Chirped substrate, resonator, filter and preparation method

Abstract

The present application provides a chirped substrate, a resonator, a filter and a preparation method. The resonator includes a piezoelectric layer, a chirped Bragg reflector layer and a substrate layer arranged in sequence from top to bottom. The chirped Bragg reflector layer is formed by stacking multiple Bragg reflectors, including a top Bragg reflector layer, an intermediate Bragg reflector layer and a bottom Bragg reflector layer from top to bottom in the stacking direction. The multiple Bragg reflectors are stacked from top to bottom by a low acoustic impedance Bragg reflector layer and a high acoustic impedance Bragg reflector layer. The thickness of the chirped Bragg reflector layer is related to the chirp rate of the chirped Bragg reflector layer and changes linearly along the stacking direction. The chirped substrate provided by the present application improves the acoustic reflectivity of the target frequency of the resonator by designing the thickness of each Bragg reflector layer to be linearly related, increases the absorption bandwidth of the substrate and the low-frequency enhanced refractive index, and makes the reflection ability of the chirped Bragg reflector layer have frequency band concentration above 4GHz, effectively suppressing the pseudo mode beside the high-frequency main mode.

Description

Technical Field

[0001] The present application relates to the technical field of MEMS radio frequency devices, and in particular to a chirped substrate, a resonator, a filter and a preparation method thereof. Background Art

[0002] The rapid development of the 5G / 6G mobile market, the demand for massive data connections, high-speed transmission and low-latency communications have put forward a series of challenges to RF filters, such as greater bandwidth, higher frequency, lower loss and greater power carrying capacity. The resonator is the basic unit of the filter and is the key core component that determines the performance of the filter. According to the structure and acoustic wave vibration mode, it can be divided into surface acoustic wave resonator (SAW), film bulk acoustic wave resonator (FBAR) and Figure 1 The solid-state assembled bulk acoustic wave resonator (SMR-BAW) shown in the figure includes an interdigitated positive electrode 101, an interdigitated negative electrode 102, a bus bar 103 and a signal port 104. In recent years, the transversely excited film bulk acoustic wave resonator (XBAR) has become a research hotspot because of its high resonant frequency and high electromechanical coupling coefficient. Resonant frequency (f), electromechanical coupling coefficient (K t 2 ) and quality factor (Q) are the three core parameters of the resonator. The resonant frequency determines the operating frequency of the filter, K t 2 The Q value determines the bandwidth of the bandpass filter, and the Q value directly affects the rectangularity and insertion loss of the bandpass filter. Therefore, the study of high-Q-value transversely excited thin film bulk acoustic resonators is crucial for the design of filters. In order to improve the Q value, the structures commonly used in resonators are mainly reflection gratings, phononic crystals, and chirped Bragg reflectors. Among them, resonators with chirped Bragg reflectors are generally called solid-state assembly resonators.

[0003] In the existing resonator design, the surface acoustic wave resonator is affected by the lithography accuracy, and the resonator frequency is concentrated below 3GHz; it is difficult to achieve multi-band integration of thin film bulk acoustic wave resonators on a single wafer; the structure of the laterally excited thin film bulk acoustic wave resonator is a thin film structure + interdigital transducer design, and the back cavity is etched to form a thin film structure, and the device stability is insufficient; the core of the solid-state assembly resonator is the chirped Bragg reflection layer, and the chirped Bragg reflection layer structure is to construct a Bragg acoustic reflection layer between the piezoelectric layer and the substrate, and the high acoustic impedance Bragg reflection layer and the low acoustic impedance Bragg reflection layer are alternately superimposed to form a composite supporting substrate with high energy reflection efficiency, but this energy reflection does not have frequency band concentration, and there is still room for improvement in the enhancement of the Q value. At the same time, the pseudo-mode problem of the resonator requires additional design to improve. Figure 2 is the longitudinal refractive index of the solid-mount resonator, Figure 2The vertical coordinate S(2,1) represents the refractive index of the two ports. The 2 in S(2,1) is port 2, and the 1 in S(2,1) is port 1. Port 2 is the second interface, and port 1 is the first interface. It can be seen that in the frequency band above 4 GHz, the reflectivity of the chirped Bragg reflector is relatively high, and it does not have frequency band concentration. It will reflect the main mode sound waves while also reflecting the pseudo mode. Summary of the invention

[0004] The present application provides a chirped substrate, which can solve the technical problems existing in the prior art such as the inability to achieve multi-band integration, insufficient device stability, and lack of frequency band concentration.

[0005] In a first aspect, the present application provides a chirped substrate, comprising a piezoelectric layer, a chirped Bragg reflection layer and a substrate layer arranged in sequence from top to bottom, wherein the chirped Bragg reflection layer is formed by stacking a plurality of Bragg reflection layers, and comprises a top Bragg reflection layer, an intermediate Bragg reflection layer, a bottom Bragg reflection layer and other Bragg reflection layers between the intermediate Bragg reflection layer and the bottom Bragg reflection layer from top to bottom in the stacking direction, wherein the plurality of Bragg reflection layers are all stacked from top to bottom by a low acoustic impedance Bragg reflection layer and a high acoustic impedance Bragg reflection layer, and the thickness of each Bragg reflection layer is related to the chirp rate of the chirped Bragg reflection layer and varies linearly along the stacking direction.

[0006] In combination with the first aspect, in one implementation, the chirp rate of the chirp Bragg reflector layer is one, and the thickness of all Bragg reflectors along the stacking direction of the chirp Bragg reflector layer is linearly related to the chirp rate; or,

[0007] The chirp-type Bragg reflection layer has two chirp rates. Starting from the boundary of the middle Bragg reflection layer, the thickness of the Bragg reflection layer upward layer by layer is linearly related to the first chirp rate, and the thickness of the Bragg reflection layer downward layer by layer is linearly related to the second chirp rate.

[0008] In combination with the first aspect, in one implementation, the linear correlation is shown as follows:

[0009] L = L0 + C × (zd / 2);

[0010] Wherein, L is the thickness of the Bragg reflector to be calculated, L0 is the thickness of the middle Bragg reflector, C is the chirp rate of the chirped Bragg reflector, d is the distance between the first interface and the second interface, and z is the distance between the Bragg reflector and the top Bragg reflector.

[0011] In combination with the first aspect, in one implementation, the material of the piezoelectric layer is AIN, PZT, lithium niobate or lithium tantalate;

[0012] The material used for the low acoustic impedance Bragg reflection layer is silicon dioxide, silicon oxycarbide or aluminum;

[0013] The material used for the high acoustic impedance Bragg reflection layer is silicon nitride, aluminum nitride, silicon carbide, molybdenum, tungsten or gold.

[0014] In combination with the first aspect, in one implementation, the material used for the substrate layer is silicon or sapphire.

[0015] In a second aspect, the present application provides a method for preparing a chirped substrate, comprising the following steps:

[0016] Selecting a basic piezoelectric substrate, the basic piezoelectric substrate comprises a piezoelectric layer, a low acoustic impedance Bragg reflection layer and a reflection layer substrate layer arranged from top to bottom;

[0017] A low acoustic impedance Bragg reflection layer and a high acoustic impedance Bragg reflection layer are alternately deposited on the piezoelectric layer to obtain a chirped Bragg reflection layer;

[0018] Depositing a first bonding layer on the high acoustic impedance Bragg reflector of the chirped Bragg reflector;

[0019] preparing a substrate layer;

[0020] depositing a second bonding layer on the substrate layer;

[0021] Bonding the first bonding layer and the second bonding layer, with the substrate layer at the bottom, and placing the chirped Bragg reflection layer upside down on the substrate layer;

[0022] Grinding and removing the reflective layer substrate layer;

[0023] The low acoustic impedance Bragg reflection layer on the top of the chirped Bragg reflection layer is removed by etching to obtain a chirped substrate.

[0024] In a third aspect, the present application provides a resonator, comprising the chirped substrate as described above and an electrode layer disposed on the chirped substrate.

[0025] In combination with the third aspect, in one embodiment, the material of the electrode layer includes but is not limited to molybdenum, aluminum, copper, and alloys.

[0026] In combination with the third aspect, in one implementation, the electrode layer is an interdigital transducer or a thin film.

[0027] In a fourth aspect, the present application provides a filter comprising the resonator as described above.

[0028] The beneficial effects brought by the technical solution provided by the embodiment of the present application include at least:

[0029] The chirped substrate provided in the present application improves the acoustic reflectivity of the target frequency of the resonator, increases the absorption bandwidth of the substrate, and enhances the refractive index in the low frequency band by designing the thickness of the chirped Bragg reflector layer to be linearly related. Above 4 GHz, the reflection ability of the chirped Bragg reflector layer has frequency band concentration, effectively suppressing the pseudo mode next to the high-frequency main mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a cross-sectional view of a solid-body resonator in the prior art;

[0031] Figure 2 A graph of the longitudinal wave refraction coefficient of a solid-body resonator in the prior art;

[0032] Figure 3 A schematic diagram of the interface of a chirped solid-state resonator provided in an embodiment of the present application;

[0033] Figure 4 (a) is a cross-sectional view of the device after step S1 in implementation example 1 provided in an embodiment of the present application; Figure 4 (b) is a cross-sectional view of the device after step S2 in implementation example 1 provided in an embodiment of the present application; Figure 4 (c) is a cross-sectional view of the device after step S3 in implementation example 1 provided in an embodiment of the present application; Figure 4 (d) is a cross-sectional view of the device after step S4 in implementation example 1 provided in an embodiment of the present application; Figure 4 (e) is a cross-sectional view of the device after step S5 in implementation example 1 provided in an embodiment of the present application; Figure 4 (f) is a cross-sectional view of the device after step S6 in implementation example 1 provided in an embodiment of the present application; Figure 4 (g) is a cross-sectional view of the device after step S7 in implementation example 1 provided in an embodiment of the present application; Figure 4 (h) is a cross-sectional view of the chirped substrate after step S8 in implementation example 1 provided in an embodiment of the present application;

[0034] Figure 5 A cross-sectional view of a chirped solid-state resonator provided in an embodiment of the present application;

[0035] Figure 6 A longitudinal wave refraction coefficient diagram of a chirped solid-mounted resonator provided in an embodiment of the present application;

[0036] Figure 7 A diagram of the admittance curve of a chirped solid-state resonator provided in an embodiment of the present application;

[0037] Figure 8 A cross-sectional view of a type II chirped solid-mounted resonator provided in an embodiment of the present application;

[0038] Fig. 9 A longitudinal wave refractive index diagram of a type II chirped solid-mounted resonator provided in an embodiment of the present application;

[0039] Fig.10 A comparison diagram of the resonator admittance curves provided in the embodiments of the present application;

[0040] Fig.11 A top view of the electrode layer of the chirped solid-mounted resonator provided in an embodiment of the present application;

[0041] Fig.12 (a) is a top view of a chirped solid-mounted resonator structure provided in an embodiment of the present application; Fig.12 (b) is a cross-sectional view of the chirped solid-mounted resonator structure provided in an embodiment of the present application;

[0042] Fig.13 (a) is a cross-sectional view of the device after step S1 in implementation example 2 provided in the embodiment of the present application; Fig.13 (b) is a cross-sectional view of the device after step S1 in implementation example 2 provided in the embodiment of the present application;

[0043] Fig.14 A cross-sectional view of a type II chirped solid-mounted resonator provided in an embodiment of the present application.

[0044] In the figure: 100, electrode layer; 101, interdigitated positive electrode; 102, interdigitated negative electrode; 103, bus bar; 104, signal port; 200, piezoelectric layer; 300, chirped Bragg reflection layer; 301, low acoustic impedance Bragg reflection layer; 302, high acoustic impedance Bragg reflection layer; 400, substrate layer; 500, reflection layer substrate layer; 600, first bonding layer; 700, second bonding layer. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices. The terms "first", "second" and "third" are used to distinguish different objects, etc., and do not represent a sequence, nor do they limit "first", "second" and "third" to different types.

[0047] In the description of the embodiments of the present application, "exemplary", "for example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary", "for example" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "for example" or "for example" is intended to present related concepts in a specific way.

[0048] In the description of the embodiments of the present application, unless otherwise specified, “ / ” means or, for example, A / B can mean A or B; the “and / or” in the text is merely a description of the association relationship of associated objects, indicating that three relationships may exist, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, “multiple” refers to two or more than two.

[0049] In some processes described in the embodiments of the present application, multiple operations or steps that appear in a specific order are included, but it should be understood that these operations or steps may not be executed in the order in which they appear in the embodiments of the present application or in parallel, and the sequence number of the operation is only used to distinguish the different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed in sequence or in parallel, and these operations or steps may be combined.

[0050] The thickness of each Bragg reflection layer of the chirped Bragg reflection layer 300 in the composite substrate used in the existing resonator is a fixed thickness, and the thickness of each layer is the same, which is 1 / 4 of the wavelength of the sound wave in the chirped Bragg reflection layer 300. The resonator has technical problems such as energy reflection not having frequency band concentration and pseudo-mode.

[0051] In view of this, the present application provides a chirped substrate.

[0052] First, some technical terms in the present application are explained to facilitate those skilled in the art to understand the present application.

[0053] MEMS: Micro Electro Mechanical Systems;

[0054] SAW: Surface Acoustic Wave, surface acoustic wave resonator;

[0055] FBAR: Film Bulk Acoustic Resonator;

[0056] SMR-BAW: Solidly Mounted Resonator- Bulk Acoustic Wave, solid-state mounted bulk acoustic wave resonator;

[0057] XBAR: Laterally excited film bulk acoustic resonator;

[0058] Q value: the quality factor of a resonator;

[0059] K t 2 : electromechanical coupling coefficient of the resonator;

[0060] f: resonant frequency of the resonator.

[0061] In the present application, the solid-mounted transversely excited thin film bulk acoustic resonator is referred to as a solid-mounted resonator.

[0062] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0063] In a first aspect, the present application provides a chirped substrate, comprising a piezoelectric layer 200, a chirped Bragg reflection layer 300 and a substrate layer 400 arranged in sequence from top to bottom, wherein the chirped Bragg reflection layer 300 is formed by stacking a plurality of Bragg reflection layers, and comprises a top Bragg reflection layer, an intermediate Bragg reflection layer, a bottom Bragg reflection layer and other Bragg reflection layers between the intermediate Bragg reflection layer and the bottom Bragg reflection layer from top to bottom in the stacking direction, wherein the plurality of Bragg reflection layers are stacked from top to bottom by a low acoustic impedance Bragg reflection layer 301 and a high acoustic impedance Bragg reflection layer 302 (the entire chirped Bragg reflection layer 300 is formed by alternately stacking the low acoustic impedance Bragg reflection layer 301 and the high acoustic impedance Bragg reflection layer 302), and the thickness of each Bragg reflection layer is related to the chirp rate of the chirped Bragg reflection layer 300, and varies linearly along the stacking direction.

[0064] The chirped substrate provided in the present application improves the acoustic reflectivity of the target frequency of the resonator, increases the absorption bandwidth of the substrate, and enhances the refractive index in the low frequency band by designing the thickness of each Bragg reflector of the chirped Bragg reflector 300 to be linearly related, so as to make the reflection ability of the chirped Bragg reflector 300 have frequency band concentration above 4 GHz, and can suppress the pseudo mode beside the high-frequency main mode.

[0065] In one embodiment, the intersection between different layers is defined as an interface. Figure 3 As shown, the chirped substrate provided by the present application has two interfaces, which are respectively called interface 1 and interface 2. Interface 1 is the interface between the piezoelectric layer 200 and the low acoustic impedance Bragg reflector 301 of the reflector layer, and interface 2 is the interface between the low acoustic impedance Bragg reflector 301 and the high acoustic impedance Bragg reflector 302. The thickness of the chirped Bragg reflector 300 is related to its chirp rate and changes linearly in the stacking direction, and also includes the linearization design of the thickness of interface 1 and interface 2, specifically, the thickness of (interface 1 + top Bragg reflector), (interface 2 + second Bragg reflector), (interface 2 + third Bragg reflector), ..., (interface 2 + middle Bragg reflector), ..., (interface 2 + bottom Bragg reflector) are all related to the chirp rate and change linearly along the stacking direction.

[0066] In one embodiment, the resonance condition of the chirped Bragg reflector 300 can be expressed as:

[0067] mλ=2n eff L

[0068] Where m is the number of Bragg reflector layers, λ is the wavelength of the sound wave in the chirped Bragg reflector layer, and n is eff is the effective refractive index in the chirped Bragg reflection layer.

[0069] The chirped Bragg reflection layer 300 is formed by stacking interfaces and Bragg reflection layers of different thicknesses, and can change the refractive index of acoustic waves within a specific frequency band.

[0070] In one embodiment, the number of stacked Bragg reflective layers is at least 6.

[0071] In one embodiment, the chirp rate of the chirp Bragg reflector 300 is one, and the thicknesses of all Bragg reflectors are linearly related along the stacking direction of the chirp Bragg reflector 300 or the longitudinal wave transmission direction of the resonator or the chirped Bragg reflector 300. This type of chirped substrate is defined as a type-I structure, and the corresponding chirp Bragg reflector 300 is a type-I structure chirped Bragg reflector.

[0072] In one embodiment, the stacking direction of the chirped Bragg reflector 300 is the longitudinal wave transmission direction of the resonator, specifically, refers to the stacking arrangement direction.

[0073] In one embodiment, the thicknesses of all the Bragg reflective layers of the chirped Bragg reflective layer 300 decrease linearly from bottom to top.

[0074] In one embodiment, the chirp-type Bragg reflector 300 has two chirp rates, namely a first chirp rate and a second chirp rate, the first chirp rate and the second chirp rate have the same absolute value, the thickness of all Bragg reflectors of the chirp-type Bragg reflector 300 is linearly related to the first chirp rate from the middle Bragg reflector layer, and the thickness of the Bragg reflectors is linearly related to the second chirp rate from the middle Bragg reflector layer. More specifically, the thickness of all Bragg reflectors is linearly related to the first chirp rate from the middle Bragg reflector layer, and linearly related to the second chirp rate from the middle Bragg reflector layer. The chirp-type substrate of this type is defined as a type II substrate, and the corresponding chirp-type Bragg reflector 300 is a type II structure chirp-type Bragg reflector.

[0075] The middle Bragg reflection layer may be a middle layer of the chirped Bragg reflection layer 300 or a Bragg reflection layer between a top Bragg reflection layer and a bottom Bragg reflection layer of the chirped Bragg reflection layer 300 .

[0076] In one embodiment, the thickness of the chirped Bragg reflector 300 is related to the chirp rate of the chirped Bragg reflector 300 and is linearly related along the stacking direction of the chirped Bragg reflector 300, as shown in the following formula:

[0077] L = L0 + C × (zd / 2)

[0078] Wherein, L is the thickness of the Bragg reflection layer to be calculated, L0 is the thickness of the middle Bragg reflection layer, C is the chirp rate of the chirped Bragg reflection layer 300, d is the distance between the first interface and the second interface, and z is the distance between the Bragg reflection layer and the top Bragg reflection layer.

[0079] In one embodiment, the material of the piezoelectric layer 200 includes but is not limited to AIN, PZT, lithium niobate, and lithium tantalate.

[0080] In one embodiment, the low acoustic impedance Bragg reflection layer 301 is made of silicon dioxide, silicon oxycarbide or aluminum, and the high acoustic impedance Bragg reflection layer 302 is made of silicon nitride, aluminum nitride, silicon carbide, molybdenum, tungsten or gold.

[0081] In one embodiment, one or more high acoustic impedance materials or low acoustic impedance materials may be selected and stacked in the chirped Bragg reflector 300 to take into account the mechanical stability of the device, the heat dissipation performance, the reflection ability of the chirped Bragg reflector 300 and the processing difficulty of the device.

[0082] In one embodiment, the substrate layer 400 is made of silicon or sapphire.

[0083] Based on the same inventive concept, Figure 4 As shown, the present application provides a method for preparing a chirped substrate, comprising the following steps:

[0084] Step S1: Select a basic piezoelectric substrate with a suitable tangent direction according to the resonator requirements. The basic piezoelectric substrate includes a piezoelectric layer 200, a low acoustic impedance Bragg reflection layer 301 and a reflection layer substrate layer 500. Figure 4 As shown in (a);

[0085] Step S2, alternately depositing low acoustic impedance Bragg reflection layers 301 and high acoustic impedance Bragg reflection layers 302 on the piezoelectric layer 200 to obtain a chirped Bragg reflection layer 300. In this step, regardless of whether it is a type I Bragg reflection layer chirped substrate or a type II Bragg reflection layer chirped substrate, the thickness of the low acoustic impedance Bragg reflection layer 301 in contact with the piezoelectric layer 200 needs to be about one quarter of the wavelength of the acoustic wave in the chirped Bragg reflection layer 300, such as Figure 4 As shown in (b);

[0086] Step S3: depositing a first bonding layer 600 on the high acoustic impedance Bragg reflection layer 302 of the chirped Bragg reflection layer 300, such as Figure 4 As shown in (c);

[0087] Step S4: prepare the substrate layer 400, such as Figure 4 As shown in (d);

[0088] Step S5, depositing a second bonding layer 700 on the substrate layer 400, the materials used in the first bonding layer 600 and the second bonding layer 700 include but are not limited to silicon dioxide, silicon oxide, Au, etc., but need not have mutually exclusive reactions with the materials in the first bonding layer 600, such as Figure 4 As shown in (e);

[0089] Step S6: Bond the first bonding layer 600 and the second bonding layer 700 to form a high acoustic impedance Bragg reflection layer 302, with the substrate layer 400 at the bottom, and place the chirped Bragg reflection layer 300 upside down on the substrate layer 400, as shown in FIG. Figure 4 As shown in (f);

[0090] Step S7: Grind and remove the reflective layer substrate 500. Figure 4As shown in (g);

[0091] Step S8: etching and removing the low acoustic impedance Bragg reflection layer 301 on the top of the chirped Bragg reflection layer 300 to obtain a chirped substrate, such as Figure 4 As shown in (h).

[0092] Based on the same inventive concept, the present application provides a resonator, comprising the chirped substrate as described above and an electrode layer 100 disposed on the chirped substrate, such as Figure 5 shown.

[0093] In one embodiment, Figure 6 It is the longitudinal wave refraction coefficient of a chirped solid-assembly resonator. The chirped Bragg reflector 300 has obvious frequency band concentration for the reflection of longitudinal waves above 4 GHz. When the chirp rate is designed appropriately, it can suppress the high-frequency pseudo-mode while enhancing the resonance response intensity of the main mode, thereby achieving the purpose of improving the quality factor.

[0094] In one embodiment, a chirped substrate is applied to a resonator to obtain a chirped solid-state resonator, whose admittance curve is as follows: Figure 7 As shown. Figure 7 It can be seen that the peak value of the admittance curve of the chirped solid-state assembly resonator is significantly enhanced, and the admittance response of the resonator at high frequencies is enhanced. At the same time, within the target frequency band, the pseudo-mode on the resonator admittance curve is suppressed, proving that the method of linearly setting the thickness of each Bragg reflection layer of the chirped Bragg reflection layer 300 can achieve a pseudo-mode suppression effect, and the pseudo-mode of a certain frequency leaks from the substrate through refraction, and the component reflected back to the central resonance area is reduced.

[0095] In one embodiment, the thickness of the first structure of the chirped Bragg reflector 300 has the greatest influence on the reflection capability. If the thickness is too large, the frequency band is concentrated, but the bandwidth is too narrow. If the thickness is too small, the frequency band is not concentrated. Therefore, the thickness of the first Bragg reflector is set to be about one-quarter of the wavelength of the acoustic wave in the chirped Bragg reflector 300.

[0096] In one embodiment, a type II chirped substrate is applied to a resonator to obtain a type II chirped solid-state resonator having a structure as shown in FIG. Figure 8 shown.

[0097] In one embodiment, the design of the first chirp rate and the second chirp rate is related to the wavelength of the sound wave and the material of the reflective layer. If the low acoustic impedance Bragg reflective layer 301 and the high acoustic impedance Bragg reflective layer 302 do not use multiple low acoustic impedance materials or multiple high acoustic impedance materials overlapping, the absolute value of the first chirp rate is the same as the absolute value of the second chirp rate.

[0098] In one embodiment, if Fig. 9 As shown, it is a refractive index diagram of the type II chirped solid-mounted resonator. The diagram shows that the chirped Bragg reflector 300 of the type II chirped solid-mounted resonator has good reflection capability within 5-7 GHz, good refraction capability in the low frequency band and above 7 GHz, and also has frequency band concentration.

[0099] In one embodiment, Fig.10 300 are the admittance curves of different chirped Bragg reflectors 300 used in the resonator. Compared with the initial structure, the second chirped Bragg reflector 300 also has a significant improvement in the peak value, and the Q value is improved. Compared with the first chirped Bragg reflector 300, the main modal resonant frequency of the second structure is improved by .

[0100] In one embodiment, the material of the electrode layer 100 includes but is not limited to molybdenum, aluminum, copper, and alloys.

[0101] In one embodiment, the electrode layer 100 may be an interdigital transducer, such as Fig.11 As shown, it includes interdigitated positive electrodes 101, interdigitated negative electrodes 102, bus bars 103 and signal ports 104. The electrode layer 100 may also be a thin film, such as Fig.12 As shown, Fig.12 (a) is a top view of a chirped solid-mounted resonator structure provided in an embodiment of the present application; Fig.12 (b) is a cross-sectional view of the chirped solid-mounted resonator structure provided in an embodiment of the present application.

[0102] The chirped substrate provided in the present application is suitable for a laterally excited thin film bulk acoustic wave resonator, a surface acoustic wave resonator and a thin film bulk acoustic wave resonator.

[0103] In one embodiment, if Fig.13 As shown, the present application also provides a method for preparing a transversely excited thin film bulk acoustic wave resonator, comprising the following steps:

[0104] Step S1: growing a metal electrode layer 100 on a chirped substrate, such as Fig.13 As shown in (a);

[0105] Step S2: patterning the metal electrode layer 100, such as Fig.13 As shown in (b).

[0106] Based on the same inventive concept, the present application provides a filter, comprising the resonator as described above.

[0107] Example 1

[0108] Based on the above preparation method, this embodiment proposes a chirped solid assembly resonator, such as Fig.12As shown, compared with the chirped solid-mounted resonator, this resonator adds an electrode layer 100 between the piezoelectric layer 200 and the low acoustic impedance Bragg reflector 301, and the top electrode layer 100 is transformed from an interdigital transducer to a thin film structure. This structure is a thickness excitation mode, and the frequency of the sound wave is mainly determined by the thickness of the piezoelectric layer 200, which is different from the finger width of the interdigital transducer. In terms of the effect of the chirped Bragg reflector 300, both can increase the absorption bandwidth of a specific frequency band and improve the high-frequency quality factor.

[0109] Example 2

[0110] Based on the above preparation method, this embodiment provides a type II chirped solid assembly resonator, such as Fig.14 As shown, a layer of bonding layer material is first deposited on the electrode layer 100, and the chirped Bragg reflection layer 300 is inverted on the bonding layer.

[0111] Example 3

[0112] This embodiment provides a filter, which includes the above-mentioned several types of chirped solid-mounted resonators. The filter is constructed by a cascade method, and the device can be integrated in the circuit to achieve filtering in a specific frequency band.

[0113] It should be noted that the serial numbers of the above-mentioned embodiments of the present application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0114] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A chirped substrate, characterized in that: The invention comprises a piezoelectric layer, a chirped Bragg reflection layer and a substrate layer which are sequentially arranged from top to bottom. The chirped Bragg reflection layer is formed by stacking a plurality of Bragg reflection layers, and comprises a top Bragg reflection layer, an intermediate Bragg reflection layer, a bottom Bragg reflection layer and other Bragg reflection layers between the intermediate Bragg reflection layer and the bottom Bragg reflection layer from top to bottom in the stacking direction. The plurality of Bragg reflection layers are stacked from top to bottom by a low acoustic impedance Bragg reflection layer and a high acoustic impedance Bragg reflection layer. The thickness of each Bragg reflection layer is related to the chirp rate of the chirped Bragg reflection layer and varies linearly along the stacking direction. The chirp rate of the chirped Bragg reflector layer is 1, and the thickness of all Bragg reflector layers along the stacking direction of the chirped Bragg reflector layer is linearly related to the chirp rate; The chirp-type Bragg reflector has two chirp rates. Starting from the boundary of the middle Bragg reflector, the thickness of the Bragg reflector layer upwards is linearly related to the first chirp rate, and the thickness of the Bragg reflector layer downwards is linearly related to the second chirp rate. The linear correlation is shown as follows: L = L0 + C × (zd / 2); Wherein, L is the thickness of the Bragg reflector to be calculated, L0 is the thickness of the middle Bragg reflector, C is the chirp rate of the chirped Bragg reflector, d is the distance between the first interface and the second interface, the first interface is the interface between the top Bragg reflector and the piezoelectric layer, the second interface is the interface between the bottom Bragg reflector and the substrate layer, and z is the distance between the Bragg reflector and the top Bragg reflector.

2. The chirped substrate according to claim 1, wherein: The material of the piezoelectric layer is AIN, PZT, lithium niobate or lithium tantalate; The material used for the low acoustic impedance Bragg reflection layer is silicon dioxide, silicon oxycarbide or aluminum; The material used for the high acoustic impedance Bragg reflection layer is silicon nitride, aluminum nitride, silicon carbide, molybdenum, tungsten or gold.

3. The chirped substrate according to claim 1, wherein: The substrate layer is made of silicon or sapphire.

4. A method for preparing a chirped substrate according to any one of claims 1 to 3, characterized in that: The steps include: Selecting a basic piezoelectric substrate, wherein the basic piezoelectric substrate comprises a piezoelectric layer, a low acoustic impedance Bragg reflection layer and a reflection layer substrate layer; A low acoustic impedance Bragg reflection layer and a high acoustic impedance Bragg reflection layer are alternately deposited on the piezoelectric layer to obtain a chirped Bragg reflection layer; Depositing a first bonding layer on the high acoustic impedance Bragg reflector of the chirped Bragg reflector; preparing a substrate layer; depositing a second bonding layer on the substrate layer; Bonding the first bonding layer and the second bonding layer, with the substrate layer at the bottom, and placing the chirped Bragg reflection layer upside down on the substrate layer; Grinding and removing the reflective layer substrate layer; The low acoustic impedance Bragg reflection layer on the top of the chirped Bragg reflection layer is removed by etching to obtain a chirped substrate.

5. A resonator, characterized in that: It comprises the chirped substrate as claimed in any one of claims 1 to 3 and an electrode layer arranged on the chirped substrate.

6. The resonator according to claim 5, characterized in that The material of the electrode layer is molybdenum, aluminum, copper or alloy.

7. The resonator according to claim 5, characterized in that The electrode layer is an interdigital transducer or a thin film.

8. A filter, characterized in that: Comprising the resonator as claimed in claim 5.

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