Solid assembly type bulk acoustic wave resonator and preparation method thereof

Abstract

The invention discloses a solid-state assembly type bulk acoustic wave resonator and a preparation method thereof, and the solid-state assembly type bulk acoustic wave resonator comprises a substrate, and a Bragg reflection structure, a supporting layer, a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially stacked on the substrate. Wherein the Bragg reflection structure comprises high-acoustic impedance layers and low-acoustic impedance layers which are alternately stacked, and cavity structures are arranged in the high-acoustic impedance layers or the low-acoustic impedance layers, in contact with the supporting layer, in the Bragg reflection structure. According to the invention, the reflection effect between solid-gas interfaces can be enhanced, and the loss of sound waves in the Bragg layer reflection process is reduced, so that the Q value of the solid assembly type bulk acoustic wave resonator is improved, and the device performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of resonators, in particular to a solid-state assembled bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] BAW resonator (Bulk Acoustic Wave Resonator, BAW) is a resonant device based on bulk acoustic wave propagation. It has the advantages of high quality factor, high frequency stability and low loss, and has been widely used in wireless communications, digital television, computers, bulk acoustic wave filters, etc. The working principle of BAW resonator is to use the piezoelectric effect of piezoelectric materials to convert electrical energy into mechanical energy, generate bulk acoustic waves, and form resonance in the resonant cavity, thereby realizing the selection and control of frequency.

[0003] There are two mainstream BAW resonators, one is the Film Bulk Acoustic Resonator (FBAR), and the other is the Solidly Mounted Resonator (SMR). Among them, the SMR includes a Bragg reflection structure, a bottom electrode, a piezoelectric layer, and a top electrode sequentially located on a substrate. The Bragg reflection structure is composed of alternating high acoustic impedance layers and low acoustic impedance layers; the FBAR includes a bottom electrode, a piezoelectric layer, and a top electrode located on a substrate, and a cavity structure located under the piezoelectric layer. The SMR uses a Bragg reflection structure instead of the cavity structure in the FBAR, which can significantly improve the mechanical strength of the device.

[0004] However, since the sound waves will be totally reflected at each interface of the Bragg reflection structure, most of the energy will be reflected back to the piezoelectric layer, but a small amount of energy will leak into the substrate, resulting in the quality factor (Q value) of the solid-mounted FBAW resonator being lower than that of the cavity-type FBAW resonator. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide a solid-state mounted bulk acoustic wave resonator and a method for preparing the same, which can improve the quality factor of the solid-state mounted thin film bulk acoustic wave resonator.

[0006] According to a first aspect of the present invention, there is provided a solid-state assembled bulk acoustic wave resonator, comprising a substrate, a Bragg reflection structure sequentially stacked on the substrate, a support layer, a first electrode layer, a piezoelectric layer, and a second electrode layer; wherein the Bragg reflection structure comprises high acoustic impedance layers and low acoustic impedance layers stacked alternately, and a cavity structure is provided in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure.

[0007] Optionally, the cross-section of the cavity structure is an inverted trapezoid.

[0008] Optionally, the material of the support layer is aluminum nitride.

[0009] Optionally, the material of the piezoelectric layer is the same as that of the supporting layer.

[0010] Optionally, the material of the high acoustic impedance layer is at least one of tungsten, titanium tungsten, molybdenum, platinum, ruthenium, iridium, hafnium, tantalum, nickel, chromium, and cobalt; the material of the low acoustic impedance layer is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, dry gel or polymer material.

[0011] Optionally, the substrate is made of at least one of silicon, germanium, quartz, silicon carbide or other organic polymer materials.

[0012] According to a second aspect of the present invention, a method for preparing a solid-state assembled bulk acoustic wave resonator is provided, comprising: forming a Bragg reflection structure on a substrate, the Bragg reflection structure comprising alternatingly stacked high acoustic impedance layers and low acoustic impedance layers; forming a groove in the high acoustic impedance layer or the low acoustic impedance layer in contact with a support layer in the Bragg reflection structure; filling a sacrificial layer in the groove and flattening it; forming a support layer on the Bragg reflection structure; forming a first electrode layer, a piezoelectric layer, and a second electrode layer in sequence on the support layer; and releasing the sacrificial layer to form a cavity structure in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure.

[0013] Optionally, the cross-section of the cavity structure is an inverted trapezoid.

[0014] Optionally, the material of the support layer is aluminum nitride.

[0015] Optionally, the material of the piezoelectric layer is the same as that of the supporting layer. Beneficial Effects

[0016] According to the solid-state assembled BAW resonator and the preparation method thereof according to the embodiments of the present invention, a cavity structure is formed in the high acoustic impedance layer and the low acoustic impedance layer where the Bragg reflection structure contacts the support layer, thereby enhancing the reflection effect at the solid-gas interface and reducing the loss of the sound wave during the reflection process of the Bragg layer, thereby increasing the Q value of the solid-state assembled BAW resonator and improving the device performance.

[0017] Furthermore, the cross-sectional shape of the cavity structure is set to an inverted trapezoid. The inverted trapezoidal structure enables the sacrificial layer material to flow more easily into the bottom of the cavity during the filling process, reducing voids and defects caused by accumulation or poor flow of the sacrificial layer material, and helping to achieve a more uniform filling effect, thereby improving the quality and reliability of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which: Figure 1 A schematic structural diagram of a solid-state assembled bulk acoustic wave resonator provided by an embodiment of the present invention is shown; Figure 2a-2g A schematic diagram showing different stages of a method for preparing a solid-state assembled bulk acoustic wave resonator provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0019] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0020] The specific implementation of the present invention is further described in detail below in conjunction with the drawings and examples.

[0021] The solid-state matching bulk acoustic wave resonator in the prior art includes a substrate, a Bragg reflection structure, a first electrode layer, a piezoelectric layer and a second electrode layer. The Bragg reflection structure is composed of high acoustic impedance layers and low acoustic impedance layers stacked alternately. The sound wave will be totally reflected at each interface of the Bragg reflection structure, and most of the energy will be reflected back to the piezoelectric layer, but a small amount of energy will leak into the substrate, resulting in the quality factor (Q value) of the solid-assembled thin film bulk acoustic wave resonator being lower than that of the cavity-type thin film bulk acoustic wave resonator. In order to solve the above problems, the present application provides a solid-state assembled bulk acoustic wave resonator, in which a cavity structure is formed in the high acoustic impedance layer and the low acoustic impedance layer where the Bragg reflection structure contacts the support layer, the reflection effect between the solid-gas interface is enhanced, and the loss of the sound wave in the reflection process of the Bragg layer is reduced, thereby improving the Q value of the solid-assembled bulk acoustic wave resonator to improve the device performance.

[0022] Figure 1 FIG. 2 is a schematic diagram showing the structure of a solid-state assembly type bulk acoustic wave resonator provided by an embodiment of the present invention. Figure 1 As shown, the solid-state assembly type BAW resonator 100 includes a substrate 110 , a Bragg reflection structure 120 , a support layer 130 , a first electrode layer 140 , a piezoelectric layer 150 and a second electrode layer 160 .

[0023] The Bragg reflection structure 120 includes alternately stacked high acoustic impedance layers 121 and low acoustic impedance layers 122. The high acoustic impedance layers 121 or low acoustic impedance layers 122 of the Bragg reflection structure 120 that are in contact with the support layer 130 have a cavity structure 170. The support layer 130 covers the cavity structure 170.

[0024] In some embodiments, the top layer of the Bragg reflection structure 120 is a high acoustic impedance layer 121, and the top high acoustic impedance layer 121 has a cavity structure 170. In some embodiments, the top layer of the Bragg reflection structure 120 is a low acoustic impedance layer 122, and the top low acoustic impedance layer 122 has a cavity structure 170. The embodiment of the present invention does not limit whether the top impedance layer of the Bragg reflection structure 120 is a high acoustic impedance layer or a low acoustic impedance layer.

[0025] The cross section of the cavity structure 170 is an inverted trapezoid.

[0026] The piezoelectric layer 150 and the support layer 130 are made of the same material. The support layer 130 is made of aluminum nitride.

[0027] The material of the high acoustic impedance layer 121 is at least one of tungsten, titanium tungsten, molybdenum, platinum, ruthenium, iridium, hafnium, tantalum, nickel, chromium, and cobalt; the material of the low acoustic impedance layer 122 is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, dry gel or polymer material.

[0028] The substrate 110 is made of at least one of silicon, germanium, quartz, silicon carbide or other organic polymer materials.

[0029] The first electrode 140 and the second electrode 160 are made of metal materials such as molybdenum.

[0030] The solid-state assembled bulk acoustic wave resonator provided in the present application forms a cavity structure in the high acoustic impedance layer and the low acoustic impedance layer where the Bragg reflection structure contacts the support layer. The support layer covers the cavity structure, thereby enhancing the reflection effect between the solid-gas interface and reducing the loss of the sound wave during the reflection process of the Bragg layer, thereby increasing the Q value of the solid-state assembled bulk acoustic wave resonator to improve the device performance.

[0031] Furthermore, the cross-section of the cavity structure is an inverted trapezoid. During the filling process, the inverted trapezoidal structure can make the sacrificial layer material flow into the bottom of the cavity more easily, reducing voids and defects caused by accumulation or poor flow of the sacrificial layer material, helping to achieve a more uniform filling effect, thereby improving the quality and reliability of the final product.

[0032] Figure 2a-2g The schematic diagram shows different stages of the method for preparing a solid-state assembled BAW resonator provided by the present invention. The method for preparing a solid-state assembled BAW resonator comprises the following steps.

[0033] In step S110 , a Bragg reflection structure 120 is formed on a substrate 110 .

[0034] Specifically, see Figure 2a , high acoustic impedance layers 121 and low acoustic impedance layers 122 are alternately deposited on the substrate 110 to form a Bragg reflection structure 120. Figure 1 The solid-state assembly type BAW resonator is used as an example for explanation. The number of periods of the Bragg reflection structure 120 can be set according to actual conditions and is not limited to that shown in the above embodiment.

[0035] The substrate 110 is made of at least one of silicon, germanium, quartz, silicon carbide or other organic polymer materials.

[0036] The material of the high acoustic impedance layer 121 is at least one of tungsten, titanium tungsten, molybdenum, platinum, ruthenium, iridium, hafnium, tantalum, nickel, chromium, and cobalt; the material of the low acoustic impedance layer 122 is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, dry gel or polymer material.

[0037] In step S120, a groove is formed in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure.

[0038] Specifically, see Figure 2b A groove 190 is formed in the top impedance layer of the Bragg reflection structure 120 by dry etching. The cross section of the groove 190 is an inverted trapezoid. The inverted trapezoidal structure can make it easier for the sacrificial layer material to flow into the bottom of the cavity when the sacrificial layer material is subsequently filled, thereby reducing voids and defects caused by the accumulation or poor flow of the sacrificial layer material.

[0039] Among them, the step of forming the groove 190 includes: coating the surface of the topmost impedance layer of the Bragg reflection structure 120 with photoresist and laying a mask, and then developing the positive photoresist using TMAH; etching the developed surface using dry etching to obtain the groove 190; and removing the resist and rinsing the dry-etched surface with deionized water, and then drying the residual liquid in a hot nitrogen environment.

[0040] In some embodiments, the top layer of the Bragg reflection structure 120 is a low acoustic impedance layer 122, and a groove 190 is formed in the top low acoustic impedance layer 122. In some embodiments, the top layer of the Bragg reflection structure 120 is a high acoustic impedance layer 121, and a groove 190 is formed in the top high acoustic impedance layer 121. The embodiment of the present invention does not limit whether the top impedance layer of the Bragg reflection structure 120 is a high acoustic impedance layer or a low acoustic impedance layer.

[0041] In step S130 , a sacrificial layer is filled in the groove and planarized.

[0042] Specifically, see Figure 2c , a sacrificial layer 180 is filled in the groove. Since the sacrificial layer 180 will overflow the groove 190 when being filled, a chemical mechanical polishing process is required to remove the excess sacrificial layer material outside the groove 190 and only retain the sacrificial layer material in the groove 190. The material of the sacrificial layer 180 is phosphorus-doped silicon dioxide.

[0043] Wherein, step S130 includes: depositing a sacrificial layer material on the top impedance layer of the Bragg reflection structure 120 after dry etching, and making the deposition thickness of the sacrificial layer material fill and be higher than the groove 190; and planarizing the sacrificial layer 180 by chemical mechanical polishing process.

[0044] In step S140 , a support layer is formed on the Bragg reflection structure.

[0045] See also Figure 2d , depositing material on the Bragg reflection structure 120 to form the support layer 130, wherein the support layer 130 covers the groove 190 and the sacrificial layer 180. The material of the support layer 130 is aluminum nitride.

[0046] In step S150, a first electrode layer, a piezoelectric layer and a second electrode layer are sequentially formed on the support layer.

[0047] Specifically, a first electrode is provided on the Bragg reflection structure 120 and a first electrode layer 140 is patterned to form the first electrode layer 140 (see Figure 2e ); providing a piezoelectric layer on the first electrode layer 140 and patterning the piezoelectric layer 150 (see Figure 2f ); providing a second electrode on the piezoelectric layer 150 and patterning to form a second electrode layer 160 (see Figure 2g ).

[0048] The piezoelectric layer 150 and the support layer 130 are made of the same material. The first electrode 140 and the second electrode 160 are made of metal materials such as molybdenum.

[0049] In step S160 , the sacrificial layer is released to form a cavity structure in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure.

[0050] In this embodiment, the sacrificial layer 180 is released to form the cavity structure 170 in the uppermost impedance layer of the Bragg reflection structure 120 . The cross section of the cavity structure 170 is an inverted trapezoid. The support layer 130 covers the cavity structure 170 .

[0051] The preparation method of the bulk acoustic wave resonator provided in the present application forms a cavity structure in the high acoustic impedance layer and the low acoustic impedance layer where the Bragg reflection structure contacts the support layer, and the support layer covers the cavity structure, which can enhance the reflection effect between the solid-gas interface and reduce the loss of the sound wave during the reflection process of the Bragg layer, thereby improving the Q value of the solid-assembled bulk acoustic wave resonator to improve the device performance.

[0052] Furthermore, the cross-section of the cavity structure is an inverted trapezoid. The inverted trapezoidal structure enables the sacrificial layer material to flow more easily into the bottom of the cavity during the filling process, reducing voids and defects caused by accumulation or poor flow of the sacrificial layer material, and helping to achieve a more uniform filling effect, thereby improving the quality and reliability of the final product.

[0053] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A solid-state assembled bulk acoustic wave resonator, characterized in that: It includes a substrate, a Bragg reflection structure, a support layer, a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially stacked on the substrate; The Bragg reflection structure comprises high acoustic impedance layers and low acoustic impedance layers stacked alternately, and a cavity structure is provided in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure.

2. The solid-state assembly type bulk acoustic wave resonator according to claim 1, characterized in that: The cross section of the cavity structure is an inverted trapezoid.

3. The solid-state assembly type bulk acoustic wave resonator according to claim 1, characterized in that: The material of the support layer is aluminum nitride.

4. The solid-state assembly type bulk acoustic wave resonator according to claim 1, characterized in that: The material of the piezoelectric layer is the same as that of the supporting layer.

5. The solid-state assembly type bulk acoustic wave resonator according to claim 3, characterized in that: The material of the high acoustic impedance layer is at least one of tungsten, titanium tungsten, molybdenum, platinum, ruthenium, iridium, hafnium, tantalum, nickel, chromium, and cobalt; the material of the low acoustic impedance layer is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, dry gel, or polymer material.

6. The solid-state assembly type bulk acoustic wave resonator according to claim 3, characterized in that: The substrate is made of at least one of silicon, germanium, quartz, silicon carbide or other organic polymer materials.

7. A method for preparing a solid-state assembled bulk acoustic wave resonator, characterized in that: include: forming a Bragg reflection structure on a substrate, wherein the Bragg reflection structure comprises high acoustic impedance layers and low acoustic impedance layers stacked alternately; forming a groove in the high acoustic impedance layer or the low acoustic impedance layer in contact with the support layer in the Bragg reflection structure; Filling the groove with a sacrificial layer and performing a planarization process; forming a support layer on the Bragg reflection structure; forming a first electrode layer, a piezoelectric layer and a second electrode layer in sequence on the support layer; The sacrificial layer is released to form a cavity structure in the high acoustic impedance layer or the low acoustic impedance layer contacting the support layer in the Bragg reflection structure.

8. The method for preparing a solid-state assembled bulk acoustic wave resonator according to claim 7, characterized in that: The cross section of the cavity structure is an inverted trapezoid.

9. The method for preparing a solid-state assembled bulk acoustic wave resonator according to claim 7, characterized in that: The material of the support layer is aluminum nitride.

10. The method for preparing a solid-state assembled bulk acoustic wave resonator according to claim 7, characterized in that: The material of the piezoelectric layer is the same as that of the supporting layer.

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