CN109546985A - Bulk acoustic wave resonator and its manufacturing method - Google Patents

Abstract

The present invention provides a kind of bulk acoustic wave resonator and its manufacturing method.Wherein the bulk acoustic wave resonator includes the silicon substrate being sequentially arranged from bottom to top, hearth electrode, piezoelectric layer, top electrode, and the air chamber in silicon substrate, it is characterized in that, bulk acoustic wave resonator further includes lateral acoustic impedance structure, and the inward flange of lateral acoustic impedance structure is located at except the resonance effective coverage of bulk acoustic wave resonator.Bulk acoustic wave resonator and its manufacturing method of the invention can limit the acoustic wave mode laterally propagated due to being provided with lateral acoustic impedance structure, to improve the performance of resonator, also have the advantages that structure is simple, technique is easy.

Description

Bulk acoustic wave resonator and method of making the same

technical field

The present invention relates to the field of micro-electromechanical technology, in particular to a bulk acoustic wave resonator and a manufacturing method thereof.

Background technique

With the rapid development of wireless communication systems, large-scale commercial deployment of communication protocols from 3G to 4G has been achieved, and it is now moving towards the 5G era. The continuous evolution of communication protocols has put forward higher requirements for the realization of communication equipment. Compared with the 3G protocol, the communication frequency bands in the 4G and 5G protocols show a trend of high frequency and densification: the frequency of communication continues to increase, the bandwidth continues to increase, and the The division of frequency bands is more dense. Therefore, the role of the filter in the RF front-end of the communication system is increasingly prominent. How to achieve low-loss, high-frequency, and high-roll-off filters has become a research focus for RF component manufacturers.

An important factor that affects the performance of the filter is the quality factor of the resonators that make up the filter. The quality factor measures the loss of a resonator at resonance. A high quality factor indicates that the smaller the loss of the resonator, the better insertion loss and passband roll-off of the final filter. The traditional filter is built with separate capacitor and inductor devices. However, this filter is limited by the manufacturing process, and the quality factor is low, usually tens of tens, and it is difficult to form excellent passband insertion loss and stopband at the same time. inhibition. Another commonly used filter is composed of electromagnetic resonant cavities. Although the electromagnetic resonant cavity can ensure high quality factor and achieve better filter performance, because the electromagnetic resonant cavity uses electromagnetic waves as the resonant energy carrier, at a certain frequency, the size of the resonant cavity is L=c/2f. where c is the speed of light and f is the resonant frequency. Because c is much larger than f, the size of the resonant cavity is very large, and it is difficult to meet the requirements of miniaturization of communication systems.

In recent years, with the development of MEMS, filters based on thin-film piezoelectric resonators have appeared. FIG. 1 is a schematic diagram of the structure of a thin film piezoelectric resonator according to the prior art. As shown in FIG. 1, the resonator is fabricated on a silicon substrate 104, 102 and 101 are metal electrodes, and the thickness is usually several hundred nanometers. 103 is a thin film of piezoelectric material, usually zinc oxide or aluminum nitride material, with a thickness of several hundreds of nanometers to several micrometers. In order to make the sound waves generated therein resonate, it is necessary to make the sound waves reflect on the surface of the top and bottom electrodes. Above the top electrode 101 in FIG. 1 is air capable of forming sound wave reflection. In order to make the sound wave also reflect on the lower surface of the bottom electrode, an air cavity 100 is formed under the bottom electrode 102 . When an alternating voltage is applied to the top electrode 101 and the bottom electrode 102, the piezoelectric material film 103 is excited to generate a piezoelectric effect to generate mechanical acoustic waves. The acoustic wave propagates and reflects between the top and bottom electrodes, forming a standing wave resonance, which in turn forms a resonance in the electrical response. Due to the use of cavities to form reflections, such resonators are called cavity reflective BAW resonators.

FIG. 2 is a schematic diagram of the structure of another bulk acoustic wave resonator according to the prior art. as shown in picture 2. Unlike cavity-type BAW resonators, this resonator utilizes a material with alternating high and low acoustic impedance deposited on a silicon substrate as a reflective layer. FIG. 2 shows two stacks of high and low acoustic impedance transformations, 206 is a low acoustic impedance material, and 205 is a high acoustic impedance material. As the acoustic wave propagates towards the substrate 204, the acoustic energy is continuously reflected and transmitted due to the discontinuity in the acoustic impedance. The transmitted sound waves are reflected at the next impedance discontinuity interface. Ultimately, most of the energy reflections are concentrated within the piezoelectric film, creating resonances. This structure is called a solid stacked bulk acoustic wave resonator.

At present, both structures are widely used in the field of wireless communication filtering. FIG. 3 is a schematic diagram of a typical cavity resonator response according to the prior art. As shown in Fig. 3, the abscissa represents the frequency, and the ordinate represents the impedance. The resonator has two resonance frequencies, the series resonance frequency Fs and the parallel resonance frequency Fp. When using bulk acoustic wave resonators to form a filter, the quality factor of the filter has a direct impact on the filter performance, as shown in Figure 4, which shows the effect of the quality factor of the filter on the filter performance according to the prior art schematic diagram. Among them, the abscissa represents the frequency, the ordinate represents the loss, the solid line is the performance curve of the high quality factor resonator, and the dashed line is the performance curve of the low quality factor resonator. As can be seen from Figure 4, a resonator with a high quality factor can provide lower insertion loss and a steeper roll-off characteristic.

At present, the technical means that can improve the quality factor of the resonator are mainly achieved by improving the growth quality of the piezoelectric film, such as improving the bottom electrode roughness, improving the machine performance of the film growth, etc., which usually increases the difficulty of the process.

Therefore, how to improve the quality factor of the resonator by changing the filter structure on the basis of the existing technology has become an important issue in the field of filters.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a bulk acoustic wave resonator and a manufacturing method thereof to solve the technical problems in the prior art.

The bulk acoustic wave resonator according to the embodiment of the present invention includes a silicon substrate, a bottom electrode, a piezoelectric layer, a top electrode and an air cavity in the silicon substrate, which are arranged in sequence from bottom to top. The acoustic wave resonator further includes a transverse acoustic impedance structure, the inner edge of the transverse acoustic impedance structure is located outside the resonance effective area of the bulk acoustic wave resonator.

Optionally, the lateral acoustic impedance structures include high acoustic impedance structures and low acoustic impedance structures that are alternately arranged laterally.

Optionally, the material of the transverse acoustic impedance structure is a single high acoustic impedance material or a single low acoustic impedance material.

Optionally, the material of the transverse acoustic impedance structure is the same as that of the bottom electrode or the top electrode.

Optionally, the thickness of the transverse acoustic impedance structure is less than or equal to the thickness of the piezoelectric layer.

Optionally, the width of the transverse acoustic impedance structure is an odd multiple of 1/4 of the wavelength of the transversely propagated acoustic wave.

The present invention also provides a method for manufacturing a bulk acoustic wave resonator, comprising: forming a groove on a silicon substrate; filling the groove with a sacrificial material; forming a bottom electrode on the silicon substrate; making a transverse acoustic impedance structure on the electrode; making the piezoelectric layer of the bulk acoustic wave resonator; making a top electrode on the surface of the piezoelectric layer; removing the sacrificial material, wherein the inner edge of the transverse acoustic impedance structure is located at the outside the effective resonance region of the BAW resonator.

Optionally, it is characterized in that, the transverse acoustic impedance structure includes a high acoustic impedance structure and a low acoustic impedance structure arranged alternately in the lateral direction; or, the material of the transverse acoustic impedance structure is a single high acoustic impedance material or a single low acoustic impedance material. Acoustic impedance material.

Optionally, the step of fabricating the piezoelectric layer of the bulk acoustic wave resonator includes: depositing a piezoelectric layer material on the silicon substrate and the bottom electrode; grinding the piezoelectric layer material to obtain a smooth surface. Piezoelectric layer.

Optionally, the thickness of the transverse acoustic impedance structure is less than or equal to the thickness of the piezoelectric layer.

As can be seen from the above, the bulk acoustic wave resonator and its manufacturing method of the present invention can limit the transversely propagated acoustic wave mode due to the transverse acoustic impedance structure, thereby improving the device performance, and has the advantages of simple and easy process.

Description of drawings

The accompanying drawings are used for better understanding of the present invention and do not constitute an improper limitation of the present invention. in:

Fig. 1 is the schematic diagram of traditional air reflection type bulk acoustic wave resonator;

2 is a schematic structural diagram of a traditional solid stacked bulk acoustic wave resonator;

Fig. 3 is the impedance-frequency electrical response curve of the traditional resonator;

4 is a schematic diagram of the influence of the quality factor of the resonator on the performance of the filter;

Figure 5 is a graph of the dispersion of the laterally propagating acoustic wave modes present in the resonator;

6 is a schematic structural diagram of a bulk acoustic wave resonator according to the first embodiment of the present invention;

7 is a Smith chart of the performance of the bulk acoustic wave resonator according to the first embodiment of the present invention;

FIG. 8(a) and FIG. 8(b) are comparison diagrams of the electrical impedance of the resonator according to the embodiment of the present invention and the traditional air cavity reflective resonator;

9 is a schematic structural diagram of a bulk acoustic wave resonator according to a second embodiment of the present invention;

10 is a schematic structural diagram of a bulk acoustic wave resonator according to a third embodiment of the present invention;

11 is a schematic structural diagram of a bulk acoustic wave resonator according to a fourth embodiment of the present invention;

12 is a schematic structural diagram of a bulk acoustic wave resonator according to a fifth embodiment of the present invention;

13(a) to 13(i) are schematic diagrams of a method for fabricating a bulk acoustic wave resonator according to an embodiment of the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. The relationship is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore It should not be construed as a limitation of the present invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

In the present invention, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrally connected; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In the present invention, unless otherwise expressly specified and limited, a first feature "on" or "under" a second feature may include the first and second features in direct contact, or may include the first and second features Not directly but through additional features between them. Also, the first feature being "above", "over" and "above" the second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature is "below", "below" and "below" the second feature includes the first feature being directly below and diagonally below the second feature, or simply means that the first feature has a lower level than the second feature.

In the process of realizing the present invention, the inventor analyzed the dispersion curve of the acoustic wave mode existing in the bulk acoustic wave resonator. FIG. 5 is a schematic diagram of a dispersion curve of an acoustic wave mode existing in a bulk acoustic wave resonator calculated by a matrix method according to the prior art. As shown in FIG. 5 , the vertical axis represents the resonant frequency of the resonator, and the horizontal axis represents the spatial wave number of acoustic waves propagating in the lateral direction of the resonator. Figure 5 shows the lowest four modes of Lamb wave sound waves, namely TE1, A1, S0, A0. There is an intersection with the four curves at the resonant frequency Fp, indicating that there are four kinds of outwardly propagating acoustic waves at the Fp frequency, which carry energy and eventually dissipate into the silicon substrate through the boundary. The inventors found that due to the existence of lateral propagation modes and dissipated energy, the acousto-electric conversion efficiency of the device is reduced, thus weakening the quality factor of the device.

In this regard, in the embodiment of the present invention, it is proposed to add a transverse acoustic impedance structure in the bulk acoustic wave resonator, so as to limit the transversely propagating acoustic wave mode. Further description will be given below in conjunction with several embodiments.

6 is a schematic diagram of a bulk acoustic wave resonator according to the first embodiment of the present invention. As shown in FIG. 6 , a bottom electrode 602 is fabricated on the silicon substrate 604 , and the bottom electrode material is a metal material with high acoustic impedance, which may be a metal such as molybdenum, aluminum, and gold. A piezoelectric layer 603 is formed on the bottom electrode 602. The piezoelectric layer 603 is made of piezoelectric crystals such as zinc oxide or aluminum nitride, and has a thickness of several hundreds of nanometers to several micrometers. A top electrode 601 is formed over the piezoelectric layer 603 . An air cavity 600 is formed under the bottom electrode. The lateral dimension of the air cavity on the upper surface of the silicon substrate is defined as the air cavity width L2. The width of the bottom electrode 602 is greater than the width of the air cavity, so as to ensure the support strength of the superstructure. The width of the top electrode 601 is smaller than the width of the air cavity. The common area where the top electrode, the bottom electrode and the air cavity overlap is the effective resonance area of the resonator. Although the width of the top electrode is smaller than that of the air cavity to ensure that the main energy of the acoustic wave propagating between the top and bottom electrodes is confined to the effective area, there is still lateral leakage of energy. On the bottom electrode 602, a high acoustic impedance structure 606 and a low acoustic impedance structure 605 are fabricated. The high acoustic impedance structure 606 and the low acoustic impedance structure 605 together constitute a transverse acoustic impedance structure. The inner boundary of the high acoustic impedance structure 606 and the outer boundary of the top electrode are defined as L1. The value of L1 is a value greater than or equal to 0. That is, the internal position of the acoustic impedance structure will not be located in the effective resonance region formed by the top electrode 601 , the piezoelectric layer 603 and the bottom electrode 602 . The value of L1 ensures that the acoustic wave propagating in the vertical direction will not be affected by the transverse impedance transformation structure. On the other hand, the width of the high acoustic impedance structure is defined as W1, and the width of the low acoustic impedance structure is defined as W2. In order to achieve better confinement of the laterally propagated acoustic wave mode, the widths of W1 and W2 can be selected as odd multiples of 1/4 of the wavelength of laterally propagated acoustic waves (it should be noted that the widths of W1 and W2 are not too wide to save materials In this way, when the transversely propagating acoustic wave mode propagates from the center of the resonator to the edge, most of the energy is confined in the effective area through the reflection of the high acoustic impedance structure 606 and the reflection of the low acoustic impedance structure 605, which improves the electromechanical conversion. Efficiency, reduced energy loss, and improved quality factor.

FIG. 7 is a Smith chart of the performance of the resonator of the first embodiment of the present invention. In this Smith chart, the closer the curve is to the edge of the circle, the lower the loss. It can be seen from Figure 7 that compared with the traditional cavity reflection BAW resonator, the resonator with the transverse impedance transformation structure is above the series resonant frequency Fs, especially near the parallel resonant frequency Fp, the curve position is closer to the circular edge. It shows that the lateral impedance transformation structure can effectively reduce the energy dissipated to the substrate due to the lateral propagation mode, thereby improving the quality factor of the resonator.

Fig. 8(a) and Fig. 8(b) are comparison diagrams of the electrical impedance of the resonator according to the embodiment of the present invention and the electrical impedance of the conventional air cavity reflective resonator, wherein Fig. 8(b) is the curve of Fig. 8(a) A zoomed-in view of the peak position. It can be seen from Figure 8(a) and Figure 8(b) that when the thickness of the thin film structure and the laminated structure are the same, the resonator with the transverse impedance transformation structure has the same capacitance outside the resonant frequency of the conventional resonator. The difference between the two is mainly concentrated above the series resonant frequency Fs, especially near the parallel resonant frequency Fp. The impedance of the resonator with the transverse impedance transformation structure is increased from 1800 ohms to about 3000 ohms. The quality factor of parallel resonance is improved.

9 is a schematic diagram of a bulk acoustic wave resonator according to a second embodiment of the present invention. As shown in FIG. 9 , a bottom electrode 902 is formed on the silicon substrate 904, and the bottom electrode material is a metal material with high acoustic impedance, which may be a metal such as molybdenum, aluminum, and gold. A piezoelectric layer 903 is formed on the bottom electrode 902. The piezoelectric layer 903 is made of piezoelectric crystals such as zinc oxide or aluminum nitride, and has a thickness of several hundreds of nanometers to several micrometers. A top electrode 901 is formed over the piezoelectric layer 903 . An air cavity 900 is formed under the bottom electrode. The width of the bottom electrode 902 is larger than the width of the air cavity, so as to ensure the support strength of the superstructure. The width of the top electrode 901 is smaller than the width of the air cavity. The common area where the top electrode, the bottom electrode and the air cavity overlap is the effective resonance area of the resonator. Although the width of the top electrode is smaller than that of the air cavity to ensure that the main energy of the acoustic wave propagating between the top and bottom electrodes is confined to the effective area, there is still lateral leakage of energy. On the bottom electrode 902, a high acoustic impedance structure 905 and a low acoustic impedance structure 906 are fabricated. The high acoustic impedance structure 905 and the low acoustic impedance structure 906 together constitute a transverse acoustic impedance structure. The inner boundary of the high acoustic impedance structure 906 and the outer boundary of the top electrode are defined as L1. The value of L1 is a value greater than or equal to 0, where L1 is 0. The value of L1 ensures that the acoustic wave propagating in the vertical direction will not be affected by the transverse impedance transformation structure. In order to achieve better confinement of the laterally propagated acoustic wave mode, the width of the high acoustic impedance structure and the width of the low acoustic impedance structure can be selected to be 1/4 of the wavelength of the laterally propagated acoustic wave. In this embodiment, the high-impedance and low-impedance transform structures have two layers respectively. When the lateral propagation propagates outward, it first passes through the inner high acoustic impedance structure 905 , then passes through the inner low acoustic impedance structure 906 , and is then reflected by the outer high acoustic impedance structure 905 and the outer low acoustic impedance structure 906 . Therefore, the transversely propagating sound waves are reflected at least 5 times, effectively confining the sound wave energy to the effective resonance region of the resonator, and improving the quality factor.

10 is a schematic diagram of a bulk acoustic wave resonator according to a third embodiment of the present invention. . As shown in FIG. 10 , a bottom electrode 1002 is formed on the silicon substrate 1004 , and the bottom electrode material is a metal material with high acoustic impedance, which can be metal such as molybdenum, aluminum, and gold. A piezoelectric layer 1003 is formed on the bottom electrode 1002. The piezoelectric layer 1003 is made of piezoelectric crystals such as zinc oxide or aluminum nitride, and has a thickness of several hundreds of nanometers to several micrometers. A top electrode 1001 is formed over the piezoelectric film 1003 . An air cavity 1000 is formed under the bottom electrode. The common area where the top electrode, the bottom electrode and the air cavity overlap is the effective resonance area of the resonator. Although the width of the top electrode is smaller than that of the air cavity to ensure that the main energy of the acoustic wave propagating between the top and bottom electrodes is confined to the effective area, there is still lateral leakage of energy. On the bottom electrode 1002 , a low acoustic impedance structure 1005 is formed, and an air gap 1006 is formed outside the low acoustic impedance structure 1005 . The height of the low acoustic impedance structure 1005 and the air gap 1006 is less than the thickness of the piezoelectric layer. The low acoustic impedance structure 1005 and the air gap 1006 together constitute a transverse acoustic impedance structure. When the transversely propagating acoustic wave mode propagates from the center to the edge of the resonator, most of the energy is confined in the effective area through the reflection inside the low acoustic impedance structure 1005 and the reflection in the air gap 1006, which improves the electromechanical conversion efficiency and reduces the energy loss, achieving an improvement in the quality factor.

11 is a schematic diagram of a bulk acoustic wave resonator according to a fourth embodiment of the present invention. As shown in FIG. 11 , a bottom electrode 1102 is formed on the silicon substrate 1104, and the bottom electrode material is a metal material with high acoustic impedance, which may be a metal such as molybdenum, aluminum, and gold. A piezoelectric layer 1103 is formed on the bottom electrode 1102. The piezoelectric layer 1103 is made of piezoelectric crystals such as zinc oxide or aluminum nitride, and has a thickness of several hundreds of nanometers to several micrometers. A top electrode 1101 is formed over the piezoelectric layer 1103 . An air cavity 1100 is formed under the bottom electrode. The common area where the top electrode, the bottom electrode and the air cavity overlap is the effective resonance area of the resonator. Although the width of the top electrode is smaller than that of the air cavity to ensure that the main energy of the acoustic wave propagating between the top and bottom electrodes is confined to the effective area, there is still lateral leakage of energy. On the bottom electrode 1102 , a transverse acoustic impedance structure 1105 is fabricated, and the material of the transverse acoustic impedance structure 1105 is the same as that of the bottom electrode 1102 and the top electrode 1101 . The thickness of the transverse acoustic impedance structure 1105 is the same as the thickness of the piezoelectric layer 1103 . When the transversely propagating acoustic wave mode propagates from the center of the resonator to the edge, it is reflected through the inner side of the transverse acoustic impedance structure 1105, and most of the energy is confined in the effective area, which improves the electromechanical conversion efficiency, reduces the energy loss, and realizes the improvement of the quality factor. improvement.

12 is a schematic diagram of a bulk acoustic wave resonator according to a fifth embodiment of the present invention. As shown in FIG. 12 , a bottom electrode 1202 is fabricated on the silicon substrate 1204, and the bottom electrode material is a metal material with high acoustic impedance, which may be a metal such as molybdenum, aluminum, or gold. A piezoelectric layer 1203 is formed on the bottom electrode 1202. The piezoelectric layer 1203 is made of piezoelectric crystals such as zinc oxide or aluminum nitride, and has a thickness of several hundreds of nanometers to several micrometers. A top electrode 1201 is formed over the piezoelectric layer 1203 . An air cavity 1200 is formed under the bottom electrode. The common area where the top electrode, the bottom electrode and the air cavity overlap is the effective resonance area of the resonator. Although the width of the top electrode is smaller than that of the air cavity to ensure that the main energy of the acoustic wave propagating between the top and bottom electrodes is confined to the effective area, there is still lateral leakage of energy. On the bottom electrode 1202 , a thin transverse acoustic impedance structure 1205 is fabricated, and the material of the transverse acoustic impedance structure 1205 is the same as that of the bottom electrode 1202 and the top electrode 1201 . The thickness of the transverse acoustic impedance structure 1205 is much smaller than that of the piezoelectric layer 1203 . When the transversely propagating acoustic wave mode propagates from the center of the resonator to the edge, it is reflected through the inner side of the transverse acoustic impedance structure 1205, and most of the energy is confined in the effective area, which improves the electromechanical conversion efficiency, reduces the energy loss, and realizes the improvement of the quality factor. improvement.

The method for manufacturing a bulk acoustic wave resonator according to an embodiment of the present invention may include the following steps: forming a groove on a silicon substrate, filling the groove with a sacrificial material, forming a bottom electrode on the silicon substrate, A transverse acoustic impedance structure is fabricated on the bottom electrode, a piezoelectric layer of the bulk acoustic wave resonator is fabricated, a top electrode is fabricated on the surface of the piezoelectric layer, and finally the sacrificial material is removed. In the above steps, the transverse acoustic impedance structure and the top electrode are fabricated so that the inner edge of the transverse acoustic impedance structure is located outside the effective resonance area of the BAW resonator, so as not to affect the normal resonance.

The transverse acoustic impedance structure may include alternately arranged high acoustic impedance structures and low acoustic impedance structures; alternatively, the material of the transverse acoustic impedance structure may also be a single high acoustic impedance material or a single low acoustic impedance material.

When making the piezoelectric layer, after depositing the piezoelectric layer material on the silicon substrate and the bottom electrode, the piezoelectric layer material can be ground to obtain a piezoelectric layer with a smooth surface, or the smoothing step can be omitted. There will be slight protrusions on the surface of the electrical layer, as shown in Figure 10 and Figure 12. In addition, the thickness of the transverse acoustic impedance structure can be equal to the thickness of the piezoelectric layer, as shown in Figure 6, Figure 9, and Figure 11; the thickness of the transverse acoustic impedance structure can also be smaller than the thickness of the piezoelectric layer, that is, the transverse acoustic impedance structure is submerged in the piezoelectric layer. layer, as shown in Figure 10 and Figure 12.

FIG. 13 is a manufacturing flow chart of the structure of the bulk acoustic wave resonator according to the embodiment of the present invention. As shown in the figure, in FIG. 13(a), a groove is formed on a silicon substrate by an etching process, and a sacrificial material is filled in the groove, and the sacrificial material may be silicon dioxide. Afterwards, the surface of the sinking bottom is ground by a polishing process, as shown in Fig. 13(b). Then, a bottom electrode pattern 13(c) is formed on the silicon substrate by a photolithography process. A high acoustic impedance material is deposited on the bottom electrode and a lateral structure is formed by photolithography, and a low acoustic impedance material is deposited and etched on this basis Figure 13(d-e). Piezoelectric layer material is deposited after the fabrication of the lateral structure is completed and ground flat is performed Figure 13(f-g). Subsequently, on the flat surface of the piezoelectric layer, the top electrode is deposited and etched. Finally, wet etching is used to remove the sacrificial layer material to obtain a resonator with a lateral impedance transformation structure as shown in Figure 13(h-i).

The above specific implementation methods do not constitute a limitation to the protection scope of the present invention. It should be apparent to those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a bulk acoustic wave resonator, comprising a silicon substrate, a bottom electrode, a piezoelectric layer, a top electrode arranged in sequence from bottom to top, and an air cavity in the silicon substrate, characterized in that, The bulk acoustic wave resonator further includes a transverse acoustic impedance structure, the inner edge of which is located outside the effective resonance region of the bulk acoustic wave resonator. 2 . The BAW resonator according to claim 1 , wherein the transverse acoustic impedance structure comprises high acoustic impedance structures and low acoustic impedance structures which are alternately arranged laterally. 3 . 3 . The BAW resonator according to claim 1 , wherein the material of the transverse acoustic impedance structure is a single high acoustic impedance material or a single low acoustic impedance material. 4 . 4 . The BAW resonator according to claim 1 , wherein the material of the transverse acoustic impedance structure is the same as that of the bottom electrode or the top electrode. 5 . 5 . The bulk acoustic wave resonator according to claim 1 , wherein the thickness of the transverse acoustic impedance structure is less than or equal to the thickness of the piezoelectric layer. 6 . 6. The BAW resonator according to any one of claims 1 to 4, wherein the width of the transverse acoustic impedance structure is an odd multiple of 1/4 of the wavelength of the transversely propagated acoustic wave. 7. A method of manufacturing a bulk acoustic wave resonator, comprising: making grooves on a silicon substrate; filling the grooves with a sacrificial material; forming a bottom electrode on the silicon substrate; making a transverse acoustic impedance structure on the bottom electrode; making the piezoelectric layer of the bulk acoustic wave resonator; Making a top electrode on the surface of the piezoelectric layer; removing the sacrificial material, Wherein, the inner edge of the transverse acoustic impedance structure is located outside the effective resonance region of the bulk acoustic wave resonator. 8. The method of claim 7, wherein The lateral acoustic impedance structure includes a high acoustic impedance structure and a low acoustic impedance structure alternately arranged laterally; or, The material of the transverse acoustic impedance structure is a single high acoustic impedance material or a single low acoustic impedance material. 9. The method according to claim 7, wherein the step of fabricating the piezoelectric layer of the BAW resonator comprises: depositing piezoelectric layer material on the silicon substrate and bottom electrode; The piezoelectric layer material is ground to obtain a piezoelectric layer with a smooth surface. 10. The method of claim 7, wherein the thickness of the transverse acoustic impedance structure is less than or equal to the thickness of the piezoelectric layer.