Resonator electrode configuration

Abstract

Herein is provided a resonator (100), comprising a resonating element (101) having a top electrode layer (L1), and wherein the resonating element (101) comprises cut(s) (201) where the top electrode layer (L1) is absent to electrically suppress a spurious resonance mode of the resonating element (101). Herein is further provided an apparatus, such as a resonator array, comprising at least one resonator (100).

Description

[0001] RESONATOR ELECTRODE CONFIGURATION

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to the field of semiconductors and semiconductor apparatuses. The disclosure relates particularly, though not exclusively, to electrode configurations of resonators.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] A key performance parameter in semiconductor apparatuses, such as resonators, such as silicon MEMS resonators is the equivalent series resistance (ESR). ESR is inversely proportional to the quality factor Q of the apparatus.

[0007] Typically, semiconductor apparatuses are configured to vibrate (oscillate) in a desired main resonance mode. In certain occasions, the apparatus may adopt another, unwanted resonance mode. The performance of the semiconductor apparatus is typically adversely affected by such unwanted resonance modes.

[0008] SUMMARY

[0009] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention. It is an object of certain embodiments of the present disclosure to provide a scheme to solve at least one of the problems related to the prior art, or at least to provide an alternative to existing technology. Accordingly, certain disclosed embodiments provide for an ingenious resonating element solving at least one of the problems related to the prior art.

[0010] According to a first example aspect of the present disclosure there is provided a resonator, comprising a resonating element having a top electrode layer, and wherein the resonating element comprises cut(s) where the top electrode layer is absent to electrically suppress a spurious resonance mode of the resonating element. In certain embodiments, the cut(s) are spurious resonance mode suppressing cut(s). In certain embodiments, the resonating element comprises cut(s) where the top electrode layer is absent to provide electrical suppression for a spurious resonance mode (or resonance modes) of the resonating element.

[0011] In certain embodiments, the top electrode layer of the resonating element comprises at least one cut. In certain embodiments, the top electrode layer of the resonating element comprises a plurality of cuts. In certain embodiments, the resonating element comprises a plurality of cuts adjacent to one another (each other). In certain embodiments, the resonating element comprises a plurality of cuts aligned with one another (each other). In certain embodiments, cut(s) (where the top electrode layer is absent) causes the top electrode (layer, material) to be absent, by making the cut(s). In certain embodiments, the cut(s) form (cause, provide) the parts, where the top electrode is absent.

[0012] In certain embodiments, the cut(s) are arranged at the area of highest strain and / or highest charge collection of the spurious resonance mode of the resonating element. In certain embodiment, the resonating element comprises cut(s) only in the area of highest strain and / or highest charge collection of the spurious resonance mode of the resonating element. In certain embodiments, the resonating element does not comprise cut(s) elsewhere in the resonating element (except in the area of highest strain and / or highest charge collection of the spurious resonance mode of the resonating element).

[0013] In certain embodiments, the resonating element comprises cut(s) in length direction (aligned with / along / parallel with length direction) of the resonating element. In certain embodiments, the resonating element comprises cut(s) in width direction of the resonating element. In certain embodiments, the resonating element comprises cut(s) in diagonal direction (diagonally) the resonating element. In certain embodiments, the cut(s) where the top electrode layer is absent run (extend, reach) from one side (end, edge) to (towards) another side of the resonating element. In certain embodiments, the cut(s) where the top electrode layer is absent run from trench to trench.

[0014] In certain embodiments, the resonating element (the top electrode thereof) comprises a plurality of cuts. In certain embodiments, the resonating element (the top electrode thereof) comprises a plurality of cuts running (extending, running) from one side (end, edge) to (towards) another side of the resonating element. In certain embodiments, the resonating element comprises a plurality of cuts running from one side to (towards) another side of the resonating element in the direction of the (main) resonance mode of the resonating element. In certain embodiments, the resonating element comprises a plurality of cuts running from one side to (towards) another side of the resonating element parallel to the (main) resonance mode of the resonating element.

[0015] In certain embodiments, the resonating element is a rectangular resonating element. In certain embodiments, the rectangular resonating element has two short(er) sides and two long(er) sides (thereby forming a rectangular shape). In certain embodiments, the rectangular resonating element has two short(er) parallel sides and two long(er) parallel sides (thereby forming a rectangular shape). In certain embodiments, the rectangular resonating element comprises a plurality of cuts running from one side to (towards) another side of the rectangular resonating element. In certain embodiments, the rectangular resonating element comprises a plurality of cuts running from one (long, short) side to (towards) another (long, short) side of the rectangular resonating element. In certain embodiments, the rectangular resonating element comprises a plurality of cuts running from one parallel side to (towards) another parallel side of the rectangular resonating element.

[0016] In certain embodiments, the cut(s) are essentially straight. In certain embodiments, the cut(s) comprise bends or turns. In certain embodiments, the cut(s) are meandering.

[0017] In certain embodiments, cut(s) reach (extend, continue) through the top electrode layer. In certain embodiments, the cut(s) reach through the top electrode layer to layer beneath the top electrode layer. In certain embodiments, the cut(s) reach through the top electrode layer to the piezoelectric layer. In certain embodiments, the cut(s) are configured to expose the layer(s) beneath the top electrode. In certain embodiments, the cut(s) are configured to expose the piezoelectric layer beneath the top electrode. In certain embodiments, the resonating element comprises a top electrode (layer) on the resonating element. In certain embodiments, the top electrode (layer) is the topmost layer (surface) of the resonating element. In certain embodiments, the top electrode is configured to cover essentially the entire resonating element.

[0018] In certain embodiments, the top electrode is implemented by a layer of metal. In certain embodiments, the top electrode comprises (is of) metal, preferably gold (Au). In certain embodiments, the top electrode is of gold, preferably doped gold. In certain embodiments, the top electrode is of gold alloy.

[0019] In certain embodiments, the top electrode (layer) is implemented by a layer of doped silicon. In certain embodiments, the silicon layer is of single-crystal silicon. In certain embodiments, the top electrode (layer) is implemented by a layer of doped polysilicon.

[0020] In certain embodiments, the resonating element comprises a piezoelectric layer, wherein the piezoelectric layer is the layer beneath the top electrode layer. In certain embodiments, the resonating element comprises a bottom electrode on the opposite side of the piezoelectric layer than the top electrode layer. In certain embodiments, the resonating element comprises a piezoelectric layer, and a bottom electrode, wherein the piezoelectric layer is the layer beneath the top electrode layer, and the bottom electrode on the opposite side of the piezoelectric layer than the top electrode layer. In certain embodiments, the bottom electrode is (implemented by) a bottom electrode layer.

[0021] In certain embodiments, the resonating element comprises a piezoelectric layer, wherein the top electrode is on the piezoelectric layer, and a bottom electrode on the opposite side of the piezoelectric layer than the top electrode. In certain embodiments, the bottom electrode comprises silicon, preferably doped silicon, such as ultra-heavily doped, UHD, silicon. In certain preferred embodiments, the silicon is of single-crystal silicon. In certain embodiments, the bottom electrode (layer) is implemented by an UHD silicon layer.

[0022] In certain embodiments, the doping level of the silicon is above 1019cm-3. In certain embodiments, the doping level of the silicon is above 102° cm-3. In certain embodiments, the doped silicon is of N-type or P-type doping.

[0023] In certain embodiments, the resonator comprises a material stack, the material stack comprising the silicon layer (the bottom electrode), the piezoelectric layer on top of the silicon layer, and a top electrode on top of the piezoelectric layer. In certain embodiments, the resonator is a piezoelectric resonator. In certain embodiments, the piezoelectric layer comprises aluminum nitride.

[0024] In certain embodiments, the resonator comprises at least one resonating element. In certain embodiments, the resonator comprises a resonating plate element. In certain embodiments, the resonating element comprises a plurality of resonating beam elements. In certain embodiments, each beam element is a sub-element of the resonating element.

[0025] In certain embodiments, the resonating element comprises a plurality of beam elements having a length and a width. In certain embodiments, the plurality of beam elements are positioned adjacent to each other. In certain embodiments, adjacent beam elements are mechanically connected to each other by connection elements. In certain embodiments, the resonating element comprises a plurality of resonating beam elements having a length and a width, the plurality of beam elements being positioned adjacent to each other, wherein the adjacent beam elements are mechanically connected to each other by connection elements.

[0026] In certain embodiments, the resonating element comprises a plurality of resonating beam elements having a length and a width, the plurality of beam elements being positioned adjacent to each other, wherein the adjacent beam elements are mechanically connected to each other by connection elements, wherein the resonating beam elements comprise cut(s) where the top electrode layer is absent to (electrically) suppress a spurious resonance mode of the resonating element.

[0027] In certain embodiments, the resonating element is a stacked beam resonating element. In certain embodiments, the stacked beam resonating element comprises a plurality of beam elements positioned side-by-side in a plane. In certain embodiments, the plurality of beam elements are positions adjacent to each other in a width direction thereof. In certain embodiments, the plurality of beam elements are positioned adjacent to each other in a width direction of the resonator. In certain embodiments, the beam elements are separated by trenches. In certain embodiments, the beam elements are connected to each other by connection elements.

[0028] In certain embodiments, the resonating element comprises a plurality of beam elements, such as seven, nine, or eleven beam elements. In certain embodiments, said adjacent beam elements are mechanically connected to each other by at least two connection elements. In certain embodiments, the beam elements of the resonating element are arranged in a rectangular array configuration. In certain embodiments, the resonating element is in a shape of a rectangle. In certain embodiments, the resonating element is in a shape of an elongated rectangle (beamshaped). In certain embodiments, the resonating element has an aspect ratio (ratio of length to width, when observed from above) different from 1 .

[0029] In certain embodiments, the resonating element has a length-to-width aspect ratio of less than 1. In certain embodiments, the resonating element is attached (supported, anchored, suspended) to a support structure. In certain embodiments, the resonating element is attached to a support structure from the outermost beam elements of the resonating element. In certain embodiments, the resonating element comprises at least one anchor configured to connect the resonating element to, and suspend the resonating element from surrounding layers (support structure). In certain embodiments the at least one anchor comprises portions of the piezoelectric layer, the top electrode and the bottom electrode. In certain embodiments, the resonating element is separated from the substrate by a cavity (cavity being beneath the resonating element).

[0030] In certain embodiments, each beam element is in a shape of a (rectangular) beam. In certain embodiments, each beam element has an aspect ratio (ratio of length to width, when observed from above) different from 1. In certain embodiments, each beam element has a length-to-width aspect ratio of more than 1 .

[0031] In certain embodiments, the resonator is fabricated on a substrate. In certain embodiments, the substrate is a wafer. In certain embodiments, the substrate is a silicon-on-insulator, SOI, wafer. In certain embodiments, the substrate comprises a silicon layer. In certain embodiments, the bottom electrode (layer) is referred to as a substrate or as a silicon layer.

[0032] In certain embodiments, the resonating beam element(s) are longitudinally aligned within 25 degrees of a <100> crystal direction of silicon (of the bottom electrode). Within at least some embodiments the resonating beam element(s) are longitudinally aligned with a <100 crystal direction of the silicon (of the bottom electrode) such that a longitudinal axis of each resonating beam is within 25 degrees of the <100> crystal direction of the silicon (of the bottom electrode).

[0033] In certain embodiments, the resonating beam element(s) are longitudinally aligned within 45 degrees, or 50 degrees of a <100> crystal direction of silicon (of the bottom electrode). Within at least some embodiments the resonating beam element(s) are longitudinally aligned with a <100> crystal direction of the silicon (of the bottom electrode) such that a longitudinal axis of each resonating beam is within 45 degrees, or 50 degrees of the <100> crystal direction of the silicon (of the bottom electrode).

[0034] In certain embodiments, the resonating beam element(s) are longitudinally aligned within 25 degrees of a

[0100] crystal direction of silicon (of the bottom electrode). Within at least some embodiments the resonating beam element(s) are longitudinally aligned with a

[0100] crystal direction of the silicon (of the bottom electrode) such that a longitudinal axis of each resonating beam is within 25 degrees of the

[0100] crystal direction of the silicon (of the bottom electrode).

[0035] In certain embodiments, the resonating beam element(s) are longitudinally aligned within 25 degrees of a

[0110] crystal direction of silicon (of the bottom electrode). Within at least some embodiments the resonating beam element(s) are longitudinally aligned with a

[0110] crystal direction of the silicon (of the bottom electrode) such that a longitudinal axis of each resonating beam is within 25 degrees of the

[0110] crystal direction of the silicon (of the bottom electrode).

[0036] In certain embodiments, the resonating beam element(s) are longitudinally aligned within 25 degrees of a

[0111] crystal direction of silicon (of the bottom electrode). Within at least some embodiments the resonating beam element(s) are longitudinally aligned with a

[0111] crystal direction of the silicon (of the bottom electrode) such that a longitudinal axis of each resonating beam is within 25 degrees of the

[0111] crystal direction of the silicon (of the bottom electrode).

[0037] In certain embodiments, the cut(s) where the top electrode layer is absent are arranged (located, placed) at the resonating beam element(s). In certain embodiments, the resonating beam element comprises a (one) cut. In certain embodiments, each resonating beam element comprises at least one cut. In certain embodiments, each resonating beam element comprises a plurality of cuts. In certain embodiments, each resonating beam element comprises a plurality of cuts, such as two cuts (aligned with one another).

[0038] In certain embodiments, the cut(s) where the top electrode layer is absent are (run, are located, are arranged, are placed) parallel with the length of the resonating beam element. In certain embodiments, the cut(s) where the top electrode layer is absent are perpendicular with the width of the resonating beam element.

[0039] In certain embodiments, the cut(s) where the top electrode layer is absent are centrally arranged (located, placed) within the (each) resonating beam element. In certain embodiments, the cut(s) where the top electrode layer is absent are centred within the resonating beam element. In certain embodiments, the cut(s) where the top electrode layer is absent are width wise centred within the resonating beam element. In certain embodiments, the cut(s) where the top electrode layer is absent run width wise centred and parallel with the length of the resonating beam element in the area of the resonating element.

[0040] In certain embodiments, the cut(s) where the top electrode layer is absent run from one beam end to another beam end of the resonating beam element. In certain embodiments, the cut(s) where the top electrode layer is absent run from one beam end to another beam end in length direction of the resonating beam element (along / parallel to the length direction).

[0041] In certain embodiments, the cut(s) where the top electrode layer is absent form an isolated region of the top electrode material within the top electrode layer. In certain embodiments, the cut(s) where the top electrode layer is absent form a rectangular isolated region of the top electrode material within the top electrode layer. In certain embodiments, the cut(s) where the top electrode layer is absent form an isolated region of the top electrode material within the top electrode layer of the resonating (beam) element (into the central region of the resonating (beam) element).

[0042] In certain embodiments, the resonator (resonating element) is configured to resonate (operate, oscillate, vibrate) in an in-plane resonance mode. In certain embodiments, the resonating element is configured to resonate in a length-extensional, LE, resonance mode. In certain embodiments, the resonator is configured to resonate in an in-plane lengthextensional, LE, (main) resonance mode. In certain embodiments, the length extensional resonance mode is configured to resonate parallel to the length direction of the resonator. In certain embodiments, the length extensional resonance mode is configured to resonate perpendicular to the width direction of the resonator.

[0043] In certain embodiments, the resonating element is configured to resonate in a squareextensional, SE, resonance mode. In certain embodiments, the resonating element is configured to resonate in a width-extensional, WE, resonance mode.

[0044] In certain embodiments, the cut(s) where the top electrode layer is absent are located (arranged) at an area of the resonating element having highest charge collection (of the spurious resonance mode). In certain embodiments, the cut(s) where the top electrode layer is absent are located at an area of the resonating element having highest charge collection of the spurious resonance mode.

[0045] In certain embodiments, the cut(s) where the top electrode layer is absent are located at an area of the highest strain of the spurious resonance mode (of the resonating element), the cut(s) where the top electrode layer is absent are located at an area of the highest strain of the spurious resonance mode of the resonating element. In certain embodiments, the cut(s) where the top electrode layer is absent are located at an area of the highest strain of the spurious (out-of-plane) flexural or (in-plane) width-extensional, WE, resonance mode.

[0046] In certain embodiments, the cut(s) where the top electrode layer is absent are located at an area having highest charge collection of the spurious resonance mode of the resonating element, or the cut(s) where the top electrode layer is absent form an isolated region of the top electrode material within the top electrode layer. In certain embodiments, the cut(s) where the top electrode layer is absent are located at an area having highest charge collection of the spurious resonance mode of the resonating element, and the cut(s) where the top electrode layer is absent form an isolated region of the top electrode material within the top electrode layer.

[0047] In certain embodiments, the resonator (resonating element) is configured to resonate in a collective resonance mode. In certain embodiments, each resonating element of the resonator is configured to resonate in the (same) collective resonance mode. In certain embodiments, the resonator is configured to resonate in a desired (main) resonance mode. In certain embodiments, each beam element of the resonator is configured to resonate in the (same) desired resonance mode.

[0048] In certain embodiments, the cut(s) are used to suppress spurious (unwanted) resonance mode(s), such as higher frequency spurious resonance modes in resonators. In certain embodiments, the cut(s) where the top electrode material is absent are configured to suppress (electrically suppress, alleviate, electrically alleviate) lessen the effect of, remove, get rid of) a spurious resonance mode of the resonating element.

[0049] In certain embodiments, the spurious resonance mode is an unwanted resonance mode. In certain embodiments, the spurious resonance mode is a resonance mode other than the desired (main) resonance mode. In certain embodiments, the spurious resonance mode resonates in a resonance mode other than the desired resonance mode. In certain embodiments, the resonating element is configured to electrically suppress (alleviate) a spurious resonance mode, such as a high frequency spurious resonance mode, of the resonating element by providing the resonating element with cut(s) where the top electrode layer is absent.

[0050] In certain embodiments, the cut(s) affect the electrical properties of the resonating element. In certain embodiments, the cut(s) change the electrical properties of the resonating element. In certain embodiments, the electrical properties of the resonating element are affected by the cut(s) to provide the electrical suppression of the spurious resonance mode(s). In certain embodiments, the change in electrical properties of the resonating element enables suppressing the spurious resonance mode. In certain embodiments, the spurious resonance mode is a flexural resonance mode. In certain alternative embodiments, the spurious mode is a width-extensional resonance mode. In certain alternative embodiments, the spurious mode is a differential resonance mode, such as a differential length-extensional resonance mode. In certain embodiments, the resonating element comprises a width-extensional, WE, spurious resonance mode and / or a flexural spurious resonance mode. In certain embodiments, the resonating element comprises an in-plane width-extensional, WE, spurious resonance mode and / or an out-of-plane flexural spurious resonance mode.

[0051] In certain embodiments, the spurious resonance mode is an out of plane resonance mode. In certain alternative embodiments, the spurious resonance mode is an in-plane resonance mode. In certain embodiments, the spurious resonance mode is an out of plane flexural resonance mode. In certain embodiments, the spurious resonance mode is an in-plane width-extensional resonance mode. In certain embodiments, the spurious resonance mode is an in-plane differential length extensional resonance mode. In certain embodiments, the resonating element comprises more than one spurious resonance mode.

[0052] In certain embodiments, the resonating element is configured to eliminate a collective spurious resonance mode (of the beam elements) of the resonating element.

[0053] In certain embodiments, the resonator is a microelectromechanical systems, MEMS, resonator. In certain embodiments, the resonator is (part of) a semiconductor device. In certain embodiments, the resonator is configured to operate in a megahertz frequency area. In certain embodiments, the resonator is configured to operate at 32 MHz frequency.

[0054] In certain embodiments, the resonator comprises a plurality of resonating elements adjacent to each other in a plane, connected to one another by a coupler. In certain embodiments, the resonator is a multi-ladder resonator, comprising a plurality of stacked beam resonating elements (forming a ladder-like configuration). In certain embodiments, each resonator comprises a plurality of resonating elements having a plurality of beam elements having a length and a width, wherein the plurality of beam elements are positioned adjacent to each other and adjacent beam elements are mechanically connected to each other by connection elements. In certain embodiments, the plurality of beam elements are separated from each other by trenches.

[0055] In certain embodiments, the resonator comprises a plurality of extensional-mode resonating elements. In certain embodiments, the resonator comprises a plurality of length extensionalmode resonating elements. In certain embodiments, the resonator comprises a plurality of flexural-mode resonating elements. In certain embodiments, the resonator comprises a mechanical coupler which connects the resonating elements to one another.

[0056] In certain embodiments, the width of the plurality of beam elements varies within the resonating element. In certain embodiments, the resonating element is configured to mechanically alleviate a spurious resonance mode of the resonating element through having the width variation. In certain embodiments, any two / three, four, five...) adjacent beam elements of the plurality of beam elements are of different width with (respect to, respective to, in comparison to) each other. In certain embodiments, the plurality of beam elements have varying widths with one another are arranged (positioned) asymmetrically in the resonating element. In certain embodiments, each of the plurality of beam elements has a unique (different) width in comparison to each other. In certain embodiments, outermost beam elements of the resonating element have same widths whilst all other beam elements of the resonating element have varying widths (amongst each other).

[0057] In certain embodiments, the width of (each of) the plurality of beam elements varies with each other less than 20%, such as less than 15% of the average width of the beam elements. In certain embodiments, the width of the plurality of beam elements varies with each other more than 1 %, such as more than 5% or more than 10% of the average width of the beam elements. In certain embodiments, the width of the beam elements varies from another beam element by 0.1 pm to 2 pm (a width difference being in between 0.1 pm and 2 pm), such as by 0.3 pm to 0.5 pm, such as by 0.4 pm.

[0058] In certain further embodiments, the resonating element is configured to mechanically alleviate a spurious resonance mode of the resonating element by varying the width of the beam elements (width variation in between beam elements) within the resonating element. In certain further embodiments, the resonating element is configured to mechanically alleviate a disturbance caused by a spurious resonance mode by varying the width of the beam elements asymmetrically within the resonating element. In certain embodiments, the resonating element is configured to mechanically alleviate the spurious resonance mode by modifying (splitting) equivalent series resistance, ESR, of said spurious resonance mode of the resonating element.

[0059] According to a second example aspect of the present disclosure there is provided an apparatus, such as a resonator array (an apparatus), comprising at least one resonator according to the first aspect or any of its embodiments. In certain embodiments, the apparatus comprises (at least) two (more than one) resonators of the first aspect or any of its embodiments coupled to each other. In certain embodiments, the apparatus is a semiconductor apparatus.

[0060] In certain embodiments, the apparatus comprises extensional-mode resonator(s). In certain embodiments, the apparatus comprises flexural mode resonator(s). In certain embodiments, (all, some of) the resonators of the apparatus are identical with one another (each other). In certain alternative embodiments, (all, some of) the resonators of a resonator are different from one another.

[0061] In accordance with certain embodiments, embodiments of the second aspect are provided, the embodiments comprising subject matter of any single embodiment presented in connection with the first aspect, or the embodiments comprising subject matter of any of the embodiments presented in connection with the first aspect combined with subject matter presented in any other embodiment or embodiments.

[0062] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspects or steps that may be utilized in different implementations. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments may apply to other example aspects as well. In particular, the embodiments described in the context of the first aspect are applicable to each further aspect. Any appropriate combinations of the embodiments may be formed.

[0063] BRIEF DESCRIPTION OF THE FIGURES

[0064] Some example embodiments will be described with reference to the accompanying figures, in which: Fig. 1 schematically shows a top view of an example resonating element in a top view demonstrating structure thereof according to an example embodiment;

[0065] Fig. 2 schematically shows a cross-section of the material stack of an example resonator according to an example embodiment;

[0066] Fig. 3a schematically shows a top view of a resonating element comprising cuts where top electrode is absent according to an example embodiment;

[0067] Fig. 3b schematically shows a top view of a resonating element comprising cuts where top electrode is absent forming isolated areas of the top electrode material according to an example embodiment;

[0068] Fig. 3c schematically shows a top view of a resonating element comprising more than one cut per resonating beam element according to an example embodiment;

[0069] Fig. 3d schematically shows a top view of a resonating element comprising more than one cut per resonating beam element forming isolated areas of the top electrode material according to an example embodiment;

[0070] Fig. 3e schematically shows a cross-section of one resonating beam element according to an example embodiment;

[0071] Fig. 4 schematically shows a top view of a resonator having multiple resonating elements coupled by a coupler according to an example embodiment;

[0072] Fig. 5a schematically shows a spurious resonance mode from top view according to an example embodiment; and

[0073] Fig. 5b schematically shows another spurious resonance mode from side view according to an example embodiment.

[0074] DETAILED DESCRIPTION

[0075] In the following description, like reference signs denote like elements or steps.

[0076] As used herein, the term “width of the resonating (beam) element” or “width-wise” refers to the horizontal direction, meaning the direction of left to right (or right to left), when observing the resonator or the resonating element from above. This refers to the x-direction according to the chosen coordinate system. In the example embodiments shown in Fig. 1 , the x- direction is equal to the width direction of the resonating element and the resonating beam element. Analogously, as used herein, the term “length of the resonating (beam) element” or “lengthwise” refers to the vertical direction, meaning the direction of up and down (or down to up, when observing the resonator or the resonating element from above). This refers to the y- direction according to the chosen coordinate system. In the example embodiments shown in Fig. 1 , the y-direction is equal to the length direction of the resonating element and the resonating beam element.

[0077] Yet analogously, as used herein, herein is also used a direction of left to right (or right to left), when observing the resonator of the resonating element from the side (cross-sectional view), meaning the z-direction according to the chosen coordinate system. In the example embodiments shown in Fig. 2, the z-direction is referred as a “height” direction of the resonator.

[0078] As used herein, the term “material stack” refers to the resonator materials that form the cross-sectional layer structure of the resonator. Thus, the term stack refers to a cross- sectional stack, meaning that the materials can be seen on top of each other once observing the cross-section of the resonator. When observed from the top, only the topmost layer of the particular region can be seen. In accordance with certain embodiments, some of the materials of the material stack originate from the substrate itself (such as the silicon layer), and some of the materials are provided / deposited onto the substrate.

[0079] As used herein, the notation ‘the layer X beneath the layer Y’ refers to the layer X being underneath the layer Y within the material stack / pile in question. Synonyms for the notation are, by way of example, under, underneath, and below. As used herein, the notation “the layer X on the layer Y” refers to the layer X being above the layer Y within the material stack in question. Synonyms for the notation are, by way of example, on top of, onto and above. In certain embodiments, these notations can be understood as “the layer X being in contact with the layer Y”. However, the instant solution is not limited to those embodiments.

[0080] As used herein, the notation “cut(s) where the top electrode layer is absent” refers to a cut or an area (region, place, location), wherein the top electrode material is removed. In certain embodiments, the top electrode material is removed from the area of the cut(s) by etching. In certain embodiments, the cut(s) where the top electrode layer is absent are provided by selective deposition of the top electrode material. In certain embodiments, the cut(s) are patterns, such as lines (grooves) in the top electrode layer. Synonyms for “cut(s) where the top electrode layer is absent” include, but are not limited to top electrode (layer) cut(s), pattern(s), groove(s), and line(s). In certain embodiments, the present solution comprises causing top electrode to be absent by making the cut(s).

[0081] Fig. 1 schematically shows a top view (from above, from up to down) of an example resonating element 101 according to an example embodiment. In certain embodiments, the resonator 100 comprises at least one resonating element 101. In certain embodiments, the resonator 100 comprises a resonating plate element 101 (not shown in Fig. 1). In certain embodiments, the resonator 100 comprises a plurality of resonating elements 101 (not shown in Fig. 1).

[0082] The resonating element 101 according to embodiment shown in Fig. 1 comprises a plurality of resonating beam elements having a length L and a width W. In certain embodiments, the resonating beam elements are beam-shaped. In the embodiment shown in Fig. 1 , the resonating element 101 comprises seven resonating beam elements (the number of beam elements may vary depending on the embodiment). In certain embodiments, the resonating beam elements are longer L than they are wide W. In certain embodiments, the coordinate system is selected so that the x-axis resides in the width direction W of the resonating elements 101 and the y-axis in the longitudinal direction L of the resonating beam elements.

[0083] According to the example embodiment shown in Fig. 1 , the plurality of resonating beam elements are positioned adjacent to each other. In certain embodiments, the plurality of resonating beam elements form a ladder-like configuration (stacked beam resonator). In certain embodiments, the plurality of resonating beam elements are positioned adjacent to each other in a width direction thereof. The adjacent resonating beam elements are mechanically connected to each other.

[0084] In certain embodiments, the resonating element 101 is formed of the plurality of resonating beam elements and a plurality of connection elements 102. In certain embodiments, said adjacent resonating beam elements are mechanically connected to each other by connection elements 102. In certain embodiments, the resonating beam elements are connected to each other (one another) by (at least) two connection elements 102. In certain embodiments, each resonating beam element is connected to another resonating beam element by (at least) two connection elements 102. In certain embodiments, the adjacent resonating beam elements are separated by trenches 104. In certain embodiments, the trenches 104 have a length TL (trench length). In certain embodiments, the length L of the beam element comprises at least the length of the trench TL and the length of at least one connection element 102.

[0085] In certain preferred embodiments, the resonating element 101 is a stacked beam resonating element comprising a plurality of resonating beam elements positioned side-by-side in a plane, separated by trenches 104 and connected by (at least two, or two) connection elements 102. In at least some stacked beam resonating elements, the resonating beam elements are positioned in the same plane. In certain stacked beam resonating elements, no two resonating beam elements are positioned atop each other.

[0086] In certain embodiments, the resonating elements 101 of the resonator 100 are arranged in a rectangular array configuration. In certain embodiments, the resonating element 101 has a length L (which is equal to the length of the beam element). In certain embodiments, the resonating element 101 has a width RW (resonating element width).

[0087] In certain embodiments, the resonating element 101 is attached to a support structure (not shown in Fig. 1). In certain embodiments, the resonating element 101 is attached to the support structure 110 from the outermost resonating beam elements of the resonating element 101 by anchoring point(s) 103. In certain embodiments, the resonator 100 comprises electrical terminal(s) at anchoring points 103. In certain embodiments, the resonating element(s) 101 is separated from the support structure 110 by (an external) trench 104’.

[0088] In certain embodiments, the resonating element 101 is of an elongated shape (having the length L smaller than their width RW). In certain embodiments, the resonating element 101 is in the shape of a rectangle (the resonating element 101 has a shape of a rectangle). In certain embodiments, the resonating element 101 has an aspect ratio (ratio of length L to width RW, when observed from above) different from 1. In certain embodiments, the resonating element 101 has a length-to-width, L-to-RW, aspect ratio of less than 1.

[0089] In certain embodiments, the resonating beam elements are of an elongated shape (having their length L larger than their width W). In certain embodiments, each resonating beam element is in the shape of a rectangular beam (beam-shaped). In certain embodiments, each resonating beam element has an aspect ratio (ratio of length L to width W, when observed from above) different from 1. In certain embodiments, each resonating beam element has a length-to-width, L-to-W, aspect ratio of more than 1. In certain example embodiments, each resonating beam element has a length-to-width, L-to-W, aspect ratio of more than 2, such as 5, 8, or 10.

[0090] In certain embodiments, each beam element is a resonating beam element. In certain embodiments, the resonating element is configured to resonate in a desired (main) resonance mode. In certain embodiments, the desired resonance mode is a collective resonance mode. In certain embodiments, each beam element of the resonating element 101 is configured to resonate in the same resonance mode.

[0091] In certain embodiments, the resonator 100 (the resonating element 101) is configured to operate in an in-plane length extensional, LE, resonance mode. In certain embodiments, the in-plane length extensional resonance mode is a main resonance mode of the resonating element 101. In certain embodiments, the beam elements of the resonating element 101 are configured to operate in an in-plane length extensional resonance mode. The beam elements (and thus the whole resonating element 101) oscillate in the LE-mode in the direction of the y-axis (in the direction of the length L direction, parallel to the longitudinal direction).

[0092] Typically, resonating element(s) 101 are configured to operate (resonate, vibrate, oscillate) in a desired (collective) main resonance mode. In certain occasions, the resonating element 101 adopts another, unwanted, spurious resonance mode. This unwanted spurious resonance mode typically comprises a lower ESR than the desired main resonance mode. Therefore, the unwanted spurious resonance mode typically dissipates less energy than the desired main resonance mode, making it eventually a dominant resonance mode for selfsustained oscillation. The performance of the resonator 100 is adversely affected by such unwanted, spurious resonance mode(s). In certain embodiments, the spurious resonance mode is a resonance mode other than the desired main resonance mode. In certain embodiments, the resonating element 101 comprises (resonates in) a spurious resonance mode (in addition to the main resonance mode).

[0093] Fig. 1 shows an area A of the resonating element 101 marked with a dashed line. The area A denotes the location of the highest strain of the possible spurious resonance mode(s) of the resonating element 101 , when the main resonance mode is the in-plane lengthextensional, LE, resonance mode. The same area A is also the area having the highest charge collection of the spurious resonance mode within the resonating element 101. As shown in Fig. 1 , said area A is (arranged, located) at the center of the resonating element 101. Said area A is located along (parallel with) the width (W) direction of the resonating beam elements (also along the resonating element width RW). Said area A is arranged length-wise (L) centered within the resonating element 101. This area A is referred to again and elaborated further later in context of Fig. 3a.

[0094] Fig. 2 schematically shows a cross-section of the material stack of a resonator 100 according to an example embodiment. Fig. 2 schematically shows an example cross section (sectional view, side view) of the resonator 100 residing on a substrate 450.

[0095] In certain embodiments, the resonator 100 is fabricated on a substrate. In the example embodiment of Fig. 2, a silicon on insulator (SOI) substrate (wafer) 450 is used. The reference numerals 401 and 402 denote bottom electrode and top electrode contacts, respectively. The reference numeral 101 denotes the location of the resonating element 101.

[0096] In certain embodiments, the resonator 100 (and the resonating element 101) comprises a material stack, the material stack comprising at least the silicon layer L4, the piezoelectric layer L2 on top of the silicon layer, and a top electrode L1 on top of the piezoelectric layer. In certain embodiments, the piezoelectric layer comprises doping, such as scandium doping.

[0097] In the example embodiment shown in Fig. 2, the top electrode is implemented in layer L1. In this example embodiment, layer L2 is a piezoelectric layer for piezoelectric actuation of the resonator. An opening in L2 is denoted by 420. In this example embodiments, layer L3 denotes a layer for the bottom electrode. In this example embodiment, layer L4 is a silicon layer for the resonator (for example resonating beam elements and their connecting elements according to certain embodiments). In this example embodiments, layer L5 is a buried oxide layer (SiO2) of the SOI wafer, and layer L6 is a silicon handle layer. In certain embodiments layer L6 comprises a cavity C1. In certain embodiments, the layer L5 follows the cavity C1 shape as shown in Fig. 2.

[0098] In certain embodiments, when a doped silicon layer is used as L4, it is possible to leave out the separate L3 bottom electrode. In such embodiments, the conductive doped silicon layer L4 acts as the bottom electrode. In certain embodiments, the silicon layer L4 comprises degenerately doped silicon. In certain embodiments, more than 50 % of the silicon layer L4 mass consists of degenerately doped silicon. In certain embodiments, the silicon layer L4 is doped to an average impurity concentration of at least 2*1019cm-3, such as at least 102° cm-3. In certain embodiments, the doped silicon is of N-type or P-type doping. In certain embodiments, the bottom electrode comprises ultra-heavily doped, UHD, silicon.

[0099] In certain embodiments, the silicon layer L4 comprises single crystalline silicon. In certain embodiments, the silicon layer L4 consists essentially of single crystalline silicon. In certain embodiments, the silicon layer L4 comprises degenerately doped single crystalline silicon.

[0100] In certain preferred embodiments, the resonator 100 comprises a material stack, the material stack comprising the silicon layer L4 (the bottom electrode), the piezoelectric layer L2 on top of the silicon layer L4, and a top electrode L1 on top of the piezoelectric layer L1. In certain embodiments, the resonator 100 is a piezoelectric resonator. In certain embodiments, the piezoelectric layer L2 comprises aluminum nitride.

[0101] In certain embodiments, the longitudinal axis L of a resonating element 101 (the resonating beam elements) is aligned with <100> crystal direction of the silicon (of the bottom electrode), such as aligned with

[0100] crystal direction of silicon (of the bottom electrode), or deviates less than 25 degrees therefrom, or less than 15 degrees therefrom in certain embodiments. In certain preferable embodiments, the longitudinal axis L of the resonating element (the resonating beam elements) 101 is aligned with <100> crystal direction of the silicon (of the bottom electrode), such as aligned with

[0100] crystal direction of the silicon (of the bottom electrode), or deviates less than 5 degrees therefrom, or less than 2 degrees therefrom in certain embodiments.

[0102] Fig. 3a schematically shows a top view of a resonating element 101 comprising cuts 201 where top electrode is absent according to an example embodiment. In certain embodiments, the cuts 201 where the top electrode layer is absent are arranged at the resonating beam elements. Accordingly, a part of the top electrode material is removed from the resonating beam elements.

[0103] As shown in Fig. 3a, in certain embodiments, the cuts where the top electrode layer is absent run parallel with the length L of the resonating beam element (directions shown in Fig. 1). As shown in Fig. 3a, in certain embodiments, the cuts 201 where the top electrode layer is absent are width Wwise centrally arranged within each resonating beam element. As shown in Fig. 3a, the top electrode material is removed from the beam element middles (middle regions, middle parts). In certain embodiments, said ‘middle’ is relative to the main resonance direction of the resonating element. In certain preferred embodiments, the main resonance mode is an in-plane length-extensional, LE, resonance mode. In certain embodiments, the spurious resonance mode is an out-of-plane flexural resonance mode and / or an in-plane width-extensional, WE, resonance mode.

[0104] In certain embodiments, as shown in Fig. 3a, the resonating element 101 (the top electrode thereof) comprises a plurality of cuts 201 that extend from one edge of the resonating element 101 to another edge of the resonating element 101. In certain embodiments, such as shown here, the cuts 201 run parallel to the (main, LE) resonance mode of the resonating element 201.

[0105] As shown herein, in certain embodiments, the resonating element 101 has two short(er) parallel sides and two long(er) parallel sides, thereby forming a rectangular shape. In certain embodiments, the rectangular resonating element 101 comprises a plurality of cuts running from one parallel side to(wards) another parallel side. In Fig. 3a, the cuts run from one long side towards another long side.

[0106] In certain embodiment, the resonating element 101 comprises cuts only in the area of highest strain and / or highest charge collection of the spurious resonance mode of the resonating element. In certain embodiments, the resonating element comprises no cuts elsewhere in the resonating element 101.

[0107] Referring back to Fig. 1 , which shows area A, wherein the resonating element has its highest strain and highest charge collection of the spurious resonance mode. Said highest charge collection is used to refer to an area having the maximum amount of collected charge. As shown in Fig. 3a, in certain embodiments, the cuts 201 where the top electrode layer is absent are arranged at an area of the resonating element having its highest strain and highest charge collection.

[0108] By arranging cuts 201 into such locations, the cuts 201 enable electrically suppressing said spurious resonance modes, but do not adversely affect (or ruin) the main resonance mode in accordance with certain embodiments. By way of an example, the spurious out-of-plane flexural resonance mode and the in-plane width-extensional, WE, resonance mode have the area of the highest strain and highest charge collection in the same location, i.e. in the beam element middle area. Accordingly, the cuts 201 in the beam element middle area enable suppressing both mentioned spurious resonance modes simultaneously. In accordance with certain embodiments, the cuts 201 are used to suppress higher frequency spurious resonance modes in resonators.

[0109] Accordingly, herein is provided a resonator 100, comprising a resonating element 101 having a top electrode layer, wherein the resonating element comprises cut(s) where the top electrode layer is absent to provide electrical suppression for a spurious resonance mode of the resonating element 101. In accordance with certain embodiments, the electrical suppression as used herein is used to refer to that the top electrode layer is omitted in region(s) where the spurious resonance mode(s) (even though the resonating element 101 would resonate in said mode(s)) would generate charges. This provides for electrical suppression for said spurious resonance mode(s).

[0110] Accordingly, in certain embodiments, the resonator 100 comprises spurious resonance mode(s) (one or more spurious modes are present), but these spurious resonance mode(s) are less harmful due to them not generating charges. Thus, it is preferred in certain embodiments to arrange the cut(s) where the top electrode layer is absent at areas of the resonating element having highest charge collection of the spurious resonance mode.

[0111] In accordance with certain embodiments, the resonating element 101 comprises means for suppressing the spurious resonance mode(s) by changing the electrical properties of the resonating element 101. In certain embodiments, said changing of electrical properties refers to electrically disengaging an area(s) of the resonating element 101 by omitting the top electrode therein (these area(s) would generate charge(s) of the spurious resonance mode(s)).

[0112] In certain preferred embodiments, as shown in Fig. 3a, the resonating element 101 comprises a plurality of resonating beam elements having a length L and a width W, the plurality of beam elements being positioned adjacent to each other, wherein the adjacent beam elements are mechanically connected to each other by connection elements 102.

[0113] Fig. 3a further shows a location C, which marks the location of the cross-section shown in the Fig. 3e.

[0114] Fig. 3b schematically shows a top view of a resonating element 101 comprising cuts 201 where top electrode is absent forming isolated areas of the top electrode material according to an example embodiment. In certain embodiments, the cuts 201 where the top electrode layer is absent form rectangular isolated regions of the top electrode material within the top electrode layer. The term ‘isolated’ refers to said region being disconnected from the remaining top electrode layer, as shown in Fig. 3b. In accordance with certain embodiments, the charge carriers (electrical current) cannot access the isolated area formed by said cuts 201.

[0115] In certain embodiments, the cuts have a length matching the trench 104 length. In certain embodiments, the cuts have a width in a range of 1 pm to 15 pm, such as 2 pm to 10 pm, preferably in a range of 3 pm to 8 pm.

[0116] Fig. 3c schematically shows a top view of a resonating element 101 comprising more than one cut per resonating beam element according to an example embodiment. As shown in Fig. 3c, in certain embodiments, each resonating beam element comprises a plurality of cuts 201. In certain alternative embodiments, such as shown in Fig. 3a, each resonating beam element comprises one cut 201 .

[0117] In certain embodiments, the top electrode layer is removed from the beam element end regions, but middle region of each beam element contains the top electrode material (as usual). This enables assisting the main length-extensional resonance mode in its resonance.

[0118] Fig. 3d schematically shows a top view of a resonating element 101 comprising more than one cut per resonating beam element, wherein the cuts 201 where top electrode is absent form isolated areas of the top electrode material in accordance with certain embodiments. As can be seen from Fig. 3d, it presents a combination of embodiments shown in Figs. 3b and 3c. Therefore, what is disclosed concerning the cut(s) in the context of Figs. 3b and 3c, apply herein as well.

[0119] According to certain embodiments, as shown in Fig. 3d, the resonating element 101 comprises cuts 201 where top electrode is absent forming rectangular isolated areas of the top electrode material. The term ‘isolated’ refers to said region being disconnected from the remaining top electrode layer. In accordance with certain embodiments, the charge carriers (electrical current) cannot access the isolated area formed by said cuts 201. In accordance with certain embodiments, as shown in Fig. 3d, each resonating beam element comprises a plurality of the cuts 201 forming said isolated areas. Fig. 3e schematically shows a cross-section C of one resonating beam element according to an example embodiment. The location of the cross-section C is shown in Fig. 3a as line C.

[0120] In certain embodiments, cuts 201 reach through the top electrode layer L1 to layer beneath the top electrode layer L1 , such as to the piezoelectric layer L2. Accordingly, in certain embodiments, the cuts 201 are configured to expose the layer L2 beneath the top electrode layer L1 (when observing from above). In certain embodiments, the cuts 201 are of same thickness (in z-direction) as the top electrode layer L1. In certain embodiments, the cuts 201 have a thickness (in z-direction) in the range of 100 nm to 1 pm, such as in the range of 150 nm to 500 nm, preferably in the range of 200 to 400 nm.

[0121] Figs. 4 schematically shows a resonator 100 comprising a plurality of resonating elements 101 in accordance with certain embodiments. In certain embodiments, the resonator 100 comprises (at least) two resonating elements 101a, 101b (stacked beam resonating elements). All embodiments described in context of a single resonating element 101 apply herein as well for the plurality of resonating elements 101 of the resonator 100 as shown herein. Accordingly, the resonating elements 101a, 101 b comprise a top electrode layer having cuts, the cuts having the top electrode layer removed within the area of said cut.

[0122] In certain embodiments, such as shown in Fig. 4, the resonator 100 comprises a mechanically coupled assembly with multiple ‘ladders’ 101 to achieve higher resonator area and improved quality factor (Q). In certain embodiments, the resonator is a multi-ladder resonator 100, comprising a plurality of stacked resonating elements 101a, 101b. In certain embodiments, the resonating elements 101a, 101b comprise a plurality of resonating beam elements positioned adjacent to each other and adjacent beam elements are mechanically connected to each other by connection elements 102, and the resonating beam elements are separated from each other by trenches 104 (forming a ladder-like configuration). In certain embodiments, the resonator 100 is separated from a support structure by an external trench 104’. In certain embodiments, the resonator 100 is coupled to (suspended from) a support structure via anchoring point(s) 103.

[0123] In certain embodiments, the resonator 100 comprises a mechanical coupler 310 which connects the resonating elements 101a, 101 b to one another. The embodiment of Fig. 4 shows a flexural mode coupler 310. Other alternatives for the coupler include, but are not limited to rigid coupler 310, such as a beam coupler, length extensional, LE, coupler 310, and Lame mode coupler 310 (not shown). Accordingly, in certain embodiments, the resonator 100 comprises (at least) two extensional-mode resonating elements 101a, 101b, and a (one or more) flexural mode coupler 310. Further, the resonator assembly comprises a (one or more) mechanical connector element 320 which connects the flexural coupler 310 to the extensional mode resonating elements 101a, 101b. In certain embodiments, at least one of the extensionalmode resonating elements 101a / 101b of the resonator 100 comprises a piezoelectric thin- film actuator for exciting the said extensional-mode resonating element 101a / 101b to a resonance mode and thereby the whole resonator 100 to a collective resonance due to mechanical coupling of the extensional-mode resonating elements 101a, 101 b. In certain alternative embodiments, the resonator 100 comprises an electrostatic actuator for exciting at least one of the extensional-mode resonating elements 101a / 101 b to a resonance mode and thereby the whole resonator 100 to a collective resonance due to mechanical coupling of the extensional-mode resonating elements 101a / 101b.

[0124] In certain embodiments, more than 50% of the mass of the resonator 100 comprise material portions of single-crystalline silicon. In certain embodiments, the coupler 310 comprises discontinuity regions (not shown). In certain embodiments, the discontinuity regions of the coupler 310 render the coupler 310 electrically inert.

[0125] In certain embodiments, (all) the resonating elements 101a, 101b of a resonator 100 are identical with one another (each other). In certain embodiments, (all, some of) the resonating elements 101a, 101b of a resonator assembly are different from one another.

[0126] In certain embodiments, the resonating beam elements of the resonating elements 101a, 101 b comprise beam width gradation. As used herein, the term beam width gradation refers to how the beam widths differ from one another within the resonating element.

[0127] As stated above, in certain embodiments, the resonator 100 is configured to electrically and mechanically suppress / alleviate spurious resonance mode of the resonating element(s) 101a, 101 b. In certain embodiments, the resonator 100 is configured to electrically suppress and mechanically alleviate spurious resonance mode of the resonating element(s) 101a, 101 b by providing top electrode cuts, the cuts having the top electrode layer removed within the area of said cut, and optionally varying the width of the beam elements (asymmetrically) within the resonating element, respectively. In certain embodiments, said width variation as used herein refers to the beam width gradation, meaning that the width of one beam element differs from the width of another beam element of the resonating element. In certain embodiments, the resonating element is configured to suppress electrically the spurious resonance mode by providing said top electrode cuts to the resonating beam elements of the resonating element, where the top electrode is absent in the area of said cuts. In certain embodiments, the resonating element is configured to alleviate mechanically the spurious resonance mode by modifying (splitting, dividing, adjusting, separating) said spurious resonance mode of the resonating element into (several) non-harmful resonance mode(s) by varying the width of the beam elements of the resonating element.

[0128] Without limiting the scope and the interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is providing a good resonator product over a wide frequency range, with no harmful disturbance caused by a spurious resonance mode. A technical effect is prevention and / or suppression of a spurious resonance mode from becoming a collective resonance mode. A further technical effect is avoiding harmful ‘locking’ of resonance mode (oscillations are self-sustained for this resonance mode) of a resonating element to a spurious resonance mode instead of the main resonance mode. A further technical effect is avoiding the spurious resonance mode from becoming a dominant resonance mode for self-sustained oscillation.

[0129] A further technical effect is leaving the main resonance mode (in certain embodiments, the in-plane length extensional resonance mode) intact in terms of performance, as well as providing a resonating element with stable high performance.

[0130] The spurious resonance mode is an unwanted resonance mode (other than the desired main resonance mode). Figs. 5a and 5b schematically show examples of spurious resonance modes of a resonating element having no spurious resonance mode suppressing cuts. In this resonating element, the main resonance mode is an in-plane length extensional resonance mode. Fig. 5a schematically shows a spurious resonance mode from a top view. In the example embodiment shown in Fig. 5a, the spurious resonance mode is a width-extensional, WE, resonance mode, in particular an in-plane widthextensional resonance mode. In this example spurious resonance mode, the displacement occurs in-plane, but in width direction instead of the desired length direction.

[0131] Fig. 5b schematically shows a spurious resonance mode from a side view. In the example embodiments shown in Fig. 5b, the spurious resonance mode is a flexural resonance mode, in particular an out of plane flexural resonance mode. In this example spurious resonance mode, the displacement occurs out of plane, instead of the desired length direction. In this example, the spurious resonance mode is beam-width directional flexural mode, BW-flex, mode. In accordance with certain embodiments, the cut(s) where the top electrode layer is absent are configured to suppress both WE and BW-flex spurious modes.

[0132] In certain alternative embodiments (not shown), the spurious mode is a differential resonance mode, such as an in-plane differential length-extensional resonance mode.

[0133] Various embodiments have been presented. It should be appreciated that in this document, words comprise, include, and contain are each used as open-ended expressions with no intended exclusivity.

[0134] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

[0135] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1 . A resonator (100), comprising a resonating element (101) having a top electrode layer (L1), and wherein the resonating element (101) comprises cut(s) (201) where the top electrode layer (L1) is absent to electrically suppress a spurious resonance mode of the resonating element (101).

2. The resonator (100) of claim 1 , wherein the cut(s) (201) where the top electrode layer (L1) is absent are located at an area having highest charge collection of the spurious resonance mode of the resonating element (101).

3. The resonator (100) of claim 1 or 2, wherein the cut(s) where the top electrode layer (L1) is absent are located at an area of the highest strain of the spurious resonance mode of the resonating element (101).

4. The resonator (100) of any preceding claim, wherein the resonating element (101) is configured to resonate in an in-plane length-extensional, LE, main resonance mode.

5. The resonator (100) of any preceding claim, wherein the resonating element (101) comprises an in-plane width-extensional, WE, spurious resonance mode and / or an out-of- plane flexural spurious resonance mode.

6. The resonator of any preceding claim, wherein the resonating element (101) comprises a plurality of resonating beam elements (101) having a length (L) and a width (W), the plurality of beam elements (101) being positioned adjacent to each other, wherein the adjacent beam elements are mechanically connected to each other by connection elements (102).

7. The resonator (100) of claim 6, wherein the resonating beam elements are longitudinally aligned within 25 degrees of a <100> crystal direction of silicon.

8. The resonator (100) of claim 6 or 7, wherein the cut(s) (201) where the top electrode layer (L1) is absent are parallel with the length (L) of the resonating beam element.

9. The resonator (100 of claim 6, 7 or 8, wherein the cut(s) (201) where the top electrode layer (L1) is absent are width (W) wise centred within the resonating beam element.

10. The resonator (100) of any preceding claim, wherein the cut(s) (201) where the top electrode layer (L1) is absent form an isolated region of the top electrode material within the top electrode layer (L1).

11. The resonator (100) of any preceding claim, wherein the resonating element (101) comprises a piezoelectric layer (L2), and a bottom electrode (L4), wherein the piezoelectric layer (L2) is the layer beneath the top electrode layer (L1), and the bottom electrode (L4) on the opposite side of the piezoelectric layer (L2) than the top electrode layer (L1).

12. The resonator (100) of claim 11 , wherein the bottom electrode (L4) comprises silicon, preferably doped silicon, such as ultra-heavily doped, UHD, silicon.

13. The resonator (100) of any preceding claim, wherein the top electrode layer (L1) comprises metal, preferably gold.

14. The resonator (100) of any of the preceding claim, wherein the resonator (100) is a microelectromechanical systems, MEMS, resonator.

15. An apparatus, such as a resonator array, comprising at least one resonator (100) according to any of claims 1-14.

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