Tuning fork resonator
The tuning fork resonator design with out-of-plane oscillating beams and integrated piezoelectric components addresses miniaturization challenges by maintaining a high quality factor, achieving efficient impedance reduction and size reduction.
Patent Information
- Authority / Receiving Office
- HK · HK
- Patent Type
- Applications
- Current Assignee / Owner
- MICRO CRYSTAL LTD
- Filing Date
- 2026-05-11
- Publication Date
- 2026-07-17
AI Technical Summary
Existing tuning fork resonators face challenges in miniaturization due to a decrease in quality factor (Q) leading to increased impedance, particularly when the thermal relaxation time (τ) of the resonator beam equals the reciprocal of the resonant angular frequency (ω), which is exacerbated by thermoelastic damping.
A tuning fork resonator design featuring resonator beams with thicknesses between 0.05% and 20% of the core post height, oscillating in an out-of-plane mode, and incorporating piezoelectric components with electrode layers to maintain a high quality factor while reducing size.
The design achieves a reduced size with a quality factor greater than 5000, preferably over 15000, by optimizing thermal and mechanical properties, and independently enhancing piezoelectric connections and thermomechanical characteristics.
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Abstract
Description
(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202511267393.7 (22) Application Date 2025.09.05 (30) Priority Data 24200062.8 2024.09.12 EP (71) Applicant Microcrystal Ltd. Address Switzerland (72) Inventor S. Dalla Piazza F. Stob (74) Patent Agency Beijing Zhongzi Law Firm 11247 Patent Attorney Gao Meiyan Wu Peng (51) Int.Cl. H03H 9 / 215 (2006.01) H03H 9 / 13 (2006.01) (54) Invention Title Tuning Fork Resonator (57) Abstract This invention relates to a tuning fork resonator designed to allow for a reduction in resonator size while maintaining a high quality factor. The tuning fork resonator includes: a core post (11) having a height (12) extending from a first base (13) to a second base (14); and a first resonator beam (15a) and a second resonator beam (15b) spaced apart from each other, the first resonator beam (15a) and the second resonator beam (15b) being connected to the core post (11) and arranged in a plane substantially perpendicular to the height (12) of the core post (11); characterized in that the thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05% and 20% of the height (12) of the core post (11). Claims 2 pages, Description 9 pages, Drawings 4 pages, CN 121664142 A 2026.03.13 CN 1 21 66 41 42 A 1. A tuning fork resonator (10) comprising: - a core post (11) having a height (12) extending from a first base (13) to a second base (14); and - a first resonator beam (15a) and a second resonator beam (15b) spaced apart from each other, the first resonator beam (15a) and the second resonator beam (15b) being connected to the core post (11) and arranged in a plane substantially perpendicular to the height (12) of the core post (11); characterized in that the thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05% and 20% of the height (12) of the core post (11). 2. The tuning fork resonator according to claim 1, characterized in that the tuning fork resonator is configured to allow the first resonator beam (15a) and the second resonator beam (15b) to oscillate in an out-of-plane mode. 3. The tuning fork resonator according to any of the preceding claims, characterized in that the first resonator beam...(15a) includes a first piezoelectric component (28a), and the second resonator beam (15b) includes a second piezoelectric component (28b). The first piezoelectric component (28a) and the second piezoelectric component (28b) are respectively disposed on the surfaces (16a, 16b) of the first resonator beam (15a) and the second resonator beam (15b). Each of the first piezoelectric component (28a) and the second piezoelectric component (28b) includes: - a first electrode layer (41a, 41b) respectively located on the surfaces (16a, 16b) of the first resonator beam (15a) and the second resonator beam (15b); - a piezoelectric layer (42a, 42b) located on the first electrode layer (41a, 41b); and - a second electrode layer (43a, 43b) located on the piezoelectric layer (42a, 42b); wherein: - The first electrode layer of the first piezoelectric component (28a) and the second electrode layer of the second piezoelectric component (28b) are electrically connected to a first mounting pad (29a), the first mounting pad (29a) being configured to be connected to a first pole of a power supply; and - the second electrode layer of the first piezoelectric component (28a) and the first electrode layer of the second piezoelectric component (28b) are electrically connected to a second mounting pad (29b), the second mounting pad (29b) being configured to be connected to the opposite pole of the power supply. 4. The tuning fork resonator according to any one of the preceding claims, characterized in that the core post (11), the first resonator beam (15a) and the second resonator beam (15b) are made of quartz, preferably Z-cut quartz, or made of lanthanum gallium silicate, GaPO4 or partially silicon oxide. 5. The tuning fork resonator according to claim 1 or 2, characterized in that the tuning fork resonator is integrally formed, wherein the first resonator beam (15a) and the second resonator beam (15b) are integrally formed with the core post (11). 6. The tuning fork resonator according to any one of the preceding claims, characterized in that the tuning fork resonator further comprises an intermediate plate (27) extending between the core post (11) and the first resonator beam (15a) and the second resonator beam (15b), the intermediate plate (27) being coplanar with the first resonator beam (15a) and the second resonator beam (15b), and preferably the intermediate plate (27) having the same thickness as the first resonator beam (15a) and the second resonator beam (15b). 7. The tuning fork resonator according to any one of the preceding claims, characterized in that the thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05 μm and 25 μm, preferably less than 10 μm. 8. The tuning fork resonator according to any one of the preceding claims, characterized in that the height of the core post (11) is...(12) Between 10 μm and 200 μm, preferably between 20 μm and 150 μm, more preferably between 80 μm and 125 μm. Claims 1 / 2 page 2 CN 121664142 A 9. The tuning fork resonator according to any one of the preceding claims, characterized in that the first resonator beam (15a) and the second resonator beam (15b) each have an attachment end and a free end, the attachment end being fixed to the core post (11) or fixed to an intermediate piece (27) located between the core post and the first resonator beam (15a) and the second resonator beam (15b), the first resonator beam (15a) and the second resonator beam (15b) further comprising: - a main body portion (MP) extending from their respective free ends to a region near their respective attachment ends; and - a horn-shaped portion (FP) that gradually widens from the main body portion MP toward their respective attachment ends. 10. The tuning fork resonator according to any one of the preceding claims, characterized in that the width (20) of the core post (11) is between 50 μm and 200 μm, preferably between 80 μm and 125 μm. 11. The tuning fork resonator according to any one of the preceding claims, characterized in that the width (18a, 18b) of the respective main body portion (MP) of the first resonator beam (15a) and the second resonator beam (15b) is between 20% and 45% of the width (20) of the core post (11). 12. The tuning fork resonator according to any one of the preceding claims, characterized in that the length (21) of the tuning fork resonator is less than 500 μm, preferably less than 400 μm. 13. The tuning fork resonator according to any one of the preceding claims, characterized in that the core post (11) has a thickness (30) measured along the direction of the first resonator beam (15a) and the second resonator beam (15b), and the length (23a, 23b) of each of the first resonator beam (15a) and the second resonator beam (15b) is greater than or equal to at least half of the thickness (30) of the core post (11). 14. The tuning fork resonator according to any one of the preceding claims, characterized in that the core post (11) includes a tapered portion (24) extending from the side (25) of the core post (11) and / or from the first base (13) or the second base (14) to a joint (26) or intermediate surface located between the core post (11) and the first resonator beam (15a) and the second resonator beam (15b), or extending to a joint (26) or surface located between the core post and an intermediate piece (27) connected to the first resonator beam (15a) and the second resonator beam (15b).15. The tuning fork resonator according to any one of the preceding claims, characterized in that the quality factor of the tuning fork resonator in vacuum at 32768 Hz is greater than or equal to 5000, preferably greater than or equal to 7500, more preferably greater than or equal to 10000, and even more preferably greater than or equal to 15000. Claims 2 / 2 Page 3 CN 121664142 A Tuning Fork Resonator Technical Field
[0001] The present invention relates to a tuning fork resonator whose geometry allows for a reduction in the size of the resonator while maintaining a high quality factor. Background Art
[0002] Tuning fork resonators typically include at least two forks (also called vibrating arms or vibrating beams) and at least one core post (or base) connecting the forks. The core post and the forks are typically coplanar. Tuning fork resonators may be made of, for example, silicon or quartz. The forks are typically arranged in parallel and symmetrically to each other. The forks are typically provided with electrodes, such as those disclosed in EP3468037, or with piezoelectric strips, such as those disclosed in EP2278709. Electrodes or piezoelectric strips can be connected to an AC voltage, causing the teeth of the tuning fork to vibrate. The teeth of a conventional tuning fork are located in and vibrate within a plane of vibration.
[0003] A characteristic of a resonator is its quality factor Q (also called the "Q factor" or "Q"), typically defined as the ratio of the energy stored in the resonator to the energy lost during the oscillation period. The higher the Q factor value, the better the resonator's resonance characteristics. A high Q factor is beneficial for achieving low impedance in the resonator.
[0004] One goal of resonator manufacturers is to reduce the size of the resonator while maintaining a high quality factor and resonant frequency value. A major problem in miniaturizing low-frequency flexural mode resonators is that a decrease in the quality factor Q leads to an increase in impedance due to thermoelastic damping. Thermoelastic damping is highest when the thermal relaxation time τ (tau) of the resonator beam in the oscillation direction is equal to the reciprocal of the resonant angular frequency ω = 2πf, i.e., if ω·τ = 1.
[0005] Due to the thermomechanical properties of quartz, we find that for a common tuning fork resonator operating at 32768 Hz, ω·τ > 1.
[0006] Reducing the given geometry will decrease τ(tau), thus decreasing ω·τ. Therefore, the Q value will decrease with size until ω·τ = 1. For even smaller structures, the Q value will increase again.
[0007] As a countermeasure, resonator designs aim to maximize τ(tau), for example by etching grooves on both sides of the resonator beam, which transforms the beam's cross-section into an H-shape with a thin film between the two sidewalls. Document EP3468037B1 describes an example of a small piezoelectric resonator with this feature. Some of these solutions involve etching grooves on the vibrating arm to reduce energy consumption by providing a more uniform electric field. On the one hand, the grooves provide thermal insulation between the compression and extension sides, thereby improving...Q-factor, reducing impedance. On the other hand, due to the thin and high boundary walls, the electric field is more uniform and stronger, thereby increasing the kinetic capacitance and thus reducing impedance. More specifically, each resonator beam includes a first groove on a first side and a second groove on the opposite side, the first and second grooves having different depths. Miniaturization of such resonators may be limited by their design complexity and fabrication possibilities.
[0008] The main function of the grooves is to enhance piezoelectric connections through their narrow and high sidewalls. In addition, the thin film between the grooves can slow down the rate of thermalization within the beam, thereby increasing τ(tau). However, this technique can only partially compensate for the problem that the Q factor decreases with increasing size.
[0009] The excellent thermal and mechanical properties of quartz make it the preferred material for tuning fork resonators.
[0010] There is a need to miniaturize tuning fork resonators (preferably quartz tuning fork resonators) and to provide new designs for such resonators to achieve the state of ω·τ<<1 in quartz, where the Q-factor increases to a reasonable level again. Specification 1 / 9 pages 4 CN 121664142 A Summary of the Invention
[0011] The present invention aims to provide a tuning fork resonator with reduced size and a high quality factor Q.
[0012] In a first aspect, the present invention relates to a tuning fork resonator comprising:
[0013] - a core post having a height extending from a first base to a second base;
[0014] - a first resonator beam and a second resonator beam spaced apart from each other, the first resonator beam and the second resonator beam being coupled to the core post and arranged in a plane substantially perpendicular to the height of the core post;
[0015] characterized in that the thickness of the first resonator beam and the second resonator beam is between 0.05% and 20% of the height of the core post.
[0016] Preferably, the tuning fork resonator is configured to allow the resonator beams to vibrate in an out-of-plane mode.
[0017] Preferably, the first resonator beam includes a first piezoelectric component, and the second resonator beam includes a second piezoelectric component. Each piezoelectric component is disposed on the surface of the respective resonator beam. Both the first and second piezoelectric components include:
[0018] - a first electrode layer located on the surface of the resonator beam;
[0019] - a piezoelectric layer located on the first electrode layer;
[0020] - a second electrode layer located on the piezoelectric layer;
[0021] wherein:
[0022] - the first electrode layer of the first piezoelectric component and the second electrode layer of the second piezoelectric component are electrically connected to a first mounting pad, which is configured to be connected to a first pole of an AC power supply;
[0023] - the second electrode layer of the first piezoelectric component and the first electrode layer of the second piezoelectric component are electrically connected to a second mounting pad, which is configured to be connected to the opposite pole of the AC power supply.
[0024] Preferably, the core and resonator beam are made of quartz, preferably Z-cut quartz. Other materials may also be selected, for example...Materials such as lanthanum gallium silicate, gallium phosphate, or partially silicon oxide, or any compound with a specific crystal orientation, make the temperature coefficient of at least the first-order frequency of the resonator zero or close to zero, for example, with an absolute value less than 1 ppm / K. The relationship between the resonant frequency f of the tuning fork resonator and the temperature T can be approximated as f(T) = β·(T-TRef) 2 + α·(T-TRef) + f(TRef), where TRef is the reference temperature (usually 25°C), and α and β are the first-order and second-order temperature coefficients, respectively. For quartz and TRef near 25°C, there is a cutting angle close to z-cut, where α of the tuning fork resonator is close to zero, for example, with an absolute value less than 1 ppm / K. Therefore, f(T) is mainly determined by the second-order term, resulting in a parabolic frequency-temperature characteristic.
[0025] Preferably, the tuning fork resonator is integrally manufactured, wherein the first resonator beam and the second resonator beam are integrally formed with the core column.
[0026] Preferably, the tuning fork resonator further includes an intermediate plate extending between the core post and the first and second resonator beams, the intermediate plate being coplanar with the first and second resonator beams and preferably having the same thickness as the first and second resonator beams. The intermediate plate may extend from either the first or second base of the core post, or from an intermediate position located between the first and second bases of the core post.
[0027] Preferably, the thickness of the first and second resonator beams is between 0.05 μm and 25 μm, preferably less than 10 μm.
[0028] Preferably, the height of the core post is between 10 μm and 200 μm, preferably between 20 μm and 150 μm, more preferably between 80 μm and 125 μm.
[0029] Preferably, both the first resonator beam and the second resonator beam have an attached end and a free end (unattached end), the attached end being fixed to the core post or intermediate plate, and the first resonator beam and the second resonator beam further include:
[0030] - a main body portion extending from its free end (unattached end) to a region near its attached end; Specification 2 / 9 pages 5 CN 121664142 A
[0031] - a flared portion that gradually widens from its main body portion to its attached end.
[0032] In some embodiments, the main body portion has a constant width.
[0033] In some embodiments, the free end of the main body portion of the first resonator beam and the second resonator beam includes an additional mass or an enlarged portion providing an additional mass.
[0034] Preferably, the core post width is between 50 μm and 200 μm, preferably between 80 μm and 125 μm.
[0035] Preferably, the width of the main body portion of each of the first and second resonator beams is between 10% and 45% of the core column width.
[0036] Preferably, the length of the tuning fork resonator is less than 500 μm, and more preferably less than 400 μm.
[0037] Preferably, the core post has a thickness measured along the direction of the resonator beam, and the lengths of the first and second resonator beams are each greater than at least half the thickness of the core post.
[0038] Preferably, the core post includes a tapered portion extending from the side of the core post and / or from the first or second base to a joint or intermediate surface located between the core post and the first and second resonator beams, or extending to a joint or intermediate surface located between the core post and an intermediate plate connecting the resonator beams.
[0039] Preferably, the tuning fork resonator has a quality factor of greater than or equal to 5000 in vacuum at 32768 Hz, preferably greater than or equal to 7500, more preferably greater than or equal to 10000, and preferably greater than or equal to 15000.
[0040] The objectives, advantages, and features of the invention will be discovered by reading the following description, which is given by way of non-limiting example only, with reference to the accompanying drawings, in which:
[0041] FIG1 shows a top view of a tuning fork resonator according to a first embodiment of the invention;
[0042] FIG2 shows a side view of a tuning fork resonator according to an embodiment of the invention;
[0043] FIG3 shows a schematic diagram of an embodiment of a tuning fork resonator including two piezoelectric components and two mounting pads;
[0044] FIG4a shows a top view of a tuning fork resonator according to a second embodiment of the invention;
[0045] FIG4b shows a top view of a tuning fork resonator according to a third embodiment of the invention;
[0046] FIG5a shows a top view of a tuning fork resonator according to a fourth embodiment of the invention;
[0047] FIG5b shows a side view of a tuning fork resonator according to a fourth embodiment of the invention.
[0048] It should be noted that, unless otherwise stated, the drawings are not drawn to scale, and modifications can be made to the designs presented in the drawings within the spirit of the invention. Detailed Description of the Embodiments
[0049] The present invention will now be described in more detail with reference to Figures 1 and 2, which show a top view and a side view of an embodiment of a tuning fork resonator according to the present invention, respectively.
[0050] The tuning fork resonator 10 according to the present invention comprises:
[0051] - a core post 11 having a height 12 extending from a first base 13 to a second base 14; and
[0052] - a first resonator beam 15a and a second resonator beam 15b spaced apart from each other, which are connected to the core post 11 and extend in a plane substantially perpendicular to the height 12 of the core post 11;
[0053] characterized in that the thickness 17a of the first resonator beam 15a and the thickness 17b of the second resonator beam 15b are between 0.05% and 20% of the height 12 of the core post 11, preferably between 0.1% and 10%, more preferably between 0.1% and 5%. (See page 3 / 9 of the specification, CN 121664142 A)More preferably, the percentage is between 0.5% and 5%. In this document, the term "connection" means:
[0054] - the first element is directly connected (physically joined or attached) to the second element; or
[0055] - the first element is indirectly connected (physically joined or attached) to the second element through at least one other element.
[0056] Preferably, the intermediate piece 27 extends between the core post 11 and the first resonator beam 15a and the second resonator beam 15b. The thickness of the intermediate piece 27 is preferably the same as the thickness of the first resonator beam 15a and the second resonator beam 15b, and the intermediate piece 27 is coplanar with the first resonator beam 15a and the second resonator beam 15b. The intermediate piece 27 may also be coplanar with the first base 13 or the second base 14 of the core post 11. As shown in FIG2, the intermediate piece 27 is coplanar with the second base 14. In an alternative embodiment, as shown in FIG5b, the intermediate piece 27 may be located at an intermediate position between the first base 13 and the second base 14 of the core post 11. In any case, the intermediate plate 27 is substantially perpendicular to the height 12 of the core post 11. The intermediate plate 27 is advantageous for the temperature inflection point T0 and for the decoupling of the resonator beams 15a, 15b from the core post 11. The first resonator beam 15a and the second resonator beam 15b have a first end attached to the intermediate plate 27 (also referred to as the "attached end") and a second end as a free end (also referred to as the "unattached end").
[0057] The term "substantially perpendicular" means that one axis, plane or surface is perpendicular to another axis, plane or surface with a tolerance of 5° or less, preferably 1° or less. In the context of the invention, the expression "substantially perpendicular to the height of the core post" means that, in the absence of any electric field between the resonator beams or any mechanical impact that causes the first and second resonator beams to vibrate, the tolerance of the vertical position of the first and second resonator beams relative to the height of the core post is 5° or less, preferably 1° or less.
[0058] The first base 13 and the second base 14 are opposite each other, preferably substantially flat, and preferably substantially parallel to each other. The term "substantially flat" encompasses a generally flat or smooth surface, although it may optionally include minor irregularities or breaks (e.g., holes) that do not affect the overall flat or smooth appearance. The term "substantially parallel" means that two substantially flat surfaces or axes are parallel to each other, thus forming a 0° angle with a tolerance of less than 5°, preferably less than 1°.
[0059] The term "resonator beam" in this disclosure may refer to an arm, fork, or cantilever element, the length of which is preferably at least 5 times its width and / or thickness, and is adapted for vibration.
[0060] As can be seen from the top view shown in FIG1, the first resonator beam 15a and the second resonator beam 15b have a main body portion MP with, for example, a constant width. The shape of the main body portion MP is not limited to a rectangle, and other suitable shapes may be designed, for example, a rectangle with rounded or chamfered free ends, or a particular shape whose width varies along the length direction, such as that shown in FIG4a.
[0061] In some embodiments, the free ends of the main body portions of the first resonator beam 15a and the second resonator beam 15b include an additional mass or provide an enlarged portion of the additional mass, as shown in FIG4b. This additional mass can shorten the length of the resonator beam.
[0062] The tuning fork resonator is configured to allow the resonator beam to oscillate in an out-of-plane mode. The large ratio of the thickness 17a of the first resonator beam 15a to the thickness 17b of the second resonator beam 15b to the core height 12 results in the core 11 having a higher inertia than the first resonator beam 15a and the second resonator beam 15b. Therefore, the core 11 is more likely to accommodate residual motion compared to a case where the thicknesses of the core 11 and the first resonator beam 15a and the second resonator beam 15b are similar. It has been found that when the first resonator beam 15a and the second resonator beam 15b are in out-of-plane oscillation mode, the residual torsional motion of the first resonator beam 15a and the second resonator beam 15b in the out-of-plane mode is negligible because the core column 11 has a larger mass and is thicker than the resonator beams. In the context of this disclosure, the term "out-of-plane oscillation mode" refers to the vibration or oscillation mode of two resonator beams in which the two resonator beams, in a resting state, lie in the same plane (or coplanar) and vibrate in opposite directions (out of phase) outside the plane under the influence of an electric field applied through the resonator beams or under the influence of a mechanical impact substantially orthogonal to the plane. Although the common in-plane mode of tuning fork resonators can be used, the out-of-plane mode is chosen for ease of manufacture. The geometry of the tuning fork resonator as described above, preferably combined with any of the embodiments presented below, can reduce the size of the tuning fork resonator while maintaining a relatively high quality factor Q at low frequencies, as described on pages 4 / 9 of the specification (7 CN 121664142 A).
[0063] The core and the first and second resonator beams are made of quartz, preferably Z-cut quartz. Other materials may also be selected, such as lanthanum gallium silicate, gallium phosphate (GaPO4), or partially silicon oxide, or any compound with a specific crystal orientation, such that the temperature coefficient of at least the first-order frequency of the resonator is zero or close to zero, for example, an absolute value less than 1 ppm / K. As described below, the first resonator beam 15a and the second resonator beam 15b according to the invention are configured to oscillate in out-of-plane modes. Z-cut quartz is well known in the art and is a preferred material due to its ease of manufacture. Since the piezoelectric connection of the out-of-plane modes in quartz is relatively weak, piezoelectric components 28a, 29a are used for actuation. This achieves separation of mechanical and electrical characteristics, which is advantageous because the two domains can be optimized independently.
[0064] Advantageously, the tuning fork resonator is integrally formed, wherein the first resonator beam 15a and the second resonator beam 15b are integrally formed with the core 11.
[0065] In one embodiment shown in FIG2, the first resonator beam 15a and the second resonator beam 15b respectively include...The second base 14 of the core post 11 has coplanar surfaces 16a and 16b.
[0066] In an alternative embodiment, the first resonator beam 15a and the second resonator beam 15b may be positioned at an intermediate position between the second base 14 of the core post and the first base 13 of the core post, as shown in FIG5b.
[0067] Advantageously, the thickness 17a of the first resonator beam and the thickness 17b of the second resonator beam are between 0.05 μm and 25 μm, preferably less than 10 μm, more preferably less than 5 μm. More advantageously, the thicknesses of the first resonator beam 15a and the second resonator beam 15b are the same.
[0068] Preferably, the height 12 of the core post 11 is between 10 μm and 200 μm, preferably between 20 μm and 150 μm, and preferably between 80 μm and 125 μm.
[0069] Preferably, both the first resonator beam 15a and the second resonator beam 15b include:
[0070] - a main body portion MP extending from its free end (unattached end) to a region near its attached end;
[0071] - a horn-shaped portion FP extending from the main body portion MP toward its attached end.
[0072] The lengths of the main body portion MP and the horn-shaped portion FP can vary from zero to the full length of the resonator beam relative to each other.
[0073] The first resonator beam 15a and the second resonator beam 15b are separated from each other by a gap 19, which remains constant between the main body portions MP of the first resonator beam 15a and the second resonator beam 15b, and decreases between the horn-shaped portions FP of the first resonator beam 15a and the second resonator beam 15b. The horn-shaped portions FP of the first resonator beam 15a and the second resonator beam 15b improve shock resistance.
[0074] The width 20 of the core post 11 is between 50 μm and 200 μm, preferably between 80 μm and 125 μm, and preferably wider than the sum of the widths of the first resonator beam 15a and the second resonator beam 15b at their connection with the core post 11.
[0075] Preferably, the width 18a of the main body portion MP of the first resonator beam 15a and the width 18b of the main body portion MP of the second resonator beam 15b are between 10% and 45% of the width 20 of the core post 11. Advantageously, the width 18a of the main body portion MP of the first resonator beam 15a and the width 18b of the main body portion MP of the second resonator beam 15b are the same.
[0076] Preferably, the length 21 of the tuning fork resonator is less than 500 μm, preferably less than 400 μm.
[0077] The core post 11 has a thickness 30 measured along the direction of the first resonator beam 15a and the second resonator beam 15b. The length 23a of the first resonator beam 15a and the length 23b of the second resonator beam 15b are both greater than or equal to at least half the thickness 30 of the core column. Advantageously, the length 23a of the first resonator beam 15a and the length 23b of the second resonator beam 15b are the same.
[0078] Preferably, the core post 11 includes a tapered portion 24 that extends laterally from the side 25 of the core post and / or from the first base 13 or the second base 14 of the core post 11 to a joint 26 or intermediate surface located between the core post 11 and the first resonator beam 15a and the second resonator beam 15b, preferably extending to a joint located between the core post 11 and an intermediate piece 27, which is located between the core post and the first resonator beam 15a and the second resonator beam 15b. A portion of the length 22 includes the thickness 30 of the core post, the width of the tapered portion 24, and the width of the intermediate piece 27, as shown in the embodiments of FIG1 or FIG5a and FIG5b. This portion of the length 22 may be between 5% and 60% of the length 21 of the tuning fork resonator 10, preferably between 20% and 45%. As shown in one embodiment of FIG2, the tapered portion 24 extends from the side 25 of the core post 11 to the junction 26 located between the intermediate plate 27 and the core post 11 at a midpoint between the first base 13 and the second base 14. As shown in another embodiment of FIG5b, the first tapered portion 24a extends from the second base 14 of the core post 11 to the intermediate plate 27, and the second tapered portion 24b extends from a position between the first base 13 and the second base 14 of the core post to the junction 26 located between the core post 11 and the intermediate plate 27.
[0079] According to the invention, as described above, the tuning fork is configured to allow the first resonator beam 15a and the second resonator beam 15b to oscillate in an out-of-plane mode. It should be noted that for common Z-cut quartz used in tuning fork resonators, the piezoelectric connection in the out-of-plane mode is very weak. This is especially true for small sizes. Therefore, direct excitation with electrodes on the quartz will produce a very small kinematic capacitance, which, due to its small quality factor, will suppress the operation of the oscillator circuit. To achieve sufficient connection and low impedance, thin strips of piezoelectric materials such as AlN (aluminum nitride), PZT (lead zirconate titanate), or KNN (potassium sodium niobate) are deposited on the resonator plate and electrically connected to the mounting pad for excitation. The advantage of this method is that the piezoelectric connection and thermomechanical properties, i.e., thermoelastic damping and frequency-temperature characteristics, can be independently optimized.
[0080] Preferably, the first resonator beam 15a and the second resonator beam 15b each further include a first piezoelectric component 28a and a second piezoelectric component 28b respectively disposed on their respective surfaces 16a and 16b. The first piezoelectric component 28a and the second piezoelectric component 28b each include:
[0081] - first electrode layers 41a and 41b respectively deposited on surfaces 16a and 16b of the first resonator beam 15a and the second resonator beam 15b;
[0082] - piezoelectric layers 42a and 42b deposited on the first electrode layers 41a and 41b;
[0083] - second electrode layers 43a and 43b deposited on the piezoelectric layers 42a and 42b.
[0084] The core post 11 also includes a first mounting pad 29a and a second mounting pad 29b preferably disposed on a first base 13 of the core post 11. As shown in FIG3, the first mounting pad 29a is configured to be electrically connected (or connected) to a first electrode (not shown) of an electrical excitation source (or power supply), a first electrode layer 41a of the first piezoelectric component 28a, and a second electrode layer 43b of the second piezoelectric component 28b. The second mounting pad 29b is configured to be electrically connected to the opposite electrode (not shown) of the electrical excitation source, the second electrode layer 43a of the first piezoelectric component 28a, and the first electrode layer 41b of the second piezoelectric component 28b. Advantageously, the first piezoelectric component 28a and the second piezoelectric component 28b are at least partially located on the horn-shaped portion FP of the first resonator beam 15a and the second resonator beam 15b. The first piezoelectric component 28a and the second piezoelectric component 28b are preferably strip-shaped.
[0085] During operation, electrical excitation generates an alternating electric field between the first electrode layer 41a and the second electrode layer 43a of the first piezoelectric component 28a, and an alternating electric field between the first electrode layer 41b and the second electrode layer 43b of the second piezoelectric component 28b. The alternating electric field causes the piezoelectric layer 42a of the first piezoelectric component 28a and the piezoelectric layer 42b of the second piezoelectric component 28b to periodically contract and expand in the longitudinal direction, with a phase difference of half a cycle between them.
[0086] When the piezoelectric layer 42a of the first piezoelectric component 28a expands longitudinally, the piezoelectric layer 42b of the second piezoelectric component 28b contracts, and the two resonator beams are forced to bend downward or upward away from the plane formed by the surfaces 16a and 16b of the resonator beams at rest.
[0087] A possible method for providing a piezoelectric component includes the step of forming a first metal film on the surface of the resonator beams. The metal film can be made of any suitable metal or alloy, such as chromium / gold or platinum. The metal film can be formed using vacuum evaporation, sputtering, or any other suitable method known to those skilled in the art. A piezoelectric thin film is then grown on the (entire) surface of the metal film. The piezoelectric thin film is preferably AlN or KNN or derivatives of the aforementioned materials. However, any other suitable piezoelectric material can be used for the piezoelectric thin film. The thickness of the piezoelectric thin film is preferably between 0.05 μm and 3 μm; most preferably about 0.2 μm. A second metal film, which can be platinum, chromium, or other suitable layers matching the lattice of the corresponding piezoelectric layer, is then deposited on the entire surface of each piezoelectric thin film. Preferably, a third metal film made of gold (Au) is formed on the second metal film.
[0088] The entire surface of the outermost metal film can be covered with photoresist and patterned to form an etching mask on the substrate side. The layers formed on the substrate and its main surface are then etched layer by layer by wet or dry etching.The structure is formed. Then, the remaining photoresist is removed from the resonator (e.g., by immersing it in a solvent), exposing the metal film.
[0089] One possible method to achieve the connection between the electrode layer and the mounting pad is to deposit conductive tracks of the metal thin film using a vapor deposition mask or photolithography. Advantageously, in the two piezoelectric components, the position of the first electrode layer is longitudinally offset from the position of the second electrode layer to prevent their respective conductive track connections from interfering with each other.
[0090] A non-limiting example of a tuning fork resonator is made of Z-cut quartz and includes a core post 11, a first resonator beam 15a, and a second resonator beam 15b, the first and second resonator beams 15a and 15b being integral with the core post 11 and extending from the core post 11 in a longitudinal direction perpendicular to the height 12 of the core post 11. The height 12 of the core post 11 is 100 μm, and the width 20 is 100 μm. The thickness 17a of the first resonator beam 15a and the thickness 17b of the second resonator beam 15b are both 1 μm, the width of the main body is 20 μm, and the length is 150 μm. The first resonator beam 15a and the second resonator beam 15b extend parallel to each other and symmetrically in the same longitudinal direction, and their cantilever portions are separated from each other by a 15 μm gap 19 between their main bodies MP. The total length of the tuning fork (including the core post) is 370 μm. The first resonator beam 15a and the second resonator beam 15b each include a first piezoelectric component 28a and a second piezoelectric component 28b deposited on their respective surfaces 16a and 16b. The first piezoelectric component 28a and the second piezoelectric component 28b respectively include a first electrode layer 41 deposited on the surface 16a of the first resonator beam 15a and the surface 16b of the second resonator beam 15b, a piezoelectric layer located on the first electrode layer, and a second electrode layer located on the piezoelectric layer. The core post 11 also includes a first mounting pad 29a and a second mounting pad 29b disposed on its first base 13. The first mounting pad 29a is electrically connected to the first electrode layer 41a of the first piezoelectric component 28a and the second electrode layer 43b of the second piezoelectric component 28b. The second mounting pad 29b is connected to the second electrode layer 43b of the first piezoelectric component 28a and the first electrode layer 41b of the second piezoelectric component 28b. The tuning fork resonator is configured to vibrate in an out-of-plane mode.
[0091] As shown in Table 1 below, the quality factor of the quartz tuning fork resonator described in the above example is compared with the quality factors of various quartz tuning fork resonators in the prior art.
[0092] Table 1:
[0093] Specification 7 / 9 pages 10 CN 121664142 A
[0094] According to the present invention, the overall size of the quartz tuning fork resonator can be reduced while maintaining an acceptable quality factor of over 10000, preferably over or equal to 15000, at 32768MHz.
[0095] List of reference numerals
[0096] 10 Tuning fork resonator
[0097] 11 Core post
[0098] 12. Height of the core post
[0099] 13. First base of the core post
[0100] 14. Second base of the core post
[0101] 15a. First resonator beam
[0102] 15b. Second resonator beam
[0103] 16a. Surface of the first resonator beam 15a
[0104] 16b. Surface of the second resonator beam 15b
[0105] 17a. Thickness of the first resonator beam 15a
[0106] 17b. Thickness of the second resonator beam 15b
[0107] 18a. Width of the main body of the first resonator beam 15a
[0108] 18b. Width of the main body of the second resonator beam 15b
[0109] 19. Gap between the main bodies of the first resonator beam 15a and the second resonator beam 15b
[0110] 20. Width of the core post
[0111] 21. Length of the tuning fork resonator
[0112] 22 Length of the core pillar
[0113] 23a Length of the first resonator beam 15a
[0114] 23b Length of the second resonator beam 15b
[0115] 24 Tapered portion
[0116] 24a First tapered portion
[0117] 24b Second tapered portion
[0118] 25 Side surface of the core pillar
[0119] 26 Joint portion
[0120] 27 Intermediate plate
[0121] 28a First piezoelectric component on the first resonator beam 15a
[0122] 28b Second piezoelectric component on the second resonator beam 15b
[0123] 29a First mounting pad
[0124] 29b Second mounting pad
[0125] 30 Thickness of the core pillar
[0126] 41a First electrode layer of the first piezoelectric component 28a
[0127] 42a The piezoelectric layer of the first piezoelectric component 28a
[0128] 43a The second electrode layer of the first piezoelectric component 28a
[0129] 41b The first electrode layer of the second piezoelectric component 28b
[0130] 42b The piezoelectric layer of the second piezoelectric component 28b
[0131] 43b The second electrode layer of the second piezoelectric component 28b Specification page 8 / 9 11 CN 121664142 A
[0132] 44a The enlarged portion or mass of the free end of the main body of the first resonator beam 15a
[0133] 44b The enlarged portion or mass of the free end of the main body of the second resonator beam 15b Specification page 9 / 9 12 CN 121664142 A Figure 1 Figure 2 Specification drawing page 1 / 4 13 CN 121664142 A Figure 3 Figure 4a Specification drawing page 2 / 4 14 CN 121664142 A Figure 4b Instruction manual illustrations, pages 3 / 4, 15 CN 121664142 A, Instruction manual illustrations.Page 4 / 4 16 CN 121664142 A Abstract The present invention relates to a tuning fork resonator whose design allows for a reduction in resonator size while maintaining a high quality factor. The tuning fork resonator includes: a core post (11) having a height (12) extending from a first base (13) to a second base (14); and a first resonator beam (15a) and a second resonator beam (15b) spaced apart from each other, the first resonator beam (15a) and the second resonator beam (15b) being connected to the core post (11) and arranged in a plane substantially perpendicular to the height (12) of the core post (11); characterized in that the thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05% and 20% of the height (12) of the core post (11).
Claims
1. A tuning fork resonator (10), comprising: - A core post (11) having a height (12) extending from a first base (13) to a second base (14); as well as - A first resonator beam (15a) and a second resonator beam (15b) spaced apart from each other, the first resonator beam (15a) and the second resonator beam (15b) are connected to the core post (11) and arranged in a plane substantially perpendicular to the height (12) of the core post (11); The feature is that the thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05% and 20% of the height (12) of the core column (11).
2. The tuning fork resonator according to claim 1, characterized in that, The tuning fork resonator is configured to allow the first resonator beam (15a) and the second resonator beam (15b) to oscillate in an out-of-plane mode.
3. The tuning fork resonator according to any one of the preceding claims, characterized in that, The first resonator beam (15a) includes a first piezoelectric component (28a), and the second resonator beam (15b) includes a second piezoelectric component (28b). The first piezoelectric component (28a) and the second piezoelectric component (28b) are respectively disposed on the surfaces (16a, 16b) of the first resonator beam (15a) and the second resonator beam (15b). Each of the first piezoelectric component (28a) and the second piezoelectric component (28b) includes: - First electrode layers (41a, 41b) located on the surfaces (16a, 16b) of the first resonator beam (15a) and the second resonator beam (15b), respectively; - A piezoelectric layer (42a, 42b) located on the first electrode layer (41a, 41b); and - A second electrode layer (43a, 43b) located on the piezoelectric layer (42a, 42b); in: - The first electrode layer of the first piezoelectric component (28a) and the second electrode layer of the second piezoelectric component (28b) are electrically connected to a first mounting pad (29a), the first mounting pad (29a) being configured to be connected to a first pole of a power source; and The second electrode layer of the first piezoelectric component (28a) and the first electrode layer of the second piezoelectric component (28b) are electrically connected to a second mounting pad (29b), which is configured to be connected to the opposite pole of the power source.
4. The tuning fork resonator according to any one of the preceding claims, characterized in that, The core post (11), the first resonator beam (15a) and the second resonator beam (15b) are made of quartz, preferably Z-cut quartz, or lanthanum gallium silicate, GaPO4 or partially silicon oxide.
5. The tuning fork resonator according to claim 1 or 2, characterized in that, The tuning fork resonator is integrally formed, wherein the first resonator beam (15a) and the second resonator beam (15b) are integrally formed with the core column (11).
6. The tuning fork resonator according to any one of the preceding claims, characterized in that, The tuning fork resonator further includes an intermediate plate (27) extending between the core post (11) and the first resonator beam (15a) and the second resonator beam (15b), the intermediate plate (27) being coplanar with the first resonator beam (15a) and the second resonator beam (15b), and preferably the intermediate plate (27) having the same thickness as the first resonator beam (15a) and the second resonator beam (15b).
7. The tuning fork resonator according to any one of the preceding claims, characterized in that, The thicknesses (17a, 17b) of the first resonator beam (15a) and the second resonator beam (15b) are between 0.05 μm and 25 μm, preferably less than 10 μm.
8. The tuning fork resonator according to any one of the preceding claims, characterized in that, The height (12) of the core post (11) is between 10 μm and 200 μm, preferably between 20 μm and 150 μm, and more preferably between 80 μm and 125 μm.
9. The tuning fork resonator according to any one of the preceding claims, characterized in that, Both the first resonator beam (15a) and the second resonator beam (15b) have an attachment end and a free end. The attachment end is fixed to the core post (11) or fixed to an intermediate plate (27) located between the core post and the first resonator beam (15a) and the second resonator beam (15b). Both the first resonator beam (15a) and the second resonator beam (15b) further include: - The main body portion (MP) extending from its respective free end to the region near its respective attachment end; and - A flared portion (FP) that gradually widens from the main body portion MP toward its respective attachment end.
10. The tuning fork resonator according to any one of the preceding claims, characterized in that, The width (20) of the core post (11) is between 50 μm and 200 μm, preferably between 80 μm and 125 μm.
11. The tuning fork resonator according to any one of the preceding claims, characterized in that, The widths (18a, 18b) of the main body portions (MP) of the first resonator beam (15a) and the second resonator beam (15b) are between 20% and 45% of the width (20) of the core column (11).
12. The tuning fork resonator according to any one of the preceding claims, characterized in that, The length (21) of the tuning fork resonator is less than 500 μm, preferably less than 400 μm.
13. The tuning fork resonator according to any one of the preceding claims, characterized in that, The core post (11) has a thickness (30) measured along the directions of the first resonator beam (15a) and the second resonator beam (15b), and the length (23a, 23b) of each of the first resonator beam (15a) and the second resonator beam (15b) is greater than or equal to at least half of the thickness (30) of the core post (11).
14. The tuning fork resonator according to any one of the preceding claims, characterized in that, The core post (11) includes a tapered portion (24) extending from the side (25) of the core post (11) and / or from the first base (13) or the second base (14) to a joint (26) or intermediate surface between the core post (11) and the first resonator beam (15a) and the second resonator beam (15b), or to a joint (26) or surface between the core post and an intermediate piece (27) connected to the first resonator beam (15a) and the second resonator beam (15b).
15. The tuning fork resonator according to any one of the preceding claims, characterized in that, The tuning fork resonator has a quality factor of 5000 or more in vacuum at 32768 Hz, preferably 7500 or more, more preferably 10000 or more, and even more preferably 15000 or more.