CN111313861B - Surface acoustic wave resonator and method of forming the same - Google Patents
Surface acoustic wave resonator and method of forming the same Download PDFInfo
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- CN111313861B CN111313861B CN202010116392.3A CN202010116392A CN111313861B CN 111313861 B CN111313861 B CN 111313861B CN 202010116392 A CN202010116392 A CN 202010116392A CN 111313861 B CN111313861 B CN 111313861B
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- 238000010897 surface acoustic wave method Methods 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 58
- 239000000463 material Substances 0.000 claims abstract description 120
- 239000000758 substrate Substances 0.000 claims description 145
- 238000005530 etching Methods 0.000 claims description 14
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 6
- 230000001902 propagating effect Effects 0.000 abstract description 5
- 239000007769 metal material Substances 0.000 description 16
- 229920002120 photoresistant polymer Polymers 0.000 description 16
- 238000010586 diagram Methods 0.000 description 9
- 238000002360 preparation method Methods 0.000 description 6
- 230000009286 beneficial effect Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 238000005137 deposition process Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
Abstract
The invention provides a surface acoustic wave resonator and a forming method thereof. The surface acoustic wave resonator is not only provided with the reflecting layer, but also provided with the cavity, so that the multiple reflection of the sound wave propagating along the vertical direction can be realized, the loss of the energy of the sound wave is reduced, and the Q value of the surface acoustic wave resonator is further improved. And the reflecting layer is mutually bonded with the bonding layer of the same material, so that the bonding between the bonding layer and the reflecting layer is easier, the bonding strength between the bonding layer and the reflecting layer can be improved, and the structural stability of the formed SAW resonator is correspondingly improved.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a surface acoustic wave resonator and a forming method thereof.
Background
Surface acoustic wave resonators (surface acoustic wave, SAW) are solid state electronic devices that primarily utilize acoustic-to-electrical transducers to perform signal conversion and processing from electrical signals to acoustic signals to electrical signals on a layer of piezoelectric material. At present, the surface acoustic wave resonator has stable frequency source function and filtering function and is widely applied, and along with the continuous development of technology, the requirements on the surface acoustic wave resonator are also higher and higher. Therefore, how to further increase the Q value of the surface acoustic wave resonator has been a hot spot of research in the industry.
In recent years, a high performance surface acoustic wave resonator (IHP-SAW) has been proposed, which not only improves the Q value (up to 4000) but also improves the frequency temperature coefficient, thereby achieving the effect of temperature compensation. Specifically, the low acoustic impedance material and the high acoustic impedance material which are periodically arranged are arranged below the piezoelectric material layer to form the Bragg emission layer, so that leaked energy can be effectively reflected to the surface of the piezoelectric material, and the purpose of improving Q value is achieved.
The surface acoustic wave resonator as described above has a piezoelectric material layer on a bragg reflection layer. However, it is often difficult to epitaxially grow a layer of piezoelectric material on the bragg reflective layer. Based on this, a solution is proposed, for example, referring to fig. 1, a method of forming a surface acoustic wave resonator may include: first, a substrate having a piezoelectric material layer 30 is provided, and a low acoustic impedance material layer 22 in a bragg reflection layer is formed on the piezoelectric material layer 30; next, another substrate 10 is provided, and a high acoustic impedance material layer 21 is formed on the other substrate 10; next, the two substrates are bonded to each other in a direction in which the low acoustic impedance material layer 22 and the high acoustic impedance material layer 21 face each other, so that the bragg reflection layer is provided under the piezoelectric material layer 30.
However, it should be noted that the bonding difficulty between the high acoustic impedance material layer 21 and the low acoustic impedance material layer 22 is generally large, making the surface acoustic wave resonator difficult to manufacture, and affecting the mechanical properties of the formed surface acoustic wave resonator.
Disclosure of Invention
The invention aims to provide a surface acoustic wave resonator, which is used for solving the problems that the existing surface acoustic wave resonator is relatively difficult to prepare and improving the mechanical property of the surface acoustic wave resonator.
In order to solve the above technical problems, the present invention provides a surface acoustic wave resonator, including:
a substrate having a cavity formed therein;
a bonding layer formed on the substrate;
a reflective layer bonded on the bonding layer and covering over the cavity, and the bonding layer and the reflective layer are the same material;
a piezoelectric material layer formed on the reflective layer; the method comprises the steps of,
and an electrode formed on the piezoelectric material layer.
Optionally, the bonding layer surrounds the periphery of the cavity, and the reflecting layer covers the opening of the cavity and is bonded with the bonding layer at the periphery of the cavity.
Optionally, the thickness of the reflecting layer is equal to one quarter of the wavelength of the acoustic wave, and forms a bragg reflector with the cavity.
Optionally, the bonding layer covers the opening of the cavity and extends to the periphery of the cavity, the reflecting layer is bonded on the bonding layer, through holes which are mutually communicated are formed in the reflecting layer and the bonding layer, and the bottoms of the through holes in the bonding layer extend to the cavity; alternatively, a through hole is formed in a portion of the substrate located below the cavity, and a top of the through hole in the substrate extends to the cavity.
Optionally, the sum of the thicknesses of the bonding layer and the reflecting layer is equal to one quarter of the wavelength of the acoustic wave, and forms a bragg reflector with the cavity.
Optionally, the materials of the bonding layer and the reflective layer each comprise silicon oxide.
In addition, the invention also provides a method for forming the surface acoustic wave resonator, which comprises the following steps:
providing a first substrate and a second substrate, wherein a cavity is formed in the first substrate, a bonding layer is formed on the first substrate, the second substrate comprises a piezoelectric material layer, and a reflecting layer is formed on the piezoelectric material layer, and the bonding layer and the reflecting layer are made of the same material;
and carrying out a bonding process with the bonding layer of the first substrate facing the reflecting layer of the second substrate, and at least covering the reflecting layer on the opening of the cavity.
Optionally, the forming method of the cavity and the bonding layer includes:
forming a bonding material layer on the first substrate, and forming a patterned mask layer on the bonding material layer;
and sequentially etching the bonding material layer and the first substrate by taking the mask layer as a mask, stopping etching in the first substrate to form the bonding layer on the first substrate and forming the cavity in the first substrate.
Optionally, in the bonding process, the reflective layer covers the opening of the cavity and bonds with the bonding layer at the periphery of the cavity.
Optionally, the forming method of the cavity and the bonding layer includes:
forming a patterned mask layer on the first substrate;
etching the first substrate by taking the mask layer as a mask and stopping etching in the first substrate to form the cavity in the first substrate;
filling a sacrificial layer in the cavity; the method comprises the steps of,
a bonding layer is formed on the first substrate, covers the sacrificial layer, and extends to the outer periphery of the sacrificial layer.
Optionally, after performing the bonding process, the method further includes:
sequentially etching the piezoelectric material layer, the reflecting layer and the bonding layer from the surface of the piezoelectric material layer, which is away from the first substrate, so as to form at least one release hole, wherein the bottom of the release hole extends to the sacrificial layer in the cavity; or etching the first substrate from a side of the first substrate facing away from the piezoelectric material layer to form at least one release hole, the release hole extending to the sacrificial layer in the cavity;
and removing the sacrificial layer through the release hole so as to release the space of the cavity.
Optionally, after performing the bonding process and before forming the electrode, the method further includes: the piezoelectric material layer is thinned from a surface of the piezoelectric material layer facing away from the first substrate.
In the surface acoustic wave resonator provided by the invention, the reflecting layer is arranged, and the cavity is arranged below the reflecting layer, so that the reflecting layer and the cavity can be utilized to realize the repeated reflection of the sound wave propagating along the vertical direction, the loss of the sound wave energy is reduced, and the Q value of the surface acoustic wave resonator is further improved. The surface acoustic wave resonator provided by the invention is particularly suitable for a high-performance surface acoustic wave resonator (IHP-SAW).
The bonding layer and the reflecting layer are also formed by adopting the same material, so that the bonding layer and the reflecting layer are mutually bonded based on the same material. Therefore, the bonding difficulty of the bonding layer and the reflecting layer is reduced, and the preparation difficulty of the surface acoustic wave resonator is correspondingly reduced; and the bonding strength of the bonding layer and the reflecting layer can be further improved, and the mechanical property of the surface acoustic wave resonator is improved.
In addition, the bonding layer and the reflecting layer are made of the same material, so that the bonding layer and the reflecting layer can jointly form a fixed reflecting layer, and the fixed reflecting layer generally has different acoustic impedances relative to an empty cavity, so that the leaked sound waves can be reflected by two reflectors with different acoustic impedances, and the total reflection of the sound waves is facilitated. That is, in the surface acoustic wave resonator provided by the invention, the bonding layer and the reflecting layer can be used for forming the fixed reflecting layer, and can also be used for improving the adhesion degree between the piezoelectric material layer and the substrate, so that the structural stability of the surface acoustic wave device is improved.
Drawings
Fig. 1 is a schematic structural diagram of a surface acoustic wave resonator in the prior art during a manufacturing process thereof;
fig. 2 is a schematic structural diagram of a saw resonator according to a first embodiment of the present invention;
fig. 3 is a flow chart of a method for forming a surface acoustic wave resonator according to a first embodiment of the present invention;
fig. 4a to 4f are schematic structural diagrams of a method for forming a surface acoustic wave resonator according to a first embodiment of the present invention during a manufacturing process;
fig. 5 is a schematic structural diagram of a saw resonator according to a second embodiment of the present invention;
fig. 6a to 6h are schematic structural diagrams of a method for forming a surface acoustic wave resonator according to a second embodiment of the present invention during the preparation process.
Wherein, the reference numerals are as follows:
10-a substrate;
21-a layer of high acoustic impedance material;
a layer of 22-low acoustic impedance material;
30-a layer of piezoelectric material;
100-a substrate;
100 a-a first substrate;
110-a cavity;
210/210' -bonding layer;
220-a reflective layer;
300-a layer of piezoelectric material;
400-electrode;
500-release holes;
600-mask layer;
700-sacrificial layer.
Detailed Description
The surface acoustic wave resonator and the method of forming the same according to the present invention are described in further detail below with reference to the accompanying drawings and specific examples. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
Example 1
Fig. 2 is a schematic structural diagram of a surface acoustic wave resonator according to a first embodiment of the present invention. As shown in fig. 2, the surface acoustic wave resonator includes: a substrate 100, and a bonding layer 210, a reflective layer 220 and a layer 300 of piezoelectric material on said substrate 100. Wherein, the substrate 100 further has a cavity 110 formed therein, and the reflective layer 220 covers an opening of the cavity 110.
Note that, in the surface acoustic wave resonator of the present embodiment, not only the reflection layer 220 is provided to reflect the leaked sound wave back into the piezoelectric material layer 300 by using the reflection layer 220. Also, a cavity 110 is provided in the substrate 100, so that the leaked sound waves can be further reflected by the cavity 110. That is, in this embodiment, the reflecting layer 220 and the cavity 110 can reflect the sound wave for multiple times, so as to ensure that the leaked sound wave can be reflected back in a large amount, thereby effectively reducing the loss of the acoustic wave energy and improving the Q value of the acoustic surface wave resonator.
In particular, the reflecting layer 220 is a solid reflector, so that the reflecting layer 220 and the cavity 110 have different acoustic impedances, so that the leaked sound wave can be reflected by two reflectors with different acoustic impedances, thereby being beneficial to improving the reflection performance of the sound wave. For example, sound waves propagating from a reflector with low acoustic impedance to a reflector with high acoustic impedance may be changed in phase by about 180 degrees, thereby facilitating total reflection of the sound waves.
Further, the reflection performance for the acoustic wave may increase as the difference in acoustic impedance between the two reflectors increases. In this embodiment, the cavity 110 generally has a relatively high acoustic impedance, and based on this, a reflective layer 220 having a relatively low acoustic impedance may be provided. Specifically, the reflective layer 220 may be a low acoustic impedance material layer, the material of which includes, for example, silicon oxide (SiO) 2 )。
In this embodiment, the reflector for reflecting the sound wave includes the reflection layer 220 with low acoustic impedance and the cavity 110 with high acoustic impedance. Further, the thickness of the reflective layer 220 may be approximately equal to or equal to one quarter of the wavelength (1/4λ) of the sound wave, and the low acoustic impedance reflective layer 200 and the high acoustic impedance cavity 110 form a bragg reflector to facilitate the total reflection performance of the sound wave.
As described above, the bonding layer 210 and the reflective layer 220 are the same material. In this embodiment, the bonding layer 210 and the reflective layer 220 are both low acoustic impedance material layers, for example, the bonding layer 210 and the reflective layer 220 each comprise silicon oxide.
Further, the bonding layer 210 and the reflective layer 220 are bonded to each other at a connection interface of both. In this embodiment, since the materials of the bonding layer 210 and the reflective layer 220 are the same, it is more advantageous to implement the bonding connection between the bonding layer 210 and the reflective layer 220 based on the same materials.
In this embodiment, the bonding layer 210 surrounds the periphery of the cavity 110, and the reflective layer 220 covers the opening of the cavity 110 and bonds with the bonding layer 210 at the periphery of the cavity 110. That is, in this embodiment, the reflective layer 220 covers the cavity 110, and the height of the space surrounded by the reflective layer is equal to the height from the bottom surface of the cavity 110 to the top surface of the bonding layer 210.
With continued reference to fig. 2, the layer of piezoelectric material 300 is located on the side of the reflective layer 220 remote from the 100 substrate. Wherein the material of the piezoelectric material layer 300 may include lithium tantalate (LiTaO) 3 ) And lithium niobate (LiNbO) 3 ) At least one of them.
Further, the saw resonator further includes an electrode 400, and the electrode 400 is formed on the surface of the piezoelectric material layer 300. In this embodiment, the electrode 400 is at least partially located directly above the cavity 110.
Still further, the electrode 400 of the saw resonator includes an input electrode and an output electrode. It should be appreciated that only a schematic cross-sectional view of one electrode is shown schematically in fig. 2. Wherein the input terminal electrode and the output terminal electrode may be interdigital electrodes, and the interdigital electrodes may be used for realizing conversion between an acoustic signal and an electrical signal, for example, in a shape like a finger-like interdigital structure of fingers of two hands. Specifically, during operation of the saw resonator, the input electrode may convert an input electrical signal into an acoustic signal by an inverse piezoelectric effect, and the acoustic signal further propagates along the surface of the piezoelectric material layer 300 and propagates to the output electrode to convert the acoustic signal into an electrical signal for output by using the output electrode.
In particular embodiments, the electrode 400 may include a patterned metal layer having a pattern including, for example, an interdigitated pattern as described above.
Based on the surface acoustic wave resonator as described above, the present embodiment also provides a method of forming the surface acoustic wave resonator. Fig. 3 is a flow chart of a method for forming a surface acoustic wave resonator according to a first embodiment of the present invention, and as shown in fig. 3, the method for forming a surface acoustic wave resonator according to the present embodiment includes:
step S100, providing a first substrate, wherein a cavity is formed in the first substrate, and a bonding layer is formed on the first substrate;
step 200, providing a second substrate, wherein the second substrate comprises a piezoelectric material layer, and a reflecting layer is formed on the piezoelectric material layer, and the bonding layer and the reflecting layer are made of the same material;
and step S300, the bonding process is performed with the bonding layer of the first substrate facing the reflecting layer of the second substrate, and at least the reflecting layer is covered on the opening of the cavity.
In this embodiment, a first substrate is provided in step S100, and then a second substrate is provided in step S200. However, it should be appreciated that in other embodiments, the second substrate may be provided first in step S100, followed by the first substrate in step S200. That is, the preparation sequence of the first substrate and the second substrate may be adjusted according to the actual requirement, which is not limited herein.
In addition, in this embodiment, the bonding layer and the reflecting layer with the same material are respectively prepared on the first substrate and the second substrate, so that the first substrate and the second substrate can be bonded with each other based on the film layer with the same material, which is beneficial to reducing the bonding difficulty between the first substrate and the second substrate, improving the bonding strength between the first substrate and the second substrate, and correspondingly guaranteeing the performance of the formed surface acoustic wave resonator. And the Q value of the formed surface acoustic wave resonator is further improved by arranging the cavity.
The method of forming the surface acoustic wave resonator will be described in detail with reference to fig. 4a to 4 f. Fig. 4a to fig. 4f are schematic structural diagrams of a method for forming a surface acoustic wave resonator according to a first embodiment of the present invention in a preparation process thereof.
In step S100, referring specifically to fig. 4a and 4b, a first substrate 100a is provided, a cavity 110 is formed in the first substrate 100a, and a bonding layer 210 is formed on the first substrate 100a. In this embodiment, the bonding layer 210 surrounds the top opening of the cavity 110.
Specifically, the forming method of the cavity 110 and the bonding layer 210 includes:
first, a bonding material layer is formed on the first substrate 100 a; wherein the bonding material layer may be formed, for example, by a deposition process;
next, referring specifically to fig. 4a, a patterned mask layer 600 is formed over the bonding material layer; wherein the patterned mask layer 600 is, for example, a patterned photoresist layer;
next, as shown in fig. 4a, the patterned mask layer 600 is used as a mask to sequentially etch the bonding material layer and the first substrate 100a, and the etching is stopped in the first substrate 100a, so as to form a cavity 110 in the first substrate 100a, and form a bonding layer 210 exposing the cavity 110 on the first substrate 100 a;
thereafter, referring specifically to fig. 4b, the mask layer is removed and the top surface of the bonding layer 210 is exposed.
In step S200, referring specifically to fig. 4c, a second substrate is provided, which includes a piezoelectric material layer 300, and a reflective layer 220 is formed on the piezoelectric material layer 300.
In this embodiment, the second substrate is a piezoelectric material substrate. Of course, in other embodiments, the second substrate may further include a base and a piezoelectric material layer formed on the base.
Wherein, similar to the bonding layer 210, the reflective layer 220 may also be formed using a deposition process. And, the bonding layer 210 and the reflective layer 220 are made of the same material, for example, the bonding layer 210 and the reflective layer 220 each comprise silicon oxide.
In step S300, referring specifically to fig. 4d, a bonding process is performed with the bonding layer 210 of the first substrate 100a facing the reflective layer 220 of the second substrate, and at least the reflective layer 220 is sealed over the opening of the cavity 110.
In this embodiment, the bonding layer 210 only surrounds the periphery of the cavity 110, and based on this, the reflective layer 220 directly covers the top opening of the cavity 110, and bonds with the bonding layer 210 at the periphery of the cavity 110.
That is, in the present embodiment, the reflection layer 220 mainly reflects sound waves. In addition, the portion of the reflective layer 220 directly above the cavity 110 is not bonded to the bonding layer 210, and thus, the thickness of the portion of the reflective layer 220 directly above the cavity can be kept stable. In other words, the reflective layer 220 in this embodiment includes a portion directly above the cavity 110, where the thickness of the portion not involved in bonding has a stable thickness, so that the thickness of the portion of the reflective layer 220 that is mainly used to achieve reflection of sound waves can be controlled more accurately.
In addition, in the present embodiment, the bonding layer 210 surrounds the periphery of the cavity 110, and the reflective layer 220 is supported by the top surface of the bonding layer 210, so that the depth of the space surrounded by the first substrate 100a and the reflective layer 220 is from the bottom surface of the cavity 110 to the top surface of the bonding layer 210.
In this embodiment, the second substrate is a piezoelectric material substrate, and based on this, referring specifically to fig. 4e, after the bonding process is performed, the method further includes: the piezoelectric material layer 300 is thinned from a surface of the piezoelectric material layer 300 facing away from the first substrate 100a.
Specifically, the thickness of the thinned piezoelectric material layer 300 may be made approximately equal to a predetermined multiple of the wavelength of the acoustic wave. For example, the thickness of the thinned piezoelectric material layer 300 may be made 4 times the acoustic wavelength (4λ), 5 times the acoustic wavelength (5λ), 6 times the acoustic wavelength (6λ), or the like.
In a further aspect, the forming method further includes: in step S400, referring specifically to fig. 4f, an electrode 400 is formed on a surface of the piezoelectric material layer 300 facing away from the first substrate 100a.
Specifically, the method for forming the electrode 400 includes: first, a metal material layer is formed on the piezoelectric material layer 300; next, a patterned photoresist layer is formed on the metal material layer, and the metal material layer is further patterned based on the patterned photoresist layer, thereby forming the electrode 400.
Alternatively, the electrode 400 may be formed by a lift-off process, which specifically includes: first, a patterned photoresist layer is formed on the piezoelectric material layer 300; next, depositing a metal material layer, wherein the metal material layer covers the top surface of the photoresist layer, and the metal material layer also covers the piezoelectric material layer which is not covered by the photoresist layer; then, the photoresist layer is stripped to remove the metal material covered on the photoresist layer, and the metal material covered on the piezoelectric material layer is remained to form the electrode 400.
Thus, the surface acoustic wave resonator as described above can be formed, and the first substrate 100a in fig. 4f constitutes the substrate 100 shown in fig. 2.
Example two
The difference from the first embodiment is that in the reflective layer of this embodiment, both the bonding layer and the reflective layer cover the opening of the cavity in the first substrate.
Fig. 5 is a schematic structural diagram of a surface acoustic wave resonator according to a second embodiment of the present invention. As shown in fig. 5, similar to the embodiment, a cavity 110 is also formed in the substrate 100 of the present embodiment. However, unlike the first embodiment, in this embodiment, the bonding layer 210 also covers the top opening of the cavity 110.
Specifically, the bonding layer 210' covers the opening of the cavity 110 and extends to the periphery of the cavity 110. And, the reflective layer 220 is bonded to each other with the entire top surface of the bonding layer 210', thereby advantageously improving the bonding strength between the bonding layer 210' and the reflective layer 220.
That is, in the present embodiment, the bonding layer 210' and the reflective layer 220 are included in the portion directly above the cavity 110, and the bonding layer 210' and the reflective layer 220 are made of the same material and have the same reflective properties, so that both the bonding layer 210' and the reflective layer 220 can be used to reflect sound waves.
Further, the sum of the thicknesses of the bonding layer 210 'and the reflecting layer 220 is, for example, equal to or approximately equal to one quarter of the wavelength (1/4λ) of the sound wave, and the bonding layer 210' and the reflecting layer 220 with low acoustic impedance form a solid reflecting layer with low acoustic impedance, and further form a bragg reflector with the cavity 110 with high acoustic impedance, so as to facilitate the total reflection performance of the sound wave.
With continued reference to fig. 5, in this embodiment, through holes are further formed in the bonding layer 210 'and the reflective layer 220, and the through holes in the bonding layer 210' and the through holes in the reflective layer 220 are vertically communicated with each other to form a release hole 500, and the bottom of the release hole 500 extends to the cavity 110. In this embodiment, the bottom of the through hole in the bonding layer 210' extends to the cavity 110.
However, in other embodiments, a through hole may be formed in a portion of the substrate 100 located under the cavity, and a top of the through hole in the substrate 100 may be extended to the cavity 110 to constitute the release hole.
The method of forming the surface acoustic wave resonator in the present embodiment will be described in detail with reference to fig. 6a to 6 h. Fig. 6a to 6h are schematic structural diagrams of a method for forming a surface acoustic wave resonator according to a second embodiment of the present invention in a preparation process thereof.
In step S100, referring specifically to fig. 6a to 6c, a first substrate 100a is provided, a cavity 110 is formed in the first substrate 100a, and a bonding layer 210' is formed on the first substrate 100a. In this embodiment, the bonding layer 210' covers the top opening of the cavity 110 and extends to the outer periphery of the cavity 110.
In this embodiment, the method for forming the cavity 110 and the bonding layer 210' includes the following steps, for example.
Step one, referring specifically to fig. 6a, a patterned mask layer 600 is formed on the first substrate 100a. Likewise, the patterned mask layer 600 may be a patterned photoresist layer directly.
Step two, referring to fig. 6a, the patterned mask layer 600 is used as a mask to etch the first substrate 100a, and the etching is stopped in the first substrate 100a, so as to form the cavity 110 in the first substrate 100a.
Step three, referring specifically to fig. 6b, the cavity 110 is filled with a sacrificial layer 700.
In this embodiment, the sacrificial layer 700 may be formed using a planarization process such that the top surface of the sacrificial layer 700 is flush with the top surface of the first substrate 100a. Of course, in other embodiments, the top surface of the sacrificial layer may further protrude from the top surface of the first substrate 100a, so that the released space corresponding to the sacrificial layer is increased after the sacrificial layer is subsequently removed.
In step four, referring specifically to fig. 6c, a bonding layer 210 'is formed on the first substrate 100a, and the bonding layer 210' covers the sacrificial layer 700 and extends to cover the first substrate 100a at the periphery of the sacrificial layer.
That is, in step S100 of the present embodiment, the cavity 110 is filled with the sacrificial layer 700, and the bonding layer 210' can be covered on the opening of the cavity 110 under the support of the sacrificial layer 700.
In step S200, a second substrate including a piezoelectric material layer 300 is provided, and a reflection layer 220 is formed on the piezoelectric material layer 300. Wherein the bonding layer 210 'and the reflective layer 220 are the same material, for example, the bonding layer 210' and the reflective layer 220 are both comprised of silicon oxide.
In this embodiment, similar to the embodiment, the second substrate may be a piezoelectric material substrate. Alternatively, the second substrate may further include a base and a piezoelectric material layer formed on the base.
In step S300, referring specifically to fig. 6d, a bonding process is performed with the bonding layer 210' of the first substrate 100a facing the reflective layer 220 of the second substrate.
In this embodiment, the bonding layer 210' and the reflective layer 220 are both sealed over the opening of the cavity 110. That is, the reflective layer 220 and the bonding layer 210' can be bonded to each other not only at the periphery of the cavity 110 but also directly above the cavity 110, increasing the bonding area between the bonding layer 210' and the reflective layer 220, and facilitating the improvement of the bonding strength between the bonding layer 210' and the reflective layer 220.
Further, similar to the embodiment, the second substrate may be a piezoelectric material substrate, based on which, as shown in fig. 6e in particular, after performing the bonding process, further includes: the piezoelectric material layer 300 is thinned from a surface of the piezoelectric material layer 300 facing away from the first substrate 100a.
In this embodiment, the cavity 110 is filled with the sacrificial layer 700, so that not only the bonding layer 210', the reflecting layer 220 and the piezoelectric material layer 300 can be supported by the first substrate 100a, but also the film layer above the bonding layer can be supported by the sacrificial layer 700, thereby improving the mechanical strength of the first substrate 100a and the second substrate bonded to each other. Based on this, when the thinning process is performed on the piezoelectric material layer 300, the reflective layer 220 and the piezoelectric material layer 300 can be made to effectively resist mechanical stress during the thinning process.
In step S400, referring specifically to fig. 6f, an electrode 400 is formed on the surface of the piezoelectric material layer 300 facing away from the first substrate 100a.
The method of forming the electrode 400 is similar to that of the embodiment. That is, a method of forming the electrode 400 includes: first, a metal material layer is formed on the piezoelectric material layer 300; next, a patterned photoresist layer is formed on the metal material layer, and the metal material layer is further patterned based on the patterned photoresist layer, thereby forming the electrode 400.
Alternatively, another method of forming the electrode 400 may specifically include: first, a patterned photoresist layer is formed on the piezoelectric material layer 300; next, depositing a metal material layer, wherein the metal material layer covers the top surface of the photoresist layer, and the metal material layer also covers the piezoelectric material layer which is not covered by the photoresist layer; then, the photoresist layer is stripped to remove the metal material covered on the photoresist layer, and the metal material covered on the piezoelectric material layer is remained to form the electrode 400.
In a further aspect, referring specifically to fig. 6g, after thinning the piezoelectric material layer 300, the method further includes: the piezoelectric material layer 300, the reflective layer 220 and the bonding layer 210' are etched in order from the surface of the piezoelectric material layer 300 facing away from the first substrate 100a to form a release hole 500, and the bottom of the release hole 500 extends to the sacrificial layer 700. And, referring to fig. 6h, the sacrificial layer is removed through the release hole 500 to release the space of the cavity 110.
Alternatively, in other embodiments, the first substrate 100a may be etched from a side of the first substrate 100a facing away from the piezoelectric material layer 300 to form at least one release hole, where the release hole extends to the sacrificial layer in the cavity, so that a space of the cavity 110 may be released from a back surface of the first substrate 100a.
In this embodiment, after the electrode 400 is formed, the release hole 500 is formed to release the space of the cavity 110. Alternatively, in other embodiments, the release holes may be preferentially formed to release the space of the cavity 110, and then the electrodes may be formed.
In summary, in the surface acoustic wave resonator described above, not only the reflective layer is disposed below the piezoelectric material layer, but also the cavity is disposed, so that multiple reflections of the acoustic wave propagating along the vertical direction can be realized by using the reflective layer and the cavity, thereby reducing the loss of acoustic energy, and being beneficial to further improving the Q value of the surface acoustic wave resonator.
In particular, the hollow cavity and the reflecting layer generally have different acoustic impedances, so that the leaked sound wave can be reflected by two reflectors with different acoustic impedances, thereby being beneficial to improving the reflection performance of the sound wave.
And, because the empty cavity generally has higher acoustic impedance, at this time, the bonding layer and the reflecting layer can be both set as low acoustic impedance material layers, so that the bonding layer and the reflecting layer have larger acoustic impedance difference value relative to the cavity 110, which is more beneficial to guaranteeing the total reflection performance of the sound wave. And the reflecting layer with low acoustic impedance can be further arranged above the cavity with high acoustic impedance, so that sound waves propagating from the reflecting layer with low acoustic impedance to the cavity with high acoustic impedance can be biased in phase, and the total reflection performance of the sound waves is further ensured.
In addition, the bonding layer and the reflecting layer of the surface acoustic wave resonator are made of the same material, so that the bonding layer also has the corresponding reflecting performance, and the bonding layer and the reflecting layer can be bonded with each other based on the same material. Therefore, the bonding difficulty of the bonding layer and the reflecting layer is reduced, and the preparation difficulty of the surface acoustic wave resonator is correspondingly reduced; and the bonding strength of the bonding layer and the reflecting layer can be further improved, and the mechanical property of the surface acoustic wave resonator is improved.
It should be noted that, in the present description, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different manner from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. And, while the present invention has been disclosed in terms of preferred embodiments, the above embodiments are not intended to limit the present invention. Many possible variations and modifications of the disclosed technology can be made by anyone skilled in the art without departing from the scope of the technology, or the technology can be modified to be equivalent. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
It should be further understood that the terms "first," "second," "third," and the like in this specification are used merely for distinguishing between various components, elements, steps, etc. in the specification and not for indicating a logical or sequential relationship between the various components, elements, steps, etc., unless otherwise indicated.
It should also be understood that the terminology described herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to "a step" or "an apparatus" means a reference to one or more steps or apparatuses, and may include sub-steps as well as sub-apparatuses. All conjunctions used should be understood in the broadest sense. And, the word "or" should be understood as having the definition of a logical "or" rather than a logical "exclusive or" unless the context clearly indicates the contrary. Furthermore, implementation of the methods and/or apparatus in embodiments of the invention may include performing selected tasks manually, automatically, or in combination.
Claims (10)
1. A surface acoustic wave resonator, comprising:
a substrate having a cavity formed therein;
a bonding layer surrounding the substrate surface outside the cavity;
a reflective layer bonded to the bonding layer and covering the cavity, wherein the bonding layer and the reflective layer are made of the same material, the thickness of the reflective layer is equal to one quarter of the wavelength of the sound wave, and the reflective layer and the cavity form a Bragg reflector;
a piezoelectric material layer formed on the reflective layer; the method comprises the steps of,
and an electrode formed on the piezoelectric material layer.
2. The saw resonator of claim 1, wherein the bonding layer and the reflective layer each comprise silicon oxide.
3. A surface acoustic wave resonator, comprising:
a substrate having a cavity formed therein;
a bonding layer covering the opening of the cavity and extending to the periphery of the cavity;
a reflective layer bonded to the bonding layer and covering over the cavity, the bonding layer and the reflective layer being of the same material and the sum of the thicknesses of the bonding layer and the reflective layer being equal to one quarter of the wavelength of the acoustic wave, and the cavity forming a Bragg reflector;
a piezoelectric material layer formed on the reflective layer; the method comprises the steps of,
and an electrode formed on the piezoelectric material layer.
4. The surface acoustic wave resonator according to claim 3, wherein the reflective layer and the bonding layer are each further formed with a through hole communicating with each other, and a bottom of the through hole in the bonding layer extends to the cavity; alternatively, a through hole is formed in a portion of the substrate located below the cavity, and a top of the through hole in the substrate extends to the cavity.
5. The saw resonator of claim 3, wherein the bonding layer and the reflective layer each comprise silicon oxide.
6. A method of forming a surface acoustic wave resonator, comprising:
providing a first substrate and a second substrate, wherein a cavity is formed in the first substrate, a bonding layer is formed on the first substrate, the bonding layer surrounds the substrate surface of the periphery of the cavity, the second substrate comprises a piezoelectric material layer, a reflecting layer is formed on the piezoelectric material layer, and the bonding layer and the reflecting layer are made of the same material;
and carrying out a bonding process with the bonding layer of the first substrate facing the reflecting layer of the second substrate so that the reflecting layer covers the opening of the cavity, the thickness of the reflecting layer is equal to one quarter of the wavelength of sound waves, and the Bragg reflector is formed by the reflecting layer and the cavity.
7. The method of forming a surface acoustic wave resonator of claim 6, wherein the forming the cavity and the bonding layer comprises:
forming a bonding material layer on the first substrate, and forming a patterned mask layer on the bonding material layer;
and sequentially etching the bonding material layer and the first substrate by taking the mask layer as a mask, stopping etching in the first substrate to form the bonding layer on the first substrate and forming the cavity in the first substrate.
8. A method of forming a surface acoustic wave resonator, comprising:
providing a first substrate and a second substrate, wherein a cavity is formed in the first substrate, a bonding layer is formed on the first substrate, the bonding layer covers an opening of the cavity and extends to the periphery of the cavity, the second substrate comprises a piezoelectric material layer, a reflecting layer is formed on the piezoelectric material layer, and materials of the bonding layer and the reflecting layer are the same;
and carrying out a bonding process with the bonding layer of the first substrate facing the reflecting layer of the second substrate so that the reflecting layer covers the opening of the cavity, and the sum of the thicknesses of the bonding layer and the reflecting layer is equal to one quarter of the wavelength of sound waves so as to form a Bragg reflector with the cavity.
9. The method of forming a surface acoustic wave resonator of claim 8, wherein the method of forming the cavity and the bonding layer comprises:
forming a patterned mask layer on the first substrate;
etching the first substrate by taking the mask layer as a mask and stopping etching in the first substrate to form the cavity in the first substrate;
filling a sacrificial layer in the cavity; the method comprises the steps of,
a bonding layer is formed on the first substrate, covers the sacrificial layer, and extends to the outer periphery of the sacrificial layer.
10. The method of forming a saw resonator of claim 9, further comprising, after performing the bonding process:
sequentially etching the piezoelectric material layer, the reflecting layer and the bonding layer from the surface of the piezoelectric material layer, which is away from the first substrate, so as to form at least one release hole, wherein the bottom of the release hole extends to the sacrificial layer in the cavity; or etching the first substrate from a side of the first substrate facing away from the piezoelectric material layer to form at least one release hole, the release hole extending to the sacrificial layer in the cavity;
and removing the sacrificial layer through the release hole so as to release the space of the cavity.
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| CN112532200A (en) * | 2020-11-11 | 2021-03-19 | 武汉衍熙微器件有限公司 | Method for manufacturing acoustic wave device and acoustic wave device |
| CN113054943B (en) * | 2021-03-29 | 2023-07-07 | 北京航天微电科技有限公司 | Method and system for improving stop band suppression, surface acoustic wave filter and electronic equipment |
| CN113890501B (en) * | 2021-12-01 | 2022-04-26 | 常州承芯半导体有限公司 | Method for forming surface acoustic wave resonance device |
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