Micromechanical resonator and method for manufacturing a micromechanical resonator, micromechanical oscillator

Abstract

The present application belongs to the field of microelectronic technology, and discloses a micromechanical resonator, a preparation method thereof and a micromechanical oscillator. The micromechanical resonator comprises a substrate silicon wafer and a device layer silicon. The substrate silicon wafer has a cavity structure, and a resonator is formed in the device layer silicon and suspended above the cavity structure. The resonator is a single continuous structure, has a closed irregular profile in a plane, and has a non-constant radial size distribution in the circumferential direction. The present application can precisely control the frequency-temperature characteristics of the resonator without relying on the crystal orientation characteristics or the doping concentration of the single crystal silicon. The micromechanical oscillator provided by the present application can meet the requirements of frequency stability in various application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology, and more specifically, relates to micromechanical resonators and their fabrication methods, and micromechanical oscillators. Background Technology

[0002] Micromechanical resonators are core frequency reference components in micromechanical oscillators, clock systems, and high-precision sensing systems. Their performance directly determines the system's frequency stability, phase noise level, and long-term reliability. (Quality factor) Q The frequency-temperature characteristic (FTC) and frequency-temperature characteristics are two key indicators for evaluating the overall performance of micromechanical resonators. Q The value determines the frequency resolution and short-term stability of the resonator, while the frequency-temperature characteristic determines the frequency stability of the resonator under varying ambient temperature conditions.

[0003] Existing micromechanical resonators mostly employ regular geometric contour structures, such as circular, rectangular, or ring structures. These structures offer the advantage of relatively simple design and fabrication, but their performance is limited under anisotropic conditions, such as with single-crystal silicon. Due to the anisotropic nature of single-crystal silicon, the equivalent modulus distribution of resonators with regular geometric contours is uneven in different directions. This easily leads to localized stress concentrations and non-uniform thermoelastic coupling during vibration, introducing additional energy losses and causing the resonator to... Q The value decreases. Meanwhile, regular geometric structures offer limited design freedom in terms of frequency-temperature characteristics. Existing structures primarily alter the temperature-dependent modulus of the material by adjusting the crystal orientation or doping concentration of the resonator. However, such methods are heavily influenced by manufacturing processes, making it difficult to precisely control the frequency-temperature characteristics of the resonator, especially the zero point of the resonator's temperature coefficient of frequency (TCF). This limitation is particularly pronounced in high-precision applications. Summary of the Invention

[0004] This invention provides a micromechanical resonator and its fabrication method, and a micromechanical oscillator, thereby solving the problem that existing technologies rely on crystal orientation selection or doping concentration to adjust the frequency-temperature characteristics of the resonator, and the control accuracy is low.

[0005] In a first aspect, the present invention provides a micromechanical resonator, comprising: a substrate silicon wafer and a device layer silicon; the substrate silicon wafer has a cavity structure, and a resonant oscillator is formed in the device layer silicon, the resonant oscillator being suspended above the cavity structure; the resonant oscillator is a single continuous structure, the resonant oscillator having a closed irregular profile in a plane, the irregular profile exhibiting a non-constant radial dimension distribution along the circumferential direction.

[0006] Preferably, the frequency-temperature characteristics of the micromechanical resonator are adjusted by regulating the geometric dimensions of the resonator at different circumferential positions.

[0007] Preferably, the irregular contour has a periodic variation feature in the circumferential direction, and the irregular contour has at least fourfold rotational symmetry.

[0008] Preferably, the irregular contour is represented in polar coordinates as an angular modulation function, which satisfies the following relationship:

[0009] In the formula, For the resonant oscillator at an angle Radial dimension in the direction, The average radial dimension parameter, For the first Angular modulation amplitude parameters, It is a positive integer greater than or equal to 1. f m It is a periodic function; The periodic function f m These are trigonometric functions, exponential functions, polynomial functions, or spline functions. By adjusting the average radial dimension parameter With the first angular modulation amplitude parameters The proportional relationship between these parameters allows for the adjustment of the frequency-temperature characteristics of the micromechanical resonator.

[0010] Preferably, the outer periphery of the resonant oscillator is provided with a support beam; the support beam is a straight beam, a T-shaped beam or a folded beam disposed at the vibration node of the resonant oscillator; or, the support beam is disposed at the extreme point position corresponding to the higher-order angular modulation term in the outer periphery contour of the resonant oscillator.

[0011] Preferably, the resonator is used alone, or forms a resonator array, or is used as a mechanical coupling structure to couple with other resonators.

[0012] Preferably, the micromechanical resonator is a single-crystal silicon structure, or the micromechanical resonator is a metal. piezoelectric layer Composite thin film structure of monocrystalline silicon; the crystal plane of monocrystalline silicon is (100) crystal plane, and the monocrystalline silicon is heavily doped with N-type or P-type, with a doping concentration range of 4.0 × 10⁻⁶. 19 / cm 3 Up to 5.0×10 20 / cm 3The crystal orientation range of the resonant oscillator includes along... <100> ,along <110> and along <100> and <110> Arranged between them.

[0013] Secondly, the present invention provides a method for fabricating a micromechanical resonator as provided in the first aspect of the present invention, wherein the micromechanical resonator is a single-crystal silicon structure, and the method for fabricating the micromechanical resonator includes the following steps: An SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer, and a device layer silicon; Metal is deposited and patterned on the silicon layer of the device to form metal pads; The device layer silicon is etched from the front, stopping on the buried oxide layer, to form a resonant oscillator with an irregular profile in the device layer silicon; The substrate silicon wafer is etched on the back side, stopping on the buried oxide layer, to form a cavity structure in the substrate silicon wafer; The buried oxide layer corresponding to the etched structure is removed to obtain the structure of the micromechanical resonator.

[0014] Thirdly, the present invention provides another method for fabricating a micromechanical resonator as provided in the first aspect of the present invention, wherein the micromechanical resonator is a composite thin film structure of metal-piezoelectric layer-monocrystalline silicon, and the method for fabricating the micromechanical resonator includes the following steps: An SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer, and a device layer silicon; A piezoelectric material and an upper electrode are sequentially deposited on the silicon device layer, and the upper electrode is patterned. A top oxide layer is deposited on the upper electrode; The top oxide layer is etched to obtain an upper electrode via and expose the upper electrode. The top oxide and the piezoelectric material are etched to obtain a lower electrode via and expose the device layer silicon. Metal is deposited and patterned in both the upper electrode via and the lower electrode via to form metal pads; The top oxide layer, the piezoelectric material, and the device layer silicon are etched from the front, stopping on the buried oxide layer, to form a resonant oscillator with an irregular profile in the device layer silicon. The substrate silicon wafer is etched on the back side, stopping on the buried oxide layer, to form a cavity structure in the substrate silicon wafer; The buried oxide layer corresponding to the etched structure is removed to obtain the structure of the micromechanical resonator.

[0015] Fourthly, the present invention provides a micromechanical oscillator, wherein the micromechanical oscillator is an uncompensated micromechanical oscillator, a temperature-compensated micromechanical oscillator, or a temperature-controlled micromechanical oscillator. When the micromechanical oscillator is the uncompensated micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as provided in the first aspect of the present invention, and an oscillation holding circuit; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator. When the micromechanical oscillator is the temperature-compensated micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as provided in the first aspect of the present invention, an oscillation holding circuit, a frequency synthesizer, and a temperature sensor; the temperature inflection point of the micromechanical resonator is at room temperature; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator; the temperature sensor is used to obtain the ambient temperature and transmit it to the frequency synthesizer; the frequency synthesizer is used to adjust the frequency to compensate for the frequency variation of the micromechanical oscillator over the entire temperature range. When the micromechanical oscillator is the temperature-controlled micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as provided in the first aspect of the present invention, an oscillation holding circuit, a temperature sensor, a temperature control circuit, and a heating cavity; the temperature inflection point of the micromechanical resonator is located above the operating temperature range of the micromechanical resonator, and the micromechanical resonator is placed inside the heating cavity; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator; the temperature sensor is used to obtain the real-time temperature of the heating cavity and transmit it to the temperature control circuit; the temperature control circuit is used to adjust the temperature of the heating cavity so that the temperature of the micromechanical resonator is maintained at its temperature inflection point.

[0016] One or more technical solutions provided in this invention have at least the following technical effects or advantages: The micromechanical resonator provided by this invention includes a substrate silicon wafer and a device layer silicon. The substrate silicon wafer has a cavity structure, and a resonant oscillator is formed in the device layer silicon, suspended above the cavity structure. The resonant oscillator is a single continuous structure with a closed irregular profile in the plane, exhibiting a non-constant radial size distribution along the circumferential direction. That is, this invention introduces a circumferential angular modulation structure into the resonant oscillator profile, causing the structure to form a non-constant radial size distribution in the circumferential direction, thereby enabling the control of resonator performance without relying on the crystal orientation characteristics or doping concentration of single-crystal silicon. By optimizing the structural dimensions at different angles, the frequency-temperature characteristics of the resonant oscillator can be adjusted, thus also enabling the adjustment of the temperature inflection point position. This invention differs from existing passive temperature compensation methods that mainly rely on crystal orientation selection or doping concentration adjustment, enabling precise control of the temperature inflection point without increasing material or process complexity. Simultaneously, the curved profile of the micromechanical resonator structure provided by this invention can change the local boundary conditions in the support anchor point region, thereby enhancing acoustic wave reflection, reducing energy leakage to the support structure, and lowering anchor point loss. Furthermore, by optimizing the structural dimensions at different angular positions, the local temperature gradient changes generated during vibration can be mitigated, thereby reducing the thermoelastic losses of the resonator. That is, this invention can also improve the boundary conditions of the support region, reduce vibration energy leakage to the anchor point, and help reduce the local temperature gradient generated during vibration, thereby reducing the thermoelastic losses of the resonator and improving the resonator's performance. Q value. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the micromechanical resonator provided in Embodiment 1 of the present invention.

[0018] Figures 2-a to 2-d This is a schematic diagram of the planar profile of trigonometric function type angular modulation resonators of different orders.

[0019] Figures 3-a to 3-b This is a schematic diagram of the outline of a mechanically coupled micromechanical resonator.

[0020] Figures 4-a to 4-e The fabrication process flow diagram of the micromechanical resonator with a single-crystal silicon structure provided in Embodiment 2 of the present invention is shown.

[0021] Figures 5-a to 5-i The fabrication process of the micromechanical resonator with a composite thin film structure of metal-piezoelectric layer-monocrystalline silicon provided in Embodiment 3 of the present invention is described.

[0022] Figures 6-a to 6-c These are schematic diagrams of micromechanical oscillators for different applications.

[0023] Figure 7The frequency shift-temperature curves of the micromechanical resonator under different scaling parameters are shown. Detailed Implementation

[0024] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0025] Example 1: Example 1 provides a micromechanical resonator, see [link to example]. Figure 1 The device includes a substrate silicon wafer 4 and a device silicon layer 6. The substrate silicon wafer 4 has a cavity structure, and a resonant oscillator 1 is formed in the device silicon layer 6. The resonant oscillator 1 is suspended above the cavity structure. The resonant oscillator 1 is a single continuous structure, and the resonant oscillator 1 has a closed irregular profile in the plane. The irregular profile exhibits a non-constant radial dimension distribution along the circumferential direction.

[0026] In Example 1, the irregular profile exhibits a non-constant radial dimension distribution along the circumferential direction, resulting in the resonant oscillator 1 having different geometric dimensions in different angular directions. By adjusting the geometric dimensions of the resonant oscillator 1 at different circumferential positions, the frequency-temperature characteristics of the micromechanical resonator can be adjusted.

[0027] For example, the irregular contour has periodic variation characteristics in the circumferential direction, and the irregular contour has at least fourfold rotational symmetry.

[0028] The irregular contour can be represented as an angular modulation function in polar coordinates, which satisfies the following relationship:

[0029] In the formula, For the resonant oscillator at an angle Radial dimension in the direction, The average radial dimension parameter, For the first Angular modulation amplitude parameters, It is a positive integer greater than or equal to 1. f m It is a periodic function.

[0030] By adjusting the average radial dimension parameter With the first angular modulation amplitude parameters The proportional relationship between these parameters allows for the adjustment of the frequency-temperature characteristics of the micromechanical resonator.

[0031] The periodic function f mThese can be trigonometric functions, exponential functions, polynomial functions, spline functions, or combinations of the above functions.

[0032] For example, trigonometric functions can be represented as: A polynomial function can be represented as: where p is the degree of the polynomial; an exponential function can be expressed as: Where, a is the amplitude modulation parameter, controlling the overall offset of the irregular contour relative to the average size; b is the shape modulation parameter, controlling the degree of nonlinearity in the angular modulation; the spline function can be expressed as: , For spline basis functions, Here, is the control coefficient, and N is the number of control points. All of the above-mentioned function forms cause the irregular profile to exhibit periodic radial dimensional variations in the circumferential direction.

[0033] For example, Figure 2-a A schematic diagram of the planar profile of a trigonometric function type first-order angular modulation resonator (M=1). Figure 2-b A schematic diagram of the planar profile of a trigonometric function type second-order angular modulation resonator (M=2); Figure 2-c A schematic diagram of the planar profile of a trigonometric function type third-order angular modulation resonator (M=3). Figure 2-d This is a schematic diagram of the planar profile of a trigonometric function type fourth-order angular modulation resonator (M=4).

[0034] In addition, a support beam 2 is provided on the outer periphery of the resonant oscillator 1. The support beam 2 is a straight beam, a T-shaped beam or a folded beam set at the vibration node of the resonant oscillator 1; or, the support beam 2 is set at the extreme point position corresponding to the higher-order angular modulation term in the outer periphery contour of the resonant oscillator 1, and the higher-order is greater than or equal to 2.

[0035] The micromechanical resonator is a single-crystal silicon structure or a composite thin-film structure of metal-piezoelectric layer-single-crystal silicon. When the micromechanical resonator is a single-crystal silicon structure, it can be implemented using any one of the following methods: electrostatic drive / electrostatic detection, electrostatic drive / piezoresistive detection. When the micromechanical resonator is a composite thin-film structure of metal-piezoelectric layer-single-crystal silicon, it can be implemented using any one of the following methods: piezoelectric drive / piezoelectric detection, electrostatic drive / electrostatic detection, piezoelectric drive / electrostatic detection, or electrostatic drive / piezoelectric detection.

[0036] Taking a piezoelectric resonator as an example, see Figure 1The micromechanical resonator includes a substrate silicon wafer 4, a buried oxide layer 5, a device silicon layer 6, a resonant oscillator 1, a support beam 2, a piezoelectric layer 7, a passivation layer 8, and a metal electrode layer 3. A cavity structure is formed on the substrate silicon wafer 4, on which the buried oxide layer 5 is disposed, and the device silicon layer 6 is disposed on the buried oxide layer 5. The resonant oscillator 1 and the support beam 2 are patterned from the device silicon layer 6 and suspended above the cavity structure. The piezoelectric layer 7 is disposed on the upper surface of the resonant oscillator 1, and a top electrode (not shown in the figure) is further disposed on the piezoelectric layer 7. The top electrode is used to cooperate with the piezoelectric layer 7 to realize piezoelectric driving and / or piezoelectric detection functions. The passivation layer 8 is disposed above the piezoelectric layer 7 and the top electrode, and a through-hole structure is formed in the passivation layer 8. The metal electrode layer 3 is electrically connected to the top electrode through the through-hole structure, thereby realizing the electrical connection between external electrical signals and the piezoelectric layer 7.

[0037] The present invention mainly adjusts the resonator frequency temperature coefficient (TCF) by adjusting the geometry of the resonator 1 to achieve temperature compensation. On this basis, the present invention can further combine heavy doping and crystal orientation adjustment to achieve better adjustment effect.

[0038] Among them, the crystal plane of the monocrystalline silicon is the (100) crystal plane, and the monocrystalline silicon is heavily doped with N-type or P-type, with a doping concentration range of 4.0 × 10⁻⁶. 19 / cm 3 Up to 5.0×10 20 / cm 3 The crystal orientation range of the resonant oscillator 1 includes along... <100> ,along <110> and along <100> and <110> The crystal orientation of the resonant oscillator is determined by the selected doping concentration. Both the doping conditions and crystal orientation of the single-crystal silicon affect the frequency-temperature characteristics of the resonant oscillator 1. The frequency-temperature coefficient of the resonant oscillator 1 can be further adjusted by combining the setting of the doping conditions and the selection of the crystal orientation.

[0039] The resonant oscillator 1 can be used alone, or arranged in an array to form a resonator array, or used as a mechanical coupling structure to couple with other resonators. That is, the resonant oscillator 1 can also be used as part of a mechanical coupling structure to mechanically couple with at least one other resonator.

[0040] For example, see Figure 3-a This illustrates a mechanically coupled resonator formed by coupling the annular structure 32 with the outer periphery of the resonant oscillator 31, which has an irregular profile, at the point of maximum extremum; for example, see [link to example]. Figure 3-b This illustrates a mechanically coupled resonator formed by coupling the annular structure 32 with the minimum extreme point of the outer periphery of the resonant oscillator 31 with an irregular profile.

[0041] In summary, the micromechanical resonator proposed in Example 1 employs a non-uniform profile structure with circumferential and angular modulation characteristics. By introducing angular modulation terms into the planar profile of the resonator, the resonator exhibits a non-constant radial dimension distribution in different angular directions, thereby altering the equivalent stiffness and stress distribution during vibration. Compared to existing micromechanical resonators with regular geometric profiles, the structure of Example 1 helps suppress local stress concentration and reduces energy loss caused by the propagation of vibration energy through the support structure. Furthermore, since the equivalent stiffness distribution of the resonator is redistributed in different angular directions, the non-uniform profile structure provided in Example 1 weakens the local temperature gradient changes caused during vibration, which helps reduce the thermoelastic losses of the resonator. By adjusting the ratio between the average radial dimension parameter and the angular modulation amplitude parameter, Example 1 can control the shape of the resonator's frequency-temperature curve, thereby adjusting the temperature inflection point. Unlike existing passive temperature compensation methods that mainly rely on crystal orientation selection or doping concentration adjustment, Example 1 can achieve precise control of the temperature inflection point without increasing material or process complexity.

[0042] The following provides a fabrication method corresponding to the micromechanical resonator provided in Example 1, which will be described in Examples 2 and 3 respectively.

[0043] Example 2: Example 2 provides a method for fabricating a micromechanical resonator, wherein the micromechanical resonator is a single-crystal silicon structure, and the fabrication method is as follows: S201. An SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer 401, a buried oxide layer 402, and a device layer silicon 403, wherein the thickness of the device layer silicon 403 is 20µm to 60µm. (See [reference needed]) Figure 4-a .

[0044] S202, Deposit a 1µm to 2µm thick metal (e.g., aluminum) on the device layer silicon 403, and pattern it to form metal pads 404, see [link to documentation]. Figure 4-b .

[0045] S203, Etching the device layer silicon 403 from the front, stopping on the buried oxide layer 402, forming a resonant oscillator with an irregular profile in the device layer silicon 403, see [link to documentation]. Figure 4-c .

[0046] The resonant oscillator is a single continuous structure with a closed irregular profile in a plane. This irregular profile exhibits a non-constant radial dimension distribution along the circumferential direction. Specific characteristics of the resonant oscillator can be understood from the description of Embodiment 1, and will not be repeated here.

[0047] S204. The substrate silicon wafer 401 is etched on the back side, stopping at the buried oxide layer 402, forming a cavity structure in the substrate silicon wafer 401. See below. Figure 4-d .

[0048] S205. Remove the buried oxide layer corresponding to the etched structure (e.g., by introducing gaseous hydrofluoric acid to release it), to obtain the micromechanical resonator structure. See [link to relevant documentation] Figure 4-e .

[0049] The micromechanical resonator provided in Example 1 is finally obtained.

[0050] Example 3: Example 3 provides a method for fabricating a micromechanical resonator, wherein the micromechanical resonator is a metal-piezoelectric layer-single-crystal silicon composite thin film structure, and the fabrication method is as follows: S301. A cavity-structured SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer 501, a buried oxide layer 502, and a device layer silicon 503, wherein the thickness of the device layer silicon 503 is 20 µm to 60 µm. See [link to documentation]. Figure 5-a .

[0051] S302, a 0.5µm to 1µm thick piezoelectric material 504 (e.g., aluminum nitride) and a 0.15µm to 0.2µm thick upper electrode 505 (e.g., molybdenum) are sequentially deposited on the silicon layer 503, and the upper electrode 505 is patterned, see [link to relevant documentation]. Figure 5-b .

[0052] S303, deposit a top oxide layer of at least 0.2 µm thick, 506, see [link to previous section]. Figure 5-c .

[0053] S304. Etch the top oxide 506 to obtain an upper electrode via and expose the material of the upper electrode 505. See [link to documentation]. Figure 5-d .

[0054] S305. Etch the top oxide 506 and the piezoelectric material 504 to obtain the lower electrode via and expose the device layer silicon 503. See [link to documentation]. Figure 5-e .

[0055] S306. Deposit and pattern metal (e.g., deposit 1µm to 2µm thick aluminum) in both the upper electrode via and the lower electrode via to form metal pads 507. See [link to previous section] Figure 5-f .

[0056] S307, front-side etching of the top oxide 506, the piezoelectric material 504, and the device layer silicon 503, stopping at the buried oxide layer 502, forming a resonant oscillator with an irregular profile in the device layer silicon 503, see [link to documentation]. Figure 5-g .

[0057] The resonant oscillator is a single continuous structure with a closed irregular profile in a plane. This irregular profile exhibits a non-constant radial dimension distribution along the circumferential direction. Specific characteristics of the resonant oscillator can be understood from the description of Embodiment 1, and will not be repeated here.

[0058] S308. The substrate silicon wafer 501 is etched on the back side, stopping at the buried oxide layer 502, forming a cavity structure in the substrate silicon wafer 501. See below. Figure 5-h .

[0059] S309. Remove the buried oxide layer corresponding to the etched structure (e.g., by introducing gaseous hydrofluoric acid to release it), to obtain the micromechanical resonator structure. See [link to relevant documentation] Figure 5-i .

[0060] The micromechanical resonator provided in Example 1 is finally obtained.

[0061] Example 4: Example 4 provides a micromechanical oscillator, which is an uncompensated micromechanical oscillator, a temperature-compensated micromechanical oscillator, or a temperature-controlled micromechanical oscillator.

[0062] That is, based on the micromechanical resonator provided in Example 1, Example 4 constructs different micromechanical oscillators for different application scenarios. The various types of micromechanical oscillators are described below.

[0063] (1) Micromechanical oscillator without temperature compensation.

[0064] like Figure 6-a As shown, the uncompensated micromechanical oscillator includes a micromechanical resonator 601 and an oscillation holding circuit 602. The oscillation holding circuit 602 provides closed-loop oscillation excitation for the micromechanical resonator 601, thereby outputting a clock signal.

[0065] (2) Temperature-compensated micromechanical oscillator.

[0066] In this invention, the frequency-temperature characteristics of the micromechanical resonator are jointly determined by the structural parameters, crystal orientation, and doping conditions of the resonant body. Specifically, by designing the angular modulation pattern of the resonant oscillator's planar profile and adjusting the ratio between the average radial dimension parameter and the angular modulation amplitude parameter, the equivalent stiffness of the resonant oscillator can be controlled, thereby altering the higher-order terms of the frequency-temperature curve. Further adjustment of the resonant oscillator's frequency-temperature coefficient can be achieved by combining the setting of doping conditions and the selection of crystal orientation.

[0067] like Figure 6-b As shown, the temperature-compensated micromechanical oscillator includes a micromechanical resonator 601, an oscillation holding circuit 602, a frequency synthesizer 603, and a temperature sensor 604. Based on the uncompensated micromechanical oscillator structure, a temperature-compensated micromechanical oscillator is obtained by adding the frequency synthesizer 603 and the temperature sensor 604. The temperature-compensated oscillator uses the temperature sensor 604 to digitally convert the temperature output to the frequency synthesizer 603 to adjust the frequency, thereby compensating for frequency variations in the micromechanical oscillator across the entire temperature range.

[0068] (3) Thermostatic control micromechanical oscillator.

[0069] By designing the angular modulation structure parameters of the resonant oscillator and combining the heavy doping conditions and crystal orientation of single-crystal silicon, the high-temperature inflection point of the micromechanical resonator can be tuned to a temperature range higher than the target operating temperature range.

[0070] like Figure 6-c As shown, the thermostatically controlled oscillator includes a micromechanical resonator 601, an oscillation holding circuit 602, a temperature sensor 604, a temperature control circuit 605, and a heating cavity 606. Based on the uncompensated micromechanical oscillator structure, the micromechanical resonator 601 is placed inside the heating cavity 606. The temperature sensor 604 measures the temperature of the heating cavity 606 in real time, and the temperature control circuit 605 adjusts the temperature of the heating cavity 606 to maintain the temperature of the micromechanical resonator 601 at its temperature inflection point. In this case, the micromechanical resonator is suitable for constructing a thermostatically controlled micromechanical oscillator.

[0071] The technical effects of the present invention will be further explained below.

[0072] This invention designs the planar profile of the resonator in a micromechanical resonator by angular modulation and adjusts the average radial dimension parameter of the resonator. r 0 and the angular modulation amplitude parameters a mBy performing matching design, the frequency offset-temperature curve of the micromechanical resonator can be controlled, thereby meeting the application requirements for frequency stability under wide temperature range conditions.

[0073] The frequency shift-temperature characteristics of the micromechanical resonator can be adjusted by changing the average radial dimension parameter. r 0 and the angular modulation amplitude parameters a m The proportional relationship between these parameters is adjusted. Different parameter ratios correspond to different equivalent stiffness and stress distribution states, resulting in different variation characteristics in the frequency shift-temperature curves.

[0074] For example, when Figure 1 The resonant oscillator shown is made of n-type super-heavily doped single-crystal silicon material, with a doping concentration greater than 1.2 × 10⁻⁶. 20 / cm 3 And the resonator along the single-crystal silicon <100> When arranging crystal orientations, Figure 7 Showing different mean radial dimension parameters r 0 and the angular modulation amplitude parameters a m The frequency shift-temperature curve of the micromechanical resonator over a wide temperature range from -70℃ to 140℃ under proportional relationships. Figure 7 The scaling parameter 1 is 0.19, scaling parameter 2 is 0.2, and scaling parameter 3 is 0.21. Furthermore, by selecting appropriate average radial dimension parameters... r 0 and the angular modulation amplitude parameters a m The proportional relationship allows the frequency shift of the micromechanical resonator to be kept within ±10ppm over a wide temperature range of -70℃ to 140℃, while simultaneously achieving a high temperature inflection point.

[0075] In summary, the micromechanical resonator proposed in this invention can achieve adjustable design of the temperature inflection point of the frequency-temperature curve, and the micromechanical oscillator built based on the micromechanical resonator can meet the frequency stability requirements of various applications. In other words, this invention can be flexibly selected according to application requirements to meet the needs of various application scenarios such as high-precision clocks, communication systems, and temperature-sensitive applications.

[0076] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A micromechanical resonator, characterized in that, include: Substrate silicon wafer and device layer silicon; The substrate silicon wafer has a cavity structure, and a resonant oscillator is formed in the device layer silicon, with the resonant oscillator suspended above the cavity structure; The resonant oscillator is a single continuous structure, and the resonant oscillator has a closed irregular profile in the plane, and the irregular profile exhibits a non-constant radial dimension distribution along the circumferential direction.

2. The micromechanical resonator according to claim 1, characterized in that, The frequency-temperature characteristics of the micromechanical resonator can be adjusted by regulating the geometric dimensions of the resonator at different circumferential positions.

3. The micromechanical resonator according to claim 1, characterized in that, The irregular contour has periodic variation characteristics in the circumferential direction, and the irregular contour has at least fourfold rotational symmetry.

4. The micromechanical resonator according to claim 1, characterized in that, The irregular contour is represented in polar coordinates as an angular modulation function, which satisfies the following relationship: In the formula, For the resonant oscillator at an angle Radial dimension in the direction, The average radial dimension parameter, For the first Angular modulation amplitude parameters, It is a positive integer greater than or equal to 1. f m It is a periodic function; The periodic function f m These are trigonometric functions, exponential functions, polynomial functions, or spline functions. By adjusting the average radial dimension parameter With the first angular modulation amplitude parameters The proportional relationship between these parameters allows for the adjustment of the frequency-temperature characteristics of the micromechanical resonator.

5. The micromechanical resonator according to claim 4, characterized in that, The outer periphery of the resonant oscillator is provided with a support beam; the support beam is a straight beam, a T-shaped beam or a folded beam disposed at the vibration node of the resonant oscillator; or, the support beam is disposed at the extreme point position corresponding to the higher-order angular modulation term in the outer periphery contour of the resonant oscillator.

6. The micromechanical resonator according to claim 1, characterized in that, The resonant oscillator can be used alone, form a resonator array, or be used as a mechanical coupling structure to couple with other resonators.

7. The micromechanical resonator according to claim 1, characterized in that, The micromechanical resonator is a single-crystal silicon structure, or the micromechanical resonator is a metal. piezoelectric layer Composite thin film structure of monocrystalline silicon; The crystal plane of monocrystalline silicon is (100). The monocrystalline silicon is heavily doped with N-type or P-type silicon, and the doping concentration ranges from 4.0 × 10⁻⁶. 19 / cm 3 Up to 5.0×10 20 / cm 3 The crystal orientation range of the resonant oscillator includes along... <100> ,along <110> and along <100> and <110> Arranged between them.

8. A method for fabricating a micromechanical resonator as described in any one of claims 1 to 7, characterized in that, The micromechanical resonator is a single-crystal silicon structure, and the fabrication method of the micromechanical resonator includes the following steps: An SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer, and a device layer silicon; Metal is deposited and patterned on the silicon layer of the device to form metal pads; The device layer silicon is etched from the front, stopping on the buried oxide layer, to form a resonant oscillator with an irregular profile in the device layer silicon; The substrate silicon wafer is etched on the back side, stopping on the buried oxide layer, to form a cavity structure in the substrate silicon wafer; The buried oxide layer corresponding to the etched structure is removed to obtain the structure of the micromechanical resonator.

9. A method for fabricating a micromechanical resonator as described in any one of claims 1 to 7, characterized in that, The micromechanical resonator is a composite thin film structure of metal-piezoelectric layer-monocrystalline silicon. The fabrication method of the micromechanical resonator includes the following steps: An SOI wafer is provided, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer, and a device layer silicon; A piezoelectric material and an upper electrode are sequentially deposited on the silicon device layer, and the upper electrode is patterned. A top oxide layer is deposited on the upper electrode; The top oxide layer is etched to obtain an upper electrode via and expose the upper electrode. The top oxide and the piezoelectric material are etched to obtain a lower electrode via and expose the device layer silicon. Metal is deposited and patterned in both the upper electrode via and the lower electrode via to form metal pads; The top oxide layer, the piezoelectric material, and the device layer silicon are etched from the front, stopping on the buried oxide layer, to form a resonant oscillator with an irregular profile in the device layer silicon. The substrate silicon wafer is etched on the back side, stopping on the buried oxide layer, to form a cavity structure in the substrate silicon wafer; The buried oxide layer corresponding to the etched structure is removed to obtain the structure of the micromechanical resonator.

10. A micromechanical oscillator, characterized in that, The micromechanical oscillator is an uncompensated micromechanical oscillator, a temperature-compensated micromechanical oscillator, or a temperature-controlled micromechanical oscillator. When the micromechanical oscillator is the uncompensated micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as described in any one of claims 1 to 7, and an oscillation holding circuit; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator; When the micromechanical oscillator is the temperature-compensated micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as described in any one of claims 1 to 7, an oscillation holding circuit, a frequency synthesizer, and a temperature sensor; the temperature inflection point of the micromechanical resonator is at room temperature; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator; the temperature sensor is used to obtain the ambient temperature and transmit it to the frequency synthesizer; the frequency synthesizer is used to adjust the frequency to compensate for the frequency variation of the micromechanical oscillator over the entire temperature range. When the micromechanical oscillator is the temperature-controlled micromechanical oscillator, the micromechanical oscillator includes a micromechanical resonator as described in any one of claims 1 to 7, an oscillation holding circuit, a temperature sensor, a temperature control circuit, and a heating cavity; the temperature inflection point of the micromechanical resonator is located above the operating temperature range of the micromechanical resonator, and the micromechanical resonator is placed inside the heating cavity; the oscillation holding circuit is used to provide closed-loop oscillation excitation for the micromechanical resonator; the temperature sensor is used to obtain the real-time temperature of the heating cavity and transmit it to the temperature control circuit; The temperature control circuit is used to adjust the temperature of the heating cavity so that the temperature of the micromechanical resonator is maintained at its temperature inflection point.

Images