Flexural resonator

Abstract

Herein is provided a resonator comprising a resonating element (100) configured to operate in a resonance mode, wherein the resonating element comprises a silicon layer (101) and a piezoelectric layer (102), and wherein the piezoelectric layer (102) covers a surface area of the resonating element (100) partially.

Description

[0001] FLEXURAL RESONATOR

[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 flexural 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 frequency versus temperature, f-vs-T, stability. Furthermore, there is an ongoing need to reduce the power consumption for instance due to environmental and practical reasons. Some semiconductor apparatuses require high power consumption, therefore rendering them unsuitable for low power consumption applications, such as internet of things, loT, applications.

[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 frequency versus temperature, f-vs-T, stability and / or enabling low power consumption when used in an oscillator.According to a first example aspect of the present disclosure there is provided a resonator comprising a resonating element configured to operate in a resonance mode, wherein the resonating element comprises a silicon layer and a piezoelectric layer, and wherein the piezoelectric layer covers a surface area of the resonating element partially.

[0010] In certain embodiments, the resonator is on a substrate. In certain embodiments, the resonator is fabricated on a substrate. In certain embodiments, the resonating element is on a substrate. In certain embodiments, the resonating element is fabricated on a substrate. In certain embodiments, the substrate is a wafer. In certain embodiments, the substrate is a silicon wafer. In certain embodiments, the substrate comprises a silicon body. In certain embodiments, the silicon body of the substrate provides the silicon layer.

[0011] In certain embodiments, the resonating element comprises a piezoelectric layer covering only partially (partly, not fully) the surface area of the resonating element. In certain embodiments, the piezoelectric layer covers the surface area of the resonating element partially as seen (looked, observed) from above (top view, from up to down).

[0012] In certain embodiments, the piezoelectric layer covers less than 90% of a surface area of the resonating element. In certain embodiments, the piezoelectric layer covers less than 80% of a surface area of the resonating element. In certain embodiments, the piezoelectric layer covers less than 60% of a surface area of the resonating element. In certain embodiments, the piezoelectric layer covers less than 50% of a surface area of the resonating element. In certain embodiments, the piezoelectric layer covers preferably less than 80%, such as less than 60% or less than 50% of the surface area of the resonating element.

[0013] In certain embodiments, the piezoelectric layer is patterned to provide the piezoelectric layer partially covering the surface area of the resonating element. In certain embodiments, the piezoelectric layer is patterned to provide the piezoelectric layer covering less than 90% of the surface area of the resonating element. In certain embodiments, the piezoelectric layer is patterned using lithography. In certain embodiments, the piezoelectric layer is patterned and etched.

[0014] 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 resonating element is configured to resonate (oscillate, move). In certain embodiments, the resonating element is configured (adapted) to operate (resonate) in an out-of-plane resonance mode. In certain embodiments, the resonating element is configured to operate in a flexural resonance mode. In certain embodiments, the resonating element is configured to operate in an out-of-plane flexural resonance mode.

[0015] In certain embodiments, the resonating element is configured (adapted) to operate (resonate) in an in-plane resonance mode. In certain embodiments, the resonating element is configured to operate in an in-plane flexural resonance mode. In certain alternative embodiments, the resonating element is configured to operate in an in-plane resonance mode. In certain alternative embodiments, the resonating element is configured to operate in an in-plane flexural resonance mode, in certain embodiments, the resonating element is configured to operate in an out-of-plane flexural resonance mode or in an in-plane flexural resonance mode.

[0016] In certain embodiments, the resonator is a piezoelectric resonator. In certain embodiments, the resonator is a cantilever resonator. In certain embodiments, the resonator is a tuning fork resonator. In certain embodiments, the resonator is a beam resonator.

[0017] In certain embodiments, the resonating element is in a shape of a (rectangular) beam. In certain embodiments, the resonating element has an aspect ratio (ratio of length to width, when observed from above) different from 1. In certain embodiments, the resonating element has an effective length-to-width aspect ratio of more than 1 , in particular more than 1. In certain embodiments, the resonating element is attached (supported, anchored) to a support structure. In certain embodiments, the resonating element is attached to a support structure from one end of the resonating element. In certain embodiments, the resonating element is separated from the support structure by trenches. In certain embodiments, the resonating element is separated from the support structure by trenches from other locations that the supported end. In certain embodiments, the resonating element is separated from the support structure by trenches extending throughout all the material layers of the resonating element.

[0018] In certain embodiments, the resonator comprises more than one resonating elements. In certain embodiments, the resonator comprises a plurality of resonating elements. In certain embodiments, the resonator is a tuning fork resonator comprising more than one resonating elements (resonating forks). In certain embodiments, the resonator is a tuning fork resonator comprising a plurality of resonating elements (resonating forks).In certain embodiments, the resonator is a MEMS, microelectromechanical systems, resonator. In certain embodiments, the resonator is configured (adapted) to operate (resonate) in a resonance frequency of less than 1 MHz. In certain embodiments, the resonator is configured to operate in a kilohertz frequency area, kHz (frequency range). In certain embodiments, the resonator is configured to operate in a resonance frequency of less than 500 kHz. In certain embodiments, the resonator is configured to operate in a resonance frequency of about (approximately) 32 kHz. In certain embodiments, the resonator is configured to operate in a resonance frequency of 32.768 kHz. In certain embodiments, the resonator is configured to operate in a kilohertz, kHz, frequency area, preferably in a resonance frequency of 32.768 kHz, or in a resonance frequency of N * 32.768 kHz, wherein N is a power of two (such as 2, 4, 8, 16 and so on).

[0019] In certain embodiments, the resonator is configured to operate in a resonance frequency of 32.768 kHz. In certain embodiments, the resonator is configured to operate in a resonance frequency of N * 32.768 kHz, wherein N is a power of 2, such as 2, 4, 8, 16 and so on. In certain embodiments, the resonator is a kilohertz frequency resonator having a 32.768 kHz resonance frequency. In certain embodiments, the resonator is a kilohertz frequency resonator having a 65.536 kHz resonance frequency.

[0020] In certain embodiments, the silicon layer comprises doping. In certain embodiments, the silicon layer comprises local doping. In certain embodiments, the silicon layer (substrate) further comprises undoped silicon. In certain embodiments, the doping comprises n-type doping. In certain embodiments, the doping comprises n++ doping. In certain embodiments, the doping comprises phosphorous doping. In certain embodiments, the doping comprises arsenic doping. In certain alternative embodiments, the doping comprises p-type doping. In certain embodiments, the doping comprises p++ doping. In certain embodiments, the doping comprises boron doping. In certain embodiments, the doping comprises gallium doping.

[0021] 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.

[0022] In certain embodiments, the resonating element comprises the piezoelectric layer on top of the silicon layer. In certain embodiments, the resonating element comprises a top electrode on the piezoelectric layer. In certain embodiments, the top electrode is a top electrode layer. In certain embodiments, the top electrode is of gold, Au. In certain embodiments, the topelectrode is patterned. In certain embodiments, the top electrode is patterned using lithography.

[0023] In certain embodiments, the resonating element comprises a material stack, the material stack comprising the silicon layer, the piezoelectric layer on top of the silicon layer, and a top electrode on top of the piezoelectric layer.

[0024] In certain embodiments, the resonating element comprises a metal layer (metallization) on top of the piezoelectric layer. In certain embodiments, the resonating element comprises a metal layer (metallization) under the piezoelectric layer. In certain embodiments, the metal layer covers only partially (partly, not fully) the surface area of the resonating element. In certain embodiments, the metal layer covers the same surface area of the resonating element as the piezoelectric layer. In certain embodiments, the metal layer covers less than 90% of a surface area of the resonating element. In certain embodiments, the metal layer covers preferably less than 80%, more preferably less than 60%, most preferably less than 50% of the surface area of the resonating element. In certain embodiments, the metal layer is patterned using lithography. In certain embodiments, the metal layer is patterned and etched.

[0025] In certain embodiments, the resonator is configured to operate in a temperature range of -40... +150°C. In certain embodiments, the resonator is configured to operate in a temperature range of -40... +125°C. In certain embodiments, the resonator is configured to operate in a temperature range of -40... +105°C. In certain embodiments, the resonator is configured to operate in a temperature range of -40 ... +85 °C. In certain embodiments, the resonator is configured to operate in a temperature range of -40... +150°C, such as in a temperature range of -40... +125°C, -40... +105°C, or -40 ... +85 °C. In certain embodiments, the resonator is configured to operate in a temperature range of -40... +150°C, preferably in a temperature range of -40... +125°C, more preferably in a temperature range of -40... +105°C, and most preferably in a temperature range of -40 ... +85 °C.

[0026] In certain embodiments, the resonator has a frequency stability of -50 ... +50 ppm (parts per million) or better. In certain embodiments, the resonator has a frequency stability of -10 ... +10 ppm or better.

[0027] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspectsor 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.

[0028] BRIEF DESCRIPTION OF THE FIGURES

[0029] Some example embodiments will be described with reference to the accompanying figures, in which:

[0030] Fig. 1a schematically shows a prior art resonating element from the top view;

[0031] Fig. 1b schematically shows a prior art resonating element from the side view;

[0032] Fig. 2a schematically shows a resonating element from the top view according to an example embodiment;

[0033] Fig. 2b schematically shows a resonating element from the side view according to an example embodiment;

[0034] Fig. 3a schematically shows a resonating element from the top view according to another example embodiment;

[0035] Fig. 3b schematically shows a resonating element from the side view according to another example embodiment;

[0036] Fig. 4a schematically shows a resonating element from atop view according to an example embodiment;

[0037] Fig. 4b schematically shows a resonating element from side view according to an example embodiment;

[0038] Fig. 4c schematically shows a resonating element resonating in an out-of-plane resonance mode from side view according to an example embodiment;

[0039] Fig. 5a schematically shows a cantilever resonator and its out-of-plane resonance mode according to an example embodiment;

[0040] Fig. 5b schematically shows a cantilever resonator and its out-of-plane resonance mode according to another example embodiment;

[0041] Fig. 5c schematically shows a cantilever resonator and its out-of-plane resonance mode according to yet another example embodiment;Fig. 5d schematically shows a cantilever resonator and its out-of-plane resonance mode according to yet further another example embodiment;

[0042] Fig. 6a schematically shows a tuning fork resonator and its out-of-plane resonance mode according to an example embodiment;

[0043] Fig. 6b schematically shows a tuning fork resonator and its out-of-plane resonance mode according to another example embodiment;

[0044] Fig. 6c schematically shows a tuning fork resonator and its out-of-plane resonance mode according to yet another example embodiment;

[0045] Fig. 7a schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to an example embodiment;

[0046] Fig. 7b schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to another example embodiment; Fig. 7c schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to yet another example embodiment; Fig. 7d schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to yet further another example embodiment;

[0047] Fig. 7e schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to still another example embodiment; Fig. 7f schematically shows an out-of-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to still yet another example embodiment;

[0048] Fig. 8a schematically shows a resonator having an in-plane resonance mode according to an example embodiment;

[0049] Fig. 8b schematically shows a resonator and its in-plane resonance mode according to an example embodiment;

[0050] Fig. 9a schematically shows an in-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to an example embodiment;

[0051] Fig. 9b schematically shows an in-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to another example embodiment; Fig. 9c schematically shows an in-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to yet another example embodiment;Fig. 9d schematically shows an in-plane tuning fork resonator comprising a piezoelectric layer covering its surface area only partially according to still another example embodiment; and

[0052] Fig. 10 shows a frequency versus temperature graph according to an example embodiment.

[0053] DETAILED DESCRIPTION

[0054] In the following description, like reference signs denote like elements or steps.

[0055] As used herein, the term a 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 and process-control unit, vacuum tube or alike. In certain embodiments, the semiconductor device has been packaged. The semiconductor apparatus may be a MEMS apparatus.

[0056] As used herein, the term surface area refers to the area of the resonating element surface. As used herein, the term surface area refers to the area of the resonating element (the element of the resonator configured to resonate), which is seen when observed from above (top view, seen from up to down). Accordingly, the surface area of the resonating element refers only to the (horizontal) top surface of the resonating element, and not to the (vertical) sides of bottom surface of the resonating element. As used herein, the term surface area refers to the surface of the resonating element which is parallel to the movement of the resonating element, when configured to operate in a resonance mode. As used herein, the term surface coverage refers to the surface area of the resonator that is covered, for example by a piezoelectric layer in accordance with certain embodiments.

[0057] Fig. 1a shows a prior art resonating element 10 from the top view (from above) and Fig. 1b shows a prior art resonating element 10 from a side view. The coordinate axes marked throughout the Figures denote the directions of observation in each particular case. The prior art resonating element is fabricated on a substrate comprising a silicon layer 11. The prior art resonating element 10 comprises a piezoelectric layer 12 covering the surface area of the resonating element 12. The piezoelectric layer 12 covers the whole surface area of the resonating element (100% coverage) as shown in Figs. 1a and 1b.

[0058] Fig. 2a shows a resonating element 100 from the top view and Fig. 2b shows the same resonating element 100 from the side view according to an example embodiment. In certainembodiments, the resonating element 100 is fabricated on a substrate. In certain embodiments, the substrate is a silicon wafer comprising a silicon layer 101. In certain embodiments, the resonator comprises mostly (essentially) silicon of the total mass of the resonator.

[0059] In certain embodiments, the piezoelectric layer 102 is of piezoelectric material. In certain embodiments, the piezoelectric layer 102 is of aluminium nitride, AIN or of scandium-doped aluminium nitride, Sc-doped AIN. The piezoelectric layer 102 is provided to enable piezoelectric connection to the resonating element 100.

[0060] In certain embodiments, the resonating element 100 comprises a piezoelectric layer 102 covering only partially the surface area of the resonating element 100. In certain embodiments, the piezoelectric layer 102 is patterned using lithography and etched, to provide the piezoelectric layer 102 partially covering the surface area of the resonating element 100.

[0061] In certain embodiments, the resonator is a beam resonator. In certain embodiments, the resonating element 100 is a beam having an aspect ratio (ratio of length L to width W) different from 1. In certain embodiments, the resonating element 100 has an aspect ratio (ratio of length L to width W) more than 1. In certain embodiments, the piezoelectric layer 102 is patterned such that the piezoelectric layer 102 forms an area (a strip, a rectangle) parallel to the length direction L of the resonating element 100 as shown in Fig. 2a.

[0062] In certain embodiments, the piezoelectric layer 102 is removed (is absent) from the edge areas of the resonating element 100 to cover only partially the surface area of the resonating element 100. In certain embodiments, the piezoelectric layer 102 is removed from the longitudinal edge areas of the resonating element 100. In certain embodiments, the piezoelectric layer 102 is removed from the (both) lengthwise aligned edges of the resonating element 100.

[0063] In certain embodiments, the piezoelectric layer 102 covers less than 90% of a surface area of the resonating element 100. In certain embodiments, the piezoelectric layer 102 covers preferably less than 80%, such as less than 60% or less than 50% of the surface area of the resonating element 100.

[0064] Fig. 3a shows a resonating element 100 from the top view and Fig. 3b shows the same resonating element 100 from the side view according to another example embodiment. As shown in Figs. 3a and 3b, in certain embodiments, the resonating element 100 comprisesthe piezoelectric layer 102 covering only partially the surface area of the resonating element 100.

[0065] In certain embodiments, the piezoelectric layer 102 is removed (is absent) from the edge areas of the resonating element 100 to cover only partially the surface area of the resonating element 100. In certain embodiments, the piezoelectric layer 102 covers the central area of the resonating element 100 (only).

[0066] In certain embodiments, the piezoelectric layer 102 is removed from the longitudinal and lateral edge areas of the resonating element 100. In certain embodiments, the piezoelectric layer 102 is removed from the (both) lengthwise aligned edges and from the width-wise aligned edges of the resonating element 100.

[0067] Figs. 4a and 4b schematically show a resonating element 100 according to an example embodiment. Fig. 4a shows the resonating element 100 from above, and Fig. 4b shows the same resonating element 100 from the side. In certain embodiments, the resonating element 100 comprises a material stack. In certain embodiments, the resonating element 100 comprises the piezoelectric layer 102 on top of the silicon layer 101. In certain embodiments, the resonating element 100 comprises a top electrode 103 on the piezoelectric layer 103. In certain embodiments, the top electrode 103 is of gold, Au.

[0068] As shown in Fig. 4a, in certain embodiments, the piezoelectric layer 102 and the top electrode layer 103 cover the surface area of the resonating element 100 partially. In certain embodiments, the piezoelectric layer 102 and the top electrode layer 103 cover the same (equal) surface area of the resonating element 100. In certain embodiments, the top electrode layer 103 is deposited onto the areas covered by the piezoelectric material 102.

[0069] In certain embodiments, the resonating element 100 comprises a metal layer (not shown) on top of and / or under the piezoelectric layer 102. In certain embodiments, the metal layer (not shown) covers the same surface area of the resonating element 100 as the piezoelectric layer 102.

[0070] In certain embodiments, the silicon layer 101 comprises doping. In certain embodiments, the doping comprises n-type doping, such as phosphorous doping. In certain embodiments, the doping comprises an average impurity concentration of at least 1*1019cm-3or more.

[0071] Fig. 4c shows the same resonating element 100 resonating as shown in Figs 4a and 4b, according to an example embodiment. In certain embodiments, the resonator comprises aresonating element 100. In certain embodiments, the resonating element 100 is a portion of the resonator configured to resonate and move in direction(s) determined by the resonance mode. In certain embodiments, the resonating element 100 is configured to operate in an out-of-plane flexural resonance mode as shown in Fig. 4b. In certain embodiments, the resonating element 100 is supported (anchored) by a support structure. In certain embodiments, the resonating element 100 is supported by the support structure at location 110 (at anchoring point, shown as dashed line). In certain embodiments, the resonating element 100 comprises a supported end and a free end. In certain embodiments, the resonating element 100 is configured to resonate in an out-of-plane resonance mode (up-and-down motion) at its free end. In certain embodiments, the resonator (element) is configured to operate in a kilohertz frequency area, kHz, such as in a resonance frequency of less than 500 kHz. In certain preferred embodiments, the resonator (element) is configured to operate in a resonance frequency of about 32 kHz, such as in a resonance frequency of 32.768 kHz, or in a resonance frequency of N * 32.768 kHz, wherein N is a power of two.

[0072] Accordingly, in certain embodiments there is provided a resonator comprising a resonating element 100 configured to operate in a resonance mode, wherein the resonating element comprises a silicon layer 101 and a piezoelectric layer 102, and wherein the piezoelectric layer 102 covers a surface area of the resonating element 100 partially.

[0073] Figs. 5a, 5b, 5c and 5d show a resonator comprising a resonating element 100 and its schematical resonance mode according to an example embodiment. In Figs. 5a, 5b, 5c, and 5d the left side figure refers to a top view (from above) and the right-side figure refers to a side view (horizontal view) of the same resonator. In Figs. 5a, 5b, 5c, and 5d the markings [+] and [-] refer to the phase of the resonance. [+] refers to a first resonance phase (shown herein as upwards from the plane), and [-] refers to a second resonance phase (shown herein as downwards from the plane), which is shifted by 180 degrees with respect to the first phase.

[0074] In certain embodiments, the resonating element 100 is configured to operate in an out-of-plane flexural resonance mode as shown in Figs. 5a, 5b, 5c, and 5d. In certain embodiments, the resonating element 100 is a piezoelectric resonating element comprising a piezoelectric layer, wherein the piezoelectric layer covers the surface area of the resonating element 100 partially (not shown in Figs. 5a, 5b, 5c and 5d).As shown in Fig. 5a, in certain embodiments, the resonating element 100 is a cantilever resonator. In certain embodiments, the resonating element 100 is attached to a support structure from one end of the resonating element (at anchoring point / location 110). In certain embodiments, the resonating element 100 is configured to resonate in an out-of-plane flexural resonance mode, wherein the free end of the resonating element 100 is excited to said resonance mode (shown herein as upwards [+] from the plane).

[0075] As shown in Fig. 5b, in certain embodiments, the resonating element 100 is attached to the support structure at the middle of the resonating element 100 (at anchoring point / location 110). In certain embodiments, the resonating element 100 is configured to resonate in an out-of-plane flexural resonance mode, wherein both free ends of the resonating element 100 are excited to said resonance mode (shown herein as upwards [+] from the plane). In certain embodiments, both free ends of the resonating element 100 are excited to a same resonance phase. In certain alternative embodiments, the free ends of the resonating element 100 are excited to a resonance phase deviating from the other by 180 degrees (not shown).

[0076] As shown in Fig. 5c, in certain embodiments, the resonating element 100 is supported by the support structure from both ends of the resonating element 100 (at anchoring points / locations 110, 110’). In certain embodiments, the resonating element 100 is configured to resonate in an out-of-plane flexural resonance mode, wherein the middle part of the resonating element 100 is excited to said resonance mode (shown herein as upwards [+] from the plane).

[0077] As shown in Fig. 5d, in certain embodiments, the resonating element 100 is supported by the support structure from two locations 110, 110’ of the resonating element 100, which both locations are at a distance from the ends of said resonating element 100. In certain embodiments, the resonating element 100 is configured to resonate in an out-of-plane flexural resonance mode, wherein both ends of the resonating element 100 and the middle part of the resonating element 100 are excited to said resonance mode. In certain embodiments, the ends of the resonating element 100 and the middle part of the resonating element 100 are excited to a resonance mode deviating from the other by 180 degrees (shown herein as the ends resonating upwards [+] from the plane, and the middle part resonating downwards [-] from the plane).

[0078] Figs. 6a, 6b and 6c show a resonator comprising a plurality of resonating elements and a schematical resonance mode according to an example embodiment. In Figs. 6a, 6b and 6cthe left side figure refers to a top view (from above) and the right-side figure refers to a side view (horizontal view) of one resonating element of the resonator. In Figs. 6a, 6b and 6c the markings [+] and [-] refer to the phase of the resonance. [+] refers to a first resonance phase (shown herein as upwards from the plane), and [-] refers to a second resonance phase (shown herein as downwards from the plane, as a striped area).

[0079] In example embodiments of Figs. 6a, 6b and 6c, the resonator is a tuning fork resonator. In example embodiments of Figs. 6a, 6b and 6c, the resonator is supported by a support structure from an end of the tuning fork resonator (at anchoring point / location 110I n certain embodiments, the resonator is a tuning fork resonator comprising a plurality of resonating forks (resonating elements). In certain embodiments, the tuning forks are adjacent tuning forks.

[0080] As shown in Fig. 6a, in certain embodiments, the resonator is a tuning fork resonator comprising two resonating forks 100A / 100B (resonating elements). In certain embodiments, the resonating forks 100A / 100B have resonance phases deviating from one another by 180 degrees.

[0081] As shown in Fig. 6b, in certain embodiments, the resonator is a tuning fork resonator comprising a plurality of resonating forks 100A / 100B / 100C (resonating elements). In certain embodiments, the tuning fork resonator comprises three resonating forks 100A / 100B / 100C. In certain embodiments, the resonating forks 100A / 100B / 100C have resonance phases deviating from one another by 180 degrees. In certain embodiments, the outermost resonating forks 100A / 100C are configured to resonate in a same resonance phase with each other. In certain embodiments, the resonance phase of the outermost resonating forks 100A / 100C and the resonance phase of the middle resonating fork 100B deviates from the other by 180 degrees.

[0082] As shown in Fig. 6c, in certain embodiments, the resonator is a tuning fork resonator comprising four resonating forks 100A / 100B / 100C / 100D (resonating elements). In certain embodiments, the resonating forks 100A / 100B / 100C / 100D have resonance phases deviating from one another by 180 degrees. In certain embodiments, the outermost resonating forks 100A / 100D are configured to resonate in a same resonance phase with each other. In certain embodiments, the innermost resonating forks 100B / 100C are configured to resonate in a same resonance phase with each other. In certain embodiments, the resonance phase of the outermost resonating forks 100A / 100D and the resonance phase of the innermost resonating forks 100B / 100C deviates from the other by 180 degrees.Figs. 7a, 7b, 7c, 7d, 7e, and 7f schematically show examples of tuning fork resonators comprising a piezoelectric layer 102 covering the surface area of the resonating elements 100A / B / C / D only partially according to example embodiments. Figs. 7a, 7b, 7c, 7d, 7e, and 7f depict a top view (from above) of example coverage patterns of the piezoelectric layer 102 for out-of-plane resonance mode tuning fork resonators.

[0083] In example embodiments of Figs. 7a, 7b, 7c, 7d, 7e, and 7f, the resonator is supported by a support structure from an end of the tuning fork resonator (at anchoring point / location 110).

[0084] In certain embodiments, as shown in Figs, 7a, 7c, and 7e, the piezoelectric layer 102 is absent from the longitudinal edge areas of the resonating element 100A / B / C / D. In certain embodiments, the piezoelectric layer 102 runs along (covers) the resonating element 100A / B in the longitudinally central alignment, leaving the edges absent from the piezoelectric material 102.

[0085] In example embodiments of Figs, 7a, 7c, and 7e, the piezoelectric layer 102 covers the x-directional central area of each resonating element 100A / B / C / D. In these example embodiments, the piezoelectric layer 102 runs (covers) the entire length of the resonating element 100A / B / C / D (from the anchoring point 110 to the other (opposing) end of each resonating element) (in the longitudinally central alignment, leaving the edges absent from the piezoelectric material 102).

[0086] In certain embodiments, as shown in Figs. 7b, 7d, and 7f, the piezoelectric layer 102 is absent from the longitudinal edge areas and from the lateral free end of the resonating element 100A / B / C / D. In certain embodiments, as shown in Figs. 7b, 7d, and 7f, the piezoelectric layer 102 is absent from the lateral free end of the resonating element 100A / B / C / D (opposite to the anchoring point 110).

[0087] In contrast to the Figs. 7a, 7c, and 7e, in the example embodiments of Figs. 7b, 7d, and 7f, the piezoelectric layer 102 does not run from the entire length of the resonating element 100A / B / C / D (from the anchoring point 110 to the other (opposing) end of each resonating element). In the example embodiments of Figs. 7b, 7d, and 7f, the piezoelectric layer 102 starts from the anchoring point 110 of the resonating element 100A / B / C / D and runs towards the (opposing) free end of the resonating element 100A / B / C / D.

[0088] In certain embodiments, the piezoelectric layer 102 forms (covers) a surface area smaller than the surface area of the resonating element 100 A / B / C / D. In certain embodiments, the piezoelectric layer 102 forms (covers) a rectangular shaped surface area. In certainembodiments, the resonator comprises beam-like (strip-like) patterns of piezoelectric material 102.

[0089] Figs. 8a and 8b schematically show a resonator having an in-plane resonance mode according to an example embodiment. In Figs. 8a and 8b the left side figure refers to a top view (from above) and the right-side figure refers to a side view (horizontal view) of one resonating element of the resonator. In example embodiments of Figs. 8a and 8b, the resonator is a tuning fork resonator. In example embodiments of Figs. 8a and 8b, the resonator is supported by a support structure from an end of the tuning fork resonator (at location 110), opposite to its free end(s). In certain embodiments, the resonating element 100 is configured to operate in an in-plane flexural resonance mode, as shown in Figs. 8a and 8b.

[0090] Fig. 8a shows a stationary resonator, and the Fig. 8b shows a resonating tuning fork resonator. As shown in Fig. 8b, the in-plane flexural resonance mode occurs in a plane (in the x-y plane as shown in the coordinate axes of the Figures). The arrows in the left-side figure of Fig. 8b denote the direction of resonance in this example embodiment. Thus, the right-side figure of Fig. 8b shows no movement (motion) out of the plane.

[0091] Figs. 9a, 9b, 9c, and 9d schematically show examples of tuning fork resonators comprising a piezoelectric layer 102 covering the surface area of the resonating elements 100A / B only partially according to example embodiments. Figs. 9a, 9b, 9c, and 9d depict a top view (from above) of example coverage patterns of the piezoelectric layer 102 for in-plane resonance mode tuning fork resonators.

[0092] In example embodiments of Figs. 9a, 9b, 9c, and 9d, the resonator is supported by a support structure from one end of the tuning fork resonator (at anchoring point / location 110).

[0093] In certain embodiments, as shown in Figs, 9a, 9b, 9c and 9d, the piezoelectric layer 102 is absent from the longitudinally central areas of the resonating element 100A / B. In these example embodiments, the piezoelectric layer 102 covers the longitudinal (in x-direction) edge area(s) of each resonating element 100A / B. In certain embodiments, such as shown in Figs. 9a and 9b, the piezoelectric layer 102 covers both longitudinal edges of the resonating elements 100A / B. On the other hand, in certain alternative embodiments, such as shown in Figs. 9c and 9d, the piezoelectric layer 102 covers one longitudinal edge of the resonating elements 100A / B. In Fig. 9c, the piezoelectric layer 102 covers the outermost longitudinal edge of each resonating elements 100A / B. In Fig. 9d, the piezoelectric layer 102 covers the innermost longitudinal edge of each resonating elements 100A / B. In theembodiment of Fig. 9d, the piezoelectric layer 102 covers also the portion in between the resonating elements 100A / B (resonating tuning forks).

[0094] In certain embodiments, the piezoelectric layer 102 runs along (covers) the resonating element 100A / B in the edges of the resonating element 100A / B (in x-directional alignment), leaving the longitudinal central area absent from the piezoelectric material 102. In certain embodiments, such as shown in Fig 9a, the piezoelectric layer 102 runs the entire length of the resonating element 100A / B / C / D (from the anchoring point 110 to the other (opposing) end of each resonating element).

[0095] In certain embodiments, as shown in Figs. 9b, 9c, and 9d, the piezoelectric layer 102 is absent from the lateral free end of the resonating elements 100A / B (opposite to the anchoring point 110).

[0096] In contrast to the Fig. 9a, in the example embodiments of Figs. 9b, 9c, and 9d, the piezoelectric layer 102 does not run from the entire length of the resonating element 100A / B (from the anchoring point 110 to the other (opposing) end of each resonating element). In the example embodiments of Figs. 9b, 9c, and 9d, the piezoelectric layer 102 starts from the anchoring point 110 of the resonating element 100A / B and runs towards the (opposing) free end of the resonating element 100A / B.

[0097] In certain embodiments, the piezoelectric layer 102 covers a surface area smaller than the surface area of the resonating element 100 A / B. In certain embodiments, the piezoelectric layer 102 forms (covers) a rectangular shaped surface area. In certain embodiments, the resonator comprises beam-like (strip-like) patterns of piezoelectric material 102.

[0098] Fig. 10 shows a frequency (Af, change in frequency, in a unit of parts per million, ppm) versus temperature (T, in a unit of degrees Celsius, °C) graph according to an example embodiment. The frequency versus temperature curves are typically in the form of downward opening parabolas. The steeper (narrower) the parabola, the less frequency stability the resonator possesses over a temperature range.

[0099] Line A refers to a prior art resonator, such as the resonator shown in Figs. 1a and 1b. Line B refers to a resonator according to the present disclosure, such as the resonator shown in Figs. 2a and 2b. As shown in Fig. 10, line B shows an improved frequency vs. temperature behavior in comparison to line A. This is achieved by utilizing a piezoelectric layer covering the surface area of the resonating element (only) partially in accordance with the present disclosure.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 frequency stability over a wide range of temperature, such as in a temperature range of -40 ... +85 °C. The improved frequency stability may be for instance -50 ... +50 ppm or even to -10 ... +10 ppm or better.

[0100] A further technical effect is to provide temperature compensated resonators, such as temperature compensated out-of-plane silicon MEMS resonators. A further technical effect is to provide frequency optimized resonators comprising piezoelectric layer.

[0101] A further technical effect is lower power consumption of an oscillator using the resonator device as the frequency defining part of its circuitry. This effect is based on the fact that the better stability of the frequency over temperature leads to, in general, less power consumption in the circuit blocks of the oscillator circuit that are used for fine-adjustment of frequency with respect to temperature changes.

[0102] 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.

[0103] 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.

[0104] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1. A resonator comprising a resonating element configured to operate in a resonance mode, wherein the resonating element comprises a silicon layer and a piezoelectric layer, and wherein the piezoelectric layer covers a surface area of the resonating element partially.

2. The resonator of claim 1 , wherein the resonating element is configured to operate in an out-of-plane flexural resonance mode.

3. The resonator of claim 1 , wherein the resonating element is configured to operate in an in-plane flexural resonance mode.

4. The resonator of any preceding claim, wherein the piezoelectric layer covers less than 90% of the surface area of the resonating element.

5. The resonator of claim 4, wherein the piezoelectric layer covers preferably less than 80%, such as less than 60% or less than 50% of the surface area of the resonating element.

6. The resonator of any preceding claim, wherein the piezoelectric layer is of aluminium nitride, AIN.

7. The resonator of claim 6, wherein the piezoelectric layer is of scandium-doped aluminium nitride, Sc-doped AIN.

8. The resonator of any preceding claim, wherein the silicon layer comprises doping.

9. The resonator of any preceding claim, configured to operate in a frequency of less than 1 MHz.

10. The resonator of any preceding claim, configured to operate in a kilohertz, kHz, frequency area, preferably in a resonance frequency of 32.768 kHz, or in a resonance frequency of N * 32.768 kHz, wherein N is a power of two.

11. The resonator of any preceding claim, wherein the resonator is a tuning fork resonator.

12. The resonator of any preceding claim, wherein the piezoelectric layer is patterned to provide the piezoelectric layer covering less than 90% of the surface area of the resonating element.

13. The resonator of any preceding claim, wherein the resonating element comprises a material stack, the material stack comprising the silicon layer, the piezoelectric layer on top of the silicon layer, and a top electrode on top of the piezoelectric layer.

Images