Piezoelectric substrate, preparation method thereof and surface acoustic wave device

Abstract

The invention provides a piezoelectric substrate, a preparation method thereof and a surface acoustic wave device. The piezoelectric substrate comprises a first piezoelectric layer, a wave-absorbing loss layer and a second piezoelectric layer, and in the first direction, the first piezoelectric layer, the wave-absorbing loss layer and the second piezoelectric layer are stacked to form a sandwich structure; the sandwich structure is provided with a first surface and a second surface which are opposite in a first direction, and the wave-absorbing loss layer is used for absorbing body waves; wherein the body waves comprise a first type of body waves and / or a second type of body waves, and the first type of body waves are sound waves entering the sandwich structure from the first surface; and the second type of bulk waves are sound waves entering the sandwich structure from the second surface. The piezoelectric substrate can inhibit the interference phenomenon of bulk wave spurious signals entering from one surface on the surface acoustic wave transmitted on the other surface, so that the out-of-band rejection effect of the surface acoustic wave device can be improved, the insertion loss of the surface acoustic wave device can be reduced, and the passband of the surface acoustic wave device can be smoothed. And the performance of the surface acoustic wave device is good.

Description

Technical Field

[0001] The embodiments in this application relate to the field of electronic device technology, specifically to piezoelectric substrates and their fabrication methods, and surface acoustic wave devices. Background Technology

[0002] Surface acoustic wave (SAW) devices play a crucial role in signal separation and filtering in mobile communications, and are therefore widely used in resonators, bandpass filters, duplexers and transformers in radio frequency (RF) and microwave communication devices (e.g., mobile phones).

[0003] The surface acoustic wave (SAW) device mainly comprises a piezoelectric material layer, and an input interdigitated electrode structure and an output interdigitated electrode structure disposed on the surface of the piezoelectric material layer. The input interdigitated electrode structure converts the input electrical signal into a SAW wave through the inverse piezoelectric effect, which then propagates on the surface of the piezoelectric material layer. When the SAW wave propagates to the output interdigitated electrode structure, it is detected by the output interdigitated electrode structure, which then converts the detected SAW wave back into an electrical signal through the piezoelectric effect for output. This enables precise selection and transmission of electrical signals of specific frequencies.

[0004] In traditional surface acoustic wave (SAW) devices, imperfections in the design of the piezoelectric material layer and interdigitated electrode structure can cause some of the SAW energy propagating on the surface of the piezoelectric material layer to "leak" into the interior of the layer, forming non-target volume waves. These volume waves are detected by the interdigitated electrode structure, interfering with the main signal propagating through it and thus affecting the performance of the SAW device. Specifically, this can lead to increased insertion loss, passband unevenness, and worsened out-of-band suppression. Therefore, it is necessary to suppress the volume wave stray signals in SAW devices. Summary of the Invention

[0005] This application provides a piezoelectric substrate that can effectively suppress bulk wave stray signals to improve the performance of surface acoustic wave devices, as well as a method for fabricating the same and the surface acoustic wave device.

[0006] In a first aspect, embodiments of this application provide a piezoelectric substrate, including a first piezoelectric layer, a wave-absorbing loss layer, and a second piezoelectric layer. In a first direction, the first piezoelectric layer, the wave-absorbing loss layer, and the second piezoelectric layer are stacked to form a sandwich structure. The sandwich structure has a first surface and a second surface opposite to each other in the first direction, and the wave-absorbing loss layer is used to absorb first type of volume wave and / or second type of volume wave. The body waves include a first type of body wave and / or a second type of body wave. The first type of body wave is a sound wave that enters the interior of the sandwich structure from the first surface; the second type of body wave is a sound wave that enters the interior of the sandwich structure from the second surface.

[0007] In some embodiments, the first surface and / or the second surface are respectively used to provide interdigital transducers for exciting surface acoustic waves, and the bulk waves are radiated by the interdigital transducers on the corresponding surfaces; The ratio of the thickness of the absorbing loss layer in the first direction to the wavelength of the surface acoustic wave is greater than or equal to 0.2.

[0008] In some embodiments, the absorbing loss layer includes an adhesive layer for bonding the first piezoelectric layer and the second piezoelectric layer together, the adhesive layer causing viscous loss to the bulk wave.

[0009] In some embodiments, the constituent material of the adhesive layer includes at least one of organic adhesives, inorganic adhesives, and amorphous silicon; The organic adhesive includes at least one of epoxy resin, polyimide, and acrylate, and the inorganic adhesive includes at least one of silicon dioxide, silicon nitride, aluminum oxide, and tantalum pentoxide.

[0010] In some embodiments, the first piezoelectric layer has a first roughening structure on the side near the absorbing loss layer and / or the second piezoelectric layer has a second roughening structure on the side near the absorbing loss layer.

[0011] In some embodiments, the first piezoelectric layer has a first roughening structure on the side near the microwave absorption loss layer, and the microwave absorption loss layer has a third roughening structure on the side near the first piezoelectric layer, wherein the third roughening structure and the second roughening structure are in an interlocking contact relationship. And / or, the second piezoelectric layer has a second roughening structure on the side near the microwave absorption loss layer, and the microwave absorption loss layer has a fourth roughening structure on the side near the second piezoelectric layer, wherein the fourth roughening structure and the second roughening structure are in an interlocking contact relationship.

[0012] In some embodiments, at least one of the first piezoelectric layer and the second piezoelectric layer is composed of lithium tantalate, lithium niobate, quartz, or aluminum nitride.

[0013] In some embodiments, the absorbing loss layer includes a first absorbing loss layer and a second absorbing loss layer stacked in the first direction, wherein the first absorbing loss layer is bonded to the first piezoelectric layer and the second absorbing loss layer is bonded to the second piezoelectric layer. The side of the first absorbing loss layer away from the first piezoelectric layer is bonded to the side of the second absorbing loss layer away from the second piezoelectric layer.

[0014] Secondly, embodiments of this application provide a method for fabricating a piezoelectric substrate as described in any of the foregoing claims, comprising: providing a first piezoelectric layer and a second piezoelectric layer, and using a wave-absorbing loss layer to bond the first piezoelectric layer and the second piezoelectric layer together to form a sandwich structure; Alternatively, a first piezoelectric layer is provided, an absorbing loss layer is formed on the first piezoelectric layer, and a second piezoelectric layer is formed on the side of the absorbing loss layer away from the first piezoelectric layer.

[0015] Thirdly, embodiments of this application provide a surface acoustic wave device, including a piezoelectric substrate and an interdigital transducer as described in any of the foregoing claims; The interdigital transducers are disposed on the first and / or second surfaces of the sandwich structure.

[0016] The piezoelectric substrates provided in the various embodiments of this application absorb bulk waves by providing a wave-absorbing loss layer sandwiched between two piezoelectric layers inside the piezoelectric substrate. This prevents bulk waves entering from one surface of the sandwich structure from being transmitted to the other surface, or reduces the intensity of the bulk waves when transmitted to the other surface. This effectively suppresses the interference caused by stray bulk wave signals entering from one surface to surface acoustic waves (SAWs) propagating on the other surface. Consequently, it improves the out-of-band suppression effect of the SAW device, reduces the insertion loss of the SAW device, and smooths the passband of the SAW device, resulting in good overall performance of the SAW device. The piezoelectric substrate fabrication method and SAW device provided in the various embodiments of this application can achieve the same technical effects as the piezoelectric substrate provided in the embodiments of this application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the admittance curve of a traditional surface acoustic wave device.

[0019] Figure 2 This is a schematic diagram of the admittance curve of a two-sided IDT surface acoustic wave device.

[0020] Figure 3 This is a schematic diagram of the structure of a piezoelectric substrate provided according to some embodiments of this application.

[0021] Figure 4 This is a schematic diagram of the surface acoustic wave device provided in the embodiments of this application.

[0022] Figure 5 This is a schematic diagram comparing the admittance curves of the surface acoustic wave device provided in this embodiment with those of a reference surface acoustic wave device.

[0023] Figure 6 A schematic diagram comparing the admittance of the surface acoustic wave device provided in this application embodiment with that of a reference surface acoustic wave device under different thicknesses of absorbing loss layers.

[0024] Figure 7 This is a schematic diagram of the structure of a surface acoustic wave device according to other embodiments of this application.

[0025] Figure 8 This is a schematic diagram of the structure of a surface acoustic wave device according to some embodiments of this application.

[0026] Figure 9 This is a schematic diagram of the preparation method provided according to some embodiments of this application.

[0027] Figure 10 This is a schematic diagram of the first piezoelectric layer structure with a first roughening structure.

[0028] Figure 11 This is a schematic diagram of the second piezoelectric layer structure with a second roughening structure.

[0029] Figure 12 This is a schematic diagram of the structure where the first absorbing loss layer covers the first piezoelectric layer.

[0030] Figure 13 This is a schematic diagram of the structure where the second absorbing loss layer covers the second piezoelectric layer.

[0031] Figure 14 This is a schematic diagram of the bonding structure between the first and second absorbing loss layers.

[0032] Explanation of reference numerals in the attached figures: Surface acoustic wave device 10, piezoelectric substrate 100, first interdigital transducer 200, second interdigital transducer 300, first piezoelectric layer 101, wave absorption loss layer 102, second piezoelectric layer 103, first wave absorption loss layer 1021, and second wave absorption loss layer 1022. Detailed Implementation

[0033] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0034] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] like Figure 1 The diagram shows the admittance curve of a traditional surface acoustic wave (SAW) device. This device includes a piezoelectric substrate and an interdigital transducer on the front side of the piezoelectric substrate. The dominant mode at the resonant frequency is a horizontal shear wave, also known as an SH wave. Figure 1 It can be seen that this traditional surface acoustic wave (SAW) device exhibits strong spurious signals at frequencies outside the resonant frequency. These strong spurious signals are mainly radiated by the interdigital transducer (IDT), propagate within the piezoelectric substrate, and are then reflected by the back of the piezoelectric substrate as bulk wave spurious signals. Once these bulk wave spurious signals are detected by the interdigital transducer, they degrade the performance of the SAW device.

[0036] To suppress bulk wave stray signals detected by interdigital transducers, one approach is to roughen the back surface of the piezoelectric substrate. This roughening causes the bulk waves to be scattered by the back surface, thereby reducing the intensity of the bulk wave stray signals detected by the interdigital transducers, or even preventing the bulk waves from being detected at all. However, with the increasing demand for miniaturization of surface acoustic wave (SAW) devices, bifacial IDTs (integrated digital transducers) with interdigital transducers formed on both sides of the piezoelectric substrate have emerged to reduce the device's area. This method of roughening the back surface of the piezoelectric substrate to suppress bulk wave stray signals has not been ideal in bifacial IDT devices. Figure 2 As shown, this is a schematic diagram of the admittance curve of a double-sided IDT surface acoustic wave device. In this double-sided IDT surface acoustic wave device, the IDT design on both sides of the piezoelectric substrate uses the same parameters, and the thickness of the piezoelectric substrate is 30 times the wavelength λ of the surface acoustic wave. From Figure 2 It can be seen that bulk wave spurious signals also appear in double-sided IDT surface acoustic wave devices. Suppressing the bulk wave spurious signals of the front IDT by roughening the back side of the piezoelectric substrate in the double-sided IDT surface acoustic wave device will lead to the deterioration of the resonance characteristics of the back IDT.

[0037] Based on this, embodiments of this application provide a piezoelectric substrate applicable to a double-sided IDT surface acoustic wave device for suppressing bulk wave noise signals, a method for fabricating the piezoelectric substrate, and a surface acoustic wave device comprising the piezoelectric substrate. However, it should be noted that the piezoelectric substrate provided in these embodiments is not limited to applications in double-sided IDT surface acoustic wave devices, but can also be adapted to single-sided IDT surface acoustic wave devices or other devices.

[0038] Please see Figure 3 The diagram shows a piezoelectric substrate 100 according to some embodiments of this application. The piezoelectric substrate 100 includes a first piezoelectric layer 101, a wave-absorbing loss layer 102, and a second piezoelectric layer 103. In a first direction, the first piezoelectric layer 101, the wave-absorbing loss layer 102, and the first piezoelectric layer 103 are stacked to form a sandwich structure. The aforementioned sandwich structure has a first surface and a second surface opposite each other in the first direction. The wave-absorbing loss layer 102 is used to absorb bulk waves propagating inside the sandwich structure. The bulk waves propagating inside the sandwich structure include first-type bulk waves and / or second-type bulk waves. The first-type bulk waves are sound waves that enter the sandwich structure from the first surface and propagate to the second surface without being absorbed by the wave-absorbing loss layer 102. The second-type bulk waves are sound waves that enter the sandwich structure from the second surface and propagate to the first surface without being absorbed by the wave-absorbing loss layer 102.

[0039] When a spur wave enters from one surface of a sandwich structure and propagates to the opposite surface, it may be detected by an interdigital transducer located on the other surface, interfering with the transducer's excitation of the main acoustic wave, thus degrading the performance of the surface acoustic wave (SAW) device. However, in this embodiment, a loss-absorbing layer is provided inside the piezoelectric substrate 100. This loss-absorbing layer absorbs the bulk wave, thereby preventing the bulk wave entering from one surface of the sandwich structure from being transmitted to the other surface, or reducing the intensity of the bulk wave when it is transmitted to the other surface. Therefore, the piezoelectric substrate 100 provided in this embodiment can effectively suppress the interference of spurious bulk wave signals entering from one surface to the SAW propagating on the other surface, thereby improving the out-of-band suppression effect of the SAW device, reducing the insertion loss of the SAW device, and smoothing the passband of the SAW device, resulting in good overall performance of the SAW device.

[0040] The materials used to form the first piezoelectric layer 101 and the second piezoelectric layer 103 can be one of the following: inorganic piezoelectric materials, organic piezoelectric materials, composite piezoelectric materials, and piezoelectric thin films. Inorganic piezoelectric materials can be piezoelectric crystals or piezoelectric ceramics. Organic piezoelectric materials can be, but are not limited to, polymers such as polyvinylidene fluoride (PVDF) and their thin films. Piezoelectric thin films can be, but are not limited to, lithium tantalate (LT) or lithium niobate (LN) thin films.

[0041] Piezoelectric crystals can be, but are not limited to, quartz, crystal, and lithium niobate ( Lithium tantalate ( The piezoelectric ceramics used are lead zirconate titanate (PZT) and aluminum nitride (including scandium-doped aluminum nitride). The first piezoelectric layer 101 and / or the second piezoelectric layer 103 are constructed using piezoelectric crystals, which improves the stability and mechanical quality factor of the piezoelectric substrate 100, and makes the piezoelectric substrate 100 suitable for use in high-frequency surface acoustic wave (SAW) filtering devices. The piezoelectric ceramics can be, but are not limited to, lead zirconate titanate (PZT). The first piezoelectric layer 101 and / or the second piezoelectric layer 103 are constructed using piezoelectric ceramics. Due to the high dielectric constant and piezoelectric coefficient characteristics of piezoelectric ceramics, the accuracy and stability of signal processing in surface acoustic wave (SAW) devices using the piezoelectric substrate 100 are improved. Using polymer materials to construct the piezoelectric substrate 100 allows it to be applied in wearable SAW devices and biomedical sensing devices based on SAW technology.

[0042] The interference of volume wave noise signals on surface acoustic waves is reduced by using the absorbing loss layer 102 to absorb or attenuate the energy of volume waves. The absorbing loss layer 102 is not required to absorb all volume waves, but rather to absorb at least a portion of them, preventing volume waves from being transmitted from one side of the sandwich surface to the other, or attenuating the volume waves transmitted to the other side surface, so that the influence of volume wave noise signals on the surface acoustic waves propagating on the other side surface is not significant.

[0043] In some embodiments, at least one of the first piezoelectric layer 101 and the second piezoelectric layer 103 is composed of lithium tantalate or lithium niobate. The shear wave velocity range of the lithium tantalate or lithium niobate constituting the piezoelectric substrate 100 can be 3000-5000 m / s, the electromechanical coupling coefficient can be greater than or equal to 0.3, and its dielectric constant is between 40 and 55. Since lithium tantalate and lithium niobate have stable performance at high frequencies, the surface acoustic wave (SAW) device using the piezoelectric substrate 100 provided in this application embodiment can be used as a radio frequency front-end filter in 5G / 6G. Furthermore, lithium tantalate and lithium niobate have low propagation losses, thereby enabling the piezoelectric substrate 100 to effectively reduce the insertion loss of the SAW device and improve its filtering performance.

[0044] In some embodiments, at least one of the first piezoelectric layer 101 and the second piezoelectric layer 103 is made of quartz. Quartz has high stability in its piezoelectric coefficient and dielectric constant, with a variation rate of only -0.016% in the range of 20 to 200°C, which is beneficial for improving the accuracy and stability of signal processing in surface acoustic wave devices. Furthermore, due to the high uniformity of the quartz crystal structure, the interface between quartz crystals can be tightly contacted with few defects. Therefore, using quartz as the first piezoelectric layer 101 and the second piezoelectric layer 103 facilitates their stacking via bonding, and the bonding process is mature and cost-effective.

[0045] In some embodiments, the first piezoelectric layer 101 and the second piezoelectric layer 103 can each be a preformed substrate with a certain thickness, and the first piezoelectric layer 101 and the second piezoelectric layer 103 can be obtained simultaneously to improve the fabrication efficiency of the piezoelectric substrate 100. The thickness of the first piezoelectric layer 101 and the second piezoelectric layer 103 refers to their thickness in the first direction, and their thicknesses can be the same or different.

[0046] The thickness of the piezoelectric substrate 100 is primarily the sum of the thicknesses of the first piezoelectric layer 101 and the second piezoelectric layer 103. The thicknesses of the first piezoelectric layer 101 and the second piezoelectric layer 103 range from 50 to 200 micrometers, thereby forming a piezoelectric substrate 100 with a thickness of 150 to 500 micrometers. In some embodiments, the thicknesses of the first piezoelectric layer 101 and the second piezoelectric layer 103 can be 80 to 120 micrometers, respectively, so that the thickness of the piezoelectric substrate 100 is 180 to 220 micrometers, to balance the performance of the surface acoustic wave device using the piezoelectric substrate 100, such as loss and electromechanical coupling. For example, the thicknesses of the first piezoelectric layer 101 and the second piezoelectric layer 103 can each be approximately 100 micrometers, so the thickness of the piezoelectric substrate 100 can be more than 200 micrometers, which is beneficial for stacking the first piezoelectric layer 101 and the second piezoelectric layer 103 to form a sandwich structure, and can also improve the performance of the surface acoustic wave device.

[0047] In some embodiments, the first piezoelectric layer 101 and the second piezoelectric layer 103 may be made of the same piezoelectric material, and the first piezoelectric layer 101 and the second piezoelectric layer 103 may be prepared using the same process, which is beneficial to reducing the manufacturing cost of the piezoelectric substrate 100.

[0048] In some embodiments, the first piezoelectric layer 101 and the second piezoelectric layer 103 may be composed of piezoelectric materials with different surface acoustic wave propagation directions. This makes it less likely that bulk waves leaking from one side of the sandwich structure into the interior of the sandwich structure will be detected by the interdigital transducer on the other side of the sandwich structure, thereby improving the suppression effect of bulk wave stray signals to a certain extent. For example, one of the first piezoelectric layer 101 and the second piezoelectric layer 103 may employ... , The first piezoelectric material propagating in the direction, the other of the first piezoelectric layer 101 and the second piezoelectric layer 103 adopts , A second piezoelectric material that propagates in a specific direction. The direction is the direction in which the surface acoustic wave propagates in the first piezoelectric material. The direction is the direction in which the surface acoustic wave propagates in the second piezoelectric material. direction and Angle between directions The scope is: . This refers to the cutting direction of the wafer made of the corresponding piezoelectric material being rotated along the Y-axis. .

[0049] Please see Figure 4 The diagram shows a schematic of the surface acoustic wave (SAW) device 10 provided in an embodiment of this application. The SAW device 10 is a SAW device using the piezoelectric substrate 100 provided in any embodiment of this application. In this embodiment, the SAW device 10 is a double-sided IDT SAW device, which includes a piezoelectric substrate 100, a first interdigital transducer 200, and a second interdigital transducer 300. The first interdigital transducer 200 is located on the first surface of the sandwich structure in the piezoelectric substrate 100, and the second interdigital transducer 300 is located on the second surface of the sandwich structure. The first surface of the sandwich structure is the side of the first piezoelectric layer 101 away from the absorption loss layer 102, and the second surface of the sandwich structure is the side of the second piezoelectric layer 103 away from the absorption loss layer 102.

[0050] The design structure of the first interdigital transducer 200 and the second interdigital transducer 300 can be the same, and they can be symmetrically arranged on both sides of the sandwich structure. In other embodiments, the surface acoustic wave device 10 can also be a single-sided IDT surface acoustic wave device, or other surface acoustic wave devices based on surface acoustic waves. In a single-sided IDT surface acoustic wave device, the sandwich structure in the piezoelectric substrate 100 has interdigital transducers on only one side surface, such as the first interdigital transducer 200 only on the first surface or the second interdigital transducer 300 only on the second surface.

[0051] Because the piezoelectric substrate 100 has an absorbing loss layer 102, when the first type of bulk wave radiated by the first interdigital transducer 200 and entering the sandwich structure from the first surface propagates to the absorbing loss layer 102, its energy is at least partially absorbed by the absorbing loss layer 102. Therefore, the first type of bulk wave that continues to propagate to the second surface via the absorbing loss layer 102 may disappear or its intensity weaken, making it difficult for the second interdigital transducer 300 to detect it, or even if it is detected, the intensity of the corresponding bulk wave spurious signal is very weak, thus achieving suppression of the first type of bulk wave spurious signal. Similarly, the second type of bulk wave radiated by the second interdigital transducer 300 and entering the sandwich structure from the second surface will also be difficult or impossible to detect by the first interdigital transducer 200 due to the absorbing loss layer 102, thus achieving suppression of the second type of bulk wave spurious signal.

[0052] Please see Figure 5 The diagram shows a comparison of the admittance curves of the surface acoustic wave (SAW) device 10 provided in this embodiment and a reference SAW device. The solid line "Prorposed" represents the admittance curve of the SAW device 10 provided in this embodiment, and the dashed line "Reference" is a structural schematic diagram of the reference SAW device. In this embodiment, the wavelength λ can be 5 micrometers, and the thickness of the absorbing loss layer 102 is twice the wavelength λ. The difference between the reference SAW device and the SAW device 10 provided in this embodiment is that the piezoelectric substrate of the reference SAW device does not have an absorbing loss layer 102 inside, resulting in relatively poor suppression of bulk stray signals, and its out-of-band smoothness is significantly inferior to that of the SAW device 10 provided in this embodiment.

[0053] The surface acoustic wave device 10 provided in this application embodiment can be a surface acoustic wave filter, resonator, or duplexer, etc. Because a wave absorption loss layer 102 is provided in the piezoelectric substrate 100, it suppresses the detection of corresponding bulk waves by the interdigital transducers on both sides of the piezoelectric substrate 100, or significantly weakens the intensity of the bulk waves detected by the interdigital transducers, thereby improving the out-of-band suppression effect, reducing insertion loss, and having a smoother passband.

[0054] In some embodiments, the ratio of the thickness of the absorbing loss layer 102 in the first direction to the wavelength λ of the surface acoustic wave is greater than or equal to 0.2, thereby ensuring that the propagation of the bulk wave in the absorbing loss layer 102 has a certain path, making the energy of the bulk wave more significantly attenuated by the absorbing loss layer 102, thereby achieving the effect of suppressing bulk wave stray signals. The first direction is perpendicular to the extension planes of the first piezoelectric layer 101, the absorbing loss layer 102, and the second piezoelectric layer 103, respectively.

[0055] The greater the thickness of the absorbing loss layer 102, the stronger its ability to suppress bulk wave stray signals, such as... Figure 6As shown, this is a schematic diagram comparing the admittance of the surface acoustic wave (SAW) device 10 with different thicknesses of the absorbing loss layer 102 provided in this application embodiment with that of a reference SAW device. The dotted line "Reference" represents the admittance curve of the reference SAW device without the absorbing loss layer 102. The long dashed line segment 0.2λ represents the admittance curve when the thickness of the absorbing loss layer 102 is 0.2 times the wavelength λ. The dotted dashed line 0.6λ represents the admittance curve when the thickness of the absorbing loss layer 102 is 0.6 times the wavelength λ. The short dashed line segment 1.0λ represents the admittance curve when the thickness of the absorbing loss layer 102 is 1 times the wavelength λ. Figure 6 As can be seen, even though the thickness of the absorbing loss layer 102 is only 0.2 times the wavelength λ, its out-of-band suppression effect is still quite significant compared to the reference surface acoustic wave. Furthermore, the greater the thickness of the absorbing loss layer 102, the stronger its ability to suppress bulk wave spurious signals. Typically, the thicknesses of the first piezoelectric layer 101 and the second piezoelectric layer 103 are much larger than the thickness of the absorbing loss layer 102. That is, the thickness of the absorbing loss layer 102 can be determined according to the requirements for bulk wave spurious signal suppression; by adjusting its thickness, the bulk wave spurious signal suppression effect can meet the requirements.

[0056] In some embodiments, the material forming the first piezoelectric layer 101 has a first shear rate, the material forming the second piezoelectric layer 103 has a second shear rate, and the material forming the absorbing loss layer 102 has a third shear rate. The third shear rate is lower than the first and second shear rates, respectively, which allows bulk waves to be effectively coupled to the absorbing loss layer 102, thereby achieving a bulk wave stray suppression effect.

[0057] In some embodiments, the absorbing loss layer 102 includes an adhesive layer through which the first piezoelectric layer 101 and the second piezoelectric layer 103 are bonded together. When a bulk wave propagates to the adhesive layer, the adhesive layer creates a viscous loss field on the bulk wave, thereby dissipating the propagation energy of the bulk wave and suppressing its detection by the interdigital transducer. In this embodiment, the adhesive layer constituting the absorbing loss layer 102 not only dissipates the propagation energy of the bulk wave to improve the suppression effect of bulk wave stray signals, but also takes into account the bonding effect between the first piezoelectric layer 101 and the second piezoelectric layer 103, thus eliminating the need for additional structures for suppressing bulk wave stray signals. Therefore, the surface acoustic wave device 10 provided in this application embodiment has a simple structure, is easy to implement, and has low manufacturing cost.

[0058] In some embodiments, the adhesive layer in the absorbing loss layer 102 is composed of an organic adhesive. The organic adhesive can be formed through processing techniques such as coating or spraying, which is simple to prepare and low in cost, thus reducing the manufacturing cost of the piezoelectric substrate 100 provided in this embodiment. Furthermore, the organic adhesive is lightweight, meeting the lightweight development requirements of the surface acoustic wave device 10.

[0059] In some embodiments, the organic adhesive forming the adhesive layer may be, but is not limited to, at least one of epoxy resin, polyimide, and acrylate. Epoxy resin, polyimide, and acrylate are high-temperature resistant materials with low requirements for bonding processes, which helps improve the reliability of the piezoelectric substrate 100 and the surface acoustic wave device 10, and reduces manufacturing costs.

[0060] In some embodiments, the adhesive layer in the absorbing loss layer 102 is made of an inorganic adhesive. In this embodiment, the first piezoelectric layer 101 and the second piezoelectric layer 103 are bonded together with an inorganic adhesive to form a sandwich structure, which can improve the adaptability of the piezoelectric substrate 100 and the surface acoustic wave device 10 in high-temperature environments. The inorganic adhesive may include at least one of silicon dioxide, silicon nitride, aluminum oxide, and tantalum pentoxide.

[0061] In some embodiments, the adhesive layer in the absorbing loss layer 102 may also be made of amorphous silicon. The density of the amorphous silicon adhesive ranges from 2.0 to 2.3. Its low mass density is beneficial to the lightweight development of the surface acoustic wave device 10. At the same time, the low price of amorphous silicon helps to reduce the production cost of the piezoelectric substrate 100 and the surface acoustic wave device 10.

[0062] Please see Figure 7 As shown, it is a structural schematic diagram of a surface acoustic wave device 10 provided according to some other embodiments of this application. The first piezoelectric layer 101 has a first roughening structure on the side near the absorbing loss layer 102. After the second type of volume wave loses energy through the absorbing loss layer 102, even if some of the second type of volume wave continues to propagate from the absorbing loss layer 102 toward the first piezoelectric layer 101, the energy of this second type of volume wave after loss will be dispersed when it propagates to the first roughening structure, thereby further losing energy and improving the suppression effect of the second type of volume wave stray signal.

[0063] Please see Figure 7As shown, it is a structural schematic diagram of a surface acoustic wave device 10 provided according to some embodiments of this application. The second piezoelectric layer 103 has a second roughening structure on the side near the absorbing loss layer 102. After the first type of volume wave loses energy through the absorbing loss layer 102, even if some of the first type of volume wave continues to propagate from the absorbing loss layer 102 to the second piezoelectric layer 103, this part of the energy of the first type of volume wave after loss will be dispersed when it is propagated to the second roughening structure, so that the energy is further lost, thereby improving the suppression effect of the first type of volume wave stray signal.

[0064] In the surface acoustic wave device 10 provided in other embodiments, the first piezoelectric layer 101 has a first roughening structure on the side near the absorption loss layer 102, and the second piezoelectric layer 103 has a second roughening structure on the side near the absorption loss layer, thereby improving the suppression effect of the first type of bulk wave spurious signal and the second type of bulk wave spurious signal. The first roughening structure and the second roughening structure may each include multiple protrusions and / or multiple depressions, and these depressions or protrusions may be uneven structures formed based on plasma bombardment of the corresponding surface.

[0065] Please continue reading. Figure 7 and Figure 8 As shown, in some embodiments, the side of the absorbing loss layer 102 closest to the corresponding piezoelectric layer also has a roughened structure that forms an interlocking contact with the roughened structure of the corresponding piezoelectric layer. This improves the quality of the contact interface between the absorbing loss layer 102 and the corresponding piezoelectric layer, thereby enhancing the performance of the surface acoustic wave device 10. Specifically, the side of the absorbing loss layer 102 closest to the first piezoelectric layer 101 has a third roughened structure that forms an interlocking contact with the first roughened structure, and the side of the absorbing loss layer 102 closest to the second piezoelectric layer 103 has a fourth roughened structure that forms an interlocking contact with the second roughened structure. It should be noted that this interlocking contact relationship does not limit the fixed connection between the absorbing loss layer 102 and the corresponding piezoelectric layer to a snap-fit ​​connection based on the aforementioned interlocking contact relationship. Rather, it simply indicates that the concave and convex formations between the corresponding roughened structures form an interlocking relationship; that is, the protruding structure of the third roughened structure interlocks with the concave structure of the first roughened structure, and the concave structure in the third roughened structure interlocks with the protruding structure of the first roughened structure.

[0066] In some embodiments, the roughening structure in the absorbing loss layer 102 may, but is not limited to, cover the surface of the corresponding piezoelectric layer with its constituent material and fill the gaps between the corresponding roughening structures, thereby forming a roughening structure conforming to the corresponding roughening structure.

[0067] In some embodiments, such as Figure 14As shown, the piezoelectric substrate 100 provided in this application has a first absorbing loss layer 1021 and a second absorbing loss layer 1022 stacked in a first direction. The first absorbing loss layer 1021 is bonded to the first piezoelectric layer 101, and the second absorbing loss layer 1022 is bonded to the second piezoelectric layer 103. It is possible, but not limited to, that the first absorbing loss layer 1021 covers the side of the first piezoelectric layer 101 that is disposed on the first roughened structure, and that the side of the first absorbing loss layer 1021 away from the first piezoelectric layer 101 is bonded to the side of the second absorbing loss layer 1022 away from the second piezoelectric layer 103. That is, in the piezoelectric substrate 100 provided in this application embodiment, the first absorbing loss layer 1021 and the second absorbing loss layer 1022 can be bonded together through a bonding surface, simplifying the process and eliminating the need for additional adhesive.

[0068] Please see Figure 9 As shown, it is a schematic diagram of the preparation method provided according to some embodiments of this application. The preparation method provided in the embodiments of this application is used to prepare a piezoelectric substrate according to any embodiment of this application, which includes S12 and S14.

[0069] S12: Provides a first piezoelectric layer and a second piezoelectric layer.

[0070] The first piezoelectric layer 101 and the second piezoelectric layer 103 in this step can be pre-formed piezoelectric wafers or piezoelectric wafers fabricated in-line.

[0071] S14: The first piezoelectric layer and the second piezoelectric layer are bonded together using a wave-absorbing loss layer to form a sandwich structure.

[0072] The first piezoelectric layer 101 and the second piezoelectric layer 103 can be bonded together by using a wave-absorbing loss layer 102. This can be achieved by using an adhesive layer that can cause viscous loss to bulk waves to bond the first piezoelectric layer 101 and the second piezoelectric layer 103 together.

[0073] In some embodiments, providing the first piezoelectric layer 101 includes providing a first piezoelectric layer 101 having a first roughened structure. A schematic diagram of the structure of the first piezoelectric layer 101 having the first roughened structure is shown below. Figure 10 As shown. The first roughening structure on one side of the first piezoelectric layer 101 can be a structure made of other materials on the surface of the first piezoelectric layer 101, or it can be an uneven structure formed on the surface of the first piezoelectric layer 101 by plasma bombardment. That is, in some embodiments, the step of providing the first piezoelectric layer 101 may include: providing the first piezoelectric layer 101, and performing plasma etching on one side of the first piezoelectric layer 101 to form the first roughening structure.

[0074] In some embodiments, providing the second piezoelectric layer 103 includes providing a second piezoelectric layer 103 having a second roughened structure. A schematic diagram of the structure of the second piezoelectric layer 103 having the second roughened structure is shown below. Figure 11 As shown. The second roughening structure on one side of the second piezoelectric layer 103 can be a structure made of other materials on the surface of the second piezoelectric layer 103, or it can be an uneven structure formed on the surface of the second piezoelectric layer 103 by plasma bombardment. That is, in some embodiments, the step of providing the second piezoelectric layer 103 may include: providing the second piezoelectric layer 103, and performing plasma etching on one side of the second piezoelectric layer 103 to form the second roughening structure.

[0075] like Figure 12 As shown, in some embodiments, the first piezoelectric layer and the second piezoelectric layer are bonded together using the microwave absorption loss layer 102 to form a sandwich structure, which may include: the first roughening structure of the first piezoelectric layer 101 covering the first microwave absorption loss layer 1021, and the forming material of the first microwave absorption loss layer 1021 filling the recessed gaps between the first roughening structures.

[0076] like Figure 13 As shown, in some embodiments, the first piezoelectric layer 101 and the second piezoelectric layer 103 are bonded together using the microwave absorption loss layer 102 to form a sandwich structure. It may also include: the second roughened structure of the second piezoelectric layer 103 covers the second microwave absorption loss layer 1022, and the forming material of the second microwave absorption loss layer 1022 fills the recessed gap between the second roughened structures.

[0077] like Figure 14 As shown, in some embodiments, the first piezoelectric layer 101 and the second piezoelectric layer 103 are bonded together using the microwave absorption loss layer 102 to form a sandwich structure. It may also include: bonding the first microwave absorption loss layer 1021 and the second microwave absorption loss layer 1022 together to form a sandwich structure.

[0078] In some embodiments, bonding the first absorbing loss layer 1021 and the second absorbing loss layer 1022 together may include: performing surface planarization on the side of the first absorbing loss layer 1021 covering the first roughened structure away from the first piezoelectric layer 101 to form a first planarized surface; performing surface planarization on the side of the second absorbing loss layer 1022 covering the second roughened structure away from the second piezoelectric layer 103 to form a second planarized surface; and bonding the first planarized surface and the second planarized surface together to form a sandwich structure.

[0079] In other embodiments, the fabrication method provided in this application is used to fabricate a piezoelectric substrate 100 according to any embodiment of this application, comprising: providing a first piezoelectric layer 101, forming a microwave absorption loss layer 102 on the first piezoelectric layer 101, and forming a second piezoelectric layer 103 on the side of the microwave absorption loss layer 102 away from the first piezoelectric layer 101. In this embodiment, the first piezoelectric layer 101, the microwave absorption loss layer 102, and the second piezoelectric layer 103 are sequentially stacked in a first direction.

[0080] The preparation methods provided in the embodiments of this application have the same technical effects as the piezoelectric substrate 100 provided in the embodiments of this application, and will not be repeated here.

[0081] It is understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0082] Unless otherwise stated, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. The singular forms "a," "the," and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0083] The above are merely specific embodiments of this application, but the scope of protection of this invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A piezoelectric substrate, characterized in that, It includes a first piezoelectric layer, a wave-absorbing loss layer and a second piezoelectric layer. In a first direction, the first piezoelectric layer, the wave-absorbing loss layer and the second piezoelectric layer are stacked to form a sandwich structure. The sandwich structure has a first surface and a second surface opposite to each other in the first direction, and the wave-absorbing loss layer is used to absorb volume waves; The body waves include a first type of body wave and / or a second type of body wave. The first type of body wave is a sound wave that enters the interior of the sandwich structure from the first surface; the second type of body wave is a sound wave that enters the interior of the sandwich structure from the second surface.

2. The piezoelectric substrate according to claim 1, characterized in that, The first surface and / or the second surface are respectively used to set interdigital transducers for exciting surface acoustic waves, and the bulk waves are radiated by the interdigital transducers on the corresponding surfaces; The ratio of the thickness of the absorbing loss layer in the first direction to the wavelength of the surface acoustic wave is greater than or equal to 0.

2.

3. The piezoelectric substrate according to claim 1, characterized in that, The absorbing loss layer includes an adhesive layer for bonding the first piezoelectric layer and the second piezoelectric layer together, and the adhesive layer causes viscous loss to the bulk wave.

4. The piezoelectric substrate according to claim 3, characterized in that, The adhesive layer is composed of at least one of organic adhesives, inorganic adhesives, and amorphous silicon. The organic adhesive includes at least one of epoxy resin, polyimide, and acrylate, and the inorganic adhesive includes at least one of silicon dioxide, silicon nitride, aluminum oxide, and tantalum pentoxide.

5. The piezoelectric substrate according to claim 1, characterized in that, The first piezoelectric layer has a first roughening structure on the side near the absorbing loss layer and / or the second piezoelectric layer has a second roughening structure on the side near the absorbing loss layer.

6. The piezoelectric substrate according to claim 5, characterized in that, The first piezoelectric layer has a first roughening structure on the side near the microwave absorption loss layer, and the microwave absorption loss layer has a third roughening structure on the side near the first piezoelectric layer. The third roughening structure and the second roughening structure are in an interlocking contact relationship. And / or, the second piezoelectric layer has a second roughening structure on the side near the microwave absorption loss layer, and the microwave absorption loss layer has a fourth roughening structure on the side near the second piezoelectric layer, wherein the fourth roughening structure and the second roughening structure are in an interlocking contact relationship.

7. The piezoelectric substrate according to any one of claims 1 to 6, characterized in that, The constituent materials of at least one of the first piezoelectric layer and the second piezoelectric layer include lithium tantalate, lithium niobate, quartz, or aluminum nitride.

8. The piezoelectric substrate according to any one of claims 1 to 6, wherein the absorbing loss layer includes a first absorbing loss layer and a second absorbing loss layer stacked in the first direction, the first absorbing loss layer being bonded to the first piezoelectric layer, and the second absorbing loss layer being bonded to the second piezoelectric layer; The side of the first absorbing loss layer away from the first piezoelectric layer is bonded to the side of the second absorbing loss layer away from the second piezoelectric layer.

9. A method for preparing a piezoelectric substrate as described in any one of claims 1 to 8, characterized in that, include: A first piezoelectric layer and a second piezoelectric layer are provided, and a wave-absorbing loss layer is used to bond the first piezoelectric layer and the second piezoelectric layer together to form a sandwich structure. Alternatively, a first piezoelectric layer is provided, an absorbing loss layer is formed on the first piezoelectric layer, and a second piezoelectric layer is formed on the side of the absorbing loss layer away from the first piezoelectric layer.

10. A surface acoustic wave device, characterized in that, Includes the piezoelectric substrate and interdigital transducer as described in any one of claims 1 to 8; The interdigital transducers are disposed on the first and / or second surfaces of the sandwich structure.

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