Ultra-small electromechanical coupling coefficient resonator, implementation method and ultra-narrow band filter

Abstract

The invention provides an ultra-small electromechanical coupling coefficient resonator, an implementation method and an ultra-narrow band filter, and the method comprises the steps: applying a preset pulse voltage to an electrode of a bulk acoustic wave resonator of which a piezoelectric layer comprises a ferroelectric layer, so as to achieve the overturning of a local polarization direction of a preset region of the ferroelectric layer of the bulk acoustic wave resonator, therefore, the bulk acoustic wave resonator with the ultra-small overall electromechanical coupling coefficient is obtained. The first pulse voltage is applied to the resonator based on the ferroelectric material, the polarization direction of the ferroelectric layer is locally turned, the bulk acoustic wave resonator with the ultra-small electromechanical coupling coefficient is obtained, and the application requirement of an ultra-high-frequency ultra-narrow-band filter is met; besides, a second piezoelectric layer can be arranged between the first electrode and the second electrode, so that the piezoelectric coefficient of the ferroelectric layer can be partially offset, the electromechanical coupling coefficient of the resonator is greatly reduced, and the filter with the ultra-narrow bandwidth is realized. And finally, the filter with narrower bandwidth is realized by selecting the material and the thickness of the electrode.

Description

Technical Field

[0001] This invention belongs to the field of electronic device technology, and in particular relates to an ultra-small electromechanical coupling coefficient resonator, its implementation method, and an ultra-narrowband filter. Background Technology

[0002] Ultra-narrowband communication, by using a very narrow operating frequency band, can improve the anti-interference capability of network connections, expand signal coverage, and support more devices to access the network simultaneously. This technology has become an important technical solution for communication systems such as the Internet of Things (IoT), Low-Power Wide-Area Network (LPWA), and Wireless Local Area Network (Wi-Fi). As communication frequencies expand to higher frequency bands, higher requirements are placed on the frequency selectivity and bandwidth control of radio frequency front-end devices.

[0003] Bulk acoustic wave (BAW) filters based on aluminum nitride (AlN) materials possess advantages such as high operating frequency, low insertion loss, high frequency selectivity, high power capacity, and strong electrostatic discharge immunity, and have been widely used in the radio frequency (RF) front-end of the communication field. However, current technology has stalled in further reducing the bandwidth of ultra-narrowband filters, mainly due to the inherently high electromechanical coupling coefficient (K²) of AlN materials, making it difficult to reduce the relative bandwidth (FBW) of the filter to below 1%.

[0004] Although bandwidth can be compressed to some extent through circuit optimization, impedance matching, or structural fine-tuning, it is impossible to overcome the physical limits of the materials themselves. Furthermore, the added circuit structure will make the RF system more complex and adversely affect other RF performance of the filter.

[0005] Therefore, there is an urgent need for a bulk acoustic wave filter structure or operating method that can achieve a narrower bandwidth while maintaining a high Q value and low loss.

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating the understanding of those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because these solutions have been described in the background section of this application. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide an ultra-small electromechanical coupling coefficient resonator, an implementation method, and an ultra-narrowband filter to solve the problem that the bulk acoustic wave filter in the prior art is difficult to achieve a narrower bandwidth while maintaining a high Q value and low loss.

[0008] To achieve the above objectives, the present invention provides a method for implementing an ultra-small electromechanical coupling coefficient resonator, the method comprising:

[0009] A preset pulse voltage is applied to the electrodes of a bulk acoustic resonator whose piezoelectric layer includes a ferroelectric layer, so as to reverse the local polarization direction of a preset region of the ferroelectric layer of the bulk acoustic resonator, thereby obtaining a bulk acoustic resonator with an ultra-small overall electromechanical coupling coefficient.

[0010] The present invention also provides an ultra-small electromechanical coupling coefficient resonator, wherein the resonator achieves an ultra-small electromechanical coupling coefficient using the above-described method for implementing an ultra-small electromechanical coupling coefficient resonator, and the resonator comprises:

[0011] The first electrode is electrically connected to a preset first pulse voltage source;

[0012] The second electrode is electrically connected to a preset second pulse voltage source, or the second electrode is grounded;

[0013] A first piezoelectric layer, wherein the first piezoelectric layer is a ferroelectric layer, and the first piezoelectric layer is located between the first electrode and the second electrode;

[0014] An acoustic mirror structure is located on the side of the second electrode away from the first piezoelectric layer.

[0015] Optionally, the material of the first piezoelectric layer is Al. (1-x) Sc x N thin film, wherein x is greater than or equal to 20%; and / or, the thickness of the first piezoelectric layer is 0.01 micrometers to 1 micrometer.

[0016] Optionally, the resonator further includes a second piezoelectric layer located between the first piezoelectric layer and the second electrode.

[0017] Optionally, the second piezoelectric layer is a ferroelectric layer with the opposite polarity to the first piezoelectric layer; or, the second piezoelectric layer is a ferroelectric layer with the same polarity as the first piezoelectric layer.

[0018] Optionally, the second piezoelectric layer is a non-ferroelectric piezoelectric thin film, and the piezoelectric stress constant thickness product of the second piezoelectric layer is 70%-130% of the piezoelectric stress constant thickness product of the first piezoelectric layer.

[0019] Optionally, the materials of the first electrode and the second electrode are at least one selected from Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf; and / or, the thickness of the first electrode and the second electrode is 0.01 micrometer to 0.5 micrometer.

[0020] Optionally, the acoustic mirror structure is at least one of the following: a Bragg reflector layer, a cavity, or a phononic crystal mirror.

[0021] The present invention also provides an ultra-narrowband filter, which is constructed by cascading two or more resonators with ultra-small electromechanical coupling coefficients as described above.

[0022] Optionally, the cascaded topology used to construct the ultra-narrowband filter from the resonator with the ultra-small electromechanical coupling coefficient can be any one of a trapezoidal structure, a lattice structure, or a hybrid structure.

[0023] As described above, the ultra-small electromechanical coupling coefficient resonator, implementation method, and ultra-narrowband filter of the present invention have the following beneficial effects:

[0024] This invention applies a corresponding first pulse voltage source to a bulk acoustic resonator with a ferroelectric layer as the first piezoelectric layer, thereby locally reversing the polarization direction of the ferroelectric layer, resulting in a bulk acoustic resonator with an ultra-small overall electromechanical coupling coefficient, which meets the practical application requirements of ultra-narrowband filters in the ultra-high frequency operating band.

[0025] This invention uses scandium-doped aluminum nitride with a specific formulation as the first piezoelectric layer, which can further reduce the bandwidth by using pulse voltage while maintaining the same high quality factor and low insertion loss as aluminum nitride, thus realizing a filter with a narrower bandwidth.

[0026] This invention achieves a significant reduction in the electromechanical coupling coefficient of the overall resonator by setting the material and equivalent piezoelectric effect of the second piezoelectric layer, combined with the local polarity reversal effect of the pulse voltage on the first piezoelectric layer, thereby further realizing the function of a filter with a narrower bandwidth;

[0027] This invention further reduces the electromechanical coupling coefficient of the resonator by selecting the material and thickness of the electrodes, thereby achieving a filter with a narrower bandwidth. Attached Figure Description

[0028] Figure 1 The diagram shown is a schematic side cross-sectional view of the structure of the ultra-small electromechanical coupling coefficient resonator in Embodiment 2 of the present invention.

[0029] Figure 2 The diagram shown is a schematic side cross-sectional view of the structure of the ultra-small electromechanical coupling coefficient resonator in Embodiment 3 of the present invention.

[0030] Explanation of icon numbers:

[0031] 1. First electrode; 2. Second electrode; 3. First piezoelectric layer; 4. Second piezoelectric layer; 5. Acoustic mirror structure; 6. First electrical lead; 7. Second electrical lead. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0033] In the detailed description of embodiments of the present invention, for ease of explanation, the schematic diagrams illustrating the device structure may be partially enlarged without adhering to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0034] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the accompanying drawings for devices in use or operation.

[0035] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0036] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex. The quantity range given in the present invention includes the two boundary values ​​of the quantity range by default unless otherwise specified.

[0037] Ultra-narrowband communication, by utilizing an extremely narrow operating frequency band, can enhance the anti-interference performance of network connections, expand signal coverage, and support more devices accessing the network simultaneously. This technology has become a key technical solution for communication systems such as the Internet of Things (IoT), Low-Power Wide-Area Network (LPWA), and Wireless Local Area Network (Wi-Fi). As communication frequencies expand to higher bands, more stringent requirements are placed on the frequency selectivity and bandwidth control of RF front-end devices. Bulk Acoustic Wave (BAW) filters based on aluminum nitride (AlN) materials possess advantages such as high operating frequency, low insertion loss, high frequency selectivity, high power capacity, and strong anti-static performance, and have been widely used in RF front-ends in the communication field. However, existing technologies have made slow progress in further narrowing the bandwidth of ultra-narrowband filters, mainly due to the inherently high electromechanical coupling coefficient (K²) of AlN materials, making it difficult to reduce the relative bandwidth (FBW) of the filter to below 1%. While current methods can compress bandwidth to some extent through circuit optimization, impedance matching, or structural fine-tuning, they cannot overcome the physical limitations of the materials themselves. Furthermore, the added circuitry complicates the RF system and negatively impacts other RF performance aspects of the filter. Additionally, traditional ferroelectric materials such as lead zirconate titanate (PZT), despite their adjustable K², suffer from high dielectric loss, low quality factor (Q), and high fabrication temperature, making them incompatible with modern complementary metal-oxide-semiconductor (CMOS) processes and hindering the achievement of high-frequency, low-loss filter performance. To address these issues, this invention provides the following solution:

[0038] Example 1:

[0039] This embodiment provides a method for implementing an ultra-small electromechanical coupling coefficient resonator, the method comprising:

[0040] A preset pulse voltage is applied to the electrodes of a bulk acoustic resonator whose piezoelectric layer includes a ferroelectric layer, so as to reverse the local polarization direction of a preset region of the ferroelectric layer of the bulk acoustic resonator, thereby obtaining a bulk acoustic resonator with an ultra-small overall electromechanical coupling coefficient.

[0041] This invention applies a preset pulse voltage to a bulk acoustic resonator whose piezoelectric layer includes a ferroelectric layer, causing a local polarization reversal in a preset region of the ferroelectric layer, thereby obtaining a bulk acoustic resonator with an ultra-small overall electromechanical coupling coefficient, which meets the practical application requirements of ultra-narrowband filters in the ultra-high frequency operating band.

[0042] Specifically, the “preset pulse voltage” in this paper refers to a pulse voltage with a specific waveform set according to the requirement of reversing the local polarization direction of a preset region of the ferroelectric layer; the “preset region of the ferroelectric layer” refers to the region where the piezoelectric effect of the ferroelectric layer as a whole can be canceled after the polarization direction of the region is reversed; both the “preset pulse voltage” and the “preset region of the ferroelectric layer” can be obtained experimentally based on the corresponding bulk acoustic resonator.

[0043] Example 2:

[0044] This embodiment provides an ultra-small electromechanical coupling coefficient resonator. The resonator achieves the ultra-small electromechanical coupling coefficient using the method described in Embodiment 1. Figure 1 As shown, the resonator includes:

[0045] First electrode 1, the first electrode 1 is electrically connected to a preset first pulse voltage source;

[0046] Second electrode 2, the second electrode 2 is grounded;

[0047] The first piezoelectric layer 3 is a ferroelectric layer and is located between the first electrode 1 and the second electrode 2.

[0048] Acoustic mirror structure 5, which is located on the side of the second electrode 2 away from the first piezoelectric layer 3.

[0049] This invention applies a corresponding first pulse voltage source to a bulk acoustic wave resonator with a ferroelectric layer as the first piezoelectric layer 3 to achieve a reversal of the local polarization direction of the ferroelectric layer. After the local polarization direction reversal is completed, a microstructure with alternating positive and negative piezoelectric coefficients is formed within the first piezoelectric layer 3. This microstructure with alternating positive and negative piezoelectric coefficients plays an important role, allowing the piezoelectric responses of the first piezoelectric layer 3 to cancel each other out at the macroscopic level. When the piezoelectric responses of the first piezoelectric layer 3 cancel each other out, the effective electromechanical coupling coefficient is suppressed to an extremely low level. At the same time, since material loss does not increase during this process, the bulk acoustic wave resonator can still maintain a high Q value. Based on the above series of operations and effects, a bulk acoustic wave resonator with an extremely small overall electromechanical coupling coefficient can finally be obtained. Compared with existing ultra-narrowband resonator implementation schemes, the scheme proposed in this invention has a simple structure and low modification cost. It does not require complex circuit structures or additional circuit components and extra films. It can be realized by relying on the resonator's own electrode-piezoelectric-electrode structure. It is realized by relying on the physical properties of the piezoelectric material itself, without introducing other materials to reduce the quality factor of the resonator. This bulk acoustic resonator with an extremely small overall electromechanical coupling coefficient has more important practical application value and can better meet the practical application requirements of ultra-narrowband filters in the ultra-high frequency operating band.

[0050] Specifically, in this embodiment, the ferroelectric layer of the ultra-small electromechanical coupling coefficient resonator corresponds to the first piezoelectric layer 3 and the first electrode 1 in the ultra-small electromechanical coupling coefficient resonator implementation method of embodiment 1.

[0051] Specifically, the first pulse voltage source connected to the first electrode 1 is determined by the bandwidth of the electromechanical coupling coefficient resonator to be implemented. When the applied electric field strength of the first pulse voltage source to the resonator is less than the breakdown field strength of the first piezoelectric layer 3, the pulse waveform, height, width or duty cycle of the first pulse voltage source are set experimentally to achieve local and quantitative flipping of the ferroelectric thin film domains of the first piezoelectric layer 3 according to the preset mode, thereby realizing the metastable or multistable adjustment of the electromechanical coupling coefficient to adapt to different bandwidth and filtering requirements.

[0052] In one embodiment, the material of the first piezoelectric layer 3 is Al. (1-x) Sc x N thin film, where x is greater than or equal to 20%.

[0053] This invention employs a scandium-doped aluminum nitride material at a specific concentration as a key component in constructing the first piezoelectric layer 3. The introduction of this material not only maintains the excellent characteristics of high quality factor and low insertion loss as conventional aluminum nitride materials, but also effectively achieves further reduction in filter bandwidth under pulsed voltage conditions. This technological breakthrough enables the filter to achieve a narrower bandwidth while maintaining its original performance, thereby meeting the stringent requirements of modern communication systems for high selectivity and low interference. Through careful design and optimization of the scandium-doped aluminum nitride concentration, this invention successfully bridges the gap between materials science and electronic engineering, making it possible to develop a new generation of high-performance filters.

[0054] In one embodiment, the first piezoelectric layer 3 can also be Al. y B (1-y) N, Al y Ga (1-y) At least one of N, LiNbO3, PZT, PbTiO3, or BTO, where y is a number greater than 0. Specifically, those skilled in the art can also replace it with other suitable ferroelectric materials according to actual needs; its piezoelectric properties within a narrow bandwidth are similar to those using Al. (1-x) Sc x While N may be somewhat degraded compared to N, it can be used to improve other required performance to meet actual needs, and all of these are within the scope of protection of this invention.

[0055] In one embodiment, the thickness of the first piezoelectric layer 3 is 0.01 micrometers to 1 micrometer.

[0056] This invention, by adjusting the thickness of the first piezoelectric layer 3, enables the resulting bulk acoustic wave filter to operate within the commonly used operating frequency bands required for ultra-narrowband filters. Specifically, the thickness of the first piezoelectric layer 3 can also be adjusted to other suitable thicknesses depending on the desired operating frequency band, all of which are within the scope of protection of this invention.

[0057] In one embodiment, the materials of the first electrode 1 and the second electrode 2 are at least one selected from Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

[0058] This invention, by selecting the materials of the first electrode 1 and the second electrode 2, enables the bulk acoustic resonator formed to achieve a lower electromechanical coupling coefficient, thereby obtaining a filter with a narrower bandwidth. Specifically, other suitable materials for the first electrode 1 and the second electrode 2 can also be selected as needed, all of which are within the scope of protection of this invention.

[0059] In one embodiment, the thickness of both the first electrode 1 and the second electrode 2 is 0.01 micrometers to 0.5 micrometers.

[0060] By adjusting the thickness of the first electrode 1 and the second electrode 2, this invention can coordinate the influence of the pulsed voltage applied to the first piezoelectric layer 3 on the electric field formed between the electrodes and the propagation of sound waves, thereby achieving a lower electromechanical coupling coefficient and a narrower bandwidth filter. Specifically, other suitable thicknesses of the first electrode 1 and the second electrode 2 can also be selected according to actual needs, all of which are within the scope of this invention.

[0061] Specifically, such as Figure 1 As shown, the first electrode 1 is led out to the surface of the resonator through the first electrical lead 6, so as to be electrically connected to the first pulse power supply through the first electrical lead 6; the second electrode 2 is led out to the surface of the resonator through the second electrical lead 7, so as to be grounded through the second electrical lead 7.

[0062] In one embodiment, the acoustic mirror structure 5 is at least one of a Bragg reflector layer, a cavity, or a phonon crystal mirror. Specifically, a suitable acoustic mirror structure 5 can be selected to cooperate with other filter structures and pulse voltages according to the actual application effect to achieve a narrow bandwidth filter with a smaller electromechanical coupling coefficient, all of which are within the protection scope of this invention.

[0063] Example 3:

[0064] This embodiment provides an ultra-small electromechanical coupling coefficient resonator. Other features of the resonator are basically the same as those in Embodiment 2, except that:

[0065] In this embodiment, as Figure 2 As shown, the resonator further includes a second piezoelectric layer 4, which is located between the first piezoelectric layer 3 and the second electrode 2.

[0066] In this embodiment, the second piezoelectric layer 4 is a ferroelectric layer with the opposite polarity to the first piezoelectric layer 3.

[0067] By setting the second piezoelectric layer 4 to be a ferroelectric layer with the opposite polarity to the first piezoelectric layer 3, the present invention can work with the first pulse voltage source to further cancel out the electro-reactive responses of the resonator, thereby further reducing the electromechanical coupling coefficient and realizing a filter with a narrower bandwidth.

[0068] Specifically, in this embodiment, the ferroelectric layer in the ultra-small electromechanical coupling coefficient resonator corresponds to the first piezoelectric layer 3 and the second piezoelectric layer 4 in the ultra-small electromechanical coupling coefficient resonator implementation method of Embodiment 1.

[0069] Example 4:

[0070] This embodiment provides an ultra-small electromechanical coupling coefficient resonator. Other features of the resonator are basically the same as those in Embodiment 3, except that:

[0071] In this embodiment, the second piezoelectric layer 4 is a ferroelectric layer with the same polarity as the first piezoelectric layer 3.

[0072] By setting the second piezoelectric layer 4 to be a ferroelectric layer with the same polarity as the first piezoelectric layer 3, the electromechanical coupling coefficient of the obtained resonator can be further reduced, thereby achieving a filter with a narrower bandwidth.

[0073] Specifically, in this embodiment, the ferroelectric layer in the ultra-small electromechanical coupling coefficient resonator corresponds to the first piezoelectric layer 3 and the second piezoelectric layer 4 in the ultra-small electromechanical coupling coefficient resonator implementation method of Embodiment 1.

[0074] Example 5:

[0075] This embodiment provides an ultra-small electromechanical coupling coefficient resonator. Other features of the resonator are basically the same as those in Embodiment 3, except that:

[0076] In this embodiment, the second piezoelectric layer 4 is a non-ferroelectric piezoelectric thin film, and the piezoelectric stress constant thickness product of the second piezoelectric layer 4 is 70%-130% of the piezoelectric stress constant thickness product of the first piezoelectric layer 3.

[0077] By setting the second piezoelectric layer 4 as a non-ferroelectric piezoelectric thin film, and by combining the relationship between the piezoelectric stress constant and thickness product of the first piezoelectric layer 3 and the second piezoelectric layer 4, as well as the control of the polarity reversal effect of the first pulse voltage source on the first piezoelectric layer 3, the electromechanical coupling coefficient of the obtained resonator can be further reduced, thereby further realizing a filter with a narrower bandwidth.

[0078] Specifically, the "piezoelectric stress constant-thickness product" is the product of the thickness of the piezoelectric material and the piezoelectric stress constant, used to represent the equivalent piezoelectric effect of the piezoelectric material.

[0079] Specifically, in this embodiment, the ferroelectric layer in the ultra-small electromechanical coupling coefficient resonator corresponds to the first piezoelectric layer 3 in the ultra-small electromechanical coupling coefficient resonator implementation method of Embodiment 1.

[0080] Specifically, the second piezoelectric layer 4 is a non-AlN, non-ferroelectric piezoelectric film. This avoids the situation where, after pure AlN and the first piezoelectric layer with its flipping capability ferroelectric film form a heterogeneous stack, the built-in electric field at the interface causes the polarization within the AlN layer to flip, resulting in near-neighbor ferroelectricity. This further improves the accuracy of the first pulse voltage source in canceling the piezoelectric effect between the first and second piezoelectric layers, achieving a smaller electromechanical coupling coefficient and obtaining a narrower bandwidth bulk acoustic wave filter.

[0081] Example 6:

[0082] This embodiment provides an ultra-small electromechanical coupling coefficient resonator. Other features of the resonator are basically the same as any of the ultra-small electromechanical coupling coefficient resonators in embodiments 2-5, except that:

[0083] like Figure 2 As shown, the second electrode 2 is electrically connected to a preset second pulse voltage source.

[0084] By setting the second electrode 2 to be electrically connected to the second pulse voltage source instead of grounding, the present invention allows the second electrode 2 to also control the polarity reversal effect of the second piezoelectric layer 4 and the first piezoelectric layer 3 near the second electrode 2 through the second pulse voltage source, thereby further reducing the electromechanical coupling coefficient of the obtained resonator and realizing a filter with a narrower bandwidth.

[0085] Specifically, in this embodiment, the electrodes in the ultra-small electromechanical coupling coefficient resonator corresponding to the ultra-small electromechanical coupling coefficient resonator implementation method of Embodiment 1 are the first electrode 1 and the second electrode 2.

[0086] Specifically, such as Figure 2 As shown, the first electrode 1 is led out to the surface of the resonator through the first electrical lead 6, so as to be electrically connected to the first pulse power supply through the first electrical lead 6; the second electrode 2 is led out to the surface of the resonator through the second electrical lead 7, so as to be electrically connected to the second pulse voltage source through the second electrical lead 7.

[0087] Example 7:

[0088] This embodiment provides an ultra-narrowband filter, which is constructed by cascading two or more resonators with ultra-small electromechanical coupling coefficients from any one or more of embodiments 2-6.

[0089] By using the cascaded bulk acoustic resonators that suppress electromechanical coupling coefficients as described in Examples 1-5, this invention can obtain an ultra-narrowband filter with high quality factor and low insertion loss, meeting the application requirements of ultra-high frequency ultra-narrowband filters.

[0090] In one embodiment, the cascaded topology used to construct the ultra-narrowband filter from the ultra-small electromechanical coupling coefficient resonator can be any one of a trapezoidal structure, a lattice structure, or a hybrid structure. Specifically, other suitable topologies can also be used to construct the ultra-narrowband filter as needed, all of which are within the scope of protection of this invention.

[0091] In summary, the ultra-small electromechanical coupling coefficient resonator, implementation method, and ultra-narrowband filter of this invention can achieve an ultra-small overall electromechanical coupling coefficient by applying a corresponding first pulse voltage source to a bulk acoustic resonator with a ferroelectric layer as the first piezoelectric layer, thereby locally reversing the polarization direction of the ferroelectric layer. This meets the practical application requirements of ultra-narrowband filters in the ultra-high frequency operating band. Simultaneously, by using scandium-doped aluminum nitride with a specific formulation as the first piezoelectric layer, the bandwidth can be further reduced using pulse voltage while maintaining the same high quality factor and low insertion loss as aluminum nitride, achieving a filter with a narrower bandwidth. Furthermore, by setting the material and equivalent piezoelectric effect of the second piezoelectric layer, combined with the local polarity reversal effect of the pulse voltage on the first piezoelectric layer, the electromechanical coupling coefficient of the overall resonator is significantly reduced, further achieving a filter with a narrower bandwidth. Finally, by selecting the material and thickness of the electrodes, the electromechanical coupling coefficient of the resulting resonator is further reduced, achieving a filter with an even narrower bandwidth.

[0092] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0093] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for implementing an ultra-small electromechanical coupling coefficient resonator, characterized in that, The method includes: A preset pulse voltage is applied to the electrodes of a bulk acoustic resonator whose piezoelectric layer includes a ferroelectric layer, so as to reverse the local polarization direction of a preset region of the ferroelectric layer of the bulk acoustic resonator, thereby obtaining a bulk acoustic resonator with an ultra-small overall electromechanical coupling coefficient.

2. A resonator with an ultra-small electromechanical coupling coefficient, characterized in that, The resonator achieves an ultra-small electromechanical coupling coefficient using the method for implementing an ultra-small electromechanical coupling coefficient resonator as described in claim 1. The resonator comprises: The first electrode is electrically connected to a preset first pulse voltage source; The second electrode is electrically connected to a preset second pulse voltage source, or the second electrode is grounded; A first piezoelectric layer, wherein the first piezoelectric layer is a ferroelectric layer, and the first piezoelectric layer is located between the first electrode and the second electrode; An acoustic mirror structure is located on the side of the second electrode away from the first piezoelectric layer.

3. The ultra-small electromechanical coupling coefficient resonator according to claim 2, characterized in that, The material of the first piezoelectric layer is Al (1-x) Sc x N thin film, wherein x is greater than or equal to 20%; and / or, the thickness of the first piezoelectric layer is 0.01 micrometers to 1 micrometer.

4. The ultra-small electromechanical coupling coefficient resonator according to claim 2 or 3, characterized in that, The resonator further includes a second piezoelectric layer, which is located between the first piezoelectric layer and the second electrode.

5. The ultra-small electromechanical coupling coefficient resonator according to claim 4, characterized in that, The second piezoelectric layer is a ferroelectric layer with the opposite polarity to the first piezoelectric layer; or, the second piezoelectric layer is a ferroelectric layer with the same polarity as the first piezoelectric layer.

6. The ultra-small electromechanical coupling coefficient resonator according to claim 4, characterized in that, The second piezoelectric layer is a non-ferroelectric piezoelectric thin film, and the piezoelectric stress constant thickness product of the second piezoelectric layer is 70%-130% of the piezoelectric stress constant thickness product of the first piezoelectric layer.

7. The ultra-small electromechanical coupling coefficient resonator according to claim 2, characterized in that, The materials of the first electrode and the second electrode are at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf; and / or the thickness of the first electrode and the second electrode is 0.01 micrometer to 0.5 micrometer.

8. The ultra-small electromechanical coupling coefficient resonator according to claim 2, characterized in that, The acoustic mirror structure is at least one of the following: a Bragg reflector layer, a cavity, or a phononic crystal.

9. An ultra-narrowband filter, characterized in that, The ultra-narrowband filter is constructed by cascading two or more resonators with ultra-small electromechanical coupling coefficients as described in any one of claims 2-8.

10. The ultra-narrowband filter according to claim 9, characterized in that, The cascaded topology used to construct the ultra-narrowband filter using an ultra-small electromechanical coupling coefficient resonator can be any one of a trapezoidal structure, a lattice structure, or a hybrid structure.

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