CN114124014B - Film bulk acoustic resonator and preparation method thereof - Google Patents

Abstract

The invention relates to a film bulk acoustic resonator and a preparation method thereof, wherein the film bulk acoustic resonator comprises a top metal electrode, a piezoelectric film layer, a bottom metal electrode and a substrate, the top metal electrode and the bottom metal electrode respectively form a first sound wave energy leakage suppression part and a second sound wave energy leakage suppression part which are opposite in position on the upper surface and the lower surface of the piezoelectric film layer, the first sound wave energy leakage suppression part comprises a groove and/or a bulge, and the corresponding second sound wave energy leakage suppression part comprises a bulge and/or a groove, so that the leakage of sound wave energy in the vertical direction can be reduced through a non-flat structure. Meanwhile, the thickness of the piezoelectric film layer in the section covered by the top metal electrode and the bottom metal electrode is consistent, namely, the upper surface and the lower surface of the piezoelectric film layer are kept parallel and have the same height at different positions in the section so as to inhibit the vertical component of an electric field, so that signals with the same frequency are coherently superposed, and the Q value of the film bulk acoustic resonator is improved.

Description

A thin-film bulk acoustic wave resonator and its preparation method

technical field

The invention relates to the technical field of radio frequency filtering, in particular to a thin film bulk acoustic wave resonator and a preparation method thereof.

Background technique

In wireless communications, RF filters are used as an intermediary to filter specific frequency signals to reduce signal interference in different frequency bands, and to implement functions such as image cancellation, spurious filtering, and channel selection in wireless transceivers. With the deployment of 5G networks and the growth of the market, the design of RF filters is also developing towards miniaturization, low power consumption and integration. Bulk Acoustic Resonator (BAR), as a new type of RF Micro-Electro-Mechanical System (MEMS) device, has become the research focus of RF front-end basic devices. At the same time, due to its high sensitivity, small size, and the ability to wirelessly send and receive signals, it has also achieved rapid development in the field of sensors.

Film Bulk Acoustic Resonator (FBAR) is an important structure in BAR resonators, which has the characteristics of high effective electromechanical coupling coefficient, high quality factor (Q), and compatibility with CMOS technology. FBAR is a thin film device with an electrode-piezoelectric film-electrode "sandwich" added to the substrate material. Its theoretical Q value is higher than that of a solidly mounted resonator (SMR), but its acoustic energy is in the vertical direction. leakage, so that the actual Q value is still limited. How to reduce the leakage of the acoustic wave energy of the thin film bulk acoustic wave resonator in the vertical direction has become a technical problem to be solved urgently.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a thin film bulk acoustic wave resonator and a preparation method thereof, so as to reduce the leakage of the acoustic wave energy of the thin film bulk acoustic wave resonator in the vertical direction and improve the Q value of the thin film bulk acoustic wave resonator.

For achieving the above object, the present invention provides the following scheme:

A thin-film bulk acoustic wave resonator comprises, from top to bottom, a top metal electrode, a piezoelectric thin film layer, a bottom metal electrode and a substrate;

the bottom metal electrode is disposed on the substrate, and the substrate has an air cavity;

The top metal electrode forms a first acoustic wave energy leakage suppressing portion on the upper surface of the piezoelectric thin film layer, and the bottom metal electrode forms a second acoustic wave energy leakage suppressing portion on the lower surface of the piezoelectric thin film layer; wherein , the number of the first acoustic wave energy leakage suppressing part and the second acoustic energy leakage suppressing part are the same and the positions are opposite; the first acoustic wave energy leakage suppressing part and the second acoustic wave energy leakage suppressing part are both located in the air cavity the upper part;

The first acoustic wave energy leakage suppressing portion includes grooves and/or protrusions, the corresponding second acoustic wave energy leakage suppressing portion includes protrusions and/or grooves, and the piezoelectric thin film layer is formed by the top metal electrode. Consistent with the thickness in the section covered by the bottom metal electrode;

The top metal electrode is attached to the upper surface of the piezoelectric thin film layer, and the bottom metal electrode is attached to the lower surface of the piezoelectric thin film layer.

Optionally, the widths of the first acoustic wave energy leakage suppressing portion and the second acoustic wave energy leakage suppressing portion are respectively an integer multiple of the acoustic wave wavelength.

Optionally, the grooves and/or protrusions included in the first acoustic wave energy leakage suppressing portion are all first sub-suppressing portions. Similarly, the protrusions and/or protrusions included in the second acoustic wave energy leakage suppressing portion are the same. /or the grooves are all second sub-suppression parts; wherein:

The sum of the widths of the first sub-suppression parts is an integer multiple of the wavelength of the acoustic wave, the sum of the widths of the second sub-suppression parts is an integral multiple of the wavelength of the acoustic waves, and the ratio of the width between the first sub-suppression parts and the second sub-suppression part is The width ratio is the same.

Optionally, the first acoustic wave energy leakage suppressing portion includes two grooves arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes two protrusions arranged sequentially along the extending direction;

Or the first acoustic wave energy leakage suppressing portion includes protrusions and grooves arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes grooves and protrusions sequentially disposed along the extending direction;

Or the first acoustic wave energy leakage suppressing portion includes grooves and protrusions arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes protrusions and grooves sequentially disposed along the extending direction;

Or the first acoustic wave energy leakage suppressing portion includes two protrusions arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes two grooves arranged sequentially along the extending direction.

Optionally, the width ratio of the two grooves arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the two grooves sequentially arranged along the extending direction in the second acoustic wave energy leakage suppressing portion have a width ratio of 1:2. The width ratio of each protrusion is 1:2;

Or the width ratio of the protrusions and the grooves arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the grooves and grooves arranged sequentially along the extending direction in the second acoustic wave energy leakage suppressing portion are 1:2. The width ratio of the protrusions is 1:2;

Or the width ratio of grooves and protrusions arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the protrusions and protrusions sequentially arranged along the extending direction in the second acoustic wave energy leakage suppressing portion have a ratio of 1:2. The width ratio of the groove is 1:2;

Or the width ratio of the two protrusions arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the two grooves sequentially arranged along the extending direction in the second acoustic wave energy leakage suppressing portion The width ratio is 1:2.

Optionally, the cross-sectional shape of any groove or protrusion is an isosceles trapezoid.

Optionally, the material of the substrate is Si, the material of the bottom metal electrode is Al, Cu, Au or Mo, the material of the piezoelectric thin film layer is piezoelectric material, and the material of the top metal electrode is Al , Cu, Au or Mo.

A preparation method for preparing a thin-film bulk acoustic resonator, the preparation method comprising:

Etch air cavities on the substrate;

depositing a sacrificial filling layer with a preset height in the air cavity;

performing cavity forming processing on the sacrificial filling layer;

A bottom metal electrode with uniform thickness is deposited on the upper surface of the shaped sacrificial filling layer, wherein the bottom metal electrode forms a second acoustic wave energy leakage suppressing part on the upper surface of the shaped sacrificial filling layer;

sputtering a piezoelectric thin film layer on the upper surface of the substrate and the bottom metal electrode;

forming the piezoelectric thin film layer; depositing a top metal electrode with a uniform thickness on the upper surface of the piezoelectric thin film layer after the forming process; wherein, the top metal electrode is formed on the upper surface of the piezoelectric thin film layer after the forming process a first acoustic wave energy leakage suppressing part;

The sacrificial fill layer is removed.

A preparation method, characterized in that it is used for preparing a thin-film bulk acoustic resonator, the preparation method comprising:

Etch air cavities on the substrate;

filming and shaping the piezoelectric material to form the piezoelectric thin film layer;

A top metal electrode is deposited on the upper surface of the piezoelectric thin film layer, and a bottom metal electrode is deposited on the lower surface of the piezoelectric thin film layer to obtain a piezoelectric laminated structure;

The piezoelectric laminate structure is disposed on the substrate.

A MEMS device includes a thin film bulk acoustic resonator.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The embodiment of the present invention discloses a thin-film bulk acoustic resonator and a preparation method thereof. The thin-film bulk acoustic resonator includes a top metal electrode, a piezoelectric thin film layer, a bottom metal electrode and a substrate. The top metal electrode and the bottom metal electrode are respectively connected to piezoelectric The upper and lower surfaces of the thin film layer form a first acoustic wave energy leakage suppressing portion and a second acoustic wave energy leakage suppressing portion, and the first acoustic wave energy leakage suppressing portion includes grooves and/or protrusions, corresponding to the first acoustic wave energy leakage suppressing portion. The second acoustic wave energy leakage suppressing part includes protrusions and/or grooves, so that the leakage of the acoustic wave energy in the vertical direction can be reduced by the non-flat structure. At the same time, the thickness of the piezoelectric thin film layer is the same in the section covered by the top metal electrode and the bottom metal electrode, that is, the upper and lower surfaces of the piezoelectric thin film layer are kept parallel and at the same height at different positions in this section to prevent The vertical component of the electric field makes the signals of the same frequency superimposed coherently, further reducing the leakage of acoustic wave energy in the vertical direction, and improving the Q value of the thin-film bulk acoustic wave resonator.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative labor.

FIG. 1 is an exemplary structure of a thin-film bulk acoustic wave resonator provided by an embodiment of the present invention;

Fig. 2 is another exemplary structure of the thin film bulk acoustic wave resonator provided by the embodiment of the present invention;

Fig. 3 is another exemplary structure of the thin film bulk acoustic wave resonator provided by the embodiment of the present invention;

Fig. 4 is another exemplary structure of the thin film bulk acoustic wave resonator provided by the embodiment of the present invention;

Fig. 5 is the structure diagram of the thin film bulk acoustic wave resonator of the existing "sandwich" structure;

Fig. 6 is the admittance curve diagram of the thin film bulk acoustic wave resonator of the existing "sandwich" structure;

7 is a graph of the quality factor of a thin-film bulk acoustic resonator of an existing "sandwich" structure;

Fig. 8 is the admittance curve diagram of the thin film bulk acoustic wave resonator shown in Fig. 2;

FIG. 9 is a graph of the quality factor of the thin-film bulk acoustic wave resonator shown in FIG. 2;

Fig. 10 is the admittance curve diagram of the thin film bulk acoustic wave resonator shown in Fig. 4;

FIG. 11 is a graph of the quality factor of the thin film bulk acoustic wave resonator shown in FIG. 4;

Fig. 12 is the admittance curve diagram of the thin film bulk acoustic wave resonator shown in Fig. 3;

FIG. 13 is a graph of the quality factor of the thin film bulk acoustic wave resonator shown in FIG. 3 .

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a thin film bulk acoustic wave resonator and a preparation method thereof, so as to reduce the leakage of the acoustic wave energy of the thin film bulk acoustic wave resonator in the vertical direction and improve the Q value of the thin film bulk acoustic wave resonator.

Example 1

As shown in Figures 1-4, Embodiment 1 of the present invention provides a thin film bulk acoustic resonator, which includes a top metal electrode 1, a piezoelectric thin film layer 2, a bottom metal electrode 3 and a substrate 4 in order from top to bottom; the bottom metal electrode 3 is arranged on the substrate 4, and the substrate 4 has an air cavity 5; wherein, the thickness of the top metal electrode 1 and the bottom metal electrode 3 is 200-250nm, and the thickness of the piezoelectric thin film layer 2 is 0.8-1.3um.

The top metal electrode 1 is attached to the upper surface of the piezoelectric thin film layer 2, a first acoustic wave energy leakage suppression part is formed on the upper surface of the piezoelectric thin film layer 2, and the bottom metal electrode 3 is attached to the lower surface of the piezoelectric thin film layer 2. , a second acoustic wave energy leakage suppressing part is formed on the lower surface of the piezoelectric film layer 2;

Wherein, the first acoustic wave energy leakage suppressing part and the second acoustic wave energy leakage suppressing part are the same in number and opposite to each other;

The number of the first acoustic wave energy leakage suppressing portion and the second acoustic energy leakage suppressing portion can be designed according to actual needs, for example, one, two, or even other numbers, which are not described and limited herein.

The first acoustic wave energy leakage suppressing portion includes grooves and/or protrusions, the corresponding second acoustic wave energy leakage suppressing portion includes protrusions and/or grooves, and the piezoelectric thin film layer 2 is formed by the top metal electrode 1 and the bottom portion. The thicknesses of the sections covered by the metal electrodes 3 are the same (or the same thickness). It should be noted that the so-called uniform thickness or the same thickness means: the theoretical thickness is the same, but the error caused by processing should be allowed, wherein the depth of the protrusion or groove is 10-100 nm.

That is, as shown in FIG. 1 , if the first acoustic wave energy leakage suppressing portion includes the groove a, the second acoustic wave energy leakage suppressing portion includes the corresponding protrusion a'. Since the upper and lower surfaces of the piezoelectric film layer are respectively attached to the top electrode and the bottom electrode, the part adjacent to the above-mentioned groove a on the upper surface of the piezoelectric film layer is groove b, and the lower surface of the piezoelectric film layer is adjacent to the above-mentioned protrusion. The part adjacent to a' is a bulge b'.

Due to the uniform thickness, on the piezoelectric film layer, the groove b and the protrusion b' are opposite in position and have the same cross-sectional shape and cross-sectional size (the same refers to the same theory here, but the error caused by processing should be allowed);

Similarly, as shown in FIG. 4 , if the first acoustic wave energy leakage suppressing portion includes a protrusion c, and the second acoustic wave energy leakage suppressing portion includes a corresponding groove c′, then the upper surface of the piezoelectric film layer The part adjacent to the protrusion c is the protrusion d, and the part adjacent to the groove c' on the lower surface of the piezoelectric film layer is the groove d'. Due to the same thickness, the groove d is opposite to the protrusion d', and the cross-sectional shape and cross-sectional size are the same (the same refers to the same theory here, but the error caused by processing should be allowed).

Therefore, it can also be said that the upper surface of the piezoelectric thin film layer includes the third acoustic energy leakage suppressing portion that is in contact with the first acoustic energy leakage suppressing portion, and the lower surface of the piezoelectric thin film layer includes the second acoustic energy leakage suppressing portion. The fourth acoustic wave energy leakage suppressing part that is in close contact with each other. The third acoustic wave energy leakage suppressing portion and the fourth acoustic wave energy leakage suppressing portion have the same number, are opposite to each other, and have the same cross-sectional shape and cross-sectional size.

In one example, the widths of the first acoustic wave energy leakage suppressing portion and the second acoustic energy leakage suppressing portion are respectively an integer multiple of the acoustic wave wavelength.

As mentioned above, the first acoustic wave energy leakage suppressing portion includes grooves and/or protrusions, and the grooves and protrusions may be collectively referred to as the first sub-suppressing portion. Similarly, the second acoustic wave energy leakage suppressing portion includes The protrusions and/or the grooves may also be collectively referred to as the second sub-inhibition portion.

In another example, the sum of the widths of the first sub-suppression parts can be designed to be an integer multiple of a wavelength, the sum of the widths of the second acoustic wave energy leakage suppression parts can be designed to be an integer multiple of a wavelength, and the first sub-suppression parts can be designed to be an integer multiple of a wavelength. The width ratio between them corresponds to the width ratio between the second sub-suppression parts. Since the electrode width ratio only exists in the whole period, the acoustic waves can be superimposed coherently throughout the piezoelectric material, resulting in better resonance performance.

The following description will be made by taking an example that the first acoustic wave energy leakage suppressing part includes two first sub-suppression parts, and the second acoustic wave energy leakage suppressing part includes two second sub-suppressing parts.

Since any first sub-suppression portion can be a groove or a protrusion, there are four combinations of shapes of the two first sub-suppression portions, which are introduced in four cases. In the four cases, the depth of the groove is 20 nm, the convex The height is 20nm.

Case 1

As shown in FIG. 1 , the first acoustic wave energy leakage suppressing portion includes two grooves a arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes two protrusions a' successively disposed along the extending direction, wherein: The width ratio of the two grooves a arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing part is 1:2. As a preferred example, the width of the first groove along the extending direction is 1 wavelength, and the second groove The width of each groove is 2 wavelengths;

The width ratio of the two protrusions a' arranged in sequence along the extending direction in the second acoustic wave energy leakage suppressing portion is 1:2.

The thickness of the middle piezoelectric thin film layer is half of the signal wavelength.

Case 2

As shown in FIG. 2 , the first acoustic wave energy leakage suppressing portion includes a protrusion c and a groove a arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes a groove c′ and a protrusion disposed sequentially along the extending direction a', where:

The width ratio of the protrusions c and the grooves a arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing part is 1:2, and the grooves c' and the grooves a sequentially arranged along the extending direction in the second acoustic wave energy leakage suppressing part have a ratio of 1:2. The width ratio of a' is 1:2, that is, the width of the protrusion c is 1 wavelength, the groove a is 2 wavelengths, and the ratio of c to a is 1:2.

Case three

As shown in FIG. 3 , the first acoustic wave energy leakage suppressing portion includes a groove a and a protrusion c arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes a protrusion a' and a groove sequentially disposed along the extending direction c'; the width ratio of the grooves and the protrusions arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the protrusions and grooves sequentially arranged along the extending direction in the second acoustic wave energy leakage suppressing portion The width ratio is 1:2.

Case 4

As shown in FIG. 4 , the first acoustic wave energy leakage suppressing portion includes two protrusions c arranged in sequence along the extending direction, and the second acoustic wave energy leakage suppressing portion includes two grooves c' sequentially disposed along the extending direction. The width ratio of the two protrusions c arranged in sequence along the extending direction in the first acoustic wave energy leakage suppressing portion is 1:2, and the widths of the two grooves c' successively arranged along the extending direction in the second acoustic energy leakage suppressing portion The ratio is 1:2.

The above-mentioned uneven structure including protrusions and/or grooves reduces the leakage of acoustic energy in the vertical direction. At the same time, the thickness of the piezoelectric thin film layer is the same in the section covered by the top metal electrode and the bottom metal electrode, that is, the upper and lower surfaces of the piezoelectric thin film layer are kept parallel and at the same height at different positions in this section. The vertical component of the electric field is suppressed, so that the signals of the same frequency are superimposed coherently, further reducing the leakage of the acoustic wave energy in the vertical direction, and improving the Q value of the thin film bulk acoustic wave resonator.

In addition, the width of the first acoustic wave energy leakage suppressing portion and the second acoustic wave energy leakage suppressing portion is set to an integer multiple of the acoustic wave wavelength, and the width ratio of the first acoustic wave energy leakage suppressing portion and the second acoustic wave energy leakage suppressing portion is consistent. , can realize the coherent superposition of the acoustic wave signal in the thin film bulk acoustic wave resonator, improve the acoustic wave energy in the thin film bulk acoustic wave resonator, and further improve the Q value of the thin film bulk acoustic wave resonator.

In other embodiments of the present invention, the cross-sectional shape of any groove or protrusion in all the embodiments is an isosceles trapezoid. Through the slope-like structure, the top electrode and the bottom electrode are kept parallel, and some positions are slope-like, which further reduces the leakage of acoustic wave energy in the vertical direction and further improves the Q value of the thin film bulk acoustic wave resonator.

As shown in Fig. 5, an existing thin film bulk acoustic wave resonator is an additive electrode (top metal electrode 1)-piezoelectric film (piezoelectric film layer 2)-electrode (bottom metal electrode 3) on the substrate material The "sandwich" FBAR thin film device, the upper and lower electrodes of this structure are generally designed in parallel, but in the actual process, this structure needs to maintain a long parallel length, and it is difficult to achieve complete parallelism. In the present application, the electrodes are divided into multiple parts (segments) by setting the first acoustic wave energy leakage suppressing part and the second acoustic wave energy leakage suppressing part, and each part can be kept in parallel, which reduces the need for parallelization. The difficulty of the process improves the parallelism. Moreover, the current process technology can realize the formation of protrusions and grooves, for example, anisotropic dry etching.

In other embodiments of the present invention, the material of the substrate in all the embodiments can be exemplified by Si, and the material of the bottom metal electrode and the top metal electrode can be exemplified by Al, Cu, Au or Mo, etc. The piezoelectric The material of the thin film layer is a piezoelectric material.

Among them, the piezoelectric material is a crystalline material that produces a voltage between the two end faces when subjected to pressure. Specifically, examples of piezoelectric materials include, but are not limited to, LiNbO ₃ , LiTaO ₃ , AlN, ZnO or PZT (lead zirconate titanate piezoelectric ceramics).

Those skilled in the art can flexibly select the materials used for each component according to their needs. For example, any material suitable for the electrode can be selected as the material for the bottom metal electrode and the top metal electrode, and any material suitable for the substrate can be selected as the implementation of the present invention. The material of the substrate in this example will not be repeated here.

Example 2

The thin film bulk acoustic wave resonator of the embodiment of the present invention can be applied to any MEMS device, and the MEMS (Micro-electro-mechanical system) device can be a liquid level sensor, an oscillator, a microphone, a radio frequency switch, a filter, and the like.

The preparation method of the MEMS device is as follows: placing the thin-film bulk acoustic wave resonator of the present invention on one or more acoustic reflectors to form a solid-state assembled resonator, and then integrating the solid-state assembled resonator with other active devices, The MEMS device is obtained by packaging.

Example 3

The embodiment of the present invention provides a preparation method for preparing the thin-film bulk acoustic wave resonator in Embodiment 1, and the preparation method includes:

1) Etch an air cavity on the substrate.

Taking the substrate material as Si as an example, the above etching specifically includes: ultrasonically cleaning the substrate 4 with acetone and isopropanol, and etching the air cavity 5 on the substrate 4 by ICP etching based on the BOSCH process.

2) Deposit a sacrificial filling layer with a preset height in the air cavity.

In one example, the sacrificial filling layer can be obtained by depositing phosphosilicate glass in an air cavity using a conventional low pressure chemical vapor deposition (LPCVD) process.

The preset height is at least equal to (and may also be greater than): the distance between the convex surface of the second acoustic wave energy leakage suppressing part and the bottom surface of the air cavity.

3) Forming the sacrificial filling layer.

Depending on the material of the sacrificial filling layer, there are various methods of forming, such as grinding, etching (eg, anisotropic dry etching), pressing, and the like.

With the aforementioned phosphosilicate glass, the above forming process specifically includes: patterning by chemical mechanical polishing (Chemical Mechanical Planarization, CMP).

The resulting pattern is complementary to that of the bottom metal electrode (especially the aforementioned second acoustic energy leakage suppressing portion).

4) A bottom metal electrode with uniform thickness is deposited on the upper surface of the sacrificial filling layer after the molding process.

In one example, it may specifically include: depositing a bottom metal electrode on the upper surface of the sacrificial filling layer after the molding process by using a method such as thermal evaporation or magnetron sputtering.

For the related description of the bottom metal electrode, please refer to the foregoing description, and will not be repeated here.

5) Sputtering a piezoelectric thin film layer on the upper surface of the substrate and the bottom metal electrode.

For the relevant description of the piezoelectric thin film layer, please refer to the foregoing description, which will not be repeated here.

6) Forming the piezoelectric film layer.

Depending on the material of the piezoelectric thin film layer, there are various methods of forming, such as grinding, etching (eg, anisotropic dry etching), pressing, and the like.

In one example, the forming process may include etching the piezoelectric thin film layer using plasma etching or magnetron sputtering.

7) A top metal electrode with a uniform thickness is deposited on the upper surface of the piezoelectric thin film layer after the molding process.

In one example, the top metal electrode may be deposited on the upper surface of the piezoelectric thin film layer after the forming process by thermal evaporation or magnetron sputtering. For the related description of the top metal electrode, please refer to the foregoing description, and will not be repeated here.

8) Remove the sacrificial filling layer.

In one example, the method specifically includes: removing the sacrificial layer by wet etching or fumigation.

Example 4

The embodiment of the present invention provides another preparation method for preparing the thin-film bulk acoustic wave resonator in embodiment 1, and the preparation method includes:

1) Etch an air cavity on the substrate.

For a detailed description, please refer to the introduction in the previous preparation method.

2) Filming and shaping the piezoelectric material to form a piezoelectric thin film layer.

In one example, the film formation may be performed by sputtering. The shaping process may include etching using plasma etching or magnetron sputtering.

Subsequently, the top metal electrode will be deposited on one surface (which can be called the upper surface) of the piezoelectric thin film layer, and the bottom metal electrode will be deposited on the other surface (which can be called the lower surface), wherein the pattern on the upper surface is the same as that of the top metal electrode (especially the top metal electrode). The pattern of the aforementioned first acoustic energy leakage suppressing portion) is complementary, and the pattern of the lower surface is complementary to that of the bottom metal electrode (especially the aforementioned second acoustic energy leakage suppressing portion). 3) A top metal electrode is deposited on the upper surface of the piezoelectric thin film layer, and a bottom metal electrode is deposited on the lower surface of the piezoelectric thin film layer to obtain a piezoelectric laminated structure.

In one example, the deposition may be performed by processes such as photoresist coating, photolithography, exposure, and etching.

4) Set the piezoelectric laminated structure (the setting here can be pasted or high-temperature pasted, etc.) on the substrate.

In order to illustrate the performance of the thin film bulk acoustic wave resonator prepared in the embodiment of the present invention, COMSOL software based on finite element method (FEM, finite-element method) is used for simulation below, and the existing thin film bulk acoustic wave resonator shown in FIG. 5 is used for simulation. The performance is compared with the thin-film bulk acoustic resonator (referred to as the target thin-film bulk acoustic resonator) prepared in the embodiment of the present invention.

Parameters that describe the performance of thin film bulk acoustic resonators include: figure of merit (FoM), effective coupling coefficient (k ² ), and quality factor (Q). Among them, the figure of merit (FoM) is the product of the effective coupling coefficient and the quality factor, the effective coupling coefficient (k ² ) is a parameter describing the electromechanical conversion efficiency of the resonator, and the quality factor (Q) is a description of the internal energy storage and dissipation of the resonator Parameter for energy ratio.

The performance verification results are shown in Figure 6-13, where:

FIG. 6 is a graph of admittance of a thin-film bulk acoustic resonator with a conventional “sandwich” structure, and FIG. 7 is a graph of a quality factor of a thin-film bulk acoustic resonator with a conventional “sandwich” structure.

FIG. 8 is a graph of the admittance of the thin film bulk acoustic wave resonator shown in FIG. 2 , and FIG. 9 is a graph of the quality factor.

FIG. 10 is a graph of admittance of the thin film bulk acoustic wave resonator shown in FIG. 4 , and FIG. 11 is a graph of its quality factor.

FIG. 12 is a graph of admittance of the thin film bulk acoustic wave resonator shown in FIG. 3 , and FIG. 13 is a graph of its quality factor.

In this performance comparison, the thin-film bulk acoustic wave resonators shown in Figures 2-4 are prepared by any of the aforementioned preparation methods, all of which are made of lithium niobate (LiNbO ₃ ) crystal, lithium tantalate (LiTaO ₃ ) crystal, Piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO) are used as the material of the piezoelectric thin film layer, and metal materials such as Al, Pt, Ni or Mo are used for the top metal electrode and the bottom metal electrode.

Based on Figs. 6-13, it can be seen that, compared with the existing thin film bulk acoustic resonator of the "sandwich" structure, the peak of the admittance of the thin film bulk acoustic resonator provided by the embodiment of the present invention is determined by the existing thin film of the "sandwich" structure. The -1 and -0.9 of the BAW resonator are improved to -10 and -190, -30 and -190, and -10 and -190, and its quality factor is improved from the existing "sandwich" structure thin-film BAW resonator of 6662.73 liters As high as 8356.41, 7778.13, and 8356.46, it can be seen that the thin film bulk acoustic wave resonator provided by the embodiment of the present invention has better energy storage capacity, and the Q value is greatly improved.

Based on the above embodiments, the thin-film bulk acoustic wave resonator of the present invention has the following technical effects:

The structure of the designed film bulk acoustic wave resonator has non-flatness, and the two convex or concave surfaces of the piezoelectric film layer ensure that the active area of the thin film bulk acoustic wave resonator has more energy, and the leakage of transverse acoustic wave energy is further reduced, thereby improving the FBAW. The Q and FoM values of the resonator reduce the insertion loss of devices such as filters and oscillators, and improve the performance of the entire system.

The top electrode and bottom electrode of the designed thin-film bulk acoustic wave resonator are still parallel, and locally present a slope shape, which can effectively reduce the leakage of acoustic wave energy in the vertical direction, so as to achieve the purpose of improving the Q value.

The widths of the first acoustic wave energy leakage suppressing portion and the second acoustic wave energy leakage suppressing portion are respectively set as integer multiples of the acoustic wave wavelength, so that the acoustic waves can be coherently superimposed in the entire piezoelectric material, thereby obtaining better resonance performance.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

In this paper, specific examples are used to illustrate the principles and implementations of the present invention. The descriptions of the above embodiments are only used to help understand the methods and core ideas of the present invention; meanwhile, for those skilled in the art, according to the present invention There will be changes in the specific implementation and application scope. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims (9)

1. A film bulk acoustic resonator is characterized by comprising a top metal electrode, a piezoelectric film layer, a bottom metal electrode and a substrate from top to bottom in sequence;

the bottom metal electrode is arranged on the substrate, and the substrate is provided with an air cavity;

the top metal electrode forms a first sound wave energy leakage suppression part on the upper surface of the piezoelectric film layer, and the bottom metal electrode forms a second sound wave energy leakage suppression part on the lower surface of the piezoelectric film layer; the first sound wave energy leakage suppression part and the second sound wave energy leakage suppression part are the same in number and opposite in position; the first acoustic energy leakage suppression part and the second acoustic energy leakage suppression part are both positioned at the upper part of the air cavity;

the first sound wave energy leakage suppression part comprises a groove and/or a bump, the corresponding second sound wave energy leakage suppression part comprises a bump and/or a groove, and the thickness of the piezoelectric film layer is consistent in a section covered by the top metal electrode and the bottom metal electrode;

the top metal electrode is attached to the upper surface of the piezoelectric film layer, and the bottom metal electrode is attached to the lower surface of the piezoelectric film layer;

the first sound wave energy leakage suppression part comprises two grooves which are sequentially arranged along the extension direction, and the second sound wave energy leakage suppression part comprises two bulges which are sequentially arranged along the extension direction;

or the first sound wave energy leakage suppression part comprises a protrusion and a groove which are sequentially arranged along the extension direction, and the second sound wave energy leakage suppression part comprises a groove and a protrusion which are sequentially arranged along the extension direction;

or the first sound wave energy leakage suppression part comprises a groove and a protrusion which are sequentially arranged along the extension direction, and the second sound wave energy leakage suppression part comprises a protrusion and a groove which are sequentially arranged along the extension direction;

or the first sound wave energy leakage suppression part comprises two bulges which are sequentially arranged along the extension direction, and the second sound wave energy leakage suppression part comprises two grooves which are sequentially arranged along the extension direction.

2. The film bulk acoustic resonator of claim 1,

the widths of the first acoustic wave energy leakage suppression portion and the second acoustic wave energy leakage suppression portion are respectively integral multiples of the acoustic wave wavelength.

3. The film bulk acoustic resonator according to claim 1 or 2,

the groove and/or the protrusion included in the first sound wave energy leakage suppression part are/is a first sub suppression part, and similarly, the protrusion and/or the groove included in the second sound wave energy leakage suppression part are/is a second sub suppression part; wherein:

the sum of the widths of the first sub suppression parts is an integral multiple of the acoustic wave wavelength, the sum of the widths of the second sub suppression parts is an integral multiple of the acoustic wave wavelength, and the width ratio between the first sub suppression parts is identical to the width ratio between the second sub suppression parts.

4. The film bulk acoustic resonator according to claim 1, wherein a width ratio of two grooves provided in the first acoustic energy leakage suppression portion in order in the extending direction is 1:2, and a width ratio of two protrusions provided in the second acoustic energy leakage suppression portion in order in the extending direction is 1: 2;

or the width ratio of the protrusion and the groove which are sequentially arranged in the first sound wave energy leakage suppression part along the extension direction is 1:2, and the width ratio of the groove and the protrusion which are sequentially arranged in the second sound wave energy leakage suppression part along the extension direction is 1: 2;

or the width ratio of the groove and the protrusion which are sequentially arranged in the first sound wave energy leakage suppression part along the extension direction is 1:2, and the width ratio of the protrusion and the groove which are sequentially arranged in the second sound wave energy leakage suppression part along the extension direction is 1: 2;

or the width ratio of two bulges arranged in sequence along the extension direction in the first sound wave energy leakage restraining part is 1:2, and the width ratio of two grooves arranged in sequence along the extension direction in the second sound wave energy leakage restraining part is 1: 2.

5. The film bulk acoustic resonator according to claim 1, wherein the cross-sectional shape of any one of the grooves or projections is an isosceles trapezoid.

6. The film bulk acoustic resonator according to claim 1, wherein the substrate material is Si, the bottom metal electrode is made of Al, Cu, Au, or Mo, the piezoelectric thin film layer is made of a piezoelectric material, and the top metal electrode is made of Al, Cu, Au, or Mo.

7. A manufacturing method for manufacturing the thin film bulk acoustic resonator according to any one of claims 1 to 6, the manufacturing method comprising:

etching an air cavity on a substrate;

depositing a sacrificial filling layer with a preset height in the air cavity;

carrying out cavity molding treatment on the sacrificial filling layer;

depositing a bottom metal electrode with a uniform thickness on the upper surface of the sacrificial filling layer after the molding treatment, wherein the bottom metal electrode forms a second acoustic wave energy leakage suppression part on the upper surface of the sacrificial filling layer after the molding treatment;

sputtering piezoelectric film layers on the upper surfaces of the substrate and the bottom metal electrode;

molding the piezoelectric film layer; depositing top metal electrodes with consistent thickness on the upper surface of the formed piezoelectric thin film layer; the top metal electrode forms a first sound wave energy leakage suppression part on the upper surface of the piezoelectric thin film layer after the molding treatment;

and removing the sacrificial filling layer.

8. A manufacturing method for manufacturing the thin film bulk acoustic resonator according to any one of claims 1 to 6, the manufacturing method comprising:

etching an air cavity on a substrate;

forming and shaping a piezoelectric material to form the piezoelectric thin film layer;

depositing a top metal electrode on the upper surface of the piezoelectric film layer, and depositing a bottom metal electrode on the lower surface of the piezoelectric film layer to obtain a piezoelectric laminated structure;

disposing the piezoelectric stack structure on the substrate.

9. A MEMS device comprising the thin film bulk acoustic resonator of any one of claims 1 to 6.

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