Electrode configuration for reduced stiffness of MEMS resonator

Abstract

Herein is provided a resonator (100), comprising a resonating element (101) having a top electrode, wherein the top electrode comprises a patterned portion (202) to reduce the stiffness of the top electrode Herein is further provided an apparatus comprising at least one resonator (100).

Description

[0001] ELECTRODE CONFIGURATION

[0002] TECHNICAL FIELD

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

[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. The minimization of ESR is often desirable. Another key performance parameter in MEMS resonators is the stability of the resonance frequency. In certain resonators, especially resonators constructed of dissimilar layers, such as resonators with metallic electrodes, the instability of the metallic layer may lead to frequency instability.

[0007] SUMMARY

[0008] 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 improve frequency stability of MEMS resonators or at least to provide an alternative to existing technology. Accordingly, certain disclosed embodiments provide for an ingenious resonator and apparatus solving at least one of the problems related to the prior art.

[0009] According to a first example aspect of the present disclosure there is provided a resonator, comprising a resonating element having a top electrode, wherein the top electrode comprises a patterned portion to reduce the stiffness of the top electrode.

[0010] In certain embodiments, the resonating element comprises a patterned portion in the top electrode thereof. In certain embodiments, the top electrode comprises a patterned portion therein. In certain embodiments, the top electrode comprises a patterned portion within. In certain embodiments, the top electrode comprises a patterned portion within the top electrode (layer).

[0011] In certain embodiments, the top electrode is in a form of a top electrode layer. In certain embodiments, the top electrode is in a form of a top electrode layer, said layer comprising (containing) a patterned portion. In certain embodiments, the top electrode layer comprises (contains, has) a patterned portion having patterns. In certain embodiments, the top electrode layer comprises (contains, has) a patterned portion having patterns where the top electrode layer (material) is absent.

[0012] In certain embodiments, the top electrode comprises a patterned portion to render the top electrode (spring) soft. In certain embodiments, the patterned portion provides stiffness relaxation of the top electrode. In certain embodiments, the patterned portion is configured to render the top electrode release any stress therein. In certain embodiments, the patterned portion comprises patterns (areas) wherein the top electrode layer is removed. In certain embodiments, the top electrode layer is removed in the patterns (of the patterned portion). In certain embodiments, the patterned portion comprises shapes wherein the top electrode layer is removed.

[0013] In certain embodiments, the resonating element comprises a top electrode (layer) on (top of, the surface of) the resonating element. In certain embodiments, the resonating element comprises a single top electrode on the resonating element. In certain embodiments, the top electrode is configured to cover essentially the entire resonating element. In certain embodiments, the top electrode comprises patterns. In certain embodiments, the top electrode is a patterned top electrode.In certain embodiments, the top electrode comprises a plurality of patterns. In certain embodiments, the top electrode comprises patterned portions. What is herein disclosed for patterned portions applies equally to a (single) patterned portion.

[0014] In certain embodiments, the patterned portions are formed of patterns. In certain embodiments, the patterned portions are formed of (further) line(s), perforation (s) or both. In certain embodiments, the patterned portions are formed of shape(s) (forms, conformations, figures, paths). In certain embodiments, the patterned portions are configured to reduce the mass of the top electrode. In certain embodiments, the patterned portions are configured to reduce the mass of the top electrode, wherein at least 5% of the top electrode has been removed by patterned portion within the resonating element. In certain embodiments, the patterned portions are formed by removing (by patterning and etching) parts of the the top electrode layer.

[0015] In certain embodiments, the patterned portions are configured to provide a pathway to charge carriers (current, electrical carriers, electricity). In certain embodiments, the pathway comprises obstacles to charge carriers (by further line(s), perforation (s) or both). In certain embodiments, the patterns of the patterned portions are the obstacles for the charge carriers. In certain embodiments, the patterned portions comprise a meandering pathway to charge carriers. In certain embodiments, the patterned portions comprise a maze (labyrinth) pathway to charge carriers.

[0016] In certain embodiments, the patterned portions comprise a meandering pathway to render the top electrode soft (reduce its stiffness, reduce its spring effect). In certain embodiments, the patterned portions comprise a meandering pathway for the charge carriers whilst rendering the top electrode soft (reduce its stiffness, reduce its spring effect).

[0017] In certain embodiments, the patterns of the patterned portions are longitudinally noncentred along the resonating element (patterns are in peripheral areas of the resonating elements). In certain embodiments, the patterns of the patterned portions are longitudinally centred along the resonating element.

[0018] In certain embodiments, there is provided a resonator, comprising a resonating element having a top electrode, wherein the top electrode comprises a cutting line through the top electrode, and patterned portions separated by the cutting line.

[0019] In certain embodiments, the patterns of the patterned portions are symmetrically arranged on each side of the cutting line. In certain embodiments, the patterns of the patternedportions are asymmetrically arranged on the top electrode of the resonating element on each side of the cutting line.

[0020] In certain embodiments, the top electrode comprises a cutting line (cut, line, groove, slit) through the top electrode. In certain embodiments, the top electrode comprises a cutting line through the resonating element. In certain embodiments, the cutting line is configured to split the top electrode. In certain embodiments, the top electrode comprises the cutting line splitting the top electrode. In certain embodiments, the top electrode comprises the cutting line going through the (entire) top electrode.

[0021] In certain embodiments, the cutting line is configured to split the top electrode into two portions (parts) of the top electrode. In certain embodiments, the cutting line is configured to split the top electrode into two (essentially) equal-sized portions of the top electrode. In certain embodiments, the top electrode comprises a cutting line that splits the top electrode into two parts (in half).

[0022] In certain embodiments, the two portions of the top electrode are not separate electrodes. In certain embodiments, the two portions of the top electrode are electrode portions of the (one, single) same top electrode. In certain embodiments, the two portions of the top electrode are same phase electrode portions (non anti-phase). In certain embodiments, the two portions of the top electrode share the same polarity. In certain embodiments, the two portions of the top electrode are connected to the same terminal. In certain embodiments, the two portions of the top electrode are connected to the same terminal by an anchor (anchoring point).

[0023] In certain embodiments, the top electrode comprises a planar cutting line through the top electrode. In certain embodiments, the top electrode comprises the cutting line through the top electrode in any horizontal plane. In certain embodiments, the top electrode comprises the cutting line through the top electrode in any width direction across the resonating element when observed from above.

[0024] In certain embodiments, the top electrode comprises the cutting line through the top electrode in an x-direction. In certain embodiments, the top electrode comprises the cutting line through the top electrode in an x-direction, or deviates at most 45 degrees from the x-direction. In certain embodiments, the top electrode comprises the cutting line throughout the top electrode in an x-direction, or deviates at most 45 degrees from the x-direction. In certain embodiments, the top electrode comprises the cutting line through(out) the top electrode in (parallel to) a width direction of a resonating element (when observed fromabove). In certain embodiments, the top electrode comprises the cutting line through the top electrode in a direction perpendicular to the length direction of a resonating element (when observed from above).

[0025] In certain embodiments, the top electrode comprises a cutting line through the resonating element from one side to the other (from one side of the resonating element to the other side of the resonating element). In certain embodiments, the top electrode comprises a cutting line through the resonating element from one trench to the other (from a trench on a one side of the resonating element to the trench on the other side of the resonating element).

[0026] In certain embodiments, the top electrode comprises the cutting line through the top electrode in a centre (in a central area, in centremost area) of the resonating element. In certain embodiments, the top electrode comprises the cutting line through the top electrode in a width direction of a resonating element in the centre (lengthwise) of the resonating element.

[0027] In certain embodiments, the top electrode comprises the cutting line through the top electrode when observed from side. In certain embodiments, the top electrode comprises the cutting line through the top electrode in z-direction. In certain embodiments, the cutting line is of same depth as the top electrode thickness.

[0028] In certain embodiments, the cutting line is configured to expose the layer(s) beneath the top electrode. In certain embodiments, the cutting line is configured to expose the piezoelectric layer beneath the top electrode. In certain embodiments, the cutting line continues through at least the top electrode layer to the piezoelectric layer. In certain embodiments, the cutting line is configured to reach (extend) to the layer(s) beneath the top electrode. In certain embodiments, the cutting line is (at least partially) embedded into the layer(s) beneath the top electrode. In certain embodiments, the cutting line is embedded (immersed) into the piezoelectric layer.

[0029] In certain embodiments, the top electrode comprises the cutting line throughout the entire top electrode (in x-direction (or deviating at most 45 degrees from the x-direction) and in z-direction) such that the cutting line prevents charge carriers from crossing the cutting line. In certain embodiments, the top electrode comprises at least two patterned portions. In certain embodiments, the top electrode comprises at least two patterned portions separated by the cutting line (one on each side).In certain embodiments, the top electrode comprises the patterned portions on both sides of the cutting line. In certain embodiments, the charge carriers are configured to travel (move) on one side of the cutting line different route than on the other side of the cutting line. In certain embodiments, the charge carriers are configured to travel on one side of the cutting line in the first patterned portion and on the other side of the cutting line in the second patterned portion.

[0030] In certain embodiments, the patterns of the patterned portions continue through the top electrode layer. In certain embodiments, the patterns of the patterned portions continue through the top electrode layer to the piezoelectric layer. In certain embodiments, the patterned portions are configured to expose the layer(s) beneath the top electrode. In certain embodiments, the patterned portions are configured to expose the piezoelectric layer beneath the top electrode. In certain embodiments, the patterned portions are configured to reach (extend, protrude, diffuse) to (into) the layer(s) beneath the top electrode. In certain embodiments, the patterned portions are (at least partially) embedded into the layer(s) beneath the top electrode. In certain embodiments, the patterned portion is embedded (immersed) into the piezoelectric layer. In certain embodiments, the patterned portion are embedded (immersed) into the piezoelectric layer.

[0031] In certain embodiments, the pattern (of the patterned portion) is a region (area) where the top electrode (material, layer) is removed. In certain embodiments, the pattern (of the patterned portion) is a region (area) where the top electrode (material, layer) is absent. In certain embodiments, the (each) pattern (of the patterned portion) is surrounded by the top electrode layer (material) and / or by a trench. In certain embodiments, the (each) pattern (of the patterned portion) is surrounded by the top electrode material on each side, or on most sides. In certain embodiments, the pattern begins from a trench (is arranged next to a trench). In certain embodiments, the (each) pattern (of the patterned portion) is surrounded by a trench on one or mode sides (and the remaining is surrounded by the top electrode material).

[0032] In certain embodiments, the top electrode layer is a uniform layer (of material) except that the top electrode layer comprises (contains, has) a patterned portion. In certain embodiments, the top electrode layer is otherwise uniform material layer but it contains patterns where the top electrode (material) is absent. In certain embodiments, the top electrode layer covers (essentially) the entire (top, topmost) surface of the resonating element (except that the top electrode layer comprises (contains, has) a patterned portion).In certain embodiments, the top electrode layer covers (essentially) the entire (top, topmost) surface of the resonating element (except that it contains patterns where the top electrode (material) is absent). In certain embodiments, the top electrode layer is intact (whole, unbroken) (except that the top electrode layer comprises (contains, has) a patterned portion). In certain embodiments, the top electrode layer is intact (whole, unbroken) (except that it contains patterns where the top electrode (material) is absent).

[0033] In certain embodiments, the top electrode layer comprises patterns where the top electrode (material) is absent. In certain embodiments, the top electrode layer comprises a patterned portion having patterns, said patterns are formed by patterning the top electrode layer. In certain embodiments, the top electrode layer comprises a patterned portion having patterns, and within the patterns the top electrode (material) is absent. In certain embodiments, the top electrode layer is a (uniform, intact) material layer that comprises (contains) a patterned portion where the patterns of the patterned portions contain no top electrode material.

[0034] In certain embodiments, the top electrode layer containing the patterned portion provides a pathway to the charge carriers. In certain embodiments, the top electrode layer is a (uniform, intact) material layer that comprises (contains) patterns (where the top electrode material is absent), by patterning said patterns into the top electrode layer a pathway to charge carriers is provided.

[0035] 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.

[0036] 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.

[0037] 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.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.

[0038] 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.

[0039] In certain embodiments, the resonator comprises at least one resonating element. In certain embodiments, the resonating element comprises a plurality of resonating sub-elements. In certain embodiments, the resonating element comprises a plurality of resonating subelements (such as beam elements), where each sub-element comprises patterns (patterned portion(s)).

[0040] 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 resonator. In certain embodiments, the resonator 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.

[0041] In certain embodiments, the resonator is a stacked beam resonator. In certain embodiments, the stacked beam resonator 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.

[0042] In certain embodiments, the resonator 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 connection elements. In certain embodiments, the beam elements of the resonator are arranged in a rectangular array configuration.In certain embodiments, the resonator is in a shape of a rectangle. In certain embodiments, the resonator is in a shape of an elongated rectangle (beam-shaped). In certain embodiments, the resonator has an aspect ratio (ratio of length to width, when observed from above) different from 1.

[0043] In certain embodiments, the resonator has a length-to-width aspect ratio of less than 1. In certain embodiments, the resonator is attached (supported, anchored, suspended) to a support structure. In certain embodiments, the resonator is attached to a support structure from the outermost beam elements of the resonator. In certain embodiments, the resonator comprises at least one anchor configured to connect the resonator to, and suspend the resonator from surrounding layers. In certain embodiments the at least one anchor comprises portions of the piezoelectric layer, the top electrode and the bottom electrode.

[0044] 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.

[0045] 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. 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).

[0046] 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).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).

[0047] 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).

[0048] 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).

[0049] In certain embodiments, the resonator 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 length-extensional, LE, 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.

[0050] 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.

[0051] In certain embodiments, the resonator 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.

[0052] 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. According to a second example aspect of the present disclosure there is provided 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 resonators are coupled to each other by a coupler. In certain embodiments, the resonators are coupled to each other by a coupler comprising discontinuity region(s).

[0053] In certain embodiments, the apparatus is a resonator array. In certain embodiments, the apparatus is a semiconductor device, comprising at least one resonator according to the first aspect or any of its embodiments. In certain embodiments, the apparatus is an encapsulated (packaged) semiconductor device. In certain embodiments, the apparatus is a sensor device.

[0054] In certain embodiments, the apparatus comprises extensional-mode resonators. In certain embodiments, the apparatus comprises a flexural mode resonator. In certain embodiments, the apparatus comprises a mechanical connector element which connects the flexural resonator to the extensional-mode resonators.

[0055] In certain embodiments, each resonator comprises 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.

[0056] According to a third example aspect of the present disclosure there is provided is provided a method for manufacturing the resonator according to the first example aspect or any of its embodiments. In certain embodiments, the method comprises the steps of: depositing layer(s) onto a substrate; depositing a top electrode layer on the layer(s); patterning the top electrode layer to provide a patterned portion within the top electrode layer to reduce the stiffness of the top electrode.In accordance with certain embodiments, embodiments of the second or third aspect are provided, the embodiments comprising subject matter of any single embodiment presented in connection with the first aspect or the second aspect, or the embodiments comprising subject matter of any of the embodiments presented in connection with the first or second aspect combined with subject matter presented in any other embodiment or embodiments. 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.

[0057] BRIEF DESCRIPTION OF THE FIGURES

[0058] Some example embodiments will be described with reference to the accompanying figures, in which:

[0059] Fig. 1 schematically shows a top view of an example resonator demonstrating dimensions thereof according to an example embodiment;

[0060] Fig. 2a schematically shows an electrode configuration according to an example embodiment;

[0061] Fig. 2b schematically shows a cross-section of the electrode configuration according to an example embodiment;

[0062] Fig. 2c schematically shows a cross-section of the electrode configuration according to another example embodiment;

[0063] Fig. 2d schematically shows a cross-section of the electrode configuration according to yet another example embodiment

[0064] Fig. 3a schematically shows a route of current in the electrode configuration according to the example embodiment;

[0065] Fig. 3b schematically shows an electrode configuration having stress release items according to the example embodiment;

[0066] Fig. 4a schematically shows an electrode configuration according to an example embodiment;

[0067] Fig. 4b schematically shows another electrode configuration according to an example embodiment;Fig. 4c schematically shows yet another electrode configuration according to an example embodiment;

[0068] Fig. 4d schematically shows further yet another electrode configuration of a resonating element according to an example embodiment;

[0069] Fig. 5a schematically shows further aspects of an electrode configuration according to an example embodiment;

[0070] Fig. 5b schematically shows yet further aspects of an electrode configuration according to an example embodiment;

[0071] Fig. 5c schematically shows yet further aspects of an electrode configuration according to another example embodiment;

[0072] Fig. 5d schematically shows an electrode configuration having arrays of meanders according to another example embodiment;

[0073] Fig. 6a schematically shows an electrode configuration comprising perforations according to an example embodiment;

[0074] Fig. 6b schematically shows another electrode configuration comprising perforations according to an example embodiment;

[0075] Fig. 6c schematically shows yet another electrode configuration comprising perforations according to an example embodiment;

[0076] Fig. 7a schematically shows an electrode configuration for a length-extensional resonance mode according to an example embodiment;

[0077] Fig. 7b schematically shows an electrode configuration for a square-extensional resonance mode according to an example embodiment;

[0078] Fig. 7c schematically shows another electrode configuration for a square-extensional resonance mode according to an example embodiment;

[0079] Fig. 8a schematically shows an electrode configuration for a flexural resonance mode in side view according to an example embodiment;

[0080] Fig. 8b schematically shows an electrode configuration for a flexural resonance mode in top view according to an example embodiment;

[0081] Fig. 8c schematically shows an electrode configuration for a flexural resonance mode in side view according to an example embodiment;

[0082] Fig. 8d schematically shows an electrode configuration for a flexural resonance mode in side view according to an example embodiment;

[0083] Fig. 8e schematically shows an electrode configuration for a flexural resonance mode in top view according to an example embodiment;Fig. 9a schematically shows another electrode configuration for a flexural resonance mode in side view according to an example embodiment;

[0084] Fig. 9b schematically shows another electrode configuration for a flexural resonance mode in top view according to an example embodiment;

[0085] Fig. 10a schematically shows yet another electrode configuration for a flexural resonance mode in side view according to an example embodiment; Fig. 10b schematically shows yet another electrode configuration for a flexural resonance mode in top view according to an example embodiment; Fig. 11 schematically shows a material stack of a resonator according to an example embodiment;

[0086] Fig. 12 schematically shows an example of a resonator array comprising patterned portions according to an example embodiment;

[0087] Fig. 13a schematically shows a top view of a resonator according to an example embodiment;

[0088] Fig. 13b schematically shows a top view of a resonator according to another example embodiment;

[0089] Fig. 14a schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0090] Fig. 14b schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0091] Fig. 14c schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0092] Fig. 14d schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0093] Fig. 14e schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0094] Fig. 14f schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0095] Fig. 14g schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0096] Fig. 14h schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0097] Fig. 14i schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;Fig. 14j schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0098] Fig. 14k schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0099] Fig. 141 schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0100] Fig. 14m schematically shows a top view of a part of a resonator showing certain patterns according to an example embodiment;

[0101] Fig. 15a schematically shows a top view of a part of a width extensional resonator according to an example embodiment; and

[0102] Fig. 15b schematically shows a top view of a part of a width extensional resonator according to another example embodiment.

[0103] DETAILED DESCRIPTION

[0104] In the following description, like reference signs denote like elements or steps.

[0105] Fig. 1 schematically shows a top view (from above, from up to down) of an example resonator demonstrating dimensions thereof 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 plurality of resonating elements 101.

[0106] The resonator 100 according to embodiment shown in Fig. 1 comprises a plurality of resonating elements 101 having a length L and a width W. In certain embodiments, the resonating elements 101 are beam elements (beam-shaped). In the embodiment shown in Fig. 1, the resonator 100 comprises seven resonating elements 101 (the number of elements 101 may vary depending on the embodiment). In certain embodiments, the resonating elements 101 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 elements 101.

[0107] According to the example embodiment shown in Fig. 1, the plurality of resonating elements 101 are positioned adjacent to each other. In certain embodiments, the plurality of resonating beam elements 101 form a ladder-like configuration (stacked beam resonator). In certain embodiments, the plurality of resonating beam elements 101 are positionedadjacent to each other in a width direction thereof. The adjacent resonating beam elements 100 are mechanically connected to each other.

[0108] In certain embodiments, the resonator 100 is formed of the plurality of resonating elements 101 and a plurality of connection elements 102. In certain embodiments, said adjacent resonating elements 100 are mechanically connected to each other by connection elements 102. In certain embodiments, the adjacent resonating elements 101 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 101 comprises at least the length of the trench TL and the length of at least one connection element 102.

[0109] In certain preferred embodiments, the resonator 100 is a stacked beam resonator comprising a plurality of resonating beam elements 101 positioned side-by-side in a plane, separated by trenches 104 and connected by connection elements 102. In at least some stacked beam resonators, the resonating beam elements 101 are positioned in the same plane. In certain stacked beam resonators, no two resonating beam elements 101 are positioned atop each other.

[0110] In certain embodiments, the resonating elements 101 of the resonator 100 are arranged in a rectangular array configuration. In certain embodiments, the resonator has a length L (which is equal to the length of the beam element). In certain embodiments, the resonator has a width RW (resonator width).

[0111] In certain embodiments, the resonator 100 is attached to a support structure (not shown in Fig. 1). In Fig. 2, support structure is shown as numeral 110). In certain embodiments, the resonator 100 is attached to the support structure 110 from the outermost resonating elements 101 of the resonator 100 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) are separated from the support structure 110 by (an external) trench 104’.

[0112] In certain embodiments, the resonator 100 is of an elongated shape (having the length L smaller than their width RW). In certain embodiments, the resonator 100 is in the shape of a rectangle (the resonator 100 has a shape of a rectangle). In certain embodiments, the resonator 100 has an aspect ratio (ratio of length L to width RW, when observed from above) different from 1. In certain embodiments, the resonator 100 has a length-to-width, L-to-RW, aspect ratio of less than 1.In certain embodiments, the resonating beam elements 101 are of an elongated shape (having their length L larger than their width W). In certain embodiments, each resonating beam element 101 is in the shape of a rectangular beam (beam-shaped). In certain embodiments, each resonating beam element 101 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 101 has a length-to-width, L-to-W, aspect ratio of more than 1. In certain example embodiments, each resonating beam element 101 has a length-to-width, L-to-W, aspect ratio of more than 2, such as 5, 8, or 10.

[0113] Fig. 2a schematically shows an electrode configuration of a resonator 100 according to an example embodiment. The example embodiment of Fig. 2a follows the same coordinate system as shown in Fig. 1. The coordinate system is selected so that the x-axis resides in the width direction of the resonating elements 101 and the y-axis in the longitudinal direction of the resonating elements 101.

[0114] Herein is provided a resonator 100, comprising at least one resonating element 101 having a top electrode, wherein the top electrode comprises a patterned portion 202 to reduce the stiffness of the top electrode. In certain embodiments, the patterned portion 202 is configured to render the top electrode spring (very) soft and release any stress therein. In certain embodiments, the patterned portions 202 are configured to neutralize the spring effect of the top electrode. In certain embodiments, the patterned portions 202 are configured to remove (minimize, alleviate) stress related modulation of the top electrode. Accordingly, a ‘flexible’ top electrode having reduced stiffness, resulting in to reduced or minimized the frequency drift is provided.

[0115] In certain embodiments, the resonator 100 is suspended to a support structure 110 via anchoring point(s) 103.

[0116] As used herein, the term top electrode is understood as the top electrode layer, meaning that the term top electrode also comprises any patterns patterned (etched) thereto. Thus, the top electrode comprises the patterned portion 202.

[0117] In certain embodiments, the resonating element 101 comprises a single patterned top electrode on the resonating element 101 covering essentially the entire resonating element 101. In certain embodiments, the patterned top electrode comprises patterns.In certain embodiments, the patterned portions are configured to reduce the mass of the top electrode, wherein at least 5% of the top electrode has been removed by each patterned portion 202 within the resonating element 101. In certain embodiments, the resonator 100 is a megahertz frequency microelectromechanical systems, MEMS, resonator.

[0118] Figs. 2b and 2c schematically show cross-sections of the patterned portion 202 according to certain embodiments. The example embodiments of Fig. 2b and 2c follow the same coordinate system as shown in Figs. 1 and 2a. The coordinate system is selected so that the y-axis is in the longitudinal direction of the resonating elements 101 and the z-axis is in the vertical (‘height’) direction of the resonating element 101.

[0119] As shown in Fig. 2b, in certain embodiments, the top electrode L1 comprises the patterned portion 202 through the top electrode layer L1 (when observed from side). In certain embodiments, the patterned portion 202 reaches through the top electrode L1 in z-direction. In certain embodiments, the patterned portion 202 is of same depth as the top electrode L1 thickness. In certain embodiments, the patterned portion 202 is configured to expose the layer(s) L2 beneath the top electrode. In certain embodiments, the patterning of the top electrode material, such as gold, frees the top electrode surface per area. In certain embodiments, the mass removal of the top electrode material L1 prevents the piezoelectric layer L2 material being held by gold as an additional effect.

[0120] As shown in Fig. 2c, in certain embodiments, the patterned portion 202 reaches (extends, is arranged) to the piezoelectric layer L2 (when observed from side). In certain embodiments, the patterned portion 202 reaches downwards into the piezoelectric layer L2 (when observed from side).

[0121] In certain embodiments, the patterned portion 202 reaches into the piezoelectric layer in z-direction. In certain embodiments, the patterned portion 202 (the patterns are) is embedded to (into) the layer(s) beneath the top electrode. In certain embodiments, the patterned portion 202 (the patterns) of the top electrode L1 is (at least partially) embedded into the piezoelectric layer L2. In certain embodiments, the top electrode layer L1 is immersed into the layer beneath the top electrode L1 , such as into the piezoelectric layer L2.

[0122] Fig. 2d schematically shows a cross-section of downwards extending protrusions S (spikes, diffused spikes) according to an example embodiment. In certain embodiments, the top electrode layer L1 material diffuses to (into) the layer(s) beneath the top electrode L1. In certain embodiments, the top electrode layer L1 comprises downward extending(protruding) protrusions S (cones, spikes). In the embodiment shown in Fig. 2d, the downward protruding protrusions S are in form or cones, triangles, or spikes.

[0123] In accordance with certain embodiments, herein is provided a method for manufacturing the resonator (100) according to the first example aspect or any of its embodiments. In certain embodiments, the method comprises the steps of: depositing layer(s) L2 onto a substrate L4; depositing a top electrode layer L1 on the layer(s) L2; patterning the top electrode layer L1 to provide a patterned portion 202 within the top electrode layer L1 to reduce the stiffness of the top electrode L1.

[0124] In certain embodiments, such as shown in Fig. 2c, the method comprises patterning also the piezoelectric layer L2 to provide the embedded top electrode layer L1 comprising the patterned portion 202 therein. In accordance with the above, the method step of patterning the top electrode layer L21 may be omitted, if the piezoelectric layer L2 is patterned (instead). In accordance with these embodiments, the patterned portion 202 of the top electrode layer L1 is provided by depositing the top electrode layer L1 into the patterns of the piezoelectric layer L1 (or any other layer that is beneath the top electrode layer L1).

[0125] In the embodiment shown in Fig. 2d, the method comprises the steps of depositing layer(s) L2 onto the substrate L4, and depositing the top electrode layer L1 on the layer(s) L2. In accordance with certain embodiments, the method further comprises diffusing the top electrode layer L1 (material) into (inwards) the layer(s) L2. Fig. 3a schematically shows a route of current in the electrode configuration according to the example embodiment. The resonator 100 shown in Fig. 3a is a similar example resonator than as shown in the example embodiment of Fig. 2.

[0126] In certain embodiments, the cutting line 201 is configured to split the top electrode of the resonating element 101. In certain embodiments, the cutting line 201 is configured to split the top electrode into two portions of the top electrode.

[0127] It should be understood that the resonating element 101 comprises only one single patterned top electrode, and the said two portions of the top electrode are not separate electrodes. In certain embodiments, the two portions of the top electrode are same phase electrode portions. In certain embodiments, the two portions of the top electrode are connected to the same electrical terminal.In certain embodiments, the cutting line 201 is a planar groove through the top electrode in a horizontal plane. The cutting line 201 prevents charge carriers from crossing it. In certain embodiments, the cutting line 201 crosses through the resonating element 101 from one side to the other, from one trench 104 to the other.

[0128] In certain embodiments, the cutting line 201 crosses the resonating element 101 through the top electrode in any width direction when observed from above. This means that the cutting line 201 is not limited to horizontal direction (x-direction) but may be angled in relation to the horizontal direction of the resonating element 101. In certain embodiments, the cutting line 201 crosses through the top electrode in an angled x-direction, and deviates at most 45 degrees from the x-direction.

[0129] In certain embodiments, the cutting line 201 is, however, in horizontal direction. In certain embodiments, the cutting line 201 travels (is arranged) through the top electrode in the width direction of a resonating element 101. In certain embodiments, the cutting line 201 travels horizontally through the resonating element 101. In certain embodiments, the cutting line 201 crosses through the top electrode in an x-direction.

[0130] As used herein, the term horizontal refers to the direction of left to right (or right to left), when observing the resonator from above, meaning the x-direction according to the chosen coordinate system. In the example embodiments shown herein, the x-direction is equal to the width direction of the resonating element.

[0131] Analogously, as used herein, the term vertical refers to the direction of up and down (or down to up, when observing the resonator from above), meaning the y-direction according to the chosen coordinate system. In the example embodiments shown herein, the y-direction is equal to the length direction of the resonating element.

[0132] Yet analogously, as used herein, herein is also used a direction of left to right (or right to left), when observing the resonator from the side, meaning the z-direction according to the chosen coordinate system. In the example embodiments shown herein, the z-direction is referred as a “height” direction of the resonator.

[0133] In certain embodiments, the top electrode comprises the cutting line 201 through the top electrode in a lengthwise (longitudinally, in relation to longitudinal axis) central area of the resonating element 101. In certain embodiments, the top electrode comprises the cuttingline 201 through the top electrode in a lengthwise non-central area of the resonating element 101.

[0134] In certain embodiments, the top electrode comprises the cutting line 201 through the top electrode layer when observed from side. In certain embodiments, the cutting line 201 reaches through the top electrode in z-direction. In certain embodiments, the cutting line 201 is of same depth as the top electrode thickness. In certain embodiments, the cutting line 201 is configured to expose the layer(s) beneath the top electrode.

[0135] In certain embodiments, the top electrode comprises at least two patterned portions 202. In certain embodiments, the at least two patterned portions are separated by the cutting line, one patterned portion 202 being on each side of the cutting line 201 and the other patterned portion 202 being on the other side of the cutting line 201.

[0136] In certain embodiments, the patterned portions 202 and the optional the cutting line 201 are made via lithographic patterning. After lithographic patterning, relevant layer(s) are removed in successive etching process steps. In certain embodiments, the width / size / diameter of the patterns in a mask prior to etching controls the depth of the etching. In certain embodiments, the top electrode is patterned via dry etching, such as deep reactive ion etching, DRIE. In certain embodiments, the top electrode is patterned via wet etching.

[0137] In certain embodiments, the patterned portions 202 are configured to provide a pathway to charge carriers, the pathway comprising a meandering pathway for the charge carriers. Therefore, in certain embodiments, the patterned portions 202 provide a meandering pathway or a maze to charge carriers to move in. An example of a pathway of the charge carriers is shown in Fig. 3a as drawn line labeled as CURRENT.

[0138] In certain embodiments, the charge carriers are configured to move on one side of the cutting line 201 a different route in comparison to the other side of the cutting line 201.

[0139] Fig. 3b schematically shows an electrode configuration having stress release items according to the example embodiment. The resonator 100 shown in Fig. 3b is a similar example resonator than as shown in the example embodiments of Fig. 2 and Fig. 3a.

[0140] In certain embodiments, the top electrode comprises a stress release item 203. In certain embodiments, the top electrode comprises a plurality of stress release items 203 (stressrelease array). In certain embodiments, the stress relates item(s) 203 are configured to release (reduce, minimize, alleviate) stress of the top electrode. In certain embodiments, the stress release item(s) 203 are further patterns patterned onto the top electrode (in addition to the patterned portion and optionally the cutting line 201 ). In certain embodiments, the stress release item(s) 203 comprise vertical (in y-direction) cuts. In certain embodiments, the In certain embodiments, the stress release item(s) 203 comprise meanders (turns, 90 degree turns).

[0141] In certain embodiments, the stress release item(s)203 are arranged at the peripheral areas of the top electrode. In certain embodiments, the stress release item(s) are arranged at ends (end parts, peripheral parts) of the resonating beams 101 (on both ends).

[0142] Figs. 4a, 4b, 4c and 4d schematically show examples of possible electrode configurations for the patterned portions according to example embodiments, observed from above. It should be noted that the electrode configurations are not limited to the examples shown herein.

[0143] Each Fig. 4a, 4b, 4c and 4d depicts a single resonating element 101 according to example embodiments. In all embodiments shown in Figs. 4a, 4b, 4c and 4d, the top electrode comprises a cutting line 201. It should be noted that the cutting line 201 is optional and the examples shown herein are provided also in absence of the cutting line 201.

[0144] As shown in Fig. 4a, in certain embodiments, the patterned portions 202 comprise patterns in shape of further lines (grooves, cuts). In this example embodiment, the patterns (further lines) are arranged to reach approximately half of the width of each resonating element 101. In the example embodiment shown in Fig. 4a, the patterns (further lines) of the patterned portions 202 are arranged to approximately 40% of the length of the resonating element 101. In certain alternative embodiments, the patterns of the patterned portions are arranged to approximately 60%, or 80% of the length of the resonating element 101.

[0145] As shown in Fig. 4b, in certain embodiments, the top electrode comprises patterned portions 202 having patterns (further lines) the entire length of the resonating element 101. In certain embodiments, as shown in Fig. 4b, the patterns (further lines) of the patterned portions 202 are arranged to reach almost the entire width of each resonating element 101. Thereby only a minor portion of the top electrode is left to enable charge carriers to move. In certain embodiments, the patterns of the patterned portions 202 are arranged to 80%, or even 90% of the width of each resonating element 101.As shown in Figs. 4a and 4b, in certain embodiments, the patterns of the patterned portions 202 are arranged in the width direction of a resonating element 101. In certain embodiments, the patterns of the patterned portions 202 are arranged horizontally within the resonating element 101. In certain embodiments, the patterns of the patterned portions 202 are arranged within the top electrode in an x-direction.

[0146] As shown in Fig. 4c, in certain embodiments, the patterns of the patterned portions 202 are not limited to horizontal direction (x-direction) but may be angled in relation to the horizontal direction of the resonating element 101. In certain embodiments, the patterns of the patterned portions 202 are arranged in the top electrode in an angled x-direction. In certain embodiments, the patterns of the patterned portions 202 are arranged in an angled x-direction that deviates by an angle between 0-90 degrees in relation to the horizontal direction (x-direction). In certain embodiments, the patterns of the patterned portions 202 are arranged in vertical (y-direction) direction along the resonating element 101.

[0147] As shown in Figs. 4a, 4b and 4c, in certain embodiments, the patterns of the patterned portions 202 are straight, such as in shape of further lines. As shown in Fig. 4d, in certain embodiments, the patterns of the patterned portions 202 are bent. In certain embodiments, the patterns of the patterned portions 202 comprise turns (angles, bends, zig-zag) to create a maze-like pathway to the charge carriers.

[0148] In certain embodiments, the patterns of the patterned portions 202 are symmetrically (such as mirror symmetry) arranged on each side of the cutting line 201 , as shown for example in Figs. 4a and 4b. In certain alternative embodiments, the patterns of the patterned portions 202 are asymmetrically arranged on each side of the cutting line 201 , as shown e.g. in Figs.

[0149] 4c and 4d.

[0150] In certain embodiments, the patterns of the patterned portion 202 are symmetrically (such as mirror symmetry) arranged on the resonating element 101. In certain alternative embodiments, the patterns of the patterned portion 202 are asymmetrically arranged on the resonating element 101.

[0151] The resonator 100 according to certain embodiments is not limited to number, width, shape and / or angle of the patterns of the patterned portion 202. In certain embodiments, the patterns of the patterned portions 202 are of different number, width, shape and / or angle along each resonating element 101. In certain embodiments, the patterns of the patterned portions 202 are of different number, width, shape and / or angle along the resonator 100body. In certain embodiments, the patterns of the patterned portions 202 (such as meanders) are a parameter for optimization in general. In certain embodiments, the patterns of the patterned portions 202 are a parameter for optimization for the resonator 100 design. In certain embodiments, the design of the patterns of the patterned portions 202 enable tuneability of the resonator 100.

[0152] Further parameters for optimization of the resonator 100 according to certain embodiments include but are not limited to material variations of the resonator 100. By way of an example, in certain embodiments, the top electrode is of metal, such as gold, or doped gold.

[0153] Figs. 5a, 5b, 5c and 5d schematically show examples of possible electrode configurations for the patterned portions 202 according to example embodiments, observed from above. It should be noted that the electrode configurations are not limited to the examples shown herein.

[0154] Each Fig. 5a, 5b and 5c depicts a single resonating element 101 according to example embodiments. In all embodiments shown in Figs. 5a, 5b and 5c, the top electrode comprises a cutting line 201. It should be noted that the cutting line 201 is optional and the examples shown herein are provided also in absence of the cutting line 201.

[0155] As shown in Fig. 5a, in certain embodiments, the patterns of the patterned portions 202 are width-wise centered along the resonating element 101. In this example embodiment, at least some of the patterns of the patterned portions 202 are not attached to a trench (that defines the resonating element 101 as an entity). As shown in the earlier Figs. 4a, 4b, 4c and 4d, in certain embodiments, the patterns of the patterned portions 202 are arranged to start from the trench.

[0156] As shown in Fig. 5a, in certain embodiments, the top electrode comprises patterned portions 202 in a lengthwise (longitudinally, in relation to longitudinal axis) non-central area of each side of the cutting line 201 of the resonating element 101. In this example embodiment, the patterns of the patterned portions 202 are arranged in the proximity of the cutting line 201 on each side. In certain alternative embodiments, the top electrode comprises patterned portions 202 in a lengthwise central area of each side of the cutting line 201 of the resonating element 101.

[0157] As shown in Fig. 5b, in certain embodiments, the resonating element 101 comprises patterns of the patterned portions 202 (in this example embodiment, further lines) in anequal-distance Dnconfiguration. In certain embodiments, the patterns of the patterned portions 202 are of equal distance Dnapart from one another.

[0158] As shown in Fig. 5c, in certain embodiments, the resonating element 101 comprises patterns of the patterned portions 202 in a gradation, wherein the distance between the patterns D-i-De increases towards the end of the resonating element (Di < D2 < D3 < D4 < D5< De). In certain alternative embodiments, the resonating element 101 comprises patterns of the patterned portions 202 in a gradation, wherein the distance between the patterns D-i-De decreases towards the end of the resonating element (Di > D2 > D3 > D4 > D5 > De).

[0159] Fig. 5d schematically shows an electrode configuration of a (single) resonating element 101 having arrays of meanders according to an example embodiment. The embodiment shown in Fig. 5d comprises no cutting line 201. The embodiment shown in Fig. 5d comprises patterned portion 202 having an array of meanders (in this embodiment, an array of 3 meanders). Instead of a single meandering pattern (such as shown in Fig. 5b), in certain embodiments, the resonating element 101 comprises arrays of meanders (parallel to each other). In these embodiments, the array of meanders comprises preferably thin patterns. In certain embodiments, the thin patterns have a width of less than 1 pm, or even less than 0.8 pm. Further, in certain embodiments, the patterns have a depth of less than 0.5 pm, or even less than 0.4 pm. Preferably, the patterns have a depth in the range of 0.2 to 0.3 pm, such as 0.25 pm. The embodiment shown in Fig. 5d enables lowering the equivalent series resistance of the resonator 100 (namely, dividing the equivalent series resistance by three as there are three meandering patterns in the array of meanders). Further, this enables relaxation of the top electrode stiffness. Further, this enables limiting the top electrode material, such as gold, grain growth after the deposition, reflow and / or aging stages.

[0160] Figs. 6a, 6b and 6c schematically show examples of possible electrode configurations for the patterned portions 202 according to example embodiments, observed from above. It should be noted that the electrode configurations are not limited to the examples shown herein.

[0161] Each Fig. 6a, 6b and 6c depicts a single resonating element 101 according to example embodiments. In all embodiments shown in Figs. 6a-6c, the top electrode comprises a cutting line 201. It should be noted that the cutting line 201 is optional and the examples shown herein are provided also in absence of the cutting line 201.In all embodiments shown in Figs. 6a-6c, the patterned portions 202 comprise perforations. In certain embodiments, the individual perforations (“dots”) are combined to form further line(s).

[0162] As shown in Fig. 6a, in certain embodiments, the resonating element 101 comprises patterned portions 202 having both perforations and further lines. In certain embodiments, the patterned portions 202 comprise perforations to provide further patterns for the charge carriers to meander and / or to further reduce the mass (reduce stiffness) of the top electrode layer.

[0163] As shown in Fig. 6b, in certain embodiments, the resonating element 101 comprises patterned portions 202 having further lines (formed by combining said perforations). In certain embodiments, some of the further lines are width-wise centered along the resonating element 101. In certain embodiments, some of the further lines are width-wise non-centered along the resonator element 101 (arranged to start from the trench).

[0164] As shown in Fig. 6c, in certain embodiments, the patterns of the patterned portions 202 are not limited to horizontal direction (x-direction) but may be angled in relation to the horizontal direction of the resonating element 101. In certain embodiments, perforations are combined to form further lines in an angled x-direction(s). In certain embodiments, the angled x-direction deviates by an angle between 0-90 degrees in relation to the horizontal direction (x-direction). In certain alternative embodiments, the perforations are combined to form further lines in vertical direction (y-direction) along the resonating element 101 (not shown).

[0165] Fig. 7a schematically shows an electrode configuration of a resonating element 101 for a length-extensional resonance mode according to an example embodiment. In certain embodiments, the resonator 100 (and therefore the resonating element 101) is configured to resonate in a length-extensional in-plane resonance mode. In certain embodiments, the length extensional resonance mode is configured to resonate parallel to the length direction (y-direction) of the resonator element 101.

[0166] In certain embodiments, the resonator 100 is configured to resonate in a collective resonance mode, wherein each resonating element 101 of the resonator 100 is configured to resonate in the same collective resonance mode.

[0167] In the embodiment shown in Fig. 7a, the patterns of the patterned portions 202 (optionally accompanied with the cutting line 201) create a flexible top electrode configuration thatminimizes the harmful effects of the top electrode grain changes during thermal treatments. In certain embodiments, the cutting line 201 is arranged in the area of the highest strain of the resonating element 101. In this embodiment, the top electrode is free to resonate and its stiffness is reduced. It has been found that the patterned portions 202 (and the cutting line 201) are especially beneficial in the length-extensional mode resonator according to certain embodiments.

[0168] Fig. 7b schematically shows an electrode configuration for the resonating element 101 for a square-extensional resonance mode according to an example embodiment. In certain embodiments, the resonating element 101 is configured to resonate in a squareextensional, SE, resonance mode. In certain embodiments, the resonating element is a plate element (square element). In certain embodiments, the top electrode of the resonating element 101 comprises patterned portions 202 to reduce the mass of the top electrode. In certain embodiments, the patterned portions 202 are arranged in the areas of the strain of the square extensional plate.

[0169] In certain embodiments, the patterned portions 202 comprise channels (cuts in the pattern) for the charge carriers to move. In certain embodiments, the patterned portions 202 comprise several channels (per patterned portion) to create a maze for the charge carriers.

[0170] In certain embodiments, other resonance modes are supported (any in-plane mode(s) or out-of-plane mode(s). In certain embodiments, the resonator 100 is configured to resonate in a width extensional, WE, resonance mode. In certain embodiments, the resonator 100 is configured to resonate in a Lame resonance mode.

[0171] Fig. 7c schematically shows another electrode configuration for the resonating element 101 for a square-extensional resonance mode according to an example embodiment. Similarly as in Fig. 7b, in certain embodiments, the top electrode of the resonating element 101 comprises patterned portions 202 to reduce the mass of the top electrode, as shown in Fig.

[0172] 7c. In certain embodiments, the patterned portions 202 are arranged in the areas of the strain of the square extensional plate. In certain embodiments, the patterned portions 202 comprise one channel (one cut in the pattern) for the charge carriers to move. In certain embodiments, the patterned portions 202 comprise a channel (one per patterned portion) to create a maze for the charge carriers.

[0173] Figs. 8a, 9a and 10a schematically show an electrode configuration of a resonating element 101 for a flexural resonance mode in side view according to an example embodiment. Figs.8b, 9b and 10b schematically shows the corresponding electrode configuration in top view according to an example embodiment.

[0174] In the embodiments shown in Figs. 8a, 8, 8c, 8d, 8e, 9a, 9b, 10 and 10b, the resonating element 101 is configured to resonate in an out-of-plane resonance mode. In certain embodiments, the resonating element 101 is configured to resonate in a flexural resonance mode. In certain embodiments, the resonator 100 is attached to the support structure 110 from the anchoring point 103. In certain embodiments, the resonator 100 comprises electrical terminal(s) at anchoring point 103. In certain embodiments, the resonator 100 comprises a plate 104 connecting the resonating elements 101 (to each other, together). In certain embodiments, the plate 104 connects (couples) the resonating elements 101 to each other. In certain embodiments, the plate 104 further couples the resonating elements 101 to the anchoring point 103. In certain embodiments, the plate 104 is a mechanical coupler plate 104. In certain embodiments, the plate 104 comprises electrode connection for the electrodes of the resonating elements 101. In certain embodiments, the charge carriers (current) are able to move from one resonating element 101 to another via the plate 104.

[0175] In certain embodiments, the patterned portion(s) 202 are arranged in proximity to the anchoring point 103, such as shown in Fig. 8a and Fig. 8b. In certain embodiments, the patterned portion(s) 202 are arranged at the area of the resonating element 101 having the highest strain. In certain embodiments, at the proximity of the anchoring point 103 of the resonating element 101 there are more charge carriers to collect. In certain embodiments, at the far end of the resonating element 101 (farthest from the anchoring point 103) there are less charge carriers to collect.

[0176] In certain embodiments, such as shown in Figs. 8c, 8d and 8e, the resonating elements 101a and 101b are out-of-phase resonating elements (antiphase resonating elements, not resonating in-phase with one another). In certain embodiments, the resonator 100 comprises a plurality of out-of-phase resonating elements 101a, 101b, such as n resonating elements 101a, 101b, coupled to each other by the plate 104. In certain embodiments, such as shown in Fig. 8e, the resonating elements 101a, 101b are resonating beam elements.

[0177] In certain embodiments, the out-of-phase resonating elements 101 are configured to resonate in opposite phases with one another. In certain embodiments, the out-of-phase resonating elements 101 comprise a 180-degree phase shift in comparison to each other.In certain embodiments, (approximately, about) half of the out-of-phase resonating elements 101a, 101b are configured to resonate in-phase with one another. In certain embodiments, n / 2 of the out-of-phase resonating elements 101a, 101b are configured to resonate in-phase with one another. This is shown in Figs. 8c, 8d and 8e as resonating elements 101a.

[0178] In certain embodiments, (approximately, about) half of the out-of-phase resonating elements 101a, 101b are configured to resonate in-phase with one another, but out-of-phase (opposite phase) with the other half of the resonating elements 101a, 101b. In certain embodiments, n / 2 of the out-of-phase resonating elements 101a, 101b are configured to resonate in-phase with one another, but out-of-phase with the other half of the resonating elements 101a, 101b. This is shown in Figs. 8c, 8d and 8e as resonating elements 101b.

[0179] In case the number n of resonating elements 101a, 101b is an odd number, either half of the resonating elements 101a, 101b can have 1 more or 1 less resonating element in comparison to the other half.

[0180] As shown in the embodiments of Figs. 8c, 8d, and 8e, the outer(most) resonating elements 101a are in-phase with one another, and the middle resonating element 101b is an antiphase (opposite phase, out-of-phase) resonating element 101b. This enables creating strain on the plate 104 (the area that couples the resonating elements 101a, 101b to each other). In certain embodiments, the plate 104 (the area that couples the resonating elements 101a, 101b to each other) is a patterned plate. In certain embodiments, the plate 104 comprises patterns (such as cuts) 202b. In certain embodiments, the plate 104 comprises patterns aligned with the (location of) the trenches between the resonating elements 101a, 101 b, as shown in Fig. 8e. In certain other embodiments, the patterns 202b cover the whole plate 104. The patterned plate 104 enables to prevent the top electrode spring effect from impacting the coupling of the resonating elements. In some other embodiments the cuts 202b can cover the whole plate 104.

[0181] As shown in Figs. 8a, 8, 8c, 8d, and 8e, in certain embodiments, the patterned portion(s) 202 are arranged in proximity to the anchoring point 103. In certain embodiments, the patterned portion(s) 202 reach from the proximity of the anchoring point 103 towards the central area of the resonating element. In

[0182] As shown in Figs. 9a and 9b, in certain embodiments, the resonating element 101 comprises a cutting line 201. In certain embodiments, the ‘last’ pattern of the resonatingelement 101 is a cutting line 201 (farthest from the anchoring point 103). In certain embodiments, the cutting line 201 is arranged at the central area of the resonating element 101. Thereby no charge carriers are able to pass to the end (portions) of the resonating element 101 (that are on the opposite side as the anchoring point 103).

[0183] In certain embodiments, as shown in Figs. 10a and 10b, certain resonating elements 101 of the resonator 100 comprise a cutting line 201, whilst other resonating elements 101 do not. In this embodiment, as shown in Fig. 10a and 10b, the outermost resonating elements 101 comprise cutting lines 201 (and the central resonating element 101 of the three resonating elements 101 does not). In certain embodiments, the cutting line 201 is arranged at the proximity of the anchoring point 103 (anchor region).

[0184] In certain embodiments, the resonating elements 101 of the resonator 100 are coupled to each other from both ends of the resonating elements 101. As mentioned, the resonating elements 101 are coupled to each other from one end by a first plate 104. In certain embodiments, the first plate 104 further couples the resonating elements 101 to the anchoring point 103. In certain embodiments, the resonating elements 101 are coupled (from the other end) to each other by a second plate 105 (a mechanical coupler plate 105). In certain embodiments, the second plate 105 comprises electrode connection for the electrodes of the resonating elements 101. In certain embodiments, the charge carriers (current) are able to move from one resonating element 101 to another via the second plate 105.

[0185] In certain embodiments, such as shown in Figs. 10a and 10b, the resonating elements 101 are in-phase resonating elements. In these embodiments, the second plate 105 ties the resonating elements 101 together (such that all the resonating elements 101 resonate in the same phase with one another).

[0186] Fig. 11 schematically shows a material stack of a resonator 100 according to an example embodiment. Fig. 11 schematically shows an example cross section (sectional view, side view) of the resonator 100 residing on a substrate.

[0187] In certain embodiments, the resonator 100 is fabricated on a substrate. In the example embodiment of Fig. 11, a silicon on insulator (SOI) substrate (wafer) 450 is used. The reference numerals 401 and 402 denote bottom electrode and top electrode contacts, respectively.In certain embodiments, the resonator 100 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.

[0188] In the example embodiment shown in Fig. 11 , the top electrode is implemented in layer L1. In this example embodiment, layer L2 is a piezoelectric layer for piezoelectric actuation of the resonator residing in the area of denoted by 100. 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 (not shown). In certain embodiments, the layer L5 follows the cavity C1 shape as shown in Fig.

[0189] 11 (not shown).

[0190] 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.

[0191] 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.

[0192] 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.

[0193] In certain embodiments, the longitudinal axis L of a resonating element (or all resonating elements) 101 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 (or all resonating 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.

[0194] In certain embodiments, the cutting line 201 and the patterns of the patterned portions 202 continue through the top electrode layer L1 to expose the piezoelectric layer beneath the top electrode.

[0195] Fig. 12 schematically shows an example of a resonator array (an apparatus) according to an example embodiment. Herein is provided an apparatus, such as a resonator array, comprising at least one resonator 100 in accordance with certain embodiments. In certain embodiments, as shown in Fig. 12, the apparatus comprises (at least) two resonators 100 (stacked beam resonators). In certain embodiments, the apparatus comprises a plurality of resonators 100 positioned adjacent to each other. In certain embodiments, the apparatus comprises a plurality of resonators 100 coupled to each other by a coupler 310. All embodiments described in context a single resonator 100 apply herein as well for the resonators 100 of the apparatus.

[0196] Accordingly, the apparatus comprises (at least two, a plurality of) resonators 100, each resonator 100 comprising patterned portions 202 and optionally a cutting line 201. In certain embodiments, the patterned portions 202 are configured to neutralize the spring effect of the top electrode. In certain embodiments, the patterned portions 202 are configured to remove (minimize, alleviate) stress related modulation of the top electrode. Accordingly, a ‘flexible’ top electrode having reduced stiffness, resulting in to reduced or minimized the frequency drift is provided.

[0197] Fig. 12 schematically shows an apparatus comprising two resonators 100 coupled to each other by a coupler 310 in accordance with certain embodiments. In certain embodiments, the coupler 310 comprises patterns. In certain embodiments, the coupler 310 is a patterned coupler. In certain embodiments, the coupler 310 comprises patterns (cuts, lines, meanders) to suppress spring constant (neutralize the spring effect) of the coupler's 310 top electrode. In certain embodiments, the coupler 310 comprises a layer of gold. In certainembodiments, the coupler 310 comprises patterns that are configured to prevent charge carriers from crossing it (full cuts, through cuts).

[0198] In certain embodiments, the coupler 310 is a flexural coupler. In certain embodiments, the flexural coupler 310 is a patterned flexural coupler. In certain embodiments, the flexural coupler 310 comprises patterns (cuts, lines, meanders) to suppress spring constant (neutralize the spring effect) of the flexural coupler’s 310 top electrode.

[0199] The apparatus shown in Fig. 12 comprises two extensional-mode resonators 100, and a (one or more) flexural mode resonator coupler 310. Further, the apparatus comprises a (one or more) mechanical connector element 320 which connects the flexural resonator coupler 310 to the extensional mode resonators 100. In certain embodiments, at least one of the extensional-mode resonators 100 of the apparatus comprises a piezoelectric thin-film actuator for exciting the said extensional-mode resonator to a resonance mode and thereby the whole apparatus to a collective resonance due to mechanical coupling of the extensional-mode resonators 100.

[0200] In certain alternative embodiments, the coupler 310 is a length-extensional coupler (not shown). In certain embodiments, the coupler comprises discontinuity regions to render the coupler electrically inert (not shown). In certain embodiments, the length-extensional coupler 310 is a patterned length-extensional coupler. In certain embodiments, the lengthextensional coupler 310 comprises patterns (cuts, lines, meanders) to suppress spring constant (neutralize the spring effect) of the length-extensional coupler’s 310 top electrode. In certain embodiments, more than 50% of the mass of the apparatus comprise material portions of single-crystalline silicon. In certain embodiments, the apparatus 100 comprises an electrostatic actuator for exciting at least one of the extensional-mode resonators 100 to a resonance mode and thereby the whole resonator to a collective resonance due to mechanical coupling of the extensional-mode resonators 100.

[0201] In certain embodiments, the resonators 100 are implemented in the form of stacked beam resonators having a plurality of adjacent resonating beam elements 101 connected by connection element(s) 102 and separated by trenches 104 (thus forming a ladder-like structure).

[0202] In certain embodiments, (all) the resonators 100 of an apparatus are identical with one another (each other). In certain alternative embodiments, (all) the resonators 100 of a apparatus are different from one another.Fig. 13a schematically shows a top view of a resonator 100 according to an example embodiment. In certain embodiments, the top electrode of the resonating element comprises patterned portion(s) 202, the patterned portions 202 comprising various patterns. In certain embodiments, the patterned portion(s) 202 comprise perforation and further lines. In certain embodiments, the patterned portions 202 comprise perforations and further lines to provide further patterns for the charge carriers to meander and / or to further reduce the mass (reduce stiffness) of the top electrode layer. In certain embodiments, the resonating element comprises a cutting line 201 configured to run through the resonating element (thereby splitting it into two portions).

[0203] Fig. 13b schematically shows a top view of a resonator 100 according to another example embodiment. In certain embodiments, the top electrode of the resonating element comprises patterned portion(s) 202, the patterned portions 202 comprising perforations. In certain embodiments, the perforations are configured to provide further patterns for the charge carriers to meander and / or to further reduce the mass (reduce stiffness) of the top electrode layer. In certain embodiments, the resonating element comprises a cutting line 201 configured to run through the resonating element (thereby splitting it into two portions).

[0204] Figs. 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h, 14i, 14j, 14h and 141 schematically show a top view of a part of a resonator 100 showing certain pattern geometries according to certain example embodiments. Only a part of the resonator 100 is shown as an illustration of the pattern. It should be noted that the pattern(s) are not limited to this area of the resonator 100 only. The resonator 100 which is partly shown here corresponds to the resonator 100 shown in Figs. 1 and 2, for example. In Figs. 14a, 14b, 14c, 14d, 14e, 14f , 14g, 14h, 14i, 14j, 14h and 141, the part of the resonator 100 shown is the area near the leftmost anchoring point 103 of the resonator 100. The Figs. 14a, 14b, 14c, 14d, 14e, 14f , 14g, 14h, 14i, 14j, 14h and 141 show two resonating elements 101 (on the leftmost side of the resonator 100), separated by trenches 104. The resonating elements 101 are connected to one another by connection elements 102. These features are marked into Fig. 14a, but the same applies to the Figs. 14b, 14c, 14d, 14e, 14f, 14g, 14h, 14i, 14j, 14h and 141, respectively.

[0205] Figs. 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h, 14i, 14j, 14h and 141 show alternative patterns of the patterned portion 202 according to certain embodiments. The resonator 100 according to certain embodiments is not limited to number, width, shape and / or angle of the patterns of the patterned portion 202. In certain embodiments, the patterns of the patterned portions 202 are of different number, width, shape and / or angle along each resonatingelement 101. In certain embodiments, the patterns of the patterned portions 202 are of different number, width, shape and / or angle along the resonator 100 body. Further, any of the example patterns shown in Figs. 14a, 14b, 14c, 14d, 14e, 14f , 14g, 14h, 14i, 14j, 14h and 141 are combinable with each other, forming yet further example pattern configurations.

[0206] In certain embodiments, the patterns of the patterned portions 202 (such as meanders) are a parameter for optimization in general. In certain embodiments, the patterns of the patterned portions 202 are a parameter for optimization for the resonator 100 design. In certain embodiments, the design of the patterns of the patterned portions 202 enable tuneability of the resonator 100.

[0207] In certain embodiments, such as shown in Figs. 14a, 14c, 14d, 14e, 14f, 14g, 14h, 14i, 14j, 14k, the patterned portion 202 is arranged on the resonating element 101 on the portion that is separated from adjacent resonating element 101 by a trench 104. In these embodiments, the patterned portion 202 is arranged on the central area of resonating element 101. In other words, the patterned portion 202 has equal length than the trench 104. In certain embodiments, the patterned portion 202 is arranged at the entire width (whole width, from trench to trench) of the resonating element 101. In these embodiments, the ends (length-wise) of the resonating (beam) elements 101 are free from patterns. In these embodiments, the connection elements 102 are free from patterns.

[0208] In certain alternative embodiments, such as shown in Figs. 14b, and 141, the patterned portion 202 is arranged at the entire length and width (whole area) of the resonating element 101. In these embodiments, the ends of the resonating (beam) elements 101 comprise patterns. In these embodiments, the connection elements 102 comprise patterns.

[0209] In certain further alternative embodiments, such as shown in Figs. 14e, the patterned portion 202 is arranged at a partial length of the resonating element 101. In certain embodiments, the length of the patterned portion 202 is greater than the length of the trench 104. In certain embodiments, the patterned portion 202 is arranged at the entire width of the resonating element 101. In these embodiments, the ends of the resonating (beam) elements 101 partly comprise patterns. In these embodiments, the connection elements 102 comprise patterns (such that the very outermost end of the resonating element 101, length-wise, is free from patterns). In these embodiments, the connection elements 102 partly comprise patterns.As shown in Fig. 14a, in certain embodiments, the patterned portion 202 comprises horizontal cuts (x-direction). In certain embodiments, the cuts are arranged in groups comprising a plurality of equal cuts, such as four or five equal cuts adjacent to each other. In certain embodiments, the cuts are arranged to start from a trench 104. In certain embodiments, the cuts are ‘open’ (a portion wherein the top electrode material is not removed by patterning) from at least one horizontal location along the width of the resonating element. In certain embodiments, the cuts are open from a proximity of a trench 104 (the trench 104 on the other side of the resonating element 101 , in case the cut starts from another trench on another side). In certain embodiments, the cuts are open in the middle (central) area of the resonating element.

[0210] As shown in Fig. 14b, in certain embodiments, the patterned portion 202 comprises periodically repeating patterns (repeating geometrical shapes). In certain embodiments, the patterned portion 202 comprises diamond-shaped repetitive patterns.

[0211] As shown in Fig. 14c, in certain embodiments, the patterned portion 202 comprises a zigzag pattern. In this embodiment, the zig-zag pattern is formed lines aligned in (approximately) 90 degree angle with respect to the other lines. In certain embodiments, the lines are grouped together in groups of plurality of lines (similarly as in Fig. 14a).

[0212] As shown in Fig. 14d, in certain embodiments, the patterned portion 202 comprises horizontal cuts (lines) in an repetitive pattern. In certain embodiments, every other cut is ‘open’ in the middle of the (width of) the resonating element 101. In certain embodiments, every other cut is ‘open’ in the proximity of the trench 104 (or in the proximity of both trenches, as shown in Fig. 14d). In certain embodiments, the patterned portion 202 (of each resonating element 101, or of the resonator 100) is a symmetric patterned portion, wherein the axis of symmetry runs in the middle of the resonating element 101 (or in the middle of the resonator 100) in length, or in width direction.

[0213] As shown in Fig. 14e, in certain embodiments, the patterned portion 202 comprises a zigzag patterns. In certain embodiments, the patterned portion 202 comprises a sharp angled patterns. In this embodiment, the patterns comprise meanders having sharp corners (instead of 90 degree corners, for example). In certain embodiments, a sharp corner is in between 10 to 80 degrees. The zig-zag geometry as shown in Fig. 4d enables shortening the electrical path (of the charge carriers) and thus, helping to have lower ESR.Figs. 14a, 14c, and 14e show a cutting line 201 according to certain embodiments. The cutting line 201 is extensively elaborated earlier in the present disclosure.

[0214] As shown in Fig. 14f, in certain embodiments, the patterned portion 202 comprises horizontal cuts, wherein the openings of the patterns provide a zig-zag shaped pathway (for the charge carriers). In certain embodiments, the zig-zag pathway runs periodically from one trench to another trench (and back, and so on) as shown in Fig. 14f . As used herein, the opening of the pattern (or wherein the pattern is open) is used to refer to a portion of the pattern wherein the top electrode material has not been removed. In the area of the pattern, the top electrode material is removed. Thereby, the openings in the patterns provide a pathway of the top electrode material, wherein the charge carriers are able to move in.

[0215] Fig. 14g shows a combination of the zig-zag patterns as shown in Figs. 14c and 14e, and the horizontal cuts as shown e.g. in Fig. 14f. In certain embodiments, the patterned portion 202 (or the resonating element 101) comprises an area free of patterns 202c on the outermost resonating (beam) element 101. In certain embodiments, the area free of patterns 202c is in the middle of the outermost resonating element 101 (lengthwise in the middle). In certain embodiments, the area free of patterns 202c has a width equal to the resonating element 101 width. In certain embodiments, the area free of patterns 202c is in the proximity of the anchoring point 103.

[0216] Fig. 14h shows a similar embodiment than the one shown in Fig. 14f . In certain embodiments, the patterned portion 202 comprises horizontal cuts, and openings in said cuts to provide a zig-zag (meandering) pathway of the top electrode material. In certain embodiments, the patterned portion 202 (or the resonating element 101) comprises an area free of patterns 202c, wherein the area free of patterns 202c is part of the width of the resonating element 101. In certain embodiments, the area free of patterns 202c is formed by leaving the proximity of the anchoring point 103 unpatterned.

[0217] As shown in Fig. 14i, in certain embodiments, the patterned portion 202 comprises horizontal cuts, having a plurality of dot-like openings. In certain embodiments, the plurality of dot-like openings in the horizontal cut are arranged in groups, adjacent to one another. In certain embodiments, the horizontal cuts above and below comprise equally placed (groups of) dot-like openings. In certain embodiments, (at least some, a plurality of) the openings of the patterns are vertically aligned with one another. In certain embodiments,the openings aligned vertically with one another for a vertical line for tha charge carriers to travel in. This creates a grid-like patterns (crisscross patterns).

[0218] As shown in Fig. 14j and similarly as in Fig. 14i, in certain embodiments, the patterned portion 202 comprises horizontal cuts and dot-like openings in said cuts. In certain embodiments, the dot-like openings are arranged to for other patterns, such as cones. In certain embodiments, the number of openings in a pattern is one. In certain embodiments, the number of openings in a pattern is more than one, such as two, three or four.

[0219] As shown in Fig. 14k, in certain embodiments, the patterned portion 202 comprises a pattern, wherein most of the top electrode material has been removed, leaving merely a strip (or plurality of strips) of the top electrode material on the resonator 100. In certain embodiments, the patterned portion 202 comprises rectangular (or square) shapes (patterns). In certain embodiments, the patterned portion comprises right-angled (90 degree angled) shapes. In certain embodiments, the resonating element 101 comprises a cone-like area free of patterns 202c at the proximity of the anchoring point. In certain embodiments, the cone like area 202c is wider in the proximity of the anchoring point, and gradually narrows towards the first trench 104 of the resonator 100.

[0220] As shown in Fig. 141 and similarly as shown in Fig. 14k, in certain embodiments, the patterned portion 202 comprises maze-like patterns having right-angles. In certain embodiments, the patterns are formed of horizontal and vertical cuts arranged to contact each other to form said patterns. In this embodiment, the area free of patterns 202c is rounded to encircle the anchoring point 103.

[0221] As shown in Fig. 14m, in certain embodiments, the patterned portion 202 comprises perforations. In certain embodiments, the patterned portion 202 comprises patterns (meanders) formed by combining adjacent perforations to one another. In certain embodiments, the patterned portion 202 comprises meanders on top of perforations.

[0222] The embodiments shown in Figs. 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h, 14i, 14j, 14h, 141 and 14m enable providing a good equivalent series resistance, ESR, (by limiting the ESR value), whilst having good stability properties.

[0223] Figs. 15a and 15b schematically show a width extensional resonator 100 according to example embodiments. In certain embodiments, the resonator 100 (the resonating element 101) is configured to resonate in a width extensional resonance mode. In certainembodiments, the resonator 100 comprises a plate resonating element 101. In certain embodiments, the plate is a rectangular (or square) plate. In certain embodiments, the plate resonating element 101 is attached to the support structure 110 by anchoring point(s) 103. In certain embodiments, the resonating element 101 is separated from the support structure 110 by (an external) trench 104’ (similarly as in Fig. 2 by way of an example).

[0224] In certain embodiments, as shown in Fig. 15a and 15b, the resonating element 101 comprises a patterned portion in the top electrode thereof. Fig. 15a shows an embodiment having an array of patterns (similarly as in Fig. 5d). In certain embodiments, the array of patterns comprises a plurality of meanders (turns, corners). In certain embodiments, the array of patterns forms a maze-like patterned top electrode. In certain embodiments, the patterns 202 are arranged parallel and perpendicular with one another (forming straight angles between each other).

[0225] Fig. 15b shows an embodiment having a patterned portion 202 comprising straight patterns (straight lines). In certain embodiments, the patterns 202 form a single meandering configuration. In certain embodiments, the patterns 202 are arranged parallel to one another. In certain embodiments, some of the patterns are arranged to begin from the trench 104’ from one side of the resonating element 101, and some of the patterns are arranged to begin from the trench 104’ from the other side of the resonating element 101. In certain embodiments, some of the patterns are arranged not to touch (separated) from a trench 104’ in any direction.

[0226] A distinction should be made in between the top electrode layer of the instant solution comprising (containing) a patterned portion and a “top electrode patterned into having a shape”. What is meant here is that a conventional top electrode may be, for instance, patterned such that it forms a shape, by way of an example a single line across the resonating element. However, in this case, the single “snake-like” top electrode does not contain any patterned portion. Instead, the ”snake-like” top electrode is, itself, in a form of a shape or a pattern. The top electrode being a shaped top electrode (regardless that this shape may be manufactured via patterning the layer) does not mean that the top electrode layer itself contains any patterned portion or patterned region having patterns within.

[0227] The instant solution provides a top electrode that comprises (contain) a patterned portion (area) within the top electrode layer itself. In other words, it may be described such that the top electrode layer is otherwise ‘intact’, but it is in some area ‘broken’ by the patternedportion. In certain embodiments, the patterns of the patterned portion are areas (regions, spots) where the top electrode layer has been removed (the top electrode layer material is absent). In certain embodiments, (most of) the patterns of the patterned portion are surrounded by the top electrode (material, layer) and / or by trenches.

[0228] Further, a distinction should be made in between a so-called ‘two-port’ solutions, wherein the electrodes of the device are arranged in the same plane, adjacent to one another. In the instant solution, the top electrode itself contains a patterned portion, but this does not render the electrode to ‘divide’ or ‘turn into’ two separate electrodes of the device.

[0229] 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 to provide a solution having improved frequency stability. In the present solution it has been found that the top electrode of the resonator contributes to the frequency instability due to its elasticity and stiffness characteristics. Typically, the top electrode is not stable in the thermal treatments of the resonator manufacturing, resulting in adverse effects to the grain structure of the electrode layer that contributes to the frequency instability.

[0230] Therefore, the technical effect of the present solution is neutralizing the spring effect of the electrode, thereby removing any stiffness or stress related modulation of the electrode. In certain embodiments, the remaining volume (or mass) of the top electrode material after this patterning to neutralize the spring effect of the top electrode is irrelevant. A technical effect is to provide a ‘flexible’ top electrode having reduced stiffness, resulting in to reduced or minimized the frequency drift. A technical effect is enabling free resonance (having no harmful stiffness / spring effect) of the resonating element due to patterned top electrode. Further, a technical effect is maintaining the equivalent series resistance, ESR, at an optimal level.

[0231] A further technical effect achieved by the patterns of the patterned portion is enabling tuneability of the resonator. The present solution is not limited to any number, width, shape and / or angle of said patterns along each resonator, or along the resonator body. The arrangement of the patterns enables tuning of the resonator according to specific needs.

[0232] A further technical effect is improving frequency over temperature (f-vs-T) characteristics while retaining low ESR. A further technical effect is reducing negative impacts caused by the electrode, for example a metal electrode, without degradation of the main function ofthe resonator. A further technical effect is reducing or negate reliability issues of the resonator. A further technical effect is reducing / avoiding reduction of degradation in resonators. A further technical effect is the reduction of reflow drift and ageing. A further technical effect is reducing / avoiding spurious resonance mode(s) of the resonator (prevention of particular unwanted resonance modes). A further technical effect is increasing or maintaining the quality factor, Q. Certain embodiments provide for a more positive linear temperature coefficient of frequency, TCF1.

[0233] 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.

[0234] 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.

[0235] 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), comprisinga resonating element (101) having a top electrode,wherein the top electrode comprises a patterned portion (202) to reduce the stiffness of the top electrode.

2. The resonator (100) of claim 1, wherein the patterned portion (202) is formed of line(s), perforation(s) or both.

3. The resonator (100) of claim 1 or 2, wherein the patterned portion (202) is configured to provide a pathway to charge carriers.

4. The resonator (100) of claim 3, wherein the patterned portion (202) comprises a meandering pathway to charge carriers.

5. The resonator (100) of any preceding claim, wherein the top electrode further comprises a cutting line (201) through the top electrode.

6. The resonator (100) of claim 5, wherein the top electrode comprises the patterned portions (202) on both sides of the cutting line (201).

7. The resonator (100) of claim 6, wherein the charge carriers are configured to travel on one side of the cutting line (201 ) different route than on the other side of the cutting line (201).

8. The resonator (100) of any of the preceding claims, wherein the top electrode comprises metal, preferably gold.

9. The resonator (100) of any of the preceding claims, wherein the resonating element (101) 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.

10. The resonator (100) of claim 9, wherein the patterned portion (202) is embedded into the piezoelectric layer.

11. The resonator (100) of claim 9 or 10, wherein the top electrode having the patterned portion (202) protrudes into the piezoelectric layer.

12. The resonator (100) of claim 9, 10 or 11, wherein the bottom electrode comprises silicon, preferably doped silicon, such as ultra-heavily doped, UHD, silicon.

13. The resonator (100) of any preceding claim, wherein the resonating element (101) comprises a plurality of resonating beam elements.

14. The resonator (100) of claim 13, wherein the resonating beam elements are longitudinally aligned within 25 degrees of a < 100> crystal direction of silicon.

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

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

17. An apparatus comprising at least one resonator (100) according to any of claims 1-

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