MEMS resonator with release electrode

Abstract

A microelectromechanical system (MEMS) resonator (100) and a method for manufacturing the MEMS resonator. The MEMS resonator has a resonant element (101) comprising: a substrate (110), a piezoelectric layer (120) on the substrate (110), and an electrode layer (130) on the piezoelectric layer (120) and opposite to the substrate (110), wherein at least one space (125) exists between the electrode layer (130) and the substrate (110).

Description

Technical Field

[0001] This invention generally relates to microelectromechanical systems (MEMS) and MEMS resonators including release electrodes. Background Technology

[0002] This section provides useful background information, but does not acknowledge that any technology described herein represents prior art.

[0003] Microelectromechanical systems (MEMS) resonators are being developed to provide the same functionality as quartz resonators, with benefits such as smaller chip size, lower cost, and greater resistance to shock and vibration.

[0004] A key performance parameter of MEMS resonators is the equivalent series resistance (ESR). ESR is inversely proportional to the resonator's quality factor Q, and minimizing ESR is often desirable. Another key performance parameter of MEMS resonators is the stability of the resonant frequency. In some MEMS resonators, especially those composed of disparate layers (such as resonators with metal electrodes), instability in the metal layers can lead to frequency instability. Summary of the Invention

[0005] Some embodiments of the present invention aim to improve the frequency stability of MEMS resonators, or at least provide an alternative to the prior art. Some embodiments of the present invention aim to reduce the negative impact of the resonator electrodes (e.g., metal electrodes) without degrading their primary function, or at least provide an alternative to the prior art. Another objective of some embodiments is to reduce or eliminate reliability issues, improve or maintain the quality factor, and / or improve frequency-temperature characteristics while maintaining low ESR. In some embodiments, these objectives are achieved by providing a MEMS resonator comprising at least partially released resonant elements and / or electrode layers. In some embodiments, the electrode layers are released such that at least one space exists between the electrode layers and the substrate layer of the MEMS resonator.

[0006] According to a first exemplary aspect of the present invention, a MEMS resonator is provided, comprising:

[0007] - A resonant element, comprising:

[0008] - Substrate,

[0009] – A piezoelectric layer located on the substrate, and

[0010] - An electrode layer located on the piezoelectric layer and opposite to the substrate.

[0011] There is at least one space between the electrode layer and the substrate.

[0012] In at least some embodiments, the space is formed at least partially by at least one gap in the piezoelectric layer.

[0013] Some embodiments also include a sacrificial layer located between the electrode layer and the piezoelectric layer, the space being formed at least in part by at least one gap in the sacrificial layer.

[0014] In some embodiments, a plurality of gaps exist in the piezoelectric layer, forming the at least one space. In other embodiments, a plurality of gaps exist in the sacrificial layer, forming the at least one space.

[0015] In at least some embodiments, the electrode layer includes perforations. In some embodiments, gaps(s) in the piezoelectric layer and / or sacrificial layer are centered around the perforations in the electrode layer. In some embodiments, the gaps in the piezoelectric layer and / or sacrificial layer are undercut relative to the perforations in the electrode layer.

[0016] In some embodiments, the MEMS resonator includes a support located in the space between the electrode layer and the substrate.

[0017] Some embodiments of MEMS resonators also include a porous layer located between the electrode layer and the piezoelectric layer. In some embodiments that include a porous layer between the electrode layer and the piezoelectric layer, the support is made of the same material as the porous layer.

[0018] In at least some embodiments, the piezoelectric layer comprises aluminum nitride. In some embodiments, the electrode layer comprises a metal, preferably gold.

[0019] In some embodiments, the substrate serves as a second electrode layer comprising silicon, preferably doped silicon, such as heavily doped silicon, and more preferably single-crystal silicon. In some embodiments, an N-type heavily doped (UHD) second electrode is present.

[0020] In this context, UHD doping refers to a doping level higher than 10. 20 cm -3 In some embodiments, the doping level of the resonant element is higher than 10. 19 cm -3 .

[0021] According to some embodiments, the resonant element includes a resonant beam. In some embodiments, the resonant element includes multiple resonant beams.

[0022] At least some embodiments include an electrode layer with perforations, or perforated electrodes. In some embodiments, the perforations of the perforated electrodes are uniformly spaced to form a grid. In some embodiments, the perforations are included in columns along the perforated resonant element, and adjacent columns of perforations are offset from each other. In some embodiments, the perforations are equally spaced throughout the perforated electrode.

[0023] According to a second exemplary aspect of the present invention, a method for manufacturing a MEMS resonator is provided, the method comprising:

[0024] - A wafer is provided, the wafer including a piezoelectric layer on a substrate and an electrode layer on the piezoelectric layer and opposite to the substrate; and

[0025] - At least one space is formed between the electrode layer and the substrate.

[0026] In at least some embodiments, providing a wafer includes: first providing a piezoelectric layer on a substrate; and forming at least one space includes: forming a gap in the piezoelectric layer before forming an electrode layer on the piezoelectric layer.

[0027] In some embodiments, the electrode layer is perforated, and forming at least one space includes etching through the perforation of the electrode layer.

[0028] In some embodiments of the second example aspect, the wafer further includes a porous layer, and the wafer is provided by depositing an electrode layer on the porous layer.

[0029] In at least some embodiments, at least one gap is formed during an etching process. In at least some embodiments, the porous layer is polycrystalline silicon.

[0030] The embodiments of the first aspect can be applied to the second aspect. For example, at least some embodiments of the second aspect are used to manufacture the MEMS resonator of the first aspect.

[0031] Various non-limiting examples and embodiments have been introduced above. The above embodiments, as well as those described later in this specification, are used to illustrate selected aspects or steps that can be utilized to implement the invention. It should be understood that the corresponding embodiments are equally applicable to other example aspects. Any suitable combination of embodiments can be formed. Attached Figure Description

[0032] The invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0033] Figure 1A A schematic top view of a MEMS resonator according to certain embodiments is shown;

[0034] Figure 1B It shows Figure 1A The resonator is along the cross-section of line AA';

[0035] Figure 1C A cross-section of the resonator including the sacrificial layer is shown;

[0036] Figure 2AA schematic top view of a MEMS resonator according to some embodiments is shown;

[0037] Figure 2B It shows Figure 2A The resonator is located along the cross-section of line BB';

[0038] Figure 2C It shows Figure 2A The resonator is located along the cross-section of line CC';

[0039] Figures 2D-2F A schematic top view and cross-section of a MEMS resonator including a sacrificial layer are shown according to some embodiments;

[0040] Figure 3A A schematic top view of a MEMS resonator according to some embodiments is shown;

[0041] Figure 3B It shows Figure 3A The resonator in the middle is located along the cross-section of line BB';

[0042] Figure 3C It shows Figure 3A The resonator in the middle is located along the cross-section of line CC';

[0043] Figure 3D A cross-section of another embodiment is shown;

[0044] Figures 3E-3G An embodiment that also includes a sacrificial layer is shown;

[0045] Figures 4A-4D A schematic top view of other MEMS resonators according to some embodiments is shown;

[0046] Figure 5 A schematic top view of a portion of an electrode layer according to certain embodiments is shown;

[0047] Figures 6A-6F The shape and arrangement of the perforations according to certain embodiments are shown;

[0048] Figure 7 A schematic top view of a MEMS resonator with a rectangular perforation according to some embodiments is shown;

[0049] Figures 8A-8C A process for manufacturing a MEMS resonator according to certain embodiments is illustrated;

[0050] Figures 9A-9D The process for manufacturing a MEMS resonator according to some embodiments is illustrated;

[0051] Figures 10A-10EA MEMS resonator including a support is shown according to some embodiments;

[0052] Figure 11 The illustration shows a method for manufacturing a MEMS resonator according to some embodiments, and

[0053] Figure 12A , Figure 12B A schematic top view of a MEMS resonator according to certain embodiments is shown, along with details of the top view. Detailed Implementation

[0054] In the following description, the same reference numerals denote the same elements.

[0055] Microelectromechanical systems (MEMS) resonators according to certain embodiments of the present invention, such as Figure 1A and Figure 1B The diagram in the image shows, where Figure 1B The MEMS resonator is shown along Figure 1A The cross section of line AA'. As illustrated, the MEMS resonator 100 includes: a resonant element 101, which includes: a substrate 110, a piezoelectric layer 120 on the substrate 110, and an electrode layer 130 on the piezoelectric layer 120 and opposite to the substrate 110, wherein there is at least one space 125 between the electrode layer 130 and the substrate 110. Figure 1A and Figure 1B Optional connecting elements 160 are also illustrated, which can be used, for example, to suspend resonant elements. Figure 1B As seen, in at least some embodiments, space 125 is formed at least partially by gaps in the layers (e.g., piezoelectric layers) of the MEMS resonator. That is, according to some embodiments, the gaps exist within what would otherwise be a solid material layer. For example, the resonant element of a MEMS resonator according to some embodiments may have a solid piezoelectric layer within the resonant element, but gaps exist within the piezoelectric layer to create space between the electrode layer and the substrate. Figure 1B As seen, these gaps can extend across the entire height of the layer, effectively eliminating the layer at the location of the gap. According to some embodiments, the gaps extend only partially across the height of the layer, for example, thereby forming a depression or pit within the piezoelectric layer including the gap.

[0056] In at least some embodiments, the term "space" is synonymous with "void." In some embodiments, there is no material within the space, for example, no material from any layer of the resonator. In some embodiments, the space is also referred to as a cavity.

[0057] As in Figure 1A and Figure 1BAs can be seen, in at least some embodiments, the gaps in the piezoelectric layer 120 allow the space 125 to extend across the entire resonant element, thereby completely releasing the electrode layer from the substrate within the range of at least one resonant beam. Figure 1A and Figure 1B In one embodiment, the gaps in the piezoelectric layers are such that the piezoelectric layers exist only within the connecting element 160, as illustrated by reference line B showing the edge of the connecting element 160.

[0058] As in Figure 1C As can be seen, at least some embodiments of the MEMS resonator also include a sacrificial layer 140. Figure 1C Implementation examples and Figure 1A Having the same schematic top view, but as Figure 1C As seen in the cross-section, the MEMS resonator also includes a sacrificial layer 140, with gaps located within the sacrificial layer 140, allowing a space 125 to extend across the entire resonant element, thereby completely releasing the electrode layer from the substrate within the range of at least one resonant beam. In at least some embodiments, the sacrificial layer is an oxide layer or a porous layer.

[0059] exist Figures 2A-2C The inner diagram illustrates a MEMS resonator 200 according to certain embodiments, wherein... Figure 2B The MEMS resonator is shown along Figure 2A The cross-section of line BB', and Figure 2C A cross-section along line CC' is shown. Figure 2A In the diagram, the dashed lines illustrate the extent of the gaps in the piezoelectric layer 220. As can be seen, in at least some embodiments, multiple gaps exist in the piezoelectric layer 220. Figure 2B and Figure 2C As shown, space 225 no longer extends across the entire resonant element 201. Instead, piezoelectric layer 220 provides a rectangular support between electrode layer 230 and substrate 210. This support may be referred to as a support frame. In at least some embodiments, the support may be formed by any remaining portion of piezoelectric layer 220. For example, the support may take a non-rectangular shape.

[0060] exist Figures 2D-2F The inner diagram illustrates a MEMS resonator 200' according to at least some embodiments, wherein Figure 2E The MEMS resonator is shown along Figure 2D The cross-section of line EE', and Figure 2F The diagram illustrates a cross-section along line FF'. (Compared to...) Figures 2A-2C Compared to the MEMS resonator 200, the MEMS resonator 200' also includes a sacrificial layer 240. Figure 2D The dashed lines within the diagram illustrate the extent of the gaps in the sacrificial layer 240. Figure 2ASimilarly, in at least some embodiments, multiple gaps exist in the sacrificial layer 240. For example... Figure 2E and Figure 2F As shown, the space 225 between the electrode layer 230 and the substrate 210 can be included in the sacrificial layer 240. In this way, the sacrificial layer 240 can act as a support for the electrode layer 230. The sacrificial layer 240 is disposed between the piezoelectric layer 220 and the electrode layer 230. In other words, the sacrificial layer 240 provides a support, such as a rectangular support, between the electrode layer 230 and the piezoelectric layer 220. Such a support can be referred to as a support frame.

[0061] As described herein, in at least some embodiments, each layer is situated on another layer or substrate, such that the layer is deposited on the other layer or substrate. The layer can be adhered to the other layer or substrate, for example, by an adhesive layer. The layer can be situated on the other layer or substrate, such that the layer is grown directly on the other layer or substrate, or grown on a piezoelectric layer. Figure 1A As illustrated, electrode layer 130 may be located on piezoelectric layer 120, such that it is positioned above piezoelectric layer 120. In some embodiments, layers are located on another layer or substrate, such that they are positioned above or below that other layer or substrate. In some embodiments, one component is located on another component, such that they are positioned adjacent to each other. In at least some embodiments, layers are located on another layer, such that an intermediate layer exists between the layer located on the other layer and the other layer.

[0062] Figures 3A-3D The illustration shows a MEMS resonator 300 according to some embodiments, wherein the electrode layer 330 includes a through-hole 350. Similarly, there is a substrate 310, a piezoelectric layer 320 on the substrate 310, an electrode layer 330 on the piezoelectric layer 320 and opposite to the substrate 310, and at least some spaces 325 between the electrode layer 330 and the substrate 310. Figure 3B The cross-section along line BB' is shown, while Figure 3C A cross-section along line CC' is shown. As can be seen, the electrode layer 330 of the resonant element 301 includes a plurality of through-holes 350. In some embodiments, however, the electrode layer includes only a single through-hole.

[0063] like Figures 3E-3G As seen, some embodiments also include a sacrificial layer 340 located between the electrode layer and the piezoelectric layer, with the space 325 formed at least partially by gaps in the sacrificial layer. In at least some embodiments, a plurality of gaps are present in the sacrificial layer, forming the at least one space. At least some embodiments including a sacrificial layer can be used without a through electrode, for example by being directly etched during a manufacturing step, or, as another example, by employing a porous layer.

[0064] like Figure 3B As seen, in some embodiments, the gaps(s) in the piezoelectric layer 320 are centered around the through-hole 350 of the electrode layer 330. In some embodiments including a sacrificial layer, the gaps in the sacrificial layer are centered around the through-hole of the electrode layer. And in some embodiments, the gaps in the piezoelectric layer 320 are undercut relative to the through-hole 350 of the electrode layer 330, such as... Figure 3B and Figure 3C As shown in the diagram. Similarly, in some embodiments that include a sacrificial layer, the gaps in the sacrificial layer are undercut relative to the perforations in the electrode layer.

[0065] like Figure 3B and Figure 3C As seen in some embodiments, there are multiple gaps in the piezoelectric layer, which form multiple spaces 325.

[0066] Figure 3D Another embodiment is illustrated, in which a single gap 325 spans multiple perforations 350 of the electrode layer. In some embodiments, a single gap exists for multiple perforations. In some embodiments, a single gap exists that spans all perforations. In some embodiments, multiple gaps form a single space, while in other embodiments, multiple gaps form multiple spaces.

[0067] Figures 3E-3G An embodiment that also includes a sacrificial layer 340 is shown. Figures 3E-3G A schematic top view of the MEMS resonator will be compared with Figure 3A The same in, among which Figure 3E The cross-section along line CC' is shown. Figure 3F The cross-section of the line along BB' is shown, while Figure 3G A cross-section along line CC' is shown. (As shown) Figures 3E-3G As seen, space 325 can be formed in the sacrificial layer. This space can be formed in a single gap (e.g., Figure 3E (as shown), or can be formed in multiple gaps (such as) Figure 3G (as seen in the text). Although in at least some embodiments, as can be seen by comparison... Figure 3E and Figure 3F It can be understood that if a portion of the sacrificial layer is retained between the two rows of perforations, two longer gaps can be formed. In at least some embodiments, this space is included only within the sacrificial layer (as seen).

[0068] As seen in Figures 1 to 3, in at least some embodiments, the electrode layer is the top layer. In some embodiments that include multiple electrode layers, the perforated electrode layer is the top electrode layer or the first electrode layer, while the opposing electrode layer is the bottom electrode layer or the second electrode layer. In at least some embodiments, the substrate serves as the second electrode layer.

[0069] In at least some embodiments, the piezoelectric layer comprises aluminum nitride. In some embodiments, the electrode layer comprises a metal, preferably gold.

[0070] According to some embodiments, the resonant element includes a resonant beam. For example, some embodiments include a single resonant beam, such that the resonant element comprises only a single resonant beam, as illustrated in Figures 1-3.

[0071] In some embodiments, the resonant element includes multiple resonant beams. For example, Figures 4A-4D The MEMS resonator 400 is described. In some embodiments, multiple resonant beams are arranged to form a stacked beam resonant element or a stacked beam resonator. A stacked beam resonator includes multiple resonator beams positioned side-by-side in a coplanar plane, separated by grooves and connected by connecting elements. In at least some stacked beam resonators, the resonant beams are positioned side-by-side in a coplanar plane such that at least a portion of each resonant beam lies in the same plane. In some stacked beam resonators, no two resonator beams are positioned on top of each other.

[0072] In some embodiments, the plurality of resonant beams 401 are separated by grooves 481. In at least some embodiments including the plurality of resonant beams, the resonant beams are connected by connecting elements 402 located between the beams. In some embodiments having connecting elements, the connecting elements include at least one through hole.

[0073] Figures 4A-4D A surrounding layer 470 according to at least some embodiments is also illustrated. As shown, the surrounding layer 470 is spaced from the resonant element via a trench 480. An anchor 460 is also illustrated for connecting and suspending the resonant element from the surrounding layer. The trench 480 is used to separate the perforated resonant element (or resonant region) formed by the perforated resonant beam 401 from the non-resonant region of the resonator 400 or the wafer.

[0074] Figures 4A-4D Different arrangements of perforations 450 and certain embodiments of multiple resonant beams 401 are shown. As can be seen, in some embodiments, the perforations are uniformly spaced. In some embodiments, the perforations are arranged to form a mesh, such as a mesh comprising uniformly spaced perforations. In at least some embodiments, a mesh electrode is formed by the perforations, and this mesh can be distributed across the entire resonant element, such as... Figure 4A As in [the previous example]. In other embodiments, such as [the previous example]... Figure 4B As seen, the mesh may only be included in a portion of the resonant element, wherein the mesh is centered on multiple resonant beams such that each beam includes a mesh with perforations centered along the beam's longitudinal direction. In other embodiments, such as Figure 4CAs seen, the mesh is primarily present at the ends of the beams. In some embodiments, there are no perforations at the longitudinal center of each resonant beam. In at least some embodiments, the perforations are concentrated towards the ends of each beam.

[0075] While perforation of the electrode layer may result in some resistive losses, the arrangement and / or control of the size and placement of the perforations can limit these losses. For example, by confining the perforations to specific portions of the resonant element (such as the central portion of the resonant beam described herein), resistive losses can be substantially avoided or even eliminated.

[0076] In some embodiments, perforations are included in the list. For example, Figures 4A-4D The perforations in the embodiments can be considered as arranged in columns. In some embodiments, the perforations are equally spaced throughout the resonant element.

[0077] Figures 4A-4D Examples of MEMS resonators 400 comprising a length-telescopic L beam 401 with perforations 450, according to certain embodiments, are also provided. In at least some embodiments, a specific portion of the length L of each beam includes a perforation 450. For example, in Figure 4B In this configuration, 33% of the length of each beam 401 includes a perforation 450, which can be centered, for example, along the length of each beam 401. As another example, Figure 4D An embodiment is shown in which 66% of each beam 401 includes perforations 450. Alternatively, as Figure 4A As shown, 100% of each beam 401 may include a perforation 450. In at least some embodiments, at least 10% of the length of each resonant beam includes a perforation. In some embodiments, at least 20% of the length of each resonant beam includes a perforation.

[0078] The perforations in the electrode layer according to embodiments of the present invention can be provided in various ways. For example, some embodiments employ photolithographic patterning. In at least some embodiments, etching can be used. In some embodiments, at least 5% of the electrode layer has been removed by perforation. In some embodiments, at least 9% of the electrode layer has been removed by perforation. In some embodiments, at least 15% of the electrode layer has been removed by perforation. For example, in some embodiments, 30% of the electrode layer has been removed by perforation, thereby providing a 30% improvement in frequency stability.

[0079] In some embodiments, the diameter of the perforation in the perforated resonant element is less than three times the thickness of the electrode layer. In some embodiments, the diameter of the perforation in the electrode layer is less than twice the thickness of the electrode layer. In some embodiments, the diameter of the perforation in the perforated resonant element is less than three times the thickness of the piezoelectric layer. In other embodiments, the diameter of the perforation is less than twice the thickness of the piezoelectric layer. In some embodiments, the diameter of the perforation in the electrode layer is less than 4.5 µm, preferably less than 3.5 µm, and most preferably less than 2.5 µm. By limiting the perforation size (as in the embodiments herein), transduction losses can be minimized.

[0080] although Figures 4A-4D The columns are generally aligned, but in some embodiments, adjacent perforated columns are offset from each other, such as... Figure 5 As seen in [the text]. Figure 5 A portion of an electrode layer 501 with perforations 550 is shown to illustrate the arrangement of the columns of perforations 550. As can be seen, the first column of perforations 551 and the second column of perforations 552 are not aligned, such that the perforations 552 of the second column are centered at half the height between the centers of the perforations 551 of the first column. In other words, Figure 5 The perforations 551 in the first column have a pitch, which is the distance between the center points of the perforations within the same column. The second column 552 is offset relative to the first column by half of this pitch, such that the center points of the perforations in the second column 552 begin half a pitch further down than the center points of the perforations in the first column 551. In at least some embodiments, each column is offset by at least a small portion of the pitch, such as a quarter pitch.

[0081] like Figures 6A-6F As shown, the shape and arrangement of the perforations can be varied. Figures 6A-6F In the diagram, the perforation is shown as the shallower part.

[0082] As can be seen, in some embodiments, the perforation is circular in shape, such as Figure 6A As in the example. In some embodiments, the perforations are octagonal in shape, and in others they form a honeycomb structure, such as... Figure 6B As in the example. Regarding the pitch discussed above, this honeycomb structure can be formed by offsetting each row of perforations by half a pitch.

[0083] like Figure 6C As shown, in some embodiments, the perforation has an octagonal shape with triangular extensions. Figure 6C In the diagram, shape 605 is indicated by dashed lines to depict the area between the octagonal body and the triangular extension. These dashed lines are illustrative only and do not alter the shape of the perforation. This embodiment provides a more uniform width of electrode material throughout the electrode layer.

[0084] exist Figure 6D The diagram illustrates perforations with a hexagonal shape, as in some embodiments. Embodiments with hexagonal perforations can also form a honeycomb structure as seen. Similarly, the perforations in each row are offset by half a pitch.

[0085] like Figure 6E As seen in some embodiments, the perforations in the electrode layer have a cross-shaped shape. Using a cross-shaped perforation provides a simpler process because it is easier to pattern the longer strips within the cross shape compared to the circular or hexagonal perforations of other embodiments.

[0086] exist Figure 6F The diagram illustrates a perforation according to certain embodiments. As illustrated, in at least some embodiments, the perforation is formed by several shapes. Figure 6F In one embodiment, ellipses are formed on the circumference of a circle, thus creating an irregular shape. In other words, ellipses are added to the upper left, upper right, lower right, and lower left of the circle. This type of embodiment allows for maintaining a uniform perforation distance throughout the electrodes while using aligned columns.

[0087] In some embodiments, the shapes of the perforations can be combined. For example, some perforations may be circular, while others may be hexagonal. As another example, some perforations may be cross-shaped, while others may be rectangular.

[0088] In several embodiments, the perforations in the electrode layer are rectangular in shape. For example, in Figure 7 The figure illustrates another embodiment, showing another type of resonant element 701 having a perforated electrode layer. Figure 7 The resonant element 701 can be part of a stack of resonant elements 701 forming a stacked resonant element; for example, the perforated resonant element 701 can be a resonant beam. As can be seen, Figure 7 The perforations 750 come in different shapes and sizes.

[0089] In embodiments including rectangular perforations, the design can be based on, for example... Figure 7 The discussion will focus on the lines and nodes marked in the diagram. In such embodiments, the lines extending along the electrodes (e.g., along a surface) can be vertical or horizontal and can have different spacing. The lines are interconnected via nodes. In some embodiments, these lines and nodes include a top electrode, such as a top electrode constituting a perforated mesh or a top electrode mesh.

[0090] exist Figure 7The diagram also illustrates various dimensions of embodiments of the rectangular perforation. For example, the spacing or gap width G1 between adjacent lines can be selected such that the edge fields of two adjacent lines overlap. Similarly, the line width E1 can be selected to reduce the series resistance of the perforated electrodes. In some embodiments, the line width E1 is uniform. In some embodiments, the line width E1 is uniform and the nodes are equally spaced. Figure 7 As shown, in some embodiments, the lengths of gaps G2 and G3 may also vary. In at least some embodiments, the length of gap G2 within the center of the resonant element is greater than the length of gap G3 at its edge.

[0091] In some embodiments, the resonant element is configured to resonate in a length-stretch (LE) resonant mode. In some embodiments, a perforation is applied to the center of the LE resonator, while solid electrodes are used elsewhere to provide minimal series resistance. For example, in at least some embodiments including resonant beams, at least 10% of the length of each resonant beam includes a perforation. In some embodiments, at least 15% of the length of each resonant beam includes a perforation; for example, in some embodiments, at least 20% of each resonant beam includes a perforation. In some embodiments, the perforation is longitudinally centered along each resonant beam.

[0092] In some embodiments, the substrate serves as a second electrode layer comprising silicon, preferably doped silicon, such as heavily doped silicon, and more preferably monocrystalline silicon. In some embodiments, an N-type heavily doped (UHD) second electrode is present. In this context, UHD doping refers to doping greater than 10-10. 20 cm -3 The doping level. In some embodiments, the doping level of the resonant element is higher than 10. 19 cm -3 .

[0093] According to at least some embodiments, a method for manufacturing a MEMS resonator is provided, the method comprising:

[0094] - A wafer is provided, the wafer including a piezoelectric layer on a substrate and a through electrode on the piezoelectric layer and opposite to the substrate;

[0095] - Form at least one gap in the piezoelectric layer to form at least one space between the substrate and the perforated electrode.

[0096] According to some embodiments, a method for manufacturing a MEMS resonator is provided, the method comprising:

[0097] - A wafer is provided, the wafer including a piezoelectric layer on a substrate and a sacrificial layer on the piezoelectric layer and opposite to the substrate;

[0098] - Form at least one gap in the sacrificial layer;

[0099] - Deposit an electrode layer opposite to the piezoelectric layer onto the sacrificial layer, such that at least one space is formed between the substrate and the electrode layer.

[0100] In such methods, for example, the electrode layer may be deposited before forming at least one gap in the sacrificial layer. For example, the electrode layer may include perforations that allow partial removal of the sacrificial layer by an etching process, even after the electrode layer has been deposited. As another example, in at least some embodiments, a porous layer is further provided on top of the sacrificial layer.

[0101] As in Figures 8A-8C As can be seen, at least some embodiments include a perforated electrode layer 830. Figures 8A-8C In the process, a wafer 800 is first provided, which includes a piezoelectric layer 820, an electrode layer 830, and a sacrificial layer 840 located between the electrode layer 830 and the piezoelectric layer 820 on a substrate 810, such as Figure 8A As shown in the image. In providing Figure 8A After the wafer is formed, a via 835 is formed in the electrode layer. In at least some embodiments, an etching process etches the via 835 into the electrode layer 830. In some embodiments, the electrode layer may be a metal electrode layer. In at least some embodiments, the method may be as follows: Figure 8B As shown, it starts from the perforated electrode. In Figure 8B and Figure 8C The next step is to form at least one gap in the sacrificial layer 840, thereby forming at least one space 845 between the substrate and the via electrode. The formation of this at least one space partially releases the electrode layer around the via. The formation of the gap in the sacrificial layer can be achieved by an etching step, such as an HF vapor etching step, which selectively etches the sacrificial layer. The extent (e.g., lateral extent) and size of the gaps, and therefore the extent and size of the space, can be controlled by adjusting the etching time.

[0102] In some embodiments of the second example aspect, the wafer includes a porous layer, and the method further includes the step of depositing a top electrode layer on the wafer after forming at least one gap in the piezoelectric layer or sacrificial layer.

[0103] In at least some embodiments, at least one space is formed during an etching process. In at least some embodiments, at least one gap in the layer is formed during an etching process. In some embodiments, the sacrificial layer is an oxide layer. In some embodiments, the sacrificial layer is a sacrificial layer that is more susceptible to the effects of the etching process than at least one other layer. In some embodiments, the sacrificial layer is a sacrificial layer that is more susceptible to the effects of the etching process than all other layers. In at least some embodiments, the porous layer is polycrystalline silicon.

[0104] Figures 9A-9D The illustration depicts a process for fabricating a MEMS resonator according to at least some embodiments. For example... Figure 9D As can be seen in a cross-section of a portion of the resulting MEMS resonator, some embodiments also include a porous layer 950 located between the electrode layer 930 (or top electrode, or metal top electrode) and the piezoelectric layer 920. Also, Figure 9D As shown in the figure, substrate 910 is present. Figure 9B A sacrificial layer 940 is shown, which is removed to form a space between the electrode layer 930 and the substrate 910. In at least some embodiments, the sacrificial layer is an oxide layer. In some embodiments, the substrate is an aluminum nitride layer.

[0105] exist Figures 9A-9D In the process, such as Figure 9A As shown, a starting material or wafer comprising a substrate 910 and a piezoelectric layer 920 is first provided. Then, as... Figure 9B As shown, for example, a sacrificial layer 940 and a porous layer 950 are formed by deposition. Then, in Figure 9C In this process, at least a portion of the sacrificial layer 940 is removed. This removal of the sacrificial layer (e.g., via etching) creates at least one space between the electrode layer 930 and the substrate 910 in the final product, such as... Figure 9D As shown in the diagram. For ease of illustration, in... Figure 9C The entire sacrificial layer 940 is shown to be removed; however, it should be understood that, as discussed above with respect to certain embodiments, portions of the sacrificial layer not shown remain. Finally, an electrode layer 930 is formed (e.g., via metallization). As can be seen, in at least some embodiments, perforated electrodes are not required.

[0106] In at least some embodiments, the sacrificial layer comprises silicon dioxide. In some embodiments, the sacrificial layer comprises polymethyl methacrylate (PMMA). In some embodiments, the porous layer comprises polycrystalline silicon.

[0107] In some embodiments, the MEMS resonator includes a support located within the space between the electrode layer and the substrate. For example, a portion of the sacrificial layer may be retained to support the electrode layer relative to the substrate. In embodiments that include a porous layer between the electrode layer and the piezoelectric layer, the support may be made of the same material as the porous layer.

[0108] Figure 10A This is a schematic top view of an embodiment with a support 1025 shown in a box, representing a portion of a sacrificial layer or porous layer that remains below the electrode layer 1030 to support the electrode layer above the piezoelectric layer 1020. The piezoelectric layer is located on the substrate 1010. These supports may be in direct contact with the electrode layer, or they may support the electrode layer via a porous layer or other intermediate layer.

[0109] Figure 10B and Figure 10C The illustration shows a cross-section of a region of a MEMS resonator including a support member 1025 according to at least some embodiments. In at least some embodiments, the support member 1025 includes... Figure 10B The porous layer 1050 seen in the previous section is made of the same material. In some embodiments, the support 1025 comprises the same material as... Figure 10C The sacrificial layer 1040 seen there is made of the same material. Figure 10B and Figure 10C Also illustrated are electrode layer 1030, porous layer 1050, sacrificial layer 1040, piezoelectric layer 1020, and substrate 1010. As can be seen, support 1025 is surrounded by one or more gaps 1045.

[0110] Figure 10D and Figure 10E A schematic top view of another embodiment including support member 1025 is illustrated. Such embodiments may be... Figures 4A-4D An alternative to the perforated embodiment. As seen, the MEMS resonator 1000 has supports 1025 positioned at various locations along the resonant beam 1001 and within anchors 1060. The resonant beam 1001 and connecting elements 1002 are included in an electrode layer visible from this top view. Figure 10A Similarly, a support 1025, shown in a box, is illustrated, representing a portion of a sacrificial layer or porous layer that remains below the electrode layer 1030 to support the electrode layer above the piezoelectric layer 1020. A surrounding layer 1070, an anchor 1060, and trenches 1080 and 1081 are also shown.

[0111] Figure 11The illustration depicts a method of fabrication according to at least some embodiments. As seen, the method includes step 1110 of providing a wafer comprising a piezoelectric layer on a substrate and an electrode layer on the piezoelectric layer and opposite to the substrate. In step 1120, the method further includes forming at least one space between the electrode layer and the substrate.

[0112] In some embodiments, providing a wafer includes first providing a piezoelectric layer on a substrate, while forming at least one gap includes forming a gap in the piezoelectric layer before forming an electrode layer on the piezoelectric layer.

[0113] In at least some embodiments, the electrode layer is perforated, and forming at least one space includes etching via the perforations in the electrode layer. In some embodiments, the wafer further includes a porous layer, and the wafer is provided by depositing the electrode layer on the porous layer.

[0114] At least some of the processes described herein provide for manufacturing MEMS resonators for other embodiments described herein.

[0115] In some embodiments, the resonant beams (multiple) are along the silicon of the second electrode layer. <100> The crystal orientation is longitudinally aligned. In at least some embodiments, the resonant beam(s) are aligned with the silicon of the second electrode layer. <100> The crystal orientation is longitudinally aligned such that the longitudinal axis of each resonant beam is aligned with the silicon of the second electrode layer. <100> Within 25 degrees of the crystal orientation.

[0116] In some embodiments, the electrode layers are implemented using metal layers. In some embodiments, the electrode layers are implemented using doped silicon layers. In some embodiments, the second electrode layer is implemented using a heavily doped UHD silicon layer, preferably a single-crystal silicon layer.

[0117] In some embodiments, the MEMS resonator includes a plurality of resonant elements, one of which is configured to resonate in a first type of resonant mode, while another of the resonant elements is configured to resonate in a different type of resonant mode (different from the first type).

[0118] In some embodiments, the resonant element is configured to resonate in a width-stretching (WE) resonant mode.

[0119] Examples of resonant mode types include in-plane length stretching (LE) mode, width stretching (WE) mode, Lamé or square stretching (SE) mode, and bending mode. In some embodiments, the movement of the resonant element is actuated by piezoelectric actuation.

[0120] Various non-limiting examples and embodiments have been introduced above. The above embodiments, as well as those described later in this specification, are used to illustrate selected aspects or steps that can be utilized to implement the invention. It should be understood that the corresponding embodiments are equally applicable to other example aspects. Any suitable combination of embodiments can be formed.

[0121] In some embodiments, the resonator is separated from its surrounding portion (e.g., the surrounding substrate) by trenches.

[0122] In some embodiments, the resonant element is configured to resonate in an in-plane length-stretching mode along the length of the resonant beam. In some embodiments, the movement of the resonant element is actuated by piezoelectric actuation.

[0123] Preferably, in the embodiment employing a length-scaling resonant mode, <100> One of the crystal orientations (most preferably

[100] ) is along the vibration direction of the length-stretching resonance mode.

[0124] Figure 12A A schematic top view of a MEMS resonator according to certain embodiments is shown, while Figure 12B The diagram shows... Figure 12A Details. Figure 12A and Figure 12B The MEMS resonator 1200 shown includes a perforation 1250, which may be referred to as a meander. According to some embodiments, the MEMS resonator 1200 includes a beam 1201 having the perforation 1250. As shown, in some embodiments, the resonant beam 1201 is separated by grooves 1281, and connecting elements 1202 are present between the beams.

[0125] like Figure 12B As shown, in some embodiments, trench 1281 extends through all layers of the MEMS resonator.

[0126] In at least some embodiments, a portion of the sacrificial layer is removed from beneath the electrode (or in some embodiments, the top metal electrode layer), as shown in the dark gray segment labeled 1255. This removal of the sacrificial layer releases the top electrode layer. In at least some embodiments, this is referred to as undercutting. Figure 12B In the diagram, the removed top electrode layer is marked as 1257, represented by a lighter gray segment. The light gray solid segment represents the metal top electrode 1259.

[0127] In some embodiments, the top electrode may be patterned, for example, through meanders. These meanders provide perforations in the top electrode layer.

[0128] In at least some embodiments (such as those employing a meandering portion), the remaining sacrificial material portion is a dimensional version of the electrode opening geometry, the size of which is designed to depend on the etching time, which determines the undercut distance. The unopened electrode portion forms a meandering pattern.

[0129] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the exemplary embodiments disclosed herein are set forth below. One technical effect is reduced performance degradation in MEMS resonators. Another technical effect is reduced backflow drift and aging effects. At least some embodiments provide an improved quality factor Q. Some embodiments provide a more positive frequency linearity temperature coefficient (TCF1). Furthermore, the embodiments improve tuning accuracy through lower fine-tuning sensitivity. Another technical effect is the maintenance of the quality factor Q over time. Another technical effect is improved frequency stability without increasing ESR.

[0130] The foregoing description, through non-limiting examples of specific implementations and embodiments of the invention, provides a full and detailed explanation of the best mode of carrying out the invention as currently conceived by the inventors. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments presented above, but can be implemented in other embodiments using equivalent means without departing from the characteristics of the invention.

[0131] Furthermore, some of the features in the embodiments disclosed above can be used alone without the need for corresponding use of other features. Thus, the foregoing description should be considered merely as an illustration of the principles of the invention, and not as a limitation thereof. Consequently, the scope of the invention is limited only by the appended claims.

Claims

1. A microelectromechanical system (MEMS) resonator (100), comprising: - Resonant element (101), said resonant element (101) comprising: - Substrate (110) - A piezoelectric layer (120) located on the substrate (110). - An electrode layer (130) is located on the piezoelectric layer (120) opposite the substrate (110), the electrode layer (130) including through holes, and - A sacrificial layer (140) is located between the electrode layer (130) and the piezoelectric layer (120). There is at least one space (125) between the electrode layer (130) and the substrate (110), the space (125) being formed at least partially by at least one gap in the sacrificial layer (140), and wherein the gap(s) in the piezoelectric layer (120) and / or the sacrificial layer (140) are centered around the perforation of the electrode layer (130).

2. The MEMS resonator according to claim 1, wherein the space (125) is formed at least partially by at least one gap in the piezoelectric layer (120).

3. The MEMS resonator according to claim 1 or 2, comprising a plurality of gaps in the piezoelectric layer (120), the plurality of gaps at least partially forming the at least one space (125).

4. The MEMS resonator according to claim 3, comprising a plurality of gaps in the sacrificial layer (140), the plurality of gaps forming the at least one space (125).

5. The MEMS resonator according to any of the preceding claims, wherein the gap in the sacrificial layer (140) is undercut relative to the perforation in the electrode layer (130).

6. The MEMS resonator according to any of the preceding claims, wherein the gap in the piezoelectric layer (120) and / or the sacrificial layer (140) is undercut relative to the perforation in the electrode layer (130).

7. The MEMS resonator according to any of the preceding claims further includes a support member located in the space (125) between the electrode layer (130) and the substrate (110).

8. The MEMS resonator according to claim 7, comprising a porous layer located between the electrode layer (130) and the piezoelectric layer (120), wherein the support is made of the same material as the porous layer.

9. The MEMS resonator of claim 7, comprising the sacrificial layer (140) located between the electrode layer (130) and the piezoelectric layer (120), wherein the support is made of the same material as the sacrificial layer.

10. The MEMS resonator according to any of the preceding claims, wherein the piezoelectric layer (120) comprises aluminum nitride.

11. The MEMS resonator according to any of the preceding claims, wherein the electrode layer (130) comprises metal, preferably gold.

12. The MEMS resonator according to claim 9, wherein the substrate (110) serves as a second electrode layer, the substrate (110) comprising silicon, preferably doped silicon, such as heavily doped silicon, more preferably monocrystalline silicon.

13. The MEMS resonator according to any of the preceding claims, wherein the resonant element (101) comprises a resonant beam.

14. The MEMS resonator according to any of the preceding claims, wherein the resonant element (101) comprises a plurality of resonant beams.

15. A method for manufacturing a MEMS resonator, comprising: - A wafer is provided, the wafer including a piezoelectric layer (120) on a substrate (110) and a sacrificial layer (140) on the piezoelectric layer (120) opposite to the substrate (110). - At least one gap is formed in the sacrificial layer (140); and - An electrode layer (130) opposite to the piezoelectric layer (120) is deposited on the sacrificial layer (140) such that at least one space (125) is formed between the substrate (110) and the electrode layer (130).

16. The method of claim 15, wherein providing the wafer comprises: First, the sacrificial layer (140) is provided on the substrate (110), and forming the at least one space (125) includes forming a gap in the sacrificial layer (140) before forming the electrode layer (130) on the sacrificial layer (140).

17. The method according to claim 15 or 16, wherein the electrode layer (130) is perforated, and forming the at least one space (125) comprises: Etching is performed through the perforations in the electrode layer (130).

18. The method according to any one of claims 15-17, wherein the wafer further comprises a porous layer deposited on top of the sacrificial layer (140).

19. The method according to any one of claims 15-18, wherein the method is used to manufacture a MEMS resonator (100) according to any one of claims 1-14.

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