Slanted resonator

Abstract

A MEMS (micro-electromechanical system) resonator (10) having a slant-type resonant element. The slant-type resonant element includes a slant-type resonant beam (11) made of single-crystal silicon, the slant-type resonant beam is configured to resonate in its longitudinal direction, and the longitudinal axis (150) of the slant-type resonant beam is silicon <100> It is tilted in that direction.

Description

Technical Field

[0001] The disclosure of the present application (hereinafter referred to as the present disclosure) generally relates to MEMS (Micro Electro Mechanical Systems) resonators. Background

[0002] This section describes useful background information, but note that it is not admitted that the technology described herein represents the state of the art.

[0003] MEMS (Micro Electro Mechanical System) resonators have been developed that achieve miniaturization of chip size, cost reduction, and improvement in robustness against shock and vibration while having the same function as a crystal resonator.

[0004] The main performance parameter of a MEMS resonator is the Equivalent Series Resistance (ESR). The ESR is inversely proportional to the quality factor Q of the resonator. Another important parameter is the Drive Level Dependency (DLD). This means the relationship between the frequency of the resonator and the excitation power. In many cases, it is desirable to minimize both the ESR and the DLD. Summary

[0005] An object of certain embodiments of the present disclosure is to reduce the DLD of a MEMS resonator or at least provide an alternative to existing technologies.

[0006] According to a first aspect of the present disclosure, a MEMS (Micro Electro Mechanical System) resonator is provided as follows. This MEMS resonator includes a slant-type resonant element including a slant-type resonant beam having single-crystalline silicon, the slant-type resonant beam is configured to resonate in its longitudinal direction, and the longitudinal axis of the slant-type resonant beam is inclined from the <100> direction of silicon.

[0007] In some embodiments, the slant-type resonant beam itself is geometrically inclined, and furthermore, the longitudinal axis of the slant-type resonant beam is silicon <100> It is tilted in the direction. When multiple slant-type resonant beams exist, these slant-type resonant beams themselves are geometrically tilted, and furthermore, the longitudinal axis of the slant-type resonant beam is silicon <100> It is tilted in that direction.

[0008] The first aspect includes both single-beam MEMS resonators, i.e., MEMS resonators having one slant-type resonant beam (or having only one slant-type resonant beam), and MEMS resonators having multiple slant-type resonant beams (where the slant-type resonant element has multiple slant-type resonant beams).

[0009] Therefore, according to one embodiment, the following MEMS (micro-electromechanical system) resonator is provided. This MEMS resonator is It comprises a slant-type resonant element equipped with a slant-type resonant beam having single-crystal silicon, The slant-type resonant beam is configured to resonate in its longitudinal direction, and the longitudinal axis of the slant-type resonant beam is silicon <100> The slant-type resonant element is tilted from the direction and contains only a single slant-type resonant beam.

[0010] Furthermore, according to one embodiment, the following MEMS (Micro-Electro-Mechanical Systems) resonator is provided. This MEMS resonator is It has a slant-type resonant element equipped with multiple slant-type resonant beams, each of which has single-crystal silicon. Each of the aforementioned slant-type resonant beams is configured to resonate in its longitudinal direction, and each of the slant-type resonant beams has its longitudinal axis as silicon <100> It is tilted in that direction.

[0011] Depending on the embodiment, the inclination is intended to reduce the influence of excitation level dependence.

[0012] Here, <100> A direction refers to the set of equivalent directions in Miller indices. For example, directions such as

[0100] ,

[0010] , and

[0001] . In the following explanation, the notation (100) refers to the plane whose normal direction is

[0100] , while the notation {100} refers to all planes that are equivalent to plane (100) due to symmetry.

[0013] In some embodiments, the slant-type resonant beam takes the form of a resonant beam tilted in one direction (and only in one direction).

[0014] Depending on the embodiment, the longitudinal axis is the <100> It is tilted at 16 to 22 degrees from the direction, more preferably 18 to 20 degrees, and most preferably 19 degrees.

[0015] In some embodiments, the slant-type resonant beam is in the shape of an inclined rectangle.

[0016] In some embodiments, the MEMS resonator includes a slant-type resonant beam having a general parallelogram shape.

[0017] Depending on the embodiment, the two shorter sides of the parallelogram are the crystal orientation <100> It is parallel to the and the angle between the two long sides and the two short sides of the parallelogram is 90°-α. Here, α is the long axis of the slant-type resonant beam and the <100> This is the angle of inclination between the direction and the object.

[0018] Depending on the embodiment, α is the above <100> The angle from the direction is in the range of 16 to 22 degrees, more preferably in the range of 18 to 20 degrees, and most preferably 19 degrees.

[0019] In some embodiments, the slant-type resonant beam has a parallelogram shape in which the lengths of adjacent sides are not equal and the angles between adjacent sides are not right angles.

[0020] Depending on the embodiment, the aspect ratio of the slant-type resonant beam is greater than 1.

[0021] Depending on the embodiment, the short side of the slant-type resonant beam faces a direction perpendicular to the <100> direction. In the case of single crystal silicon, this perpendicular direction may be another <100> direction.

[0022] Depending on the embodiment, the slant-type resonant beam is within the plane of the resonant element and has the form of an oblique rectangular parallelepiped that is inclined along an axis perpendicular to the first-mentioned <100> direction (the first <100> direction).

[0023] Depending on the embodiment, the oblique rectangle is not oblique in the first <100> direction.

[0024] Depending on the embodiment, the oblique rectangle is inclined (oblique) by 16 to 22 degrees, more preferably 18 to 20 degrees, and most preferably 19 degrees from the first <100> direction (near one of the corners of the rectangle).

[0025] Depending on the embodiment, the resonant element is fixed to a node (nodal point) of the resonant element.

[0026] Depending on the embodiment, the resonant element includes a suspension portion for fixing the resonant element to the surrounding structure at a node of the resonant element.

[0027] Depending on the embodiment, the suspension portion is arranged at the center of the long side of the slant-type resonant beam.

[0028] Depending on the embodiment, the suspension portion is aligned in a direction perpendicular to the long axis of the slant-type resonant beam.

[0029] Depending on the embodiment, the suspension portion is oblique with respect to the first <100> direction of silicon in the same manner as the resonant beam.

[0030] In some embodiments, the MEMS resonator includes a plurality of slant resonant beams adjacent to each other, separated by trenches, and connected by connecting elements, the plurality of slant resonant beams being connected by the connecting elements to form a stacked beam resonator.

[0031] In some embodiments, the plurality of adjacent slant-type resonant beams have the same shape.

[0032] In some embodiments, the short sides of multiple adjacent slant-type resonant beams are aligned with each other.

[0033] In some embodiments, each of the plurality of slant-type resonant beams is made of silicon <100> They are tilted in the same direction from one direction to the other.

[0034] Depending on the embodiment, the slant-type resonant element itself, or the resonant beam, is tilted without rotating the entire resonant element (or resonator).

[0035] In some embodiments, the plurality of adjacent slant-type resonant beams are configured to resonate in a collective resonant mode, preferably in a length-extended resonant mode.

[0036] In some embodiments, the plurality of adjacent slant-type resonant beams have a common resonant mode shape.

[0037] In some embodiments, 50% or more of the mass of the slant-type resonant element is made of single-crystal silicon.

[0038] Depending on the embodiment, the resonator is a (100) or {100} silicon wafer, or silicon <100> It is composed of layers of single-crystal silicon in which the surface normals are aligned in the crystal direction.

[0039] In some embodiments, the MEMS resonator comprises a material laminate having an upper electrode layer, a piezoelectric layer below the upper electrode layer, and a lower electrode layer of single-crystal silicon below the piezoelectric layer.

[0040] In some embodiments, the material laminate is uniform throughout the entire slant resonant element (resonant element).

[0041] Depending on the embodiment, the MEMS resonator has an average impurity concentration of at least 2 × 10⁻⁶ 10 cm -3 , more preferably at least 1 × 10 20 cm -3 It contains a doped single-crystal silicon layer.

[0042] According to the second aspect, a MEMS (micro-electromechanical system) resonator is provided, which has a parallelogram-shaped resonant element. In this resonator, the two shorter sides are crystal orientations. <100> It is parallel to the curve, and the two longer sides point at an angle of 90°-α relative to the two shorter sides.

[0043] Depending on the embodiment, α is the above <100> The angle from the direction is in the range of 16 to 22 degrees, more preferably in the range of 18 to 20 degrees, and most preferably 19 degrees.

[0044] In some embodiments, the resonator is formed from single-crystal silicon.

[0045] In some embodiments, the resonant element (or beam) has a normal vector of silicon <100> It has an upper surface oriented in the crystal direction.

[0046] In some embodiments, the resonator is made of (100) a silicon wafer, or the surface thereof <100> It consists of single-crystal silicon layers perpendicular to the orientation.

[0047] In some embodiments, the resonator is configured to be excited by piezoelectric drive.

[0048] While various interpretations and embodiments have been presented, these are not intended to limit the scope of the invention. These embodiments, and those described later, are merely used to illustrate specific aspects and steps that may be used in carrying out the present invention. Corresponding embodiments may also be applicable to other exemplary aspects. The embodiments presented may be combined as appropriate. [Brief explanation of the drawing]

[0049] Next, the present invention will be described only illustratively with reference to the accompanying drawings. [Figure 1] This shows a conventional multilayer beam MEMS resonator. [Figure 2] A schematic top view of a MEMS resonator according to one embodiment of the present disclosure is shown. [Figure 3a] The deformation of the MEMS resonator shown in Figure 2 during resonance, according to a certain embodiment, is illustrated. [Figure 3b] The deformation of the MEMS resonator shown in Figure 2 during resonance, according to a certain embodiment, is illustrated. [Figure 4] A schematic top view of a MEMS resonator according to another embodiment is shown. [Figure 5] A detailed top view of a resonant beam according to one embodiment is shown. [Figure 6] An example of a MEMS resonator material stacking structure according to one embodiment is schematically shown. [Figure 7] An example of the observed excitation level dependence is shown schematically. [Figure 8] This shows the simulated resonant mode shape of a rotated MEMS resonator. Detailed description

[0050] In the following explanation, similar numbers indicate similar elements.

[0051] Figure 1 shows a top view of a conventional silicon MEMS resonator. This resonator consists of multiple resonant beams arranged in parallel and connected by connecting elements. The resonant beams are made of silicon <100> It is aligned with the crystal axis.

[0052] Figure 2 shows a schematic top view of a MEMS resonator 10 according to one embodiment of the present disclosure. The MEMS resonator 10 has slant-type (i.e., inclined) resonant elements (resonating elements). The resonant elements have one or more slant-type (i.e., inclined) resonant beams 11. In the example shown in Figure 2, the number of resonant beams 11 is 10, but in other embodiments, the number of resonant beams 11 may differ.

[0053] The resonant beams 11 are made of single-crystal silicon. Adjacent resonant beams 11 are separated from each other by trenches 13. In some embodiments, the trenches 13 lead to a cavity (not shown) below the resonant element. In some embodiments, this cavity separates the resonant element from the substrate wafer (e.g., SOI (silicon on insulator) wafer). Adjacent resonant beams are connected (coupled) at their ends by connecting elements 12. This forms a stacked beam resonator.

[0054] Each resonant beam 11 is configured to resonate in its longitudinal direction. The longitudinal axis 150 of each resonant beam 11 is silicon <100> The beams are tilted (inclined) in a specific direction. In other words, each resonant beam 11 is inclined at an angle. This inclination is to reduce the effects of excitation level dependence (DLD).

[0055] Depending on the embodiment, the longitudinal axis of the resonant beam 11 is such that the influence of DLD is minimized. <100> It is tilted from the direction by 16 to 22 degrees, more preferably 18 to 20 degrees, and most preferably 19 degrees.

[0056] In some embodiments, as shown in Figure 2, each resonant beam 11 has the shape of a slant resonant beam in only one direction (here, the x-direction). Each resonant beam 11 has the shape of an inclined rectangle, with adjacent sides of unequal length and angles that are not right angles, thus forming a parallelogram. The aspect ratio of the resonant beam 11 is greater than 1. The shorter side of the resonant beam 11 is as described above. <100> It is oriented perpendicular to the direction. In the case of single-crystal silicon, this perpendicular direction is another <100> Direction (“Second <100> The direction may be the same as the first one. The inclined rectangle is in the plane (preferably the {100} plane) of the resonant element and is as described earlier. <100> Direction (1st <100> It is inclined along an axis perpendicular to the direction. The inclined rectangle is the first <100> The inclination is eliminated in the direction. In some embodiments, the inclined rectangle is the first <100> It is tilted (inclined) by 16 to 22 degrees, more preferably 18 to 20 degrees, and most preferably 19 degrees from the direction (near one of the corners of the rectangle).

[0057] The resonant element is fixed at the nodal point of the resonant element. In some embodiments, as shown in Figure 2, the resonant element is provided with suspension parts 14 at the nodal point of the resonant element for fixing the resonant element to the surrounding structure. In some embodiments, each of the suspension parts 14 is located at the center of the outer long side of the resonant beam 11 at both ends. In some embodiments, the suspension parts 14 are oriented perpendicular to the longitudinal axis of the resonant beam 11. In some embodiments, the suspension parts 14 are first silicon, similar to the resonant beam 11. <100> It is tilted in that direction.

[0058] In some embodiments, as shown in Figure 2, adjacent resonant beams 11 have the same shape. The short sides of the resonant beams 11 are aligned with each other. The resonant beams 11 are configured to resonate in a collective resonance mode, preferably in a length-extensional (LE) resonance mode.

[0059] Figures 3a and 3b show the deformation of the MEMS resonator 10 during resonance according to a certain embodiment. Figure 3a shows one end of the vibration where the resonant beam is in its shortest form (contracted form), and Figure 3b shows the other end of the vibration where the resonant beam is in its longest form (extended form). The shades of color in Figures 3a and 3b indicate the displacement from the stationary position. Note that all resonant beams 11 have substantially the same resonant mode shape.

[0060] Figure 4 shows a schematic top view of a MEMS resonator 20 according to another embodiment. In this embodiment, the resonant element has only one resonant beam 11. Otherwise, the embodiment shown in Figure 4 corresponds to the structure and operation of the previously described embodiment. Thus, the resonant beam 11 is configured to resonate in its longitudinal direction. Similar to the previously described embodiment, the longitudinal axis 150 of the resonant beam 11 is silicon <100> It is tilted (inclined) in that direction. In other words, the resonant beam 11 is tilted at an angle.

[0061] This slant-type resonant beam 11 (inclined rectangle) is, <100> It is inclined at 16 to 22 degrees from the direction, more preferably 18 to 20 degrees, and most preferably 19 degrees.

[0062] Figure 5 shows a more detailed top view of a resonant beam 11 according to one embodiment. The resonant beam 11 may be a resonant beam that constitutes part of the MEMS resonator 10 or 20 described above. The resonant beam 11 has a generally parallelogram shape, and the two long sides are the first <100> It is oriented at an angle α with respect to the crystal orientation (e.g., the

[0100] direction), and the two short sides are second <100> It is parallel to the crystal orientation (for example, the

[0010] direction). Therefore, the two long sides of the resonant beam 11 make an angle of 90°-α with respect to the two short sides. <100> The direction is located within the {100} plane (wafer plane) of the relevant substrate wafer. Third <100> The crystal orientation (e.g., the

[0001] direction) is perpendicular to the wafer plane. Therefore, it lies within the plane of the silicon substrate wafer, and within that plane there are two <100> Having a crystal orientation and one perpendicular to its plane <100> A resonant beam 11 having a crystal orientation is disclosed. The longitudinal direction of the resonant beam 11 is one in the plane <100> It is angled relative to the direction.

[0063] Figure 6 schematically shows a MEMS resonator material laminate according to one embodiment. This material laminate is applicable to the illustrated resonators 10 and 20.

[0064] The material laminate comprises an upper electrode layer 63, a piezoelectric layer 62 positioned below the upper electrode layer 63 for piezoelectrically driving the resonant element into a resonant mode, and a single-crystal silicon lower electrode layer 61 positioned below the piezoelectric layer 62. In some embodiments, the material laminate is uniform throughout the entire resonant element. Note that the material laminate structure shown in Figure 6 is merely one example of an applicable material laminate structure. Different material laminate structures may be used depending on the embodiment. In some embodiments, the upper electrode layer 63 is a metal layer such as a gold layer. In some embodiments, the piezoelectric layer 62 is AlN. Therefore, in some embodiments, the material laminate structure is a Si / AlN / Au material laminate structure. In some embodiments, the material laminate includes an SiO2 layer. This is to improve the thermal frequency stability of the MEMS resonator in some embodiments, such as compensating for changes in the frequency temperature coefficient TCF (e.g., TCF1) or more negative temperature coefficients caused by the gradient. In some embodiments, the SiO2 layer is positioned below (or directly below) the single-crystal silicon layer 61. In some embodiments, the SiO2 layer is positioned above the single-crystal silicon layer 61 (for example, between the single-crystal silicon layer 61 and the piezoelectric layer 62). In some embodiments, the SiO2 layer is located above the piezoelectric layer 62 (for example, between the piezoelectric layer 62 and the upper electrode layer 63). In some embodiments, the SiO2 layer is located above the upper electrode layer 63. In such embodiments, the SiO2 layer may be mounted so as to cover only a portion of the upper electrode layer 63 (e.g., the central region) (e.g., by patterning) in order to allow for necessary trimming of the upper electrode layer 63 (e.g., trimming of gold).

[0065] In some embodiments, 50% or more of the mass of the resonator element is made of single-crystal silicon. In some embodiments, the single-crystal silicon layer (layer 61) has an average impurity concentration of at least 2 × 10⁻¹⁶ 19 cm -3 , more preferably at least 1 × 10 20 cm -3 They are doped in such a way.

[0066] Without limiting the technical scope and interpretation of the claimed invention, one or more technical effects of the exemplary embodiments disclosed herein are listed below. One technical effect is the reduction of the excitation level dependence (DLD) of the silicon MEMS resonator. Further technical effects include a reduction in ESR and an improvement in the quality factor Q.

[0067] These technical effects will be described in more detail using Figures 7 and 8. Figure 7 schematically shows an example of the observed excitation level dependence (DLD) in a resonant beam with a specific orientation. DLD is <100> In an oriented resonant beam, the positive, for example <110> It is observed that the resonant beam becomes negative in the oriented resonant beam. Therefore, the resonant beam <100> By tilting the resonator, a DLD reduction effect can be obtained. Figure 8 shows the resonance mode shape obtained by simulation when the stacked beam MEMS resonator 30 is rotated as a whole. Compared to the resonator 10 shown in Figures 3a and 3b, it can be observed that the resonance mode shape of the resonator 30 is considerably inferior. In other words, by tilting it, a better Q value and, consequently, a lower ESR value can be obtained. Furthermore, the rotated resonator 30 requires a larger orthogonal footprint on the die compared to the slant-type MEMS resonator.

[0068] The above description provides a complete and useful explanation of the best mode currently considered by the inventors for carrying out the present invention, through non-limiting examples of specific implementations and embodiments of the present invention. However, as will be apparent to those skilled in the art, the details of the above embodiments are not limiting to the present invention and can be implemented in other embodiments using equivalent means without departing from the features of the present invention.

[0069] Furthermore, the features of the embodiments of the present invention disclosed above may be used without using other corresponding features. However, the above description should be understood as merely an example to illustrate the principles of the present invention and not as a limiting reference. Therefore, the scope of the present invention is limited only by the appended claims.

Claims

1. A MEMS (Micro-Electro-Mechanical Systems) resonator, It comprises a slant-type resonant element equipped with a slant-type resonant beam having single-crystal silicon, The slant-type resonant beam is configured to resonate in its longitudinal direction, and the longitudinal axis of the slant-type resonant beam is inclined from the <100> direction of silicon. MEMS resonator.

2. The MEMS resonator according to claim 1, wherein the slant-type resonant element includes only a single slant-type resonant beam.

3. The MEMS resonator according to claim 1 or 2, wherein the longitudinal axis is inclined at 16 to 22 degrees, more preferably 18 to 20 degrees, and most preferably 19 degrees from the <100> direction.

4. The MEMS resonator according to any of the preceding claims, wherein the slant-type resonant beam is in the shape of an inclined rectangle.

5. The MEMS resonator according to any of the preceding claims, wherein the slant-type resonant beam is located in the plane of the resonant element and has the shape of an oblique rectangular parallelepiped, tilted along an axis perpendicular to the <100> direction.

6. The MEMS resonator according to any of the preceding claims, wherein the slant-type resonant element is fixed to the nodal point of the slant-type resonant element.

7. The MEMS resonator according to any of the preceding claims, wherein the MEMS resonator comprises a plurality of slant resonant beams adjacent to each other, separated by trenches and connected by connecting elements, the plurality of slant resonant beams being connected by the connecting elements to form a stacked beam resonator.

8. The MEMS resonator according to claim 7, wherein the plurality of adjacent slant-type resonant beams are configured to resonate in a collective resonant mode, preferably in a length-extended resonant mode.

9. The MEMS resonator according to claim 7 or 8, wherein the plurality of adjacent slant-type resonant beams have a common resonant mode shape.

10. The MEMS resonator according to any of the preceding claims, wherein 50% or more of the mass of the slant-type resonant element is composed of single-crystal silicon.

11. A MEMS resonator according to any of the preceding claims, comprising a material laminate having an upper electrode layer, a piezoelectric layer below the upper electrode layer, and a lower electrode layer of single-crystal silicon below the piezoelectric layer.

12. The average impurity concentration is at least 2 × 10 １０ cm －３ , more preferably at least 1 × 10 ２０ cm －３ A MEMS resonator according to any prior claim, comprising a doped single-crystal silicon layer.

13. A MEMS resonator according to any of the preceding claims, comprising the slant-type resonant beam having a general parallelogram shape.

14. The MEMS resonator according to claim 13, wherein the two shorter sides of the parallelogram are parallel to the crystal orientation <100>, the angle between the two longer sides of the parallelogram and the two shorter sides is 90°-α, where α is the inclination angle between the major axis of the slant-type resonant beam and the crystal orientation <100>.

15. The MEMS resonator according to claim 14, wherein α is in the range of 16 to 22 degrees from the <100> direction, more preferably in the range of 18 to 20 degrees, and most preferably 19 degrees.

16. The MEMS resonator according to any one of claims 7 to 15, wherein the short sides of a plurality of adjacent slant-type resonant beams are aligned with each other.

17. The MEMS resonator according to any one of claims 7 to 16, wherein each of the plurality of slant-type resonant beams is tilted in the same direction from the <100> direction of silicon.

18. The MEMS resonator according to any one of claims 7 to 17, wherein the plurality of adjacent slant-type resonant beams are identical in shape.

Images