top electrode, the moving element being constituted by a resonator portion of the first layer, suspended in a cantilever manner relative to an internal cavity provided in the second layer, and suspended on opposite sides relative to a housing cavity provided in the cover; the piezoelectric material region being arranged on the moving element on the first surface of the body; and a top electrode being arranged on the piezoelectric material region, the moving element constituting a bottom electrode of the piezoelectric resonator structure.

Description

Technical Field

[0001] The present solution relates to a piezoelectric MEMS (Micro Electro Mechanical System) resonator device and a corresponding manufacturing process. Background Art

[0002] As is well known, resonator devices typically have a clock function within portable or fixed electronic devices (e.g., mobile phones, video cameras or cameras, automotive equipment, household appliances, data collection terminals, smart card readers, etc.) to count the passage of real time (in years, months, days, hours, minutes and seconds) even when the corresponding electronic device is turned off.

[0003] A resonator device for RTC applications typically includes an oscillator provided with a suitable resonant structure (also referred to simply as a "resonator"), the oscillator being configured to generate an operating frequency (or resonant frequency), the operating frequency being, for example, equal to 32.768 kHz or a multiple of 32.768 kHz; a processing circuit coupled to the oscillator for providing a suitable bias signal and counting the passage of time based on the above-mentioned operating frequency; and a suitable power supply for supplying power to the device.

[0004] While quartz technology has dominated the field of frequency generation for decades (also for the above-mentioned real-time clock applications), MEMS resonator devices based on semiconductor technology, in particular silicon semiconductor technology, have recently been proposed with increasing success.

[0005] The advantages associated with the use of MEMS resonator devices are first of all significant size control and cost reduction, due to the fact that the resonant mechanical structure and the corresponding electronic circuit (in the form of an ASIC application-specific integrated circuit) can be integrated in the same package using standard semiconductor manufacturing processes and at low cost.

[0006] Furthermore, MEMS resonator devices are generally more resistant to shock and mechanical stress than traditional quartz solutions and have lower electrical consumption levels (a particularly important characteristic, especially for portable type applications).

[0007] A MEMS resonator device comprises a structure obtained using micromachining techniques that is induced to vibrate at its natural resonant frequency due to an appropriate stimulus (via an electrical bias signal). These micromechanical structures typically include at least one moving element that is resonantly set by the applied bias signal.

[0008] In particular, capacitive MEMS resonator devices are known in which a moving element and a fixed electrode structure to which it is coupled form a capacitor, and in which resonant vibration of the moving element causes a capacitance change of the capacitor which is converted into an output signal at a desired operating frequency.

[0009] However, the known solutions envisage expensive and complex manufacturing processes, requiring, for example, the use of a SOI (Silicon On Insulator) substrate of the C-SOI (Cavity Bonded SOI) type as a starting structure, inside which a preformed buried cavity is provided.

[0010] Furthermore, the known solutions do not envisage the integration of a package for covering and protecting the resonant element at the level of the microelectromechanical structure, and therefore an external cover of, for example, metal or ceramic material is required; consequently, the overall dimensions of the resonator device are large and the performance, for example in terms of parasitic capacitances, is not optimal. Summary of the Invention

[0011] The present disclosure provides an improved solution for piezoelectric MEMS resonator devices that enables overcoming one or more disadvantages associated with known solutions.

[0012] Thus, according to the present solution, a piezoelectric MEMS resonator device and a corresponding manufacturing process are provided.The MEMS resonator device may for example be advantageously used in real time clock (RTC) applications, to which application the following discussion will make specific reference without loss of generality. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to better understand the present disclosure, preferred embodiments of the present disclosure will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0014] Figure 1 A schematic diagram showing a model of a capacitive MEMS resonator;

[0015] Figures 2A to 2I is a cross-sectional view of a piezoelectric MEMS resonator device at successive steps in a manufacturing process according to one embodiment of the present disclosure; and

[0016] Figure 3 is a general block diagram of an electronic device incorporating a microelectromechanical resonator device according to another aspect of the present disclosure. DETAILED DESCRIPTION

[0017] Figure 1 1 is a schematic diagram of a structural model of a capacitive MEMS resonator.

[0018] The MEMS resonator 1 comprises a mass 2 to which is coupled an arm (or beam) 3 having a main longitudinal extension, the arm 3 extending in a suspended manner from the same mass 2 in a cantilever manner.

[0019] The MEMS resonator 1 further comprises a first electrode 4 and a second electrode 5 facing and arranged parallel to the arm 3 on opposite sides of the arm.

[0020] During operation, application of a suitable bias voltage between the first electrode 4 (acting as a drive electrode) and the arm 3 causes the same arm 3 to move at resonance at the mechanical resonance frequency.

[0021] Subsequent movement towards or away from the second electrode 5 (acting as a sensing electrode) causes a change in the capacitive coupling, which enables an associated electrical signal to be generated at the resonance frequency by electronic circuitry (not shown herein) associated with the MEMS resonator 1 .

[0022] The applicant has found that the capacitive MEMS resonator 1 described previously suffers from a number of problems which prevent its full exploitation.

[0023] In some embodiments, the distance (or gap, in Figure 1 The gap (denoted by g in FIG) is shown to be critical for the electrical performance of the device; in practice, very small gaps, for example of the order of a few hundred nanometers, are desired to have low power consumption. Therefore, in some embodiments of the above-mentioned gap, the manufacturing process used should be able to precisely control the size.

[0024] Furthermore, the device 1 uses an actuation device of the non-linear type and, therefore, a dedicated electronic circuit, and therefore the device 1 cannot directly replace a conventional quartz resonator operating based on the piezoelectric effect.

[0025] Piezoelectric MEMS resonator devices (e.g., devices that operate based on the piezoelectric effect) can overcome some of the aforementioned problems. In such solutions, a moving element is driven to resonate by applying an appropriate electrical bias to an area of piezoelectric material coupled to the same moving element. Piezoelectric solutions can be advantageous over capacitive solutions because, similar to traditional quartz solutions, they can be integrated into existing electronic circuits based on the piezoelectric effect (and thus can directly replace traditional quartz resonators).

[0026] refer to Figure 2A , one embodiment of a process for fabricating a piezoelectric MEMS resonator device according to one aspect of the present disclosure is now described.

[0027] The manufacturing process envisions providing an SOI wafer 10 having a front surface 10a and a back surface 10b, the front surface 10a and the back surface 10b extending in a horizontal plane xy defined by a first horizontal axis x and a second horizontal axis y and facing each other along a vertical axis z, and including a structural substrate 11, which defines the front surface 10a and is made of single-crystal silicon doped to be conductive. As will be described in detail herein, the structural substrate 11 includes a bottom electrode for a piezoelectric resonator structure; a supporting substrate 12 defining the back surface 10b; and a dielectric layer 13 (e.g., silicon oxide) interposed between the structural substrate 11 and the supporting substrate 12.

[0028] like Figure 2A As shown, the structural substrate 11 is first chemically etched from the front surface 10a (using an appropriate photolithographic mask, not shown herein) to dig out grooves extending through the entire thickness of the same structural layer 11 until the dielectric layer 13 is reached, and in some embodiments: the defining groove 14 is configured to define the arrangement, geometry and dimensions of the resonator portion 11a of the above-mentioned structural substrate 11, as will be highlighted herein, the resonator portion 11a constituting the moving element of the piezoelectric resonator structure; and in addition, the insulating groove 15 is arranged, for example, along a first horizontal axis x, at a certain distance from the defining groove 14 in the transverse direction, and is configured to define a first bottom interconnection portion 11b and a second bottom interconnection portion 11c of the same structural layer 11 therebetween, which are insulated from each other, as will be highlighted below, which will help to define electrical interconnection elements towards the bottom electrode and the top electrode of the piezoelectric resonator structure.

[0029] like Figure 2B As shown, the SOI wafer 10 is then subjected to a thermal oxidation process from the front surface 10a, which results in the formation of a surface dielectric layer 16. In some embodiments of silicon oxide, the surface dielectric layer 16 extends above the same front surface 10a and fills the above-mentioned definition trenches 14 and insulation trenches 15 in the trenches previously defined with the help of the structural substrate 11 (and thus provides electrical insulation between the above-mentioned first bottom interconnection portion 11b and the second bottom interconnection portion 11c of the structural substrate 11).

[0030] The surface dielectric layer 16 is then chemically etched (using an appropriate photolithographic mask, not shown herein) to define a sacrificial portion 16 a and an insulating portion 16 b, the sacrificial portion 16 a being arranged in an area above the resonator portion 11 a of the structural substrate 11 (and having a lateral extension in the horizontal plane xy that is greater than the lateral extension of the resonator portion 11 a); and an insulating portion 16 b being arranged laterally (along the above-mentioned first horizontal axis x) relative to the sacrificial portion 16 a in a position vertically corresponding to the above-mentioned first bottom interconnect portion 11 b and second bottom interconnect portion 11 c of the structural substrate 11 and defining an opening 17 therebetween.

[0031] like Figure 2C As shown, an epitaxial growth process is then performed from the front surface 10 a, followed by planarization to form an epitaxial silicon layer 18, which is arranged on the front surface 10 a and provides a coating for the surface dielectric layer 16. In some embodiments, the epitaxial silicon layer 18 also fills the opening 17.

[0032] like Figure 2C As shown in FIG, first and second contact pads 19a and 19b are then formed on the epitaxial silicon layer 18 in positions vertically corresponding to the first and second bottom interconnect portions 11b and 11c of the structural substrate 11, respectively. As will be highlighted below, the first and second contact pads 19a and 19b are configured to enable electrical contact to be made toward the top and bottom electrodes of the piezoelectric resonator structure, respectively. The first and second contact pads 19a and 19b can be formed by depositing and etching a layer of conductive material (e.g., a metal material).

[0033] Epitaxial silicon layer 18 is then etched from its corresponding top surface 18a, which is not in contact with structural substrate 11, to form an insulating opening 20 laterally relative to the first and second contact pads 19a and 19b. Insulating opening 20 defines therebetween a first top interconnection portion 21a and a second top interconnection portion 21b of epitaxial silicon layer 18, thereby forming extensions along the vertical axis z of first and second bottom interconnections 11b and 11c of structural substrate 11, respectively. First and second top interconnections 21a and 21b, together with the extensions, form interconnection elements of the piezoelectric resonator structure. Thus, insulating opening 20 provides electrical insulation between first and second top interconnections 21a and 21b of epitaxial silicon layer 18.

[0034] like Figure 2DAs shown, SOI wafer 10 is then coupled to a so-called handle wafer 24, which is also made of a semiconductor material such as silicon, by temporary or permanent bonding. In some embodiments, an adhesive layer 25 of a suitable dielectric (e.g., a non-conductive bonding material, such as a glass bonding material such as glass solder) is interposed between the front surface of SOI wafer 10 (now defined by the top surface 18a of the aforementioned epitaxial silicon layer 18) and the facing bonding surface 24a of handle wafer 24. In the example, this adhesive layer 25 also fills the aforementioned insulating openings 20 and coats the aforementioned first and second contact pads 19a and 19b. It should be noted that, alternatively or additionally, adhesive layer 25 can be formed locally, for example, using a technique such as screen printing, only in certain areas of top surface 18a; in this case, insulating openings 20 may not be filled with the same adhesive layer 25.

[0035] Same as Figure 2D As shown, the stack formed by the SOI wafer 10 and the handle wafer 25 is then turned over, for example by a so-called flip-chip operation, so that the rear surface 10b of the SOI wafer 10 defined by the corresponding support substrate 12 faces upwards and is thus available for subsequent manufacturing steps.

[0036] like Figure 2E As shown, the supporting substrate 12 of the SOI wafer 10 is then completely removed, for example by a so-called grinding operation to remove surface material. Furthermore, a substantial portion of the dielectric layer 13 of the same SOI wafer 10 is removed, with the exception of its remaining portion 13a, which is arranged vertically relative to the first and second contact pads 19a, 19b and is laterally offset relative thereto. In other words, the remaining portion 13a of the dielectric layer 13 defines, between it and in positions vertically corresponding to the aforementioned contact pads 19a, 19b, the first and second bottom interconnect portions 11b, 11c of the structural substrate 11, as well as the first and second top interconnect portions 21a, 21b of the epitaxial silicon layer 18.

[0037] Same as Figure 2E As shown, a layer of piezoelectric material (e.g., aluminum nitride (AlN)) is then deposited over the surface of the structural substrate 11 (which is exposed and accessible) (opposite the epitaxial silicon layer 18 along the vertical axis z); the layer of piezoelectric material is appropriately defined by photolithographic etching to form a region of piezoelectric material 28 directly opposite the resonator portion 11a of the structural substrate 11.

[0038] A layer of conductive material (a metallic material such as molybdenum in some embodiments) is then deposited and defined over the region of piezoelectric material 28 to form what will become a top electrode region 30 of the piezoelectric resonator structure.

[0039] In the embodiment shown, the definition of the above-described piezoelectric material layer also results in the formation of another piezoelectric region 31 over the remaining portion 13a of the dielectric layer 13, which is laterally arranged relative to the above-described region of piezoelectric material 28. In some embodiments, the other piezoelectric region 31 fills the second opening 26b arranged in a position vertically corresponding to the second contact pad 19b, leaving the first opening 26a arranged in a position vertically corresponding to the first contact pad 19a exposed and accessible.

[0040] Furthermore, the definition of the conductive material layer also results in the formation of a conductive path 32, which extends over the further piezoelectric region 31 and, in some embodiments, into the first opening 26a, thereby making direct contact with the underlying interconnect element that will become the piezoelectric resonator structure (formed by the first bottom interconnect portion 11b of the structural substrate 11 and the first top interconnect portion 21a of the epitaxial silicon layer 18) and electrically contacting the first contact pad 19a.

[0041] In addition, Figure 2E In the manner shown in the cross-sectional view of , the conductive path 32 is provided to be in electrical contact with the top electrode region 30 .

[0042] As shown in FIG. 2F , the wafer 10 is then etched (e.g., wet etching or vapor etching using hydrofluoric acid HF) to completely remove the dielectric material contained in the defining trenches 14 and the dielectric material in the sacrificial trenches 16 a of the surface dielectric layer 16 (resulting in the formation of an internal cavity 39 in the epitaxial layer 18), thereby releasing the resonator portion 11 a of the structural substrate 11 described above, thereby forming a moving element (herein indicated by 40) of the piezoelectric resonator structure.

[0043] Note that the etching process described above does not result in the removal of the remaining dielectric region, which is actually inaccessible from the processed top surface (eg, the surface of the structural substrate 11 opposite the epitaxial silicon layer 18 ).

[0044] like Figure 2G As shown, a cap wafer 42 made of, for example, a semiconductor material (in some embodiments, silicon) is then coupled to the SOI wafer 10 on the support layer 11 (on the side opposite to the aforementioned epitaxial silicon layer 18) by interposing bonding elements 43 of a suitable material (in some embodiments, the material is a dielectric material, for example, a glass material such as glass solder). These bonding elements 43 are arranged laterally relative to the previously described structure (in some embodiments, relative to the moving element 40 and the further piezoelectric region 31) and define the separation distance between the SOI wafer 10 and the cap wafer 42.

[0045] The cover wafer 42 itself has a housing cavity 44 in a position vertically corresponding to the moving element 40 .

[0046] In some embodiments, a suitable vacuum level may be defined within the housing cavity 44 by, for example, forming (eg, depositing) a getter region 45 within the housing cavity 44 (eg, on a corresponding wall facing the moving element 40 ).

[0047] The top surface of the cap wafer 42 (opposite the surface 42 a facing the SOI wafer 10 ) may be thinned by removing material and / or chemical etching to obtain a desired thickness, eg, along the vertical axis z.

[0048] like Figure 2H As shown, the stack formed by the SOI wafer 10, the handle wafer 25 and the cap wafer 42 is then turned over, for example by a flip-chip operation, so that the handle wafer 24 faces upward and can be used for subsequent manufacturing steps.

[0049] In some embodiments, the subsequent manufacturing steps described above contemplate the complete removal of the handle wafer 24 and, in addition, the removal of all or part of the adhesive layer 25; for example, as described above. Figure 2H In the example shown, a portion of the adhesion layer 25 may remain within the insulating opening 20 and / or over a portion of the outer surface of the epitaxial silicon layer 18 to provide protection and coating functions (but not covering the contact pads 19a, 19b).

[0050] The manufacturing process then concludes with dicing the SOI wafer 10 (and cap wafer 42) to define the following: Figure 2I The final resonator device shown, generally designated 50 (note that the Figure 2I , it is assumed that the above-mentioned adhesive layer 25 has been completely removed in a previous manufacturing step).

[0051] The resonator device 50 therefore includes a body 52 (obtained by cutting the above-mentioned SOI wafer 10), which has a first surface 52a and a second surface 52b opposite to each other along the vertical axis z, and is composed of the following items: a structural substrate 11 made of doped single-crystal silicon, which defines the above-mentioned first surface 52a; and an epitaxial silicon layer 18 grown on the structural substrate 11, which defines the above-mentioned second surface 52b of the body 52.

[0052] The resonator device 50 further comprises a cover 54 resulting from cutting of the above-mentioned cover wafer 42, the cover 54 having a respective first surface 54a and a respective second surface 54b, the respective first surface 54a and the respective second surface 54b being opposite to each other along the vertical axis z and being bonded to the first surface 52a of the body 52 by means of a bonding element 43.

[0053] The resonator device 50 thus has a packaging of the so-called wafer-level type, wherein the above-mentioned second surface 52b of the body 52 and the above-mentioned second surface 54b of the cover 54 constitute the outer surfaces in contact with the external environment (in a manner not shown, a coating of, for example, epoxy resin may be formed on the second surface 52b of the body 52; alternatively, a portion of the adhesive layer 25 may be present on the same second surface 52b in case the adhesive layer is only partially removed during the manufacturing process).

[0054] In some embodiments, the resonator device 50 internally and as a whole defines a piezoelectric resonator structure 60, which includes: a moving element 40 formed by the resonator portion 11a of the structural substrate 11, the moving element 40 being appropriately coupled (in a manner not shown herein) to the above-mentioned structural substrate 11 so as to be suspended in a cantilever manner, facing the internal cavity 39 formed in the epitaxial layer 18 and the housing cavity 44 formed in the cover 54 on the opposite side; and a region of piezoelectric material 28 arranged on the same moving element 40 on the first surface 52a of the body 52; and a top electrode 30 arranged on the region of piezoelectric material 28 (to form a so-called piezoelectric stack).

[0055] The piezoelectric resonator structure 60 further comprises a bottom electrode of the same material as the moving element 40 (single crystal silicon), and further comprises a first interconnection element 62 a and a second interconnection element 62 b, which electrically connect the above-mentioned top and bottom electrodes to a first contact pad 19 a and a second contact pad 19 b, which are arranged on the second surface 52 b of the body 52 (in such a way as to be accessible from the outside).

[0056] As described above, these interconnection elements 62a, 62b are electrically insulated from each other (due to the presence of the insulating trench 15 filled with dielectric material and the insulating opening 20 that may be filled with the material of the adhesion layer 25 when the adhesion layer 25 is not completely removed or is formed in a localized manner and is not within the insulation opening 20), and are respectively formed by the superposition of the first top interconnection portion 21a and the second top interconnection portion 21b of the epitaxial silicon layer 18 and the first bottom interconnection portion 11b and the second bottom interconnection portion 11c of the structural substrate 11.

[0057] In some embodiments, the first contact pad 19a is electrically connected to the top electrode 30 (for biasing the piezoelectric resonator structure 60 and detecting an electrical signal at an appropriate oscillation frequency generated by the corresponding movement at the resonant frequency) by means of a conductive path 32 formed on the first surface 52a of the body 52; and the second contact pad 19b is electrically connected to the bottom electrode (composed of the same moving element 40 as described above) (again for biasing the piezoelectric resonator structure 60 and detecting a corresponding electrical signal at the oscillation frequency).

[0058] The advantages of the present solution are clear from the foregoing description.

[0059] In some embodiments, it is emphasized that the resonator device 50 has a low temperature dependence of the corresponding oscillation frequency due to the temperature stability of the material used (doped single crystal silicon).

[0060] Additionally, due to the use of wafer-level packaging and due to the reduced thickness of the lid 54 (via an operation of thinning the lid wafer 42, which utilizes the temporarily existing handle wafer 24), the resonator device 50 has a small size and, in some embodiments, a smaller thickness of the stack along the vertical axis z.

[0061] Advantageously again, again for the sake of size reduction, the contact pads 19 a, 19 b are arranged on the outer surface of the epitaxial layer 18, which is grown directly on the structural substrate 11 with interconnection elements 62 a, 62 b connecting the contact pads 19 a, 19 b to the top and bottom electrodes of the piezoelectric resonator structure 60, thus traversing the entire thickness of the same structural substrate 11 and the epitaxial silicon layer 18.

[0062] In some embodiments, lid 54 is bonded to body 52 by glass solder bonding, enabling hermetic packaging of piezoelectric resonator structure 60 (with a desired vacuum level that can be achieved inside getter region 45 ).

[0063] The formation of the piezoelectric stack obtained by stacking an area of piezoelectric material 28 and a top electrode area 30 advantageously enables the electrical properties of the piezoelectric resonator structure 60, for example with respect to frequency shift, to be adjusted and calibrated by precisely defining the dimensions of the formed material areas, a so-called trimming operation, which may alternatively or additionally involve the resonator portion 11a of the moving element 40 constituting the piezoelectric resonator structure.

[0064] Furthermore, it is emphasized that, unlike known solutions requiring complex and expensive manufacturing steps, for example starting from a C-SOI substrate, the present disclosure allows obtaining an internal cavity 39 by etching a previously grown sacrificial material of the same epitaxial layer, for example using standard semiconductor techniques, with the mobile element 40 being suspended in a cantilevered manner within the epitaxial material layer relative to the internal cavity 39, thus with low complexity and cost.

[0065] The resonator device 50 may advantageously replace a conventional resonant quartz structure in a pre-existing oscillator circuit, for example for RTC applications, and in some embodiments may constitute a direct replacement, for example using the same pins and contacts of a pre-existing quartz resonator, employing in fact the same piezoelectric principle and being therefore fully compatible with the associated electronic circuitry.

[0066] In this regard, Figure 3 An electronic device 70 is schematically illustrated and includes an application circuit 71 configured to execute one or more applications that require timing by a clock signal clk, and a clock circuit 72 configured to provide the clock signal clk to the application circuit 71 .

[0067] The clock circuit 72 includes the aforementioned MEMS resonator device 50 and associated electronic readout circuitry 73 .

[0068] Finally, it is obvious that modifications and variations can be made to what has been described and illustrated herein without departing from the scope of the present disclosure.

[0069] In some embodiments, it is emphasized that the geometry, dimensions, and coupling of the structural substrate 11 to the moving element 40 of the piezoelectric resonator structure 60 may vary relative to what has been previously illustrated.

[0070] Furthermore, it is emphasized that, in addition to the real-time clock applications to which specific reference has been previously made, the resonator device 50 may be advantageously used in a wide range of other applications, for example, in reference high-frequency oscillators (e.g., for providing a suitable frequency reference for demodulation operations in electronic circuits).

[0071] The various embodiments described above can be combined to provide other embodiments. Aspects of the embodiments may be modified as needed using the concepts of various patents, applications, and publications to provide further embodiments. These and other changes may be made to the embodiments in light of the above detailed description. Generally, in the appended claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but rather should be interpreted as including all possible embodiments and the full range of equivalents claimed by such claims. Therefore, the claims are not limited by the disclosure.

Claims

1. A micro-electromechanical system resonator device comprising: a body having a first layer and a second layer, the first layer having a first surface, the second layer having a second surface opposite the first surface along an axis, the second layer having an inner cavity facing the first layer along the axis, the first layer including a moving element, the moving element overlapping the inner cavity and suspended relative to the inner cavity in a cantilever manner; bonding elements; a cover having a first surface and a second surface opposite to each other along the axis, the first surface of the cover being keyed to the first surface of the body by the keying element, the cover including a housing cavity overlapping the inner cavity, the moving element being suspended in the cantilever manner relative to the housing cavity; as well as A piezoelectric resonator structure comprising: The moving element is configured as a bottom electrode; a piezoelectric region of piezoelectric material disposed on the moving element at the first surface of the body; and A top electrode is disposed on the piezoelectric region.

2. The apparatus of claim 1, wherein the first layer is a structural substrate of doped single-crystal silicon; and wherein the second layer is an epitaxial layer grown from the structural substrate.

3. The apparatus according to claim 1, comprising: a first contact element and a second contact element arranged on the second layer at the second surface of the body; as well as First and second interconnecting elements electrically couple the top and bottom electrodes of the piezoelectric resonator structure to the first and second contact elements, respectively, the first and second interconnecting elements extending through the thickness of the body along the axis.

4. The apparatus of claim 3 , further comprising an insulating region extending through the body along the axis, wherein the first interconnecting element and the second interconnecting element each comprise a stack of a first interconnecting portion of the second layer and a second interconnecting portion of the first layer; and the first interconnecting element and the second interconnecting element are electrically insulated from each other by the insulating region.

5. The apparatus of claim 4, wherein the insulating region comprises: an insulating trench in the first layer, the insulating trench being filled with a dielectric material, and The insulating opening in the second layer overlaps the dielectric material filling the insulating trench along the axis.

6. The apparatus of claim 4, further comprising at least one path of conductive material disposed on the first surface of the body and electrically coupling the first interconnect element to the top electrode of the piezoelectric resonator structure.

7. The apparatus of claim 1, wherein the bonding element is a dielectric material laterally separated from the moving element, the first surface of the body being spaced apart from the first surface of the cover by the bonding element. 8 . The apparatus of claim 1 , further comprising a getter region within the housing cavity, the getter region being arranged on a wall of the housing cavity facing the moving element.

9. The device of claim 1, comprising a wafer-level package, wherein the second surface of the body and the second surface of the cover constitute exterior surfaces in contact with an external environment.

10. A method for manufacturing a micro-electromechanical system resonator device, comprising: forming a body having a first surface of a first layer, a second surface of a second layer opposite the first surface along an axis, and a piezoelectric resonator structure on the first surface, the second layer having an inner cavity facing the first layer along the axis, the piezoelectric resonator structure comprising: The resonator portion of the first layer overlaps the inner cavity and is suspended in a cantilever manner relative to the inner cavity. a piezoelectric region of piezoelectric material on the resonator portion at the first surface of the body, and an electrode on the piezoelectric region; forming a cover having a first surface and a second surface opposite each other along the axis, the first surface of the cover comprising a housing cavity; The first surface of the cover is bonded to the first surface of the body by a bonding element, and the resonator portion overlaps the housing cavity and is suspended in a cantilevered manner relative to the housing cavity.

11. The method of claim 10, wherein forming the body comprises: receiving a silicon-on-insulator wafer comprising the first layer of doped single crystal silicon, a support substrate, and a dielectric layer between the first layer and the support substrate; forming a defining groove throughout the thickness of the first layer along the axis, the groove laterally surrounding the resonator portion of the first layer; forming a surface dielectric layer over the first layer and within the defined trench; forming a sacrificial portion of the surface dielectric layer on the resonator portion by patterning the surface dielectric layer, the sacrificial portion having a lateral extension exceeding the resonator portion in a lateral direction; forming the second layer by growing epitaxial silicon on the first layer and coating the sacrificial portion; releasing the resonator portion of the first layer by removing dielectric material within the defined trench; as well as The inner cavity is formed in the second layer by removing the sacrificial portion.

12. The method of claim 11, wherein forming the body further comprises: bonding a handle wafer to the silicon-on-insulator wafer; flipping the silicon-on-insulator wafer by using the handle wafer; as well as The working surface of the first layer is exposed by completely removing the support substrate and removing the dielectric layer.

13. The method according to claim 12, further comprising: forming a piezoelectric material layer over the working surface of the first layer; as well as The piezoelectric region is formed over the resonator portion by patterning the piezoelectric material layer.

14. The method according to claim 11, further comprising: forming an insulating trench laterally across the entire thickness of the first layer relative to the defining trench, the insulating trench defining a first bottom interconnect portion and a second bottom interconnect portion of the first layer therebetween, wherein the forming of the surface dielectric layer fills the insulating trench; forming a first contact element and a second contact element on the second layer at positions vertically overlapping the first bottom interconnection portion and the second bottom interconnection portion of the first layer, respectively; as well as By forming an insulating opening through the second layer, a first top interconnection portion and a second top interconnection portion of the second layer are formed, respectively overlapping the first bottom interconnection portion and the second bottom interconnection portion.

15. The method according to claim 14, further comprising: At least one path of conductive material is formed over the first surface of the body and couples the first bottom interconnect to the electrode of the piezoelectric resonator structure.

16. The method of claim 10, wherein forming the cover comprises: providing a cover wafer; forming the housing cavity within the first surface of the lid wafer; and wherein the bonding comprises bonding the lid wafer to the first layer via the bonding element of dielectric material, the resonator portion faces the housing cavity, the bonding element is laterally spaced relative to the resonator portion, and the lid wafer is spaced a distance from the first layer on the axis.

17. The method according to claim 16, further comprising: A getter region is formed on a wall of the housing cavity facing the resonator portion, the getter region defining a vacuum level within the housing cavity.

18. The method according to claim 16, further comprising: The second surface of the lid wafer is thinned to a certain thickness along a vertical axis.

19. A resonant structure comprising: a first body having a piezoelectric resonator structure, the piezoelectric resonator structure being suspended in a first direction above a first cavity embedded in the first body, the dimension of the first cavity in a second direction encompassing the dimension of the piezoelectric resonator structure in the second direction, the second direction being transverse to the first direction, the piezoelectric resonator structure comprising a first electrode, a second electrode, and a piezoelectric layer located between the first electrode and the second electrode in the first direction; a second body having a second cavity, the second cavity overlapping the piezoelectric resonator structure in the first direction, the size of the second cavity in the second direction including the size of the piezoelectric resonator structure in the second direction; as well as A bonding layer is between the first body and the second body in the first direction. 20 . The resonant structure of claim 19 , wherein the piezoelectric layer protrudes beyond a surface of the first body toward the second cavity, the surface of the first body facing the second body in the first direction.

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