Low-loss planar vibration double-tuning-fork resonator based on AlN-on-Si structure

Abstract

The invention belongs to the technical field of micro electro mechanical systems (MEMS), and particularly provides a low-loss planar vibration double-tuning-fork resonator based on an AlN-on-Si structure. The double-tuning-fork resonator provided by the invention comprises resonant beams, coupling beams, anchor points, piezoelectric layers, metal layers and insulating layers, the two resonant beams are connected through the double-end coupling beams, and then double-end fixing constraint is carried out through the anchor points on the two sides; the piezoelectric layer and the metal layer on the surface of the resonant beam form an active area, and the active areas are arranged on the upper surface and the lower surface of the resonant beam at the same time and used for exciting an in-plane mode of the double-tuning-fork resonator, limiting out-of-plane displacement, reducing energy dissipation between an anchor point and the outside, achieving low loss and a high Q value, and improving the performance of the double-tuning-fork resonator. The complicated snakelike electrode design in the prior art is also avoided; furthermore, a clamping coupling beam structure is introduced between the two resonant beams, the displacement of the resonator is further limited in a plane, meanwhile, the area and the displacement of an active region are increased, and the signal strength is improved.

Description

Technical Field

[0001] This invention belongs to the field of micro-electro-mechanical systems (MEMS) technology, specifically providing a low-loss planar vibrating double tuning fork resonator based on an aluminum nitride-on-silicon (AlN-on-Si) structure. Background Technology

[0002] As core frequency control components in modern communication, sensing, and timing systems, the performance of microelectromechanical systems (MEMS) resonators directly determines the key performance characteristics of modules such as the size, accuracy, and power consumption of RF front-ends, sensors, and oscillators. With the rapid development of 5G and future mobile communications, the Internet of Things (IoT), and wearable devices, there is an urgent need for resonators with higher frequencies, smaller sizes, lower power consumption, higher quality factors (Q values), and compatibility with semiconductor processes. Quartz crystal resonators have attracted widespread attention due to their excellent mechanical and physical properties, such as low power consumption, high stability, and high quality factor. However, limitations in the processing of quartz materials and their relatively low intrinsic frequency make it difficult to miniaturize and increase the frequency of quartz crystal resonators, and they are also incompatible with integrated circuit processes. Resonators based on aluminum nitride-on-silicon (AlN-on-Si) piezoelectric thin film structures operate through piezoelectric transduction. Compared to the more commonly used capacitive transduction resonators, they do not require a DC bias voltage or operate in a high vacuum environment. Piezoelectric resonators are characterized by their small size, high electromechanical conversion efficiency, and ability to achieve a high quality factor under atmospheric pressure. They are also compatible with complementary metal-oxide-semiconductor (CMOS) processes, which reduces the complexity of design and packaging and facilitates lower manufacturing costs. Therefore, they are widely regarded as one of the most promising structures to replace quartz crystal resonators.

[0003] The double tuning fork resonator is a classic resonator design widely used in aluminum nitride thin film structures on silicon. It converts strain into changes in resonant frequency to achieve sensing functions such as temperature, acceleration, and magnetic fields. Depending on the displacement direction of the resonant beams, it has two operating modes: in-plane and out-of-plane. Traditional double tuning fork resonators generally operate in the out-of-plane mode. In this mode, the vibration of the two resonant beams is asymmetrical, requiring additional stress to be applied through anchor points to maintain momentum balance. This results in energy loss in the interaction between the anchor points and the external environment, leading to a decrease in the Q value. In contrast, operating in the in-plane mode involves nearly perfect symmetry, allowing the resonator to maintain momentum balance on its own without the need for additional stress through anchor points. Currently, many designs for exciting in-plane modes use serpentine electrode structures. These require changing the electrode orientation at specific locations on the resonant beams according to the stress polarity boundary to alter the strain direction, making the design complex. Furthermore, in-plane modes are often accompanied by some out-of-plane displacement, causing anchor point losses, stress cancellation, and signal strength reduction. Therefore, it is necessary to provide an in-plane vibrating double tuning fork resonator with a simple structure and low loss. Summary of the Invention

[0004] The purpose of this invention is to provide a low-loss planar vibration dual tuning fork resonator based on an AlN-on-Si structure. It employs a double-ended structure with active regions simultaneously located above and below the resonant beam. This structure is used to excite in-plane modes, avoiding the complex serpentine electrode design found in existing technologies. This invention effectively limits out-of-plane displacement, reduces energy dissipation between the anchor point and the external environment, achieves low loss, and achieves a high quality factor (Q value) under one atmosphere of pressure. Simultaneously, it increases electromechanical coupling efficiency and improves signal strength.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A low-loss planar vibrating double tuning fork resonator based on an AlN-on-Si structure includes: a resonant beam, a piezoelectric layer, a metal electrode layer, a coupling beam, anchor points, and an insulating layer; characterized in that:

[0007] The double tuning fork resonator is centrally symmetrical, with two resonant beams connected in parallel between two coupling beams, and the outer sides of the two coupling beams are fixed at both ends by anchor points;

[0008] The upper and lower surfaces of the resonant beam are symmetrically arranged, with active and passive regions arranged on each surface. The two active regions are arranged at both ends of the resonant beam, and the passive region is arranged between the two active regions. The active regions on the upper and lower surfaces of the resonant beam are respectively provided with an upper piezoelectric layer and a lower piezoelectric layer. The upper surface of the upper piezoelectric layer is provided with an upper metal electrode layer, and the lower surface of the lower piezoelectric layer is provided with a lower metal electrode layer. The upper and lower metal electrode layers serve as the input and output terminals of the double tuning fork resonator, respectively, forming a double-ended resonator.

[0009] Furthermore, both the upper and lower metal electrode layers adopt a rectangular ring structure, and an insulating layer is set between the metal electrode layers and the resonant beam, and an insulating layer is also set between the metal electrode layers and the coupling beam.

[0010] Furthermore, the area of ​​the active region on the surface of the resonant beam accounts for 20% to 80%.

[0011] Furthermore, the double tuning fork resonator also includes a clamping coupling beam, which is vertically connected between the two resonant beams and located in the middle of the resonant beams.

[0012] Furthermore, the resonant beam, anchor point, and coupling beam are all made of single-crystal silicon with a thickness of 10 mm. ~200 .

[0013] Furthermore, the piezoelectric layer is made of aluminum nitride and has a thickness of 0.5 mm. ~2 .

[0014] Furthermore, the metal electrode layer is made of silver, copper, gold, aluminum, nickel, lead, or other metals, and has a thickness of 0.5 mm. ~2 .

[0015] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0016] 1. This invention proposes a low-loss planar vibration double tuning fork resonator based on an AlN-on-Si structure. It utilizes piezoelectric transduction to achieve a large electromechanical transduction efficiency and a high quality factor (Q value) under one atmosphere. Furthermore, by arranging active regions on both the upper and lower sides of the resonant beam, it can excite in-plane modes without setting up a complex serpentine electrode pattern, and the displacement can be basically confined to the plane. The strains of the two beams are symmetrical, achieving low loss.

[0017] 2. The present invention further proposes a structure by adding a clamping coupling beam at the center of the two resonant beams, which constrains the displacement of the resonator to a greater extent within the plane, reduces losses, increases the area of ​​the active region, increases the strain on the resonator, increases the electromechanical coupling efficiency, and thus improves the signal strength. Attached Figure Description

[0018] Figure 1 This is a three-dimensional structural diagram of the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 1 of the present invention.

[0019] Figure 2This is a schematic cross-sectional view of the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 1 of the present invention.

[0020] Figure 3 This is a schematic diagram showing the mode shapes and displacements of the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 1 of the present invention, operating in both in-plane and out-of-plane modes.

[0021] Figure 4 The curves showing the ratio of external displacement to the thickness of the resonant beam for the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 1 of the present invention are shown in different active region proportions.

[0022] Figure 5 This is a three-dimensional structural diagram of the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 2 of the present invention.

[0023] Figure 6 This is a schematic diagram of the mode shape and displacement of the low-loss planar vibration double tuning fork resonator based on the AlN-on-Si structure in Embodiment 2 of the present invention when it operates in the first-order in-plane mode.

[0024] In the above figures: 1-double tuning fork resonant beam; 2-piezoelectric layer, 201-upper piezoelectric layer, 202-lower piezoelectric layer; 3-metal electrode layer, 301-upper metal electrode layer; 302-lower metal electrode layer; 4-coupling beam, 401-clamping coupling beam; 5-anchor point; 6-insulating layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention.

[0026] Example 1

[0027] Traditional dual tuning fork resonators based on silicon piezoelectric thin film structures generally operate in out-of-plane modes, resulting in high resonator losses. Exciting in-plane modes requires specific electrode patterns and involves some out-of-plane displacement during operation, leading to energy leakage and losses, which in turn reduces the Q value of the resonator. Furthermore, in existing structures, the active region needs to change the electrode polarity at a specific ratio, making the design complex and the excitation area fixed.

[0028] To overcome the shortcomings of existing technologies, this embodiment proposes a low-loss planar vibration double tuning fork resonator based on an AlN-on-Si structure. It utilizes the method of simultaneously arranging active regions above and below the resonant beam to excite in-plane modes. The structure is simple, and by optimizing the ratio (area ratio) of the active region to the resonant beam, the out-of-plane displacement is minimized, thereby reducing losses to the greatest extent.

[0029] Specifically, the low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure described in this embodiment is as follows: Figure 1 and Figure 2 As shown, the double tuning fork resonator is centrally symmetrical and specifically includes: a double tuning fork resonator beam 1, a piezoelectric layer 2, a metal electrode layer 3, a coupling beam 4, an anchor point 5, and an insulating layer 6, wherein:

[0030] The double tuning fork resonant beam 1 includes a first resonant beam and a second resonant beam; the piezoelectric layer 2 includes an upper piezoelectric layer 201 and a lower piezoelectric layer 202; the metal electrode layer 3 includes an upper metal electrode layer 301 and a lower metal electrode layer 302; and the coupling beam 4 includes a first double-ended coupling beam and a second double-ended coupling beam.

[0031] The first resonant beam and the second resonant beam are connected by a first double-ended coupling beam and a second double-ended coupling beam, and the first double-ended coupling beam and the second double-ended coupling beam are fixed at both ends by the outer anchor point 5.

[0032] The first resonant beam and the second resonant beam adopt the same layout, and the upper and lower surfaces of any resonant beam adopt a symmetrical layout, with active and passive regions arranged in each; for any surface of any resonant beam, two active regions are arranged at both ends of the resonant beam, and a passive region is arranged between the two active regions. The active regions are provided with piezoelectric layers, and the passive regions are provided with insulating layers. The active regions on the upper and lower surfaces are respectively provided with upper piezoelectric layer 201 and lower piezoelectric layer 202.

[0033] The upper metal electrode layer 301 and the lower metal electrode layer 302 adopt a rectangular ring structure. The upper metal electrode layer 301 is disposed on the upper surface of the upper piezoelectric layer 201, and the lower metal electrode layer 302 is disposed on the lower surface of the lower piezoelectric layer 202. An insulating layer is disposed between the metal electrode layer and the resonant beam, and an insulating layer is also disposed between the metal electrode layer and the coupling beam.

[0034] The upper metal electrode layer 301 and the lower metal electrode layer 302 serve as the input and output terminals of the resonator, respectively, forming a double-ended resonator.

[0035] Furthermore, in this embodiment, the resonant beam is made of single-crystal silicon with a thickness of 10 mm. The piezoelectric layer is made of aluminum nitride and has a thickness of 0.5 mm. The electrode layer is made of aluminum and has a thickness of 1 mm. The insulating layer is made of silicon dioxide and has a thickness of 0.5 mm. .

[0036] In terms of working principle, this embodiment has active regions arranged above and below the resonant beam, forming a double-ended resonator. When an electrical signal is applied to the input terminal, the resonant beam excites in-plane modes through the inverse piezoelectric effect, such as... Figure 3 As shown in the left-middle figure, darker colors represent larger displacements. In this case, the resonant beam mainly produces in-plane displacement in the middle region. The first and second resonant beams produce displacements and strains of the same magnitude and symmetrically. The displacements of the first double-ended coupled beam, the second double-ended coupled beam, and the anchor points on both sides are similar, and the displacement amounts are relatively small, resulting in lower losses. In contrast, when the active region is only arranged above the resonant beam, the dual tuning fork resonator can only excite out-of-plane modes, such as... Figure 3 As shown in the figure, there are large displacements at both the coupling beam and the anchor point. The energy stored in the resonator is lost in the interaction forces between the anchor point and the external environment, resulting in a low Q value.

[0037] Based on this, this embodiment performs simulation optimization on the area ratio of the active region to the resonant beam, and the results are as follows. Figure 4 As shown, for the excited in-plane mode, the greater the out-of-plane displacement, the more anchor point loss will be generated. As can be seen from the figure, for the dual tuning fork resonator proposed in this embodiment, the minimum out-of-plane displacement is achieved when the active region area accounts for 44.8%, thus obtaining the lowest loss.

[0038] Example 2

[0039] Based on Example 1, this example proposes a low-loss planar vibration dual tuning fork resonator based on an AlN-on-Si structure. A clamping coupling beam is added at the center of the two resonant beams to increase the area of ​​the active region, improve the signal strength, and make the resonator design more flexible.

[0040] like Figure 5 As shown, in this embodiment, a clamping coupling beam 401 is added at the center position of the first resonant beam and the second resonant beam. At the same time, the area of ​​the piezoelectric layer 2 is increased, and its end extends to the intersection line of the clamping coupling beam 401 and the first resonant beam.

[0041] like Figure 6 As shown, the resonator with added clamping coupling beam 401 can still excite in-plane modes and generates large in-plane displacement and strain throughout the active region. According to the piezoelectric effect principle, larger piezoelectric layer deformation can generate more charge, thereby improving signal strength. At the same time, the displacement at the two double-ended coupling beams and anchor point 5 is well restricted, thus further reducing anchor point loss and improving the Q value of the device.

[0042] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A low-loss planar vibrating double tuning fork resonator based on an AlN-on-Si structure, comprising: The resonant beam, piezoelectric layer, metal electrode layer, coupling beam, anchor point, and insulating layer are characterized by: The double tuning fork resonator is centrally symmetrical, with two resonant beams connected in parallel between two coupling beams, and the outer sides of the two coupling beams are fixed at both ends by anchor points; The upper and lower surfaces of the resonant beam are symmetrically arranged, with active and passive regions arranged on each surface. The two active regions are arranged at both ends of the resonant beam, and the passive region is arranged between the two active regions. The active regions on the upper and lower surfaces of the resonant beam are respectively provided with an upper piezoelectric layer and a lower piezoelectric layer. The upper surface of the upper piezoelectric layer is provided with an upper metal electrode layer, and the lower surface of the lower piezoelectric layer is provided with a lower metal electrode layer. The upper and lower metal electrode layers serve as the input and output terminals of the double tuning fork resonator, respectively, forming a double-ended resonator.

2. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, Both the upper and lower metal electrode layers adopt a rectangular ring structure. An insulating layer is set between the metal electrode layer and the resonant beam, and an insulating layer is also set between the metal electrode layer and the coupling beam.

3. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, The active region on the surface of the resonant beam accounts for 20% to 80% of the area.

4. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, The double tuning fork resonator also includes a clamping coupling beam, which is vertically connected between the two resonant beams and located in the middle of the resonant beams.

5. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, The resonant beam, anchor point, and coupling beam are all made of monocrystalline silicon with a thickness of 10 mm. ~200 .

6. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, The piezoelectric layer is made of aluminum nitride and has a thickness of 0.5 mm. ~2 .

7. The low-loss planar vibrating double tuning fork resonator based on the AlN-on-Si structure according to claim 1, characterized in that, The metal electrode layer is made of silver, copper, gold, aluminum, nickel, lead, or other metals, and has a thickness of 0.5 mm. ~2 .

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