MEMS resonator with perforated resonating element

Abstract

A microelectromechanical system (MEMS) resonator (100) includes a perforated resonant element (101), the perforated resonant element comprising: a piezoelectric layer (110), an electrode layer (120) on the piezoelectric layer (110), a second electrode layer (130) on the piezoelectric layer (110) opposite to the electrode layer (120), and at least one anchor (160) configured to connect the perforated resonant element (101) to and suspend the perforated resonant element (101) from the surrounding layer, wherein the electrode layer (120) includes perforations (150 / 250 / 350 / 450 / 650).

Description

Technical Field

[0001] This invention generally relates to MEMS resonators that include perforated resonant elements. Background Technology

[0002] This section illustrates helpful background information, but does not acknowledge that any techniques described herein represent existing technology.

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

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

[0005] The purpose of certain embodiments of the present invention is to reduce the negative impact of resonator electrodes (e.g., metal electrodes) without degrading their primary function, or at least to provide an alternative to existing technologies. Another purpose of certain embodiments is to reduce or eliminate reliability issues, increase or maintain the quality factor, and / or improve frequency-temperature characteristics while retaining low ESR. In some embodiments, these objectives are achieved by providing a MEMS resonator that includes a perforated resonant element. Due to edge field effects, this perforation allows the electric field used for electromechanical transduction to be equivalent or nearly equivalent to the electric field of the solid electrode, thereby allowing the retention of low ESR.

[0006] According to a first exemplary aspect of the present invention, a microelectromechanical system (MEMS) resonator is provided, comprising: a perforated resonant element including: a piezoelectric layer, an electrode layer on the piezoelectric layer, and a second electrode layer on the piezoelectric layer opposite to the electrode layer; and at least one anchor configured to connect the perforated resonant element to a surrounding layer and suspend the perforated resonant element from the surrounding layer, wherein the electrode layer includes a perforation. In some embodiments, the at least one anchor includes portions of the piezoelectric layer, the electrode layer, and the second electrode layer.

[0007] Some embodiments also include a treatment layer attached to at least one anchor.

[0008] In at least some embodiments, the piezoelectric layer comprises aluminum nitride. In some embodiments, the electrode layer comprises a metal, preferably gold.

[0009] In some embodiments, the second electrode layer is referred to as a substrate. In some embodiments, the second electrode layer comprises silicon, preferably doped silicon, such as heavily doped UHD silicon, more preferably monocrystalline silicon. In some embodiments, an N-type or P-type heavily doped UHD second electrode is present.

[0010] In this context, UHD doping refers to a doping level higher than 10. 20 cm -3 In some embodiments, the doping level of UHD silicon is higher than 10. 19 cm -3 .

[0011] According to some embodiments, the perforated resonant element includes resonant bundles. In some embodiments, the perforated resonant element includes a stacked bundle resonator having multiple adjacent bundles connected by multiple connecting elements.

[0012] 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 20% of the length of each resonant beam includes a perforation. In some embodiments, the perforation is centered along the longitudinal direction of each resonant beam. In some embodiments, the perforation is centered on an axis that intersects the beam length perpendicularly at the center of the beam.

[0013] In some embodiments, the perforation of the perforated resonant element extends through at least the piezoelectric layer. In some embodiments, the perforation of the perforated resonant element extends through both the piezoelectric layer and the second electrode layer.

[0014] In some embodiments, at least 5% of the electrode layer has been perforated within the perforated resonant element. In some embodiments, at least 9% of the electrode layer has been perforated within the perforated resonant element. In some embodiments, at least 15% of the electrode layer has been perforated. For example, in some embodiments, 30% of the electrode layer has been perforated, thereby providing a 30% improvement in frequency stability.

[0015] In some embodiments, the perforation diameter of the perforated resonant element is less than three times the thickness of the electrode layer. In some embodiments, the perforation diameter of the perforated resonant element is less than three times the thickness of the piezoelectric layer. In some embodiments, the perforation diameter of the perforated resonant element is less than twice the thickness of the electrode layer. In some embodiments, the perforation diameter of the perforated resonant element is less than twice the thickness of the piezoelectric layer. In some embodiments, the perforation diameter of the perforated resonant element is less than 4.5 μm, preferably less than 3.5 μm, and most preferably less than 2.5 μm.

[0016] In some embodiments, the perforation of the perforated resonant element is hexagonal. In some embodiments, the perforation of the perforated resonant element is hexagonal with triangular extensions. In some embodiments, the perforation of the perforated resonant element is cross-shaped. In many embodiments, the perforation of the perforated electrode is rectangular. In some embodiments, the perforation of the perforated resonant element is circular, with a plurality of ellipses placed at the edge of the circle.

[0017] In some embodiments, the perforated resonant element is configured to resonate in the LE resonant mode with its length extended. In some embodiments, the perforated resonant element is configured to resonate in the WE resonant mode with its width extended.

[0018] In some embodiments, the resonant beams (multiple) of silicon in the second electrode layer <100> Longitudinal alignment within 25 degrees of crystal orientation.

[0019] In at least some embodiments, the perforations of the perforated resonant element are uniformly spaced to create 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 resonant element.

[0020] 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 UHD silicon layer, preferably monocrystalline silicon.

[0021] 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, and another of which is configured to resonate in a different type of resonant mode. At least one of these resonant elements is a perforated resonant element.

[0022] At least some embodiments of the present invention can be used in transducers having a moving body that is non-conductive or electrically insulating. For example, a MEMS resonator according to certain embodiments can be used in a microphone.

[0023] Examples of resonant mode types include in-plane length extension (LE) mode, width extension (WE) mode, Lamé or square extension (SE) mode, and bending mode.

[0024] Various non-limiting exemplary aspects and embodiments have been presented in the foregoing. The above embodiments and those described later in this description are used to explain selected aspects or steps that may be used in implementations of the invention. It should be understood that the corresponding embodiments are also applicable to other exemplary aspects. Any suitable combination of embodiments may be formed. Attached Figure Description

[0025] The present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0026] Figure 1A A schematic top view of a MEMS resonator according to a particular embodiment is shown;

[0027] Figure 1B It shows Figure 1A The resonator is located along the cross-section of line BB';

[0028] Figure 1C It shows Figure 1A The resonator is located along the cross-section of line CC';

[0029] Figure 1D and Figure 1E A cross-section along line BB' is shown in another embodiment;

[0030] Figure 2A A schematic top view of a MEMS resonator having a processing layer and a surrounding layer according to some embodiments is shown;

[0031] Figure 2B It shows Figure 2A The resonator is located along the cross-section of line BB';

[0032] Figure 2C It shows Figure 2A The resonator is located along the cross-section of line CC';

[0033] Figures 3A to 3D A schematic top view of other MEMS resonators according to some embodiments is shown;

[0034] Figure 4 A schematic top view of a portion of a MEMS resonator according to certain embodiments is shown;

[0035] Figures 5A to 5F The shapes and arrangements of the perforations according to certain embodiments are shown; and

[0036] Figure 6 A schematic top view of a MEMS resonator with a rectangular perforation according to some embodiments is shown. Detailed Implementation

[0037] In the following description, the same reference numerals denote the same elements.

[0038] MEMS resonators according to certain embodiments of the present invention Figure 1A , Figure 1B and Figure 1C The diagram in the middle shows that... Figure 1A A schematic top view of a MEMS resonator is shown. Figure 1B The MEMS resonator is shown along Figure 1A The cross-section of line BB', and Figure 1C A cross-section of the MEMS resonator along line CC' is shown. As illustrated, the MEMS resonator 100 includes: a perforated resonant element 101, which includes: a piezoelectric layer 110, an electrode layer 120 on the piezoelectric layer 110, a second electrode layer 130 on the piezoelectric layer 110 opposite to the electrode layer 120; and at least one anchor 160 configured to connect the perforated resonant element 101 to and suspend the perforated resonant element from the surrounding layers, wherein the electrode layer includes a perforation 150.

[0039] In some embodiments, the second electrode layer 130 comprises silicon, preferably doped silicon, such as heavily doped silicon, more preferably monocrystalline silicon. In some embodiments, a heavily doped UHD N-type second electrode is present. In this context, UHD doping refers to a doping level greater than 10. 20 cm -3 In some embodiments, the doping level of the perforated resonant element is higher than 10. 19 cm -3 .

[0040] like Figure 1C As seen in some embodiments, at least one anchor includes portions of a piezoelectric layer, an electrode layer, and a second electrode layer. Figure 1A As seen in the images, in at least some embodiments, the perforated resonant element includes a plurality of anchors configured to connect the perforated resonant element to and suspend the perforated resonant element from the surrounding layers.

[0041] As described herein, in at least some embodiments, a layer is situated on another layer or substrate, such that the layer is deposited on the other layer or substrate. The layer may be adhered to the other layer or substrate, for example, via an adhesive layer. The layer may be situated on another layer or substrate, such that the layer is grown directly on the other layer or substrate or a piezoelectric layer. In some embodiments, layers are situated on another layer or substrate, such that they are positioned above or below the other layer or substrate. In some embodiments, one component is situated on another component, such that they are positioned adjacent to each other. In at least some embodiments, a layer is situated on another layer, such that an intermediate layer exists between the layer and the other layer.

[0042] In at least some embodiments, electrode layer 120 is located on piezoelectric layer 110, such that the electrode layer is deposited on the piezoelectric layer. The electrode layer can be adhered to the piezoelectric layer, for example, via an adhesive layer. Electrodes can be located on the piezoelectric layer, such that the electrodes are grown directly on the piezoelectric layer or an intermediate layer. Figure 1AAs illustrated, electrode layer 120 may be on piezoelectric layer 110 such that it is positioned above piezoelectric layer. In some embodiments, one component is positioned on top of another component such that they are positioned adjacent to each other.

[0043] The perforations 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.

[0044] like Figure 1B As seen in the diagram, in at least some embodiments, electrode layer 120 is the topmost layer. In some embodiments, the perforated electrode layer is the topmost electrode layer or the first electrode layer, and the opposing electrode layer is the bottommost electrode layer or the second electrode layer.

[0045] In at least some embodiments, the piezoelectric layer comprises aluminum nitride. In some embodiments, the electrode layer 120 comprises a metal, preferably gold.

[0046] Figure 1D Some embodiments are illustrated, wherein the perforation 150 of the perforated resonant element 101 extends at least through the piezoelectric layer 110. For example... Figure 1E As seen in some embodiments, the through-hole 150 of the through-hole resonant element extends through both the piezoelectric layer 110 and the second electrode layer 130. These embodiments can be implemented, for example, by using a trench mask (such as a single trench mask) and photolithographic patterning to remove all layers in successive etching process steps. In some embodiments, the diameter of the hole left in the trench mask before etching controls the etching depth, thereby controlling how many layers are removed. For example, some embodiments are implemented using three consecutive etching steps after photolithography. Wet or dry etching is used to remove the electrode layer, wet or dry etching is used to remove the piezoelectric layer, and then deep reactive ion etching is performed on the second electrode layer or substrate.

[0047] Figures 2A to 2C The illustration shows a MEMS resonator according to at least some embodiments. Figure 2B The resonator is shown along Figure 2A The cross-section of line BB', and Figure 2C A cross-section along line CC' is shown. As illustrated, the MEMS resonator 200 includes: a through-hole resonant element 201, which includes: a piezoelectric layer 210 and an electrode layer 220 on the piezoelectric layer 210, wherein the electrode layer includes a through-hole 250; and a second electrode layer 230 on the piezoelectric layer 210 opposite to the electrode layer 220, wherein at least the first electrode layer 220 includes a through-hole 250.

[0048] Also Figures 2A to 2CAs seen in the diagram, the resonant element 201 is surrounded by a surrounding layer 270 and supported by a processing layer 240 attached to at least one anchor 260. In at least some embodiments, the surrounding layer 270 is formed of the same layer as the resonant element. That is, the piezoelectric layer 210, the electrode layer 220, and the second electrode layer 230 extend through the resonator 200 at least in the surrounding layer 270 and the perforated resonant element 201, such that the perforated resonant element 201 or the resonator region is defined by a trench 280 and separated from the surrounding layer 270 or the non-resonator region by the trench 280.

[0049] like Figures 2A to 2C As seen in at least some embodiments, electrode layer 220 is present in the region of resonant element 201 and in the region of at least one anchor 260. Electrode layer 220 present in the region of at least one anchor 260 can act as a trace extending from the resonant element to pads located elsewhere on the resonator for connecting signals to the electrode layer of the resonant element. While in Figure 2C The image is shown as an anchor extending across each side of the resonant element, but in at least some embodiments with more than one anchor, the electrode layer exists only in the region of one of the anchors.

[0050] Figure 2B and Figure 2C Further illustration shows a processing layer 240, on which all other layers are deposited in at least some embodiments. As illustrated, the processing layer 240 can be used as a carrier and to allow mechanical processing of a wafer including a resonator. Within this processing layer, cavities 290, or multiple cavities in some embodiments, are patterned to allow the resonant element 201, including a piezoelectric layer 210, a first electrode layer 220, and a substrate or a second electrode layer 230, to be suspended. As seen, the first electrode layer 220 includes through-holes 250.

[0051] In at least some embodiments, such as Figure 2C The embodiments shown include at least one anchor 260 extending from layers 210, 220, and 230 to suspend resonant elements from the processing layer. Also as illustrated, in at least some embodiments, an insulating layer 245, preferably silicon dioxide, exists between the processing layer 240 and the substrate 230, which acts as an electrical insulator between the processing layer and the substrate.

[0052] In addition to providing cavity 290, in at least some embodiments, trench 280 also provides resonator structure 201 for release from surrounding layers.

[0053] In some embodiments, the second electrode layer 230 comprises silicon, preferably doped silicon, such as heavily doped silicon, more preferably monocrystalline silicon. In some embodiments, a heavily doped UHD N-type second electrode is present. In this context, UHD doping refers to a doping level greater than 10.20 cm -3 In some embodiments, the doping level of the perforated resonant element is higher than 10. 19 cm -3 .

[0054] In at least some embodiments, a second electrode layer 230 (also referred to as a substrate in at least some embodiments) is situated on the piezoelectric layer 210, such that the piezoelectric layer is deposited on the second electrode layer, and vice versa. The second electrode layer may be adhered to the piezoelectric layer, for example, via an adhesive layer. The second electrode layer may be situated on the piezoelectric layer, such that the piezoelectric layer is grown directly on the second electrode layer or an intermediate layer. In some embodiments, the second electrode layer is situated on the piezoelectric layer, such that there are multiple intermediate layers between the piezoelectric layer and the second electrode layer. In some embodiments, such intermediate layers are insulating layers. In at least some embodiments, the second electrode layer is a bottom electrode. In some embodiments, one component is situated on top of another component, such that they are positioned adjacent to each other.

[0055] According to some embodiments, the perforated resonant element includes a perforated resonant beam. For example, some embodiments include a single resonant beam, such that the perforated resonant element includes only a single perforated resonant beam, such as... Figure 1A and Figure 2A As shown in the diagram.

[0056] In some embodiments, the perforated resonant element includes multiple resonant beams. For example, Figures 3A to 3D The MEMS resonator 300. 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 plane, separated by trenches and connected by connecting elements. In at least some stacked beam resonators, the resonator beams are positioned side-by-side in a plane such that at least a portion of each resonator lies in the same plane. In some stacked beam resonators, no two resonator beams are positioned on top of each other.

[0057] In some embodiments, the plurality of resonant beams 301 are separated by a groove 381. In at least some embodiments including a plurality of resonant beams, the resonant beams are connected by a connecting element 302 between the beams. In some embodiments having a connecting element, the connecting element includes a plurality of through holes.

[0058] exist Figures 3A to 3D The diagram also illustrates a peripheral layer 370 according to at least some embodiments. As shown, the peripheral layer 370 is separated from the resonant element via a trench 380. An anchor 360 is also illustrated for connecting the resonant element to and suspending the resonant element from the peripheral layer 370. The trench 380 is used to separate the perforated resonant element, or resonant region, composed of the perforated resonant bundle 301, from the non-resonant region of the resonator 300 or the wafer.

[0059] Figures 3A to 3D Some embodiments of perforations 350 and multiple resonant beams 301 with different arrangements are shown. As can be seen, in some embodiments, the perforations are uniformly spaced. In some embodiments, the perforations are arranged to create a mesh, such as a mesh comprising uniformly spaced perforations. In at least some embodiments, the mesh electrodes are formed by the perforations, and this mesh can be included throughout the resonant element, in conjunction with... Figure 3A The same applies in other embodiments, such as... Figure 3B As seen in the diagram, the mesh can be included only in a portion of the resonant element, wherein the mesh is centered on multiple resonant beams, such that each beam includes a perforated mesh centered longitudinally along that beam. In other embodiments, such as Figure 3C As seen in the diagram, the mesh is primarily present at the ends of the bundles. In some embodiments, there is no perforation at the longitudinal center of each resonant bundle. In at least some embodiments, the perforations are concentrated towards the ends of each bundle.

[0060] While perforating the electrode layer may result in some resistive losses, these losses can be limited by controlling the size and location of the perforations. For example, if resistive losses cannot be substantially avoided, they can be offset by confining the perforations to certain portions of the resonant element, such as the central portion of the resonant beam described herein.

[0061] In some embodiments, perforations are included in columns along the resonant element. For example, Figures 3A to 3D The perforations in the embodiments can be considered as arranged in columns. In some embodiments, the perforations are equally spaced throughout the resonant element.

[0062] Figures 3A to 3D Examples of LE MEMS resonators 300 according to certain embodiments are also provided, which include LE bundles 301 having perforations 350. A specific portion of the length L of each bundle includes the perforation 350. For example, in Figure 3B In this configuration, 33% of the length of each bundle 301 includes a perforation 350, which may, for example, be centered along the length of each bundle 301. As another example, Figure 3D One embodiment is shown, wherein 66% of each bundle 301 includes perforations 350. Alternatively, as... Figure 3A As shown, 100% of each bundle 301 may include perforations 350.

[0063] In some embodiments, the perforated resonant element is configured to resonate in a width-extended WE resonant mode.

[0064] In some embodiments, at least 5% of the electrode layer has been perforated within the perforated resonant element. For example, in some embodiments, at least 30% of the electrode layer has been perforated, thereby providing a 30% improvement in frequency stability.

[0065] Although Figures 3A to 3D The columns are generally aligned, but in some embodiments, adjacent perforated columns are offset from each other, such as... Figure 4 It can be seen in [the text]. Figure 4 The image shows a portion of a perforated resonant element 401 with perforations 450, illustrating the arrangement of columns of perforations 450. As can be seen, the first column of perforations 451 and the second column of perforations 452 are not aligned, such that the perforations in the second column 452 are centered between the centers of the perforations in the first column 451. In other words, Figure 4 The perforations in the first column 451 have a pitch, that is, the distance between the center points of the perforations within the same column. Then, the second column 452 is offset by half of this pitch, such that the center points of the perforations in the second column 452 begin at a position half a pitch lower than the perforations in the first column 451. At least some embodiments include offsetting the perforations such that a column is at least partially offset from the first column. For example, a column may be offset by a quarter pitch, or it may be offset by a half pitch, such as... Figure 4 As shown.

[0066] like Figures 5A to 5F As shown, the shape and arrangement of the perforations can be varied. Figures 5A to 5F In the figure, the perforation is shown as the shallower part.

[0067] As can be seen, in some embodiments, the perforation is circular in shape, and... Figure 5A The same as in the middle. Although in some embodiments the perforation is octagonal, in other embodiments it is formed with... Figure 5B The same honeycomb structure as described above. Regarding the pitch discussed above, this honeycomb structure can be formed by shifting each row of perforations by half a pitch.

[0068] like Figure 5C As shown, in some embodiments, the perforation has an octagonal shape with triangular extensions. Figure 5C In the diagram, shape 505, marked with a dashed line, is used to delineate the area between the octagonal and triangular extensions. This dashed line is merely illustrative and does not alter the shape of the perforation. This embodiment provides a more uniform width of electrode material on the electrode.

[0069] exist Figure 5D The diagram illustrates perforations with a hexagonal shape in some embodiments. As can be seen, embodiments with hexagonal perforations can also form a honeycomb structure. Similarly, the perforations are shifted by half a pitch between columns.

[0070] like Figure 5E As seen in some embodiments, the perforations of the perforated resonant element have a cross-shaped design. Using a cross-shaped perforation provides easier manufacturing processes because it makes it easier to pattern longer strips, such as those in a cross shape, compared to the relatively smaller circular and hexagonal holes of other embodiments.

[0071] exist Figure 5F The diagram illustrates a perforation according to certain embodiments. As illustrated, in at least some embodiments, the perforation is composed of several shapes. Figure 5F In this embodiment, ellipses are formed around the circumference of the circle to create an irregular shape. In other words, ellipses are added to the upper left, upper right, lower right, and lower left of the circle. This embodiment allows for maintaining a uniform perforation distance across the electrodes while using aligned columns.

[0072] In some embodiments, the shapes of the perforations are combined. For example, some of the perforations may be circular, while some of the perforations may be hexagonal. As another example, some of the perforations may be cross-shaped, while others may be rectangular.

[0073] In several embodiments, the perforations in the perforated electrode are rectangular in shape. For example, Figure 6 The embodiment shown in the figure illustrates another type of perforated resonant element 601. Figure 6 The perforated resonant element 601 can be part of a stack of resonant elements 601 forming a stacked bundle resonant element; for example, the perforated resonant element 601 can be a resonant bundle. As can be seen, Figure 6 The perforations 650 in the middle have different shapes and sizes.

[0074] In embodiments including rectangular perforations, it can be based on Figure 6 The design is discussed using marked lines and nodes. In this embodiment, the lines extending along the resonator (e.g., along a surface) can be vertical or horizontal and can have different spacing. The lines are interconnected via nodes. In some embodiments, the lines and nodes include top electrodes, such as a top electrode mesh comprising an array or matrix of perforated holes.

[0075] exist Figure 6 The diagram also illustrates various dimensions of the rectangular perforation embodiments. For example, the spacing between adjacent lines or the width of the gap G1 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 equidistantly spaced. The gap lengths G2 and G3 can also be varied in some embodiments, such as... Figure 6As shown. In at least some embodiments, the gap length G2 at the center is greater than the gap length G3 at the edge of the resonant element.

[0076] In some embodiments, the perforated resonant element is configured to resonate in an extended LE resonant mode. In some embodiments, the perforation is applied in the middle of the LE resonator, while all-solid electrodes are used at other locations 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 at least some embodiments, at least 20% of the length of each resonant beam includes a perforation. In some embodiments, the perforation is centered longitudinally along each resonant beam.

[0077] In some embodiments, the perforation diameter of the perforated resonant element is less than three times the thickness of the electrode layer. In some embodiments, the perforation diameter of the perforated resonant element is less than twice the thickness of the electrode layer. In some embodiments, the perforation diameter of the perforated resonant element is less than three times the thickness of the piezoelectric layer. In other embodiments, the perforation diameter of the perforated resonant element is less than twice the thickness of the piezoelectric layer. In some embodiments, the perforation diameter of the perforated resonant element 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 described in the embodiments herein, transduction losses can be minimized.

[0078] In some embodiments, the resonant beams (multiple) travel along the silicon of the second electrode layer. <100> Crystal orientation longitudinal alignment. In at least some embodiments, the (multiple) resonant beams are aligned with the silicon of the second electrode layer. <100> The crystal orientation is aligned longitudinally, such that the longitudinal axis of each resonant beam is in the silicon of the second electrode layer. <100> Within 25 degrees of crystal orientation.

[0079] 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 UHD-doped silicon layer, preferably monocrystalline silicon.

[0080] 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, and another of which is configured to resonate in a different type of resonant mode (different from the first type).

[0081] Examples of resonant mode types include in-plane length extension (LE) mode, width extension (WE) mode, Lamé or square extension (SE) mode, and bending mode. In some embodiments, the movement of the resonant element is actuated by piezoelectric actuation.

[0082] Various non-limiting exemplary aspects and embodiments have been presented in the foregoing. The above embodiments and those described later in this description are used to explain selected aspects or steps that may be used in implementations of the invention. It should be understood that the corresponding embodiments are also applicable to other exemplary aspects. Any suitable combination of embodiments may be formed.

[0083] In some embodiments, the resonator is separated from its surrounding portion (e.g., the surrounding piezoelectric layer) by a trench.

[0084] In some embodiments, the resonant element is configured to resonate in an in-plane length-extension mode along the length of the resonant beam. In some embodiments, the movement of the resonant element is actuated by piezoelectric actuation.

[0085] Preferably, in embodiments employing a length-extended resonant mode, <100> One of the crystal orientations (most preferably

[100] ) is along the vibration direction of the length-extending resonant mode.

[0086] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more exemplary embodiments disclosed herein are listed below. One technical effect is reduced degradation of the MEMS resonator. Another technical effect is reduced recirculation drift and aging. At least some embodiments provide an improved quality factor Q. Some embodiments provide a corrected frequency linearity temperature coefficient TCF1. Furthermore, embodiments provide reduced trimming sensitivity, thereby improving trimming accuracy.

[0087] The foregoing description has provided a complete and informative description of the best mode of carrying out the invention as currently contemplated by the inventors, through non-limiting examples of specific implementations and embodiments of the invention. 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 components without departing from the characteristics of the invention.

[0088] Furthermore, some features of the embodiments disclosed above can be advantageously used without corresponding use of other features. Therefore, 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 patent claims.

Claims

1. A MEMS resonator (100), comprising: The perforated resonant element (101) includes: Piezoelectric layer (110). The electrode layer (120) on the piezoelectric layer (110) includes perforations (150 / 250 / 350 / 450 / 650). A second electrode layer (130) is located on the piezoelectric layer (110) opposite to the electrode layer (120), and At least one anchor (160) is configured to connect the perforated resonant element (101) to the surrounding layer and suspend the perforated resonant element (101) from the surrounding layer. The characteristic feature is that the diameter of the perforation (150 / 250 / 350 / 450 / 650) of the perforated resonant element (101) is less than 3 times the thickness of the piezoelectric layer (110).

2. The MEMS resonator according to claim 1, wherein the at least one anchor (160) comprises a portion of the piezoelectric layer (110), the electrode layer (120), and the second electrode layer (130).

3. The MEMS resonator according to claim 1 or 2, wherein the electrode layer (120) comprises metal, preferably gold.

4. The MEMS resonator according to any one of the preceding claims, the resonator (100) further comprising a processing layer (240) attached to the at least one anchor (160).

5. The MEMS resonator according to any one of the preceding claims, wherein the second electrode layer (130) comprises silicon, preferably doped silicon, such as heavily doped silicon, more preferably monocrystalline silicon.

6. The MEMS resonator according to any one of the preceding claims, wherein the perforated resonant element (101) comprises a resonant beam (301).

7. The MEMS resonator according to any one of the preceding claims, wherein the perforated resonant element (101) comprises a plurality of resonant beams (301) forming a stacked beam resonator.

8. The MEMS resonator according to claim 6 or 7, wherein at least 10% of the length of each resonant beam (301) includes perforations (150 / 250 / 350 / 450 / 650).

9. The MEMS resonator of claim 8, wherein the perforations (150 / 250 / 350 / 450 / 650) are centered longitudinally along each resonant beam (301).

10. The MEMS resonator according to any one of the preceding claims, wherein the perforation (150 / 250 / 350 / 450 / 650) of the perforated resonant element (101) extends through at least the piezoelectric layer (110).

11. The MEMS resonator according to any one of the preceding claims, wherein the perforation (150 / 250 / 350 / 450 / 650) of the perforated resonant element (101) extends through both the piezoelectric layer (110) and the second electrode layer (130).

12. The MEMS resonator according to any one of the preceding claims, wherein at least 5% of the electrode layer (120) has been removed by perforations (150 / 250 / 350 / 450 / 650) within the perforated resonant element (101).

13. The MEMS resonator according to any one of the preceding claims, wherein the diameter of the perforation (150 / 250 / 350 / 450 / 650) of the perforated resonant element (101) is less than 3 times the thickness of the electrode layer (120).

14. The MEMS resonator according to any one of the preceding claims, wherein the diameter of the perforation (150 / 250 / 350 / 450 / 650) of the perforated resonant element (101) is less than 4.5 μm, preferably less than 3.5 μm, and most preferably less than 2.5 μm.

15. The MEMS resonator according to any one of the preceding claims, wherein the perforated resonant element (101) is configured to resonate in a length-extended LE resonant mode.

16. The MEMS resonator according to any one of the preceding claims, wherein the resonant beam (301) is in <100> Longitudinal alignment within 25 degrees of crystal orientation.

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