A single-crystal thin-film bulk acoustic wave resonator, its preparation method and application

Abstract

The present invention provides a single-crystal thin-film bulk acoustic wave resonator, a preparation method thereof and an application. The resonator sequentially includes a substrate layer, a Bragg reflection layer, a first bonding layer, a second bonding layer, a piezoelectric layer and an electrode layer in order from bottom to top; the width of the electrode layer is smaller than that of the piezoelectric layer; the resonator further includes a first silicon oxide layer and a second silicon oxide layer, the first silicon oxide layer and the second silicon oxide layer respectively surround the first bonding layer and the second bonding layer, and a plurality of horizontally arranged first air holes and a plurality of horizontally arranged second air holes are respectively arranged in the first silicon oxide layer and the second silicon oxide layer; a plurality of the first air holes correspond to and communicate with a plurality of the second air holes one by one; the piezoelectric layer material is AlN or lithium niobate. The resonator of the present invention can improve the quality factor and reduce the power loss.

Description

Technical Field

[0001] The present invention relates to the technical field of bulk acoustic wave resonators, and particularly to a single-crystal thin-film bulk acoustic wave resonator, a preparation method thereof, and an application thereof. Background Art

[0002] The development of wireless communication technology has put forward requirements for miniaturization and high frequency of radio frequency front-end devices. However, traditional ceramic dielectric filters cannot meet the integration requirements due to their large volume, while surface acoustic wave filters cannot meet the high-frequency conditions due to processing technology limitations. The thin-film bulk acoustic wave resonator converts an electrical signal with an extremely long wavelength into an acoustic signal with a shorter wavelength through the piezoelectric effect. The acoustic wave undergoes total reflection at the interface between the upper and lower electrodes and air, forming an interference effect. By controlling the thickness of the piezoelectric thin film, the frequency of the filter can be controlled. With the innovation and development of semiconductor technology, the thickness of the piezoelectric material can be controlled within a few hundred nanometers. Therefore, the thin-film bulk acoustic wave resonator is suitable for high-frequency and miniaturized scenarios. Traditional bulk acoustic wave resonators are easily corroded by the sacrificial layer release solution due to structural defects and have poor performance. At the same time, part of the acoustic wave will leak into the surrounding substrate through the piezoelectric material, resulting in a low quality factor. And the piezoelectric materials of traditional thin-film bulk acoustic wave resonators are mostly polycrystalline materials, and the high defect density of polycrystalline piezoelectric materials will also cause a reduction in the quality factor of the resonator. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the present invention provides a single-crystal thin-film bulk acoustic wave resonator, a preparation method thereof, and an application thereof, and solves the problems of low quality factor and large insertion loss existing in the existing single-crystal thin-film bulk acoustic wave resonators. The technical solution of the present invention is as follows:

[0004] In a first aspect, the present invention provides a single-crystal thin-film bulk acoustic wave resonator, which sequentially includes a substrate layer, a Bragg reflection layer, a first bonding layer, a second bonding layer, a piezoelectric layer, and an electrode layer from bottom to top; the width of the electrode layer is smaller than that of the piezoelectric layer; the resonator further includes a first silicon oxide layer and a second silicon oxide layer, the first silicon oxide layer and the second silicon oxide layer respectively surround the first bonding layer and the second bonding layer, and a plurality of horizontally arranged first air holes and a plurality of horizontally arranged second air holes are respectively provided in the first silicon oxide layer and the second silicon oxide layer; a plurality of the first air holes and a plurality of the second air holes correspond to each other one by one and are communicated; the piezoelectric layer material is AlN or lithium niobate.

[0005] Optionally, the substrate layer material is silicon.

[0006] Further, the Bragg reflection layer is a structure of 2 or more layers, formed by a molybdenum layer and a silicon oxide layer.

[0007] Preferably, the number of layers of the Bragg reflection layer is 9 layers.

[0008] Furthermore, the materials of the first bonding layer and the second bonding layer are Au and Sn respectively, and the thickness is between 100 and 700 nm.

[0009] Furthermore, the thicknesses of the first silicon oxide layer and the second silicon oxide layer are between 100 and 700 nm.

[0010] Furthermore, the first air holes and the second air holes are arranged in a horizontal array.

[0011] Optionally, the number of the first air holes and the second air holes is more than 2.

[0012] Preferably, the number of the first air holes and the second air holes is 6.

[0013] Furthermore, in the first air holes and the second air holes, the distance between adjacent air holes is one quarter of the acoustic wavelength.

[0014] In a second aspect, the present invention provides a method for manufacturing a single-crystal thin-film bulk acoustic resonator, including the following steps:

[0015] (1) Prepare two substrate layers: a first substrate layer and a second substrate layer. First, prepare a Bragg reflection layer on the surface of the first substrate layer;

[0016] (2) Magnetron sputter a first bonding layer on the Bragg reflection layer and perform patterning. Prepare a first silicon oxide layer around the first bonding layer, and prepare periodically arranged first air holes in the first silicon oxide layer;

[0017] (3) Prepare an AlN piezoelectric layer or a lithium niobate piezoelectric layer on the surface of the second substrate layer;

[0018] (4) Magnetron sputter a second bonding layer on the upper surface of the piezoelectric layer and perform patterning. Prepare a second silicon oxide layer around the second bonding layer, and prepare periodically arranged second air holes in the second silicon oxide layer. The positions of the second air holes correspond to those of the first air holes;

[0019] (5) Bond the component in step (4) to the first bonding layer of the component in step (2) in a flip-chip manner through the second bonding layer;

[0020] (6) Remove the second substrate layer, and magnetron sputter a top electrode layer to obtain the product.

[0021] Preferably, the method for preparing the Bragg reflection layer in step (1) includes magnetron sputtering, PECVD or LPCVD.

[0022] Preferably, the method for preparing the piezoelectric layer in step (3) is AC magnetron sputtering or MOCVD.

[0023] Preferably, the bonding method in step (5) is thermocompression bonding.

[0024] In a third aspect, the present invention provides an electronic component, including the above-mentioned single-crystal thin-film bulk acoustic wave resonator.

[0025] Further, the electronic component includes: a duplexer, a multiplexer, and a bulk acoustic wave filter.

[0026] Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0027] (1) In the resonator of the present invention, a silicon oxide layer is introduced in the structure, which improves the mechanical reliability of the resonator, reduces the deformation of the bonding layer during the bonding process, and a plurality of horizontally arranged air holes are provided in the silicon oxide layer. The setting of the air holes enhances the reflection performance of the acoustic wave, reduces the loss of the laterally transmitted acoustic wave leaking into the substrate, and finally improves the quality factor of the resonator. The reflection layer and the single-crystal piezoelectric material act synergistically to jointly improve the quality factor of the resonator and reduce the power loss of the resonator.

[0028] (2) The preparation method of the resonator of the present invention is simple and reliable, and can prepare a high-quality single-crystal thin-film bulk acoustic wave resonator. Compared with the traditional polycrystalline thin-film bulk acoustic wave resonator, the crystal quality of the piezoelectric layer is greatly enhanced, the defect density is significantly reduced, the electromechanical coupling coefficient of the resonator is improved, and the insertion loss is reduced. Description of the Drawings

[0029] Figure 1 It is a cross-sectional view of the Bragg reflection layer on the first silicon substrate in Embodiment 1 of the present invention.

[0030] Figure 2 It is a cross-sectional view of the first bonding layer and the first silicon oxide layer on the Bragg reflection layer in Embodiment 1 of the present invention.

[0031] Figure 3 It is a cross-sectional view of the first air hole on the first silicon oxide layer in Embodiment 1 of the present invention.

[0032] Figure 4 It is a cross-sectional view of the piezoelectric layer on the second silicon substrate in Embodiment 1 of the present invention.

[0033] Figure 5 It is a cross-sectional view of the second bonding layer, the second silicon oxide layer, and the second air hole on the piezoelectric layer in Embodiment 1 of the present invention.

[0034] Figure 6 It is a cross-sectional view of the bonding of the first bonding layer and the second bonding layer in Embodiment 1 of the present invention.

[0035] Figure 7 This is a cross-sectional view of the resonator after removing the second silicon substrate in Embodiment 1 of the present invention.

[0036] Figure 8 This is a cross-sectional view of the finally prepared resonator in Embodiment 1 of the present invention.

[0037] Figure 9 is Figure 8 top view.

[0038] Figures 1 - 9 Among them: the first silicon substrate 101, the Bragg reflector layer 102, the first bonding layer 103, the first silicon oxide layer 104, the first air holes 105, the second silicon substrate 106, the piezoelectric layer 107, the second bonding layer 108, the second silicon oxide layer 109, the second air holes 110, and the electrode layer 111. Detailed implementation manners

[0039] In the description of the present invention, it should be noted that for those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0040] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention. The protection scope of the present invention includes but is not limited to the following embodiments. Any modification made to the details and forms of the technical solution of the present invention without departing from the spirit and scope of the present application falls within the protection scope of the present invention. Embodiment 1

[0041] This embodiment provides a single-crystal thin-film bulk acoustic wave resonator, the structure of which is as Figure 8 and 9 shown. Sequentially from bottom to top, it includes a silicon first silicon substrate 101, a Bragg reflector layer 102, a first bonding layer 103, a second bonding layer 108, a piezoelectric layer 107, and an electrode layer 111; it also includes a first silicon oxide layer 104 and a second silicon oxide layer 109. The first silicon oxide layer 104 and the second silicon oxide layer 109 are respectively arranged to surround the first bonding layer 103 and the second bonding layer 108. A number of horizontally arranged first air holes 105 and a number of horizontally arranged second air holes 110 are respectively provided in the first silicon oxide layer 104 and the second silicon oxide layer 109; a number of the first air holes 105 and a number of the second air holes 110 correspond to each other one by one and are communicated; the material of the piezoelectric layer 107 is AlN.

[0042] The Bragg reflection layer 102 is composed of alternating metal Mo layers and silicon oxide layers in the order from bottom to top, with a total of 9 layers of structure.

[0043] The thickness of the piezoelectric layer 107 is 1 μm.

[0044] The material of the first bonding layer 103 is Au, the material of the second bonding layer 108 is Sn, the thickness of the Au layer is 300 nm, the thickness of the Sn layer is 100 nm, and the total thickness of the first bonding layer 103 and the second bonding layer 108 is 400 nm.

[0045] The thicknesses of the first silicon oxide layer 104 and the second silicon oxide layer 109 are 400 nm.

[0046] The first air holes and the second air holes are arranged in a horizontal array, and the numbers of both the first air holes 105 and the second air holes 110 are 6. Among the first air holes and the second air holes, the distance between adjacent air holes is one quarter of the acoustic wave wavelength.

[0047] The material of the electrode layer 111 is metal Mo, and the thickness is 400 nm. The width of the electrode layer is smaller than that of the piezoelectric layer.

[0048] This embodiment also provides a method for manufacturing the single-crystal thin-film bulk acoustic wave resonator as described above, including the following steps:

[0049] (1) Select a Si substrate as the first silicon substrate 101, soak the substrate in acetone and hydrofluoric acid buffer solution in sequence and then dry it. Use the magnetron sputtering method to prepare a layer of metal Mo, and use the PECVD method to prepare a layer of silicon oxide thin film, and alternate them to prepare a total of nine Bragg reflection layers 102 (as Figure 1 shown).

[0050] (2) Use the magnetron sputtering method to prepare an Au first bonding layer 103 above the Bragg reflection layer, then perform patterning, and use the PECVD method to prepare a first silicon oxide layer 104 around the Au first bonding layer 103 (as Figure 2 shown).

[0051] (3) Use the plasma etching method to etch air holes 105 in the silicon oxide layer 104 (as Figure 3 shown).

[0052] (4) Use the alternating current magnetron sputtering method to deposit a layer of aluminum nitride thin film 107 on the surface of the second silicon substrate 106 (as Figure 4 shown).

[0053] (5) Deposit the Sn second bonding layer 108 on the surface of the aluminum nitride film 107 by magnetron sputtering, then perform patterning, prepare the second silicon oxide layer 109 around the Sn second bonding layer 108 by PECVD, and finally prepare periodic air holes 110 by plasma etching (as Figure 5 shown).

[0054] (6) Thermally compressively bond the first bonding layer 103 and the second bonding layer 108 (inverted) (as Figure 6 shown).

[0055] (7) Remove the second silicon substrate 108 by mechanical thinning (as Figure 7 shown).

[0056] (8) Prepare the Mo electrode layer 111 above the piezoelectric material by lift-off (as Figure 8 shown).

[0057] The quality factor of the resonator obtained in this embodiment is 3200, and the power loss is about 0.02 watts. Embodiment 2

[0058] This embodiment provides a single-crystal thin-film bulk acoustic wave resonator, which is different from Embodiment 1 in that: the Bragg reflector layer has 4 layers, which are, from bottom to top: 2 silicon oxide layers and 2 Mo layers. The thicknesses of the first bonding layer and the second bonding layer are 700 nm.

[0059] The quality factor of the resonator obtained in this embodiment is 600, and the power loss is about 0.1 watts. Embodiment 3

[0060] This embodiment provides a single-crystal thin-film bulk acoustic wave resonator, which is different from Embodiment 1 in that: the Bragg reflector layer has 2 layers, which are, from bottom to top: 1 silicon oxide layer and 1 Mo layer. The thicknesses of the first bonding layer and the second bonding layer are 100 nm.

[0061] The quality factor of the resonator obtained in this embodiment is 200, and the power loss is about 0.3 watts. Comparative Example 1

[0062] This comparative example provides an existing polycrystalline resonator, the structure of which includes a silicon cavity, a bottom electrode, a piezoelectric layer, and a top electrode. This is a relatively conventional resonator in the art and will not be described in detail here. The thicknesses of both the bottom electrode and the top electrode are 400 nm, and the thickness of the piezoelectric layer AlN is 1 μm.

[0063] The quality factor of the resonator obtained in this comparative example is 700, and the power loss is about 0.09 watts.

[0064] Table 1 Performance Parameters of Resonators in Examples 1 - 3 and Comparative Example 1

[0065] Case Quality factor Power loss Example 1 3200 0.02 Example 2 600 0.1 Example 3 200 0.3 Comparative example 1 700 0.09

[0066] The data in Table 1 show that the single - crystal thin - film bulk acoustic wave resonator obtained in this example has the best quality factor, low power loss, the quality factor is increased by 3.57 times compared with the existing resonator, and the power loss is reduced by 77.78%. The single - crystal thin - film bulk acoustic wave resonators obtained in Example 2 and Example 3 are much worse than those in the example, but the performance parameters are barely acceptable.

[0067] The above - described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A single-crystal thin-film bulk acoustic wave resonator, characterized in that: It sequentially includes a substrate layer, a Bragg reflector layer, a first bonding layer, a second bonding layer, a piezoelectric layer, and an electrode layer in the order from bottom to top; the width of the electrode layer is smaller than that of the piezoelectric layer; the resonator further includes a first silicon oxide layer and a second silicon oxide layer, the first silicon oxide layer and the second silicon oxide layer respectively surround the first bonding layer and the second bonding layer, and a plurality of horizontally arranged first air holes and a plurality of horizontally arranged second air holes are respectively provided in the first silicon oxide layer and the second silicon oxide layer; the plurality of first air holes and the plurality of second air holes correspond to each other one by one and are communicated; the piezoelectric layer material is AlN or lithium niobate; in the first air holes and the second air holes, the distance between adjacent air holes is one quarter of the acoustic wavelength.

2. The single-crystal thin-film bulk acoustic wave resonator according to claim 1, characterized in that: The Bragg reflector layer has a structure of two or more layers and is formed by a molybdenum layer and a silicon oxide layer.

3. The single-crystal thin-film bulk acoustic wave resonator according to claim 2, characterized in that: The number of layers of the Bragg reflector layer is nine.

4. The single-crystal thin-film bulk acoustic wave resonator according to claim 1, characterized in that: The materials of the first bonding layer and the second bonding layer are Au and Sn respectively, and the thickness is between 100 and 700 nm.

5. The single-crystal thin-film bulk acoustic wave resonator according to claim 1, characterized in that: The thicknesses of the first silicon oxide layer and the second silicon oxide layer are between 100 and 700 nm.

6. A method for preparing the single-crystal thin-film bulk acoustic wave resonator according to any one of claims 1 to 5, characterized in that: It includes the following steps: (1) Prepare two substrate layers: a first substrate layer and a second substrate layer. First, prepare a Bragg reflector layer on the surface of the first substrate layer; (2) Magnetron sputter a first bonding layer on the Bragg reflector layer and perform patterning, prepare a first silicon oxide layer around the first bonding layer, and prepare periodically arranged first air holes in the first silicon oxide layer; (3) Prepare an AlN piezoelectric layer or a lithium niobate piezoelectric layer on the surface of the second substrate layer; (4) Magnetron sputter a second bonding layer on the upper surface of the piezoelectric layer and perform patterning, prepare a second silicon oxide layer around the second bonding layer, and prepare periodically arranged second air holes in the second silicon oxide layer, and the positions of the second air holes correspond to those of the first air holes; (5) Bond the component in step (4) to the first bonding layer of the component in step (2) in a flip-chip manner through the second bonding layer; (6) Remove the second substrate layer, and magnetron sputter a top electrode layer to obtain the product.

7. An electronic component, characterized in that: It includes the single-crystal thin-film bulk acoustic wave resonator according to any one of claims 1 to 5 or the single-crystal thin-film bulk acoustic wave resonator obtained by the manufacturing method according to claim 6.

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