CN115622528A - A MEMS resonator system - Google Patents

Abstract

The invention discloses a MEMS resonator system. The entire resonator system includes six resonant rings, coupling beams connecting the resonant rings, driving/detecting electrodes located inside and outside the rings, and a central anchor point that fixes the entire structure. Each resonant ring vibrates in a breathing mode, and the coupled beam vibrates in a longitudinal extension mode. The symmetrical hexagonal structure of the system improves stability and impact resistance, good modal coupling with a single anchor point reduces energy loss, multiple ring structures and the arrangement of inner and outer electrodes increase the coupling electrode area and improve The electromechanical coupling coefficient is increased, the output power is increased, the parallel arrangement of six resonant rings and coupling beams reduces the dynamic resistance, and the differential drive and detection reduces the complexity of the back-end maintenance circuit.

Description

A MEMS resonator system

technical field

The invention relates to the technical field of RF-MEMS, in particular to a MEMS resonator system.

Background technique

One of the bottlenecks of radio frequency and microwave communication systems is the lack of passive devices with high Q value (quality factor, ~1000) in the matching circuit. At present, the Q value of the device processed by the standard IC process is low, and the Q value of the spiral inductor Only around 100, so how to obtain a resonator with a high Q value is one of the hot spots in the current research of radio frequency microwave systems. Although other devices such as quartz-based resonators and film bulk acoustic resonators (FBARs) have been used in many devices, these devices are difficult to integrate with the corresponding control circuits, occupy a large volume and require high cost for mass production. Therefore, traditional radio frequency microwave technology is difficult to adapt to the development of microwave communication field.

Silicon-based micro-electromechanical systems (MEMS) technology can break through these difficulties. As the main material for MEMS manufacturing, silicon has excellent electrical properties, is compatible with IC processes, and can be effectively integrated and produced at low cost. And the silicon-based MEMS resonator has a higher Q value and a higher resonance frequency, which is helpful for the development of higher frequency band resources. Therefore, silicon-based MEMS resonators have great potential for development.

Besides high Q value, high electromechanical coupling coefficient, low dynamic impedance and high output power are also crucial for resonators. High electromechanical coupling coefficient can improve energy utilization, low dynamic impedance can reduce the difficulty of impedance matching in peripheral circuits, and high output power can improve the signal-to-noise ratio of the resonator and optimize the phase noise performance of the entire system.

However, silicon-based MEMS resonators have problems such as low electromechanical coupling coefficient and large dynamic resistance. Although they can be improved by increasing the bias voltage, this leads to breakdown and cost problems, and the degree of improvement is limited. Aiming at the above problems, a solution is proposed as follows.

Contents of the invention

The purpose of the present invention is to provide a MEMS resonator system, which has the advantages of high Q value, high frequency, high electromechanical coupling coefficient, low dynamic resistance and high output power.

Above-mentioned technical purpose of the present invention is achieved through the following technical solutions:

A MEMS resonator system comprising

There are six resonant rings, and the structures of the six resonant rings are the same; coupling beams, each of which is connected to two resonant rings;

A central anchor point, the central anchor point is located at the center of the entire system, and the central anchor point is used to support several coupling beams;

Driving/detecting electrodes, the driving/detecting electrodes are located on the inner side and the outer side of the resonant ring respectively.

Preferably, the six resonant rings work in breathing mode, and in the breathing mode, the resonant structure of the resonant ring expands or contracts radially.

Preferably, the length of the coupling beams is 1/2 of the resonant wavelength of the resonant ring, several coupling beams are evenly distributed around the central anchor point, and the angle between two adjacent coupling beams is 60 degrees.

Preferably, the connection point between the coupling beam and the resonant ring is the maximum amplitude position of the coupling beam, and the connection point between the coupling beam and the central anchor point is the minimum amplitude position of the coupling beam.

Preferably, the driving/detecting electrodes include all electrodes inside and outside the six resonant rings, and at least one driving electrode of the resonant ring is connected to an external AC source.

Preferably, a DC voltage is coupled to the central anchor point, and the DC voltage is used to provide a DC bias for the system.

Preferably, the drive/detection electrodes include drive electrodes and detection electrodes, the drive electrodes are simultaneously set on the outer or inner electrodes of the six resonant rings, and the detection electrodes are also set on the other side electrodes, which is defined as a single-way mode.

Preferably, the drive electrodes include positive drive electrodes and negative drive electrodes, the detection electrodes include positive detection electrodes and negative detection electrodes, and the positive drive electrodes and positive detection electrodes are simultaneously arranged on the outside and inside of three adjacent resonant rings The electrodes, the negative drive electrode and the negative detection electrode are arranged on the inner and outer electrodes of the other three resonators, defined as differential mode.

Preferably, the resonant ring, the coupling beam, the central anchor point and the driving/detecting electrode are made of polysilicon, single crystal silicon, SiC or piezoelectric material.

The beneficial effects of the present invention are: the six resonant rings are constructed of raw materials such as monocrystalline silicon, and work in the breathing mode at the same time, the coupling beam works in the longitudinal extension mode, the mode coupling is good, and the single anchor point is supported on the vibration node of the coupling beam location, reducing energy loss and meeting high Q value requirements;

Multiple ring structures and the use of inner and outer electrodes are used to increase the coupling area and improve the electromechanical coupling coefficient;

The six resonant rings make full use of the space, and the symmetrical structure improves the impact resistance of the resonator;

The array construction of six resonant rings improves the output power of the entire resonator system and optimizes the phase noise performance of the system.

The driving electrodes and detecting electrodes are located in different resonant rings, and three coupling beams are evenly arranged around a central point every 60 degrees to realize the parallel connection of dynamic resistance and reduce the dynamic resistance of the whole system.

Description of drawings

FIG. 1 is a schematic diagram of the overall structure of a multi-ring MEMS resonator system according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of the breathing mode in the finite element analysis of the resonant ring.

Fig. 3 is a schematic diagram of finite element analysis of a resonant system composed of a resonant ring and a coupling beam.

Fig. 4 is a schematic diagram of a differential driving mode of a resonant system composed of two resonant rings and a coupling beam.

Fig. 5 is a schematic diagram of finite element analysis of a resonant system composed of two resonant rings and coupling beams.

FIG. 6 is a schematic diagram of a differential driving mode according to an embodiment of the present invention.

7 is a schematic diagram of the finite element analysis of the breathing mode of the multi-ring MEMS resonator system according to the embodiment of the present invention.

Reference signs: 1. Resonant ring; 2. Coupling beam; 3. Inner electrode; 4. Outer electrode; 5. Central anchor point.

detailed description

The invention provides an embodiment and a specific construction method of a multi-ring MEMS resonator system. "Resonator" refers to a structure that can provide the desired resonant frequency. When the resonant ring of the present invention is matched with an external drive circuit, it will expand or contract in a breathing mode at a fixed resonant frequency, and the coupling beam will extend longitudinally at the same frequency. , the center of the structure of coupled beams can be used to anchor the entire resonator system, supporting the entire structure.

As shown in Figure 1, a multi-ring MEMS resonator system includes: six resonant rings, all working in the breathing mode; three coupling beams, connected to the resonant rings to couple and transfer energy, working in the longitudinal extension mode The largest amplitude is the coupling point, which is evenly arranged every 60 degrees around the center. The resonant frequency of the coupling beam in the longitudinal extension mode is equal to the resonant frequency of the resonant ring working in the breathing mode. Each resonant ring is provided with an inner electrode and an outer electrode. The inner electrode is located on the inner side of each resonant ring and can be connected to a driving electrode or a detection electrode; the outer electrode is located on the outer side of each resonant ring and can be connected to a driving electrode or The detection electrode; the central support structure is arranged at the center of the coupling beam to support the entire structure.

As shown in Figure 2, according to the finite element analysis, it can be seen that when the driving frequency reaches the resonant frequency of the resonant ring, the resonant ring vibrates in the breathing mode. Breathing mode refers to the radial vibration of the ring structure. This behavior of the resonator can be explained by wave theory. When there is a full-cycle or half-cycle standing wave in the resonator, the resonator ring will expand and contract. The specific acquisition of the resonant frequency that can cause the resonant ring to vibrate in the breathing mode can be obtained according to the following calculation formula:

Wherein, f is the resonant frequency, L is the circumference of the resonant ring, E is the Young's modulus of the structural material, ρ is the mass density of the structural material, ri is the radius of the inner wall of the resonant ring, and _w is the width of the resonant ring.

As shown in Fig. 3, the length of the coupling beam is 1/4 of the resonant wavelength of the resonant ring, wherein the resonant wavelength of the resonant ring is equal to the circumference of the resonant ring (λ=L=2π(ri+ _w /2)). The left end of the coupling beam is coupled with the resonant ring, and the right end is the anchor point. The resonant ring resonates in the breathing mode, and the coupling beam vibrates in the longitudinal extension mode, and the vibration frequency is consistent with the resonant frequency of the resonant ring, so good coupling can be performed at the connection.

The Q value of a resonator can be expressed by dividing the energy stored by the energy dissipated during mechanical vibration, that is:

Energy dissipation can be attributed to several loss mechanisms, mainly including anchor point loss, load loss, air damping loss, and volume and area defects. Among them, the load loss is much larger than the load due to the structural impedance of silicon materials, so the load loss can Negligible; the entire structure can be vacuum-sealed, eliminating the loss of air damping, while the entire resonator system is bulk vibration, with little influence from volume and surface defects, and low loss. The connection between the resonant ring and the resonant beam achieves good modal coupling. The whole structure has only one supporting anchor point, which is located at the node of vibration, which reduces the loss of the anchor point, thus realizing the requirement of a high Q value.

Fig. 4 is a schematic diagram of a basic resonant system formed by two resonant rings and coupling beams, including inner electrodes and outer electrodes, and an anchoring support is provided in the middle of the coupling beams for support.

As shown in Figure 4, a DC bias (Vdc) is applied to the anchor 12 and coupled to the ground, the same magnitude, and the opposite AC voltage (Vac) is applied as a drive (Drive) signal to the outer electrode 6 and the inner electrode 6 respectively. On the electrode 11, the applied voltage generates a time-varying electrostatic excitation force between the resonators, and the electrostatic force can be expressed by the following formula:

In the formula, F is the electrostatic force, A is the relative area of the coupling capacitance between the electrode and the ring, d is the gap distance between the electrode and the ring, x is the distance changed when the resonant ring vibrates (x<<d), ε ₀ is the dielectric constant of vacuum, and ω is the AC voltage frequency. If the changing frequency ω of the electrostatic force is the same as the natural frequency of the resonator, the driving force component with this frequency is amplified by the DC voltage, and the resonator resonates to vibrate in a breathing mode.

When the resonator system vibrates, the resonant ring will vibrate between the inner electrode and the outer electrode in a breathing mode, which will cause periodic changes in the capacitance between the ring structure and the electrodes, if the inner electrode is used as a driving electrode and the outer electrode is used as a detection Electrode, applied DC bias (Vdc) plus periodic AC drive signal, the AC signal can be detected at the output terminal of the detection electrode.

The capacitive electromechanical coupling coefficient can be expressed by the following formula:

In the formula, _ηcap represents the capacitive electromechanical coupling coefficient, A is the electrode area, Vdc is the DC bias voltage, _ε0 is the vacuum dielectric constant, and d is the distance between the electrode and the ring. Compared with the disc structure, which can only use the outer surface as the electrode coupling surface, the ring structure with inner and outer electrodes provides a larger electrode area and improves the electromechanical coupling coefficient.

The resonator structure can be equivalent with a series RLC model, where the dynamic impedance can be expressed as:

In the formula, b is the damping coefficient. It can be seen that the multi-ring structure combined with the large coupling area brought by the inner and outer electrodes can reduce the dynamic impedance while ensuring a high coupling coefficient.

Fig. 5 is a schematic diagram of the finite element analysis of the structure shown in Fig. 4. As shown in the figure, the two resonant rings vibrate in the breathing mode, and the coupling beam vibrates in the longitudinal extension mode. It can be seen from Fig. 5 that a solid The support does not affect the vibration of the structure.

Fig. 6 is a schematic diagram of the differential drive of the embodiment of the present invention, the positive pole of the AC driving voltage is applied to the outer electrodes of three adjacent rings, the negative pole is applied to the inner electrodes of the other three rings, and the remaining inner and outer electrodes Get detection voltage.

7 is a schematic diagram of the finite element analysis of the multi-ring MEMS resonator system of the embodiment of the present invention. The structural material is single crystal silicon, the Young's modulus is 168GPa, the mass density is 2.33g/cm ³ , the Poisson's ratio is 0.29, and the resonant ring The inner radius is ri=24 μm, the outer radius is ro=32 μm, the length of the coupling beam is 88 μm, and the resonance frequency of the whole system is 48.6 MHz. All six resonant rings resonate in the same breathing mode. The whole system can be regarded as six structures shown in Figure 3 arranged at intervals of 60 degrees, all anchored on the central support structure.

The dynamic impedance of the MEMS resonant ring can be extended to formula (6), where the parameter m _r is the equivalent mass of the ring, _ω0 is the resonant frequency, A is the relative area of the coupling capacitance between the electrode and the ring, d is the electrode and the ring The gap distance between the rings, _ε0 is the vacuum permittivity, Vdc is the _DC bias voltage, and Q is the quality factor of the resonator. Due to the limitations of factors such as technology or power, the DC bias voltage cannot be too high, so the coupling area and gap distance can only be adjusted. The setting of the inner and outer ring electrodes can increase the coupling area, and since the resonant frequency of the resonant ring is not affected by the thickness, the method of increasing the thickness can be increased within the limit of the process, while maintaining the high resonant frequency and high Q value, increasing the coupling area to reduce dynamic impedance. The simplest resonator system can be formed by combining double rings with coupling beams. The multi-ring structure is equivalent to the combination of three double ring systems at the central anchor point. The dynamic impedance can also be regarded as the parallel connection of the dynamic impedance of the three double ring systems. The overall six-ring MEMS resonator system has a smaller dynamic impedance.

In the reference oscillator used in the field of radio frequency communication, the phase noise near and far from the carrier should be reduced as much as possible, especially the phase noise near the carrier. The SSB phase noise and carrier power ratio L{fm} at a frequency fm close to the carrier frequency can be expressed by a formula similar to the Leeson equation

Among them, P _N is the noise power, P _O is the output power of the resonator, i _N is the noise current, and i _O is the output current of the resonator. It can be seen that the noise performance can be optimized by improving the Q value and increasing the output current.

It can be seen from Equation 8 that through the design of six resonant rings, the coupling area can be increased to increase the output current, so that the output power of the resonator system is higher than that of a single ring resonator, and the noise performance is optimized.

The above-mentioned specific implementation method has carried out a more detailed introduction to the purpose, technical advantages and implementation methods of the present invention. It should be understood that the above description is only a specific embodiment of the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (9)

1. A MEMS resonator system comprising

The resonator comprises six resonator rings (1), wherein the structures of the six resonator rings (1) are the same;

the coupling beam (2), each coupling beam (2) is connected with two resonance rings (1);

the central anchor point (5) is positioned in the center of the whole system, and the central anchor point (5) is used for supporting a plurality of coupling beams (2);

drive/detection electrodes respectively located inside and outside the resonance ring (1).

2. A MEMS resonator system according to claim 1, characterized in that six of said resonant rings (1) operate in a breathing mode, in which the resonant structure of the resonant rings (1) expands or contracts radially.

3. A MEMS resonator system according to claim 1, characterized in that the length of the coupling beams (2) is 1/2 of the resonance wavelength of the resonance ring (1), several coupling beams (2) are distributed evenly around the central anchor point (5), and the angle between two adjacent coupling beams (2) is 60 degrees.

4. A MEMS resonator system according to claim 3, characterized in that the coupling beam (2) and the resonance ring (1) are connected at the maximum amplitude position of the coupling beam (2), and the coupling beam (2) and the central anchor point (5) are connected at the minimum amplitude position of the coupling beam (2).

5. A MEMS resonator system according to claim 1, characterized in that the drive/sense electrodes comprise all electrodes inside and outside the six resonant rings (1), and that the drive electrode of at least one of the resonant rings (1) is connected to an external alternating current source.

6. A MEMS resonator system according to claim 1, characterized in that a dc voltage is coupled at the central anchor point (5), said dc voltage being used to provide a dc bias to the system.

7. A MEMS resonator system according to claim 1, characterized in that the drive/detection electrodes comprise drive electrodes and detection electrodes, the drive electrodes being arranged simultaneously on the outer or inner electrodes (3) of the six resonant rings (1), and the detection electrodes being arranged simultaneously on the other side, defining a single-pass mode.

8. A MEMS resonator system according to claim 1, characterized in that the driving electrodes comprise positive driving electrodes and negative driving electrodes, the detection electrodes comprise positive detection electrodes and negative detection electrodes, the positive driving electrodes and the positive detection electrodes are arranged on the outer and inner electrodes (3) of three adjacent resonator rings (1) simultaneously, and the negative driving electrodes and the negative detection electrodes are arranged on the inner and outer electrodes (4) of the other three resonators, defining a differential mode.

9. A MEMS resonator system according to claim 1, characterized in that the materials of the resonance ring (1), the coupling beam (2), the central anchor point (5) and the drive/detection electrodes are polysilicon, monocrystalline silicon, siC or piezoelectric materials.

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