A solid-state bulk acoustic wave resonator based on a coplanar electrode structure

Abstract

The application discloses a solid-state assembled bulk acoustic resonator based on a coplanar electrode structure, which is characterized in that a coplanar left electrode layer and a coplanar right electrode layer are arranged on the uppermost layer, and a piezoelectric oscillation stack is formed between the coplanar left electrode layer and the coplanar right electrode layer and the corresponding area of the suspended electrode layer and the middle piezoelectric thin film layer to generate high-frequency electromechanical oscillation. Thus, the application can be regarded as being composed of two single solid-state assembled resonators in series, the coplanar left electrode layer and the coplanar right electrode layer do not need to be led out by a lower electrode, and a radio frequency excitation signal can be directly loaded on the coplanar left electrode layer and the coplanar right electrode layer. The coplanar left electrode layer and the coplanar right electrode layer of the application do not need to be led out by a lower electrode, and a radio frequency excitation signal can be directly loaded on the coplanar left electrode layer and the coplanar right electrode layer, so that the process manufacturing steps and difficulty are reduced, the yield is improved, and the large-scale production of the solid-state assembled bulk acoustic resonator is facilitated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of bulk acoustic wave resonators, and more particularly relates to a solidly mounted bulk acoustic wave resonator based on a coplanar electrode structure. BACKGROUND

[0002] Film Bulk Acoustic Resonator (FBAR) is a high-frequency bulk acoustic wave resonator processed by piezoelectric film. It has the advantages of small size, low cost, low power consumption, high quality factor, and is compatible with the mainstream CMOS (Complementary Metal Oxide Semiconductor) process of the current integrated circuit. Compared with the existing quartz crystal resonator and surface acoustic wave resonator, the film bulk acoustic wave resonator has higher working frequency and larger working capacity, and is widely used in core radio frequency components such as radio frequency filters, oscillators, duplexers, and low-noise amplifiers.

[0003] The film bulk acoustic wave resonator mainly includes cavity type, back etching type, uniform glue type and solidly mounted resonator (SMR) type, wherein,

[0004] For the solidly mounted film bulk acoustic wave resonator, the Bragg reflection grating usually deposits high acoustic impedance and low acoustic impedance thin film materials alternately on the substrate to form multiple reflection interfaces. When the sound wave passes through each interface, it will be totally reflected, thereby achieving the purpose of limiting the sound wave energy in the piezoelectric film layer. It is because of the Bragg reflection grating used in the solidly mounted structure that it has better thermal performance, better mechanical stability, and larger power capacity, and is more suitable for high-frequency device applications.

[0005] The existing film bulk acoustic wave resonator etches a via in the piezoelectric film layer to realize the lead-out of the lower electrode. This requires photolithography of the piezoelectric film layer through a mask plate and adding an electrode pad on the electrode layer, which further increases the manufacturing steps of the solidly mounted film bulk acoustic wave resonator, increases the difficulty of the manufacturing process, greatly reduces the yield, and is not conducive to large-scale production. Therefore, in order to take into account the better thermal performance, better mechanical stability, and larger power capacity of the solidly mounted bulk acoustic wave resonator, and reduce the difficulty of process steps, it is necessary to propose a new type of solidly mounted bulk acoustic wave resonator to solve the above problems. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and proposes a solidly mounted bulk acoustic wave resonator based on a coplanar electrode structure to reduce the cost and steps of the solidly mounted bulk acoustic wave resonator manufacturing process, improve the yield, and realize large-scale production of the solidly mounted bulk acoustic wave resonator.

[0007] To achieve the above-mentioned object, the application is a solid-state assembled bulk acoustic resonator based on coplanar electrode structure, comprising:

[0008] a substrate layer at the bottom;

[0009] characterized in that it further comprises:

[0010] a Bragg reflection grating above the substrate layer, which is composed of six layers of periodically alternating high and low impedance acoustic layers to achieve maximum acoustic reflection;

[0011] a suspended electrode layer above the Bragg reflection grating;

[0012] a piezoelectric thin film layer on the suspended electrode layer;

[0013] a coplanar left electrode layer and a coplanar right electrode layer on the piezoelectric thin film layer, the coplanar left electrode layer is composed of an excitation electrode layer with concave-convex periodic structure on the left side boundary, and the coplanar right electrode layer is composed of an excitation electrode layer with concave-convex periodic structure on the right side boundary;

[0014] the coplanar left electrode layer and the suspended electrode layer form a piezoelectric oscillation stack with the middle piezoelectric thin film layer to generate high-frequency mechanical-electrical oscillation;

[0015] the coplanar right electrode layer and the suspended electrode layer form a piezoelectric oscillation stack with the middle piezoelectric thin film layer to generate high-frequency mechanical-electrical oscillation.

[0016] The object of the application is achieved in this way.

[0017] The application is based on a solid-state assembled bulk acoustic wave resonator with a coplanar electrode structure. By arranging a coplanar left electrode layer and a coplanar right electrode layer on the uppermost layer, each forms a piezoelectric oscillation stack with the opposite area region between the suspended electrode layer and the intermediate piezoelectric thin film layer to generate high-frequency electromechanical oscillation. Thus, the application can be considered as composed of two single solid-state assembled resonators in series. The coplanar left electrode layer and the coplanar right electrode layer do not need to be connected to the lower electrode, and the radio frequency excitation signal can be directly loaded on the coplanar left electrode layer and the coplanar right electrode layer. The solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the application is different from the existing solid-state assembled bulk acoustic wave resonator which uses a via to connect the lower electrode. The existing technology usually etches a via on the piezoelectric thin film layer to leak out the lower electrode, and then connects the lower electrode on the piezoelectric thin film layer to realize electrical connection. This process requires alignment of the lower electrode with the via and etching using photolithography technology, making the manufacturing process more difficult. The coplanar left electrode layer and the coplanar right electrode layer of the application do not need to be connected to the lower electrode, and the radio frequency excitation signal can be directly loaded on the coplanar left electrode layer and the coplanar right electrode layer, reducing the process manufacturing steps and difficulty, improving the yield, and facilitating mass production of solid-state assembled bulk acoustic wave resonators.

[0018] In addition, the application has the following beneficial effects:

[0019] 1. The application designs a concave-convex periodic structure on the left side boundary of the coplanar left electrode layer and the right side boundary of the coplanar right electrode layer. This concave-convex periodic structure on the boundary of the effective resonance area reflects the lateral leakage acoustic waves, allowing more lateral energy to return to the effective resonance area, while reducing the acoustic energy that leaks into the substrate through the boundary. The concave structure in the concave-convex periodic structure helps to weaken parasitic vibrations, and the convex structure can constrain the energy of the acoustic wave in the resonance area, thereby improving the resonance quality factor of the device.

[0020] 2. The application cancels the design of the via and the lower electrode lead, reducing the alignment errors and process defects that may be introduced during manufacturing, thereby greatly improving the reliability and stability of the device. In the traditional method, the alignment process of the via and the lower electrode lead is prone to small errors, affecting the performance and service life of the resonator. The application simplifies the structure design to avoid these problems, ensuring high-performance output and long-term stable operation of the resonator. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a three-dimensional structure schematic diagram of a specific embodiment of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the application;

[0022] Figure 2 is Figure 1 the layered structure schematic diagram of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure shown in the figure.

[0023] Figure 3 is Figure 1 a cross-sectional schematic view of a solidly mounted bulk acoustic resonator based on a coplanar electrode structure;

[0024] Figure 4 is Figure 1 a mechanical-electrical equivalent model diagram of a solidly mounted bulk acoustic resonator based on a coplanar electrode structure;

[0025] Figure 5 is Figure 1 a circuit equivalent diagram of a solidly mounted bulk acoustic resonator based on a coplanar electrode structure;

[0026] Figure 6 is Figure 1 a graph of an impedance curve of a solidly mounted bulk acoustic resonator based on a coplanar electrode structure when a radio frequency excitation signal is applied;

[0027] Figure 7 is Figure 1 a simulation diagram of a vibration displacement of a solidly mounted bulk acoustic resonator based on a coplanar electrode structure when a radio frequency excitation signal is applied. DETAILED DESCRIPTION

[0028] The specific embodiments of the present application will be described below with reference to the drawings, so that those skilled in the art can better understand the present application. It should be particularly noted that in the following description, when the detailed description of known functions and designs may obscure the main content of the present application, these descriptions will be omitted here.

[0029] Figure 1 、 2 , 3 are respectively a three-dimensional structure schematic view, a layered structure schematic view and a cross-sectional schematic view of one specific embodiment of the solidly mounted bulk acoustic resonator based on a coplanar electrode structure of the present application.

[0030] In the present embodiment, as Figure 1 、 2The solid-state assembled bulk acoustic resonator based on the coplanar electrode structure shown in Fig. 3 comprises a substrate layer 6 at the bottom layer, a Bragg reflection grating 5 above the substrate layer, a suspended electrode layer 4 above the Bragg reflection grating, a piezoelectric thin film layer 3 above the suspended electrode layer, a coplanar left electrode layer 1 above the piezoelectric thin film layer, and a coplanar right electrode layer 2. The Bragg reflection grating 5 is composed of six layers of periodically alternating high and low impedance acoustic layers 501-506, i.e. a first low acoustic impedance layer 501, a first high acoustic impedance layer 502, a second low acoustic impedance layer 503, a second high acoustic impedance layer 504, a third low acoustic impedance layer 505, and a third high acoustic impedance layer 506, to achieve maximum acoustic reflection. The coplanar left electrode layer 1 is an excitation electrode layer with a concave-convex periodic structure at the left boundary, and the coplanar right electrode layer 2 is an excitation electrode layer with a concave-convex periodic structure at the right boundary. The area region directly opposite between the coplanar left electrode layer 1 and the suspended electrode layer 4 and the piezoelectric thin film layer 3 in the middle forms a piezoelectric oscillation stack to generate high-frequency mechanical-electrical oscillation. The area region directly opposite between the coplanar right electrode layer 2 and the suspended electrode layer 4 and the piezoelectric thin film layer 3 in the middle forms a piezoelectric oscillation stack to generate high-frequency mechanical-electrical oscillation. Thus, the present application can be regarded as composed of two single solid-state assembled resonators in series, and the coplanar left electrode layer 1 and the coplanar right electrode layer 2 do not need to be connected to the lower electrode, and the radio frequency excitation signal can be directly loaded on the coplanar left electrode layer 1 and the coplanar right electrode layer 2.

[0031] In the present embodiment, the substrate layer 6, the Bragg reflection grating 5, and the piezoelectric thin film layer 3 are all rectangular, and the length and width dimensions are the same. The coplanar left electrode layer 1 and the coplanar right electrode layer 2 are both rectangular with the same size and shape. In the present embodiment, the main oscillation parts are all square with the same size, and the side length is 150 μm.

[0032] In the present embodiment, the Bragg reflection grating 5 is a commonly used W (tungsten) and SiO2 (silicon dioxide) periodically alternating high and low impedance acoustic layer. The first low acoustic impedance layer 501, the second low acoustic impedance layer 503, and the third low acoustic impedance layer 505 are made of W material, and the first high acoustic impedance layer 502, the second high acoustic impedance layer 504, and the third high acoustic impedance layer 506 are made of SiO2 material. The first low acoustic impedance layer 501, the second low acoustic impedance layer 503, and the third low acoustic impedance layer 505 are made of W material because the acoustic impedance of W and SiO2 is quite different, which can maximize the reflection of acoustic waves, reduce the bulk acoustic wave loss, and improve the quality factor of the device, thereby improving the detection sensitivity.

[0033] The substrate layer 6 is made of Si material, which plays a supporting role for the composite solid-state assembled resonator.

[0034] In the present embodiment, the electrode material of the coplanar left electrode layer 1, the coplanar right electrode layer 2, and the suspended electrode layer 4 is Al (aluminum) metal, and they are not directly connected.

[0035] In the present embodiment, the piezoelectric thin film layer 3 is a material having a piezoelectric effect, such as piezoelectric ceramic PZT (lead zirconate titanate), AlN (aluminum nitride), piezoelectric single crystal PMN-PT (lead magnesium niobate-lead titanate), etc. As the most preferred option, the piezoelectric thin film layer 3 is made of AlN (aluminum nitride) material, which has good thermal conductivity, insulation and thermal stability.

[0036] In order to verify the feasibility of the proposed solid assembly bulk acoustic wave resonator with the coplanar electrode structure of the present application, the electromechanical vibration equation of the piezoelectric thin film layer in the resonant state can be derived by using the piezoelectric equation of the piezoelectric thin film material, and the electromechanical equivalent model of the piezoelectric thin film can be obtained by the electromechanical analogy method, as shown in Figure 4 , and the electromechanical equivalent model of the solid assembly bulk acoustic wave resonator can be established by combining the equivalent acoustic model of the ordinary material layer:

[0037]

[0038] wherein, ρ m is the density of the mth material layer, c m is the Young's modulus of the mth material layer, v m is the acoustic velocity of the mth material layer, k m is the wave number of the mth material layer, d m is the thickness of the mth material layer, S is the effective area of each film layer, f is the vibration frequency, and m = 1, 2, 3, …, 6 respectively represent the coplanar left electrode layer 1 or the coplanar right electrode layer 2, the piezoelectric thin film layer 3, the suspended electrode layer 4, the low acoustic impedance layer in the Bragg reflection grating 5, the high acoustic impedance layer in the Bragg reflection grating 5, and the substrate layer 6.

[0039] From the transmission line theory, we have:

[0040]

[0041] wherein, C0 is the static capacitance of the piezoelectric thin film layer; n = hC0 is the electromechanical conversion coefficient of the piezoelectric thin film layer, which is equivalent to the number of turns of the coil of a transformer, and h is the piezoelectric stiffness constant; F 11 and are the stress and vibration velocity of the bottom surface of the substrate layer, respectively;

[0042] Let:

[0043]

[0044] M 12 is the equivalent transmission matrix of the upper electrode layer and the piezoelectric thin film layer:

[0045]

[0046] M3 is the transfer matrix of the suspended electrode:

[0047]

[0048] M4 is the transfer matrix of the low acoustic impedance layer:

[0049]

[0050] M5 is the transfer matrix of the high acoustic impedance layer:

[0051]

[0052] M6 is the transfer matrix of the substrate layer:

[0053]

[0054] Let:

[0055]

[0056] Then:

[0057]

[0058] Since M 2×2 is a second-order matrix, it is expanded and brought into the above formula to obtain:

[0059]

[0060] In the formula, m 11 , m 12 , m 21 , and m 22 are four elements of the second-order matrix M 2×2 . The total impedance from the electrical input end is:

[0061]

[0062] Since the bottom surface of the substrate layer 6 is in contact with air, F 11 = 0, which is brought into the above formula to obtain:

[0063]

[0064] The solid-state assembled bulk acoustic resonator based on the coplanar electrode structure can be regarded as being composed of two single solid-state assembled resonators in series, and therefore, the impedance can be represented as:

[0065] Ztotal = 2 * Z; (14)

[0066] The resonant frequency is a solution satisfying the equation, under the condition that the material parameters of each film layer are determined, the frequency spectrum graph of total impedance |Z(f)| is drawn, and then the resonant frequency value is read from the impedance curve, and then the resonant frequency of the sensor is obtained. Through formula derivation, it is further obtained that the resonant frequency of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the application can be characterized by numerical calculation, and then the resonant characteristics of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the application are verified.

[0067] Figure 5 is Figure 1 The circuit equivalent diagram of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure is shown.

[0068] As Figure 5 shown, the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the application is equivalent to the series connection of two single solid-state assembled bulk acoustic wave resonators. The solid-state assembled bulk acoustic wave resonator proposed in the embodiment is built in the simulation software, the simulation experimental conditions are simulated, and the frequency impedance curve and vibration displacement simulation results of the piezoelectric thin film layer 3 are respectively as shown in Figure 6 Figure 7 As shown, it is further illustrated that the coplanar electrode solid-state assembled bulk acoustic wave resonator proposed in the embodiment has the resonant characteristics of the general solid-state assembled bulk acoustic wave resonator.

[0069] Although the above describes the specific embodiments of the application for the purpose of facilitating the understanding of the application by those skilled in the art, it should be clear that the application is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the application defined and determined by the appended claims, all the application and creation utilizing the concept of the application are included.

Claims

1. A solid-state assembled bulk acoustic resonator based on a coplanar electrode structure, comprising: The substrate layer located at the bottom layer; Its characteristic is that it further includes: The Bragg reflector grating, located above the substrate, consists of six periodically alternating acoustic layers of high and low impedance to achieve maximum sound wave reflection. A suspended electrode layer located above the Bragg reflector grating; The piezoelectric thin film layer located in the levitation electrode layer; The coplanar left electrode layer and coplanar right electrode layer are located on the piezoelectric thin film layer. The coplanar left electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure on the left side boundary, and the coplanar right electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure on the right side boundary. The coplanar left electrode layer and coplanar right electrode layer do not need to be led out with a lower electrode. The radio frequency excitation signal is directly applied to the coplanar left electrode layer and coplanar right electrode layer. The area between the coplanar left electrode layer and the suspended electrode layer and the middle piezoelectric thin film layer forms a piezoelectric oscillator stack to generate high-frequency electromechanical oscillations. The coplanar right electrode layer and the suspended electrode layer form a piezoelectric oscillator stack between the opposing area regions of the piezoelectric thin film layer to generate high-frequency electromechanical oscillations. The electrode materials of the coplanar left electrode layer, coplanar right electrode layer and floating electrode layer are aluminum metal, and they are not directly connected; The substrate, Bragg reflector, and piezoelectric thin film are all rectangular with the same length and width. The coplanar left electrode layer and coplanar right electrode layer are also rectangular with the same size and shape.

2. The solid-state assembled bulk acoustic resonator based on a coplanar electrode structure according to claim 1, characterized in that, The six-layered acoustic layer with alternating high and low impedance is composed of a first low acoustic impedance layer, a first high acoustic impedance layer, a second low acoustic impedance layer, a second high acoustic impedance layer, a third low acoustic impedance layer, and a third high acoustic impedance layer. The first low acoustic impedance layer, the second low acoustic impedance layer, and the third low acoustic impedance layer are made of tungsten material, while the first high acoustic impedance layer, the second high acoustic impedance layer, and the third high acoustic impedance layer are made of silicon dioxide material.

3. The solid-state assembled bulk acoustic resonator based on a coplanar electrode structure according to claim 1, characterized in that, The piezoelectric thin film layer material is aluminum nitride.

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