Resonator material configuration

Abstract

Herein is provided a resonator (100), comprising a resonating element (101), wherein the resonator comprises at least one first region (201), and a second region (202), wherein material stacks of the first region (201) and the second region (202) are different from one another, and wherein the first region (201) and the second region (202) have matching resonance frequencies Herein is further provided an apparatus, such as a resonator array, comprising at least one resonator (100).

Description

[0001] RESONATOR MATERIAL CONFIGURATION

[0002] TECHNICAL FIELD

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

[0004] BACKGROUND

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

[0006] There is an ongoing need to provide resonators with good quality factor Q. The quality factor Q may be adversely impacted by the thermoelastic dissipation (TED) within the resonator. More specifically, the material choices of the resonator have an effect of the TED of the resonator.

[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.

[0009] It is an object of certain embodiments of the present disclosure solve problem(s) existing in existing technology, or at least to provide an alternative solution to existing technology. Accordingly, certain disclosed embodiments provide a resonator having good quality factor Q by minimizing the thermoelastic dissipation of the resonator materials.

[0010] According to a first example aspect of the present disclosure there is provided a resonator, comprising a resonating element, wherein the resonator comprises at least one first region,and a second region, wherein material stacks of the first region and the second region are different from one another, wherein the first region and the second region have matching resonance frequencies (with one another, with each other).

[0011] In certain embodiments, the first and the second region have matching (the same, equal, identical) resonance frequencies despite their material stacks being different (from one another, from each other). In certain embodiments, the ‘matching’ resonance frequencies is used to refer to said regions having same (or corresponding, or equal) resonance frequency values. In certain embodiments, the first region has a different material stack (stack of materials on the substrate) compared to the second region (and vice versa). In certain embodiments, the first region has the same resonance frequency with the second region, despite the material stacks being different.

[0012] In certain embodiments, at least one dimension of resonator is adjusted (changed, modified, intentionally varied) to match the resonance frequencies of the first region and the second region. In certain embodiments, said at least one dimension is a dimension of the first region or the second region. In certain embodiments, at least one dimension of the first region or the second region is adjusted to match the resonance frequencies of the first region and the second region. In certain embodiments, said at least one dimension of the first region or the second region is its length direction, or width direction. In certain embodiments, said at least one dimension of the first region or the second region is an aspect ratio of said region. In certain embodiments, said at least one dimension is a dimension of a trench. In certain embodiments, said at least one dimension of the trench is its width direction. In certain embodiments, said at least one dimension is a dimension of the first region or the second region and / or said at least one dimension is a dimension of a trench.

[0013] In certain embodiments, the material stack of the first region comprises all the materials of the resonator’s material stack. In certain embodiments, the material stack of the first region comprises a full material stack. In certain embodiments, the material stack of the first region is the (only) region of the resonator comprising all the materials of the resonator’s material stack. In certain embodiments, the material stack of the first region is the only region of the resonator comprising all the materials of the resonator’s material stack, such that the material stack of the second (third, fourth...) region comprises fewer material layers than the material stack of the first region.

[0014] In certain embodiments, material stacks of the first region and the second region are different from one another (differ from one another, different in comparison to each other,different than each other). In certain embodiments, the resonator is divided into the first and the second region.

[0015] In certain embodiments, the material stacks of the first region and the second region are different from one another. In certain embodiments, the material layers of the material stacks of the first region and the second region are different from one another. In certain embodiments, the first region and the second region comprise different material layers compared to one another. In certain embodiments, the first region and the second region comprise different material stacks compared to one another. In certain embodiments, the first region and the second region comprise different materials compared to one another. In certain embodiments, the material stacks of the first region and the second region are different from one another with respect to type (kind, material) of the material layers of the material stack. In certain embodiments, the material stacks of the first region and the second region are different from one another with respect to number of material layers of the material stack.

[0016] In certain embodiments, the material stack of the first region comprises a top electrode layer, a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer, and the top electrode layer is on the piezoelectric layer. In certain embodiments, the material stack of the first region comprises the top electrode layer is on the piezoelectric layer, and the silicon layer is on the opposite side of the piezoelectric layer than the top electrode layer. In certain embodiments, the material stack of the first region comprises the silicon layer, the piezoelectric layer on top of the silicon layer, and a top electrode layer on top of the piezoelectric layer.

[0017] In certain embodiments, the top electrode layer is the topmost layer of the resonator (the material stack of the resonator). In certain embodiments, the top electrode layer is implemented by a layer of metal. In certain embodiments, the top electrode layer comprises (is of, is made of, is fabricated from, contains) metal, preferably gold (Au). In certain embodiments, the top electrode layer comprises metal, such as gold (Au), aluminium (Al), or molybdenum (Mo). In certain embodiments, the top electrode layer is of gold, preferably doped gold. In certain embodiments, the top electrode layer is of gold alloy. In certain embodiments, the top electrode layer is implemented by a layer of doped silicon. In certain embodiments, the top electrode layer is implemented by a layer of doped polysilicon.In certain embodiments, the top electrode layer has a thickness in a range of 0.05 pm to 0.6 pm. In certain embodiments, the top electrode layer has a thickness in a range of 0.1 pm to 0.4 pm, such as 0.25 pm.

[0018] In certain embodiments, a bottom electrode of the resonator is implemented by the silicon layer. In certain embodiments, the bottom electrode comprises (is of, is implemented by) silicon. In certain embodiments, the bottom electrode is implemented by a doped silicon layer. In certain embodiments, the bottom electrode implemented by the silicon layer comprises doped silicon, such as ultra-heavily doped, UHD, silicon. In certain embodiments, the bottom electrode comprises silicon, preferably doped silicon, such as ultra-heavily doped, UHD, silicon. In certain embodiments, the silicon layer is a doped silicon layer. In certain preferred embodiments, the silicon is of single-crystalline silicon. In certain embodiments, the bottom electrode of the resonator is implemented by the silicon layer, preferably comprising doped silicon, such as ultra-heavily doped, UHD, silicon.

[0019] In certain embodiments, the silicon layer comprises local doping. In certain embodiments, the silicon layer (substrate) further comprises undoped silicon.

[0020] In certain embodiments, the doped silicon is of N-type or P-type doping. In certain embodiments, the doped silicon comprises n-type doping. In certain embodiments, the doped silicon comprises n++ doping. In certain embodiments, the doping comprises phosphorous doping. In certain embodiments, the doped silicon comprises arsenic doping.

[0021] In certain alternative embodiments, the doped silicon comprises p-type doping. In certain embodiments, the doped silicon comprises p++ doping. In certain embodiments, the doping comprises boron doping. In certain embodiments, the doped silicon comprises gallium doping.

[0022] In certain embodiments, the doping comprises an average impurity concentration of at least 1*1019cm-3or more. In certain embodiments, the doping comprises an average impurity concentration of at least 2*1019cm-3or more, such as 102° cm-3or more.

[0023] In certain embodiments, the resonator is a piezoelectric resonator. In certain embodiments, the piezoelectric layer is a piezoelectric transducer layer. In certain embodiments, the piezoelectric layer is of piezoelectric material. In certain embodiments, the piezoelectric layer is of aluminium nitride, AIN. In certain embodiments, the piezoelectric layer is of scandium-doped aluminium nitride, Sc-doped AIN.In certain embodiments, the piezoelectric layer has a thickness in a range of 0.5 pm to 3 pm. In certain embodiments, the piezoelectric layer has a thickness in a range of 1.3 pm to 1.7 pm, such as 1.5 pm.

[0024] In certain embodiments, the material stack of the second region comprises (contains) a silicon layer. In certain embodiments, the material stack of the second region contains only a silicon layer. In certain embodiments, the second region is a silicon (only) region. In certain embodiments, the second region comprises (is of, contains) silicon, such as doped silicon, such as ultra-heavily doped, UHD, silicon.

[0025] In certain embodiments, the material stack of the second region comprises (contains) a silicon layer and a silicon nitride layer. In certain embodiments, the material stack of the second region comprises (contains) a silicon layer, and a silicon nitride layer on top of the silicon layer.

[0026] In certain embodiments, the material stack of the second region comprises (contains) a doped silicon layer. In certain embodiments, the material stack of the second region comprises (contains) a doped silicon layer, whilst the material stack of the first region comprises (contains) an undoped (or less doped) silicon layer. In certain embodiments, the silicon layer of the second region is doped to a higher impurity concentration in comparison to the silicon layer of the first region. In certain embodiments, the silicon layer at the second region is doped to a higher impurity concentration than the silicon layer at the first region.

[0027] In certain embodiments, the resonator further comprises a third region (or a further / additional region). In certain embodiments, the resonator further comprises a third region (or a further / additional region), wherein material stack of the third region differs from the material stacks of the first region and the second region. In certain embodiments, the material stacks of the first region, the second region and the third region (or a further / additional region) are different from one another (differ from one another, different in comparison to each other, different than each other). In certain embodiments, material stack of the third region comprises a piezoelectric layer, and a silicon layer. In certain embodiments, material stack of the third region comprises a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer. In certain embodiments, the resonator further comprises a third region, wherein material stack of the third region differs from the material stacks of the first region and the second region, wherein the material stack of the third region preferably comprises a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer.In certain embodiments, the resonator further comprises a fourth region (or a further / additional region). In certain embodiments, the resonator further comprises a fourth region (ora further / additional region), wherein material stack of the fourth region differs from the material stacks of the first region and the second region. In certain embodiments, the resonator further comprises a fourth region (or a further / additional region), wherein material stack of the fourth region differs from the material stacks of the first region, the second region and the third region. In certain embodiments, the material stacks of the first region, the second region, the third region and the fourth region (or a further / additional region) are different from one another (differ from one another, different in comparison to each other, different than each other). In certain embodiments, material stack of the fourth region comprises at least a trimming material layer. In certain embodiments, material stack of the fourth region comprises a trimming material layer and a silicon layer. In certain embodiments, material stack of the fourth region comprises a trimming material layer and a silicon layer, wherein the trimming material layer is on the silicon layer. In certain embodiments, the resonator further com prises a fourth region, wherein material stack of the fourth region differs from the material stacks of the first region and the second region, wherein the material stack of the fourth region preferably comprises at least a trimming material layer.

[0028] In certain embodiments, the resonator further comprises a third region, wherein material stack of the third region differs from the material stacks of the first region and the second region, wherein the material stack of the third region preferably comprises a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer, and / or wherein the resonator further comprises a fourth region, wherein material stack of the fourth region differs from the material stacks of the first region and the second region, wherein the material stack of the fourth region preferably comprises at least a trimming material layer.

[0029] In certain embodiments, the material stacks of all the regions of the resonator are different from one another (differ from one another, different in comparison to each other, different than each other). In certain embodiments, the resonator comprises a plurality of regions, each having a different (varying, not same) material stack with each other. In certain embodiments, the resonator comprises at least two regions, each having a different material stack with each other. In certain embodiments, the resonator is divided into a plurality of regions, each having a different material stack with each other.

[0030] In certain embodiments, the resonator is designed to comprise at least two regions, one with ‘full1material stack and another with silicon (substrate) only. In certain embodiments,the resonator comprises the first region and the second region, wherein the first region contains ‘full1material stack, and the second region contains silicon (substrate) only. In certain embodiments, the full material stack comprises a silicon layer (substrate), a piezoelectric layer, and a top electrode layer (in that order, starting from the lowest layer). In certain embodiments, the silicon layer of the first region and the second region is the same silicon layer (the regions share a silicon layer / substrate).

[0031] In certain embodiments, the first region is provided for transduction purposes. In certain embodiments, the first region enables transduction for the resonator. In certain embodiments, the ‘full1material stack region is provided for transduction purposes. In certain embodiments, the ‘full' material stack region enables transduction for the resonator.

[0032] In certain embodiments, the second region is provided for high quality factor, Q, purposes. In certain embodiments, the second region enables high quality factor, Q, for the resonator. In certain embodiments, the silicon only region is provided for high quality factor, Q, purposes. In certain embodiments, the silicon only region enables high quality factor, Q, for the resonator.

[0033] In certain embodiments, the first region is (provided) for providing transduction of the resonator, and the second region is (provided) for providing high quality factor, Q, of the resonator. In certain embodiments, the first region provides transduction of the resonator, and the second region provides high quality factor, Q, of the resonator. In certain embodiments, the first region enables providing transduction of the resonator, and the second region enables providing high quality factor, Q, of the resonator.

[0034] In certain embodiments, the second region is (placed, arranged, provided) in between (at least) two first regions. In certain embodiments, the second region couples (connects) (at least) two first regions together. In certain embodiments, all the regions combined cover the entire surface (area) of the resonator. In certain embodiments, each of the regions cover only partially (partly, not fully) the surface area of the resonator (as seen (looked, observed) from above (top view, from up to down)). In certain embodiments, the first (second, third, fourth, further) regions covers less than 60% of a total surface area of the resonator. In certain embodiments, the first (second, third, fourth, further) regions covers less than 50% of a total surface area of the resonator. In certain embodiments, the first region covers a surface area of 25% to 75% of the total surface area of the resonator. In certain embodiments, the first region covers a surface area of 50% to 60% of the total surface area of the resonator. In certain embodiments, the second region covers a surface area of 25%

[0035]

[0036] covers a surface area of 40% to 50% of the total surface area of the resonator. In certain embodiments, a ratio of the first region to the second region (full material stack region to silicon-only region) is optimized to balance the (desired) quality factor, Q, and equivalent series resistance, ESR.

[0037] In certain embodiments, the regions covering partially the surface area of the resonator are provided (manufactured, fabricated) via deposition, such as via sputtering. In certain embodiments, the regions covering partially the surface area of the resonator are provided (manufactured, fabricated) via patterning and etching. In certain embodiments, the regions are patterned using lithography.

[0038] In certain embodiments, the resonating element of the resonator comprises at least a first region, and a second region, and wherein material stacks of the first region and the second region are different from one another. What is above disclosed in the context of the resonator comprising the first and the second region, applies also herein in the context of the resonating element comprising the first and second regions.

[0039] In certain embodiments, the first region and the second region are separated by one another by trench(es) and / or isolation regions. In certain embodiments, trench (cavity) is an empty space separating relevant regions. In certain embodiments, the isolation region comprises electrically insulating material (layer), such as the piezoelectric material (layer). In certain embodiments, the isolation region comprises a silicon layer and an insulating material layer. In certain embodiments, the isolation region comprises a silicon layer and a piezoelectric material layer. In certain embodiments, the material stack of the isolation region comprises a silicon layer and the insulating material layer on the silicon layer. In certain embodiments, the isolation region prevents (is configured to prevent) a short circuit between the first region and the second region.

[0040] In certain embodiments, at least one dimension of the first region or the second region is adjusted (changed, corrected, modified) to match the resonance frequencies of the first region and the second region. In accordance with certain embodiments, the matching of the frequencies refers to rendering the resonance frequencies same (or essentially same). In certain embodiments, the first and the second region have matching resonance frequencies (even though their material stacks are different).In certain embodiments, the first region and the second region each comprise at least one dimension that is different from the corresponding dimension of the other region. In certain embodiments, one dimension of the first region is different from the corresponding dimension of the second region. In certain embodiments, length (dimension) of the first region is different from the length (dimension) of the second region. In certain embodiments, width (dimension) of the first region is different from the width (dimension) of the second region.

[0041] In certain embodiments the first and the second region (are configured to) resonate in an (essentially) same resonance frequency. In certain embodiments, the first and the second regions comprise dimension variation of respective dimensions to match the frequencies of the regions. In certain embodiments, the first region and the second region each comprise at least one dimension that is different from the corresponding dimension of the other region to match (adjust, make same) the resonance frequencies of the regions.

[0042] In certain embodiments, the resonating element is separated from the support structure by a cavity, rendering the resonating element to be encircled by a trench (trenches). In certain embodiments, the resonating element is surrounded by trenches in all sides thereof.

[0043] In certain embodiments, the resonator comprises at least one resonating element. In certain embodiments, the resonator comprises at least one resonating plate element. In certain embodiments, the resonating element comprises a plurality of resonating elements, such as resonating beam elements. In certain embodiments, the resonating element comprises a plurality of resonating beam elements (resonating beams). In certain embodiments, each beam element is a sub-element of the resonator. In certain embodiments, the resonating element comprises a plurality of resonating beam elements side by side in a plane, connected to one another by connection elements and separated from one another by trenches.

[0044] In certain embodiments, the resonating element comprises a plurality of resonating beam elements. In certain embodiments, the resonating beam elements are separated from one another by trenches. 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. In certain embodiments, each adjacent beam element is mechanically connected to another beamelement by connection elements. In certain embodiments, each adjacent beam element is mechanically connected to another beam element by (at least) two connection elements.

[0045] 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 resonating element comprises a plurality of resonating beam elements adjacent to each other in a plane, connected to one another by connection elements and separated from one another by trenches. In certain embodiments, the resonating beam elements are longitudinally aligned within 25 degrees of a <100> crystal direction of silicon.

[0046] In certain embodiments, the plurality of beam elements are positioned 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.

[0047] 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 (the resonating element) is in the shape of a rectangle. In certain embodiments, the resonator (the resonating element) is in the shape of an elongated rectangle (beam-shaped). In certain embodiments, the resonator (the resonating element) has an aspect ratio (ratio of length to width, when observed from above) different from 1.

[0048] 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 (anchoring point) configured to connect the resonator to, and suspend the resonator from surrounding layers. In certain embodiments the at least one anchor (anchoring point) comprises portions of the piezoelectric layer, the top electrode layer and the bottom electrode.In certain embodiments, each beam element is in the 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.

[0049] In certain embodiments, the resonator is on a substrate. 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.

[0050] 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).

[0051] 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).

[0052] 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).

[0053] 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 eachresonating beam is within 25 degrees of the

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

[0054] 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).

[0055] In certain embodiments, the resonating (beam) element is a slanted element. In certain embodiments, the slanted element comprises a slanted resonating beam. In certain embodiments, the slanted resonating (beam) element is configured to resonate in its length direction, and wherein a longitudinal axis of the slanted resonating (beam) element is slanted from a <100 direction of silicon. In certain embodiments, said slanting is to reduce the effect of drive level dependency. In certain embodiments, the longitudinal axis is slanted 16 to 22 degrees, more preferably 18 to 20 degrees, most preferably 19 degrees from said <100> direction. In certain embodiments, the slanted resonating (beam) element is in the form of a skewed rectangle. In certain embodiments, the slanted resonating (beam) element is in the form of a resonating (beam) element skewed in one (and only one) direction. In certain embodiments, the resonating element is a slanted resonator element, wherein a longitudinal axis of the slanted resonating element is tilted from a <100> direction of silicon. In certain embodiments, the slanted resonator element comprises a slanted resonating beam comprising single-crystalline silicon. In accordance with certain embodiments, a slanted resonating element according to published patent application WO2024 / 218431 A1 may be provided herein.

[0056] 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. In certain embodiments, the resonating element is configured to resonate in a square-extensional, SE, resonance mode. In certainembodiments, the resonating element is configured to resonate in a width-extensional, WE, resonance mode.

[0057] 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.

[0058] 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. In certain embodiments, the resonator is configured to operate in an overtone resonance frequency of 32 MHz. In certain embodiments, the resonator is configured to operate in a resonance frequency of 76.8 MHz.

[0059] In certain embodiments, the resonator comprises a plurality of resonating elements adjacent to each other in a plane, connected to one another by a coupler. In certain embodiments, the resonator is a multi-ladder resonator, comprising a plurality of stacked beam resonating elements (forming a ladder-like configuration). In certain embodiments, each resonator comprises a plurality of resonating elements having a plurality of beam elements having a length and a width, wherein the plurality of beam elements are positioned adjacent to each other and adjacent beam elements are mechanically connected to each other by connection elements. In certain embodiments, the plurality of beam elements are separated from each other by trenches.

[0060] In certain embodiments, the resonator comprises a plurality of extensional-mode resonating elements. In certain embodiments, the resonator comprises a plurality of length extensionalmode resonating elements. In certain embodiments, the resonator comprises a plurality of flexural-mode resonating elements. In certain embodiments, the resonator comprises a mechanical coupler which connects the resonating elements to one another.

[0061] In certain embodiments, the resonator comprises at least a first region, and a second region, wherein the first region comprises at least one resonating element, and the second region comprises at least another resonating element (area of the resonating element), in certainembodiments, the material stacks of the one resonating element and the another resonating element are different from one another.

[0062] In certain embodiments, the first region and the second region have matching temperature coefficient of frequencies, TCFs. matched according to example embodiments. In certain embodiments, the first and the second region have matching (the same, equal, identical) TCFs despite their material stacks being different (from one another, from each other). In certain embodiments, the ‘matching’ of the TCFs is used to refer to said regions having same (or corresponding, or equal) temperature coefficient of frequency values.

[0063] In certain embodiments, said TCF matching is provided by decreasing the size of the trenches of the second region (in comparison to the trenches of the first region). In certain embodiments, said TCF matching is provided by decreasing the length of the trenches of the second region (in comparison to the trenches of the first region). In certain embodiments, said TCF matching is provided by removal of trenches from the second region (whilst the trenches of the first region remain).

[0064] In certain embodiments, the resonator comprises at least one first region, and a second region, wherein material stacks of the first region and the second region are different from one another, wherein the first region and the second region have matching temperature coefficient of frequencies, TCFs (with one another, with each other).

[0065] In certain embodiments, at least one dimension of resonator is adjusted to match the TCFs of the first region and the second region. In certain embodiments, said at least one dimension is a size (a length) of a trench (trenches) of the second region. In certain embodiments, said at least one dimension is an aspect ratio of the first region or the second region.

[0066] In accordance with certain embodiments, any embodiment of the present solution concerning, for example, the resonator, the resonating element, the first region, the second region, the material stacks of the regions can be applied to the TCF matching embodiment. According to a second example aspect of the present disclosure there is provided an apparatus, such as a resonator array (an apparatus), comprising at least one resonator according to the first aspect or any of its embodiments. In certain embodiments, the apparatus comprises (at least) two (more than one) resonators of the first aspect or any of its embodiments coupled to each other. In certain embodiments, the apparatus is a semiconductor apparatus, or a semiconductor device.In accordance with certain embodiments, embodiments of the second aspect are provided, the embodiments comprising subject matter of any single embodiment presented in connection with the first aspect, or the embodiments comprising subject matter of any of the embodiments presented in connection with the first aspect combined with subject matter presented in any other embodiment or embodiments.

[0067] 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.

[0068] BRIEF DESCRIPTION OF THE FIGURES

[0069] Some example embodiments will be described with reference to the accompanying figures, in which:

[0070] Fig. 1a schematically shows a top view of an example resonating element structure according to an example embodiment;

[0071] Fig. 1b schematically shows a cross-sectional view of a full material stack of an example resonator according to an example embodiment;

[0072] Fig. 2a schematically shows a top view of a resonating element having two regions of varying material stacks according to an example embodiment;

[0073] Fig. 2b schematically shows a cross-sectional view of a resonating element having two regions of varying material stacks according to an example embodiment;

[0074] Fig. 2c schematically shows a cross-sectional view of a resonating element having two regions of varying material stacks according to another example embodiment;

[0075] Fig. 3a schematically shows a top view of a resonating element having regions of varying material stacks according to another example embodiment;

[0076] Fig. 3b schematically shows a cross-sectional view of a resonating element having regions of varying material stacks according to another example embodiment;

[0077] Fig. 4a schematically shows a top view of a resonating element having regions of varying material stacks according to yet another example embodiment;Fig. 4b schematically shows a first cross-sectional view of a resonating element having regions of varying material stacks according to yet another example embodiment;

[0078] Fig. 4c schematically shows a second cross-sectional view of a resonating element having regions of varying material stacks according to yet another example embodiment; Fig. 5a schematically shows a top view of a resonating element having regions of varying material stacks according to still yet another example embodiment;

[0079] Fig. 5b schematically shows a first cross-sectional view of a resonating element having regions of varying material stacks according to still yet another example embodiment; Fig. 5c schematically shows a second cross-sectional view of a resonating element having regions of varying material stacks according to still yet another example embodiment;

[0080] Fig. 6a schematically shows a top view of a resonating element having two regions of varying material stacks according to a further example embodiment;

[0081] Fig. 6b schematically shows a cross-sectional view of a resonating element having two regions of varying material stacks according to a further example embodiment;

[0082] Fig. 7a schematically shows a top view of a resonating element having regions of varying material stacks with frequency matching according to an example embodiment; Fig. 7b schematically shows a top view of a resonating element having regions of varying material stacks with frequency matching according to another example embodiment;

[0083] Fig. 8a schematically shows a top view of a resonator having multiple resonating elements coupled by a rigid coupler, the resonator having regions of varying material stacks according to an example embodiment;

[0084] Fig. 8b schematically shows a top view of a resonator having multiple resonating elements coupled by a rigid coupler, the resonator having regions of varying material stacks according to another example embodiment;

[0085] Fig. 8c schematically shows a top view of a resonator having multiple resonating elements coupled by a rigid coupler, the resonator having regions of varying material stacks according to yet another example embodiment;

[0086] Fig. 8d schematically shows a top view of a resonator having multiple resonating elements coupled by a flexural coupler, the resonator having regions of varying material stacks according to an example embodiment;Fig. 8e schematically shows a top view of a resonator having multiple resonating elements coupled by a flexural coupler, the resonator having regions of varying material stacks according to another example embodiment;

[0087] Fig. 9a schematically shows a top view of a resonator having multiple resonating elements coupled by a LE-beam coupler, the resonator having regions of varying material stacks according to an example embodiment;

[0088] Fig. 9b schematically shows a top view of a resonator having multiple resonating elements coupled by a LE-beam coupler, the resonator having regions of varying material stacks according to another example embodiment;

[0089] Fig. 9c schematically shows a top view of a resonator having multiple resonating elements coupled by a LE-beam coupler, the resonator having regions of varying material stacks according to yet another example embodiment;

[0090] Fig. 10a schematically shows a top view of a resonator having LE- and Lame mode resonating elements coupled by a coupler, the resonator having regions of varying material stacks according to an example embodiment;

[0091] Fig. 10b schematically shows a top view of a resonator having LE- and Lame mode resonating elements coupled by a coupler, the resonator having regions of varying material stacks according to another example embodiment;

[0092] Fig. 11a schematically shows a top view of a resonating element having the first and the second regions with temperature coefficient of frequencies matched according to an example embodiment; and

[0093] Fig. 11b schematically shows a top view of a resonating element having the first and the second regions with temperature coefficient of frequencies matched according to another example embodiment.

[0094] DETAILED DESCRIPTION

[0095] In the following description, like reference signs denote like elements or steps.

[0096] As used herein, the term “(semiconductor) apparatus” or “device” refers to any kind of apparatus or device that may appear in a semiconductor industry, such as a chip, circuitry, microchip, microprocessor, silicon chip, computer chip, resonator, sensor, accelerometer, gyroscope, actuator, energy harvester and process-control unit, vacuum tube or alike. Incertain embodiments, the semiconductor device has been packaged. The semiconductor apparatus may be a MEMS apparatus.

[0097] As used herein, the term “material stack” refers to the resonator materials that form the cross-sectional layer structure of the resonator. Thus, the term stack refers to a cross-sectional stack, meaning that the materials can be seen on top of each other once observing the cross-section of the resonator. When observed from the top, only the topmost layer of the particular region can be seen. In accordance with certain embodiments, some of the materials of the material stack originate from the substrate itself (such as the silicon layer), and some of the materials are provided / deposited onto the substrate.

[0098] As used herein, the notation “the layer X on the layer Y” refers to the layer X being above the layer Y within the material stack in question. Synonyms for the notation are, by way of example, ‘the layer X on top of the layer Y’, ‘the layer X onto the layer Y’, and ‘the layer X above the layer Y’. As used herein, the notation ‘the layer X below the layer Y’ refers to the layer X being underneath the layer Y within the material stack in question. Synonyms for the notation are, by way of example, ‘the layer X under the layer Y’, and ‘the layer X underneath the layer Y’.

[0099] As used herein, the terms “first / second / third / fourth region” refer to an area or areas of the resonator. In accordance with certain embodiments, the “region” may be one area, such as one rectangular shaped area within the resonator. Alternatively, the “region” may be divided into several areas (sub-regions) within the resonator, separated from each other by other region(s) or other resonator features, such as by a coupler or a trench. Regardless of any such division - herein the term “region” encompasses all the divided areas (sub-regions) of the resonator under the one common term “region”. The region(s) are not limited to a particular shape, size and location within the resonator in accordance with certain embodiments. Synonyms for “region” include, but are not limited to a part, section, and area. The regions of the resonator may be observed in top view, wherein the regions can be identified by the different topmost layers in accordance with certain embodiments. The regions of the resonator may also be observed in a cross-sectional side view, wherein the regions can be identified based on the different material stacks thereof and having varying thicknesses in comparison to one another in accordance with certain embodiments.

[0100] Fig. 1a schematically shows a top view (from above, from up to down) of an example resonator demonstrating an example structure thereof according to an example embodiment. In certain embodiments, the resonator 100 comprises a resonating element101. In certain alternative embodiments, the resonator 100 comprises a plurality of resonating element 101.

[0101] The resonator 100 according to embodiment shown in Fig. 1a comprises a resonating element 101. The resonating element 101 comprises a plurality of resonating beam elements having a length L and a width W. In certain embodiments, the resonating beam elements are beam elements (beam-shaped). In the embodiment shown in Fig. 1a, the resonating element 101 comprises seven resonating beam elements (the number of beam elements may vary depending on the embodiment). In certain embodiments, the resonating beam elements are longer L than they are wide W. In certain embodiments, the coordinate system is selected so that the x-axis resides in the width direction W of the resonating beam element and the y-axis in the longitudinal direction L of the resonating beam elements.

[0102] According to the example embodiment shown in Fig. 1a, the plurality of resonating beam elements are positioned adjacent to each other. In certain embodiments, the plurality of resonating beam elements form a ladder-like configuration (stacked beam resonator). In certain embodiments, the plurality of resonating beam elements are positioned adjacent to each other in a width direction thereof. The adjacent resonating beam elements are mechanically connected to each other.

[0103] In certain embodiments, the resonating element is formed of the plurality of resonating beam elements and a plurality of connection elements 102. In certain embodiments, said adjacent resonating beam elements are mechanically connected to each other by connection elements 102 (such as two connection elements 102). In certain embodiments, the adjacent resonating beam elements are separated by trenches 104. In certain embodiments, the trenches 104 have a length TL (trench length). In certain embodiments, the length L (y-directional length) of the beam element comprises at least the length of the trench TL and the length of at least one connection element 102.

[0104] In certain preferred embodiments, the resonator 100 is a stacked beam resonator comprising a plurality of resonating beam elements 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 are positioned in the same plane. In certain stacked beam resonators, no two resonating beam elements are positioned atop each other.In certain embodiments, the resonating beam elements of the resonating element 101 are arranged in a rectangular array configuration. In certain embodiments, the resonating element 101 has a length L (which is equal to the length of the beam element). In certain embodiments, the resonating element 101 has a width RW (resonating element width, also called as x-directional length of the resonating element).

[0105] In certain embodiments, the resonating element 101 is attached to a support structure (support structure not shown in Fig. 1a). In certain embodiments, the resonating element 101 is suspended to the support structure via an anchoring point 103a / 103b. In certain embodiments, the resonating element 101 is suspended to the support structure via more than one anchoring point 103a / 103b, such as two anchoring points 103a / 103b. In certain embodiments, the resonating element 101 is attached to the support structure 110 from the outermost resonating beam elements by anchoring point(s) 103a / 103b. In certain embodiments, the anchoring points 103a / 103b are connected to respective electrical terminal. In certain embodiments, the electrical terminal(s) are arranged at the anchoring point(s) 103a / 103b. In certain embodiments, the resonating element is separated from the support structure 110 by (an external) trench 104’.

[0106] In certain embodiments, the resonating element 101 is of an elongated shape (having the length L smaller than their width RW). In certain embodiments, the resonating element 101 is in the shape of a rectangle (the resonator 100 has a shape of a rectangle). In certain embodiments, the resonating element 101 has an aspect ratio (ratio of length L to width RW, when observed from above) different from 1. In certain embodiments, the resonating element 101 has a length-to-width, L-to-RW, aspect ratio of less than 1.

[0107] In certain embodiments, the resonating beam elements are of an elongated shape (having their length L larger than their width W). In certain embodiments, each resonating beam element is in the shape of a rectangular beam (beam-shaped). In certain embodiments, each resonating beam element has an aspect ratio (ratio of length L to width W, when observed from above) different from 1. In certain embodiments, each resonating beam element has a length-to-width, L-to-W, aspect ratio of more than 1. In certain example embodiments, each resonating beam element has a length-to-width, L-to-W, aspect ratio of more than 2, such as 5, 8, or 10.

[0108] In certain embodiments, the resonator 100 is a megahertz frequency microelectromechanical system, MEMS, resonator. In certain embodiments, the resonator 100 is configured to resonate in an in-plane length-extensional, LE, resonance mode.In certain embodiments, the longitudinal axis L of a resonating element 101 (or the resonating beam element) 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 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.

[0109] Fig. 1b schematically shows a “full” material stack of a resonator according to an example embodiment. Fig. 1b schematically shows an example cross section (sectional view, side view) of the resonating element 101 residing on a substrate. Certain further features of the instant solution are described in detail in the context of Figs. 2a-9b.

[0110] In certain embodiments, the resonator 100 (and the resonating element 101) is fabricated on a substrate. In the example embodiment of Fig. 1b, a silicon on insulator (SOI) substrate (wafer) 450 is used. The reference numerals 401 and 402 denote bottom electrode and top electrode (top electrode layer) contacts, respectively.

[0111] In certain embodiments, the resonator 100 (and the resonating element 101) comprises a material stack, the material stack comprising at least the silicon layer L4, the piezoelectric layer L2 on top of the silicon layer, and a top electrode layer L1 on top of the piezoelectric layer. In certain embodiments, the top electrode layer L1 is the top electrode of the resonator 100. In certain embodiments, the piezoelectric layer comprises doping, such as scandium doping.

[0112] In the example embodiment shown in Fig. 1b, the top electrode layer is implemented in layer L1. In this example embodiment, layer L2 is a piezoelectric layer for piezoelectric actuation of the resonating element residing in the area of denoted by 101. An opening in L2 is denoted by 420. In this example embodiments, layer L3 denotes a layer for the bottom electrode. In this example embodiment, layer L4 is a silicon layer for the resonator (for example resonating beam elements and their connecting elements according to certain embodiments). In this example embodiments, layer L5 is a buried oxide layer (SiO2) of the SOI wafer, and layer L6 is a silicon handle layer. In certain embodiments layer L6 comprises a cavity C1. In certain embodiments, the layer L5 follows the cavity C1 shape as shown in Fig. 1b.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.

[0113] 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. In certain embodiments, more than 50% of the mass of the resonator comprises material portions of single-crystalline silicon.

[0114] In certain embodiments, the resonator 100 (and the resonating element 101) 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 layer L1 on top of the piezoelectric layer L1. In certain embodiments, the resonator 100 is a piezoelectric resonator. In certain embodiments, the resonating element 101 is a piezoelectric resonating element. In certain embodiments, the piezoelectric layer L2 comprises aluminium nitride. In certain embodiments, the top electrode layer L1 is the top electrode of the resonator 100.

[0115] Figs. 2a and 2b schematically show a top view and a cross-sectional view, respectively, of a resonating element 101 having two regions 201, 202 of varying material stacks according to an example embodiment. The example resonating element 101 of Fig. 2a corresponds to the example shown in Fig. 1a. The Fig. 2a shows a dashed line marked 2b-2b, which shows the location of the cross-section shown in Fig. 2b.

[0116] Accordingly, herein is provided a resonator 100, comprising a resonating element 101, wherein the resonator 100 comprises at least one first region 201 , and a second region 202, and wherein material stacks of the first region 201 and the second region 202 are different from one another. As shown in Figs. 2a and 2b, the resonating element 101 is divided into the first 201 and the second region 202. The first region 201 is shown in Fig. 2a as white background with black dots, and the second region 202 is shown in Fig. 2a as grey.As shown in Fig. 2a, the first region 201 comprises two sub-regions, one on each side of the second region 202 in accordance with certain embodiments. In certain embodiments, the first region 201 and / or the second region 202 extend the (entire) length of the resonating element 101 (extending / reaching from one side of the resonating element 101 to another side, extending from a trench 104 to trench 104). In certain embodiments, the first region 201 and / or the second region 202 comprise the area of the resonating beam elements and the connection elements 102.

[0117] In certain embodiments, the first region 201 and / or the second region 202 are formed of (individual / a plurality of) beam element(s) of the stacked beam resonator 100. In certain embodiments, the location of change from the first region 201 to the second region 202 (and vice versa) is located at the trench 104 (and the connection elements 102 on each side of the trench 104). In the embodiment shown in Fig. 2a, the first region 201 comprises the area of four resonating beam elements, and the second region 202 comprises the area of three resonating beam elements.

[0118] As shown in Fig. 2a, in certain embodiments, all the regions 201, 202 combined cover the entire surface (area) of the resonating element 101. In certain embodiments, each of the regions 201, 202 cover partially the surface area of the resonating element 101. In certain embodiments, the first region 201 is provided for transduction purposes, and the second region 202 is provided for high quality factor, Q, purposes. Accordingly, the first region 201 can be called a ‘high transduction’ region 201, and the second region can be called a ‘high quality factor, Q’ region 202.

[0119] In certain embodiments, a ratio of the first region 201 to the second region 202 (areas, surface areas within the resonator), or the second region 202 to the first region 201 is optimized to balance the quality factor, Q, and equivalent series resistance, ESR, of the resonator. In certain embodiments, the ratio of the second region 202 in surface area to the first region 201 in surface area (when observed from above) is in a range of 1:4 to 3:4, preferably in between 2:5 to 1:2. In certain embodiments, the second region 202 covers in surface area (when observed from above) an area that is in the range of 25% to 75%, preferably in between 40% to 50%, of the total surface area of the resonator.

[0120] The quality factor, Q of the resonator can be evaluated such that Q is the inverse of the total losses in the resonator. The total losses of the resonator can be defined based on losses of each region 201 / 202 weighted by their ratio within the resonator. In accordance with certain embodiments, and by way of an example, a 1.5-1.7x improvement in Q-factor hasbeen observed with a resonator having a division of 50-60 % first region area and 40-50 % of second region area (in comparison to a resonator with no division to regions 201 / 202).

[0121] In certain embodiments, the second region 202 enable (are designed to) minimizing thermoelastic dissipation (TED) losses, thereby increasing the quality factor (Q) of the resonator.

[0122] In certain embodiments, the first region 201 is arranged on the proximity of the anchoring point(s) 103a / 103b. In certain embodiments, the first region 201 is arranged to contact the anchoring point(s) 103a / 103b. In certain embodiments, the first region 201 enabling the transduction for the resonating element 101 arranged to contact the anchoring point(s) 103a / 103b provides an electrical connection from the electrical terminals through the anchoring point(s) 103a / 103b to the resonating element 101. In certain embodiments, the transducing beam elements of the first region 201 are placed externally (outer regions, outermost areas) for easier electrical connection to pads through the anchoring points (pads not shown in Fig. 2a).

[0123] As shown in Fig. 2b, in certain embodiments, material stacks of the first region 201 and the second region 202 differ from each other. In certain embodiments, the material stack of the first region 201 comprises all the materials of the resonator’s 100 material stack, rendering the first region 201 to a full material stack region 201 (an example of a ‘full’ stack resonator 100 is also shown in the Fig. 1b). As shown in Fig. 2b, in certain embodiments, the material stack of the first region 201 comprises a top electrode layer L1 , a piezoelectric layer L2, and a silicon layer L4, wherein the piezoelectric layer L2 is on the silicon layer L4, and the top electrode layer L1 is on the piezoelectric layer L2.

[0124] Optionally, the material stack of the first region 201 comprises a bottom electrode layer L3 (not drawn in Fig. 2b, but visible in Fig. 1b). In certain preferred embodiments, like shown in Fig. 2b, the bottom electrode of the resonator 100 is implemented by the silicon layer L4. In certain embodiments, the bottom electrode implemented by the silicon layer L4 comprises doped silicon, such as ultra-heavily doped, UHD, silicon, having the average impurity concentration of at least 1*1019cm-3or more, such as at least 2*1019cm-3or more, such as 102° cm-3or more.

[0125] As shown in Fig. 2b, in certain embodiments, the top electrode layer L1 is the topmost layer of the material stack. In certain embodiments, the top electrode layer L1 comprises metal, such as gold (Au), aluminum (Al), or molybdenum (Mo). In certain embodiments, the topelectrode layer L1 has a thickness in a range of 0.05 m to 0.6 pm, preferably in a range of 0.1 pm to 0.4 pm, such as 0.25 pm.

[0126] In certain embodiments, the piezoelectric layer L2 is of aluminium nitride, AIN, or of scandium-doped aluminium nitride, Sc-doped AIN. In certain embodiments, the piezoelectric layer has a thickness in a range of 1 pm to 3 pm, preferably in a range of 1.3 pm to 1.7 pm, such as 1.5 pm.

[0127] As shown in Fig. 2b, in certain embodiments, the second region 202 comprises only a silicon layer L4, rendering it a silicon-only region. In certain embodiments, the second region 202 contains silicon, such as doped silicon, such as ultra-heavily doped, UHD, silicon. In certain embodiments, the first region 201 and the second region 202 share the same (similar) silicon layer L4.

[0128] In certain alternative embodiments, the silicon layer L4 of the second region 202 is doped to a higher impurity concentration in comparison to the silicon layer L4 of the first region 201. This is achieved by local doping. In certain preferred embodiments, the silicon layer L4 of the second region 202 is doped to ultra-heavy, UHD, doping. In accordance with certain embodiments, said doping of the silicon in the second region 202 to a locally higher impurity concentration than in the first region(s) 201 enables reducing the TCF (temperature coefficient of frequency) of the second region 202. This enables matching the TCFs of the first region and the second region with each other.

[0129] In certain embodiments, the top electrode layer L1 and the silicon layer L4 do not touch one another (as it would create a short circuit, within the first region 201 or in between the first region 201 and the second region 202). In certain embodiments, the first region 201 and the second region 202 are electrically isolated (separated, insulated). As shown in Figs. 2a and 2b, the first region 201 and the second region 202 are separated from each other by isolation regions 215 and trenches 104. In certain embodiments, the isolation region 215 comprises electrically insulating material, such as the piezoelectric material. In certain embodiments, the isolation region 215 comprises a silicon layer L4 and a piezoelectric material layer L2 on top of the silicon layer L4. In certain embodiments, the first region 201 and the isolation region 215 share the layer L2. In certain embodiments, the isolation regions 215 travel (reach) along the length direction (y-direction, y-axis) of the resonating beams. In certain embodiments, the isolation region 215 is a co-linear extension of a trench 104. In certain embodiments, the isolation region 215 reaches from trench 104 to an external trench 104’.In certain embodiments, the isolation region 215 is a narrow strip of electrically isolating material in between the firstand second region. In certain embodiments, the isolation region 215 prevents a short circuit between the first region 201 and the second region 202.

[0130] Fig. 2c schematically shows an embodiment, wherein the material stack of the second region 202 comprises a silicon layer L4 and a silicon nitride layer L7. In certain embodiments, the silicon nitride layer L7 is deposited on top of the silicon layer L4.

[0131] In certain embodiments, the layer of silicon nitride L7 on the silicon layer L4 assists in matching the TCFs (temperature coefficient of frequency) of the first region and the second regions. In certain embodiments, the silicon nitride layer L7 is deposited on the silicon layer L4 to make the second region’s 202 TCF more negative. In certain embodiments, the silicon nitride stoichiometry is tuned to match the negative TCF of piezoelectric layer L2 of the first region 201. In certain embodiments, the layer thickness of the silicon nitride layer L7 can be adjusted to match TCF of the piezoelectric layer L2 of the first region 201. Figs. 3a and 3b schematically show a top view and a cross-sectional view, respectively, of a resonating element 101 having regions 201, 202 of varying material stacks according to another example embodiment. The example resonating element 101 of Fig. 3a corresponds to the example shown in Fig. 1a. The Fig. 3a shows a dashed line marked 3b-3b, which shows the location of the cross-section shown in Fig. 3b. The layer(s) of the material stacks of the first region 201 and the second region 202 shown herein correspond to the material stacks disclosed in the context of Figs. 2a and 2b.

[0132] As shown in Figs. 3a and 3b, the second region 202 is divided into two sub-regions. As shown, in certain embodiments, the second region 202 contains the area of the resonating beam elements (length of the second region 202 equals to the trench length TL). In certain embodiments, the second region 202 sub-regions are encircled by the first region 201. In certain embodiments, the first region 201 extends the (entire) length of the resonating element 101, from one side of the resonating element 101 to another side. In certain embodiments, the first region 201 comprises both the resonating beam elements and the connection elements 102.

[0133] In certain embodiments, the connection elements 102 within the first region 201 enable electrical connection (electrical current, charge carriers) across the resonating element 101. In certain embodiments, as shown in Figs. 3a and 3b, the centermost beam of the resonating element 101 is part of the first region 201. In accordance with certain embodiments, it is preferable to place a transducing (first region 201) resonating beamelement in the center of the resonating element, as most displacement typically occurs in the center. In certain embodiments, the first region 201 arranged to contact the anchoring point(s) 103a / 103b provides an electrical connection from the electrical terminals through the anchoring point(s) 103a / 103b to the resonating element 101.

[0134] In certain embodiments, as shown in Fig. 3a, the first region 201 and second region 202 are electrically separated from one another by a narrow isolation region 215. This prevents a short-circuit between the regions 201 , 202.

[0135] Figs. 4a, 4b and 4c schematically show a top view, a first cross-sectional view and a second cross-sectional view, respectively, of a resonating element 101 having regions of varying material stacks according to yet another example embodiment. The example resonating element 101 of Fig. 4a corresponds to the example shown in Fig. 1a. The Fig. 4a shows two dashed lines marked 4b-4b, and 4c-4c. The dashed lines show the locations of the cross-sections shown in Fig. 4b and 4c, respectively.

[0136] As shown in Figs. 4a, 4b and 4c, in certain embodiments, the resonator further comprises a third region 203. The third region 203 is shown in Figs. 4a, 4b and 4c as grey backslash lines on a white background. In accordance with certain embodiments, the third region 203 may be called a further region, or an additional region, depending on an embodiment. In certain embodiments, the third region 203 can be also called as isolation region, or an extended isolation region (since it serves a similar purpose in certain parts of the resonator as the isolation region 215 as explained in context of Figs. 2a and 2b, and Figs. 3a, and 3b). In between the first region 201 and the second region 202, in accordance with certain embodiments, there is a trench or a third region 203 (analogous with isolation regions 215), or both. This prevents a short-circuit between the regions 201, 202.

[0137] In certain embodiments, the third region 203 is divided into a plurality of sub-regions. In certain embodiments, the material stack of the third region 203 differs from the material stacks of the first region 201 and the second region 202. The material stacks of the first region 201 and the second region 202 shown herein correspond to the material stacks disclosed in the context of Figs. 2a and 2b.

[0138] As shown in Figs. 4a, 4b and 4c, in certain embodiments, the material stack of the third region 203 comprises a piezoelectric layer L2, and a silicon layer L4, wherein the piezoelectric layer L2 is on the silicon layer L4. As shown in the embodiments of Figs. 4b and 4c, in certain embodiments, the first region 201, the second region 202 and the thirdregion 203 share the same silicon layer L4. As shown in the embodiments of Figs. 4b and 4c, in certain embodiments, the first region 201 and the third region 203 share the same piezoelectric layer L2.

[0139] As shown in Fig. 4a, in certain embodiments, the third region 203 is provided at the peripheral area(s) of the resonating element 101 (at the resonating beam element ends / at the area of the connection elements 102). In certain embodiments, the provision of the third region 203 enables aiding in matching the resonance frequencies of the different regions.

[0140] In certain embodiments, the third region 203 is patterned such that it does not prevent the movement of charge carriers within the first region 201. This is shown in Fig. 4a by way of an example, wherein the third region 203 is patterned to draw inwards at the trenches 104. This way, the charge carries are enabled to travel within the first region 201 (not stopped by the trenches 104 and the third region 203). Thereby, an electrical connection to all the beam elements is provided in accordance with certain embodiments.

[0141] Figs. 5a, 5b and 5c schematically show a top view, a first cross-sectional view and a second cross-sectional view, respectively, of a resonating element 101 having regions of varying material stacks according to still yet another example embodiment. The example resonating element 101 of Fig. 5a corresponds to the example shown in Fig. 1a. The Fig. 5a shows two dashed lines marked 5b-5b, and 5c-5c. The dashed lines show the locations of the cross-sections shown in Fig. 5b and 5c, respectively.

[0142] As shown in Figs. 5a, 5b and 5c, in certain embodiments, the resonator further comprises a fourth region 204. The fourth region 204 is shown in Figs. 5a, 5b and 5c as white dots on a black background. In accordance with certain embodiments, the fourth region 204 may be called a further region, or an additional region, depending on an embodiment. In certain embodiments, the material stack of the fourth region 204 differs from the material stacks of the first region 201 and the second region 202. In certain embodiments, material stack of the fourth region 204 comprises at least a trimming material layer, such as a trimming material layer on the silicon layer L4. In certain embodiments, the trimming material layer comprises (is of, consists of) metal, such as gold, Au.

[0143] In certain embodiments, the provision of the trimming material layer of the fourth region 204 enables trimming of the resonator frequency. In certain embodiments, the provision of the trimming material layer of the fourth region 204 further enables assisting in matching the resonance frequencies of the different regions.In certain embodiments, the fourth region 204 is arranged at the peripheral areas of the resonating element 101 (at the resonating beam element ends / at the area of the connection elements 102). In certain embodiments, the peripherals of the resonating element 101 form a point of high velocity, rendering the peripherals having higher frequency sensitivity for material trimming. In certain embodiments, during the length-extensional resonance, the peripherals of the resonating element 101 form a point of low strain and stress, resulting in low thermoelastic dissipation, TED, losses (due to the fourth region 204).

[0144] In certain embodiments, as shown in Figs. 5a, 5b and 5c, the resonator comprises the first region 201, the second region 202 and the fourth region 204. In certain still other embodiments, the resonator comprises the first region 201, the second region 202, and the third region (but not the fourth region 204). In certain still other embodiments, the resonator comprises a first region 201, a second region 202, the third region and the fourth region 204. In certain embodiments, the resonator comprises still further regions (the resonator is not limited to four regions in accordance with certain embodiments). In certain embodiments, the material stacks of all the regions 201, 202, 203, 204 of the resonator 100 are different from each other. In certain embodiments, the resonator comprises a plurality of regions 201, 202, 203, 204, each having a unique material stack in comparison to each other.

[0145] In certain embodiments, as shown in Figs. 5a and 5b, the first region 201 and second region 202 are electrically insulated from one another by an isolation region 215 of piezoelectric material (from the layer L2). This prevents a short-circuit between the regions 201, 202. The isolation region 215 allows easing of manufacturing tolerances. Figs. 6a and 6b schematically show a top view and a cross-sectional view, respectively, of a resonating element having two regions of varying material stacks according to a further example embodiment. The example resonating element 101 of Fig. 6a corresponds to the example shown in Fig. 1a. The Fig. 6a shows a dashed line marked 6b-6b, which shows the location of the cross-section shown in Fig. 6b. The layer(s) of the material stacks of the first region 201 and the second region 202 shown herein correspond to the material stacks disclosed in the context of Figs. 2a and 2b.

[0146] As shown in Figs. 6a and 6b, the second region 202 is divided into three sub-regions. As shown, in certain embodiments, the second region 202 is provided into the area of the resonating beam elements. In certain embodiments, the length of the second region 202 is less than the trench length TL (and less than the resonating beam length). In certain embodiments, the length of the second region 202 is n % of the trench length TL, whereinn is a number in between 1 and 99. In certain embodiments, the second region 202 subregions are encircled by the first region 201. In certain embodiments, the first region 201 comprises both the resonating beam elements and the connection elements 102.

[0147] In certain embodiments, as shown in Figs. 6a and 6b, the adjacent beam elements have alternating order of the first region 201 and the second region 202. In certain embodiments, the first region 201 and the second region 202 alternate within the resonating element 101. In certain embodiments, the first region 201 and the second region 202 alternate within the resonating element 101, such that every other beam element comprises (at least partly) the first region 201 and every other beam element comprises (at least partly) the second region 202. The alternating arrangement of the first region 201 and the second region enables applying a more uniform force.

[0148] In certain embodiments, as shown in Fig. 6a, the first region 201 and second region 202 are electrically disconnected from one another by an isolation region 215. In certain embodiments, the isolation regions 215 travel (reach) along the width direction (x-direction, x-axis) of the resonating beams. In certain embodiments, the first region 201 and the second region 202 are electrically isolated (different, separated) regions.

[0149] Figs. 7a and 7b schematically show a top view of a resonating element 101 having regions of varying material stacks with frequency matching according to an example embodiment. The example resonating elements of Figs. 7a and 7b corresponds to the example shown in Fig. 1a. In certain embodiments, at least one dimension of resonator is adjusted to match the resonance frequencies of the first region and the second region. In certain embodiments, said at least one dimension is a dimension of the first region or the second region. This embodiment is shown in Figs. 7a and 7b.

[0150] In certain embodiments, the resonating element 101 in area of the first region 201 and the resonating element 101 in area of the second region 202 have different dimensions in comparison to one another. The corresponding dimension D1, D2 may be, by way of examples, length, width, diameter, radius, or any other dimension observable from the resonating element 101. In the examples shown in Figs. 7a and 7b, the corresponding dimension is the length of the resonating element 101 (marked as L in Fig. 1a). In certain embodiments (not shown), the aspect ratio of the first region 201 or the second region 202 is adjusted to match the frequencies.

[0151] As shown in Fig. 7a, in certain embodiments, the corresponding dimension D1 of the first region 201 is smaller than the corresponding dimension D2 of the second region 202. Asshown in Fig. 7b, in certain embodiments, the corresponding dimension D1 of the first region 201 is larger than the corresponding dimension D2 of the second region 202. In certain embodiments, the difference between the dimension D1 and the dimension D2 is in the range of 0.1 pm to 3 pm, preferably in the range of 0.2 pm to 1 pm, such as 0.4 pm.

[0152] In certain embodiments, the trenches 104 have varying (different) widths with one another, to match the resonance frequencies of the first and the second regions. Accordingly, said at least one dimension D adjusted to match the resonance frequencies of the first region and the second region is a dimension of a trench, such as its width (not shown in Figs. 7a and 7b, but further elaborated in context of Fig. 8c). In certain alternative embodiments, the trenches 104 have same (essentially same, comparable) widths with one another. In these embodiments, said dimension D to be adjusted is a dimension of the first region 201 and / or the second region 202, as explained above.

[0153] In accordance with certain embodiments, the change of dimension(s) within the resonating element 101 enables tuning the resonating element 101 geometry to achieve matching resonance frequencies of the different regions. In certain embodiments, all the regions of the resonator are configured to resonate in the (essentially) same resonance frequency. In certain embodiments, the thickness of the piezoelectric layer is varied (adjusted, changed, designed) to adjust (optimize, change, design) the resonance frequency of the first region 201. This also provides an aid in matching resonance frequencies of the different regions.

[0154] Accordingly, herein is provided a resonator 100, comprising a resonating element 101, wherein the resonator 100 comprises at least one first region 201, and a second region 202, wherein material stacks of the first region 201 and the second region 202 are different from one another, and wherein the first region 201 and the second region 202 have the same (identical, matching) resonance frequencies with one another. In other words, the resonance frequency of the first region 201 matches (is the same as, is equal to) the resonance frequency of the second region (and vice versa). In accordance with certain embodiments, the first region 201 and the second region 202 comprise at least one dimension D1, D2 that is different from the corresponding dimension D1, D2 of the other region.

[0155] Figs. 8a, 8b, 8c, 8d, 8e, 9a, 9b, 10a and 10b schematically show a top view of example resonators 100 having multiple resonating elements 101a, 101b, 101c, 101 d coupled by a coupler 310 / 311, the resonator 100 having regions of varying material stacks according to an example embodiment. What is disclosed above in the context of a single resonatingelement applies herein as well (depending on the embodiment), in accordance with certain embodiments.

[0156] In the embodiments of 8a, 8b, 8c, 8d, 8e, 9a, 9b, 10a and 10b, the resonator 100 comprises a mechanically coupled assembly with multiple ‘ladders’ 101 to achieve higher resonator area and improved quality factor (Q). In these embodiments, the resonator is a multi-ladder resonator 100, comprising a plurality of stacked resonating elements 101a, 101b, 101c (each stacked resonating element 101a, 101b, 101c forming a ladder-like configuration). In these embodiments, the resonating elements 101a, 101b, 101c comprise a plurality of resonating beam elements positioned adjacent to each other and adjacent beam elements are mechanically connected to each other by connection elements, and the resonating beam elements are separated from each other by trenches 104 (forming a ladder-like configuration). In certain embodiments, the resonator 100 is separated from a support structure by an external trench 104’. In certain embodiments, the resonator 100 is coupled to (suspended from) a support structure via anchoring point(s) 103. As shown for example in Fig. 8c, in certain embodiments, the anchoring points 103 of the center resonating beam element 101b are omitted.

[0157] In certain embodiments, the resonator 100 comprises at least a first region 201, and a second region 202. The material stacks of the first region 201 and the second region 202 shown herein correspond to the material stacks disclosed in the context of Figs. 2a and 2b, Figs. 3a and 3b, and / or Figs. 6a and 6b. In certain embodiments, the resonator 100 comprises further region(s), such as disclosed in context of Figs. 4a, 4b, 4c and / or in context of 5a, 5b, 5c. Accordingly, in certain embodiments, the material stacks of some of the resonating elements differ from the material stack(s) of some of the resonating element(s).

[0158] Figs. 8a, 8b and 8c schematically show a top view of a resonator 100 having multiple resonating elements coupled by a rigid coupler 310, the resonator 100 having regions of varying material stacks according to an example embodiment. In certain embodiments, the resonator 100 comprises a mechanical coupler 310 which connects the resonating elements to one another. As shown in the embodiments of Figs. 8a, 8b and 8c, the first region 201 and the second region 202 are separated from one another by the rigid couplers 310. In certain embodiments, the couplers 310 (the area of the couplers 310) are comprised into the second region 202.

[0159] The rigid couplers 310 in Fig. 8a reach the entire length of the resonator 100 (in x-direction) in accordance with certain embodiments. In certain embodiments, the rigid coupler 310couples the resonating elements 101a, 110b, 110c to one another only in the middle of the resonating elements, (not extending the entire length of the resonator 100), such as shown in Fig. 8b.

[0160] As shown in Figs. 8a and 8b, the resonating elements 101a, 101b, 101c are coupled to one coupler 310 in each coupling area (one coupler 310 on each side of resonating element 101b). In certain embodiments, such as shown in Fig. 8c, instead of a single coupler 310, the resonating elements 101a, 101b, 101c are coupled to one another via a plurality of couplers 310. In the embodiment of Fig. 8c, the resonating elements 101a, 101b, 101c are coupled to each other by three couplers 310 in each coupling area (three couplers 310 on each side of resonating element 101b).

[0161] In certain embodiments, the first region 201 covers at least one resonating element 101a, 101b, 101c, and the second region 202 covers at least one resonating element 101a, 101b, 101c. In the embodiments shown in Figs. 8a, 8b and 8c, the first region 201 covers two resonating elements 101a, 101c, and the second region 202 covers one resonating element 101b. In certain embodiments, the second region 201 resonating element 101b is arranged in the middle of the two first region 201 resonating elements 101a, 101c. In accordance with certain embodiments, the second region 202 (resonating element) couples the first regions 201 (resonating elements) together. In certain embodiments, the first region 201 and second region 202 are electrically isolated from one another by an isolation region 215.

[0162] In certain alternative embodiments (not shown), the first region 201 resonating element 101b is arranged in the middle of the two second region 202 resonating elements 101a, 101c. The first region 201 resonating element and the second region 202 resonating elements arrangements with respect to each other are not limited to the examples shown herein in Figs. 8a, 8b, and 8c.

[0163] In certain embodiments, the first region 201 and the second region 202 of the resonator 100 are configured to resonate out-of-phase with one another. This is the case, by way of an example, in Figs. 8a, 8b, and 8c, wherein the two first region 201 resonating elements 101a, 101c are configured to resonate in-phase with one another. In this embodiment, the second region 202 resonating element 101b is configured to resonate out-of-phase (in comparison to the two first region 201 resonating elements 101a, 101c).

[0164] In certain alternative embodiments, the first region 201 and the second region 202 of the resonator 100 are configured to resonate in-phase with one another.In certain embodiments, the first region 201 and the second region 202 of the resonator 100 are configured to resonate in the same resonance modes with one another, such as in a 3rd harmonic length-extensional resonance mode. This is the case, by way of an example, in Fig. 8a, wherein the entire resonator 100 is configured to resonate in the same, collective length-extensional resonance mode. In certain embodiments, at least one dimension of the resonator 100 is adjusted to match the resonance frequencies of the first region 201 and the second region 202. In accordance with certain embodiments, said dimension is a dimension of the first 201 or the second region 202, or a dimension of the trench 104, 104’.

[0165] In certain embodiments, at least one dimension of the first region 201 or the second region 202 is adjusted to match the resonance frequencies of the first region 201 and the second region 202. As shown in Figs. 8a, 8b and 8c, the dimension D of the resonating elements 101b is adjusted. In this case, the dimension D is the x-directional length of the resonating element 101b (RW, resonating element width, as shown in Fig. 1). As shown in Figs. 8a, 8b and 8c, the central (middle) resonating element 101b has longer dimension D2 than the leftmost and rightmost resonating elements’ 101a, 101c dimension D1. Accordingly, the resonance frequencies of the resonating elements 101a, 101b, 101c is matched to one another (they share the same resonance frequency). In these embodiments, the internal trenches 104 (and optionally the external trenches 104’) have same (essentially same, comparable) widths.

[0166] In certain alternative or additional embodiments, the (internal) trenches 104 have varying (different) widths with one another, to match the resonance frequencies of the first and the second regions as shown in Fig. 8c . In Fig. 8c, the trenches 104 of the first region 201 are of different width than the trenches 104 on the second region 202 (shown in Fig. 8c as Dw-201 and DW-202, respectively).

[0167] In certain embodiments, the trenches 104 of the first region 201 are narrower than the trenches 104 of the second region 202 (or vice versa). In certain example embodiments, the trenches 104 of the first region 201 have a width of in the range of 2 to 4 pm, and the trenches 104 of the second region 202 have a width in the range of 3 to 5 pm, wherein the width DW-2OI of the first region 201 trenches 104 is narrower than the second region 202 trenches 104 width Dw-202. Accordingly, said at least one dimension D adjusted to match the resonance frequencies of the first region 201 and the second region 202 is a dimension of a trench 104, preferably the trench width Dw-201 and Dw-202.It should be noted that the frequency matching via adjusting of the resonator dimension can be performed by adjusting the dimension(s) of the resonating elements 101a, 101b, 101c, such as the length thereof, and / or by adjusting the dimension(s) of the trenches 104 in the first 201 and the second region 202 (alternatively or additionally with one another). In the embodiment shown in Fig. 8c, both the resonating element 101a, 101b, 101c lengths D1, D2 is adjusted and the trench 104 widths Dw-201 and Dw-202 are adjusted.

[0168] The frequency matching is performed since the material stacks of the resonating elements are different in the first and the second regions. Typically, elements with different kinds of material stacks (and same dimensions) do not resonate in a same resonance frequency, since the material choices have an effect on the frequency of the resonator. In accordance with the present solution, the first 201 and the second region 202 have matching resonance frequencies even though they have different material stacks due to the ingenious frequency matching.

[0169] Figs. 8d and 8e schematically show a top view of a resonator 100 having multiple resonating elements 101a, 101b, 101c coupled by a flexural coupler 310, the resonator 100 having regions 201 , 202 of varying material stacks according to an example embodiment. In certain embodiments, the resonator 100 comprises a flexural coupler 310 which connects the resonating elements to one another. In certain embodiments, the coupler 310 is an in-plane flexural coupler.

[0170] In the embodiment shown in Fig. 8d, the resonating elements 101a, 101b, 101c correspond to the individual element 101 shown in Figs. 2a and 2b. The embodiments disclosed in the context of Figs. 2a and 2b for individual element apply herein as well for the multi-ladder resonator 100. As shown in Fig. 8d, in certain embodiments, the couplers 310 (the area of the couplers 310) are comprised into the second region 202. In certain embodiments, the first region 201 and second region 202 are electrically isolated from one another by an isolation region 215.

[0171] As shown in Fig. 8e, in certain embodiments, the resonator 100 comprises a plurality of (more than three) resonating elements 101. In the embodiment of Fig. 8e, the resonator 100 comprises five resonating elements 101. The configuration of Fig. 8e corresponds in certain parts to embodiments of Figs. 8a, 8b and 8c, namely in that the first region 201 and the second region 202 occupy entire resonating elements 101. The relevant embodiments of Figs. 8a, 8b and 8c therefore apply herein as well. Said first region 201 resonating elements and the second region 202 resonating elements alternate in the embodiment ofFig. 8e. It should be noted that the coupler in the embodiment of Fig. 8e is a flexural coupler, whilst Figs. 8a, 8b and 8c show rigid couplers 310.

[0172] In certain embodiments, at least one dimension of the first region 201 or the second region 202 is adjusted to match the resonance frequencies of the first region 201 and the second region 202. In certain embodiments, the length dimension of the resonating elements 101 is adjusted with respect to other resonating elements (adjacent, neighbouring elements). Accordingly, the resonance frequencies of the first region 201 and the second region 202 is matched to one another (they share the same resonance frequency). In these embodiments, the trenches 104, 104’ have same (essentially same, comparable) widths. In certain alternative embodiments, the trenches 104, 104’ have varying (different) widths with one another, to match the resonance frequencies of the first and the second regions (not shown). The first region 201 and the second region 202 arrangements (configurations) with respect to each other are not limited to the examples shown herein in Figs. 8d, and 8e. Figs.

[0173] 9a, 9b and 9c schematically show a top view of a resonator 100 having multiple resonating elements coupled by a LE-beam coupler 311, the resonator 100 having regions of varying material stacks according to an example embodiment.

[0174] In the embodiment shown in Figs. 9a, 9b, and 9c the first region 201 is (provided, located) at the resonating elements 101a, 101b, 101c, and the second region 202 is (provided, located) at the resonating couplers 311. In accordance with certain embodiments, the coupler 311 acts both as a coupling element, and also as a further resonator (resonating element). In certain embodiments, the coupler 311 couples (is configured to couple) the ladders 101. In certain embodiments, the ladders 101 vibrating (resonating) in-phase with one another are coupled to one another by a coupler 311 vibrating (resonating) out-of-phase.

[0175] Figs. 9a, 9b and 9c show length-extensional mode couplers 311. In certain embodiments, the coupler(s) 311 are resonating elements (they resonate). In certain embodiments, the couplers 311 are silicon beams. In these embodiments, the coupler 311 is not a “mere coupler”, and instead it can be described for example as a resonating coupler 311. Instead, herein the coupler 311 is a resonating element, providing the high Q region (the second region) 202 for the resonator. In this embodiment, the coupler(s) 311 is a length-extensional mode resonator. In accordance with these embodiments, the coupler 311 shares the same resonance mode as the first region 201 and the second region 202.In certain embodiments, the coupler 311 is configured to resonate in a length-extensional resonance mode. In these embodiments, the coupler 311 dimensions, such as its length, is tuned (adjusted) to match the resonance frequency of the couplers 311 with the resonance frequency of the resonating elements (ladders) 101a, 101b, 101c. Accordingly, the first region 201 and the second region 202 resonance frequencies are matched. As shown in Figs. 9a, 9b and 9c, in certain embodiments, the first region 201 and second region 202 are electrically isolated from one another by an isolation region 215.

[0176] The embodiments shown in Fig. 9b and 9c correspond to the embodiment shown in Fig. 9a, except that some of the parts of the structure are removed. In the embodiment shown in Fig. 9b, some of the connection elements 102 (shown e.g. in Figs. 1 and 2a) are removed. This allows incorporation of a further overtone resonating element with high aspect ratio (elements 101a combined with beams 311). In accordance with certain embodiments, the overtone resonating element is coupled only on the leftmost and rightmost sides thereof (via the connection elements 102).

[0177] Fig. 9c shows a further embodiment of the overtone resonating element, wherein more parts of the original structure of Fig. 9a have been removed. In the embodiment of Fig. 9c, the beams 311 form the second region 202. In this embodiment, the second region 202 beams 311 (coupler beams 311) are coupled directly to the first region 201 beams. As shown in Fig. 9c, the connection elements 102 are present only in the left- and right-side peripherals of the resonator 100. In accordance with certain embodiments, the Figs. 9a, 9b and 9c show an overtone resonator 100, wherein the second (silicon-only) region 202 is provided on the out of phase portion of the resonating beams.

[0178] In certain embodiments, the resonator 100 operates in an overtone thereof to achieve higher resonator area and improved quality factor, Q. In certain embodiments, the resonator is configured to operate in an overtone resonance frequency. In certain embodiments, the resonator is configured to operate in an overtone resonance frequency of N x 32 MHz, wherein N is 2, 3, 4, 5.... In certain embodiments, the resonator is configured to operate in an overtone resonance frequency of 76 MHz. In certain embodiments, the overtone resonance enables providing enhanced equivalent series resistance, ESR, and quality factor, Q.

[0179] In certain embodiments, the first region 201 and the second region 202 of the resonator 100 are configured to resonate in different resonance modes with one another. This is the case shown, by way of an example, in Figs. 10a and 10b. Figs. 10a and 10b schematically showa top view of a resonator 100 having LE- and Lame mode resonating elements coupled by a coupler 310, the resonator 100 having regions of varying material stacks according to an example embodiment.

[0180] Fig. 10a shows in-plane length-extensional resonating elements 101a, 101b, 101c and Lame mode resonating elements 101 d. In certain embodiments, the resonating elements are coupled to one another by couplers 310.

[0181] In certain embodiments, the first region 201 is arranged at the length-extensional mode resonating elements 101a, 101b and 101c. In certain embodiments, the second region 202 is arranged at the Lame mode resonating elements 101 d. In the embodiment shown in Fig.

[0182] 10a, the resonating elements 101 d (second region 202) are configured to resonate in Lame resonance mode, and the resonating elements 101a, 10b, 101c (first region 201) are configured to resonate in a length-extensional resonance mode. In certain embodiments, the Lame mode resonating elements 101d dimensions are designed such that the frequency of the Lame mode resonating element 101d (the second region 202) is (essentially) the same as the frequency of LE mode resonating elements 101a, 101b, 110c (the first region 201). In this embodiment, all the Lame resonating elements 101 d resonate in-phase with one another.

[0183] In certain embodiments, the Lame mode resonating elements 101 d are each coupled to two LE-mode resonating elements 101a, 101b, 101c by couplers 310. In certain embodiments, the couplers 310 are arranged within the second region 202. In certain embodiments, the first region 201 and second region 202 are electrically isolated from one another by an isolation region 215.

[0184] In certain embodiments, the Lame mode resonating elements 101 d provide a high quality factor, Q, and does not result in TED losses. In certain embodiments, the Lame mode resonating elements 101 d are doped to compensate for drive level dependency effects of the resonator 100, preferably via N-type doping.

[0185] The embodiment shown in Fig. 10b differs from the embodiment of Fig. 10a with respect to coupling of the Lame mode resonating elements 101 d. As shown in Fig. 10b, one of the Lame mode resonating elements 101d is not coupled to the LE-mode resonating elements 101a, 101b, 101c at all. In this embodiment, the middle Lame mode resonating elements 101 d (of the three Lame resonating elements 101 d reciting atop one another) is not coupled to the LE-mode resonating elements 101a, 101b, 101c. In this embodiment, the middleLame mode resonating element 101d is coupled to the top and bottom Lame mode resonating element 101 d via couplers 310.

[0186] In this embodiment, the top and bottom Lame mode resonating element 101 d resonate in-phase with one another. In this embodiment, the middle (central) Lame mode resonating element 101 d resonated out-of-phase with the other two Lame mode resonating elements 101d.

[0187] In certain further embodiments (not shown), the resonating elements 101d is a squareextensional resonating element (instead of a Lame mode element).

[0188] Figs. 11a and 11b schematically shows a resonating element 101 having the first 201 and the second 202 regions with temperature coefficient of frequencies matched according to example embodiments. The resonating elements of Figs. 11a and 11b correspond with the resonating element shown in Fig. 7b.

[0189] Due to the different material stacks of the first region 201 and the second region 202, these regions may have a mismatch in the temperature coefficient of frequencies, TCFs, in accordance with the certain embodiments. In other words, the first 201 and the second regions 202 may have different temperature coefficient of frequencies, TCFs, with one another, in accordance with the certain embodiments.

[0190] In certain embodiments, the mismatch of the TCFs is caused by the different material stacks of the regions 201 , 202. In certain embodiments, the piezoelectric material of the first region 201 decreases the TCF of the first region 201, compared to the second region 202 wherein there is no piezoelectric material in accordance with certain embodiments. In certain embodiments, the first region 201 has more negative TCF value than the second region 202, if no TCF matching is performed.

[0191] In accordance with certain embodiments, the TCFs of the first region 201 and the second region 202 are matched (have the same TCFs, corresponding TCFs, equal TCFs with each other).

[0192] In certain embodiments, as shown in Fig. 11a, said TCF matching is provided by shortening the trenches 104 of the second region 202 (in comparison to the trenches 104 of the first region 201). In other words, the trench length TL in the second region 202 is shorter (smaller, reduced) than the trench length in the first region 201 , in accordance with certain embodiments. When the trench length TL is smaller, the width CW of the connectionelements 102 increases, as shown in Fig. 11a. Therefore, the same phenomenon (decreasing trench length TL) can be described as increasing the width CW of the connection elements 102 in accordance with certain embodiments.

[0193] The decreased trench length TL (and increased connection element width CW) enables reducing the TCF of the second region 202, to match with the TCF of the first region 201.

[0194] In certain embodiments, as shown in Fig. 11b, said TCF matching is provided by removal of the trenches 104 from the second region 202. In this embodiment the connection element width CW is “increased to a maximum”, meaning that the trenches 104 are completely absent in the second region 202.

[0195] The embodiments of Fig. 11a and Fig. 11b enable reducing or eliminating the spurious resonance modes of the resonator over temperature changes, caused by the TCF mismatch. This then enables preventing any yield activity dropping caused by said spurious modes.

[0196] In accordance with the embodiments of the present solution, said TCF matching can be implemented in a single resonating element (single ladder) such as shown in examples Fig.

[0197] 11a and 11b, and in any embodiments with multiple resonating elements. Furthermore, in accordance with the embodiments of the present solution, the TCF matching is provided together with the frequency matching of the resonator, in certain embodiments.

[0198] 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 of the invention is providing a resonator having improved quality factor Q piezoelectric resonators (without requiring electrostatic transduction). A further technical effect obtained via the higher Q is less phase noise in the close to carrier region.

[0199] This is obtained via a trade-off with transduction: the resonator of the instant solution comprises a region for transduction purposes, and a region for high Q resonance. This trade-of can be mitigated by making bigger resonators. In effect, by making the resonator as large as the cavity allows, a resonator with higher Q and good ESR is provided.

[0200] A further technical effect is to provide a pin-to-pin compatible resonator (with quartz). A further technical effect is retaining good temperature compensation features of the resonator.A further technical effect is providing a more positive overall temperature coefficient of frequency, TCF. More positive overall TCF is reached due to reduced piezoelectric coverage of the instant solution. Simultaneously, the instant solution enables providing decreased capacitance, and providing enhanced figure of merit, FOM, of the resonator. The capacitance is decreased because due to the TCF being (very) positive, increase of piezoelectric material thickness increases in order to achieve flat f-vs-T behavior in accordance with certain embodiments. The thickness increase of the piezoelectric layer reduces capacitance. A further technical effect is providing a resonator having reduced tuning sensitivity due to the reduced capacitance of the resonator.

[0201] A further technical effect is providing the above advantages without too complex / critical processing steps, such as lithography, as no narrow gaps are required within the resonator structure. It is known that mass producing such narrow gaps in a repeatable way is challenging. Such narrow gaps may be, for instance, needed in order to reach the high Q in purely electrostatic resonators. Furthermore, the electrostatic solutions require high DC bias voltage and this is not required in the instant solution.

[0202] 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.

[0203] 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.

[0204] 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

1. CLAIMS1. A resonator,comprising a resonating element,wherein the resonator comprises at least one first region, and a second region, wherein material stacks of the first region and the second region are different from one another, andwherein the first region and the second region have matching resonance frequencies.

2. The resonator of claim 1 , wherein at least one dimension of resonator is adjusted to match the resonance frequencies of the first region and the second region.

3. The resonator of claim 2, wherein said at least one dimension is a dimension of the first region or the second region, and / or wherein said at least one dimension is a dimension of a trench.

4. The resonator of any of the preceding claims, wherein the material stack of the first region comprises a top electrode layer, a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer, and the top electrode layer is on the piezoelectric layer.

5. The resonator of claim 4, wherein a bottom electrode of the resonator is implemented by the silicon layer, preferably comprising doped silicon, such as ultra-heavily doped, UHD, silicon.

6. The resonator of any of the preceding claims, wherein the material stack of the second region comprises a silicon layer.

7. The resonator of any of the preceding claims, wherein the material stack of the second region comprises a silicon layer and a silicon nitride layer on top of the silicon layer.

8. The resonator of claim 4, 5, 6 or 7, wherein the silicon layer at the second region is doped to a higher impurity concentration than the silicon layer at the first region.

9. The resonator of any of the preceding claim, wherein the second region couples at least two first regions together.

10. The resonator of any of the preceding claims, wherein the resonator further comprises a third region, wherein material stack of the third region differs from the material stacks ofthe first region and the second region, wherein the material stack of the third region preferably comprises a piezoelectric layer, and a silicon layer, wherein the piezoelectric layer is on the silicon layer, and / or wherein the resonator further comprises a fourth region, wherein material stack of the fourth region differs from the material stacks of the first region and the second region, wherein the material stack of the fourth region preferably comprises at least a trimming material layer.

11. The resonator of any of the preceding claims, wherein the resonating element comprises a plurality of resonating beam elements adjacent to each other in a plane, connected to one another by connection elements and separated from one another by trenches.

12. The resonator of any of the preceding claim, wherein the first region provides transduction of the resonator, and the second region provides high quality factor, Q, of the resonator.

13. The resonator of any of the preceding claim, comprising a plurality of resonating elements adjacent to each other in a plane, connected to one another by a coupler.

14. The resonator of any of the preceding claim, wherein the resonating element is a slanted resonator element, wherein a longitudinal axis of the slanted resonating element is tilted from a <100> direction of silicon.

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

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