A micromechanical resonator with a filling slot and a method for manufacturing the same

Abstract

This invention relates to the field of resonator technology, and particularly to a micromechanical resonator with a filled groove and its fabrication method. The resonator includes a substrate, a cavity, a device layer, a piezoelectric layer, a top electrode, a bottom electrode, a pad, a buried oxide layer, a resonator structure, and an anchor structure. At least one filled groove is provided on the resonator structure. The filled groove is made of silicon dioxide or SiOF material, utilizing its low thermal conductivity to suppress thermoelastic damping and its positive temperature frequency coefficient to compensate for the negative temperature frequency coefficients of other layers, achieving both high quality factor and high temperature stability without increasing size or power consumption. This invention achieves both high quality factor and low temperature drift without increasing device size or power consumption, making it suitable for high-precision timing devices.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, and in particular to a micromechanical resonator with a filled groove and its fabrication method. Background Technology

[0002] With the rapid development of electronic systems, the trends of miniaturization and integration are becoming increasingly apparent. Clock devices typically need to be integrated into miniature electronic devices with limited space and operate stably for extended periods in complex environments. Therefore, miniaturized, low-power, and high-precision clock technologies are crucial. As the core component of an oscillator, the size, losses, and thermal stability of the resonator are key factors determining the oscillator's size and stability. Quartz resonators are relatively large, and electrostatic MEMS resonators have high power consumption; existing technologies struggle to simultaneously meet the requirements of miniaturization, low power consumption, and high precision.

[0003] Piezoelectric MEMS resonators have advantages such as small size (micrometer scale) and low driving power consumption, but their accuracy still lags behind that of atomic clocks and quartz clocks, requiring further improvement. Since the accuracy of piezoelectric MEMS clocks is mainly affected by the resonator's quality factor and temperature frequency drift, there is an urgent need for methods that can simultaneously improve both the quality factor and temperature stability.

[0004] To address the aforementioned issues, existing research has made several attempts. For example, Reference 1 (Experimental Study of Q-Boosting in TpoS Resonators using Conventional and Coupled Resonator Architecture) discloses a mechanically coupled resonator structure that improves the quality factor by combining a piezoelectric MEMS resonator with an electrostatic MEMS resonator. However, the size of this structure is significantly increased, typically several times that of a single piezoelectric MEMS resonator. Reference 2 (A Micro-Oven Controlled Dual-Mode Piezoelectric MEMS Resonator With ±190 ppb Stability Over -40 to 105 ℃ Temperature Range) discloses a micro-oven controlled dual-mode piezoelectric MEMS resonator that improves temperature stability through Joule heating, but its power consumption is high, and the overall structure is still large. Therefore, existing technologies often sacrifice size and power consumption to improve the quality factor or temperature stability, making it difficult to achieve high performance simultaneously without increasing size and power consumption.

[0005] Therefore, there is a need for a micromechanical resonator structure that can maintain small size and low power consumption while also having a high quality factor and good temperature stability. Summary of the Invention

[0006] The purpose of this invention is to provide a micromechanical resonator with a filled groove and its fabrication method, thereby solving the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a micromechanical resonator with a filling groove, the micromechanical resonator including a substrate, a cavity, a device layer, a piezoelectric layer, a top electrode, a pad, a resonator structure, and an anchor structure, and further including at least one filling groove, the cavity being formed above the substrate and below the device layer; The filling groove is formed on the resonant structure, the piezoelectric layer is disposed above the device layer, and the top electrode is disposed above the piezoelectric layer; The device layer, filling groove, piezoelectric layer and top electrode together constitute a resonator structure; The resonator structure is a stacked structure suspended above the cavity, which excites mechanical vibration through the piezoelectric effect. The anchor structure connects the substrate and the resonator structure, fixing the resonator structure to the substrate.

[0008] Preferably, it also includes a buried oxide layer, which is disposed between the device layer and the substrate.

[0009] Preferably, it further includes a bottom electrode disposed between the piezoelectric layer and the device layer, wherein the bottom electrode is disposed on the lower surface of the piezoelectric layer and the top electrode is disposed on the upper surface of the piezoelectric layer.

[0010] Preferably, the piezoelectric layer is directly disposed on the upper surface of the device layer, and the top electrode is disposed on the upper surface of the piezoelectric layer.

[0011] Preferably, the pads further include pad one, pad two, and pad three. Pad one and pad two are electrically connected to the top electrode and are used to apply electrical signals to the resonator structure or output detection signals therefrom. Pad three is used for encapsulation.

[0012] Preferably, the material of the device layer is one of silicon, SiC or diamond; The silicon includes intrinsic silicon, high-resistivity silicon, heavily doped or lightly doped N-type silicon or P-type silicon.

[0013] Preferably, the filling groove is one of the following: rectangular, square, plate-shaped, circular, annular, triangular, polygonal, elliptical, teardrop-shaped, semi-elliptical, or interdigitated. The internal material of the filling tank is one or more of silicon dioxide (SiO2) or SiOF.

[0014] Preferably, the pad is one or more of the following shapes: rectangular, square, plate-shaped, circular, annular, triangular, polygonal, interdigitated, or elliptical. The bottom electrode and top electrode are one or more of the following shapes: rectangular, square, plate-shaped, circular, ring-shaped, triangular, polygonal, interdigitated, or elliptical. The materials of the bottom electrode and the top electrode are one or more of Al, Cu, Au, Ag, Ti, Mo, Pt, Pi, Co, Cr, Mg or W; The piezoelectric layer is made of one or more of the following materials: LiNbO3, LiTaO3, AlN, ScAlN, AlN / ScAlN stack, ZnO, Al2O3, GaN, NaNbO3, lead zirconate titanate, or lead magnesium niobate.

[0015] Preferably, the shape of the resonator structure is rectangular, square, circular, annular, polygonal, elliptical, teardrop-shaped, semi-elliptical, cantilever beam-shaped, or interdigitated, and the alignment direction of the resonator structure is... <100> Crystal orientation or <110> Crystal orientation or alignment in any direction.

[0016] A method for fabricating a micromechanical resonator with a filled groove includes the following steps: S1. Provide a substrate wafer and a device wafer. The lower surface of the device wafer is provided with a buried oxide layer. A cavity is pre-etched in the substrate wafer. The device wafer is bonded to the substrate wafer with the cavity to form a complete wafer with a pre-etched cavity. S2. Grind and polish the device layer of the complete wafer to reduce it to the target thickness; S3. Sequentially deposit a bottom layer metal, a piezoelectric material, and a top layer metal stack on the upper surface of the thinned device layer, and pattern the top layer metal to form a top electrode. S4. Etch piezoelectric material to form through holes for connecting the bottom electrode; S5. Sequentially etch the piezoelectric material and the underlying metal; S6. Deposit pad metal material and pattern it to form pads; S7. Deposit and fill the groove material and pattern it; S8. Finally, the buried oxide layer material, equipment layer material, bottom metal, and piezoelectric material are etched in sequence to define the resonator structure and anchor structure and release the micromechanical resonator with the filling groove.

[0017] Therefore, the present invention provides a micromechanical resonator with a filling groove. Compared with the prior art, by introducing the filling groove and optimizing its material, size, shape and position, the quality factor and temperature stability are improved, resulting in the following beneficial effects: This invention incorporates a filling groove between the device layer and the bottom electrode. This filling groove effectively blocks the heat flow within the bottom electrode, piezoelectric layer, and top electrode during vibration, thereby suppressing thermoelastic damping, the primary energy loss mechanism. When the filling groove is made of SiO2 material and its appropriate size is selected, there is no need to change the resonator's planar dimensions or add additional driving circuitry, significantly improving the resonator's quality factor.

[0018] In this invention, the filling groove not only suppresses energy loss but also provides temperature compensation. When the filling groove is made of SiO2 or SiOF, which have a positive temperature frequency coefficient, its positive TCF characteristics can cancel out the negative TCF characteristics of other layers, thereby significantly reducing the frequency variation of the resonator with temperature and improving the temperature stability of the resonator. Attached Figure Description

[0019] Figure 1 This is a cross-sectional schematic diagram of the first structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention; Figure 2 This is a top view of a first structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention; Figure 3 This is a top view of a second structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention; Figure 4 This is a cross-sectional schematic diagram of a second structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention; Figure 5 This is a cross-sectional schematic diagram of a third structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention. This cross-section does not include the bottom electrode. Figure 6 This is a cross-sectional schematic diagram of a fourth structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention. This cross-section does not include the buried oxide layer. Figure 7 The figures show the quality factor variation and temperature-frequency variation of a micromechanical resonator with a filling groove under different filling groove sizes, as described in Embodiment 1 of the present invention. Figure 8 This is a top view of the fourth structure of a micromechanical resonator with a filled groove according to Embodiment 1 of the present invention; Figure 9 This is a top view of the structure of a micromechanical resonator with a filled groove according to Embodiment 2 of the present invention; Figure 10 The figures show the quality factor variation and temperature-frequency variation of a micromechanical resonator with a filling groove in different sizes of filling grooves according to Embodiment 2 of the present invention. Figure Labels 1. Substrate; 2. Cavity; 3. Device layer; 4. Filler groove; 5. Bottom electrode; 6. Piezoelectric layer; 7. Top electrode; 8. Buried oxide layer; 101. Resonator structure; 102A. Anchor structure one; 102B. Anchor structure two; 103A. Pad one; 103B. Pad two; 103C. Pad three. Detailed Implementation

[0020] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0021] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] Example 1 This embodiment provides a micromechanical resonator with a filled groove, the cross-sectional structure of which is as follows: Figure 1 As shown, it mainly includes substrate 1, cavity 2, device layer 3, filling groove 4, bottom electrode 5, piezoelectric layer 6, top electrode 7, buried oxide layer 8, and pads 103A, 103B, and 103C. The top view structure is as follows. Figure 2 As shown, the layout of the resonator structure 101, anchor structure 102A, anchor structure 102B, and pads is further illustrated.

[0024] In this design, substrate 1 is made of single-crystal silicon and serves as the supporting substrate for the entire device. Cavity 2 is formed above substrate 1 and below device layer 3, providing free vibration space for the resonator structure 101, thereby effectively reducing the leakage of vibrational energy to substrate 1. Device layer 3 is made of N-type phosphorus-doped single-crystal silicon with a doping concentration of 6.6 × 10⁻⁶. 19 cm -3 The thickness is 5 micrometers, and the equipment layer 3 bears the mechanical vibration.

[0025] A filler groove 4 is disposed on the resonator structure 101. In this embodiment, two filler grooves 4 are disposed, both of which are rectangular. The filler grooves 4 are made of silicon dioxide material, and each filler groove 4 is 200-240 micrometers long and 8 micrometers wide. The filler groove 4 can effectively block the intralayer heat flow of the piezoelectric layer and the upper and lower electrode layers along the width direction, thereby suppressing thermoelastic damping and significantly improving the quality factor of the resonator. On the other hand, SiO2 has a positive temperature coefficient of frequency (TCF), while the other layers have negative TCF. The filler groove structure can cancel each other out with the negative TCF characteristics of the other layers through the positive TCF characteristics, thereby improving the temperature stability of the micromechanical resonator.

[0026] A bottom electrode 5, a piezoelectric layer 6, and a top electrode 7 are sequentially disposed on the upper surface of device layer 3. The bottom electrode 5 is made of molybdenum (Mo) and has a thickness of 0.2 micrometers; the piezoelectric layer 6 is made of aluminum nitride (AlN) and has a thickness of 1 micrometer; the top electrode 7 is also made of molybdenum and has a thickness of 0.2 micrometers. The bottom electrode and the top electrode work together to apply an electric field to the piezoelectric layer to excite the piezoelectric effect, thereby driving the resonator structure to vibrate. Pads 103A and 103B are electrically connected to the top electrode 7 and the bottom electrode 5, used to apply excitation signals or output detection signals, while pad 103C is used for packaging.

[0027] The resonator structure 101 is rectangular, 270 micrometers long and 150 micrometers wide. It is a multi-layered structure composed of a device layer 3, a filling groove 4, a bottom electrode 5, a piezoelectric layer 6, and a top electrode 7, suspended above the cavity 2, and is the working part of the micromechanical resonator. Anchor structures 102A and 102B are located at both ends of the resonator structure 101, connecting the substrate 1 and the resonator structure, and have dimensions of 10 micrometers long and 8 micrometers wide. In this embodiment, the resonator structure 101 is aligned with the device layer 3. <100> Crystal orientation.

[0028] The micromechanical resonator of this embodiment can be fabricated using the following process: First, a cavity is pre-formed in the substrate silicon wafer by etching. Then, the device wafer with the buried oxide layer 8 is bonded to the substrate wafer at high temperature to form a complete wafer with the pre-etched cavity. Subsequently, the device layer 3 is thinned to 5 micrometers through grinding and polishing. Next, a bottom metal, piezoelectric material, and top metal stack material are deposited, and the top metal is patterned to form the top electrode 7. Then, the piezoelectric material is etched to form through-holes for connecting the bottom electrode 5, and then the piezoelectric material and the bottom metal are etched sequentially. Pad metal material is deposited and patterned to form pads, and filler trench material is deposited and patterned. Finally, the buried oxide layer material, device layer material, bottom metal, and piezoelectric material are etched to define the resonator structure 101 and the anchor structure, and the micromechanical resonator with SiO2 filler trenches is released.

[0029] By adjusting the size of the filling groove 4, both the quality factor and temperature stability can be optimized simultaneously. For example... Figure 7 As shown, with the increase of the filler slot size, the thermoelastic damping-related quality factor of the resonator is improved by 3.4 times compared with the resonator without filler slots. Meanwhile, within the temperature range of -40℃ to 85℃, the frequency drift gradually overcompensates from +166ppm to -540ppm in the absence of filler slots to -697ppm to +415ppm. When the filler slot length is selected between 200-260 micrometers, the quality factor and temperature stability of the micromechanical resonator can be improved. When the filler slot length is 260 micrometers and the width is 5 micrometers, the frequency drift decreases from -193ppm to 12ppm. Therefore, without increasing the device planar size or power consumption, this embodiment achieves both a high quality factor and low temperature drift compared to traditional resonators without filler slots.

[0030] like Figure 3 and 4 As shown, in another variation of this embodiment, the filling groove 4 is disposed inside the resonator structure 101, and there are 4 filling grooves 4.

[0031] like Figure 8 As shown, in another variation of this embodiment, the resonator structure 101 is cantilever beam shaped, and each cantilever beam is provided with filling grooves 4.

[0032] like Figure 5 As shown, in another variation of this embodiment, the resonator structure 101 does not have a bottom electrode 5, the top electrode 7 is disposed on the upper surface of the piezoelectric layer 6, and the lower surface of the piezoelectric layer 6 is in direct contact with the device layer 3. The filling groove 4 still has the dual function of suppressing thermoelastic damping and compensating for temperature frequency drift.

[0033] In yet another variation of this embodiment, such as Figure 6 The buried oxide layer 8 is not continuous between the entire device layer 3 and the substrate 1. No buried oxide layer is provided below the resonator structure 101. The cavity 2 is still formed above the substrate 1 and below the device layer 3. The remaining structures, including the filler groove 4, bottom electrode 5, piezoelectric layer 6, and top electrode 7, are the same as in the aforementioned variant. This structure can also suppress thermoelastic damping and achieve temperature frequency compensation through the filler groove, improving the quality factor and temperature stability.

[0034] It should be noted that the specific values ​​given in this embodiment (such as doping concentration, thickness, size, etc.) are only examples. Those skilled in the art can make appropriate adjustments according to the target frequency and process conditions, and these adjustments do not depart from the protection scope of this invention.

[0035] Example 2 This embodiment has the same basic structure as Embodiment 1, the difference being the shape of the filling groove. For example... Figure 4 As shown, the resonator structure 101 in this embodiment is still a rectangular plate.

[0036] like Figure 9 In this embodiment, the filling groove 4 is zigzag-shaped and is disposed on the resonator structure 101. The bottom electrode 5 is located above the device layer 3, the piezoelectric layer 6 covers the bottom electrode 5, and the top electrode 7 is located on the upper surface of the piezoelectric layer 6. An excitation voltage is applied to the top electrode 7, thereby exciting an electric field in the piezoelectric layer 6 and driving the resonator to generate mechanical vibration.

[0037] The other structures remain consistent with those in Example 1: substrate 1 is monocrystalline silicon, buried oxide layer 8 is located between device layer 3 and substrate 1, cavity 2 is formed below device layer, and device layer 3 is N-type phosphorus-doped monocrystalline silicon with a thickness of 5 micrometers and a doping concentration of 6.6 × 10⁻⁶. 19 cm -3 The filling groove 4 is made of SiO2 material, with a width of 0-10 micrometers. Anchor structure 102A and anchor structure 102B are both 10 micrometers long and 8 micrometers wide. The resonator structure 101 is aligned... <100> Crystal orientation. Pad 103A and pad 103B are electrically connected to the top and bottom electrodes, respectively, and pad 103C is used for packaging.

[0038] like Figure 10 As shown, experimental results indicate that the thermoelastic damping of the device first decreases and then increases as the filling groove 4 moves further away from the center of the resonator. When the length of the filling groove 4 is 260 micrometers and its distance from the center of the resonator is 20 micrometers... Figure 10 When the horizontal axis Y1 is reached, the thermoelastic damping-related quality factor of the device reaches its maximum value. As the size of the filler groove 4 increases, the frequency drift of the device in the range of -40℃ to 85℃ is overcompensated from +166ppm to -540ppm to -689ppm to +414ppm. When the filler groove is 260 μm long and 3 μm wide, the drift ranges from -191ppm to 0ppm, which can improve the quality factor and temperature stability of the micromechanical resonator. Both the bottom electrode and bottomless electrode variants can achieve the above technical effects. Among them, the bottomless electrode variant reduces the surface loss due to the reduction of the metal layer, which is beneficial to improving the quality factor.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A micromechanical resonator with a filled groove, the micromechanical resonator comprising a substrate, a cavity, a device layer, a piezoelectric layer, a top electrode, a pad, a resonator structure, and an anchor structure, characterized in that, It also includes at least one filling groove, the cavity being formed above the substrate and below the device layer; The filling groove is formed on the resonant structure, the piezoelectric layer is disposed above the device layer, and the top electrode is disposed above the piezoelectric layer; The device layer, filling groove, piezoelectric layer and top electrode together constitute a resonator structure; The resonator structure is a stacked structure suspended above the cavity, which excites mechanical vibration through the piezoelectric effect. The anchor structure connects the substrate and the resonator structure, fixing the resonator structure to the substrate.

2. A micromechanical resonator with a filled groove according to claim 1, characterized in that: It also includes a buried oxide layer, which is disposed between the device layer and the substrate.

3. A micromechanical resonator with a filled groove according to claim 1, characterized in that: It also includes a bottom electrode, which is disposed between the piezoelectric layer and the device layer. The bottom electrode is disposed on the lower surface of the piezoelectric layer, and the top electrode is disposed on the upper surface of the piezoelectric layer.

4. A micromechanical resonator with a filled groove according to claim 1, characterized in that: The piezoelectric layer is directly disposed on the upper surface of the device layer, and the top electrode is disposed on the upper surface of the piezoelectric layer.

5. A micromechanical resonator with a filled groove according to claim 1, characterized in that: The pads also include pad one, pad two, and pad three. Pad one and pad two are electrically connected to the top electrode and are used to apply electrical signals to the resonator structure or output detection signals therefrom. Pad three is used for encapsulation.

6. A micromechanical resonator with a filled groove according to claim 1, characterized in that: The material of the device layer is one of silicon, SiC or diamond; The silicon includes intrinsic silicon, high-resistivity silicon, heavily doped or lightly doped N-type silicon or P-type silicon.

7. A micromechanical resonator with a filled groove according to claim 1, characterized in that: The filling groove is one of the following shapes: rectangular, square, plate-shaped, circular, annular, triangular, polygonal, elliptical, teardrop-shaped, semi-elliptical, or interdigitated. The internal material of the filling tank is one or more of silicon dioxide (SiO2) or SiOF.

8. A micromechanical resonator with a filled groove according to claim 2, characterized in that: The pads are one or more of the following shapes: rectangular, square, plate-shaped, circular, annular, triangular, polygonal, interdigitated, or elliptical. The bottom electrode and top electrode are one or more of the following shapes: rectangular, square, plate-shaped, circular, ring-shaped, triangular, polygonal, interdigitated, or elliptical. The materials of the bottom electrode and the top electrode are one or more of Al, Cu, Au, Ag, Ti, Mo, Pt, Pi, Co, Cr, Mg or W; The piezoelectric layer is made of one or more of the following materials: LiNbO3, LiTaO3, AlN, ScAlN, AlN / ScAlN stack, ZnO, Al2O3, GaN, NaNbO3, lead zirconate titanate, or lead magnesium niobate.

9. A micromechanical resonator with a filled groove according to claim 1, characterized in that: The resonator structure can be rectangular, square, circular, ring-shaped, polygonal, elliptical, teardrop-shaped, semi-elliptical, cantilever beam-shaped, or interdigitated, and the alignment direction of the resonator structure is... <100> Crystal orientation or <110> Crystal orientation or alignment in any direction.

10. A method for fabricating a micromechanical resonator with a filled groove, used to fabricate the micromechanical resonator with a filled groove as described in claim 1, characterized in that, Includes the following steps: S1. Provide a substrate wafer and a device wafer. The lower surface of the device wafer is provided with a buried oxide layer. A cavity is pre-etched in the substrate wafer. The device wafer is bonded to the substrate wafer with the cavity to form a complete wafer with a pre-etched cavity. S2. Grind and polish the device layer of the complete wafer to reduce it to the target thickness; S3. Sequentially deposit a bottom layer metal, a piezoelectric material, and a top layer metal stack on the upper surface of the thinned device layer, and pattern the top layer metal to form a top electrode. S4. Etch piezoelectric material to form through holes for connecting the bottom electrode; S5. Sequentially etch the piezoelectric material and the underlying metal; S6. Deposit pad metal material and pattern it to form pads; S7. Deposit and fill the groove material and pattern it; S8. Finally, the buried oxide layer material, equipment layer material, bottom metal, and piezoelectric material are etched in sequence to define the resonator structure and anchor structure and release the micromechanical resonator with the filling groove.

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