Acoustic resonator and method of manufacturing the same

Abstract

To provide an acoustic resonator that pursues optimization of thin film bulk acoustic resonator technology.SOLUTION: The acoustic resonator defines a resonance priority region, in which the substrate, the buffer thin film, the reflective structure, the lower electrodes, the crystalline thin film, and the upper electrodes are stacked together. The buffer thin film includes a flat region overlapping with the resonance priority region, and the flat region has a roughness less than 5nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resonator, particularly an acoustic resonator, and a method for manufacturing the same. [Background technology]

[0002] With the comprehensive upgrade and widespread application of mobile devices, the demand for acoustic resonators has also increased significantly to enhance the communication capabilities of radio frequency systems. Among them, thin-film bulk acoustic resonators (FBARs) are formed by depositing piezoelectric dielectric materials on silicon wafers or semiconductor substrates to form thin-film elements, which have compact structural characteristics and can simultaneously exert piezoelectric properties to generate resonance, making thin-film bulk acoustic resonators particularly suitable for 5G communication technology.

[0003] However, conventional resonators still have problems to be solved. For example, performance improvement, quality improvement, loss reduction, cost reduction, etc. are all focuses of filter development, so the technical method of optimized resonators remains a goal pursued by related fields. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an acoustic resonator that seeks to optimize thin-film bulk acoustic resonator (FBAR) technology. [Means for solving the problem]

[0005] The acoustic resonator provided by the present invention includes, from bottom to top, a substrate, a buffer thin film, a reflective structure, a lower electrode, a crystal thin film, and an upper electrode, and defines a resonance-priority region and a non-resonance-priority region. In the resonance-priority region, the substrate, the buffer thin film, the reflective structure, the lower electrode, the crystal thin film, and the upper electrode are stacked one on top of the other, and the buffer thin film includes a flat region overlapping the resonance-priority region, the surface roughness of the flat region is less than 5 nm, and the non-resonance-priority region is the remaining region other than the resonance-priority region.

[0006] In the acoustic resonator of the present invention, the non-resonance priority region is disposed along the outer periphery of the resonance priority region.

[0007] In the acoustic resonator of the present invention, the substrate has material properties of a low dielectric constant, corrosion resistance, a low coefficient of thermal expansion, and high mechanical strength.

[0008] In the acoustic resonator of the present invention, the substrate is formed of a material selected from the group consisting of bismaleimide triazine (BT), glass, ceramic, lithium tantalate (LT), and lithium niobate (LN).

[0009] In the acoustic resonator of the present invention, the buffer thin film has a thickness of 10 nm to 50 μm, and is a silicon oxide layer, a silicon nitride layer, a polysilicon layer, a combination thereof, or a stack of the aforementioned film layers.

[0010] In the acoustic resonator of the present invention, the buffer thin film is formed on the substrate in a pattern.

[0011] In the acoustic resonator of the present invention, the crystal thin film is a metal nitride film, and the full width at half maximum (FWHM) value of the crystal thin film is at least less than 15 degrees.

[0012] In the acoustic resonator of the present invention, the metal nitride film includes aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), barium strontium titanate (BST), indium nitride (InN), gallium nitride (GaN), or aluminum scandium nitride (AlScN).

[0013] In the acoustic resonator of the present invention, the reflecting structure is a cavity or a Bragg reflecting layer.

[0014] The present invention provides providing a substrate; placing a buffer thin film on the surface of the substrate; performing a planarization process on a portion of the surface of the buffer thin film to form a flat region with a roughness of less than 5 nm; placing a lower electrode at least partially corresponding to the flat area above the flat area, forming a reflective structure between the flat area and the lower electrode, and the reflective structure covers the flat area; forming a thin crystal film on at least a portion of the surface of the buffer thin film and / or the lower electrode, so that at least a portion of the thin crystal film corresponds to an upper portion of the flat region; forming an upper electrode on at least a portion of the surface of the crystal thin film, with at least a portion of the upper electrode corresponding to an upper portion of the flat region; There is further provided a method for manufacturing an acoustic resonator, comprising: [Effects of the Invention]

[0015] Furthermore, by directly forming the acoustic resonator on the substrate, the present invention can directly reduce material costs and replace traditional resonators that require silicon (Si) material as the substrate. The acoustic resonator of the present invention is packaged during molding during manufacturing, which directly eliminates the additional packaging process that traditional resonators require after manufacturing, effectively reducing the volume and manufacturing steps. Furthermore, by selecting the material of the substrate, a better heat dissipation effect can be achieved.

[0016] Furthermore, after the planarization process to form the planarized region on the buffer thin film, the acoustic resonator is divided into the resonance-priority region and the non-resonance-priority region, and the acoustic resonator not only prevents sound waves from leaking vertically through the reflective structure located in the resonance-priority region, but also suppresses sound wave leakage in the lateral direction by utilizing the non-resonance-priority region located on the periphery, thereby achieving the effect of improving the Q value (Quality Factor). [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a manufacturing flow chart of a preferred embodiment of the present invention. [Figure 2] 1 is a cross-sectional view illustrating a first preferred embodiment of the present invention. [Figure 3] 1 is a manufacturing flowchart of a first preferred embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view illustrating a second preferred embodiment of the present invention. [Figure 5] 4 is a manufacturing flow chart of a second preferred embodiment of the present invention. [Figure 6] 10 is a manufacturing flow chart of the third preferred embodiment of the present invention. [Figure 7] FIG. 10 is a comparison of performance tests of a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1, the present invention provides an acoustic resonator and a method for manufacturing the acoustic resonator. The acoustic resonator includes a substrate 10, a buffer thin film 20, a reflective structure 30, a lower electrode 33, a crystal thin film 40, and an upper electrode 43. The acoustic resonator resonates the crystal thin film 40 in response to signals applied to the lower electrode 33 and the upper electrode 43, thereby generating a resonant frequency and an anti-resonant frequency.

[0019] Among these, the acoustic resonator is divided into a resonance-priority region C and a non-resonance-priority region C1, and in the resonance-priority region C, the substrate 10, at least a portion of the buffer thin film 20, at least a portion of the reflective structure 30, at least a portion of the lower electrode 33, at least a portion of the crystal thin film 40, and at least a portion of the upper electrode 43 are stacked on top of each other, and the region of the buffer thin film 20 corresponding to the resonance-priority region C is a flat region 21, and the roughness of the flat region 21 is less than 5 nm, and the crystal thin film corresponding to the non-resonance-priority region C1 is a non-flat region.

[0020] Preferably, the resonance priority region C is located in the central region of the acoustic resonator, and the non-resonance priority region C1 is located along the outer periphery of the resonance priority region C.

[0021] The steps for fabricating the acoustic resonator provided by the present invention include: S1: Prepare the substrate 10. The substrate 10 has material properties such as a low dielectric constant, corrosion resistance, a low thermal expansion coefficient, and high mechanical strength. The substrate 10 is made of bismaleimide triazine (BT), glass, ceramic, lithium tantalate (LT), or lithium niobate (LN). Preferably, the substrate 10 is a ceramic substrate.

[0022] After cleaning, the substrate 10 can proceed to subsequent steps. S2: The buffer thin film 20 is disposed on the surface of the substrate 10, and the thickness of the buffer thin film 20 is 10 nm to 50 μm.

[0023] The buffer thin film 20 may be a silicon oxide layer, a silicon nitride layer, a polysilicon layer, a combination thereof, or a stack of the above-mentioned layers. Preferably, the buffer thin film 20 is made of silicon dioxide (SiO2), phosphosilicate glass (PSG), or borophosphosilicate glass (BPSG).

[0024] The buffer thin film 20 can be formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD), which may include pulsed laser deposition (PLD), sputtering, or evaporation, but is not limited thereto.

[0025] The buffer thin film 20 may be uniformly distributed over the entire substrate 10 or may be patterned on the substrate 10 .

[0026] S3: A flattening process is performed on a part of the surface of the buffer thin film 20, and a flat region 21 having a roughness of less than 5 nm is formed on a part of the surface of the buffer thin film 20.

[0027] The planarization process may be achieved by techniques such as, but not limited to, ion beam, chemical-mechanical planarization (CMP), or chemical liquid etching.

[0028] S4: The lower electrode 33 is installed, and at least a portion of the lower electrode 33 corresponds to the upper part of the flat area 21, and the reflective structure 30 is formed between the lower electrode 33 and the flat area 21, and the reflective structure 30 covers the upper part of the flat area 21. The reflective structure 30 has sound reflection properties and can block sound waves from leaking vertically to the substrate 10 and the buffer thin film 20 below, thereby reducing sound loss.

[0029] 3 to 5, the reflecting structure 30 may be a cavity 31 or a Bragg reflecting layer 32. Step S4 provides two kinds of manufacturing steps, S4-1 and S4-2, depending on the type of the reflecting structure 30.

[0030] S4-1: The lower electrode 33 is disposed above the buffer thin film 20, and the cavity 31 is formed between the portion of the lower electrode 33 corresponding to the flat region 21 and the buffer thin film 20 (see FIGS. 2 and 3).

[0031] In one embodiment, during planarization, the flat region 21 creates a groove on the surface of the buffer thin film 20, and when the lower electrode 33 is installed, the lower electrode 33 can create the cavity 31 between the flat region 21 and the buffer thin film 20.

[0032] In one embodiment, the cavity 31 can be formed by first depositing a sacrificial layer 31A on the surface of the flat region 21, depositing the lower electrode 33, and then removing the sacrificial layer 31A.

[0033] Here, the sacrificial layer 31A may be a binary compound semiconductor such as gallium arsenide, a ternary compound semiconductor such as indium gallium phosphide (InGaP) or indium gallium arsenide (InGaAs), a quaternary compound semiconductor such as aluminum gallium indium phosphide (AlInGaP), or the like.

[0034] Here, the material of the sacrificial layer 31A may include titanium tungsten alloy (TiW), copper (Cu), borosilicate glass (BSG), or the like.

[0035] Here, the sacrificial layer 31A may further optionally include a photoresist material or other suitable sacrificial material or polymer thereof, but the present invention is not limited thereto.

[0036] Here, since the material selected by the sacrificial layer 31A and the material selected by the buffer thin film 20 are at least partially different, there is an etching selectivity between the sacrificial layer 31A and the buffer thin film 20, and a selective etching effect (removal of the sacrificial layer 31A) can be achieved.

[0037] S4-2: The Bragg reflector layer 32 is disposed above the buffer thin film 20, and the lower electrode 33 is formed on the surface of the Bragg reflector layer 32. At least a portion of the lower electrode 33 corresponds to the upper portion of the flat region 21 (see FIGS. 4 and 5).

[0038] The Bragg reflector layer 32 includes a first reflector layer 321 having a first acoustic impedance and a second reflector layer 322 having a second acoustic impedance lower than the first acoustic impedance, which are alternately stacked.

[0039] The alternating stacking arrangement of the first reflective layer 321 and the second reflective layer 322 allows sound waves to be reflected vertically, preventing sound waves from leaking to the substrate 10 and the buffer thin film 20 below.

[0040] Here, the Bragg reflecting layer 32 is formed by using a thin film deposition technique to form an arrangement in which the first reflecting layer 321 and the second reflecting layer 322 are alternately stacked.

[0041] Then, continue with the following steps: S5: The crystal thin film 40 is formed on at least a portion of the surface of the buffer thin film 20 and / or the lower electrode 33, and the coverage of the crystal thin film 40 includes the flat region 21 and the non-flat region of the buffer thin film 20. The crystal thin film 40 converts electrical energy into mechanical energy in the form of elastic waves due to the piezoelectric effect.

[0042] The crystal thin film 40 is a metal nitride film. Examples of the metal nitride film include aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), barium strontium titanate (BST), indium nitride (InN), gallium nitride (GaN), and aluminum scandium nitride (AlScN), but the present invention is not limited to these.

[0043] Here, the full width at half maximum (FWHM) value of the crystal thin film 40 is at least less than 15 degrees, and is used as an evaluation of the crystallinity of the crystal thin film 40 .

[0044] Here, the crystal thin film 40 is formed by a method such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0045] Still referring to FIG. 6, the thin crystal film 40 can be completed using a two-step deposition scheme, the steps including: S5-1: forming a first crystalline layer 41 having a thickness of more than 1 nm under first conditions; S5-2: A second crystalline layer 42 is formed on the surface of the first crystalline layer 41 under second conditions.

[0046] Here, the deposition temperature under the first condition is higher than the deposition temperature under the second condition, and the deposition rate and deposition pressure under the first condition are lower than the deposition rate and deposition pressure under the second condition.

[0047] Furthermore, the first condition is that the deposition rate is less than 100 nm / min, the deposition temperature is greater than 100° C., and the deposition pressure is less than 0.1 torr.

[0048] Preferably, the first crystal layers 41 are arranged to cover the resonance priority regions C and correspond to each other. In one embodiment, the crystal thin film 40 includes a first crystal layer 41 and a second crystal layer 42 formed on the first crystal layer 41, and the first crystal layer 41 is arranged to cover the resonance priority region C.

[0049] S6: The upper electrode 43 is formed on at least a part of the surface of the crystal thin film 40, and at least a part of the upper electrode 43 corresponds to the upper part of the flat region 21.

[0050] The lower electrode 33 and the upper electrode 43 are formed of a conductive material, such as molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof, but the present invention is not limited thereto.

[0051] Furthermore, by directly forming the acoustic resonator on the substrate 10, the present invention can directly reduce material costs and replace traditional resonators that require silicon (Si) as the substrate. The acoustic resonator of the present invention is packaged on a wafer during manufacturing, integrating the wafer process with the packaging process. This eliminates the need for additional packaging processes required by traditional resonators after manufacturing, thereby realizing wafer-level packaging (WLP), and effectively reducing the volume and manufacturing steps. By selecting the material of the substrate 10, a better heat dissipation effect can be achieved.

[0052] In addition, in the Smith chart of Figure 7, the present invention compares the performance between an embodiment in which the resonance-priority region C is created after a planarization process to form the flat region 21 using the buffer thin film 20, and a comparative example in which the entire buffer thin film 20 is planarized. In the comparative example, spurious modes (also known as lateral vibrations) are clearly generated, as shown by the ring indicated by arrow A. However, the occurrence of parasitic modes is significantly reduced in the examples provided by the present invention. Furthermore, since the parasitic mode phenomenon is clearly generated in the comparative example, the curve of the comparative example is concave in the region near the right pole (indicated by arrow B). The closer the curve is to the right pole, the greater the impedance and the improved resonance performance. As can be seen from the detection results, the acoustic resonator is divided into the resonance-priority region C and the non-resonance-priority region C1. The acoustic resonator not only prevents sound waves from leaking vertically through the reflecting structure 30 located in the resonance-priority region C, but also suppresses lateral sound wave leakage by utilizing the flattening process of the flat region 21 and the relative positional relationship between the resonance-priority region C and the non-resonance-priority region C1 located on the periphery, thereby improving the Q value.

[0053] It should be noted that, based on the explanations and details of the above specification, those skilled in the art may make changes and modifications to the above-mentioned implementation methods. Therefore, the present invention is not limited to the specific implementation methods disclosed and described above, and equivalent modifications and variations to the present invention should also be included in the scope of protection of the claims of the present invention. In addition, although specific terms are used in this specification, these terms are for the convenience of explanation and do not limit the present invention. [Explanation of symbols]

[0054] 10 Substrate 20 Buffer thin film 21 flat area 30 reflective structure 31 Cavity 31A Sacrificial Layer 32 Bragg reflector layer 321 1st reflective layer 322 2nd reflective layer 33 Lower electrode 40 Crystalline Thin Film 41 First crystal layer 42 Second crystal layer 43 Upper electrode C resonance priority region C1 Non-resonant priority region A arrow B arrow S1 Step S2 Step S3 Step S4 Step S5 Step S6 Step

Claims

1. 1. An acoustic resonator comprising, from bottom to top, a substrate, a buffer thin film, a reflective structure, a lower electrode, a crystal thin film, and an upper electrode, defining a resonance-priority region and a non-resonance-priority region, wherein in the resonance-priority region, the substrate, the buffer thin film, the reflective structure, the lower electrode, the crystal thin film, and the upper electrode are stacked one on top of the other, and the buffer thin film includes a flat region overlapping the resonance-priority region, the surface roughness of the flat region being less than 5 nm, and the non-resonance-priority region is the remaining region other than the resonance-priority region.

2. The acoustic resonator according to claim 1 , wherein the non-resonance priority region is disposed along the outer periphery of the resonance priority region.

3. 3. The acoustic resonator of claim 2, wherein the substrate has material properties of low dielectric constant, corrosion resistance, low coefficient of thermal expansion, and high mechanical strength.

4. 4. The acoustic resonator of claim 3, wherein the substrate is formed from a material selected from the group consisting of bismaleimide triazine resin, glass, ceramic, lithium tantalate, and lithium niobate.

5. 4. The acoustic resonator of claim 3, wherein the buffer thin film has a thickness of 10 nm to 50 μm, and the buffer thin film is a silicon oxide layer, a silicon nitride layer, a polysilicon layer, a combination thereof, or a stack of the aforementioned film layers.

6. 6. The acoustic resonator according to claim 5, wherein the buffer thin film is formed on the substrate by patterning.

7. 6. The acoustic resonator according to claim 5, wherein the crystal thin film is a metal nitride film, and the full width at half maximum of the crystal thin film is at least less than 15 degrees.

8. 8. The acoustic resonator of claim 7, wherein the metal nitride film comprises aluminum nitride, zinc oxide, lead zirconate titanate, barium strontium titanate, indium nitride, gallium nitride, or aluminum scandium nitride.

9. 9. The acoustic resonator according to claim 1, wherein the reflecting structure is a cavity or a Bragg reflecting layer.

10. 10. The acoustic resonator according to claim 9, wherein the crystal thin film includes a first crystal layer and a second crystal layer formed on the first crystal layer, the first crystal layer being disposed so as to cover the resonance-priority region.

11. providing a substrate; placing a buffer thin film on the surface of the substrate; performing a planarization process on a portion of the surface of the buffer thin film to form a flat region with a roughness of less than 5 nm; placing a lower electrode at least partially corresponding to the flat area above the flat area, forming a reflective structure between the flat area and the lower electrode, and the reflective structure covers the flat area; forming a crystal thin film on at least a portion of the surface of the buffer thin film and / or the lower electrode, so that at least a portion of the crystal thin film corresponds to an upper portion of the flat region; forming an upper electrode on at least a portion of the surface of the crystal thin film, with at least a portion of the upper electrode corresponding to an upper portion of the flat region; A method for manufacturing an acoustic resonator, comprising:

12. The reflecting structure is a cavity, and the step of covering the flat area with the reflecting structure includes: the buffer film, upon planarization, creates the flat area of ​​the groove in the surface of the buffer film; a lower electrode is disposed above the buffer thin film, and a cavity is formed between the buffer thin film and a portion of the lower electrode corresponding to the flat region; The method of claim 11 , comprising:

13. The reflecting structure is a cavity, and the step of covering the flat area with the reflecting structure includes: placing a sacrificial layer on the surface of the flat area; placing the lower electrode above the buffer thin film and the sacrificial layer; removing the sacrificial layer to form the cavity; The method of claim 11 , comprising:

14. The reflective structure is a Bragg reflective layer, and the step of covering the reflective structure above the flat region includes: placing the Bragg reflection layer above the buffer thin film; forming the lower electrode on the surface of the Bragg reflection layer; The method of claim 11 , comprising:

15. The crystal thin film is formed by a deposition method, the deposition method comprising: forming a first crystalline layer under first conditions, the first crystalline layer having a thickness greater than 1 nm; forming a second crystalline layer on the surface of the first crystalline layer under second conditions; Including, 15. The manufacturing method according to claim 11, wherein the deposition temperature under the first condition is higher than the deposition temperature under the second condition, and the deposition rate and deposition pressure under the first condition are lower than those under the second condition.

16. 16. The manufacturing method of claim 15, wherein the first condition includes a deposition rate of less than 100 nm / min, a deposition temperature of greater than 100° C., and a deposition pressure of less than 0.1 torr.

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