MEMS resonator and manufacturing method thereof
By designing a convex curved vibration electrode and a planar lower surface structure in a MEMS resonator, combined with anchor heat dissipation and conductive post insulation, the Q value is improved and the power consumption is reduced under low vacuum conditions. This solves the problem of vacuum limitation in existing technologies and expands the application range.
Patent Information
- Application Number
- CN202511412395.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-29
- Publication Date
- 2026-01-09
AI Technical Summary
The improvement of the Q value of existing MEMS resonators is limited by the vacuum level of the packaging. The vacuum level of the bonding packaging is limited, while the gas components of the epitaxial packaging enter the sealed cavity, which limits the application range of the device.
Design a MEMS resonator with a structure in which the outer periphery of the upper surface of the vibrating electrode is convex and the lower surface is planar, mimicking the principle of aircraft takeoff to reduce air viscous drag. Heat dissipation is achieved through an anchor structure, and the self-excitation effect is realized by combining the insulation protection of the conductive post and the electrode layer.
Without increasing the vacuum level, the Q value of MEMS resonators was significantly improved, power consumption was reduced, and their application range was expanded to the aerospace field.
Smart Images
Figure CN121308708A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of microelectromechanical systems technology, specifically to a MEMS resonator and its fabrication method. Background Technology
[0002] MEMS (Micro-Electro-Mechanical Systems) resonators, as a replacement for quartz oscillators, can be integrated as frequency reference devices or clock devices. In recent years, with the increasing integration and miniaturization of the chip industry, the market has placed higher and higher demands on the accuracy of oscillators and resonators, while requiring lower and lower power consumption, which means that the Q value (quality factor) of the devices needs to be higher and higher.
[0003] The Q value of MEMS resonators is affected by many damping mechanisms, such as the effects of air viscosity and acoustic properties (Q1), the effects of mechanical structural imbalance or anchoring (Q2), and the effects of material properties (Q3). Among these, the influence of material properties on the Q value includes material purity, dislocations, and thermoelastic losses caused by material properties.
[0004] To improve the Q-factor of devices, MEMS devices generally require a higher vacuum level within the packaging cavity. (Reference) Figure 1 Experiments show that a pressure change from 10 Pa to 0 Pa increases the Q value of MEMS resonators by three orders of magnitude. Currently, MEMS resonators are packaged in two ways: 1) Bonding, which, depending on the device, can achieve a vacuum level of approximately 1,000 to tens of Pa; and 2) Epitaxial packaging, which requires a seed layer, typically an oxide layer. This technology is only implemented at Bosch, and its packaging vacuum level is not particularly low. Because the gas component of the epitaxial layer is hydrogen or helium, hydrogen and helium escape through the oxide layer during subsequent annealing, ultimately achieving a vacuum level of 1 Pa within the sealed cavity. It is precisely because of this that the presence of the oxide layer limits the device's operating environment, as hydrogen and helium can also enter the sealed cavity through the oxide layer. Therefore, devices fabricated using this technology cannot be used in the aerospace field.
[0005] Current technologies offer limited vacuum levels achievable through bonding packaging, while epitaxial packaging, though capable of achieving vacuum levels below 1 Pa, restricts the device's application range. Therefore, for domestic manufacturers of MEMS resonators, improving the Q-value of the device by increasing the vacuum level within the sealed cavity has reached a bottleneck. Summary of the Invention
[0006] Given that the vacuum level achievable by bonding packaging, one of the current technologies for improving the Q value of devices, is limited, thus reducing the Q value of the devices, and that gas components from epitaxial packaging, another technology for improving the Q value of devices, can enter the sealed cavity and limit the application range of the devices, this application proposes a solution to improve the Q value of devices without increasing the vacuum level inside the sealed cavity of the devices.
[0007] In the first aspect, this application proposes a MEMS resonator and adopts the following technical solution.
[0008] A MEMS resonator includes an upper electrode assembly, a lower electrode layer, a nitride layer, an upper oxide layer, and a silicon substrate.
[0009] The upper oxide layer covers the upper surface of the silicon substrate and is embedded within the silicon substrate, and the nitride layer covers the upper surface of the upper oxide layer. The lower electrode layer is deposited on the nitride layer. The upper electrode assembly includes a vibrating electrode.
[0010] The vibrating electrode includes a vibrating plate and several connecting posts. The lower surface of the vibrating plate is planar, and the outer peripheral area of the upper surface is convex curved.
[0011] Each of the connecting posts connects the lower surface of the vibrating plate to the lower electrode layer, while the other parts of the vibrating plate are suspended.
[0012] It should be noted that the design of the MEMS resonator is based on the device's own resonance. Due to damping, the vibration gradually weakens, so the resonator requires both DC and AC excitation to maintain effective vibration. By adopting the above technical solution, the vibrating electrode mimics the principle of an aircraft taking off. The outer periphery of the upper surface of the vibrating electrode is convex, while the lower surface is flat. During vibration, the air viscous resistance above the vibrating electrode decreases with the curvature of the convex surface, resulting in low air damping in the outer periphery of the vibrating plate and increased gas velocity at the edge, leading to lower pressure above the vibrating electrode. Meanwhile, the lower surface of the vibrating electrode is flat, resulting in slower airflow and higher air pressure compared to the upper surface, creating a pressure difference, i.e., upward force. This provides excitation once in each vibration cycle, thereby reducing the attenuation of the device's vibration. This improves the Q value of the MEMS resonator and reduces its power consumption without increasing the vacuum level within the sealed cavity.
[0013] A preferred structure of the MEMS resonator is that the vibration electrode includes two connecting posts, which are respectively connected to both ends of the lower surface of the vibration plate.
[0014] By adopting the above technical solution, the two connecting columns provide strong support for the vibrating plate, making the vibration of the vibrating plate more stable, less prone to cracking, and with a long service life.
[0015] A preferred structure for this MEMS resonator is that the lower surface area of the vibrating plate is 20 to 100 times the cross-sectional area of the connecting column.
[0016] By adopting the above technical solution, the vibrating plate has both high vibratory capacity and high stability during vibration.
[0017] A preferred structure of this MEMS resonator is that the middle region of the upper surface of the vibrating plate is planar or convex curved. The outer peripheral region surrounds and connects to the middle region.
[0018] By adopting the above technical solution, the air viscous resistance above the vibrating plate is small and the air flow rate is fast, so that it will be excited once in each vibration cycle, thereby reducing the attenuation of device vibration.
[0019] A preferred structure of the MEMS resonator is that, at the edge of the vibrating plate, the angle between the outer periphery of the upper surface and the lower surface of the vibrating plate is 20~50°.
[0020] By adopting the above technical solution, the included angle is similar to the included angle between the upper and lower surfaces of an aircraft wing. During the upward vibration process, the vibrating plate experiences less airflow resistance, greater lift, and less vibration attenuation.
[0021] A preferred structure of the MEMS resonator includes an anchor pin in the upper electrode assembly. The anchor pin comprises a cap and a shank. The shank is connected upwards to the lower surface of the cap, extends downwards through the lower electrode layer, the nitride layer, and the upper oxide layer, and abuts against the silicon substrate. The upper surface of the cap is convex, and the lower surface is planar. The lower surface of the cap does not contact the lower electrode layer.
[0022] By adopting the above technical solution, the anchor connects the lower electrode layer, the nitride layer and the upper oxide layer in series, which can conduct heat from each layer. In addition, the upper surface of the anchor head is convex curved, which makes the vibration resistance of the upper surface of the anchor smaller and the attenuation of device vibration smaller.
[0023] A preferred structure of the MEMS resonator is that, at the edge of the nail head, the included angle between the lower and upper surfaces of the nail head is 20~50°.
[0024] By adopting the above technical solution, the included angle results in less air viscous resistance on the upper surface of the anchor and less vibration loss caused by the anchor.
[0025] A preferred structure of the MEMS resonator includes a conductive post. The conductive post extends from the lower surface of the silicon substrate to the upper surface of the silicon substrate. The portion of the upper oxide layer embedded in the silicon substrate encloses the conductive post.
[0026] By adopting the above technical solution, the conductive post is used for the transmission and detection of electrical signals. The conductive post and the silicon substrate are separated by an upper oxide layer, so that the conductive post and the silicon substrate form an insulating connection, which blocks the path of oxidation of the silicon substrate and protects the silicon substrate.
[0027] A preferred structure of the MEMS resonator includes a lower oxide layer and a bottom metal layer. The lower oxide layer covers the lower surface of the silicon substrate. A portion of the bottom metal layer covers the lower surface of the lower oxide layer, and another portion of the bottom metal layer is embedded in the lower oxide layer and abuts against the silicon substrate, without contacting the conductive post.
[0028] By employing the above technical solution, the lower oxide layer is used to protect the silicon substrate. The bottom metal layer is used for electrical connection with the outside.
[0029] Secondly, this application also proposes a method for fabricating the MEMS resonator, and adopts the following technical solution.
[0030] A method for fabricating a MEMS resonator as described above includes: S1, The silicon substrate is patterned by etching process, so that the silicon substrate forms the first window.
[0031] S2, a portion of the upper oxide layer is grown on the inner wall of the first window, and the first window is reduced to a second window.
[0032] S3, deposit a first epitaxial layer on the silicon substrate, and then pattern the first epitaxial layer by photolithography to obtain a conductive pillar existing in the second window.
[0033] S4, deposit a second epitaxial layer on the silicon substrate to obtain another portion of the upper oxide layer covering the silicon substrate.
[0034] S5, deposit a third epitaxial layer on the upper oxide layer to obtain the nitride layer.
[0035] S6, deposit a fourth epitaxial layer on the nitride layer, and pattern the fourth epitaxial layer by photolithography to obtain the lower electrode layer.
[0036] S7, deposit a sacrificial layer on the lower electrode layer, and use an etching process to make the sacrificial layer on the lower electrode layer at the two middle locations form two third windows.
[0037] S8, through an etching process, two fourth windows are formed by the sacrificial layer, the lower electrode layer, the nitride layer and the upper oxide layer that are longitudinally stacked on both outer sides.
[0038] S9, a fifth epitaxial layer is deposited on the sacrificial layer. Using photolithography, the fifth epitaxial layer is patterned by adjusting the temperature and gas flow rate of the photolithography process to obtain the anchor and the vibrating electrode. The vibrating electrode fills the third window and forms the vibrating plate above the sacrificial layer. The anchor fills the fourth window and forms the anchor head above the sacrificial layer.
[0039] S10, etch away the sacrificial layer.
[0040] By adopting the above technical solution and method, a MEMS resonator with a convex curved surface on the outer periphery of the upper surface of the vibration electrode and a convex curved surface on the upper surface of the anchor can be obtained. The lower surfaces of both the vibration electrode and the anchor are planar, similar to the upper and lower surface structure of an airplane wing. When the resonator drives the vibration electrode to vibrate and generate a resonant frequency, the wing-like structure of the vibration electrode helps to reduce air damping during the vibration process, thereby improving the Q value of the resonator. The anchor is used for heat dissipation, and its wing-like structure has small vibration damping at the anchor head, resulting in small vibration attenuation of the resonator and reducing the power consumption of the resonator.
[0041] In summary, the MEMS resonator and its fabrication method of this application have the following beneficial effects: Bonding and packaging can increase the vacuum level to improve the Q value of the resonator, but the device cannot reach an absolute vacuum, so the Q value of the resonator cannot be further improved. The solution in this application can further reduce the air damping while reducing the vacuum level of the device operation, thereby improving the Q value of the resonator.
[0042] Compared to solutions that rely on epitaxial sealing processes due to their high complexity and are unsuitable for aerospace applications, this solution represents a further structural improvement based on existing processes. It is less complex to implement, does not alter the basic structure or performance characteristics of the device, and can therefore be applied in the aerospace field.
[0043] The solution proposed in this application achieves a self-excitation effect, exciting the device once in each vibration cycle, enabling the device to resist losses caused by various damping to a certain extent, increasing the Q value while reducing the power consumption of the device. Attached Figure Description
[0044] Figure 1 The background technology involves a curve showing the Q-value of a MEMS resonator as a function of pressure.
[0045] Figure 2 This is a diagram of the first structure of a MEMS resonator.
[0046] Figure 3 This is a schematic diagram of the gas flow and damping effect when the moving electrode plate vibrates.
[0047] Figure 4 This is an image showing the etching effect on the top of the vibration electrode in a MEMS resonator.
[0048] Figure 5 This is a diagram of the second structure of a MEMS resonator.
[0049] Figure 6 This is a structural diagram of steps S1 to S4 in the fabrication method of a MEMS resonator.
[0050] Figure 7 The structural diagrams for steps S5 to S9 in the fabrication method of a MEMS resonator are shown.
[0051] Figure 8 This is a structural diagram of steps S10-S13 in the fabrication method of a MEMS resonator. Reference numerals: 1. Upper electrode assembly; 2. Lower electrode layer; 3. Nitride layer; 4. Upper oxide layer; 5. Silicon substrate; 11. Vibrating electrode; 111. Connecting post; 112. Vibrating plate; 1121. Outer peripheral region; 1122. Middle region; 12. Anchor pin; 121. Anchor pin cap; 122. Anchor pin rod; 13. Conducting post; 6. Lower oxide layer; 7. Bottom metal layer; 501. First window; 502. Second window; 8. Sacrificial layer; 801. Third window; 802. Fourth window; 601. Fifth window. Detailed Implementation
[0052] The present application will be further described below with reference to the accompanying drawings.
[0053] Currently, MEMS resonator products are divided into three main categories: the first category is a vertically aligned capacitor plate structure; the second category is a horizontal comb-like structure; and the third category is a disk- or polygonal structure based on Lamé modes, which is still in the research laboratory stage. All three types of structures are highly sensitive to air damping. This solution is more suitable for the first type of design. The second and third types of devices, due to their design limitations, have a larger mass and require higher vacuum levels, making them only suitable for epitaxial hermetically sealed packaging. This solution is designed specifically for bonded hermetically sealed packaging.
[0054] like Figure 2 A MEMS resonator includes an upper electrode assembly 1, a lower electrode layer 2, a nitride layer 3, an upper oxide layer 4, and a silicon substrate 5.
[0055] The silicon substrate 5 is made of silicon. Part of the upper oxide layer 4 covers the upper surface of the silicon substrate 5, and the other part is embedded in the silicon substrate 5.
[0056] like Figure 2The MEMS resonator also includes a conductive post 13. The conductive post 13 extends from the lower surface of the silicon substrate 5 to the upper surface of the silicon substrate 5. A portion of the upper oxide layer 4 embedded in the silicon substrate 5 encloses the conductive post 13, creating an insulated connection between the conductive post 13 and the silicon substrate 5. The conductive post 13 is used for the transmission and detection of electrical signals. The upper oxide layer 4 separates the conductive post 13 from the silicon substrate 5, preventing oxidation of the silicon substrate 5 and protecting it.
[0057] A nitride layer 3 covers the upper surface of the upper oxide layer 4. Both the nitride layer 3 and the upper oxide layer 4 are insulating layers, providing insulation and protection for the silicon substrate 5. The upper oxide layer 4 is easily worn, while the nitride layer 3 is more robust. However, the adhesion of the nitride layer 3 to the silicon substrate 5 is weaker, while the upper oxide layer 4 has better adhesion. Therefore, placing the upper oxide layer 4 between the nitride layer 3 and the silicon substrate 5 can improve the adhesion of the nitride layer 3 to the silicon substrate 5, while also providing wear resistance and long-term protection. The upper oxide layer 4 can be made of silicon dioxide. The nitride layer 3 can be made of materials such as silicon nitride or boron nitride.
[0058] The lower electrode layer 2 is deposited on top of the nitride layer 3. The material of the lower electrode layer 2 can be silver, which has good conductivity and is used for electrical connection to external devices.
[0059] The upper electrode assembly 1 includes a central vibrating electrode 11 and anchors 12 on both sides. The lower electrode layer 2 is used to fix the vibrating electrode 11. Specifically, the lower end of the vibrating electrode 11 is connected to the lower electrode layer 2, and the other parts of the vibrating electrode 11 are suspended above the lower electrode layer 2. The vibrating electrode 11 is used to generate a resonant frequency. The anchors 12 are used to connect the layers and dissipate heat.
[0060] like Figure 2 To reduce power consumption and vibration attenuation while maintaining a stable resonant frequency, this application designs a vibration electrode 11 with low air damping. Specifically, the outer peripheral region 1121 of the upper surface of the vibration electrode 11 is designed as a convex curved surface to reduce air damping, while the lower surface is designed as a planar surface to generate a stable oscillation signal. This structure can reduce vibration power consumption and vibration attenuation. The vibration electrode 11 can be made of silver, which has good vibration frequency stability.
[0061] The airflow and air damping of a typical vibrating electrode 11 during vibration are as follows: Figure 3As shown. The design of MEMS resonators is based on the resonance of the device itself. Due to the existence of damping, the vibration will gradually weaken. Therefore, the resonator needs DC and AC excitation to maintain effective vibration during operation. The vibration electrode 11 of this application imitates the principle of aircraft takeoff. When the aircraft moves in the air, the upper arc design reduces air resistance and guides the airflow, making the airflow speed above the wing faster and the airflow speed below slower. According to Bernoulli's principle, the air pressure on the upper surface of the wing is lower and the air pressure on the lower surface of the wing is higher, thus generating an upward lift force, which enables the aircraft to take off smoothly. Similarly, the outer peripheral region 1121 of the upper surface of the vibration electrode 11 is designed as a convex curved surface, and the lower surface is designed as a flat surface. When the vibration electrode 11 vibrates, the air viscous resistance on the upper surface of the vibration electrode 11 decreases with the arc of the curved edge, reducing air damping and accelerating the gas flow velocity at the edge, resulting in lower pressure on the upper surface of the vibration electrode 11. Since the lower surface of the vibration electrode 11 is a flat surface, the airflow is relatively slow, and the air pressure is larger than that on the upper surface of the vibration electrode 11, forming a pressure difference, i.e., upward force. This provides an excitation in each vibration cycle, reducing the attenuation of device vibration, improving the Q value of the MEMS resonator, and reducing the power consumption of the device.
[0062] like Figure 2 The vibrating electrode 11 includes two connecting posts 111 and a vibrating plate 112. Each connecting post 111 is connected upward to one end of the lower surface of the vibrating plate 112, and the connecting post 111 is connected downward to the lower electrode layer 2. The other positions of the vibrating plate 112 are suspended.
[0063] The outer peripheral area 1121 of the upper surface of the aforementioned vibrating electrode 11 is convex curved, while the lower surface is designed to be planar. Similarly, the outer peripheral area 1121 of the upper surface of the vibrating plate 112 is convex curved, and the lower surface of the vibrating plate 112 is designed to be planar. To generate stable vibration, the area of the lower surface of the vibrating plate 112 can be designed to be 20 to 100 times the cross-sectional area of the connecting column 111, for example, 50 times.
[0064] like Figure 4 The middle area 1122 of the upper surface of the vibrating plate 112 can be planar, and the outer peripheral area 1121 is smoothly connected to the periphery of the middle area 1122.
[0065] like Figure 5 The middle area 1122 of the upper surface of the vibrating plate 112 can also be a convex curved surface, so that the upper surface of the vibrating plate 112 forms a uniform convex curved surface.
[0066] The middle area 1122 of the upper surface of the vibrating plate 112 is either planar or convex curved, which can make the vibrating electrode 11 vibrate regularly. Combined with the shape of the upper and lower surfaces of the vibrating electrode 11, it can obtain upward excitation during the vibration process, reduce vibration attenuation, and reduce device power consumption.
[0067] refer to Figure 4 At the edge of the vibrating plate 112, the angle between the lower and upper surfaces of the vibrating plate 112 is 20~50°, for example, 44°. This angle at the edge may not be equal everywhere; in practice, due to manufacturing reasons, the angle at different locations at the edge generally has slight differences. This angle range is comparable to the angle between the upper and lower surfaces of an airfoil. During vibration, the vibrating plate 112 experiences a significant buoyancy force from the surrounding gas environment, which provides upward excitation during vibration, reducing vibration attenuation and lowering device power consumption.
[0068] like Figure 2 Each anchor 12 includes a head 121 and a shank 122. The shank 122 is connected to the lower surface of the head 121. The shank 122 passes through the lower electrode layer 2, the nitride layer 3, and the upper oxide layer 4, and abuts against the silicon substrate 5. The head 121 is shaped similarly to a vibrating plate 112, with its upper surface being approximately spherical and its lower surface being planar. The anchor 12 is used to connect the aforementioned layers in series, providing heat dissipation for the lower electrode layer 2, the nitride layer 3, the upper oxide layer 4, and the silicon substrate 5. The spherical upper surface of the head 121 results in lower vibration resistance, reducing device vibration attenuation, improving the device's Q value, and lowering power consumption.
[0069] The anchor 121 and the vibrating plate 112 are formed in the same process. The included angle between the lower and upper surfaces of both is approximately equal. At the edge of the anchor 121, the included angle between the lower and upper surfaces is 20-50°, for example, 40-50°. This edge angle structure of the anchor 12 mimics the structure of an airfoil, resulting in low vibration loss and low airflow resistance on the upper surface, thus improving the Q value of the device.
[0070] like Figure 5 The MEMS resonator also includes a lower oxide layer 6 and a bottom metal layer 7. The lower oxide layer 6 covers the lower surface of the silicon substrate 5 and protects the silicon substrate 5. A portion of the bottom metal layer 7 is deposited on the lower surface of the lower oxide layer 6, and another portion is embedded in the oxide layer 6 and abuts against the silicon substrate 5. However, the bottom metal layer 7 is not connected to the conductive post 13. This bottom metal layer 7 is used to achieve electrical connection with the outside world. Adjusting the electrical parameters can adjust the vibration frequency of the resonator.
[0071] refer to Figure 6 and Figure 7 The fabrication method of the above MEMS resonator includes the following steps: S1, the silicon substrate 5 is patterned through an etching process, forming four first windows 501 in the silicon substrate 5. The silicon substrate 5 is made of silicon.
[0072] S2, protect the upper and lower surfaces of the silicon substrate 5, introduce oxygen, heat the silicon substrate 5, control the heating time, grow silicon dioxide on the inner wall of each first window 501, that is, a part of the upper oxide layer 4, and the first window 501 shrinks into the second window 502.
[0073] S3, the upper surface of the silicon substrate 5 is exposed. A first epitaxial layer is deposited on the silicon substrate 5. The first epitaxial layer can be made of materials such as copper or aluminum. This first epitaxial layer fills the second window 502 and the upper surface of the silicon substrate 5. Then, the first epitaxial layer is patterned by photolithography to obtain conductive pillars 13 that exist only in the four second windows 502. The conductive pillars 13 can be used for optical communication, electrical sensing, etc. The conductive pillars 13 are wrapped by the upper oxide layer 4, thereby isolating them from the silicon substrate 5, reducing the oxidation effect of the conductive pillars 13 on the silicon substrate 5, and reducing the occurrence of short circuits.
[0074] S4, a second epitaxial layer is deposited on the silicon substrate 5 to obtain another portion of the upper oxide layer 4 covering the silicon substrate 5. This portion of the upper oxide layer 4 is connected to the upper oxide layer 4 encapsulating the conductive post 13. The material of the second epitaxial layer can be the same as that of the first epitaxial layer, for example, both can be silicon dioxide.
[0075] S5, deposit a third epitaxial layer on the upper oxide layer 4 to obtain the nitride layer 3. This step can be performed using chemical vapor deposition, by introducing ammonia and silane to excite plasma and deposit silicon nitride to obtain the silicon nitride layer.
[0076] S6, deposit the fourth epitaxial layer on the nitride layer 3, and pattern the fourth epitaxial layer by photolithography to obtain the lower electrode layer 2, which contains four modules.
[0077] S7, a sacrificial layer 8 is deposited on the lower electrode layer 2. Through an etching process, two third windows 801 are formed on the sacrificial layer 8 above the two middle modules of the lower electrode layer 2. The sacrificial layer 8 can be made of polycrystalline silicon.
[0078] S8, through an etching process, the sacrificial layer 8, the lower electrode layer 2, the nitride layer 3 and the upper oxide layer 4 stacked vertically form two fourth windows 802 at the two module positions outside the lower electrode layer 2.
[0079] S9, a fifth epitaxial layer is deposited on the sacrificial layer 8, filling the third window 801 and the fourth window 802. Using photolithography, suitable temperature and gas flow parameters can be obtained through multiple experiments. The fifth epitaxial layer is then patterned to obtain the target shape of the vibrating plate 112 and the anchor 121. The vibrating plate 112 and the epitaxial material filling the third window 801 constitute the vibrating electrode 11, and the anchor 121 and the epitaxial material filling the fourth window 802 constitute the anchor 12. The material of the fifth epitaxial layer can be the same as that of the first epitaxial layer, for example, both being copper or both being aluminum.
[0080] S10, Etching to remove sacrificial layer 8. Taking polycrystalline silicon as an example, this removal method can be achieved by introducing xenon fluoride gas to remove the polycrystalline silicon.
[0081] refer to Figure 8 The above MEMS resonator can be further fabricated using the following steps.
[0082] S11, deposit an oxide layer 6 on the lower surface of the silicon substrate 5. The material of the lower oxide layer 6 can be the same as that of the upper oxide layer 4, for example, both being silicon dioxide.
[0083] S12, pattern the lower oxide layer 6 so that the lower oxide layer 6 forms two fifth windows 601.
[0084] S13, a metal layer, such as silver, copper, or aluminum, is deposited on the lower surface of the lower oxide layer 6, and then patterned to obtain a bottom metal layer 7. A portion of the bottom metal layer 7 fills the fifth window 601, and another portion adheres to the lower surface of the oxide layer 6. The bottom metal layer 7 is used for electrical connection with external devices.
[0085] Using the above-described fabrication method, a MEMS resonator can be obtained with a convex curved surface outer peripheral region 1121 on the upper surface of the vibration electrode 11 and an approximately spherical upper surface on the anchor 12. When the resonator drives the vibration electrode 11 to vibrate, the wing-like structure of the vibration electrode 11 helps to reduce air damping during the vibration process. The air pressure on the upper surface is lower than that on the lower surface, which can create a pressure difference between the upper and lower electrode plates, thereby giving the electrode plates an upward force and achieving a self-excitation effect. It is excited once in each vibration cycle, enabling the device to resist the losses caused by various damping, increasing the Q value while reducing the power consumption of the device.
[0086] The above are merely preferred embodiments of this application and are not intended to limit the scope of protection of this application. Those skilled in the art can make various equivalent substitutions and modifications based on the above description, and all such substitutions and modifications should be covered within the scope of protection of this application.
Claims
1. A MEMS resonator, characterized in that, It includes an upper electrode assembly (1), a lower electrode layer (2), a nitride layer (3), an upper oxide layer (4), and a silicon substrate (5); The upper oxide layer (4) covers the upper surface of the silicon substrate (5) and is embedded in the silicon substrate (5); the nitride layer (3) covers the upper surface of the upper oxide layer (4); the lower electrode layer (2) is deposited on the nitride layer (3); the upper electrode assembly (1) includes a vibrating electrode (11). The vibrating electrode (11) includes a vibrating plate (112) and a plurality of connecting posts (111); the lower surface of the vibrating plate (112) is planar, and the outer peripheral area (1121) of the upper surface is convex curved. Each of the connecting posts (111) connects the lower surface of the vibrating plate (112) to the lower electrode layer (2), while the other positions of the vibrating plate (112) are suspended.
2. The MEMS resonator according to claim 1, characterized in that, The vibration electrode (11) includes two connecting posts (111), which are respectively connected to the two ends of the lower surface of the vibration plate (112).
3. The MEMS resonator according to claim 1, characterized in that, The area of the lower surface of the vibrating plate (112) is 20 to 100 times the cross-sectional area of the connecting column (111).
4. The MEMS resonator according to claim 1, characterized in that, The middle area (1122) of the upper surface of the vibrating plate (112) is planar or convex curved; the outer peripheral area (1121) surrounds and connects the middle area (1122).
5. The MEMS resonator according to claim 4, characterized in that, At the edge of the vibrating plate (112), the angle between the outer peripheral area (1121) of the upper surface and the lower surface of the vibrating plate (112) is 20~50°.
6. The MEMS resonator according to any one of claims 1 to 4, characterized in that, The upper electrode assembly (1) further includes an anchor (12); the anchor (12) includes a head (121) and a shank (122); the shank (122) is connected upward to the lower surface of the head (121), passes downward through the lower electrode layer (2), the nitride layer (3) and the upper oxide layer (4), and abuts against the silicon substrate (5); the upper surface of the head (121) is convex curved, and the lower surface of the head (121) is planar; the lower surface of the head (121) does not contact the lower electrode layer (2).
7. The MEMS resonator according to claim 6, characterized in that, At the edge of the nail head (121), the angle between the lower surface and the upper surface of the nail head (121) is 20~50°.
8. The MEMS resonator according to claim 6, characterized in that, The MEMS resonator also includes a conductive post (13); the conductive post (13) penetrates from the lower surface of the silicon substrate (5) to the upper surface of the silicon substrate (5); the upper oxide layer (4) partially encapsulates the conductive post (13) within the silicon substrate (5).
9. The MEMS resonator according to claim 8, characterized in that, The MEMS resonator also includes a lower oxide layer (6) and a bottom metal layer (7); the lower oxide layer (6) covers the lower surface of the silicon substrate (5); a portion of the bottom metal layer (7) covers the lower surface of the lower oxide layer (6), and another portion of the bottom metal layer (7) is embedded in the lower oxide layer (6) and abuts against the silicon substrate (5), and the bottom metal layer (7) does not contact the conductive post (13).
10. A method for fabricating a MEMS resonator as described in claim 8 or 9, characterized in that, include: S1, the silicon substrate (5) is patterned by etching process, so that the silicon substrate (5) forms a first window (501). S2, a portion of the upper oxide layer (4) is grown on the inner wall of the first window (501), and the first window (501) is reduced to a second window (502). S3, deposit a first epitaxial layer on the silicon substrate (5), and then pattern the first epitaxial layer by photolithography to obtain a conductive pillar (13) existing in the second window (502). S4, deposit a second epitaxial layer on the silicon substrate (5) to obtain another portion of the upper oxide layer (4) covering the silicon substrate (5). S5, deposit a third epitaxial layer on the upper oxide layer (4) to obtain the nitride layer (3). S6, deposit a fourth epitaxial layer on the nitride layer (3), and pattern the fourth epitaxial layer by photolithography to obtain the lower electrode layer (2). S7, deposit a sacrificial layer (8) on the lower electrode layer (2), and through an etching process, make the sacrificial layer (8) on the lower electrode layer (2) at the two middle locations form two third windows (801). S8, through an etching process, the sacrificial layer (8), the lower electrode layer (2), the nitride layer (3) and the upper oxide layer (4) with longitudinal stacking on both outer sides form two fourth windows (802). S9, a fifth epitaxial layer is deposited on the sacrificial layer (8). The fifth epitaxial layer is patterned by adjusting the temperature and gas flow rate of the photolithography process to obtain the anchor (12) and the vibration electrode (11). The vibration electrode (11) fills the third window (801) and forms the vibration plate (112) above the sacrificial layer (8). The anchor (12) fills the fourth window (802) and forms the nail head (121) above the sacrificial layer (8). S10, etch away the sacrificial layer.