A bulk acoustic wave filter and a communication device

Abstract

The embodiment of the present application provides a bulk acoustic wave filter and a communication device. The bulk acoustic wave filter comprises a top electrode, a piezoelectric layer, a bottom electrode and a support layer which are sequentially stacked; a first Bragg reflection layer connected to a side of the support layer away from the bottom electrode, an intermediate substrate layer is arranged on a side of the first Bragg reflection layer away from the support layer, and the length of the intermediate substrate layer is less than the length of the first Bragg reflection layer; a second Bragg reflection layer connected to the other side of the intermediate substrate layer; and a bottom substrate layer connected to a side of the second Bragg reflection layer away from the intermediate substrate layer. By arranging the intermediate substrate layer and the two Bragg reflection layers, the low-frequency bulk acoustic wave loss cavity is separated from the target frequency reflection working cavity, the temperature rise of the working cavity is slowed down, the temperature drift effect of the bulk acoustic wave filter is reduced, and the filter frequency stability is maintained.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication and terminal technology, and in particular to a bulk acoustic wave filter and a communication device. Background Art

[0002] Currently, the construction of 5G (5th Generation Mobile Communication Technology) networks has increased service wireless frequencies to sub6G (frequency bands) or even higher. A single mobile terminal device, such as a mobile phone, must simultaneously operate multiple networks, including 2 / 3 / 4 / 5G / Bluetooth / WIFI (wireless communication technology). A single mobile terminal device accesses numerous frequency bands, with spectrum spacing shrinking and guard bands often compressed to the order of 10MHz (megahertz). This requires the use of a large number of high-performance RF filters to achieve isolation. RF filters continue to face pressure for miniaturization. After evolving through LC filters (passive filters), cavity filters, dielectric filters, and surface acoustic wave filters, RF filter miniaturization technology has gradually converged on bulk acoustic wave (BAW) technology, forming the BAW filter product category. Among these, SMR-BAW (solid-mounted BAW filters, also known as Bragg reflection BAW filters) filters are commonly used for filtering. However, SMR-BAW relies on forming a standing wave to strengthen the target frequency, while other frequencies are suppressed due to wavelength mismatch. The energy loss of other frequencies generates heat, which can easily cause the SMR-BAW filter to temperature rise and frequency drift, thereby reducing the frequency stability. Summary of the Invention

[0003] In view of the above problems, embodiments of the present invention are proposed to provide a bulk acoustic wave filter and a corresponding communication device that overcome the above problems or at least partially solve the above problems.

[0004] In order to solve the above problems, in a first aspect of the present invention, an embodiment of the present invention discloses a bulk acoustic wave filter, comprising:

[0005] stacking and connecting a top electrode, a piezoelectric layer, a bottom electrode and a support layer in sequence;

[0006] a first Bragg reflector connected to a side of the support layer away from the bottom electrode, wherein an intermediate substrate layer is provided on the side of the first Bragg reflector away from the support layer, and a length of the intermediate substrate layer is smaller than a length of the first Bragg reflector;

[0007] a second Bragg reflection layer connected to the other side of the intermediate substrate layer;

[0008] The bottom substrate layer is connected to a side of the second Bragg reflective layer away from the middle substrate layer.

[0009] Optionally, the first Bragg reflector layer includes a first low acoustic impedance layer and a first high acoustic impedance layer alternately stacked and connected; wherein the intermediate substrate layer is located in the first high acoustic impedance layer on a side of the first Bragg reflector layer away from the support layer.

[0010] Optionally, the length of the intermediate substrate layer is greater than the wavelength of the acoustic shear wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter, and is less than the wavelength of the acoustic shear wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0011] Optionally, the length of the first low acoustic impedance layer and the length of the first high acoustic impedance layer are greater than the wavelength of the shear wave of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0012] Optionally, the thickness of the first low acoustic impedance layer and the thickness of the first high acoustic impedance layer are one quarter of the wavelength of the longitudinal wave of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter.

[0013] Optionally, the second Bragg reflector layer includes a second low acoustic impedance layer and a second high acoustic impedance layer that are alternately stacked and connected.

[0014] Optionally, the thickness of the second low acoustic impedance layer and the thickness of the second high acoustic impedance layer are one quarter of the wavelength of the longitudinal wave of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter.

[0015] Optionally, the length of the second low acoustic impedance layer and the length of the second high acoustic impedance layer are greater than the wavelength of the shear wave of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0016] Optionally, the middle substrate layer and the bottom substrate layer are made of the same material.

[0017] In a second aspect of the present invention, an embodiment of the present invention further discloses a communication device, comprising the bulk acoustic wave filter as described above.

[0018] The embodiments of the present invention include the following advantages:

[0019] In an embodiment of the present invention, a top electrode, a piezoelectric layer, a bottom electrode, and a support layer are sequentially stacked and connected; a first Bragg reflector is connected to a side of the support layer away from the bottom electrode, an intermediate substrate layer is provided on a side of the first Bragg reflector away from the support layer, and a length of the intermediate substrate layer is less than that of the first Bragg reflector; a second Bragg reflector is connected to the other side of the intermediate substrate layer; and a bottom substrate layer is connected to a side of the second Bragg reflector away from the intermediate substrate layer. By providing two Bragg reflector layers and an intermediate substrate layer between the two Bragg reflector layers, the two Bragg reflector layers have different working areas, with the first Bragg reflector layer close to the support layer forming a characteristic frequency reflection area and the second Bragg reflector layer close to the support layer forming a low-frequency sound wave reflection area, thereby distinguishing the characteristic frequency and low-frequency sound wave reflection areas. This allows the characteristic frequency sound waves to pass through the first Bragg reflector layer, while some low-frequency sound waves pass through the intermediate substrate layer through diffraction and enter the second Bragg reflector layer. This allows the first Bragg reflector layer to suppress the temperature drift of the filter frequency within a relatively low temperature rise range, while the second Bragg reflector layer generates loss and temperature rise, thereby reducing the influence of temperature rise on the temperature drift of the frequency, thereby reducing the temperature drift effect of the bulk acoustic wave filter and maintaining the filter frequency stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram of an embodiment of a bulk acoustic wave filter in the prior art;

[0021] Figure 2 is a structural block diagram of an embodiment of a bulk acoustic wave filter of the present invention;

[0022] Figure 3 is a schematic structural diagram of another bulk acoustic wave filter embodiment of the present invention;

[0023] Figure 4 Schematic diagram of acoustic wave transmission of a bulk acoustic wave filter embodiment of the present invention;

[0024] Figure 5a 1 is a temperature rise diagram of a bulk acoustic wave filter embodiment of the present invention;

[0025] Figure 5b This is a temperature rise diagram of a bulk acoustic wave filter embodiment in the prior art;

[0026] Figure 6 This is a workflow diagram of a bulk acoustic wave filter embodiment of the present invention.

[0027] Description of the accompanying drawings: 1-top electrode, 2-piezoelectric layer, 3-bottom electrode, 4-support layer, 5-low acoustic impedance layer, 6-high acoustic impedance layer, 7-substrate layer;

[0028] 100 - top electrode, 200 - piezoelectric layer, 300 - bottom electrode, 400 - support layer, 500 - first Bragg reflection layer, 510 - first low acoustic impedance layer, 520 - first high acoustic impedance layer, 600 - intermediate substrate layer, 700 - second Bragg reflection layer, 710 - second low acoustic impedance layer, 720 - second high acoustic impedance layer, 800 - bottom substrate layer. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0030] Reference Figure 1 shows a structural schematic diagram of an embodiment of a bulk acoustic wave filter in the prior art.

[0031] The existing (SMR-BAW) filter is from top to bottom, respectively, top electrode 1, piezoelectric layer 2, bottom electrode 3, support layer 4, multiple layers of alternating low acoustic impedance layer 5 and high acoustic impedance layer 6, and substrate layer 7. The top electrode 1 and the bottom electrode 3 generate acoustic wave signals through the inverse piezoelectric effect, and the acoustic longitudinal wave signals are reflected at the junction of the low acoustic impedance layer 5 and the high acoustic impedance layer 6. For acoustic signals with a characteristic wavelength consistent with the acoustic thickness of the impedance layer, a full reflection is generated, while other wavelength longitudinal wave signals are suppressed, completing the filtering process. Finally, the acoustic wave signal is reflected back to the piezoelectric layer 2, and the filtered electrical signal is generated through the positive piezoelectric effect.

[0032] Because the non-characteristic wavelength acoustic waves are lost at the junction of the low acoustic impedance layer 5 and the high acoustic impedance layer 6 (i.e. the Bragg reflection layer) due to wavelength mismatch, they are converted into heat, causing temperature rise. And the material acoustic propagation speed of the low acoustic impedance layer 5 and the high acoustic impedance layer 6 will change due to the temperature rise, which further causes the characteristic frequency of the bulk acoustic wave filter to drift, which is called "frequency temperature drift". It can be seen that all the energy of the existing bulk acoustic wave filter is lost at the junction of the low acoustic impedance layer 5 and the high acoustic impedance layer 6, resulting in temperature rise and causing "frequency temperature drift", which leads to the decrease of the stability of the filtering frequency, which is not conducive to the miniaturization and high power of the bulk acoustic wave filter. Therefore, the embodiment of the present application is proposed to reduce the frequency temperature drift and improve the stability of the filtering frequency, which provides the realizability for the miniaturization and high power of the bulk acoustic wave filter.

[0033] Reference Figure 2 shows a structural block diagram of an embodiment of a bulk acoustic wave filter of the present application. The bulk acoustic wave filter can specifically include the following modules:

[0034] Top electrode 100, piezoelectric layer 200, bottom electrode 300, support layer 400, first Bragg reflection layer 500, intermediate substrate layer 600, second Bragg reflection layer 700, and bottom substrate layer 800.

[0035] In an embodiment of the present invention, the top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 are stacked and connected in sequence, that is, with the top surface of the top electrode 100 as the top, the bottom surface of the top electrode 100 is connected to the top surface of the piezoelectric layer 200, the bottom surface of the piezoelectric layer 200 is connected to the top surface of the bottom electrode 300, and the bottom surface of the bottom electrode 300 is connected to the top surface of the support layer 400. The top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 are stacked to form a sandwich structure. Among them, the cross-sectional area of ​​the top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 can be the same. In terms of thickness, the thickness of the piezoelectric layer 200 can be greater than the thickness of the top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400, while the thickness of the top electrode 100 and the bottom electrode 300 can be the same. As for the material, the material of the top electrode 100, the piezoelectric layer 200, and the bottom electrode 300 can be aluminum nitride (AlN), zinc oxide (ZnO), or lead zirconate titanate (PZT). Those skilled in the art can choose according to their needs, and the embodiment of the present invention does not make specific limitations on this.

[0036] The first Bragg reflector 500 is connected to the side of the support layer 400 away from the bottom electrode 300, that is, the first Bragg reflector 500 is connected to the bottom surface of the support layer 400. The first Bragg reflector 500 serves as the working cavity of the BAW filter, and is used to transmit the acoustic wave corresponding to the electrical signal at the BAW filter's characteristic frequency and reflect all of the acoustic wave corresponding to the electrical signal at the BAW filter's characteristic frequency back to the piezoelectric layer 200, allowing the piezoelectric layer 200 to generate a filtered electrical signal through the positive piezoelectric effect, thereby enabling the BAW filter to extract its characteristic frequency from the signal. The first Bragg reflector 500 is also used to transmit the acoustic wave corresponding to the low-frequency electrical signal filtered out by the BAW filter and to output the acoustic wave corresponding to the low-frequency electrical signal filtered out by the BAW filter to the second Bragg reflector 700.

[0037] An intermediate substrate layer 600 is disposed on the side of the first Bragg reflector 500 away from the support layer 400, that is, on the bottom surface of the first Bragg reflector 500. The intermediate substrate layer 600 is used to block the transmitted sound waves corresponding to the characteristic frequency signal of the BAW filter, providing impedance. Upon reaching the intermediate substrate layer 600, the sound waves corresponding to the characteristic frequency signal of the BAW filter are no longer transmitted downward, but are instead reflected within the first Bragg reflector 500. The length of the intermediate substrate layer 600 is shorter than that of the first Bragg reflector 500. This allows the sound waves corresponding to the characteristic frequency signal of the BAW filter to continue transmitting downward to the second Bragg reflector 700 while blocking the sound waves corresponding to the characteristic frequency signal of the BAW filter.

[0038] The second Bragg reflector 700 can be the same as the first Bragg reflector 500. To distinguish them from the first Bragg reflector 500, the second Bragg reflector 700 is distinguished from the first Bragg reflector 500 in order to distinguish them from each other in different locations within the BAW filter. The second Bragg reflector 700 is connected to the other side of the intermediate substrate layer 600, that is, it is connected to the bottom of the intermediate substrate layer 600. The second Bragg reflector 700 acts as a low-frequency BAW loss cavity, dissipating the sound waves corresponding to the low-frequency electrical signals filtered by the BAW filter, which are transmitted by the first Bragg reflector 500. This dissipates the heat generated by the BAW filter, which then filters the low-frequency electrical signals, and converts it into heat. This heat is concentrated within the cavity. Since the second Bragg reflector 700 is separate from the first Bragg reflector 500, the heat generated does not affect the first Bragg reflector 500, thereby mitigating the temperature rise of the first Bragg reflector 500.

[0039] The bottom substrate layer 800 is connected to the side of the second Bragg reflector 700 away from the middle substrate layer 600. That is, the bottom substrate layer 800 is connected to the bottom of the second Bragg reflector 700. The bottom substrate layer 800 is the bottom layer of the bulk acoustic wave filter. The top electrode 100, piezoelectric layer 200, bottom electrode 300, support layer 400, first Bragg reflector 500, middle substrate layer 600, and second Bragg reflector 700 are stacked in sequence on the bottom substrate layer 800.

[0040] In an embodiment of the present invention, a top electrode 100, a piezoelectric layer 200, a bottom electrode 300, and a support layer 400 are stacked and connected in sequence; a first Bragg reflector 500 is connected to the side of the support layer 400 away from the bottom electrode 300, an intermediate substrate layer 600 is provided on the side of the first Bragg reflector 500 away from the support layer 400, and the length of the intermediate substrate layer 600 is less than the length of the first Bragg reflector 500; a second Bragg reflector 700 is connected to the other side of the intermediate substrate layer 600; and a bottom substrate layer 800 is connected to the side of the second Bragg reflector 700 away from the intermediate substrate layer 600. By providing two Bragg reflector layers and disposing an intermediate substrate layer 600 between the two Bragg reflector layers, the two Bragg reflector layers have different working areas, with the first Bragg reflector layer 500 close to the support layer 400 forming a characteristic frequency reflection area, and the second Bragg reflector layer 700 away from the support layer 400 forming a low-frequency sound wave reflection area. These areas distinguish the characteristic frequency and low-frequency sound wave reflection areas, allowing characteristic frequency sound waves to be reflected in the first Bragg reflector layer 500, while some low-frequency sound waves are diffracted through the intermediate substrate layer 600 and enter the second Bragg reflector layer 700. This allows the first Bragg reflector layer 500 to suppress temperature drift of the filter frequency within a relatively low temperature rise range, while the second Bragg reflector layer 700 generates loss and temperature rise, minimizing the impact of temperature rise on frequency temperature drift. This reduces the temperature drift effect of the BAW filter and maintains filter frequency stability.

[0041] Reference Figure 3 , shows a schematic structural diagram of another BAW filter embodiment of the present invention, which may specifically include the following modules:

[0042] A top electrode 100 , a piezoelectric layer 200 , a bottom electrode 300 , a support layer 400 , a first Bragg reflection layer 500 , an intermediate substrate layer 600 , a second Bragg reflection layer 700 , and a bottom substrate layer 800 .

[0043] The top electrode 100 and the bottom electrode 300 are used to convert the electrical signal received by the BAW filter into an acoustic wave signal through the inverse piezoelectric effect, thereby starting the filtering process.

[0044] The piezoelectric layer 200 is used to convert the acoustic wave signal reflected by the first Bragg reflector 500 after filtering through the positive piezoelectric effect into an electrical signal.

[0045] The support layer 400 is used to ensure the mechanical strength of the top electrode 100 , the piezoelectric layer 200 and the bottom electrode 300 , so as to ensure the mechanical strength of the BAW filter.

[0046] The top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 are sequentially stacked and connected. The size of the top electrode 100, the piezoelectric layer 200 and the bottom electrode 300 can be the same, and the size of the support layer 400 can be larger than that of the top electrode 100, the piezoelectric layer 200 and the bottom electrode 300, so as to provide better support effect. The top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 are stacked to form an integral whole. It should be noted that the stacking of the top electrode 100, the piezoelectric layer 200, the bottom electrode 300 and the support layer 400 means that the four are sequentially formed on the semiconductor material to form different functional layers, thereby achieving stacked connection.

[0047] The first Bragg reflection layer 500 is connected to the side of the support layer 400 away from the bottom electrode 300. The first Bragg reflection layer 500 is used to reflect the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter back to the piezoelectric layer 200, and transmit the acoustic wave corresponding to the low-frequency electrical signal filtered by the bulk acoustic wave filter into the second Bragg reflection layer 700. The first Bragg reflection layer 500 has a plurality of Bragg reflection surfaces, forming a bulk acoustic wave filter structure of SMR structure.

[0048] Specifically, the first Bragg reflection layer 500 includes a first low acoustic impedance layer 510 and a first high acoustic impedance layer 520 which are alternately stacked and connected.

[0049] The first Bragg reflection layer 500 is composed of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520. The first low acoustic impedance layer 510 is formed by filling a low acoustic impedance material, which can be processed on a substrate material by radio frequency magnetron sputtering, chemical vapor deposition, pulsed laser deposition and the like. The first high acoustic impedance layer 520 is formed by filling a high acoustic impedance material, which can be processed on a substrate material by radio frequency magnetron sputtering, chemical vapor deposition, pulsed laser deposition and the like. In actual application, the processing technology of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 can use the same processing technology or different technologies. In an example of the present application, the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 are generated by using the same processing technology, so as to facilitate the production of the bulk acoustic wave filter and improve the production efficiency of the bulk acoustic wave filter. The contact surface of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 is the Bragg reflection surface. In order to have better filtering effect, the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 are both multi-layer, i.e. the first Bragg reflection layer 500 is alternately connected by a plurality of first low acoustic impedance layers 510 and a plurality of first high acoustic impedance layers 520 with matching layer numbers.

[0050] The first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 have the same size, so that the sound wave can be smoothly transmitted when transmitting through the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520, without producing a mutation, and the filtering effect is ensured.

[0051] The acoustic impedance layer far from the support layer 400 on the side of the first Bragg reflection layer 500 is the first high acoustic impedance layer 520, that is, the acoustic impedance layer farthest from the support layer 400 on the side of the first Bragg reflection layer 500 is the first high acoustic impedance layer 520. The first high acoustic impedance layer 520 is in the intermediate substrate layer 600, and the length of the intermediate substrate layer 600 is less than the length of the first Bragg reflection layer 500. It can be seen that the intermediate substrate layer 600 is located in the first high acoustic impedance layer 520 of the lowermost layer of the first Bragg reflection layer 500, the periphery of the intermediate substrate layer 600 is surrounded by the first high acoustic impedance layer 520 of the lowermost layer of the first Bragg reflection layer 500, and the length difference between the intermediate substrate layer 600 and the first Bragg reflection layer 500 is filled with a high acoustic impedance material.

[0052] Specifically, the length of the intermediate substrate layer 600 is greater than the transverse wave wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter, and less than the transverse wave wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the bulk acoustic wave filter.

[0053] In actual application, the transverse wave wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter can be calculated by using a general formula of transverse wave wavelength:

[0054] λ = V / F (Formula 1)

[0055] Wherein, λ is the transverse wave wavelength, V is the acoustic wave velocity, and F is the frequency.

[0056] For example, the wave velocity in aluminum nitride (ALN) is 5480 m / s (meters per second), and the typical 3GHz electrical signal is substituted into Formula 1 to obtain the corresponding acoustic transverse wave wavelength of 1.82 microns.

[0057] The transverse wave wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter and the transverse wave wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the bulk acoustic wave filter can be calculated respectively, and then a suitable length within the length range from the transverse wave wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the bulk acoustic wave filter to the transverse wave wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter is selected as the length of the intermediate substrate layer 600. Those skilled in the art can select within the above length range according to the needs, and the embodiments of the present application do not make specific limitations.

[0058] Furthermore, the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 have the same thickness to facilitate reflection of the sound waves corresponding to the electrical signal at the characteristic frequency of the BAW filter. In an optional embodiment of the present invention, the thickness of the first low acoustic impedance layer 510 and the thickness of the first high acoustic impedance layer 520 are one-quarter of the longitudinal wavelength of the sound waves corresponding to the electrical signal at the characteristic frequency of the BAW filter.

[0059] In practical applications, the longitudinal wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter can be calculated first, and then one-quarter of the longitudinal wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter can be subtracted from the thickness of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520, so that the thickness of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 match the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter. The acoustic wave signal is reflected at the junction of the first low acoustic impedance layer 510 and the second high acoustic impedance layer 720, and the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter is totally reflected, and the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter is reflected back to the piezoelectric layer 200.

[0060] Furthermore, to ensure that the acoustic wave transmission path is complete and does not produce abrupt changes, the lengths of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 can be the same. In an optional embodiment of the present invention, the lengths of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 are greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0061] In practical applications, the above formula 1 can also be used to calculate the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the BAW filter. The lengths of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 are selected to be greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the BAW filter. To avoid wasting low-acoustic impedance and high-acoustic impedance materials, the lengths of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 can be selected to be slightly greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the BAW filter. This allows the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 to achieve a filtering effect while avoiding waste of acoustic impedance materials.

[0062] The second Bragg reflector 700 is connected to the side of the intermediate substrate layer 600 away from the first Bragg reflector 500. Specifically, one side of the intermediate substrate layer 600 is the first Bragg reflector 500, and the other side is the second Bragg reflector 700. The second Bragg reflector 700 can be manufactured using the same process as the first Bragg reflector 500. The second Bragg reflector 700 is used to receive the sound waves corresponding to the low-frequency electrical signals filtered out by the bulk acoustic wave filter. This sound wave is lost in its internal Bragg reflector surface, eliminating the sound waves corresponding to the low-frequency electrical signals filtered out by the bulk acoustic wave filter, thereby removing noise. The second Bragg reflector 700 comprises multiple Bragg reflector surfaces.

[0063] Specifically, the second Bragg reflector 700 includes second low acoustic impedance layers 710 and second high acoustic impedance layers 720 that are alternately stacked and connected.

[0064] The second Bragg reflector 700 may be composed of multiple layers of alternately stacked second low acoustic impedance layers 710 and second high acoustic impedance layers 720. That is, when there is one second low acoustic impedance layer 710, the next layer is the second high acoustic impedance layer 720, and vice versa.

[0065] In practical applications, the second low acoustic impedance layer 710 and the first low acoustic impedance layer 510 can be made of the same low acoustic impedance material and the same process. Similarly, the second high acoustic impedance layer 720 and the first high acoustic impedance layer 520 can also be made of the same high acoustic impedance material and the same process.

[0066] In an optional embodiment of the present invention, the thickness of the second low acoustic impedance layer 710 and the thickness of the second high acoustic impedance layer 720 are one quarter of the longitudinal wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter.

[0067] In practical applications, the thickness of the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720 can be the same as the thickness of the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 to facilitate processing of the BAW filter. The thickness of the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720 can be one-quarter of the longitudinal wavelength of the acoustic wave corresponding to the characteristic frequency electrical signal of the BAW filter. When the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter are transmitted to the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720, since the thickness of the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720 do not match the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter, the Bragg reflection surface where the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720 intersect cannot reflect the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter. The sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter will be lost at the Bragg reflection surface, thereby all the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter that are transmitted to the second Bragg reflection layer 700 will be lost at the second low acoustic impedance layer 710. The second Bragg reflector 700 is a consumable cavity, and the heat generated by the heat generated thereby causes a temperature drift effect, which has little impact on the filtering effect of the BAW filter. Furthermore, since the second Bragg reflector 700 is close to the bottom substrate layer 800, an additional heat dissipation means can be provided on the bottom substrate layer 800. This allows the heat generated by the second Bragg reflector 700 when the BAW filter filters out the sound waves corresponding to the low-frequency electrical signals to be quickly dissipated, thereby further reducing the impact of the temperature drift effect on the BAW filter.

[0068] In an optional embodiment of the present invention, the length of the second low acoustic impedance layer 710 and the length of the second high acoustic impedance layer 720 are greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0069] In an embodiment of the present invention, the lengths of the second low-acoustic impedance layer 710 and the second high-acoustic impedance layer 720 are greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the BAW filter. This allows the second low-acoustic impedance layer 710 and the second high-acoustic impedance layer 720 to completely consume the acoustic waves corresponding to the low-frequency electrical signal filtered by the BAW filter on their Bragg reflection surfaces, thereby achieving a filtering effect. In practical applications, the lengths of the second low-acoustic impedance layer 710 and the second high-acoustic impedance layer 720 can be slightly greater than the shear wavelength of the acoustic wave corresponding to the low-frequency electrical signal filtered by the BAW filter, thereby reducing the amount of acoustic impedance material required for the second low-acoustic impedance layer 710 and the second high-acoustic impedance layer 720.

[0070] The bottom substrate layer 800 is connected to the side of the second Bragg reflector layer 700 away from the middle substrate layer 600 . The bottom substrate layer 800 is used to support other layers to form a bulk acoustic wave filter.

[0071] In an optional embodiment of the present invention, the middle substrate layer 600 and the bottom substrate layer 800 are made of the same material.

[0072] In practical applications, the middle substrate layer 600 and the bottom substrate layer 800 can be made of the same material, that is, the middle substrate layer 600 and the bottom substrate layer 800 are made of the same material, and the corresponding dimensions match the corresponding Bragg reflector layers. Specifically, the middle substrate layer 600 and the bottom substrate layer 800 can be made of silicon, gallium nitride, etc. as the substrate material.

[0073] In order to enable those skilled in the art to more clearly understand the acoustic wave transmission process of the BAW filter according to the embodiment of the present invention, the acoustic wave transmission path of the BAW filter is described below:

[0074] Reference Figure 4 , which shows a schematic diagram of acoustic wave transmission in an embodiment of a bulk acoustic wave filter according to the present invention. The solid line in the figure indicates the transmission path of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter, while the dashed line indicates the transmission path of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

[0075] Specifically, after the sound wave corresponding to the characteristic frequency electrical signal is generated, it is transmitted to the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520. Because the shear wavelength of the sound wave corresponding to the characteristic frequency electrical signal is smaller than the size of the intermediate substrate layer 600, the sound wave corresponding to the characteristic frequency electrical signal cannot continue to propagate downward after the intermediate substrate layer 600. The first low acoustic impedance layer 510 and the first high acoustic impedance layer 520 reflect all the sound waves corresponding to the characteristic frequency electrical signal back to the piezoelectric layer 200, and the piezoelectric layer 200 generates a filtered electrical signal through the positive piezoelectric effect.

[0076] After the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter are generated, they are transmitted to the first low acoustic impedance layer 510 and the first high acoustic impedance layer 520. Because the shear wavelength of the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter is comparable to that of the intermediate substrate layer 600, the sound waves diffract and are then transmitted to the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720. Because the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter do not match the thickness of the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720, the sound waves corresponding to the low-frequency electrical signals filtered out by the BAW filter are continuously consumed in the second low acoustic impedance layer 710 and the second high acoustic impedance layer 720, thus achieving a filtering function.

[0077] In order to enable those skilled in the art to more clearly understand the temperature rise effect of the BAW filter according to the embodiment of the present invention, the temperature rise in the prior art is compared with the temperature rise of the BAW filter according to the embodiment of the present invention.

[0078] Reference Figure 5a , which shows a temperature rise schematic diagram of a bulk acoustic wave filter embodiment of the present invention;

[0079] In an embodiment of the present invention, in the first Bragg reflector, all sound waves corresponding to the BAW filter's characteristic frequency electrical signal are reflected back to the piezoelectric layer. Only a small portion of the sound waves corresponding to the low-frequency electrical signal filtered out by the BAW filter is dissipated in the first Bragg reflector. Therefore, the first Bragg reflector, acting as a working cavity, generates only a small amount of heat, representing a low-temperature rise region. However, in the second Bragg reflector, the sound waves corresponding to the low-frequency electrical signal filtered out by the BAW filter are completely dissipated in the second Bragg reflector, generating a large amount of heat, representing a high-temperature rise region. Because the second Bragg reflector is close to the underlying substrate layer, it is easy to implement other heat dissipation measures. Furthermore, the second Bragg reflector does not reflect the sound waves corresponding to the BAW filter's characteristic frequency electrical signal. Therefore, the temperature drift effect caused by its temperature rise has little impact on the filtering effect of the first Bragg reflector.

[0080] Reference Figure 5b , shows a temperature rise schematic diagram of a bulk acoustic wave filter embodiment in the prior art.

[0081] The sound waves corresponding to the characteristic frequency electrical signal of a bulk acoustic wave filter are reflected by the Bragg reflector. The sound waves corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter are also dissipated on the Bragg reflector. This means that the low and high acoustic impedance layers of the working cavity generate heat, creating a balanced temperature rise area. As the temperature rises, a temperature drift effect occurs, causing the filtering effectiveness of the low and high acoustic impedance layers of the working cavity to decrease.

[0082] In order to enable those skilled in the art to more clearly understand the BAW filter according to the embodiment of the present invention, the working process of the BAW filter is described below:

[0083] Reference Figure 6 , which shows a workflow diagram of a bulk acoustic wave filter embodiment of the present invention.

[0084] The multi-frequency electrical signal passes through the top electrode and the bottom electrode, and generates a multi-frequency acoustic wave signal through the inverse piezoelectric effect.

[0085] The optimized filter (bulk acoustic wave filter of the embodiment of the present invention) shunts bulk acoustic waves of different frequencies. Specifically: the bulk acoustic waves corresponding to the characteristic frequency cannot diffract and bypass the middle substrate layer due to their wavelength, and the bulk acoustic waves corresponding to the characteristic frequency are reflected in the first Bragg reflection layer, that is, they are fully reflected above the middle substrate layer, with low consumption, low temperature rise, and small temperature drift. The bulk acoustic waves corresponding to the characteristic frequency are fully reflected to the piezoelectric layer, and the piezoelectric layer restores the characteristic frequency electrical signal through the forward and inverse piezoelectric effects. Since the wavelength of the low-frequency bulk acoustic wave is close to the middle substrate layer, the low-frequency bulk acoustic wave bypasses the middle substrate layer through diffraction and enters the lower cavity (that is, the second Bragg reflection layer). The low-frequency bulk acoustic wave is lost due to mismatching in the lower cavity, the temperature rises, and the heat is dissipated nearby.

[0086] In an embodiment of the present invention, a top electrode, a piezoelectric layer, a bottom electrode, and a support layer are sequentially stacked and connected; a first Bragg reflector is connected to a side of the support layer away from the bottom electrode, an intermediate substrate layer is provided on a side of the first Bragg reflector away from the support layer, and a length of the intermediate substrate layer is less than that of the first Bragg reflector; a second Bragg reflector is connected to the other side of the intermediate substrate layer; and a bottom substrate layer is connected to a side of the second Bragg reflector away from the intermediate substrate layer. By providing two Bragg reflector layers and an intermediate substrate layer between them, the two Bragg reflector layers have different working areas. The first Bragg reflector layer close to the support layer forms a characteristic frequency reflection area, while the second Bragg reflector layer far from the support layer forms a low-frequency sound wave reflection area. This distinguishes the characteristic frequency and low-frequency sound wave reflection areas. This allows characteristic frequency sound waves to be reflected in the first Bragg reflector layer, while some low-frequency sound waves pass through the intermediate substrate layer through diffraction and enter the second Bragg reflector layer. This allows the first Bragg reflector layer to suppress temperature drift of the filter frequency within a relatively low temperature rise range, while the second Bragg reflector layer generates loss and temperature rise, minimizing the impact of temperature rise on frequency drift. Furthermore, the intermediate substrate layer and the second Bragg reflector layer are close to the bottom substrate layer, facilitating the use of various heat dissipation measures. This further reduces the temperature drift effect of the BAW filter, maintains filter frequency stability, optimizes non-target frequency suppression and heat dissipation mechanisms, and opens up new opportunities for further miniaturization and high power development of Bragg reflector-type BAW filters.

[0087] An embodiment of the present invention further discloses a communication device, comprising the bulk acoustic wave filter as described above.

[0088] The signal is filtered by a bulk acoustic wave filter to reduce the noise in a specific network when the communication device communicates using the network.

[0089] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0090] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, apparatus, or computer program products. Thus, embodiments of the present invention may take the form of a fully hardware embodiment, a fully software embodiment, or an embodiment combining software and hardware. Furthermore, embodiments of the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0091] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the process in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0092] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0093] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device so that a series of operating steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable terminal device to implement the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0094] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0095] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

[0096] The bulk acoustic wave filter and communication device provided by the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A bulk acoustic wave filter, characterized in that: include: stacking and connecting a top electrode, a piezoelectric layer, a bottom electrode and a support layer in sequence; a first Bragg reflector connected to a side of the support layer away from the bottom electrode, wherein an intermediate substrate layer is provided on the side of the first Bragg reflector away from the support layer, and a length of the intermediate substrate layer is smaller than a length of the first Bragg reflector; a second Bragg reflection layer connected to the other side of the intermediate substrate layer; The bottom substrate layer is connected to a side of the second Bragg reflective layer away from the middle substrate layer.

2. The bulk acoustic wave filter according to claim 1, wherein The first Bragg reflector layer includes a first low acoustic impedance layer and a first high acoustic impedance layer that are alternately stacked and connected; wherein the intermediate substrate layer is located in the first high acoustic impedance layer on a side of the first Bragg reflector layer away from the support layer.

3. The bulk acoustic wave filter according to claim 1 or 2, wherein: The length of the intermediate substrate layer is greater than the wavelength of the acoustic shear wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter, and is less than the wavelength of the acoustic shear wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

4. The bulk acoustic wave filter according to claim 2, wherein The length of the first low acoustic impedance layer and the length of the first high acoustic impedance layer are greater than the wavelength of the shear wave of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

5. The bulk acoustic wave filter according to claim 2 or 4, characterized in that The thickness of the first low acoustic impedance layer and the thickness of the first high acoustic impedance layer are one quarter of the wavelength of the longitudinal wave of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter.

6. The bulk acoustic wave filter according to claim 1, wherein The second Bragg reflection layer includes a second low acoustic impedance layer and a second high acoustic impedance layer that are alternately stacked and connected.

7. The bulk acoustic wave filter according to claim 6, wherein The thickness of the second low acoustic impedance layer and the thickness of the second high acoustic impedance layer are one quarter of the wavelength of the longitudinal wave of the acoustic wave corresponding to the characteristic frequency electrical signal of the bulk acoustic wave filter.

8. The bulk acoustic wave filter according to claim 6 or 7, characterized in that The length of the second low acoustic impedance layer and the length of the second high acoustic impedance layer are greater than the wavelength of the shear wave of the acoustic wave corresponding to the low-frequency electrical signal filtered out by the bulk acoustic wave filter.

9. The bulk acoustic wave filter according to claim 1, wherein The middle substrate layer and the bottom substrate layer are made of the same material.

10. A communication device, characterized in that: The method comprises the bulk acoustic wave filter according to any one of claims 1 to 9.

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