Electrode and material layer configuration

Abstract

Herein is provided a device (100), comprising a resonating element (101) having a top electrode layer (L1), wherein the top electrode layer (L1) has a corrugated interface (201) with a layer or layers beneath the top electrode layer (L1). Herein is further provided a method for manufacturing the device (100), comprising the steps of: depositing a layer or layers onto a substrate (L6), forming a corrugated surface, depositing a top electrode layer (L1) on the layer(s) to provide a corrugated interface (201) in between the top electrode layer (L1) and the layer(s) beneath the top electrode layer (L1), wherein the method comprises forming a corrugated surface onto the layer(s) to provide said corrugated interface (201). Herein is further provided an apparatus, such as a device array, comprising at least one device (100).

Description

[0001] ELECTRODE AND MATERIAL LAYER CONFIGURATION

[0002] TECHNICAL FIELD

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

[0004] BACKGROUND

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

[0006] A key performance parameter in semiconductor devices, such as MEMS devices, such as resonators, such as silicon MEMS resonators is the equivalent series resistance (ESR). ESR is inversely proportional to the quality factor Q of the apparatus. The minimization of ESR is often desirable. Another key performance parameter in MEMS devices is the stability of the resonance frequency. In certain devices, such as devices with metallic electrodes, the instability of the metallic layer may lead to frequency instability.

[0007] SUMMARY

[0008] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention.

[0009] It is an object of certain embodiments of the present disclosure to provide improve frequency stability of MEMS devices or at least to provide an alternative to existing technology. Accordingly, certain disclosed embodiments provide for an ingenious device, apparatus and a method for manufacturing the device solving at least one of the problems related to the prior art.

[0010] According to a first example aspect of the present disclosure there is provided a device, comprising a resonating element having a top electrode layer, wherein the top electrode layer has a corrugated interface with a layer or layers (layer(s)) beneath the top electrode layer.

[0011] In certain embodiments, the corrugated interface comprises an uneven surface (non- uniform, not flat, bumpy). In certain embodiments, the corrugated interface is a profiled interface. In certain embodiments, the corrugated interface is a wavy interface. In certain embodiments, the corrugated interface is a ribbed interface. In certain embodiments, the corrugated interface comprises three dimensional shapes. In certain embodiments, the corrugated interface comprises a corrugation. In certain embodiments, the corrugated interface comprises (a plurality of) corrugations. What is herein disclosed for corrugations applies equally to a (single) corrugation.

[0012] In certain embodiments, the corrugations comprise parallel corrugations. In certain embodiments, the corrugations comprise parallel and / or crossing (intersecting) corrugations. In certain embodiments, the corrugations comprise parallel ridges and grooves. In certain embodiments, the corrugated interface comprises a meandering (meander-like), groovy, ridged and / or wavy cross-section. In certain embodiments, the corrugated interface comprises a meandering (meander-like), groovy, ridged and / or wavy profile.

[0013] In certain embodiments, the top electrode layer follows the shapes (patterns, conformations, z-directional shapes) of the layer(s) beneath. In certain embodiments, the top electrode layer follows the corrugations of the layer(s) beneath. In certain embodiments, the top electrode layer follows the corrugations of the layer(s) beneath, to provide the corrugated interface therebetween.

[0014] In certain embodiments, the top electrode layer has a corrugated interface between layer(s) beneath the top electrode layer and the top electrode layer. In certain embodiments, the top electrode layer has a corrugated interface, the corrugated interface being in between the top electrode layer and layer(s) beneath the top electrode layer. In certain embodiments, the corrugated interface comprises corrugations in z-direction. In certain embodiments, the layer(s) beneath the top electrode layer is not corrugated throughout the layer. In other words, in certain embodiments, the layer(s) beneath the top electrode layer is not entirely corrugated, but instead, its surface is corrugated. In certain embodiments, the entire layer(s) beneath the top electrode layer is not in the (same) corrugated shape as the surface of the layer(s) beneath the top electrode layer.

[0015] In certain embodiments, the layer(s) beneath the top electrode layer comprises a corrugated surface (corrugated profile) to provide the corrugated interface with the top electrode layer. In certain embodiments, the layer(s) beneath the top electrode layer is patterned to comprise a corrugated surface. In certain embodiments, the corrugated interface is formed by interchanging thickness of the layer(s) beneath the top electrode layer. In certain embodiments, the corrugated interface is formed by interchanging thickness of the layer(s) beneath the top electrode layer, providing (creating) a meandering, groovy, ridged, or wavy cross-section of the corrugated interface.

[0016] In certain embodiments, the layer directly beneath the top electrode layer comprises a corrugated surface (corrugated profile) to provide the corrugated interface with the top electrode layer. In certain embodiments, the layer directly beneath the top electrode layer comprises an uneven surface. In certain embodiments, the layer directly beneath the top electrode layer is patterned to comprise a corrugated surface. In certain embodiments, the corrugated interface is formed by interchanging thickness of the layer directly beneath the top electrode layer. In certain embodiments, the corrugated interface is formed by interchanging thickness of the layer directly beneath the top electrode layer, providing (creating) a meandering, groovy, ridged, or wavy cross-section of the corrugated interface.

[0017] In certain embodiments, the corrugated interface is not used to refer to a large scale cavities or trenches of the substrate, but to smaller scale corrugations on the surface of a layer. In other words, in certain embodiments, the corrugated interface should be distinguished from a smooth interface which exists between (conformally provided) thin film layers. In certain embodiments, the corrugated interface should be distinguished from a smooth interface which exists between (conformally provided) thin film layers provided onto a large scale substrate cavities (trenches / holes / vias). In certain embodiments, the corrugated interface is not smooth (but instead, uneven).

[0018] In certain embodiments, the corrugated interface is configured to increase (increases) the contact area between the top electrode layer and the layer(s) beneath the top electrode layer. In certain embodiments, the corrugated interface is configured to increase (increases) the contact area between the top electrode layer and the layer(s) beneath the top electrode layer, thereby enhancing the quality factor, Q, of the device.

[0019] In certain embodiments, the resonating element comprises a layer beneath top electrode layer. In certain embodiments, the resonating element comprises layers beneath the top electrode layer. In certain embodiments, the layers beneath the top electrode are positioned adjacent to one another (sharing the same plane). In certain embodiments, the layers beneath the top electrode layer are atop one another. In certain embodiments, the layers beneath the top electrode are positioned partially atop one another.

[0020] In certain embodiments, the corrugations (of the corrugated surface / interface) are oriented in a plane of the layer(s) beneath the top electrode layer (a direction normal to the plane of the layer(s)). In certain embodiments, the corrugations (of the corrugated surface / interface) are oriented in a plane of the piezoelectric layer (a direction normal to the plane of the piezoelectric layer).

[0021] In certain embodiments, the corrugated interface comprises upwards protruding shapes (sections, bumps, forms). In certain embodiments, the corrugated interface comprises downward sinking (contracting, extending) shapes (sections, bumps, forms). In certain embodiments, the corrugations protrude upwards (and / or sink downwards) from the plane of the layer(s) beneath the top electrode layer (thereby creating 3D shapes).

[0022] In certain embodiments, the corrugations (of the corrugated surface / interface) extend (run, reach) across the resonating element. In certain embodiments, the corrugations extend from one edge of the resonating element to another edge (from side to side), In certain embodiments, the corrugations extend from one trench to another trench.

[0023] In certain embodiments, the corrugations comprise straight (or essentially straight) lines. In certain embodiments, the corrugations extend from side to side of the resonating element in length direction, width direction, or in diagonal direction. In certain embodiments, the corrugations are parallel to each other (all running in the same direction).

[0024] In certain embodiments, the corrugations comprise a first set of parallel corrugations, extending from one side to other side in a first direction, and a second set of parallel corrugations, extending from one side to other side in a second direction. In certain embodiments, the first set of parallel corrugations and the second set of parallel corrugations intersect each other. In certain embodiments, the first direction is orthogonal in relation to the second direction. In certain embodiments, the first set of parallel corrugations and the second set of parallel corrugations intersect each other, creating right angles (90 degree angles) therebetween.

[0025] In certain embodiments, the resonating element comprises corrugations in the layer(s) beneath the top electrode thereof. In certain embodiments, the resonating element comprises corrugations in the layer(s) beneath the top electrode to render resonating element (spring) soft. In certain embodiments, the corrugations provide stiffness relaxation of the resonating element. In certain embodiments, the corrugations are configured to render the resonating element release any stress therein.

[0026] In certain embodiments, the corrugations provide a meandering pathway for the charge carriers (electric current, electricity) in z-direction of the resonating element. In certain embodiments, the corrugations provide a meandering pathway for the charge carriers (electric current) in z-direction of the resonating element to render the resonating element (top electrode) soft (reduce its stiffness, reduce its spring effect).

[0027] In certain embodiments, the corrugations are symmetrically arranged on the resonating element. In certain embodiments, the corrugations are asymmetrically arranged on the resonating element.

[0028] In certain embodiments, the resonating element comprises a top electrode (layer) on the resonating element. In certain embodiments, the top electrode (layer) is the topmost layer (surface) of the resonating element. In certain embodiments, the top electrode is configured to cover essentially the entire resonating element.

[0029] In certain embodiments, the top electrode is in a form of a top electrode layer. In certain embodiments, the top electrode is implemented by a layer of metal. In certain embodiments, the top electrode comprises (is of) metal, preferably gold (Au). In certain embodiments, the top electrode is of gold, preferably doped gold. In certain embodiments, the top electrode is of gold alloy.

[0030] In certain embodiments, the top electrode (layer) is implemented by a layer of doped silicon. In certain embodiments, the silicon layer is of single-crystal silicon. In certain embodiments, the top electrode (layer) is implemented by a layer of doped polysilicon. In certain embodiments, the top electrode layer is a multilayer top electrode, the multilayer top electrode comprising a plurality of material layers, preferably a plurality of metal layers.

[0031] In certain embodiments, the top electrode layer comprises patterns (line(s), groove(s), perforation(s) or both). In certain embodiments, the perforation(s) are of round, oval, square, triangle, or cross shaped. In certain embodiments, the top electrode comprises patterns therein (within). In certain embodiments, the top electrode comprises patterns within the top electrode (layer). In certain embodiments, the top electrode (layer) comprises (contains, has) patterns where the top electrode layer (material) is absent. In certain embodiments, the pattern is a region (area) where the top electrode (material, layer) is removed. In certain embodiments, said patterns are formed by patterning the top electrode layer

[0032] In certain embodiments, the patterns are configured to reach (extend) to (into) the layer(s) beneath the top electrode (layer). In certain embodiments, the patterns of the top electrode layer continue through the top electrode layer. In certain embodiments, the patterns of the top electrode layer continue through the top electrode layer to the piezoelectric layer. In certain embodiments, patterns of the top electrode layer are configured to expose the layer(s) beneath the top electrode. In certain embodiments, the patterns are configured to expose the piezoelectric layer beneath the top electrode.

[0033] In certain embodiments, the top electrode (layer) is a uniform layer (of material). In certain embodiments, the top electrode (layer) covers (essentially) the entire (top, topmost) surface of the resonating element.

[0034] In certain embodiments, the top electrode layer is a uniform layer (of material) except where the top electrode layer comprises (contains, has) patterns. In certain embodiments, the top electrode (layer) covers (essentially) the entire (top, topmost) surface of the resonating element except where the top electrode (layer) comprises (contains, has) patterns.

[0035] In certain embodiments, the patterns are configured to reduce the mass of the top electrode. In certain embodiments, the patterns are configured to reduce the mass of the top electrode, wherein at least 5% of the top electrode has been removed by patterns within the resonating element.

[0036] In certain embodiments, the resonating element comprises a bottom electrode. In certain embodiments, the resonating element comprises a bottom electrode layer. In certain embodiments, the bottom electrode layer comprises silicon. In certain embodiments, the bottom electrode layer is implemented within a silicon layer. In certain embodiments, the bottom electrode layer is implemented by a silicon layer.

[0037] In certain embodiments, the resonating element comprises a piezoelectric layer, wherein the piezoelectric layer is the layer beneath the top electrode layer. In certain embodiments, herein is provided a device, comprising a resonating element having a top electrode layer and a piezoelectric layer beneath the top electrode layer, wherein the top electrode layer has a corrugated interface with the piezoelectric layer. In certain embodiments, the resonating element comprises a bottom electrode on the opposite side of the piezoelectric layer than the top electrode layer.

[0038] In certain embodiments, the resonating element comprises a piezoelectric layer, wherein the top electrode is on the piezoelectric layer, and a bottom electrode on the opposite side of the piezoelectric layer than the top electrode. In certain embodiments, the bottom electrode comprises silicon, preferably doped silicon, such as ultra-heavily doped, UHD, silicon. In certain preferred embodiments, the silicon is of single-crystal silicon. In certain embodiments, the bottom electrode (layer) is implemented by an UHD silicon layer. In certain embodiments, a bottom electrode (of the device) is implemented by the silicon layer, wherein the silicon layer (preferably) comprises doped silicon, such as ultra-heavily doped, UHD, silicon.

[0039] In certain embodiments, the doping level of the silicon is above 1019cm-3. In certain embodiments, the doping level of the silicon is above 102° cm"3. In certain embodiments, the doped silicon is of N-type or P-type doping.

[0040] In certain embodiments, the corrugated interface is provided by the corrugated surface of the piezoelectric layer or the corrugated surface of the silicon layer. In certain embodiments, the layers (the top electrode layer, and in certain embodiments also the piezoelectric layer) on top of said corrugated surface follow the corrugations beneath, to provide the corrugated interface.

[0041] In certain embodiments, the device (resonator) comprises a material stack, the material stack comprising the silicon layer (the bottom electrode), the piezoelectric layer on top of the silicon layer, and a top electrode on top of the piezoelectric layer. In certain embodiments, the device is a piezoelectric device. In certain embodiments, the piezoelectric layer comprises aluminum nitride. In certain embodiments, the device (resonator) comprises at least one resonating element. In certain embodiments, the device comprises a resonating plate element. In certain embodiments, the resonating element comprises a plurality of resonating sub-elements. In certain embodiments, the resonating element comprises a plurality of resonating subelements (such as beam elements). In certain embodiments, the resonating element comprises a plurality of resonating beam elements. In certain embodiments, each beam element is a sub-element of the resonating element.

[0042] In certain embodiments, the resonating element comprises a plurality of beam elements having a length and a width. In certain embodiments, the plurality of beam elements are positioned adjacent to each other. In certain embodiments, adjacent beam elements are mechanically connected to each other by connection elements.

[0043] In certain embodiments, the resonating element is a stacked beam resonating element. In certain embodiments, the stacked beam resonating element comprises a plurality of beam elements positioned side-by-side in a plane. In certain embodiments, the plurality of beam elements are positions adjacent to each other in a width direction thereof. In certain embodiments, the plurality of beam elements are positioned adjacent to each other in a width direction of the device. In certain embodiments, the beam elements are separated by trenches. In certain embodiments, the beam elements are connected to each other by connection elements.

[0044] In certain embodiments, the resonating element comprises a plurality of beam elements, such as seven, nine, or eleven beam elements. In certain embodiments, said adjacent beam elements are mechanically connected to each other by at least two connection elements. In certain embodiments, the beam elements of the resonating element are arranged in a rectangular array configuration.

[0045] In certain embodiments, the resonating element is in a shape of a rectangle. In certain embodiments, the resonating element is in a shape of an elongated rectangle (beamshaped). In certain embodiments, the resonating element has an aspect ratio (ratio of length to width, when observed from above) different from 1 .

[0046] In certain embodiments, the resonating element has a length-to-width aspect ratio of less than 1. In certain embodiments, the resonating element is attached (supported, anchored, suspended) to a support structure. In certain embodiments, the resonating element is attached to a support structure from the outermost beam elements of the resonating element. In certain embodiments, the resonating element comprises at least one anchor configured to connect the resonating element to, and suspend the resonating element from surrounding layers (support structure). In certain embodiments the at least one anchor comprises portions of the piezoelectric layer, the top electrode and the bottom electrode. In certain embodiments, the resonating element is separated from the substrate by a cavity (cavity being beneath the resonating element).

[0047] In certain embodiments, each beam element is in a shape of a (rectangular) beam. In certain embodiments, each beam element has an aspect ratio (ratio of length to width, when observed from above) different from 1. In certain embodiments, each beam element has a length-to-width aspect ratio of more than 1 .

[0048] In certain embodiments, the device 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.

[0049] 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).

[0050] 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).

[0051] 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). In certain embodiments, the resonating beam element(s) are longitudinally aligned within 25 degrees of a

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

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

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

[0052] 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).

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

[0054] In certain embodiments, the device (resonating element) is configured to resonate (operate, oscillate, vibrate) in an in-plane resonance mode. In certain embodiments, the resonating element is configured to resonate in a length-extensional, LE, resonance mode. In certain embodiments, the device 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 device. In certain embodiments, the length extensional resonance mode is configured to resonate perpendicular to the width direction of the device.

[0055] In certain embodiments, the resonating element is configured to resonate in a squareextensional, SE, resonance mode. In certain embodiments, the resonating element is configured to resonate in a width-extensional, WE, resonance mode.

[0056] In certain embodiments, the device (resonating element) is configured to resonate in a collective resonance mode. In certain embodiments, each resonating element of the device is configured to resonate in the (same) collective resonance mode. In certain embodiments, the device is configured to resonate in a desired (main) resonance mode. In certain embodiments, each beam element of the device is configured to resonate in the (same) desired resonance mode.

[0057] According to a second example aspect of the present disclosure there is provided an apparatus, such as a device array (an apparatus), comprising at least one device according to the first aspect or any of its embodiments. In certain embodiments, the apparatus comprises (at least) two (more than one) devices of the first aspect or any of its embodiments coupled to each other.

[0058] In certain embodiments, the apparatus comprises extensional-mode device(s). In certain embodiments, the apparatus comprises flexural mode device(s). In certain embodiments, (all, some of) the devices of the apparatus are identical with one another (each other). In certain alternative embodiments, (all, some of) the devices of a device are different from one another.

[0059] According to a third example aspect of the present disclosure there is provided method for manufacturing the device according to the first aspect or any of its embodiments, comprising the steps of: depositing a layer or layers (layer(s)) onto a substrate; forming a corrugated surface on the layer(s); depositing a top electrode layer on the corrugated surface of the layer(s) to provide a corrugated interface in between the top electrode layer and the layer(s) beneath the top electrode layer.

[0060] In certain embodiments, the method comprises the steps of: depositing a layer or layers onto a substrate; depositing a top electrode layer on the layer(s) to provide a corrugated interface in between the top electrode layer and the layer(s) beneath the top electrode layer, wherein the method comprises forming a corrugated surface onto the layer(s) to provide said corrugated interface.

[0061] In certain embodiments, the method comprises the steps of: o depositing a layer or layers (layer(s)) onto a substrate; o forming a corrugated surface on the layer(s); o depositing a top electrode layer on the corrugated surface of the layer(s) to provide a corrugated interface in between the top electrode layer and the layer(s) beneath the top electrode layer. In accordance with the above, the steps of depositing a top electrode layer and forming a corrugated surface on the layer(s) to provide a corrugated interface in between the top electrode layer and the layer(s) beneath the top electrode layer may be in either order.

[0062] In certain embodiments, the substrate comprises a silicon layer, preferably a doped silicon layer, such as UHD silicon layer. In certain embodiments, the bottom electrode of the device (resonator) is implemented by the silicon layer.

[0063] In certain embodiments, the method comprises depositing a piezoelectric layer on a substrate. In certain embodiments, the depositing comprises sputtering.

[0064] In certain embodiments, the method comprises forming a corrugated surface on the piezoelectric layer. In certain embodiments, the method comprises forming a corrugated surface on the piezoelectric layer by interchanging the thickness of the piezoelectric layer.

[0065] In certain embodiments, the forming the corrugated surface comprises using lithography and etching (onto the layer(s) beneath the top electrode layer). In certain embodiments, the forming the corrugated surface comprises using lithography and etching. In certain embodiments, the forming the corrugated surface comprises using lithography and etching to provide (create, make, manufacture, fabricate) meander(s), groove(s), ridge(s), wave(s), and / or perforation(s) (hole(s)) onto the layer(s) beneath the top electrode layer (on the piezoelectric layer).

[0066] In certain embodiments, the method comprises forming a corrugated cross-section of the electrode layer(s). In certain embodiments, the method comprises forming a corrugated cross-section of the piezoelectric layer. In certain embodiments, the method comprises forming a corrugated cross-section of the device (resonator) body (Si-layer).

[0067] In certain embodiments, said lithography is lithographic patterning. In certain embodiments, after lithographic patterning, relevant material (of the layer(s) beneath the top electrode layer) is removed in (successive) etching step(s). In certain embodiments, the width / size / diameter of the corrugations in a mask prior to etching controls the depth of the etching. In certain embodiments, the etching comprises dry etching, such as deep reactive ion etching, DRIE. In certain embodiments, the etching comprises wet etching.

[0068] In certain embodiments, the method comprises depositing a top electrode layer on the corrugated surface of the layer(s) beneath the top electrode layer to provide a corrugated interface therebetween. In certain embodiments, the method comprises depositing a top electrode layer on the corrugated surface of the piezoelectric layer. In certain embodiments, the depositing the top electrode layer comprises depositing (uniform) layer thereof onto the corrugated surface. In certain embodiments, the depositing the top electrode layer comprises depositing (uniform) layer thereof onto the corrugated surface, resulting in the corrugated interface. In certain embodiments, the depositing the top electrode layer comprises depositing (uniform) layer thereof onto the corrugated surface, resulting in a meandering, groovy, ridged or wavy cross-section of the corrugated interface.

[0069] In accordance with certain embodiments, embodiments of the second or third aspect are provided, the embodiments comprising subject matter of any single embodiment presented in connection with the first or second aspect, or the embodiments comprising subject matter of any of the embodiments presented in connection with the first or second aspect combined with subject matter presented in any other embodiment or embodiments.

[0070] 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.

[0071] BRIEF DESCRIPTION OF THE FIGURES

[0072] Some example embodiments will be described with reference to the accompanying figures, in which:

[0073] Fig. 1 schematically shows a top view of an example resonating element in a top view demonstrating structure thereof according to an example embodiment;

[0074] Fig. 2 schematically shows a cross-section of the material stack of an example device according to an example embodiment;

[0075] Fig. 3a schematically shows an example cross-section of the corrugations according to an example embodiment;

[0076] Fig. 3b schematically shows an example resonating element in top view having parallel corrugations according to an example embodiment; Fig. 3c schematically shows an example resonating element in top view having intersecting corrugations according to an example embodiment;

[0077] Fig. 3d schematically shows an example resonating element in top view having intersecting corrugations according to another example embodiment;

[0078] Fig. 3e schematically shows an example resonating element in top view having intersecting corrugations according to yet another example embodiment;

[0079] Fig. 3f schematically shows an example resonating element having beam elements in top view having corrugations according to an example embodiment;

[0080] Fig. 4a schematically shows an example configuration of the corrugations in top view according to an example embodiment;

[0081] Fig. 4b schematically shows an example configuration of the corrugations and patterns on the top electrode in top view according to an example embodiment;

[0082] Fig. 4c schematically shows a cross-section of the corrugations and patterns on the top electrode according to an example embodiment;

[0083] Fig. 4d schematically shows a cross-section of the corrugations and patterns on the top electrode according to another example embodiment;

[0084] Fig. 4e schematically shows a cross-section of the corrugated silicon layer according to an example embodiment;

[0085] Fig. 4f schematically shows a cross-section of the corrugated silicon layer according to another example embodiment; and

[0086] Fig. 5 schematically shows an example of a multi-ladder device according to an example embodiment.

[0087] DETAILED DESCRIPTION

[0088] In the following description, like reference signs denote like elements or steps.

[0089] As used herein, the term “device” refers to any kind of MEMS apparatus or device that may appear in a semiconductor industry, such as a resonator, chip, circuitry, microchip, microprocessor, filter, silicon chip, computer chip, sensor, accelerometer, gyroscope, energy harvester, actuator and process-control unit, vacuum tube or alike. In certain embodiments, the semiconductor apparatus has been packaged. Accordingly, the device is a semiconductor apparatus. In certain embodiments, the mechanical body of the device is resonating in nature. In certain embodiments, the mechanical body of the device is transferring charges (electric current, charge carriers) and vibrations (without resonance). In certain embodiments, the device is a microelectromechanical systems, MEMS, device. In certain embodiments, the device is a resonator, such as a MEMS resonator.

[0090] As used herein, the term horizontal refers to the direction of left to right (or right to left), when observing the device or the resonating element from above, meaning the x-direction according to the chosen coordinate system. In the example embodiments shown in Fig. 1 , the x-direction is equal to the width direction of the resonating element and the resonating beam element.

[0091] Analogously, as used herein, the term vertical refers to the direction of up and down (or down to up, when observing the device or the resonating element from above), meaning the y-direction according to the chosen coordinate system. In the example embodiments shown in Fig. 1 , the y-direction is equal to the length direction of the resonating element and the resonating beam element.

[0092] Yet analogously, as used herein, herein is also used a direction of left to right (or right to left), when observing the device of the resonating element from the side (cross-sectional view), meaning the z-direction according to the chosen coordinate system. In the example embodiments shown in Fig. 2, the z-direction is referred as a “height” direction of the device.

[0093] As used herein, the term “material stack” refers to the device materials that form the cross- sectional layer structure of the device. 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 crosssection of the device. 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.

[0094] As used herein, the notation ‘the layer X beneath the layer Y’ refers to the layer X being underneath the layer Y within the material stack / pile in question. Synonyms for the notation are, by way of example, under, underneath, and below. As used herein, the notation “the layer X on the layer Y” refers to the layer X being above the layer Y within the material stack in question. Synonyms for the notation are, by way of example, on top of, onto and above. In certain embodiments, these notations can be understood as “the layer X being in contact with the layer Y”. However, the instant solution is not limited to those embodiments.

[0095] Fig. 1 schematically shows a top view (from above, from up to down) of an example resonating element 101 according to an example embodiment. In certain embodiments, the device 100 comprises at least one resonating element 101. In certain embodiments, the device 100 comprises a resonating plate element 101 (not shown in Fig. 1). In certain embodiments, the device 100 comprises a plurality of resonating elements 101 (not shown in Fig. 1).

[0096] The resonating element 101 according to embodiment shown in Fig. 1 comprises a plurality of resonating beam elements having a length L and a width W. In certain embodiments, the resonating beam elements are beam-shaped. In the embodiment shown in Fig. 1 , the resonating element 101 comprises seven resonating beam elements (the number of beam elements may vary depending on the embodiment). In certain embodiments, the resonating beam elements are longer L than they are wide W. In certain embodiments, the coordinate system is selected so that the x-axis resides in the width direction W of the resonating elements 101 and the y-axis in the longitudinal direction L of the resonating beam elements.

[0097] According to the example embodiment shown in Fig. 1 , the plurality of resonating beam elements are positioned adjacent to each other. In certain embodiments, the plurality of resonating beam elements form a ladder-like configuration (stacked beam device). 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.

[0098] In certain embodiments, the resonating element 101 is formed of the plurality of resonating beam elements and a plurality of connection elements 102. In certain embodiments, said adjacent resonating beam elements are mechanically connected to each other by connection elements 102. In certain embodiments, the resonating beam elements are connected to each other (one another) by (at least) two connection elements 102. In certain embodiments, each resonating beam element is connected to another resonating beam element by (at least) two connection elements 102. In certain embodiments, the adjacent resonating beam elements are separated by trenches 104. In certain embodiments, the trench 104 extend through (all) the material layers of the resonating element 101. In certain embodiments, the trenches 104 have a length TL (trench length). In certain embodiments, the length L of the beam element comprises at least the length of the trench TL and the length of at least one connection element 102.

[0099] In certain preferred embodiments, the resonating element 101 is a stacked beam resonating element comprising a plurality of resonating beam elements positioned side-by-side in a plane, separated by trenches 104 and connected by (at least two, or two) connection elements 102. In at least some stacked beam resonating elements, the resonating beam elements are positioned in the same plane. In certain stacked beam resonating elements, no two resonating beam elements are positioned atop each other.

[0100] In certain embodiments, the resonating elements 101 of the device 100 are arranged in a rectangular array configuration. In certain embodiments, the resonating element 101 has a length L (which is equal to the length of the beam element). In certain embodiments, the resonating element 101 has a width RW (device width).

[0101] In certain embodiments, the resonating element 101 is attached to a support structure (not shown in Fig. 1). In certain embodiments, the resonating element 101 is attached to the support structure 110 from the outermost resonating beam elements of the resonating element 101 by anchoring point(s) 103. In certain embodiments, the device 100 comprises electrical terminal(s) at anchoring points 103. In certain embodiments, the resonating element(s) 101 is separated from the support structure 110 by (an external) trench 104’. In certain embodiments, the trench 104’ extends through (all) the material layers of the resonating element (thereby separating it from its surroundings).

[0102] In certain embodiments, the resonating element 101 is of an elongated shape (having the length L smaller than their width RW). In certain embodiments, the resonating element 101 is in the shape of a rectangle (the resonating element 101 has a shape of a rectangle). In certain embodiments, the resonating element 101 has an aspect ratio (ratio of length L to width RW, when observed from above) different from 1. In certain embodiments, the resonating element 101 has a length-to-width, L-to-RW, aspect ratio of less than 1.

[0103] 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.

[0104] Fig. 2 schematically shows a cross-section of the material stack of a device 100 according to an example embodiment. Fig. 2 schematically shows an example cross section (sectional view, side view) of the device 100 residing on a substrate 450.

[0105] In certain embodiments, the device 100 is fabricated on a substrate. In the example embodiment of Fig. 2, a silicon on insulator (SOI) substrate (wafer) 450 is used. The reference numerals 401 and 402 denote bottom electrode and top electrode contacts, respectively. The reference numeral 101 denotes the location of the resonating element 101.

[0106] In certain embodiments, the device 100 (and the resonating element 101) comprises a material stack, the material stack comprising at least the silicon layer L4, the piezoelectric layer L2 on top of the silicon layer, and a top electrode L1 on top of the piezoelectric layer. In certain embodiments, the piezoelectric layer comprises doping, such as scandium doping.

[0107] In the example embodiment shown in Fig. 2, the top electrode is implemented in layer L1. In certain embodiments, the top electrode layer L1 is a multilayer top electrode. In certain embodiments, the multilayer top electrode L1 comprises a plurality of material layers (atop each other, on top one another, as a pile), together forming the top electrode layer L1. In certain preferable embodiments, the multilayer top electrode L1 comprises a plurality of metal layers.

[0108] In certain embodiments, the multilayer top electrode L1 comprises alternating layers of (at least) two different metals. In certain embodiments, the multilayer top electrode L1 comprises alternating layers of gold, Au and platinum, Pt. In certain embodiments, the multilayer top electrode L1 comprises N material layers, preferably N metal layers, wherein N is the number of layers. In certain embodiments, the N material layers (metal layers) together for the top electrode L1 of the device.

[0109] In this example embodiment, layer L2 is a piezoelectric layer for piezoelectric actuation of the device. In certain embodiments, further material layer(s), preferably metal layer(s), are (arranged, provided, placed) in between the layer L1 and the layer L2. 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 device (for example resonating beam elements and their connecting elements according to certain embodiments). In this example embodiments, layer L5 is a buried oxide layer (SiO2) of the SOI wafer, and layer L6 is a silicon handle layer. In certain embodiments layer L6 comprises a cavity C1. In certain embodiments, the layer L5 follows the cavity C1 shape as shown in Fig. 2.

[0110] 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.

[0111] 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.

[0112] In certain preferred embodiments, the device 100 comprises a material stack, the material stack comprising the silicon layer L4 (the bottom electrode), the piezoelectric layer L2 on top of the silicon layer L4, and a top electrode L1 on top of the piezoelectric layer L1. In certain embodiments, the device 100 is a piezoelectric device. In certain embodiments, the piezoelectric layer L2 comprises aluminum nitride.

[0113] In certain embodiments, the longitudinal axis L of a resonating element 101 (the resonating beam elements) is aligned with <100> crystal direction of the silicon (of the bottom electrode), such as aligned with

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

[0100] crystal direction of the silicon (of the bottom electrode), or deviates less than 5 degrees therefrom, or less than 2 degrees therefrom in certain embodiments. Fig. 3a schematically shows an example cross-section (a profile) of the corrugations 20T according to the example embodiment. It should be noted that the cross-section of Fig. 3a applies to any direction in x- and y-plane (referring to top views shown in Figs. 3b, 3c, 3d, 3e by way of an example).

[0114] As shown in Fig. 3a, in certain embodiments, the corrugated interface 201 is an uneven surface. In certain embodiments, the corrugated interface comprises bumps in various shapes (such as cube-like, pyramid-like or ball-like bumps). Fig. 3a shows an embodiment with rectangular cube-shaped bumps. It should be noted that the corrugated interface is a three-dimensional interface, having three-dimensional, 3D, shapes. Evidently, this is not shown in Fig. 3a, and instead Fig. 3a shows a 2D illustration of the corrugated interface 201.

[0115] As shown in Fig. 3a, the resonating element comprises a top electrode layer L1 and a layer L2 beneath top electrode layer. In certain embodiments, the layer L2 beneath the top electrode layer L1 has a corrugated surface to provide the corrugated interface 201. In certain embodiments, the corrugated interface 201 is formed by interchanging (varying, changing) the thickness of the layer L2. In certain embodiments, the thickness of the layer L2 is varied within the layer L2. This provides a meandering / groovy / ridged cross-section of the corrugated interface 201 , as shown in the embodiment of Fig. 3a.

[0116] As shown in Fig. 3a, in certain embodiments, the top electrode layer L1 obtains the same shape as the corrugated layer L2 beneath. The top electrode layer L1 is deposited onto the corrugated surface of the layer L2 in accordance with certain embodiments. The top electrode layer L1 forms a uniform layer, covering the corrugated surface of the layer L2 in accordance with certain embodiments. In accordance with certain embodiments, herein is provided a non-planar top electrode. Accordingly, in certain embodiments, the top electrode layer L1 follows the corrugations 20T of the layer L2, to provide the corrugated interface 201 therebetween. Further accordingly, in certain embodiments, the corrugated interface 201 increases the contact area between the top electrode layer L1 and the layer L2, thereby enhancing the quality factor, Q, of the device 100. In certain embodiments, an increase of 1.5x in the contact area is obtained.

[0117] As shown in Fig. 3a, in certain embodiments, the corrugations 20T are oriented in a plane of the layer L2, protruding upwards from said plane. In certain embodiments, the corrugations 20T are uneven z-directional shapes (such as “hills”) formed into the layer L2. In certain embodiments, the corrugations 201’ are a z-directed meander. In certain embodiments, the corrugations 20T provide a pathway for the charge carriers in z-direction of the resonating element 101 (the charge carriers travelling within the top electrode layer L1 provided on the corrugations 201’). This renders the top electrode layer L1 of the resonating element 101 softer (reduce its stiffness) and minimizes the spring contribution of the top electrode layer L1 in z-direction. Accordingly, a ‘flexible’ top electrode having reduced stiffness and spring contribution, resulting in to reduced or minimized the frequency drift is provided.

[0118] In certain embodiments, the corrugations 20T are not reaching (extending) through the entire layer L2 in z-direction. In certain embodiments, the corrugations 20T are not configured to expose the layer(s) beneath the layer L2. In certain embodiments, the corrugations 20T have a depth D that is less than the layer L2 thickness. In certain embodiments, the corrugations 20T have a depth D within a range of single atomic layer thickness to the whole thickness of the layer L2 (in certain embodiments, the piezoelectric layer). In certain embodiments, the corrugations 20T have a depth D in the range from 0.05 pm to 1.5 pm, such as 0.25 pm to 0.5 pm.

[0119] In certain embodiments, the corrugations 20T protrude (extend) into the silicon layer (not shown).

[0120] In the embodiment shown in Fig. 3a, the corrugations 20T are of rectangular shape, forming rectangular ridges C1 , and grooves C2 in between said ridges. In certain embodiments, the corrugation’s ridges C1 have a width of 0.5 pm to 5 pm, such as 0.5 pm to 1 pm. In certain embodiments, the corrugation’s grooves C2 have a width of 0.5 pm to 5 pm, such as 0.5 pm to 1 pm.

[0121] In certain embodiments, the top electrode layer L1 has a thickness T within a range of 0.05 pm to 0.6 pm, such as in the range of 0.1 pm to 0.6 pm, or in the range of 0.05 pm to 0.25 pm, depending on the embodiment.

[0122] As shown in Fig. 3a, the top electrode L1 and the layer L2 interface may be imperfect or nonperiodic in corrugation 20T depth D, width C1 / C2, shape (symmetric shape, bent / imperfect shape) and top electrode layer L1 thickness T in accordance with certain embodiments. In these embodiments, there are no strict tolerances for depth D, width C1 / C2, shape (symmetric shape, bent / imperfect shape) and top electrode layer L1 thickness T. In certain alternative embodiments, the top electrode L1 and the layer L2 interface is as perfect and periodic as possible, taking into consideration the manufacturing tolerances (not shown in Fig. 3a).

[0123] In accordance with certain embodiments, the corrugations 20T aim to maximize the contact area in between the top electrode layer L1 and the layer L2, and increase the top electrode spatial springing. In these embodiments, the corrugation 20T depth D is increased, whilst the widths C1 and C2 are decreased.

[0124] The device 100 according to certain embodiments is not limited to number, width, shape and / or angle of the corrugations 20T. In certain embodiments, the corrugations 20T are of different number, width, shape and / or angle along the (each) resonating element(s) 101. In certain embodiments, the corrugations 20T are a parameter for optimization of the device 100 design.

[0125] Further parameters for optimization of the device 100 according to certain embodiments include but are not limited to material variations of the device 100. By way of an example, in certain embodiments, the top electrode layer L1 is of metal, such as gold, or doped gold. In certain embodiments, however, the top electrode layer L1 consists of multiple material layers, such as metal layers, thereby forming a multilayer top electrode. Accordingly, herein is provided a device 100, comprising a resonating element 101 having a top electrode layer L1 , wherein the top electrode layer L1 has a corrugated interface 201 with layer(s) beneath the top electrode layer L1. In certain preferred embodiments, the resonating element 101 comprises a piezoelectric layer L2, wherein the piezoelectric layer L2 is beneath the top electrode layer L1 , wherein the top electrode layer L1 has a corrugated interface 201 with the piezoelectric layer L2.

[0126] Figs. 3b, Fig. 3c, Fig. 3d and Fig. 3e schematically show example resonating elements 101 in top view having parallel and intersecting corrugations 20T, respectively, according to the example embodiments. As shown in Figs. 3b, 3c, 3d and 3e, the device 100 comprises one resonating plate element 101 in certain embodiments. In certain embodiments, the resonating element 101 is suspended to a support structure (not shown) via an anchoring point 103.

[0127] As shown in Fig. 3b, in certain embodiments, the corrugations 20T comprise parallel corrugations 20T (in Fig. 3b, the ‘corners’ of the corrugations are shown as narrow black lines within the resonating element 101). In certain embodiments, the corrugations 20T comprise parallel ridges and grooves, such as shown in Fig. 3a. As shown in Fig. 3b, in certain embodiments, the corrugations 201’ are essentially straight, extending across the resonating element 101. In certain embodiments, the corrugations 201’ extend from side to side in x-direction of the resonating element 101. In certain embodiments, the corrugations 20T are non-intersecting, as shown in Fig. 3b. In certain embodiments, the corrugations 201’ are non-straight, such as meandering, wavy or groovy (in top view) (not shown).

[0128] As shown in Fig. 3c, the corrugations 201’ comprise a first set of parallel corrugations, extending across the resonating element 101 in x-direction of the resonating element 101 , in accordance with certain embodiments. In these embodiments, the corrugations 201’ also comprise a second set of parallel corrugations, extending across the resonating element 101 in a y-direction of the resonating element 101. In certain embodiments, the first set of corrugations and the second set of corrugations intersect each other, forming a grid of corrugations 20T as shown in Fig. 3c. In certain embodiments, the first set of corrugations runs in orthogonal direction in relation to the second set of corrugations, creating right angles (90-degree angles) in the intersections. In certain embodiments, the intersecting corrugations 201’ form square or rectangular shapes, as shown in Fig. 3c.

[0129] As shown in Fig. 3d, in certain embodiments, the corrugations 20T comprise parallel intersecting corrugations 201’. In certain embodiments, the corrugations 20T run (extend, reach) through the resonating element 101. In certain embodiments, the corrugations 201’ run (extend, reach) through the resonating element 101 in a direction other than x-direction, or y-direction. In certain embodiments, the corrugations 20T run from corner to corner of the resonating element 101 . In certain embodiments, the intersecting corrugations 201 ’ form diamond or parallelogram shapes, as shown in Fig. 3d.

[0130] As shown in Fig. 3e, in certain embodiments, the corrugations 20T are randomly arranged within the resonating element 101. In certain embodiments, the corrugations 20T are nonperpendicular (and non-orthogonal) with each other. In certain embodiments, the corrugations 201’ form acute or obtuse angles in the intersections of the corrugations (nonright angles, no 90-degree angles). In certain embodiments, the corrugations 20T do not reach (entirely, all the way) through the resonating element 101. In certain embodiments, the intersecting corrugations 201’ form random shapes, as shown in Fig. 3e. In certain embodiments, the corrugations 201’ are non-straight, such as meandering, wavy or groovy (in top view) (not shown). Fig. 3f schematically shows example resonating element 101 having beam elements in top view having corrugations according to the example embodiment. The embodiment shown in Fig. 3f corresponds to the example resonating element 101 shown in Fig. 1 , except that Fig. 3f shows corrugations 20T. It should be noted that any corrugation configuration of Figs. 3b, 3c, 3d or 3e is applicable also in the resonating element 101 having beam elements.

[0131] In certain embodiments, the resonating element 101 comprises a plurality of resonating sub-elements (in Fig. 3f, resonating beam elements). In certain embodiments, the resonating sub-elements are separated from one another by trenches 104. In certain embodiments, the corrugations 20T extend from one trench 104 to another trench 104.

[0132] In certain embodiments, the resonating sub-elements of the resonating element 101 are coupled to one another by at least two connection elements 102. In certain embodiments, the connection elements 102 comprise corrugations 20T (not shown in Fig. 3f).

[0133] Figs. 4a and 4b schematically show example configurations of the corrugations 20T, optionally having patterns 202 on the top electrode L1 according to example embodiments. Figs. 4c and 4d schematically show cross-sections of the corrugations 20T and the optional patterns 202 on the top electrode L1 according to example embodiments. Figs. 4e and 4f schematically show cross-sections of the top electrode layer L1 having a corrugated interface 201 with the layer L2 beneath the top electrode layer L1 provided via a ‘zig-zag’ silicon layer. This is another manner to realize corrugated interface 201 according to certain embodiment.

[0134] The patterns 202 are schematically shown in Figs. 4b, 4c and 4d as dotted area (black dots) on a white background. Similarly as in Figs. 3b, 3c and 3d, Figs. 4a and 4b show a schematical top view of the corrugations 20T and the ‘corners’ of the corrugations 20T are drawn as narrow black lines within the resonating element 101. The anchoring points are omitted from the illustrations of Figs. 4a and 4b for reasons of clarity. It should be noted that the cross-sections shown in Figs. 4c, 4d, 4e and 4f are not limited to only x- or y-directions but apply to any direction in x / y-plane, similarly as Fig. 3a.

[0135] Fig. 4a shows a similar top view than Fig. 4b, the difference being that Fig. 4b further shows patterns 202 on the top electrode. As the patterns of the top electrode L1 are optional and present in certain embodiments, the Figs. 4c and 4d can be also observed as not containing the patterns 202 of the top electrode L1 . In these cases, the top view of the cross-sections of Figs. 4c and 4d schematically looks like the one shown in Fig. 4a.

[0136] Fig. 4b shows a top view of the embodiments of Figs. 4c and 4d. Even though the Figs. 4c and 4d show different cross-sectional embodiments, both of these look the same from the schematical top view.

[0137] As shown in Figs. 4b, 4c and 4d, in certain embodiments, the top electrode layer L1 comprises patterns 202. In certain embodiments, the patterns 202 are in the form of line(s), perforation(s) or both. In certain embodiments, the patterns 202 reach through the top electrode layer L1 in z-direction. In certain embodiments, patterns 202 of the top electrode layer L1 expose the layer L2 beneath the top electrode L1 .

[0138] As shown in Fig. 4c, the corrugated interface 201 between the top electrode layer L1 and the layer L2 beneath it comprises triangle-shaped (cone-shaped, spike-shaped, or pyramidshaped) protrusions. In certain embodiments, the protrusions P are formed into the layer L2. In certain embodiments, the protrusions are formed by etching the layer L2. In certain embodiments, the layer L2 comprises an uneven (corrugated, wavy, groovy) profile. In certain embodiments, the profile of the layer L2 is copied (adopted by) the top electrode layer L1 (since it is provided onto the layer L2). In certain embodiments, the width C3 of the corrugations is in the range of 0.5 pm to 5 pm, such as in the range of 0.8 pm to 4 pm. It should be noted that in the context of the protrusions P, the triangle shape is an example, and the same principle applies to any shape of protrusions.

[0139] In certain embodiments, the top electrode layer L1 has a uniform layer thickness, n certain embodiments, the layer L2 has a non-uniform layer thickness, due to the protrusions thereof.

[0140] In certain embodiments, the patterns 202 are arranged at the face (the slanted surface) of the triangle-shaped protrusions, as shown in Fig. 4c. In certain embodiments, the patterns 202 are arranged on both faces of the triangle-shaped protrusions (not shown).

[0141] Fig. 4d shows an embodiment wherein the resonating element 101 comprises two layers (two materials) L2, L2’ beneath the top electrode layer L1. In certain embodiments, the layers L2, L2’ are both beneath the top electrode L1. In certain embodiments, the layers L2, L2’ are partially atop one another such that layer L2’ is on top of the layer L2. In certain preferred embodiments, the layer L2 is a piezoelectric layer, formed of aluminum nitride. In accordance with certain embodiments, the layer L2’ can be called an intermediate layer. In certain embodiments, the layer L2’ is of (comprises) metal, preferably of platinum, Pt. As shown in Fig. 4d, the layer L2’ is non-uniform (patterned into ‘rails’ as shown in Fig. 4d). In certain embodiments, the (approximate) distance C4 between the corrugation rails as shown in Fig. 4d is in the range of 0.5 pm to 3 pm, such as in the range of 0.8 pm to 4 pm. In certain embodiments, the thickness C5 of the layer L2’ (and the thickness of the corrugation rails as shown in Fig. 4d) is in the range of 0.05 pm to 1 pm, such as in the range of 0.1 pm to 0.4 pm. In certain further embodiments, further material layer(s) are (arranged, placed) in between the layer L2 and the intermediate layer L2’ (not shown). In certain embodiments, these further material layer(s) are of metal.

[0142] Accordingly, in certain embodiments, the top electrode layer L1 has the corrugated interface 201 with the layers L2, L2’ beneath the top electrode layer L1 , wherein the corrugated interface 201 is formed based on both layers L2, L2’. Accordingly, in these embodiments, the layers L2, L2’ provide the corrugated surface together. The uniformly deposited top electrode layer L1 adapts the corrugated surface provided by both layers L2, L2’ in accordance with these embodiments.

[0143] As shown in for example Figs. 4c and 4d, in certain embodiments, the resonating element 101 comprises a bottom electrode L4 of silicon on the opposite side of the piezoelectric layer L2 than the top electrode layer L1.

[0144] Figs. 4e and 4f show the corrugated interface 201 between the top electrode layer L1 and the layer L2 beneath it. By way of example, Figs. 4e and 4f show triangle-shapes (cone- shaped, spike-shaped, or pyramid-shaped). It should be noted that the principle disclosed herein is applicable to corrugations with any shape and triangle is used merely as an example.

[0145] In the embodiments of Figs. 4e and 4f, the silicon layer L4 (substrate) comprises protrusions. In certain embodiments, the protrusions P of the silicon layer L4 are provided via etching the silicon layer L4. In certain embodiments, the silicon layer L4 has a corrugated profile (cross-section). In certain embodiments, the layer L2 copies the same profile (upon deposition / growing process thereof), rendering the layer L2 also comprising protrusions (the shape of the protrusions). In certain embodiments, the top electrode layer L1 also copies (follows, adopts) the same profile (the same curvature) (upon deposition / growing process thereof). Thereby the corrugated interface 201 in between the top electrode layer L1 and the layer L2 beneath it is provided, in accordance with certain embodiments.

[0146] In certain embodiments, the layer L2 has a uniform layer thickness. In certain embodiments, the top electrode layer L1 has a uniform layer thickness.

[0147] Fig. 4f shows a further modification of the same embodiment as shown in Fig. 4e. In the embodiment shown in Fig. 4f, the silicon layer L4 is etched to have a corrugated surface on both sides thereof. In accordance with these embodiments, the silicon layer L4 comprises a corrugated top surface and a corrugated bottom surface. In certain embodiments, the silicon layer L4 comprises protrusions P1 on the top side, and protrusions P2 on the bottom side.

[0148] Accordingly, in certain embodiments, the corrugated interface 201 with the layer L2 beneath the top electrode layer L1 is provided via a corrugated profile of the layer L2. In these embodiments, the following layers copy the same corrugated profile of the previous layer. In certain embodiments, the layer L2 beneath the top electrode layer L1 comprises a corrugated surface to provide the corrugated interface 201 with the top electrode layer L1.

[0149] Further, in certain embodiments, the corrugated interface 201 with the layer L2 beneath the top electrode layer L1 is provided via a corrugated profile of the silicon layer L4 beneath the layer L2. In these embodiments, the following layers copy the same corrugated profile of the previous layer. In certain embodiments, the silicon layer L4 beneath the top electrode layer L1 comprises a corrugated surface to provide the corrugated interface 201 with the top electrode layer L1 .

[0150] In certain embodiments, this reduces spurious frequencies of the device due to the less reflecting boundary in z-direction thereof. Further, in certain embodiments, this reduces Frequency Drive Level Dependency (FDLD) of the device.

[0151] Herein is further provided a method for manufacturing the device according to the first aspect or any of its embodiments, comprising the steps of depositing the layer(s) onto a substrate, forming a corrugated surface on the layer(s); depositing a top electrode layer L1 on the corrugated surface of the layer(s) to provide a corrugated interface 201 in between the top electrode layer L1 and the layer(s) beneath the top electrode layer L1. In certain embodiments, said layer(s) are material layer(s). In certain embodiments, the method comprises the steps of depositing the layer(s) onto a substrate, depositing the top electrode layer L1 on the layer(s) to provide a corrugated interface 201 in between the top electrode layer L1 and the layer(s) beneath the top electrode layer L1 , wherein the method comprises forming a corrugated surface onto the layer(s) to provide said corrugated interface 201.

[0152] In accordance with the example embodiments of Figs. 3a, and 4c, the method comprises depositing the layer L2 onto a substrate L4, forming the corrugated surface on the layer L2, and depositing the top electrode layer L1 on the corrugated surface of the layer L2 to provide a corrugated interface 201 in between the top electrode layer L1 and the layer L2 beneath the top electrode layer L1 .

[0153] In accordance with the embodiment shown in Fig. 4d, the method comprises also the steps of depositing a layer L2’ onto the layer L2, and patterning the layer L2’ to form the corrugated surface by the layers L2 and L2’.

[0154] In certain embodiments, the substrate comprises the silicon layer L4, preferably a doped silicon layer, such as UHD silicon layer. In certain embodiments, the bottom electrode of the device 100 is implemented by the silicon layer L4.

[0155] In certain embodiments, the depositing of the layer L2 (and L2’) and / or the top electrode layer L1 comprises sputtering.

[0156] In certain embodiments, the method comprises forming a corrugated surface on the layer L2 by changing the thickness of the layer L2. In certain embodiments, this is achieved by using lithography and etching, to form meander(s), groove(s), ridge(s) and / or wave(s) onto the layer L2 / L2’ beneath the top electrode layer L1. The resulting configuration comprises the corrugated interface in between layers L1 and L2.

[0157] In certain embodiments, the method comprises forming a corrugated surface on the silicon layer L4 by changing the thickness of the layer L4. In certain embodiments, this is achieved by using lithography and etching, to form meander(s), groove(s), ridge(s) and / or wave(s) onto the layer L4, which are then copied to the layer L2 beneath the top electrode layer L1 , and finally also to the top electrode layer L1. The resulting configuration comprises the corrugated interface in between layers L1 and L2. Fig. 5 schematically shows an example of a multi-ladder device according to an example embodiment. In certain embodiments, as shown in Fig. 5, the device 100 comprises (at least) two resonating elements 101 (stacked beam resonating elements). In certain embodiments, the device 100 comprises a plurality of resonating elements 101 positioned adjacent to each other. In certain embodiments, the device 100 comprises a plurality of resonating elements 101 coupled to each other by a coupler 310. All embodiments of the present disclosure described in context a single resonating element 101 apply herein as well for the resonating elements 101 in accordance with certain embodiments.

[0158] In certain embodiments, the devices 100 are implemented in the form of stacked beam resonating elements 101 having a plurality of adjacent resonating beam elements connected by connection element(s), such as two connection elements, 102 and separated from one another by trenches 104 (thus forming a ladder-like structure).

[0159] Similarly as disclosed in the context of Fig. 3c, Fig. 5 shows parallel corrugations that intersect each other, forming a grid (crisscross) of corrugations 201’. Further, similarly as disclosed in the context of Fig. 3f, Fig. 5 shows the corrugations 201’ extending from one trench 104 to another trench 104 across the resonating beam elements in width direction thereof. As shown in Fig. 5, the connection elements 102 (and the anchoring points 103) are absent from corrugations 20T.

[0160] Accordingly, the device 100 comprises (at least two, a plurality of) resonating elements 101 , each resonating elements 101 comprising a corrugated interface 201 in between the top electrode layer and the layer(s) beneath the top electrode layer. In certain embodiments, the corrugations are configured to neutralize the spring effect of the resonating elements 101 (or the top electrode thereof). In certain embodiments, the corrugations are configured to remove (minimize, alleviate) stress related modulation of the resonating elements 101. Accordingly, herein are provided ‘flexible’ resonating elements 101 having reduced stiffness, resulting in to minimized the frequency drift.

[0161] Fig. 5 schematically shows a device 100 comprising two resonating elements 101 coupled to each other by a coupler 310 in accordance with certain embodiments. In certain embodiments, the coupler 310 comprises corrugations (not shown in Fig. 5). In certain embodiments, the coupler 310 comprises corrugations to suppress spring constant (neutralize the spring effect) of the coupler 310 (or the top electrode thereof). In certain embodiments, the coupler 310 comprises a layer of gold. In certain embodiments, the coupler 310 is absent from corrugations 20T, as shown in Fig. 5. In certain embodiments, the coupler 310 comprises corrugations (not shown).

[0162] In certain embodiments, the coupler 310 is a flexural coupler. The device 100 shown in Fig. 5 comprises two extensional-mode resonating elements 101 , and a (one or more) flexural mode coupler 310. Further, the device 100 comprises a (one or more) mechanical connector element 320 which connects the flexural coupler 310 to the extensional mode resonating elements 101. In certain embodiments, at least one of the extensional-mode resonating elements 101 of the device 100 comprises a piezoelectric thin-film actuator for exciting the said extensional-mode device to a resonance mode and thereby the whole device 100 to a collective resonance due to mechanical coupling of the extensional-mode resonating elements 101.

[0163] In certain alternative embodiments, the coupler 310 is an extensional mode coupler or a rigid coupler (not shown in Fig. 5). In certain alternative embodiments, the coupler 310 is a length-extensional coupler (not shown in Fig. 5). In certain embodiments, more than 50% of the mass of the device 100 comprise material portions of single-crystalline silicon. In certain embodiments, the device 100 comprises an electrostatic actuator for exciting at least one of the extensional-mode resonating elements 101 to a resonance mode and thereby the whole device 100 to a collective resonance due to mechanical coupling of the extensional-mode resonating elements 101.

[0164] In certain embodiments, (all, some of) the resonating elements 101 of a device 100 are identical with one another (each other). In certain alternative embodiments, (all) the resonating elements 101 of a device 100 are different from one another.

[0165] Without limiting the scope and the interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is improving the system of interfaces of semiconductor devices, such as MEMS devices.

[0166] It should be noted that the embodiments of the present solution relate to not only electrode geometry configuration but the whole interface of the electrode layer and the layer beneath that, in certain embodiments the piezoelectric layer in devices, such as MEMS devices. In accordance with certain embodiments, the interface is not flat and homogenous, but instead corrugated, curved, and / or grooved. A technical effect is to enable reduced dependency of the device on the top electrode material, such as gold Au, mechanical structure instability. Thereby better mechanical stability of the top electrode layer over time, and over temperatures is provided. A further technical effect is enabling reducing any local residual stresses of the top electrode layer.

[0167] A technical effect is to provide a solution having improved frequency stability and reduced frequency drift of the device. The technical effect of the present solution is neutralizing the spring effect of the electrode, thereby reducing or removing contribution for electrode stiffness or stress to frequency.

[0168] A technical effect is to provide a ‘flexible’ top electrode having reduced stiffness, resulting in to reduced or minimized the frequency drift. A technical effect is enabling free resonance (having no harmful stiffness / spring effect) of the resonating element.

[0169] A technical effect is at least maintaining the equivalent series resistance, ESR, at an optimal level, or improving the ESR characteristics of the device by reducing the ESR. The larger surface area in between the top electrode layer and the layer beneath it provides enhanced electrical contact, thereby increasing the charges transferred in the interface. This further lowers the electrical resistance at this interface. The larger surface area in between the top electrode layer and the layer beneath it further contributes to better vibration energy transfer and lower motional resistance. All the above enhance the overall ESR of the device.

[0170] A further technical effect is increasing the transduction factor and the quality factor, Q, of the device, namely by increasing the surface area between the piezoelectric layer and the top electrode layer.

[0171] A further technical effect is enabling effortless trimming of the device, due to the arrangements of the topmost metal layer of the device. A further technical effect is a simple provision of the instant solution that is easily adaptable to the existing manufacturing processes. Merely minor changes may be needed, if any, to the existing processes.

[0172] A further technical effect is reducing negative impacts caused by the electrode, for example a metal electrode, without degradation of the main function of the device. A further technical effect is reducing or negate reliability issues of the device. A further technical effect is reducing / avoiding reduction of degradation in devices. A further technical effect is the reduction of reflow drift and ageing. A further technical effect is enabling the reduction of the spurious frequencies of the device due to the less reflecting boundary in z-direction thereof. A further technical effect is the reduction of Frequency Drive Level Dependency (FDLD) of the device.

[0173] 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.

[0174] 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.

[0175] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1. A microelectromechanical systems, MEMS, device (100), comprising a resonating element (101) having a top electrode layer (L1), wherein the top electrode layer (L1) has a corrugated interface (201) with a layer or layers beneath the top electrode layer (L1).

2. The device (100) of claim 1 , wherein the layer(s) beneath the top electrode layer (L1) comprises a corrugated surface to provide the corrugated interface (201) with the top electrode layer (L1).

3. The device (100) of claim 1 or 2, wherein the top electrode layer (L1) follows the corrugations of the layer(s) beneath, to provide the corrugated interface (201) therebetween.

4. The device (100) of any preceding claim, wherein the corrugated interface (201) is formed by interchanging thickness of the layer(s) beneath the top electrode layer (L1).

5. The device (100) of any preceding claim, wherein the corrugated interface (201) comprises a meandering, groovy, ridged and / or wavy cross-section.

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

7. The device (100) of claim 6, wherein a bottom electrode is implemented by the silicon layer (L4), wherein the silicon layer (L4) comprises doped silicon, such as ultra-heavily doped, UHD, silicon.

8. The device (100) of claims 6 or 7, wherein the corrugated interface (201) is provided by the corrugated surface of the piezoelectric layer (L2) or the corrugated surface of the silicon layer (L4).

9. The device (100) of claim 8, wherein the layers (L1 , L2) on top of said corrugated surface follow the corrugations beneath, to provide the corrugated interface (201).

10. The device (100) of any preceding claim, wherein the resonating element (101) comprises a plurality of resonating beam elements.11 . The device (100) of claim 10, wherein the resonating beam elements are longitudinally aligned within 25 degrees of a <100> crystal direction of silicon.

12. The device (100) of any preceding claim, wherein the top electrode layer (L1) is a multilayer top electrode (L1), the multilayer top electrode (L1) comprising a plurality of material layers, preferably a plurality of metal layers.

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

14. An apparatus, such as a device array, comprising at least one device (100) according to any of claims 1-13.

15. A method for manufacturing the device (100) according to any of claims 1-13, comprising the steps of:- depositing a layer or layers onto a substrate; - forming a corrugated surface on the layer(s);- depositing a top electrode layer (L1) on the corrugated surface of the layer(s) to provide a corrugated interface (201) in between the top electrode layer (L1) and the layer(s) beneath the top electrode layer (L1).

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