CN113630099A - Bulk acoustic wave resonator, method of manufacturing bulk acoustic wave resonator, bulk acoustic wave resonator assembly, filter, and electronic apparatus - Google Patents

Abstract

The present invention relates to a bulk acoustic wave resonator and a method of manufacturing the same. The resonator includes: a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer, wherein: the overlapping parts of the acoustic mirror, the top electrode, the bottom electrode and the piezoelectric layer in the thickness direction of the resonator form an effective area of the resonator; at least one of the upper side and the lower side of the piezoelectric layer is provided with a concave part, and the bottom of the concave part is a flat surface; and the corresponding electrodes in the top electrode and the bottom electrode are arranged in the area of the sunken part. The invention also relates to a bulk acoustic wave resonator assembly, a filter and an electronic device.

Description

Bulk acoustic wave resonator and manufacturing method, bulk acoustic wave resonator assembly, filter and electronic equipment

technical field

Embodiments of the present invention relate to the field of semiconductors, and in particular, to a bulk acoustic wave resonator and a method for manufacturing the same, a filter having the resonator, a bulk acoustic wave resonator assembly, and an electronic device.

Background technique

With the increasing development of 5G communication technology, the requirements for data transmission rate are getting higher and higher. Corresponding to the data transmission rate is the high utilization rate of spectrum resources and the complexity of spectrum. The complexity of the communication protocol puts forward strict requirements for various performances of the radio frequency system. In the radio frequency front-end module, the radio frequency filter plays a crucial role, which can filter out out-of-band interference and noise to meet the requirements of the radio frequency system and the Communication protocol requirements for signal-to-noise ratio.

Traditional RF filters are limited by structure and performance and cannot meet the requirements of high-frequency communication. As a new type of MEMS device, thin film bulk acoustic resonator (FBAR) has the advantages of small size, light weight, low insertion loss, high frequency bandwidth and high quality factor. It has become one of the research hotspots in the field of communication. However, since the frequency of the FBAR is determined by the thickness, the existing technology can only obtain a small-range frequency adjustment by adding an appropriate mass loading layer. Therefore, how to integrate different frequency RF filters with large frequency intervals on a single substrate is still It is a major challenge faced by FBAR technology.

On the other hand, the series resonator and the parallel resonator of the prior art filter work together to form the passband characteristic of the filter. By setting the series resonance frequencies of the series resonators to be different from each other and the variation of the electromechanical coupling coefficient Kt ² of the series resonators, the roll-off characteristic on the right side of the passband of the filter can be effectively improved. It is easy to achieve good roll-off characteristics by applying a small Kt ² resonator to the filter, but once the design indicators (bandwidth, insertion loss, out-of-band rejection, etc.) are determined, the Kt ² of the resonator is basically determined, so that the filter bandwidth and filter The good roll-off characteristics of the resonator are contradictory. It is difficult to achieve good roll-off characteristics in the design of wide-bandwidth filters under the conventional architecture. The change of Kt ² of the 50Ohm resonator is only about ±0.5%, and the improvement of the filter roll-off characteristic is limited. Therefore, releasing the restriction of the degree of freedom of Kt ² between each resonator is beneficial to improve the roll-off performance of the entire filter.

SUMMARY OF THE INVENTION

In order to improve the degree of freedom in selecting Kt ² of the bulk acoustic wave resonator, the present invention proposes a technical solution for adjusting the thickness of the piezoelectric layer of the bulk acoustic wave resonator.

Based on this technical solution, it is also suitable to fabricate piezoelectric layers of different thicknesses on the same wafer. In this aspect, the electromechanical coupling coefficient of the bulk acoustic wave resonator can be adjusted in a wide range, which is beneficial to the Kt ² of the resonator in a single filter. The selection of the value provides a greater degree of freedom, and on the other hand, the monolithic integration of multiple filters of different frequencies with a large frequency interval can also be realized.

According to an aspect of the embodiments of the present invention, a bulk acoustic wave resonator is proposed, comprising:

base;

acoustic mirror;

bottom electrode;

top electrode; and

piezoelectric layer,

in:

The overlapping portion of the acoustic mirror, the top electrode, the bottom electrode and the piezoelectric layer in the thickness direction of the resonator constitutes an effective area of the resonator;

At least one of the upper and lower sides of the piezoelectric layer is provided with a concave portion, and the bottom of the concave portion is a flat surface;

Corresponding electrodes of the top electrode and the bottom electrode are disposed in the area of the recessed portion.

Embodiments of the present invention also relate to a bulk acoustic wave resonator assembly comprising a first resonator and a second resonator, wherein the first resonator and the second resonator are both bulk acoustic wave resonators, and at least the second resonator is In the above resonator, the first resonator and the second resonator share the same piezoelectric layer, and the original thickness of the piezoelectric layer of the first resonator is the original thickness of the piezoelectric layer of the second resonator.

The invention also relates to a method for manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode connected to the electrode lead-out portion; a top electrode connected to the top electrode lead-out portion; and a piezoelectric layer, disposed between the bottom electrode and the top electrode, the method comprising the steps of:

A recessed portion is provided on at least one of the upper and lower sides of the piezoelectric layer, and the bottom of the recessed portion is a flat surface; and

Corresponding ones of the top electrode and the bottom electrode are provided in the area of the recessed portion.

Embodiments of the present invention also relate to a method of adjusting an electromechanical coupling coefficient of a resonator in a filter, the filter comprising at least one first resonator and at least one second resonator, at least the second resonator being The above-mentioned bulk acoustic wave resonator, the method comprises the steps:

The depth of the recess is selected to adjust the electromechanical coupling coefficient of the second resonator based on the thickness of the piezoelectric layer of the second resonator within the active region.

Embodiments of the present invention also relate to a filter comprising the above-described bulk acoustic wave resonator or resonator assembly.

Embodiments of the present invention also relate to an electronic device comprising the above-mentioned filter or the above-mentioned resonator or component.

Description of drawings

These and other features and advantages of the various disclosed embodiments of the present invention may be better understood by the following description and accompanying drawings, in which like reference numerals refer to like parts throughout, wherein:

1 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, the upper and lower sides of the piezoelectric layer of the right resonator have depressions, and the left There is no depression in the piezoelectric layer of the resonator on the side;

Figures 2a-2s exemplarily illustrate the fabrication process of the bulk acoustic wave resonator assembly shown in Figure 1;

3 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which differs from FIG. 1 in that the piezoelectric layer of the right resonator is Only the underside has a depression;

4 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which is different from FIG. 1 in that the piezoelectric layer of the right resonator has a Only the upper side has a depression;

5 is a schematic cross-sectional view of a BAW resonator assembly according to an exemplary embodiment of the present invention, wherein two BAW resonators are shown, which differs from FIG. 1 in that the resonator mass-loading layer on the right is disposed on the bottom electrode side;

6 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which differs from FIG. 1 in that the resonator mass load layers on the right side are respectively provided on top and bottom electrodes;

7 is a schematic cross-sectional view of a BAW resonator assembly according to an exemplary embodiment of the present invention, wherein two BAW resonators are shown, which differs from FIG. 1 in that the electrode thickness of the left resonator is different from that of the right resonator The electrode thickness of the resonator is different;

8 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, which is different from the structure shown in FIG. 1 in that in FIG. 8 , the outer side of the sidewall of the second acoustic impedance layer is connected to the piezoelectric The included angle of the layers is greater than 90°, while in FIG. 1 , the included angle between the outer side of the sidewall of the first acoustic impedance layer and the piezoelectric layer is greater than 90°.

Detailed ways

The technical solutions of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals refer to the same or similar parts. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention, and should not be construed as a limitation of the present invention. Some, but not all, embodiments of the invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

First of all, the reference numerals in the accompanying drawings of the present invention are explained as follows:

1: The first substrate or auxiliary substrate, the optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc., or lithium niobate, lithium tantalate, potassium niobate, etc. Single crystal piezoelectric substrate.

2: Piezoelectric layer, which can be a single crystal piezoelectric material, optional, such as: single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate (PZT), single crystal Potassium niobate, single crystal quartz film, or single crystal lithium tantalate and other materials can also be polycrystalline piezoelectric materials (corresponding to single crystal, non-single crystal materials), optional, such as polycrystalline aluminum nitride, Zinc oxide, PZT, etc., can also be a rare earth element doped material containing a certain atomic ratio of the above materials, for example, can be doped aluminum nitride, and doped aluminum nitride contains at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like.

3: The first hard mask layer: it can be the first barrier layer, and the material can be selected from silicon nitride, molybdenum, silicon oxide and the like.

4: Bottom electrode, the material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or the composite of the above metals or their alloys.

5: The acoustic reflection layer or the first acoustic impedance layer can be selected from silicon nitride, silicon dioxide, polysilicon, amorphous silicon, aluminum nitride and other materials.

6: The sacrificial layer, which is also the second acoustic impedance layer, can be made of silicon dioxide, doped silicon dioxide, polysilicon, amorphous silicon and other materials, but it is different from the material of the first acoustic impedance layer 5, and the sacrificial layer is The etchant is not easy to etch or does not etch the first acoustic impedance layer 5 .

7: The second substrate, the optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

8: The second hard mask layer: it can be a second barrier layer, and the material can be selected from silicon nitride, molybdenum, silicon oxide, etc.

9: Electrode connection hole, conductive metal is arranged in the hole, and the optional material is metal material, such as molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, platinum, iridium, osmium, chromium or the composite of the above metals or its alloy, etc.

10: Top electrode, the material can be the same as the bottom electrode, and the material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or the composite of the above metals or their alloys. The top and bottom electrode materials are generally the same, but can also be different.

11: Electrode connection part (PAD), the material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or the composite of the above metals or their alloys.

12: Acoustic mirror, which can be a cavity, or a Bragg reflector and other equivalent forms. The embodiment of the present invention adopts the form of a cavity.

13 and 14: frequency adjustment layer or mass load layer, the material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or their alloys. Dielectric materials such as silicon dioxide, aluminum nitride, zinc oxide, and PZT can also be selected, and also include rare earth element doped materials with a certain atomic ratio of the above piezoelectric materials.

1 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention. In FIG. 1 , the bulk acoustic wave resonator assembly includes two bulk acoustic wave resonators arranged in the same piezoelectric layer, and the resonance on the right side is The upper and lower sides of the piezoelectric layer of the resonator have recesses, and the piezoelectric layer of the left resonator has no recesses. In the present invention, the same layer arrangement means that the bottom side or the upper side of the two piezoelectric layers are on the same plane or formed in the same piezoelectric layer forming step.

More specifically, for the resonator on the right side in FIG. 1, it includes: a substrate 7; an acoustic mirror 12; a bottom electrode 4; a top electrode 10; and a piezoelectric layer 12, wherein: the upper and lower sides of the piezoelectric layer 2 are provided There is a recessed portion, the bottom of the recessed portion is a flat surface, the bottom electrode is arranged in the lower recessed portion, and the top electrode is arranged in the upper recessed portion.

For BAW resonators, the frequency is determined by the thickness of each layer, and is inversely proportional, that is, a decrease in the thickness of any layer will lead to an increase in frequency. At the same time, the electromechanical coupling coefficient is determined by the thickness ratio of each layer. From the overall trend, when the ratio of the total thickness of the upper and lower electrodes to the thickness of the piezoelectric layer is larger, the electromechanical coupling coefficient is smaller. Timing, when the thickness ratio of the upper and lower electrodes is 1, the electromechanical coupling coefficient is the largest, and when the ratio of the upper and lower electrodes is greater than 1 or less than 1, the electromechanical coupling coefficient will decrease.

In Figure 1, for the right resonator, the thickness of the piezoelectric layer is smaller than that of the left resonator. When the electrode thickness is the same as the left one, the resonant frequency will be higher, and the electromechanical coupling coefficient will be lower. Optionally, a mass loading layer may be further provided on the top electrode of the right resonator, thereby reducing the frequency and further reducing its electromechanical coupling coefficient. Therefore, by reasonably selecting the depth of the recess (ie, the thickness of the piezoelectric layer) and the thickness of the mass-loading layer, the frequencies of the left and right resonators are equal, but the electromechanical coupling coefficients are quite different.

As shown in FIG. 1 , the concave depth of the upper concave portion is h1, the concave depth of the lower concave portion is h2, the original thickness of the piezoelectric layer is h4, and the thickness of the piezoelectric layer between the two concave portions is h3.

In an embodiment of the present invention, h1 and h2 may be the same or different. Optionally, h1 or h2 does not exceed one-half of h4. Optionally, h3 is not less than one-fifth of h4.

Also shown in FIG. 1 is the angle α between the groove wall of the depression and the depression bottom (flat surface), which angle α, in an alternative embodiment, is in the range of 90°-160°. When the depth of the recessed portion is smaller, the angle can be selected to be close to 90°; and when the depth of the recessed portion is larger, the selection of the angle should be larger, such as 120°. When the depth of the concave portion is large, if the angle is close to 90°, the electrode (which can be the top electrode or the bottom electrode) on the interface will be poorly covered, and faults will easily occur, thus causing adjacent different piezoelectric layers. The electrical connection of the thickness of the resonator is broken.

As shown in FIG. 1 , an acoustic impedance structure is disposed between the piezoelectric layer 4 and the substrate 7, and the acoustic impedance structure includes a first acoustic impedance layer 5 and a second acoustic impedance layer or The sacrificial layer 6, the acoustic impedance of the first acoustic impedance layer 5 and the second acoustic impedance layer 6 are different, and the acoustic mirror is located between the first acoustic impedance layer 5 in the lateral direction of the resonator, in other words, in Fig. 1 In the illustrated embodiment, where the acoustic mirror 12 is in the form of a cavity, the boundary of the acoustic mirror cavity in the transverse direction of the resonator is defined by the first acoustic impedance layer 5 .

In the present invention, the acoustic impedances of the first acoustic impedance layer 5 and the second acoustic impedance layer 6 are different to form impedance mismatch, form continuous reflection of acoustic waves, and form a reflection structure for transverse acoustic waves, thereby preventing transverse acoustic waves. leakage, which is beneficial to lock the energy in the resonator, thereby improving the Q value.

In the present invention, when the piezoelectric layer is a single crystal piezoelectric material, the piezoelectric loss can be lower, so that a higher Q value of the resonator can be obtained, and the electromechanical coupling coefficient and power capacity can be improved at the same time.

In a further embodiment, the widths of the portions of the first acoustic impedance layer 5 and the second acoustic impedance layer 6 in contact with the piezoelectric layer 2 are respectively mλ ₁ /4 and nλ ₂ /4, where m and n are both odd numbers , for example, 1, 3, 5, 7, etc., and λ ₁ and λ ₂ are the wavelengths of acoustic waves propagating laterally at the resonance frequency of the first acoustic impedance layer 5 and the second acoustic impedance layer 6 , respectively. The resonant frequency is a certain frequency within the resonant interval of the resonator, which can be the series resonant frequency or the parallel resonant frequency of the resonator, or a certain frequency between the series and parallel resonant frequencies, or slightly lower than the series resonant frequency or A frequency slightly higher than the parallel resonant frequency. In FIG. 1 , the width of the first acoustic impedance layer 5 is denoted by A, and the width of the second acoustic impedance layer 6 is denoted by B. Selecting the above-mentioned width is beneficial to form an effective acoustic impedance mismatch, prevent transverse acoustic wave leakage, and further improve the Q value of the resonator. m and n may be the same or different, all within the protection scope of the present invention.

The materials for forming the first acoustic impedance layer 5 include aluminum nitride, silicon dioxide, silicon nitride, polysilicon, and amorphous silicon, and the materials for forming the second acoustic impedance layer 6 include silicon dioxide, doped silicon dioxide, and polysilicon. , Amorphous silicon. The material of the first acoustic impedance layer 5 and the material of the second acoustic impedance layer 6 are different from each other. Optionally, the material for forming the first acoustic impedance layer 5 includes silicon dioxide, and the material for forming the second acoustic impedance layer 6 includes polysilicon. Alternatively, the material for forming the first acoustic impedance layer 5 includes silicon nitride or aluminum nitride, and the material for forming the second acoustic impedance layer 6 includes silicon dioxide or doped silicon dioxide. In the present invention, in order to improve the degree of acoustic mismatch at the junction of the first acoustic impedance layer 5 and the second acoustic impedance layer 6, the difference between the acoustic impedances of the two can be selected as large as possible.

As described later with reference to FIGS. 2a-2s, in the process of manufacturing the resonator, the second acoustic impedance layer 6 is also used as a sacrificial layer, so when releasing the sacrificial layer, it is necessary to select a suitable release etchant so that the The etchant etches only the first acoustic impedance material and does not etch or etch a very small amount of the second acoustic impedance material.

As shown in Fig. 1, the end faces of the non-electrode connecting ends of the bottom electrode 4 (the left end of the left resonator in Fig. 1, and the right end of the right resonator in Fig. 1) under the connecting edge of the top electrode are in the transverse direction with the acoustic impedance structure The first acoustic impedance layers 5 are spaced apart, so that the acoustic wave also forms total reflection at the lateral interface between the non-electrode connecting end of the bottom electrode and the gap, thereby reducing acoustic wave leakage. Based on the void structure at the non-electrode connection end, transverse acoustic wave leakage can be further prevented and the Q value of the resonator can be improved. On the other hand, if the end face of the non-electrode connecting end of the bottom electrode 4 below the connecting edge of the top electrode (the left end of the left resonator in FIG. 1, and the right end of the right resonator) is covered by the first acoustic impedance layer 5, A parasitic capacitance is formed with the part of the top electrode outside the cavity, thereby affecting the electromechanical coupling coefficient of the resonator.

In an alternative embodiment, in a longitudinal section of the resonator passing through the electrode connecting end of the bottom electrode 4 (eg, the cross-sectional view shown in FIG. 1 ), the end face of the non-electrode connecting end of the bottom electrode 4 is transversely aligned with the The acoustic impedance structures are spaced apart by a distance in the range of 0.5 μm to 10 μm. The distance may be, for example, 5 μm, 7 μm, or the like, in addition to the end value.

In the embodiment shown in FIG. 1 , the bottom electrode 4 is surrounded by a continuous reflection layer or an acoustic impedance structure formed by the first acoustic impedance layer 5 and the second acoustic impedance layer 6 on one side of the electrode connection end. More specifically, Covered by the first acoustic impedance layer 5, on the one hand, this structure is beneficial to improve the mechanical stability of the resonator, and it is easier to conduct the heat generated during the operation of the resonator to the substrate or the substrate through the electrodes and the first acoustic impedance layer 5. On the other hand, although the energy will leak into the first acoustic impedance layer 5 from the end face of the bottom electrode, due to the existence of the reflection interface formed by the second acoustic impedance layer and the first acoustic impedance layer, Therefore, it is beneficial to lock as much energy as possible inside the resonator, so that the resonator maintains a high Q value.

In the embodiment shown in FIG. 1 , the electrode connection end of the bottom electrode 4 is covered by the first acoustic impedance layer 5 , but the present invention is not limited thereto. For example, the electrode connection end of the bottom electrode 4 may also be spaced apart from the first acoustic impedance layer 5 by a distance in the lateral direction. At this time, because the end face of the non-electrode connection end of the bottom electrode 4 and the end face of the electrode connection end are in the lateral direction The upper part is spaced apart from the first acoustic impedance layer 5, so that the sound wave also forms total reflection at the lateral interface between the bottom electrode and the void, thereby reducing the sound wave leakage and improving the Q value of the resonator. Compared with the structure shown in Fig. 1, the gap is also provided at the electrode connection end, which is beneficial to further prevent the leakage of transverse acoustic waves. However, since the electrode does not form direct contact with the first acoustic impedance layer, the heat must pass through the piezoelectric material indirectly. Conducted into the first acoustic impedance layer and the substrate, resulting in poor power capability.

In an alternative embodiment, in another longitudinal section of the resonator passing through the non-electrode connection end of the bottom electrode 4 and the non-electrode connection end of the top electrode 10, the end face of the non-electrode connection end of the bottom electrode 4 may It is spaced apart from the acoustic impedance structure, and the separation distance is in the range of 0.5 μm-10 μm; or, the non-electrode connection end of the bottom electrode 4 is formed by the first acoustic impedance layer 5 and the second acoustic impedance layer The impedance structure is wrapped, more specifically, covered by the first acoustic impedance layer 5 .

In the present invention, the first acoustic impedance layer 5 and the second acoustic impedance layer 6 may together constitute an acoustic impedance structure. However, the present invention is not limited to this, in other words, the arrangement of the acoustic impedance layers is not limited to this. It may include a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to one another in the lateral direction, or a first acoustic impedance layer, a second acoustic impedance layer, and a first acoustic impedance layer, or a combination of the above. combination.

In the BAW resonator assembly shown in FIG. 1 , three acoustic impedance layers, a first acoustic impedance layer, a second acoustic impedance layer and a first acoustic impedance layer are included between the acoustic mirrors of the two resonators. The two resonators share at least the second acoustic impedance layer 4 located in the middle. Thus, for a single resonator, the acoustic impedance structure surrounding the acoustic mirror 12 includes a first acoustic impedance layer and a second acoustic impedance layer sequentially arranged from the inside to the outside.

In the embodiment shown in FIG. 1 , the first acoustic impedance layer 5 , the second acoustic impedance layer 6 and the first acoustic impedance layer 5 are disposed between the two resonators, but the present invention is not limited thereto. For example, five acoustic impedance layers are included between the acoustic mirrors of the two resonators, the first acoustic impedance layer, the second acoustic impedance layer, the first acoustic impedance layer, the second acoustic impedance layer and the first acoustic impedance layer . The two resonators share at least the first acoustic impedance layer 5 located in the middle. Thus, for a single resonator, the acoustic impedance structure surrounding the acoustic mirror 12 includes a first acoustic impedance layer, a second acoustic impedance layer, and a first acoustic impedance layer sequentially arranged from the inside to the outside. Therefore, the acoustic impedance structure between the two resonators shares at least one first acoustic impedance layer 5 or at least one second acoustic impedance layer 6 .

3 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which differs from FIG. 1 in that the piezoelectric layer of the right resonator is Only the lower side has a depression.

4 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which is different from FIG. 1 in that the piezoelectric layer of the right resonator has a Only the upper side has a depression.

5 is a schematic cross-sectional view of a BAW resonator assembly according to an exemplary embodiment of the present invention, wherein two BAW resonators are shown, which differs from FIG. 1 in that the resonator mass-loading layer on the right is disposed on the On the bottom electrode side, although the mass loading layer is placed below the bottom electrode in the figure, it is easy to understand that the mass loading layer can also be placed between the bottom electrode and the piezoelectric layer.

6 is a schematic cross-sectional view of a bulk acoustic wave resonator assembly according to an exemplary embodiment of the present invention, wherein two bulk acoustic wave resonators are shown, which differs from FIG. 1 in that the resonator mass load layers on the right side are respectively provided on the top and bottom electrodes. Adding a mass load layer on the top electrode and the bottom electrode can flexibly change the thickness ratio of the bottom electrode, the piezoelectric layer and the top electrode, so as to ensure better electrical performance on the basis of adjusting the electromechanical coupling coefficient, such as higher the Q value.

7 is a schematic cross-sectional view of a BAW resonator assembly according to an exemplary embodiment of the present invention, wherein two BAW resonators are shown, which differs from FIG. 1 in that the electrode thickness of the left resonator is different from that of the right resonator The electrode thicknesses of the resonators are different. In an alternative embodiment, the electrode thickness of the left resonator is thicker than that of the right one, and the piezoelectric layer is also thicker than that of the right one, so that the left resonator has a higher thickness. At low frequencies, the integration of two filters with a larger frequency span (such as two filters in a duplexer) can be achieved. By adjusting the thicknesses of the top electrode, piezoelectric layer, and bottom electrode of the two resonators respectively, the combination of resonators with arbitrary frequencies and electromechanical coupling coefficients on a single wafer can be realized, which can be used in different application scenarios.

The fabrication process of the bulk acoustic wave resonator assembly shown in FIG. 1 is exemplarily described below with reference to FIGS. 2a-2s.

Step 1: As shown in Figure 2a, deposit a single crystal piezoelectric thin film layer (ie single crystal piezoelectric layer) 2 on the surface of the substrate or auxiliary substrate 1 (eg silicon, silicon carbide), such as single crystal aluminum nitride (AlN ), gallium nitride (GaN), the deposition process used includes but is not limited to MOCVD (metal organic chemical vapor deposition), MBE (molecular beam epitaxy), CBE (chemical molecular beam epitaxy), LPE (liquid phase epitaxy), etc.; or by A boundary layer is formed on the surface of the auxiliary substrate 1 (such as lithium niobate, lithium tantalate substrate) by ion implantation, and a piezoelectric thin film layer 2 is formed above the boundary layer. The material of the substrate 1 is the same.

Step 2: As shown in FIG. 2b, a hard mask layer 3 serving as a barrier layer is deposited and etched on the surface of the piezoelectric layer 2, and the hard mask layer may be silicon nitride. In the present invention, other materials can also be used as the blocking layer of the piezoelectric layer, as long as the blocking layer can block, for example, the trimming process in the following step 3 to form the concave portion, without affecting other parts of the resonator. The thickness of the piezoelectric layer may be sufficient, and for example, the barrier layer may remain at the end of the trimming. The barrier layer can be further selected so that the barrier layer is removed without excessive piezoelectric layer losses.

Step 3: As shown in Figure 2c, using a trimming process (trim), use particle beam bombardment, such as bombarding the target surface with argon gas, the single crystal piezoelectric layer 2 and the hard mask layer 3, during the trimming process, the hard The thinning speed of the mask layer is slower than that of the single crystal piezoelectric layer, until a depression of a predetermined depth appears on the piezoelectric layer 2, as shown in FIG. 2c, the bottom of the depression is a flat surface.

(

是适合使用修整方法实现的范围,超出该范围则会导致工艺时间过长，此时可以采用部分刻蚀+修整两者相结合的方式来实现)，实际大概在

这种控制精度是刻蚀没有办法比拟的。用修整的方式可以非常精准的控制被轰击的材料层的厚度，工艺简单，且精度高。In the present invention, the trimming here is to physically bombard the target surface with a particle beam. The bombardment does not have any chemical reaction, and the control accuracy is relatively high, and the thickness accuracy can be controlled within 3%. For example, the target needs to be trimmed off.

(

It is a suitable range for the use of trimming methods. Beyond this range, the process time will be too long. At this time, a combination of partial etching and trimming can be used.), the actual

This control precision is incomparable to etching. The thickness of the bombarded material layer can be very precisely controlled by trimming, the process is simple, and the precision is high.

Step 4: As shown in FIG. 2d, the hard mask layer remaining on the piezoelectric layer 2 is removed by a dry or wet etching process to expose the entire surface of the piezoelectric layer. Regardless of the dry method or the wet method, it is necessary to fully consider the effect on the piezoelectric layer when removing the hard mask layer.

Step 5: As shown in FIG. 2e , a bottom electrode material layer is deposited and etched, thereby forming the bottom electrode 4 .

Step 6: As shown in FIG. 2f, deposit a layer of first acoustic impedance material on the surface of the piezoelectric layer 2 and the bottom electrode 4 of the structure obtained in step 5, and pattern it to form the first acoustic impedance layer 5. An acoustic impedance material may be aluminum nitride, silicon dioxide, silicon nitride, polysilicon, amorphous silicon, or the like.

Step 7: As shown in FIG. 2g, deposit a second acoustic impedance material or a sacrificial layer material on the surfaces of the piezoelectric layer 2, the first acoustic impedance layer 5 and the bottom electrode 4 of the structure obtained in step 6, and the second acoustic impedance The layer material may be silicon dioxide, doped silicon dioxide, polysilicon, amorphous silicon, etc., but is different from the material of the first acoustic impedance layer.

The above-mentioned steps 6 and 7 may also change the processing sequence. For example, in step 6, the second acoustic impedance material is first deposited and patterned, and in step 7, the first acoustic impedance layer material is deposited. The resulting structure is shown in Figure 8. In FIG. 8 , the angle between the outside of the sidewall of the second acoustic impedance layer and the piezoelectric layer is greater than 90°, while in FIG. 1 , the angle between the outside of the sidewall of the first acoustic impedance layer and the piezoelectric layer is greater than 90° .

Step 8: As shown in FIG. 2h, the second acoustic impedance material is polished by CMP (chemical mechanical polishing) method until the first acoustic impedance layer 5 is exposed, and the second acoustic impedance layer located on the outer side of the first acoustic impedance layer 5 is exposed. The impedance material constitutes the second acoustic impedance layer 6, and the second acoustic impedance material between the first acoustic impedance layers 5 constitutes the sacrificial layer. In other words, in this embodiment, the second acoustic impedance material is also a sacrificial material.

Step 9: As shown in FIG. 2i , bonding the substrate 7 on the lower sides of the first acoustic impedance layer 5 and the second acoustic impedance layer 6 . Optionally, the surface of the substrate 7 may also have an auxiliary bonding layer (not shown in the figure), such as silicon dioxide, silicon nitride and other materials.

Step 10: As shown in FIG. 2j, the substrate or the auxiliary substrate 1 is removed by grinding, etching process or ion implantation layer separation to expose the upper surface of the piezoelectric layer 2, and optionally, the interface is separated. CMP treatment is performed to make the surface smooth with low roughness.

Step 11: As shown in FIG. 2k, deposit and etch a hard mask layer 8 on the structure of step 10. The hard mask layer can also be silicon nitride, or a mask layer different from the hard mask layer 3 . The process of step eleven is similar to step two.

Step 12: As shown in FIG. 21, using a trimming process (trim), the single crystal piezoelectric layer 2 and the hard mask layer 8 are bombarded with a particle beam. During the trimming process, the thinning speed of the hard mask layer is slower than that of the single crystal layer. The thinning speed of the crystalline piezoelectric layer is adjusted until a depression of a predetermined depth appears on the piezoelectric layer 2. As shown in FIG. 21, the bottom of the depression is a flat surface. The process of step 12 is similar to that of step 3.

Step 13: As shown in FIG. 2m , the hard mask layer 8 remaining on the piezoelectric layer 2 is removed by dry or wet etching to expose the entire upper surface of the piezoelectric layer 2 . The process of step thirteen is similar to that of step four.

Step 14: As shown in FIG. 2n, the through hole 9 is etched in the piezoelectric layer 2 through the process of photolithography and etching, and at the same time, the sacrificial layer release hole is etched on the piezoelectric layer 2 (not shown in the figure). out), the through hole directly leads to the electrode connection end of the bottom electrode 4, or the release hole directly communicates with the cavity of the acoustic mirror or directly to the second acoustic impedance material, ie, the sacrificial layer, located in the cavity of the acoustic mirror.

Step 15: As shown in FIG. 2o, deposit an electrode material layer for the top electrode 10, the electrode material layer covering the top surface of the piezoelectric layer 2 and entering the through holes 9 and the release holes.

Step sixteen: As shown in FIG. 2p , deposit a mass-loading material layer on the top electrode 9 .

Step 17: As shown in FIG. 2q , the top electrode material layer and the mass loading material layer are etched to remove the electrode material in the release holes, and patterned to form the top electrode 10 and the mass loading layer 13 . In the present invention, the method of thickening the top electrode can be used to compensate the frequency at the same time. Steps sixteen and seventeen can also be omitted.

Step 18: As shown in FIG. 2r, a conductive material is deposited and then patterned by a thin film deposition process to form an electrode connection portion 11, including a top electrode connection portion and a bottom electrode connection portion. As shown in Fig. 2r, electrode connecting portions 11 are deposited and patterned to electrically connect the electrode lead-out portions (conductive vias) of the bottom electrodes of the two resonators.

Step 19: As shown in FIG. 2s , pass an etchant through the release hole to release the material of the second acoustic impedance layer or the sacrificial layer in the cavity 12 of the acoustic mirror, so as to obtain the structure corresponding to FIG. 1 .

The above steps are exemplary steps. As can be understood by those skilled in the art, the above processing sequence is not unique. For example, the top electrode 10 can be formed by deposition and patterning first, then the through hole 9 can be formed, and then the bottom electrode connection can be deposited and formed. Section 11. Those of ordinary skill in the art can adjust the sequence of the above steps on the basis of known technologies, which all fall within the protection scope of the present invention.

2a-2s described above is the manufacturing process of arranging depressions on both the upper and lower sides of the piezoelectric layer of one side resonator, and the above process can also be used to manufacture the structures shown in FIGS. 3 and 4 . For example, for the structure of FIG. 3, the above-mentioned steps 2k-2m may be omitted, while for the structure shown in FIG. 4, the above-mentioned steps 2a-2d may be omitted.

Based on the above manufacturing process for the bulk acoustic wave resonator assembly, the present invention also proposes a method for manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator includes a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer, provided between the bottom electrode and the top electrode, and the method includes the steps of: disposing a concave portion on at least one of the upper and lower sides of the piezoelectric layer, the bottom of the concave portion being a flat surface; and disposing a top portion in the area of the concave portion The corresponding electrodes in the electrode and the bottom electrode.

The invention utilizes thinning of the piezoelectric layer of the resonator, and adjusts the frequency and/or electromechanical coupling coefficient of the resonator in a wide range by coordinating the thickness of the top electrode and the bottom electrode, thereby realizing a single-chip multi-frequency filter. integration, as well as providing greater freedom in the choice of Kt ² values for the resonators within the filter. If the difference between the electromechanical coupling coefficients of the two resonators in the resonator assembly shown in FIG. 1 is expected to be large, for example, more than 10%, trimming can be done from both the upper and lower sides of the piezoelectric layer on the right side in FIG. 1 process, so that the thickness of the piezoelectric layer is reduced more than the original thickness, so as to have a greater impact on the electromechanical coupling coefficient of the right resonator. If the difference between the electromechanical coupling coefficients of the two resonators in the resonator assembly shown in FIG. 1 is desired to be small, for example, below 10%, only one side of the piezoelectric layer on the right side in FIG. 1 can be subtracted. The thinning process, as shown in the figure, only thins the lower side (Fig. 3) or only the upper side (Fig. 4) so that the thickness of the piezoelectric layer is not reduced much relative to the original thickness, with a small effect on the right resonator. Electromechanical coupling coefficient.

In the embodiment shown in FIG. 7, the thicknesses h3-h8 shown in FIG. 7 can also be selected to further affect the electromechanical coupling coefficient of each resonator. In FIG. 7, h5-h8 are the thicknesses of the corresponding electrodes.

In the embodiment shown in FIG. 3, the electromechanical coupling coefficient of each resonator is also adjusted by selecting the mass loading layer.

In the present invention, the single crystal piezoelectric layer is used as an example for description, but in the present invention, the material of the piezoelectric layer may also be a non-single crystal material.

In the present invention, when there are grooves on the upper and lower sides, the edges of the grooves on the upper and lower sides are not limited to the upper and lower alignment as shown in the drawings of the corresponding embodiments, and the projections of the upper grooves in the vertical direction can also be The lower groove, or the lower groove falls into the vertical projection of the upper groove, or the upper and lower grooves have a certain overlapping area, which are all within the protection scope of the present invention.

It should also be pointed out that in the present invention, two resonators are set on the same substrate as an example to illustrate the BAW resonator assembly, but the present invention is not limited to this, for example, more resonators can be set on the same substrate, and The plurality of resonators may have two or more piezoelectric layer thicknesses. For example, there may be three resonators in the resonator assembly, and two of the resonators have upper and lower recesses, and at the same time, the depths of the upper and lower recesses of the two resonators are different.

In the present invention, the inner and outer are relative to the center of the effective area of the resonator in the lateral direction or the radial direction, the side or one end of a component close to the center is the inner or inner end, and the component The side or end away from the center is the outer or outer end.

In the present invention, upper and lower are relative to the bottom surface of the base of the resonator. For a component, the side close to the bottom surface is the lower side, and the side away from the bottom surface is the upper side.

In the present invention, the mentioned numerical range can be not only the endpoint values, but also the median or other values between the endpoint values, which are all within the protection scope of the present invention.

As can be appreciated by those skilled in the art, BAW resonators according to the present invention may be used to form filters or other semiconductor devices.

Based on the above, the present invention proposes the following technical solutions:

1. A bulk acoustic wave resonator, comprising:

base;

acoustic mirror;

bottom electrode;

top electrode; and

piezoelectric layer,

in:

The overlapping portion of the acoustic mirror, the top electrode, the bottom electrode and the piezoelectric layer in the thickness direction of the resonator constitutes an effective area of the resonator;

At least one of the upper and lower sides of the piezoelectric layer is provided with a concave portion, and the bottom of the concave portion is a flat surface;

Corresponding electrodes of the top electrode and the bottom electrode are disposed in the area of the recessed portion.

2. The resonator according to 1, wherein:

The concave depth of the concave portion is not more than half of the thickness of the piezoelectric layer.

3. The resonator according to 1, wherein:

The upper and lower sides of the piezoelectric layer are provided with concave portions, and the top electrode and the bottom electrode are respectively disposed in the corresponding concave portions.

4. The resonator according to 3, wherein:

In the thickness direction of the resonator, the thickness of the piezoelectric layer between the recessed portions is not less than one-fifth of the original thickness of the piezoelectric layer.

5. The resonator according to 1, wherein:

The angle between the side wall of the at least one recess and the bottom of the recess is in the range of 90°-160°.

6. The resonator of any one of 1-5, wherein:

An acoustic impedance structure is arranged between the piezoelectric layer and the substrate;

The acoustic impedance structure includes a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to each other in the lateral direction, the acoustic impedance of the first acoustic impedance layer and the second acoustic impedance layer are different, and the acoustic mirror is in the The resonator is located between the first acoustic impedance layers in the lateral direction.

7. The resonator according to 6, wherein:

The widths of the parts of the first acoustic impedance layer and the second acoustic impedance layer in contact with the piezoelectric layer are mλ ₁ /4 and nλ ₂ /4, respectively, where m and n are odd numbers, and λ ₁ and λ ₂ are respectively the first Wavelengths of acoustic waves propagating laterally at the resonant frequency of the acoustic impedance layer and the second acoustic impedance layer.

8. The resonator according to 7, wherein:

m is the same as n.

9. The resonator according to 6, wherein:

A material forming one of the first acoustic impedance layer and the second acoustic impedance layer is selected from aluminum nitride, silicon dioxide, silicon nitride, polysilicon, and amorphous silicon to form the first acoustic impedance layer and the second acoustic impedance layer The material of another layer in the impedance layer is selected from silicon dioxide, doped silicon dioxide, polycrystalline silicon, and amorphous silicon, and the material forming the first acoustic impedance layer is different from the material forming the second acoustic impedance layer.

10. The resonator according to 6, wherein:

The acoustic mirror is an acoustic mirror cavity;

The boundary of the acoustic mirror cavity in the lateral direction of the resonator is defined by the first acoustic impedance layer.

11. The resonator of any of 1-10, wherein:

The piezoelectric layer is a single crystal piezoelectric layer.

12. A bulk acoustic wave resonator assembly, comprising:

The first resonator and the second resonator, the first resonator and the second resonator are both bulk acoustic wave resonators, and at least the second resonator is the resonator according to any one of 1-11, the A resonator and a second resonator share the same piezoelectric layer, and the original thickness of the piezoelectric layer of the first resonator is the original thickness of the piezoelectric layer of the second resonator.

13. The resonator assembly of 12, wherein:

The first resonator and the second resonator are adjacent in the lateral direction and have a first acoustic impedance structure and a second acoustic impedance structure, respectively, and the two acoustic impedance structures share at least one first acoustic impedance layer or at least one second acoustic impedance layer.

14. The resonator assembly of 12 or 13, wherein:

The thickness of the piezoelectric layer of the first resonator within its active area is the original thickness of the piezoelectric layer of the second resonator.

15. The assembly of any of 12-14, further comprising:

A third resonator, the third resonator being a bulk acoustic wave resonator and the resonator according to any one of 1-11, the third resonator being connected to the first resonator and the second resonator share the same piezoelectric layer.

16. The assembly of 15, wherein:

The thickness of the piezoelectric layer of the third resonator located in the effective area of the third resonator is different from the thickness of the piezoelectric layer of the second resonator located in the effective area of the second resonator.

17. The assembly of any of 12-16, wherein:

The sum of the thicknesses of the top and bottom electrodes of at least one resonator is different from the sum of the thicknesses of the top and bottom electrodes of the other resonators, or the thickness of one electrode of the at least one resonator is different from the corresponding electrodes of the other resonators thickness; and/or

At least one resonator is provided with a mass loading layer.

18. A method for manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer disposed between the bottom electrode and the top electrode, the method comprising the steps :

A recessed portion is provided on at least one of the upper and lower sides of the piezoelectric layer, and the bottom of the recessed portion is a flat surface; and

Corresponding ones of the top electrode and the bottom electrode are provided in the area of the recessed portion.

19. The method of 18, wherein: the method comprises:

Step 1: forming a piezoelectric layer on a substrate, and the substrate is arranged on the first side of the piezoelectric layer;

Step 2: forming a second concave portion on the second side of the piezoelectric layer, and the bottom of the second concave portion is a flat surface;

Step 3: depositing and patterning a bottom electrode material layer on the second side of the piezoelectric layer to form a bottom electrode within the second recess;

Step 4: After Step 3, a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to each other in the lateral direction are formed on the piezoelectric layer. A side wall bridging the second recess, an acoustic mirror space is formed between the adjacent first acoustic impedance layers in the lateral direction, at least a part of the bottom electrode is located in the space in the lateral direction, and the first acoustic mirror space is formed in the lateral direction. The acoustic impedance of an acoustic impedance layer is different from that of the second acoustic impedance layer;

Step 5: bonding the substrate with the first and second acoustic impedance layers, and removing the substrate to expose the first side of the piezoelectric layer; and

Step 6: forming a top electrode and a corresponding electrode electrical connection structure on the first side of the piezoelectric layer.

20. The method of 19, wherein:

Step 6 includes:

Step 61 : forming a first concave portion on the first side of the piezoelectric layer, and the bottom of the first concave portion is a flat surface;

Step 62: Depositing and patterning a layer of top electrode material on the first side of the piezoelectric layer to form a top electrode within the first recess.

21. The method of 18, wherein: the method comprises:

Step 1: forming a piezoelectric layer on a substrate, and the substrate is arranged on the first side of the piezoelectric layer;

Step 2: depositing and patterning a layer of bottom electrode material on the second side of the piezoelectric layer to form a bottom electrode;

Step 3: After Step 2, a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to each other in the lateral direction are formed on the piezoelectric layer, and the adjacent first acoustic impedance layers in the lateral direction are formed. An acoustic mirror space is formed between them, at least a part of the bottom electrode is located in the space in the lateral direction, and the acoustic impedance of the first acoustic impedance layer is different from that of the second acoustic impedance layer;

Step 4: connecting the substrate with the first acoustic impedance layer and the second acoustic impedance layer, and removing the substrate to expose the first side of the piezoelectric layer;

Step 5: forming a first concave portion on the first side of the piezoelectric layer, and the bottom of the first concave portion is a flat surface;

Step 6: depositing and patterning a top electrode material layer on the first side of the piezoelectric layer to form a top electrode and a corresponding electrode electrical connection structure in the first recess.

22. The method according to any one of 19-21, wherein:

The step of forming a recess on one side of the piezoelectric layer includes:

forming and patterning a barrier layer on the side of the piezoelectric layer;

Using a trimming process to thin the barrier layer and the exposed piezoelectric layer at the same time, the thinning speed of the barrier layer is less than that of the piezoelectric layer, and based on the thinning of the exposed piezoelectric layer, on the side of the piezoelectric layer forming a depression with a flat bottom;

The barrier layer remaining on the side of the piezoelectric layer is removed.

23. The method according to any one of 19-22, wherein:

The widths of the parts of the first acoustic impedance layer and the second acoustic impedance layer in contact with the piezoelectric layer are mλ ₁ /4 and nλ ₂ /4, respectively, where m and n are odd numbers, and λ ₁ and λ ₂ are respectively the first Wavelengths of acoustic waves propagating laterally at the resonant frequency of the acoustic impedance layer and the second acoustic impedance layer.

24. A method of adjusting the electromechanical coupling coefficient of a resonator in a filter, the filter comprising at least one first resonator and at least one second resonator, at least the second resonator being according to 1-11 The bulk acoustic wave resonator of any one, the method comprising the steps of:

The depth of the recess is selected to adjust the electromechanical coupling coefficient of the second resonator based on the thickness of the piezoelectric layer of the second resonator within the active region.

25. The method of 24, wherein:

The filter includes at least two second resonators, and the method includes the step of varying the thickness of the piezoelectric layer within the active area of one of the at least two second resonators based on the depth of the recess. The thickness of the piezoelectric layer in the active region is adjusted to be different from that of another second resonator of the at least two second resonators, so that the at least two second resonators have a difference in electromechanical coupling coefficient.

26. The method according to 24 or 25, further comprising the steps of:

Select the sum of the thicknesses of the top and bottom electrodes of the at least one second resonator, and/or the thickness of the individual electrodes of the at least one second resonator, and/or provide a mass-loading layer at the at least one second resonator to adjust The electromechanical coupling coefficient of the second resonator.

27. A filter comprising the BAW resonator of any one of 1-11, or the BAW resonator assembly of any one of 12-17.

28. An electronic device comprising the filter according to 27, or the BAW resonator according to any one of 1-11, or the BAW resonator assembly according to any one of 12-17 .

The electronic equipment here includes but is not limited to intermediate products such as RF front-end, filter and amplifier modules, and terminal products such as mobile phones, WIFI, and drones.

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is determined by It is defined by the appended claims and their equivalents.

Claims (28)

1. A bulk acoustic wave resonator comprising:

a substrate;

an acoustic mirror;

a bottom electrode;

a top electrode; and

a piezoelectric layer is formed on the substrate,

wherein:

the overlapping parts of the acoustic mirror, the top electrode, the bottom electrode and the piezoelectric layer in the thickness direction of the resonator form an effective area of the resonator;

at least one of the upper side and the lower side of the piezoelectric layer is provided with a concave part, and the bottom of the concave part is a flat surface;

and the corresponding electrodes in the top electrode and the bottom electrode are arranged in the area of the sunken part.

2. The resonator of claim 1, wherein:

the depression has a depression depth of no more than half of the original thickness of the piezoelectric layer.

3. The resonator of claim 1, wherein:

the upper side and the lower side of the piezoelectric layer are provided with concave parts, and the top electrode and the bottom electrode are respectively arranged in the corresponding concave parts.

4. The resonator of claim 3, wherein:

the thickness of the piezoelectric layer between the recesses is not less than one fifth of the original thickness of the piezoelectric layer in the thickness direction of the resonator.

5. The resonator of claim 1, wherein:

the side wall of at least one recess is at an angle in the range of 90-160 deg. to the bottom of the recess.

6. The resonator of any of claims 1-5, wherein:

an acoustic impedance structure is arranged between the piezoelectric layer and the substrate;

the acoustic impedance structure includes a first acoustic impedance layer and a second acoustic impedance layer disposed adjacent to each other in a lateral direction, the first acoustic impedance layer being different in acoustic impedance from the second acoustic impedance layer, the acoustic mirror being located between the first acoustic impedance layers in the lateral direction of the resonator.

7. The resonator of claim 6, wherein:

the widths of the parts of the first acoustic impedance layer and the second acoustic impedance layer in contact with the piezoelectric layer are m lambda₁A/4 and n lambda₂A/4, where m and n are both odd numbers, λ₁And λ₂Respectively, the acoustic wave wavelengths propagated in the lateral direction at the resonance frequency by the first acoustic impedance layer and the second acoustic impedance layer.

8. The resonator of claim 7, wherein:

m is the same as n.

9. The resonator of claim 6, wherein:

the material forming one of the first and second acoustic impedance layers is selected from the group consisting of aluminum nitride, silicon dioxide, silicon nitride, polysilicon, amorphous silicon, the material forming the other of the first and second acoustic impedance layers is selected from the group consisting of silicon dioxide, doped silicon dioxide, polysilicon, amorphous silicon, and the material forming the first acoustic impedance layer is different from the material forming the second acoustic impedance layer.

10. The resonator of claim 6, wherein:

the acoustic mirror is an acoustic mirror cavity;

the boundary of the acoustic mirror cavity in the lateral direction of the resonator is defined by the first acoustic impedance layer.

11. The resonator of any of claims 1-10, wherein:

the piezoelectric layer is a single crystal piezoelectric layer.

12. A bulk acoustic wave resonator assembly comprising:

first and second resonators, both being bulk acoustic wave resonators, and at least the second resonator being a resonator according to any of claims 1-11, the first and second resonators sharing the same piezoelectric layer, and the original thickness of the piezoelectric layer of the first resonator being the original thickness of the piezoelectric layer of the second resonator.

13. The resonator assembly of claim 12 wherein:

the first resonator and the second resonator are adjacent in the transverse direction and respectively have a first acoustic impedance structure and a second acoustic impedance structure, and the two acoustic impedance structures share at least one first acoustic impedance layer or at least one second acoustic impedance layer.

14. The resonator assembly of claim 12 or 13, wherein:

the thickness of the piezoelectric layer of the first resonator in its active area is the original thickness of the piezoelectric layer of the second resonator.

15. The assembly of any of claims 12-14, further comprising:

a third resonator being a bulk acoustic wave resonator and being a resonator according to any of claims 1-11, the third resonator sharing the same piezoelectric layer as the first and second resonators.

16. The assembly of claim 15, wherein:

the thickness of the piezoelectric layer of the third resonator within the active area of the third resonator is different from the thickness of the piezoelectric layer of the second resonator within the active area of the second resonator.

17. The assembly of any of claims 12-16, wherein:

the sum of the thicknesses of the top electrode and the bottom electrode of at least one resonator is different from the sum of the thicknesses of the top electrode and the bottom electrode of the other resonator, or the thickness of one electrode of at least one resonator is different from the thickness of the corresponding electrode of the other resonator; and/or

At least one resonator is provided with a mass loading layer.

18. A method of manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer disposed between the bottom electrode and the top electrode, the method comprising the steps of:

at least one side of the upper side and the lower side of the piezoelectric layer is provided with a concave part, and the bottom of the concave part is a flat surface; and

corresponding ones of the top and bottom electrodes are disposed within the area of the recess.

19. The method of claim 18, wherein: the method comprises the following steps:

step 1: forming a piezoelectric layer on a substrate, the substrate being disposed on a first side of the piezoelectric layer;

step 2: forming a second recess on a second side of the piezoelectric layer, wherein the bottom of the second recess is a flat surface;

and step 3: depositing and patterning a layer of bottom electrode material on the second side of the piezoelectric layer to form a bottom electrode in the second recess;

and 4, step 4: after step 3, forming a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to each other in the lateral direction on the piezoelectric layer, one of the first acoustic impedance layer and the second acoustic impedance layer bridging a sidewall of the second recess, an acoustic mirror space being formed between the first acoustic impedance layers adjacent in the lateral direction, at least a portion of the bottom electrode being located in the space in the lateral direction, the first acoustic impedance layer being different in acoustic impedance from the second acoustic impedance layer;

and 5: interfacing the base with the first and second acoustic impedance layers, and removing the substrate to expose the first side of the piezoelectric layer; and

step 6: a top electrode and a corresponding electrode electrical connection structure are formed on a first side of the piezoelectric layer.

20. The method of claim 19, wherein:

the step 6 comprises the following steps:

step 61: forming a first concave part on the first side of the piezoelectric layer, wherein the bottom of the first concave part is a flat surface;

step 62: a layer of top electrode material is deposited and patterned on the first side of the piezoelectric layer to form a top electrode within the first recess.

21. The method of claim 18, wherein: the method comprises the following steps:

step 1: forming a piezoelectric layer on a substrate, the substrate being disposed on a first side of the piezoelectric layer;

step 2: depositing and patterning a layer of bottom electrode material on the second side of the piezoelectric layer to form a bottom electrode;

and step 3: after step 2, forming a first acoustic impedance layer and a second acoustic impedance layer arranged adjacent to each other in the lateral direction on the piezoelectric layer, an acoustic mirror space being formed between the first acoustic impedance layers adjacent in the lateral direction, at least a part of the bottom electrode being located in the space in the lateral direction, the first acoustic impedance layer being different in acoustic impedance from the second acoustic impedance layer;

and 4, step 4: interfacing the base with the first and second acoustic impedance layers, and removing the substrate to expose the first side of the piezoelectric layer;

and 5: forming a first concave part on the first side of the piezoelectric layer, wherein the bottom of the first concave part is a flat surface;

step 6: a layer of top electrode material is deposited and patterned on the first side of the piezoelectric layer to form a top electrode and corresponding electrode electrical connection structure within the first recess.

22. The method of any one of claims 19-21, wherein:

the step of forming a recess on one side of the piezoelectric layer includes:

forming and patterning a barrier layer on the one side of the piezoelectric layer;

thinning the barrier layer and the exposed piezoelectric layer simultaneously by using a trimming process, wherein the thinning speed of the barrier layer is less than that of the piezoelectric layer, and forming a concave part with a flat bottom on one side of the piezoelectric layer based on thinning of the exposed piezoelectric layer;

removing the barrier layer remaining on the one side of the piezoelectric layer.

23. The method of any one of claims 19-22, wherein:

the widths of the parts of the first acoustic impedance layer and the second acoustic impedance layer in contact with the piezoelectric layer are m lambda₁A/4 and n lambda₂A/4, where m and n are both odd numbers, λ₁And λ₂Respectively, the acoustic wave wavelengths propagated in the lateral direction at the resonance frequency by the first acoustic impedance layer and the second acoustic impedance layer.

24. A method of adjusting the electromechanical coupling coefficients of resonators within a filter, the filter comprising at least one first resonator and at least one second resonator, at least the second resonator being a bulk acoustic wave resonator according to any of claims 1-11, the method comprising the steps of:

the depth of the recess is selected to adjust an electromechanical coupling coefficient of the second resonator based on a thickness of a piezoelectric layer of the second resonator within the active area.

25. The method of claim 24, wherein:

the filter comprising at least two second resonators, the method comprising the steps of: adjusting a thickness of the piezoelectric layer of one of the at least two second resonators within the active area to be different from a thickness of the piezoelectric layer of the other of the at least two second resonators within the active area based on the depth of the recess such that there is a difference in electromechanical coupling coefficient for the at least two second resonators.

26. The method according to claim 24 or 25, further comprising the step of:

the sum of the thicknesses of the top and bottom electrodes of at least one second resonator, and/or the thickness of the individual electrodes of at least one second resonator, is selected, and/or a mass loading layer is provided at least one second resonator to adjust the electromechanical coupling coefficient of the second resonator.

27. A filter comprising a bulk acoustic wave resonator according to any of claims 1-11, or a bulk acoustic wave resonator assembly according to any of claims 12-17.

28. An electronic device comprising a filter according to claim 27, or a bulk acoustic wave resonator according to any of claims 1-11, or a bulk acoustic wave resonator assembly according to any of claims 12-17.

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