Constant temperature surface acoustic wave filter and preparation method thereof

Abstract

The present invention relates to the field of wireless communication technology, and provides a constant temperature surface acoustic wave filter and a preparation method thereof. The preparation method comprises the following steps: selecting a piezoelectric substrate, and forming a first groove and a second groove on the upper surface of the piezoelectric substrate; depositing polysilicon from the upper surface of the piezoelectric substrate to completely fill the grooves; grinding the polysilicon until the piezoelectric substrate is exposed; implanting ions into the polysilicon to form an n-type thermocouple pair and a p-type thermocouple pair; forming a first dielectric layer on the upper surface of the silicon substrate; forming a first thermocouple pair interconnection layer, a second thermocouple pair interconnection layer, and a third thermocouple pair interconnection layer in the first groove, the second groove, and the third groove formed in the first dielectric layer; forming a second dielectric layer on the upper surface of the first dielectric layer; forming an interdigital structure and a third dielectric layer on the lower surface of the piezoelectric substrate; and obtaining a constant temperature surface acoustic wave filter. The constant temperature surface acoustic wave filter of the present invention can improve temperature stability and power tolerance.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communications, and in particular to a constant temperature surface acoustic wave filter and a preparation method thereof. Background Art

[0002] The temperature drift problem of surface acoustic wave (SAW) filters refers to the phenomenon that its key performance parameters (such as center frequency, bandwidth, insertion loss and out-of-band rejection) shift with changes in ambient temperature. This phenomenon is essentially due to the basic physical properties of surface acoustic wave devices: when the temperature changes, the piezoelectric substrate material (such as or The lattice constant of the CMOS device undergoes thermal expansion, causing a change in the propagation velocity of surface acoustic waves (the speed of sound decreases by approximately 0.02% for every 1°C increase in temperature). Simultaneously, the thermal expansion of the metal electrodes of the interdigital transducer (IDT) also changes the electrode period. These two effects result in a typical negative temperature coefficient (approximately -30 to -45 ppm / °C) in the device's center frequency.

[0003] In high-frequency applications such as 5G communications, this temperature drift can cause serious system problems. For example, a 3.5GHz SAW filter can experience frequency drift of up to 3MHz within an operating temperature range of -40°C to +85°C. This can not only cause passband mismatch and adjacent channel leakage, but also degrade key performance indicators such as EVM (Error Vector Magnitude) and ACLR (Adjacent Channel Leakage Ratio). To address this challenge, various innovative solutions have been developed. For example, TC-SAW (temperature-compensated surface acoustic wave) filters utilize a SiO2 temperature compensation layer deposited on a conventional LiTaO3 substrate (its positive temperature coefficient partially offsets the substrate's negative temperature effect), reducing the temperature drift coefficient to -10 to -15ppm / °C. IHP-SAW (Incredible High Performance) technology reduces the temperature drift coefficient to -15 to -25ppm / °C by optimizing the electrode structure and material stack, achieving improved temperature stability while maintaining low insertion loss (<1.5dB).

[0004] However, these improvements often require a trade-off between performance, cost, and size, forcing system designers to select the appropriate filter solution based on different application scenarios (for example, base stations require better temperature stability, while mobile terminals are more concerned with size and cost). In the future, as 6G communications require higher frequency bands (such as terahertz) and wider temperature ranges, the temperature drift problem of SAW filters will continue to drive innovations in materials science, micro-nanofabrication, and thermal management technologies.

[0005] Therefore, although the related technologies TC-SAW and IHP-SAW improve the temperature drift problem of traditional SAW filters, their temperature drift coefficients are still inferior to BAW filters (bulk acoustic wave filters). They are prone to problems such as high design complexity, high material costs, and poor power tolerance. Summary of the Invention

[0006] In view of the above deficiencies in the prior art, the present invention proposes a constant temperature surface acoustic wave filter and a preparation method thereof to solve the problems of poor temperature drift suppression and power tolerance of the existing surface acoustic wave filters.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] In a first aspect, an embodiment of the present invention provides a method for preparing a temperature-controlled surface acoustic wave filter, the method comprising the following steps:

[0009] Step S1, selecting a piezoelectric substrate, and forming a first groove and a second groove on the upper surface of the piezoelectric substrate;

[0010] Step S2: depositing polysilicon on the upper surface of the piezoelectric substrate to completely fill the first trench and the second trench;

[0011] Step S3, grinding and thinning the polysilicon until the upper surface of the piezoelectric substrate is completely exposed;

[0012] Step S4, implanting ions into the polysilicon in the first trench and the second trench to form an n-type thermocouple pair and a p-type thermocouple pair, respectively;

[0013] Step S5, forming a first dielectric layer on the upper surface of the piezoelectric substrate, and making the first dielectric layer completely cover the piezoelectric substrate, the n-type thermocouple pair, and the p-type thermocouple pair;

[0014] Step S6: Opening windows in the first dielectric layer to form a first groove, a second groove, and a third groove at intervals, exposing the n-type thermocouple pair and the p-type thermocouple pair through the first groove, the second groove, and the third groove, and forming a first thermocouple pair interconnection layer, a second thermocouple pair interconnection layer, and a third thermocouple pair interconnection layer in the first groove, the second groove, and the third groove, respectively; wherein the first thermocouple pair interconnection layer extends along the inner wall of the first groove and forms an electrical connection with the n-type thermocouple pair, the second thermocouple pair interconnection layer extends along the inner wall of the second groove and electrically connects the n-type thermocouple pair and the p-type thermocouple pair, and the third thermocouple pair interconnection layer extends along the inner wall of the third groove and forms an electrical connection with the p-type thermocouple pair;

[0015] Step S7, forming a second dielectric layer on the upper surface of the first dielectric layer, so that the second dielectric layer completely covers the first thermocouple pair interconnection layer, the second thermocouple pair interconnection layer and the third thermocouple pair interconnection layer;

[0016] Step S8, forming an interdigital structure and a third dielectric layer on the lower surface of the piezoelectric substrate, and making the third dielectric layer completely cover the lower surface of the piezoelectric substrate and the interdigital structure;

[0017] Step S9: Open a window in the second dielectric layer to expose the first thermocouple pair interconnection layer and the third thermocouple pair interconnection layer; open a window in the third dielectric layer to expose the contact portion of the interdigital structure, and grow solder balls on the contact portion to obtain a constant temperature surface acoustic wave filter.

[0018] Preferably, in step S1, the depths of the first trench and the second trench are both 2um-10um, and the formation process is any one of reactive ion etching, wet etching and dry etching.

[0019] Preferably, the depth of the first groove and the second groove are both 4 μm.

[0020] Preferably, in step S2, the deposition method is a low pressure chemical vapor deposition process.

[0021] Preferably, in step S3, the polysilicon is ground by mechanical grinding or chemical mechanical polishing until the piezoelectric substrate is exposed.

[0022] Preferably, the first dielectric layer, the second dielectric layer and the third dielectric layer are all made of SiN material or SiO2 material.

[0023] Preferably, in step S6, windows are opened in the first dielectric layer by etching using wet etching or dry etching.

[0024] Preferably, in step S8, the interdigital structure is made of aluminum, titanium-aluminum alloy, aluminum-copper alloy, or a laminated material of aluminum and titanium.

[0025] Preferably, in step S9 , windows are opened in both the second dielectric layer and the third dielectric layer by etching using wet etching or dry etching.

[0026] In a second aspect, an embodiment of the present invention provides a temperature-controlled surface acoustic wave filter, which is manufactured based on the above-mentioned method for manufacturing a temperature-controlled surface acoustic wave filter.

[0027] Compared with the related art, in an embodiment of the present invention, through the above-mentioned steps S1 to S9, ions are respectively injected into the polysilicon in the first groove and the second groove formed in the piezoelectric substrate to form an n-type thermocouple pair and a p-type thermocouple pair. When the ambient temperature changes, the voltage magnitude and direction at both ends of the thermocouple pair are controlled by the control circuit to heat or cool the resonator to maintain a constant temperature of the resonator, thereby eliminating the temperature drift of the surface acoustic wave resonator and improving the temperature stability and power tolerance performance of the surface acoustic wave filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in detail below with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and easier to understand through the detailed description made with reference to the following drawings. In the accompanying drawings:

[0029] Figure 1 A flow chart of a method for preparing a constant temperature surface acoustic wave filter provided in Example 1 of the present invention;

[0030] Figure 2 A specific process flow chart of the method for preparing a constant temperature surface acoustic wave filter provided in Example 1 of the present invention;

[0031] Figure 3 This is a structural diagram of a temperature-controlled surface acoustic wave filter provided in the second embodiment of the present invention.

[0032] Among them, 100, constant temperature surface acoustic wave filter, 1, piezoelectric substrate, 101, first groove, 102, second groove, 2, polysilicon, 21, n-type thermocouple pair, 22, p-type thermocouple pair, 3, first dielectric layer, 4, first groove, 5, second groove, 6, third groove, 7, first thermocouple pair interconnection layer, 8, second thermocouple pair interconnection layer, 9, third thermocouple pair interconnection layer, 10, second dielectric layer, 11, third dielectric layer, 12, interdigital structure, 121, contact part, 13, solder ball, 14, external device, 15, wire. DETAILED DESCRIPTION

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of the application are for the purpose of describing specific embodiments only and are not intended to limit this application. 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. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

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

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] Example 1

[0037] See also Figure 1-Figure 2 As shown, an embodiment of the present invention provides a method for preparing a constant temperature surface acoustic wave filter, the preparation method comprising the following steps:

[0038] Step S1 : selecting a piezoelectric substrate 1 , and forming a first groove 101 and a second groove 102 on the upper surface of the piezoelectric substrate 1 .

[0039] Step S2: Depositing polysilicon 2 on the upper surface of the piezoelectric substrate 1 to completely fill the first trench 101 and the second trench 102. By selecting a corresponding piezoelectric substrate 1 and etching the piezoelectric substrate 1 to obtain the first trench 101 and the second trench 102, it is convenient to deposit polysilicon 2 in the first trench 101 and the second trench 102 to obtain a polysilicon 2 material layer.

[0040] Step S3: Grind and thin the polysilicon 2 until the piezoelectric substrate 1 is completely exposed. By grinding and thinning the polysilicon 2, the upper surface of the piezoelectric substrate 1 around the first groove 101 and the second groove 102 is flush with the polysilicon 2, completely exposing the piezoelectric substrate 1 to facilitate further processing and production.

[0041] Step S4 : Ions are implanted into the polysilicon 2 in the first trench 101 and the second trench 102 , respectively, to form an n-type thermocouple pair 21 and a p-type thermocouple pair 22 .

[0042] Specifically, an n-type thermocouple pair 21 and a p-type thermocouple pair 22 are formed by directly injecting single crystal silicon ions into the piezoelectric substrate 1, and a thermoelectric stack constant temperature structure of a semiconductor thermocouple pair based on the Peltier effect and the Seebeck effect is provided under the filter. This can ensure that the device is continuously cooled by the thermopile under high-power working conditions, which not only reduces the temperature drift, but also improves the power tolerance of the device.

[0043] The Peltier effect is based on the physical principle that charge carriers moving from higher energy levels to lower energy levels in different materials release excess heat, while the reverse direction requires heat absorption from the outside world. When current flows through a loop composed of n-type and p-type semiconductors, one junction absorbs heat while the other releases it. This effect is reversible; reversing the direction of the current also changes the junction that absorbs and releases heat.

[0044] The Seebeck effect, also known as the first thermoelectric effect, refers to the thermoelectric phenomenon in which a voltage difference between two different conductors or semiconductors is caused by a temperature difference. The direction of the thermoelectric potential is generally defined as electrons flowing from negative to positive at the hot end. In a circuit consisting of two metals A and B, if the temperatures of the two contact points are different, a current will flow in the circuit, called a thermoelectric current. The corresponding electromotive force is called the thermoelectric potential, and its direction depends on the direction of the temperature gradient.

[0045] Step S5: Form a first dielectric layer 3 on the upper surface of the piezoelectric substrate 1, so that the first dielectric layer 3 completely covers the piezoelectric substrate 1, the n-type thermocouple pair 21, and the p-type thermocouple pair 22. The first dielectric layer 3 can passivate, protect, and insulate the n-type thermocouple pair 21 and the p-type thermocouple pair 22, providing good protection.

[0046] Step S6: Open windows in the first dielectric layer 3 to form a first groove 4, a second groove 5, and a third groove 6 at intervals. The n-type thermocouple pair 21 and the p-type thermocouple pair 22 are exposed through the first groove 4, the second groove 5, and the third groove 6. A first thermocouple pair interconnection layer 7, a second thermocouple pair interconnection layer 8, and a third thermocouple pair interconnection layer 9 are formed in the first groove 4, the second groove 5, and the third groove 6, respectively. The first thermocouple pair interconnection layer 7 extends along the inner wall of the first groove 4 and forms an electrical connection with the n-type thermocouple pair 21. The second thermocouple pair interconnection layer 8 extends along the inner wall of the second groove 5 and forms an electrical connection with the n-type thermocouple pair 21 and the p-type thermocouple pair 22. The third thermocouple pair interconnection layer 9 extends along the inner wall of the third groove 6 and forms an electrical connection with the p-type thermocouple pair 22. The n-type thermocouple pair 21 and the p-type thermocouple pair 22 are connected to form a via through the second thermocouple pair interconnection layer 8 , and then pass through the first thermocouple pair interconnection layer 7 and the third thermocouple pair interconnection layer 9 .

[0047] Step S7: Form a second dielectric layer 10 on the upper surface of the first dielectric layer 3 so that the second dielectric layer 10 completely covers the first thermocouple interconnect layer 7, the second thermocouple interconnect layer 8, and the third thermocouple interconnect layer 9. The second dielectric layer 10 can passivate, protect, and insulate the first thermocouple interconnect layer 7, the second thermocouple interconnect layer 8, and the third thermocouple interconnect layer 9, thereby providing excellent protection.

[0048] Step S8: Form an interdigital structure 12 and a third dielectric layer 11 on the lower surface of the piezoelectric substrate 1, with the third dielectric layer 11 completely covering the lower surface of the piezoelectric substrate 1 and the interdigital structure 12. By connecting an external device 14 to the interdigital structure 12, the filter can achieve functions such as electrical-to-acoustic signal conversion and frequency-selective filtering. The third dielectric layer 11 can provide passivation, protection, and insulation for the interdigital structure 12.

[0049] Step S9: Open a window in the second dielectric layer 10 to expose the first thermocouple pair interconnect layer 7 and the third thermocouple pair interconnect layer 9; open a window in the third dielectric layer 11 to expose the contact portion 121 of the interdigital structure 12, and grow a solder ball 13 on the contact portion 121 to obtain a constant temperature surface acoustic wave filter 100. The first thermocouple pair interconnect layer 7 and the third thermocouple pair interconnect layer 9 are connected to an external voltage via a wire 15 to achieve a power supply path. By opening a window in the third dielectric layer 11 to expose the contact portion 121 of the interdigital structure 12, growing a solder ball 13 on the contact portion 121, and connecting other external devices 14 through the solder ball 13, the filter can be applied to a variety of scenarios and has a wide range of uses.

[0050] Specifically, through the above steps S1 to S9, ions are respectively injected into the polysilicon 2 in the first groove 101 and the second groove 102 formed in the piezoelectric substrate 1 to form an n-type thermocouple pair 21 and a p-type thermocouple pair 22. When the ambient temperature changes, the voltage magnitude and direction at both ends of the thermocouple pair are controlled by the control circuit to heat or cool the resonator to maintain a constant temperature of the resonator, thereby eliminating the temperature drift of the surface acoustic wave resonator and improving the temperature stability and power tolerance performance of the surface acoustic wave filter.

[0051] In this embodiment, in step S1, the first trench 101 and the second trench 102 are both 2 μm to 10 μm deep. The formation process is reactive ion etching, wet etching, or dry etching. By providing trenches of appropriate depth, it is possible to easily form a pair of thermocouples of mutually appropriate thicknesses.

[0052] Reactive ion etching (RIE), a dry etching technique that combines physical sputtering and chemical reaction etching, is widely used in semiconductor and nanodevice manufacturing to precisely etch desired structures on substrate surfaces. RIE's vertical etching profile makes it suitable for structures with high aspect ratios, while also offering high etching precision and broad compatibility.

[0053] Wet etching involves a liquid chemical (etchant) reacting with the target material, selectively dissolving and removing the material to form a window pattern. Wet etching equipment is simple and low-cost, making it suitable for uniformly etching large areas. Its high selectivity and low cost make wet etching suitable for fabricating large, low-precision windows, such as contact holes and sacrificial layer releases.

[0054] Dry etching utilizes active particles (ions, free radicals) in plasma to physically sputter or chemically react with the material, achieving targeted material removal. It offers good anisotropy and high control precision. While selectivity is moderate, overetching time must be controlled to prevent mask penetration. Due to its anisotropy advantages, dry etching has become a core technology for submicron-level fine pattern processing, making it particularly irreplaceable in high-aspect-ratio structures and low-damage processes.

[0055] In this embodiment, the first trench 101 and the second trench 102 are both 4 μm deep. When the n-type thermocouple pair 21 and the p-type thermocouple pair 22 are both 4 μm deep, the constant temperature structure of the thermopile formed by the n-type thermocouple pair 21 and the p-type thermocouple pair 22 can ensure that the device is continuously cooled by the thermopile under high-power operating conditions, thereby reducing temperature drift and improving the power tolerance of the device.

[0056] In this embodiment, in step S2, the deposition method is a low-pressure chemical vapor deposition process. Low-pressure chemical vapor deposition (LPCVD) is a key process for preparing thin films in semiconductor manufacturing. By causing the reaction gases to undergo a chemical reaction under a low-pressure environment and depositing the resulting film on the wafer surface, LPCVD has the advantages of good film uniformity and strong step coverage.

[0057] In this embodiment, in step S3, the polycrystalline silicon 2 is ground by mechanical grinding or chemical mechanical polishing until the piezoelectric substrate 1 is exposed. This can improve grinding efficiency and production quality. Among them, mechanical grinding is a process of removing material through the action of physical mechanical force. The abrasive (such as diamond particles, silicon carbide) on the surface of the grinding tool (such as a hard grinding disc, a grinding wheel) contacts the processed material (polycrystalline silicon 2), and the friction and cutting force generated by the rotation or reciprocating motion of the grinding disc are used to grind away the polycrystalline silicon 2 layer by layer until the piezoelectric substrate 1 underneath is exposed. In this way, during the rough processing stage when the thickness of the polycrystalline silicon 2 layer is relatively thick, most of the material is quickly removed, reducing the workload of subsequent polishing.

[0058] Chemical Mechanical Polishing (CMP) is a composite process that combines chemical etching and mechanical grinding: chemical reagents in the polishing liquid react with polysilicon 2 to produce chemical reactions such as oxidation and dissolution, generating an easily removable softened layer, and the softened layer is removed by mechanical friction of the polishing pad, achieving high-precision material removal and surface flattening. ) oxidizes the surface of the polysilicon 2 to silicon dioxide. Acidic or alkaline components (such as citric acid or potassium hydroxide) accelerate the dissolution of the oxide layer. The polishing liquid composition must be tailored to the materials of the polysilicon 2 and the piezoelectric substrate 1. The polishing time must also be precisely controlled to prevent "over-polishing" that could damage the surface of the piezoelectric substrate 1. The combination of these two processes efficiently and precisely removes the polysilicon 2 layer, exposing the intact piezoelectric substrate 1 and laying the foundation for the subsequent fabrication of SAW devices or MEMS structures.

[0059] In this embodiment, the first dielectric layer 3, the second dielectric layer 10 and the third dielectric layer 11 are all made of SiN or Materials. Among them, SiN and The dielectric layer in a surface acoustic wave filter performs three core functions: acoustic property regulation, structural protection, and process compatibility. This allows for comprehensive optimization of the filter's frequency response, loss, and reliability. Material selection requires careful consideration of the application frequency band (low / high frequency), environmental requirements (temperature, humidity), and cost targets, taking into account properties such as acoustic velocity, impedance, and mechanical strength.

[0060] In this embodiment, in step S6 , windows are opened in the first dielectric layer 3 by etching using wet etching or dry etching.

[0061] Wet etching, with its simple equipment and low cost, is suitable for uniform etching of large areas. Its high selectivity and low cost make it suitable for fabricating large, low-precision windows, such as contact holes and sacrificial layer releases. Dry etching utilizes active particles (ions, free radicals) in a plasma to physically sputter or chemically react with the material, achieving targeted material removal with good anisotropy control and high precision.

[0062] In this embodiment, in step S8, the interdigital structure 12 is made of aluminum, titanium-aluminum alloy, aluminum-copper alloy, or a laminate of aluminum and titanium. By forming an alloy or laminate with elements such as titanium, the shortcomings of pure aluminum in terms of adhesion and mechanical strength can be further compensated, making it a preferred electrode material for micro-nano devices such as SAW filters. This allows the interdigital structure 12 to exhibit high acoustic-electrical coupling and low electrical resistance. Alternatively, the interdigital structure 12 can be made of a variety of materials, not limited to the aforementioned aluminum and titanium.

[0063] In this embodiment, in step S9, the second dielectric layer 10 and the third dielectric layer 11 are both etched by wet etching or dry etching to form windows. The etching method is simple, has good etching effect, and is convenient for quickly forming windows.

[0064] Example 2

[0065] See also Figure 2-Figure 3 As shown, an embodiment of the present invention provides a constant temperature surface acoustic wave filter 100 , which is manufactured based on the manufacturing method of the constant temperature surface acoustic wave filter 100 of the first embodiment.

[0066] In this embodiment, the constant temperature surface acoustic wave filter 100 includes a piezoelectric substrate 1, a first groove 101 and a second groove 102 recessed in the upper surface of the piezoelectric substrate 1, polycrystalline silicon 2 filled in the first groove 101 and the second groove 102, an n-type thermocouple pair 21 and a p-type thermocouple pair 22 formed in the polycrystalline silicon 2, a first dielectric layer 3 stacked and fixed on the upper surface of the piezoelectric substrate 1, a first groove 4, a second groove 5 and a third groove 6 passing through the first dielectric layer 3 and spaced apart, a first thermocouple pair interconnection layer 7 arranged in the first groove 4, a second thermocouple pair interconnection layer 8 arranged in the second groove 5, a third thermocouple pair interconnection layer 9 arranged in the third groove 6, a second dielectric layer 10 stacked and fixed on the upper surface of the first dielectric layer 3, an interdigitated structure 12 arranged on the lower surface of the piezoelectric substrate 1, and a third dielectric layer 11 stacked and fixed on the lower surface of the piezoelectric substrate 1. The first dielectric layer 3 completely covers the n-type thermocouple pair 21 and the p-type thermocouple pair 22. The third dielectric layer 11 also has two notches, each containing a contact portion 121 of the interdigital structure 12 for connection to an external device 14 via a solder ball 13. Ions are implanted into the polysilicon 2 within the first trench 101 and the second trench 102 formed in the piezoelectric substrate 1, respectively, to form the n-type thermocouple pair 21 and the p-type thermocouple pair 22. When the ambient temperature changes, the control circuit controls the magnitude and direction of the voltage across the thermocouple pair, heating or cooling the resonator to maintain a constant temperature. This prevents temperature drift of the surface acoustic wave resonator and improves the temperature stability and power handling performance of the surface acoustic wave filter.

[0067] It should be noted that the various embodiments described above with reference to the accompanying drawings are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Those skilled in the art should understand that any modifications or equivalent substitutions to the present invention that do not depart from the spirit and scope of the present invention are intended to be encompassed within the scope of the present invention. Furthermore, unless the context otherwise requires, words appearing in the singular include the plural form, and vice versa. Furthermore, unless otherwise specified, all or part of any embodiment may be used in combination with all or part of any other embodiment.

Claims

1. A method for preparing a constant temperature surface acoustic wave filter, characterized in that: The preparation method comprises the following steps: Step S1, selecting a piezoelectric substrate, and forming a first groove and a second groove on the upper surface of the piezoelectric substrate; Step S2: depositing polysilicon on the upper surface of the piezoelectric substrate to completely fill the first trench and the second trench; Step S3, grinding and thinning the polysilicon until the upper surface of the piezoelectric substrate is completely exposed; Step S4, implanting ions into the polysilicon in the first trench and the second trench to form an n-type thermocouple pair and a p-type thermocouple pair, respectively; Step S5, forming a first dielectric layer on the upper surface of the piezoelectric substrate, and making the first dielectric layer completely cover the piezoelectric substrate, the n-type thermocouple pair, and the p-type thermocouple pair; Step S6: Opening windows in the first dielectric layer to form a first groove, a second groove, and a third groove at intervals, exposing the n-type thermocouple pair and the p-type thermocouple pair through the first groove, the second groove, and the third groove, and forming a first thermocouple pair interconnection layer, a second thermocouple pair interconnection layer, and a third thermocouple pair interconnection layer in the first groove, the second groove, and the third groove, respectively; wherein the first thermocouple pair interconnection layer extends along the inner wall of the first groove and forms an electrical connection with the n-type thermocouple pair, the second thermocouple pair interconnection layer extends along the inner wall of the second groove and electrically connects the n-type thermocouple pair and the p-type thermocouple pair, and the third thermocouple pair interconnection layer extends along the inner wall of the third groove and forms an electrical connection with the p-type thermocouple pair; Step S7, forming a second dielectric layer on the upper surface of the first dielectric layer, so that the second dielectric layer completely covers the first thermocouple pair interconnection layer, the second thermocouple pair interconnection layer and the third thermocouple pair interconnection layer; Step S8, forming an interdigital structure and a third dielectric layer on the lower surface of the piezoelectric substrate, and making the third dielectric layer completely cover the lower surface of the piezoelectric substrate and the interdigital structure; Step S9: Open a window in the second dielectric layer to expose the first thermocouple pair interconnection layer and the third thermocouple pair interconnection layer; open a window in the third dielectric layer to expose the contact portion of the interdigital structure, and grow solder balls on the contact portion to obtain a constant temperature surface acoustic wave filter.

2. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 1, wherein: In the step S1 , the first trench and the second trench both have a depth of 2 μm-10 μm, and are formed by reactive ion etching, wet etching, or dry etching.

3. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 2, wherein: The depth of the first groove and the second groove are both 4 μm.

4. The method for preparing a constant temperature surface acoustic wave filter according to claim 1, wherein: In the step S2, the deposition method is a low pressure chemical vapor deposition process.

5. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 1, wherein: In step S3, the polysilicon is ground by mechanical grinding or chemical mechanical polishing until the piezoelectric substrate is exposed.

6. The method for preparing a constant temperature surface acoustic wave filter according to claim 1, wherein: The first dielectric layer, the second dielectric layer and the third dielectric layer are all made of SiN material or SiO2 material.

7. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 1, wherein: In step S6, windows are opened in the first dielectric layer by etching using wet etching or dry etching.

8. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 1, wherein: In step S8, the interdigital structure is made of aluminum, titanium-aluminum alloy, aluminum-copper alloy, or a laminated material of aluminum and titanium.

9. The method for preparing a temperature-controlled surface acoustic wave filter according to claim 1, wherein: In the step S9 , windows are opened in both the second dielectric layer and the third dielectric layer by etching using wet etching or dry etching.

10. A constant temperature surface acoustic wave filter, characterized in that: The constant temperature surface acoustic wave filter is manufactured based on the method for manufacturing a constant temperature surface acoustic wave filter according to any one of claims 1 to 9.

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