Solid-state assembly type bulk acoustic wave resonator based on coplanar electrode structure

Abstract

The invention discloses a solid assembly type bulk acoustic wave 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 the coplanar left electrode layer and the coplanar right electrode layer respectively form a piezoelectric oscillation pile with the opposite area between a suspension electrode layer and a middle piezoelectric film layer so as to generate high-frequency electromechanical oscillation. The device can be regarded as being formed by connecting two single solid-state assembled resonators in series, the coplanar left electrode layer and the coplanar right electrode layer do not need to lead out a lower electrode, and a radio frequency excitation signal is 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 do not need to lead out a lower electrode, and radio frequency excitation signals are directly loaded to 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 large-scale production of the solid-state assembly bulk acoustic wave resonator is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of bulk acoustic wave resonators, and more specifically, relates to a solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure. Background Art

[0002] Film Bulk Acoustic Resonator (FBAR) is a high-frequency bulk acoustic wave resonator made of piezoelectric thin 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 current integrated circuits. Compared with existing quartz crystal resonators and surface acoustic wave resonators, film bulk acoustic wave resonators have higher operating frequencies and larger operating capacity. Therefore, they are widely used in core RF components such as RF filters, oscillators, duplexers, and low-noise amplifiers.

[0003] Film bulk acoustic wave resonators mainly include cavity type, back-etched type, glue-coated type and solid-mounted resonator (SMR) type.

[0004] For solid-state assembled thin film bulk acoustic resonators, Bragg reflectors usually deposit thin film materials with high acoustic impedance and low acoustic impedance alternately on the substrate to form multiple reflection interfaces. The sound wave will be totally reflected when passing through each interface, thereby achieving the purpose of limiting the sound wave energy in the piezoelectric film layer. It is precisely because the solid-state assembled structure uses Bragg reflectors that it has better thermal performance, better mechanical stability, and greater power capacity, and is therefore more suitable for high-frequency device applications.

[0005] Existing thin film bulk acoustic wave resonators mostly etch vias in the piezoelectric film layer to realize the lead-out of the lower electrode, which requires photolithography of the piezoelectric film layer through a mask plate and adding electrode pads to the electrode layer above it, which further increases the already cumbersome manufacturing steps of the solid-state assembled thin film bulk acoustic wave resonator, increases the difficulty of the manufacturing process, greatly reduces the yield rate, and is not conducive to large-scale production. Therefore, in order to take into account the better thermal performance, better mechanical stability, and greater power capacity characteristics of the solid-state assembled bulk acoustic wave resonator, and reduce the difficulty of the process steps, it is necessary to propose a new solid-state assembled bulk acoustic wave resonator to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a solid-state assembled BAW resonator based on a coplanar electrode structure to reduce the cost and steps of the solid-state assembled BAW resonator manufacturing process, improve the yield rate, and realize the large-scale production of solid-state assembled BAW resonators.

[0007] To achieve the above-mentioned purpose, the present invention provides a solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure, comprising:

[0008] The substrate layer is located at the bottom;

[0009] It is characterized by further comprising:

[0010] The Bragg reflector located on the substrate layer is composed of six acoustic layers of high and low impedance that are periodically arranged alternately to achieve maximum sound wave reflection;

[0011] a suspended electrode layer located above the Bragg reflector;

[0012] A piezoelectric film layer located at the suspended electrode layer;

[0013] A coplanar left electrode layer and a coplanar right electrode layer located on the piezoelectric film layer, wherein the coplanar left electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure at the left edge, and the coplanar right electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure at the right edge;

[0014] The facing area between the coplanar left electrode layer and the suspended electrode layer and the middle piezoelectric film layer forms a piezoelectric oscillation stack to generate high-frequency electromechanical oscillation;

[0015] The facing area between the coplanar right electrode layer and the suspended electrode layer and the middle piezoelectric film layer forms a piezoelectric oscillation stack to generate high-frequency electromechanical oscillation.

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

[0017] The present invention is a solid-state assembled bulk acoustic wave resonator based on a coplanar electrode structure. By arranging a coplanar left electrode layer and a coplanar right electrode layer on the top layer, each of which forms a piezoelectric oscillation stack with the area facing each other between the suspended electrode layer and the middle piezoelectric film layer to generate high-frequency electromechanical oscillation. In this way, the present invention can be regarded as consisting of two single solid-state assembled resonators in series. The coplanar left electrode layer and the coplanar right electrode layer do not need to lead out 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 a coplanar electrode structure of the present invention is different from the existing solid-state assembled bulk acoustic wave resonator that uses a via to lead out the lower electrode. The prior art usually requires etching a via on the piezoelectric film layer using photolithography technology to leak out the lower electrode, and then leading out the lower electrode on the piezoelectric film layer to achieve electrical connection. This process requires alignment with the via when the lower electrode is led out and requires etching using photolithography technology, which increases the difficulty of the manufacturing process. The coplanar left electrode layer and the coplanar right electrode layer of the present invention do not need to lead out the lower electrode, and the radio frequency excitation signal is directly loaded on the coplanar left electrode layer and the coplanar right electrode layer, which reduces the process manufacturing steps and difficulty, improves the yield rate, and facilitates the large-scale production of solid-state assembly acoustic wave resonators.

[0018] In addition, the present invention also has the following beneficial effects:

[0019] 1. The present invention designs a concave-convex periodic structure at the left boundary of the coplanar left electrode layer and the right boundary of the coplanar right electrode layer, and uses this concave-convex periodic structure designed at the boundary of the effective resonance region to realize the reflection of the lateral leakage sound wave, so that more lateral energy returns to enter the effective resonance region, while reducing the sound 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 sound wave in the resonance region, thereby realizing the improvement of the device resonance quality factor.

[0020] 2. The present invention eliminates the design of vias and lower electrode leads, reducing the alignment errors and process defects that may be introduced during the manufacturing process, thereby greatly improving the reliability and stability of the device. In traditional methods, the alignment process of vias and lower electrode leads is prone to produce small errors, affecting the performance and life of the resonator. The present invention avoids these problems by simplifying the structural design, ensuring the high performance output and long-term stable operation of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 2 yes Figure 1 A schematic diagram of the layered structure of a solid-state assembled bulk acoustic wave resonator based on a coplanar electrode structure is shown;

[0023] Figure 3 yes Figure 1 A cross-sectional schematic diagram of a solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure is shown;

[0024] Figure 4 yes Figure 1 The electromechanical equivalent model diagram of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure is shown;

[0025] Figure 5 yes Figure 1 The circuit equivalent diagram of the solid-state assembly type bulk acoustic wave resonator based on the coplanar electrode structure is shown;

[0026] Figure 6 yes Figure 1 The impedance curve of the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure when the radio frequency excitation signal is applied;

[0027] Figure 7 yes Figure 1 The figure shows a simulation diagram of the vibration displacement of a solid-state assembled bulk acoustic wave resonator based on a coplanar electrode structure when an RF excitation signal is applied. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0029] Figure 1 , 2 3 are respectively a three-dimensional structural schematic diagram, a layered structural schematic diagram and a cross-sectional schematic diagram of a specific implementation of the solid-state assembled bulk acoustic wave resonator based on a coplanar electrode structure of the present invention.

[0030] In this embodiment, if Figure 1 , 2As shown in Figure 3, the solid-state assembled bulk acoustic wave resonator based on the coplanar electrode structure of the present invention includes: a substrate layer 6 located at the bottom layer, a Bragg reflection grating 5 located above the substrate layer, a suspended electrode layer 4 located above the Bragg reflection grating, a piezoelectric film layer 3 located on the suspended electrode layer, a coplanar left electrode layer 1 located on the piezoelectric film layer, and a coplanar right electrode layer 2. The Bragg reflector 5 is composed of six layers of periodically alternately arranged high and low impedance acoustic layers 501-506, namely, 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, so as to achieve maximum sound wave reflection. The coplanar left electrode layer 1 is composed of an excitation electrode layer with a concave-convex periodic structure on the left boundary, and the coplanar right electrode layer 2 is composed of an excitation electrode layer with a concave-convex periodic structure on the right boundary. The coplanar left electrode layer 1 and the facing area between the suspended electrode layer 4 and the middle piezoelectric film layer 3 form a piezoelectric oscillation stack to generate high-frequency electromechanical oscillations. The coplanar right electrode layer 2 and the facing area between the suspended electrode layer 4 and the middle piezoelectric film layer 3 form a piezoelectric oscillation stack to generate high-frequency electromechanical oscillations. In this way, the present invention can be regarded as consisting of two single solid-state assembled resonators connected in series. The coplanar left electrode layer 1 and the coplanar right electrode layer 2 do not need to be led out of the lower electrode, and the RF excitation signal can be directly loaded on the coplanar left electrode layer 1 and the coplanar right electrode layer 2.

[0031] In this embodiment, the substrate layer 6, the Bragg reflector 5 and the piezoelectric film layer 3 are all rectangular, and have the same length and width, and the coplanar left electrode layer 1 and the coplanar right electrode layer 2 are rectangular with the same size and shape. In this embodiment, the main oscillating parts are all squares of equal size with a side length of 150 μm.

[0032] In this embodiment, the Bragg reflector 5 is a high and low impedance acoustic layer of commonly used W (tungsten) and SiO2 (silicon dioxide) periodically and alternately arranged. 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, 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, and 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 sound waves, reduce the loss of body acoustic waves, and improve the quality factor of the device, thereby improving the detection sensitivity.

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

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

[0035] In this embodiment, the piezoelectric film layer 3 is a material having a piezoelectric effect, such as piezoelectric ceramics PZT (lead zirconate titanate), AlN (aluminum nitride), piezoelectric single crystal PMN-PT (lead magnesium niobate-lead titanate), etc. As the best choice, the piezoelectric 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 solid-state assembled bulk acoustic wave resonator with coplanar electrode structure proposed in the present invention, the piezoelectric equation of the piezoelectric film material can be used to derive the electromechanical vibration equation of the piezoelectric film layer under the resonant state, and the electromechanical equivalent model of the piezoelectric film can be obtained by the electromechanical analogy method, such as Figure 4 As shown, combined with the equivalent acoustic model of the common material layer, the electromechanical equivalent model of the solid-state assembly acoustic wave resonator can be established:

[0037]

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

[0039] From the transmission line theory we can get:

[0040]

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

[0042] make:

[0043]

[0044] M 12 It is the equivalent transmission matrix of the two layers of materials: the upper electrode layer and the piezoelectric film layer:

[0045]

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

[0047]

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

[0049]

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

[0051]

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

[0053]

[0054] make:

[0055]

[0056] but:

[0057]

[0058] Due to M 2×2 is a second-order matrix. By expanding it and substituting it into the above formula, we can get:

[0059]

[0060] In the formula, m 11 、m 12 、m 21 、m 22 They are the second-order matrices M 2×2 The total impedance seen from the electrical input is:

[0061]

[0062] Since the bottom surface of the substrate layer 6 is in contact with the air, F 11 =0, and we can get the following result by substituting it into the above formula:

[0063]

[0064] The solid-state mounted bulk acoustic wave resonator based on the coplanar electrode structure of the present invention can be regarded as composed of two single solid-state mounted resonators connected in series, so the impedance can be expressed as:

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

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

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

[0068] like Figure 5 As shown in the figure, the solid-state assembled BAW resonator based on the coplanar electrode structure of the present invention is equivalent to two single solid-state assembled BAW resonators connected in series. The solid-state assembled BAW resonator proposed in this embodiment is built in the simulation software, and the experimental conditions are simulated to obtain the simulated frequency impedance curve and vibration displacement simulation results of the piezoelectric film layer 3, respectively, as shown in FIG. Figure 6 Figure 7 As shown, it is further illustrated that the coplanar electrode solid-state assembly BAW resonator proposed in this embodiment has the resonance characteristics of a general solid-state assembly BAW resonator.

[0069] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure, comprising: The substrate layer is located at the bottom; It is characterized by further comprising: The Bragg reflector located on the substrate layer is composed of six acoustic layers of high and low impedance that are periodically arranged alternately to achieve maximum sound wave reflection; a suspended electrode layer located above the Bragg reflector; A piezoelectric film layer located at the suspended electrode layer; A coplanar left electrode layer and a coplanar right electrode layer located on the piezoelectric film layer, wherein the coplanar left electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure at the left edge, and the coplanar right electrode layer is composed of an excitation electrode layer with a concave-convex periodic structure at the right edge; The facing area between the coplanar left electrode layer and the suspended electrode layer and the middle piezoelectric film layer forms a piezoelectric oscillation stack to generate high-frequency electromechanical oscillation; The facing area between the coplanar right electrode layer and the suspended electrode layer and the middle piezoelectric film layer forms a piezoelectric oscillation stack to generate high-frequency electromechanical oscillation.

2. The solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure according to claim 1, characterized in that: The six periodically alternating high and low impedance acoustic layers are 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, and 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 assembly type bulk acoustic wave resonator based on a coplanar electrode structure according to claim 1, characterized in that: The electrode materials of the coplanar left electrode layer, the coplanar right electrode layer and the suspended electrode layer are aluminum metal and are not directly connected.

4. The solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure according to claim 1, characterized in that: The material of the piezoelectric film layer is aluminum nitride.

5. The solid-state assembly type bulk acoustic wave resonator based on a coplanar electrode structure according to claim 1, characterized in that: The substrate layer, the Bragg reflector and the piezoelectric film layer are all rectangular and have the same length and width. The coplanar left electrode layer and the coplanar right electrode layer are rectangular with the same size and shape.

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