Transverse excitation bulk acoustic wave resonator and preparation method thereof

Abstract

The invention discloses a transverse excitation bulk acoustic resonator and a preparation method thereof, and the transverse excitation bulk acoustic resonator comprises a substrate, and a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure which are sequentially stacked on the substrate. The first Bragg reflection structure comprises first high acoustic impedance layers and first low acoustic impedance layers which are alternately stacked; the second Bragg reflection structure includes a second high acoustic impedance layer and a second low acoustic impedance layer that are alternately stacked. By forming the second Bragg reflection structure on the interdigital electrode, pollutants can be prevented from invading the interdigital electrode, the influence of humidity and gas on the resonator is avoided, the air resistance of the device is effectively considered, the performance stability is improved, the performance deterioration of the resonator is avoided, a vacuum cavity or a sealing cavity does not need to be arranged around the resonator subsequently, and the manufacturing cost is reduced. The cost can be reduced, risks occurring in the packaging process are reduced, and the production yield of products and the stability of the resonator are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a transversely excited bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] Against the backdrop of the rapid development of modern communication technology, acoustic resonator technology is crucial to meeting the multi-frequency and integrated requirements of mobile communication devices.

[0003] As an emerging piezoelectric micromechanical acoustic resonator, the laterally excited bulk acoustic wave resonator (XBAR) is composed of an interdigital electrode (IDE) and a piezoelectric layer. It uses interdigital electrodes to excite Lamb wave propagation and reflection to form standing wave resonance. The resonance frequency depends on the thickness of the piezoelectric layer and the electrode period. Multiple frequency resonators can be designed in the same mask plate, and electrical excitation can be achieved with the help of interdigital electrodes similar to surface acoustic wave resonators. It can also be prepared based on the existing BAW resonator process platform, combining the advantages of surface acoustic wave resonators (SAW) and bulk acoustic wave resonators (BAW). It is currently the only acoustic resonator technology that can achieve multi-frequency, high quality factor and small size on a single wafer.

[0004] However, XBAR has many problems. In terms of manufacturing process, the substrate needs to be etched to allow the piezoelectric layer to vibrate freely, which is difficult. The piezoelectric layer without substrate support is prone to breakage or collapse due to stress, and its physical reliability is low. In addition, the lack of substrate heat dissipation limits the power capacity, and the frequency temperature coefficient is low, requiring additional temperature compensation.

[0005] To solve the above problems, a Bragg reflection structure consisting of alternating high-impedance layers and low-impedance layers is formed between the piezoelectric layer and the substrate to achieve energy reflection and improve the quality factor. This type of resonator is a laterally excited solid-mounted bulk acoustic wave resonator (XSMR). However, the Bragg reflection structure cannot achieve 100% energy reflection, resulting in energy loss along the thickness direction, which reduces the quality factor, and the contact material under the piezoelectric layer greatly reduces the coupling coefficient.

[0006] In addition, changes in ambient temperature will cause changes in piezoelectric material constants, causing the resonant frequency of the lateral solid-state assembled bulk acoustic wave resonator to drift with temperature, affecting its application in RF terminals. Temperature compensation is required to improve frequency stability. In the chip packaging process, for XSMR, although vacuum packaging can reduce chip oxidation, remove impurities, and improve packaging accuracy and stability, the manufacture of vacuum chambers and sealed chambers requires complex packaging technology and high-quality materials, and the production cost is high; due to its small size, the manufacture of seals and vacuum chambers requires high-precision control, requiring advanced precision manufacturing equipment, increasing costs and risks; and when creating a vacuum chamber or sealed chamber, it is necessary to ensure sufficient sealing to prevent the intrusion of contaminants, which can easily complicate the packaging process and increase the risk of production failure. Summary of the invention

[0007] In view of the above problems, an object of the present invention is to provide a transversely excited bulk acoustic wave resonator and a method for preparing the same.

[0008] According to a first aspect of the present invention, there is provided a laterally excited bulk acoustic wave resonator, comprising a substrate and a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure sequentially stacked on the substrate, wherein the first Bragg reflection structure comprises a first high acoustic impedance layer and a first low acoustic impedance layer stacked alternately; and the second Bragg reflection structure comprises a second high acoustic impedance layer and a second low acoustic impedance layer stacked alternately.

[0009] Optionally, the thickness of each layer of the first Bragg reflection structure and / or the second Bragg reflection structure is 1 / 4 to 3 / 4 of the wavelength of the shear wave when the layer resonates.

[0010] Optionally, the material of the first low acoustic impedance layer is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, xerogel or polymer material, and the material of the second low acoustic impedance layer is silicon dioxide with a positive temperature coefficient.

[0011] Optionally, the materials of the first high acoustic impedance layer and the second high acoustic impedance layer are the same or different, and the material of the first high acoustic impedance layer and the second high acoustic impedance layer is at least one of aluminum nitride, tungsten oxide, tungsten nitride, molybdenum and tungsten.

[0012] Optionally, the first Bragg reflection structure and the second Bragg reflection structure have the same or different number of layers, and the number of layers ranges from 5 to 9.

[0013] Optionally, the material of the piezoelectric layer is one of aluminum nitride, lithium niobate, lithium tantalate or gallium nitride, and the thickness is 0.2 μm-1 μm.

[0014] Optionally, the material of the interdigital electrodes is molybdenum, aluminum, copper, gold, silver, tungsten, ruthenium or one of other conductive materials.

[0015] Optionally, the thickness of the interdigitated electrode is 1 / 10 to 1 / 2 of the thickness of the piezoelectric layer, the width of the interdigitated electrode is 0.5 μm to 20 μm, the spacing between the interdigitated electrodes is 2 to 20 times the width of the interdigitated electrodes, the length of the interdigitated electrodes is 50 μm to 200 μm, the aperture of the interdigitated electrodes is 45 μm to 180 μm, and the number of interdigitated electrode pairs is 4 to 50.

[0016] According to a second aspect of the present invention, there is provided a method for preparing the above-mentioned lateral excitation bulk acoustic wave resonator, comprising: sequentially forming a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure on a substrate; wherein the first Bragg reflection structure comprises a first high acoustic impedance layer and a first low acoustic impedance layer stacked alternately; and the second Bragg reflection structure comprises a second high acoustic impedance layer and a second low acoustic impedance layer stacked alternately. Beneficial Effects

[0017] According to the laterally excited bulk acoustic wave resonator and the preparation method thereof of the embodiments of the present invention, by forming a second Bragg reflection structure on the interdigital electrodes, it is possible to prevent pollutants from invading the interdigital electrodes, avoid the influence of humidity and gas on the resonator, effectively take into account the gas resistance of the device, improve the performance stability, avoid the deterioration of the resonator performance, and subsequently there is no need to set up a vacuum chamber or a sealed chamber around the resonator, which can reduce costs, reduce the risks in the packaging process, and improve the product production yield and the stability of the resonator.

[0018] Furthermore, the second low-impedance layer in the second Bragg reflection structure uses silicon oxide with a positive temperature coefficient, which can reduce the resonance frequency drift caused by temperature changes and improve the stability of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which: Figure 1 A schematic diagram showing the structure of a transversely excited thin film bulk acoustic resonator in the related art is shown; Figure 2 A schematic diagram showing the structure of a transversely excited solid-assembly type bulk acoustic wave resonator in the related art is shown; Figure 3 A schematic diagram showing the structure of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention is shown; Figure 4 A schematic diagram showing interdigitated electrodes; Figure 5 A schematic diagram showing impedance curves of a lateral excitation solid-assembly type lateral excitation bulk acoustic wave resonator at different temperatures in the related art is shown; Figure 6A schematic diagram showing impedance curves of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention at different temperatures; Figure 7 Show Figure 2 The transversely excited bulk acoustic wave resonator shown in Figure 2 The interdigital electrodes of the transversely excited BAW resonator shown are covered with epoxy resin and Figure 3 A schematic diagram of an impedance curve of the second reflective structure of the lateral excitation bulk acoustic wave resonator covered with epoxy resin is shown. DETAILED DESCRIPTION

[0020] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0021] The specific implementation of the present invention is further described in detail below in conjunction with the drawings and examples.

[0022] In the related art, see Figure 1 The transversely excited thin film bulk acoustic wave resonator includes a substrate 100, a piezoelectric film 110 located on the substrate 100, and an interdigital electrode 120. Among them, the substrate 100 needs to be etched to form a cavity so that the piezoelectric film 110 can vibrate freely, which has certain difficulties in process manufacturing; and because the substrate 100 has a cavity, the piezoelectric film 110 lacks the support of the substrate 100, and the piezoelectric film suspended in the middle is easily broken or collapsed due to stress, and the physical reliability is low. In addition, the thin film structure lacks the heat dissipation of the substrate, and the power capacity will not be very high; the temperature coefficient of frequency (TCF) is low, and additional temperature compensation is also required.

[0023] In order to solve the above problems, a Bragg reflection structure is formed between the substrate and the piezoelectric film to form a lateral excitation solid-state assembly type bulk acoustic wave resonator. Figure 2 The lateral excitation solid-state assembly type bulk acoustic wave resonator includes a substrate 200, a Bragg reflection structure 230 located on the substrate 200, a piezoelectric film 210 and an interdigital electrode 220. The Bragg reflection structure 230 includes alternately stacked low acoustic impedance layers 231 and high acoustic impedance layers 232. Although the Bragg reflection structure can achieve energy reflection and improve the quality factor, the Bragg reflection structure cannot achieve 100% energy reflection, resulting in energy loss propagating along the thickness direction, which reduces the quality factor, and the contact material under the piezoelectric layer affects the coupling coefficient greatly.

[0024] In addition, changes in ambient temperature can cause changes in piezoelectric material constants, causing the resonant frequency of the lateral solid-state assembled bulk acoustic wave resonator to drift with temperature, affecting its application in RF terminals. Temperature compensation is required to improve frequency stability. In the chip packaging process, for XSMR, although vacuum packaging can reduce chip oxidation, remove impurities, and improve packaging accuracy and stability, the manufacture of vacuum chambers and sealed chambers requires complex packaging technology and high-quality materials, and the production cost is high; due to its small size, the manufacture of seals and vacuum chambers requires high-precision control, requiring advanced precision manufacturing equipment, increasing costs and risks; and when creating a vacuum chamber or sealed chamber, it is necessary to ensure sufficient sealing to prevent the intrusion of contaminants, which can easily complicate the packaging process and increase the risk of production failure.

[0025] In order to solve the above problems, an embodiment of the present application provides a laterally excited bulk acoustic wave resonator. By forming a second Bragg reflection structure on the interdigital electrodes, it is possible to prevent contaminants from invading the interdigital electrodes, avoid the influence of humidity and gas on the resonator, effectively take into account the gas resistance of the device, and improve performance stability.

[0026] See also Figure 3 The transversely excited bulk acoustic wave resonator provided in the embodiment of the present application includes a substrate 300 and a first Bragg reflection structure 330, a piezoelectric layer 310, an interdigital electrode 320 and a second Bragg reflection structure 340 sequentially stacked on the substrate.

[0027] The material of the piezoelectric layer 310 is one of aluminum nitride, lithium niobate, lithium tantalate or gallium nitride, and the thickness is 0.2 μm-1 μm.

[0028] The material of the interdigital electrode 320 is molybdenum, aluminum, copper, gold, silver, tungsten, ruthenium or one of other conductive materials. The thickness d2 of the interdigital electrode is 1 / 10 to 1 / 2 of the thickness d1 of the piezoelectric layer. Figure 4 , the width w of the interdigital electrodes is 0.5 μm to 20 μm. The spacing d3 of the interdigital electrodes is 2 to 20 times the width of the interdigital electrodes, and the length l1 of the interdigital electrodes is 50 μm to 200 μm. The overlapping part of the interdigital electrodes is the aperture, and the length l2 of the aperture of the interdigital electrodes is 45 μm to 180 μm. The number of interdigital electrode pairs is 4 to 50.

[0029] The first Bragg reflection structure 330 includes first low acoustic impedance layers 331 and first high acoustic impedance layers 332 that are alternately stacked; the second Bragg reflection structure 340 includes second low acoustic impedance layers 341 and second high acoustic impedance layers 342 that are alternately stacked.

[0030] In this embodiment, the thickness of each layer of the first Bragg reflection structure 330 and / or the second Bragg reflection structure 340 is 1 / 4 to 3 / 4 of the shear wave wavelength of the layer when it resonates. The number of layers of the first Bragg reflection structure 330 and the second Bragg reflection structure 340 is the same or different, and the number of layers ranges from 5 to 9.

[0031] The material of the first low acoustic impedance layer 331 is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, xerogel or polymer material, and the material of the second low acoustic impedance layer 341 is silicon dioxide with a positive temperature coefficient.

[0032] The impedance curves of the lateral excitation bulk acoustic wave resonator in the related art at different temperatures are as follows: Figure 5 As shown, when the temperature changes from -30℃ to 85℃, the series frequency decreases from 5.399GHz to 5.385GHz, with a shift of 14MHz. The frequency temperature coefficient TCF=, is the series resonant frequency when the ambient temperature is T, and is the series resonant frequency when the ambient temperature is. According to this formula, its frequency temperature coefficient (TCF) is -2.25e-5 / ℃.

[0033] The impedance curves of the transversely excited bulk acoustic wave resonator of the embodiment of the present application at different temperatures are as follows: Figure 6 As shown, the temperature changes from -30°C to 85°C, the series resonant frequency decreases from 5.370Ghz to 5.361GHz, the frequency shifts by 9MHz, and its temperature coefficient of frequency (TCF) is -1.46e-5 / °C. The effect of temperature on frequency is reduced, and the second low acoustic impedance layer 321 in the second Bragg reflection structure uses silicon dioxide with a positive temperature coefficient to play a role in temperature compensation.

[0034] The materials of the first high acoustic impedance layer 332 and the second high acoustic impedance layer 342 are the same or different. The materials of the first high acoustic impedance layer and the second high acoustic impedance layer are at least one of aluminum nitride, tungsten oxide, tungsten nitride, molybdenum, and tungsten.

[0035] See also Figure 7 In the related art, the performance of the transversely excited bulk acoustic wave resonator is seriously deteriorated after a layer of epoxy resin is directly covered on the interdigital electrodes. However, after a layer of epoxy resin is covered on the top of the second Bragg reflection layer of the transversely excited bulk acoustic wave resonator of the present application, the bulk acoustic wave resonance frequency is almost unchanged compared to the case without epoxy resin, and the impedance is slightly reduced. This means that the second Bragg reflection structure can avoid the influence of the external environment, so that the transversely excited bulk acoustic wave resonator with a double Bragg reflection structure does not need to be vacuum packaged to protect it from the influence of the external environment.

[0036] According to the laterally excited bulk acoustic wave resonator of the embodiment of the present invention, by forming a second Bragg reflection structure on the interdigital electrodes, it is possible to prevent contaminants from invading the interdigital electrodes, avoid the influence of humidity and gas on the resonator, effectively take into account the gas resistance of the device, improve performance stability, avoid deterioration of resonator performance, and subsequently there is no need to set up a vacuum chamber or a sealed chamber around the resonator, which can reduce costs, reduce the risks of the packaging process, and improve product production yield and the stability of the resonator.

[0037] Furthermore, the second low-impedance layer in the second Bragg reflection structure uses silicon oxide with a positive temperature coefficient, which can reduce the resonance frequency drift caused by temperature changes and improve the stability of the resonator.

[0038] An embodiment of the present application also provides a method for preparing the above-mentioned lateral excitation bulk acoustic wave resonator, comprising: sequentially forming a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure on a substrate; wherein the first Bragg reflection structure comprises a first high acoustic impedance layer and a first low acoustic impedance layer stacked alternately; and the second Bragg reflection structure comprises a second high acoustic impedance layer and a second low acoustic impedance layer stacked alternately.

[0039] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A transversely excited bulk acoustic wave resonator, characterized in that: The invention comprises a substrate and a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure which are sequentially stacked on the substrate. The first Bragg reflection structure includes a first high acoustic impedance layer and a first low acoustic impedance layer that are alternately stacked; and the second Bragg reflection structure includes a second high acoustic impedance layer and a second low acoustic impedance layer that are alternately stacked.

2. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The thickness of each layer of the first Bragg reflection structure and / or the second Bragg reflection structure is 1 / 4 to 3 / 4 of the wavelength of the shear wave when the layer resonates.

3. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The material of the first low acoustic impedance layer is at least one of silicon dioxide, silicon nitride, magnesium oxide, nanoporous mixture, aerogel, xerogel or polymer material, and the material of the second low acoustic impedance layer is silicon dioxide with a positive temperature coefficient.

4. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The materials of the first high acoustic impedance layer and the second high acoustic impedance layer are the same or different. The materials of the first high acoustic impedance layer and the second high acoustic impedance layer are at least one of aluminum nitride, tungsten oxide, tungsten nitride, molybdenum and tungsten.

5. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The number of layers of the first Bragg reflection structure and the second Bragg reflection structure is the same or different, and the number of layers ranges from 5 to 9.

6. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The material of the piezoelectric layer is one of aluminum nitride, lithium niobate, lithium tantalate or gallium nitride, and the thickness is 0.2 μm~1 μm.

7. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The material of the interdigital electrodes is molybdenum, aluminum, copper, gold, silver, tungsten, ruthenium or one of other conductive materials.

8. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The thickness of the interdigitated electrode is 1 / 10 to 1 / 2 of the thickness of the piezoelectric layer, the width of the interdigitated electrode is 0.5 μm to 20 μm, the spacing between the interdigitated electrodes is 2 to 20 times the width of the interdigitated electrodes, the length of the interdigitated electrodes is 50 μm to 200 μm, the aperture of the interdigitated electrodes is 45 μm to 180 μm, and the number of interdigitated electrode pairs is 4 to 50.

9. A method for preparing a transversely excited bulk acoustic wave resonator according to any one of claims 1 to 8, characterized in that: include: forming a first Bragg reflection structure, a piezoelectric layer, an interdigital electrode and a second Bragg reflection structure in sequence on a substrate; The first Bragg reflection structure includes a first high acoustic impedance layer and a first low acoustic impedance layer that are alternately stacked; and the second Bragg reflection structure includes a second high acoustic impedance layer and a second low acoustic impedance layer that are alternately stacked.

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