Surface acoustic wave filter with high temperature stability and its preparation method and application

Abstract

The present invention discloses a surface acoustic wave filter with high temperature stability, and a preparation method and application thereof. The surface acoustic wave filter includes a piezoelectric substrate having at least one plane; an interdigital transducer electrode, which is fixedly arranged on the plane of the piezoelectric substrate; an insulating protective layer, which has two opposite surfaces, one of which is laminated and bonded on the plane of the piezoelectric substrate and covers the interdigital transducer electrode; and a plurality of spaced protrusions are formed on the other surface. The surface acoustic wave filter has a low frequency temperature coefficient and a low Rayleigh wave parasitic response phenomenon, and has the advantages of stable working performance and long service life. In addition, the process conditions of the preparation method are controllable, which can effectively ensure that the prepared surface acoustic wave filter with high temperature stability has stable performance, high yield and low cost.

Description

Technical Field

[0001] The invention belongs to the field of microelectronic technology, and in particular relates to a surface acoustic wave filter with high temperature stability and a preparation method and application thereof. Background Art

[0002] Surface acoustic wave refers to the propagation of sound waves on the surface of elastic bodies. This wave is called elastic surface acoustic wave. The propagation speed of surface acoustic wave is about 100,000 times slower than that of electromagnetic wave. Surface acoustic wave filters generally use piezoelectric materials such as quartz crystals and piezoelectric ceramics. They are a kind of special filtering device made by using their piezoelectric effect and the physical characteristics of surface acoustic wave propagation. The so-called piezoelectric effect is the phenomenon that when a crystal is subjected to mechanical action, an electric field proportional to the pressure will be generated. When a crystal with piezoelectric effect is subjected to an electrical signal, it will also produce elastic deformation and emit mechanical waves (sound waves), which can convert electrical signals into sound signals. Since this sound wave only propagates on the surface of the crystal, it is called a surface acoustic wave.

[0003] The English abbreviation of surface acoustic wave filter is SAWF. Surface acoustic wave filter has small size, light weight, reliable performance and no need for complex adjustment. It is a key component for realizing adjacent frequency transmission in cable TV system. Surface acoustic wave filter has the advantages of flat frequency response, good rectangular coefficient and can use amplifier to compensate for level loss. Therefore, the surface acoustic wave filter has been widely used in the fields of communication and video.

[0004] The Gulf War at the end of the 20th century was the starting point of modern new wars, in which high-speed information transmission and confrontation played a key role. The control of high-speed information transmission is a new commanding height for both sides of modern new wars. Based on the advantages of SAWF, SAWF has become an important frequency component in military information transmission and confrontation equipment, including civilian information transmission equipment. However, due to the influence of the frequency temperature coefficient of conventional SAWF filters, when considering practical applications, the passband width needs to be greatly increased during design, which inevitably occupies a large amount of valuable spectrum resources. Moreover, due to the large frequency temperature coefficient of conventional SAWF filters, in military and civilian application environments with large temperature changes, changes in the electrical properties of conventional SAWF filters will deteriorate the performance indicators of military and civilian equipment. For example, SAWF filters are important components in the T / R channels of phased array radars. Due to heat or the influence of the external environment, each T / R channel of the phased array radar has a large temperature change, which causes the conventional SAWF to have changes in electrical performance parameters such as frequency drift due to the large frequency temperature coefficient, thereby causing phase changes in each channel unit of the phased array radar, thereby affecting the overall electrical performance of the phased array radar. In addition, it is found that the existing SAWF filter still has Rayleigh wave parasitic response phenomenon.

[0005] Although it is disclosed that a protective layer is covered on the fingers in the existing SAWF filter, the protective layer is only for protection and cannot effectively solve the Rayleigh wave parasitic response phenomenon of the SAWF filter, nor can it reduce the problem of the large frequency temperature coefficient of the SAWF filter. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and to provide a surface acoustic wave filter with high temperature stability and a preparation method thereof, so as to solve the shortcomings of the existing SAWF in that the temperature coefficient is large and causes changes in electrical performance parameters such as frequency drift.

[0007] In order to achieve the above-mentioned object, the present invention provides a surface acoustic wave filter with high temperature stability. The surface acoustic wave filter with high temperature stability comprises:

[0008] A piezoelectric substrate having at least one plane;

[0009] An IDT electrode, wherein the IDT electrode is fixedly disposed on the plane of the piezoelectric substrate;

[0010] The insulating protective layer has two opposite surfaces, one of which is laminated and bonded on the plane of the piezoelectric substrate and covers the IDT electrodes; and the other surface is formed with a plurality of protrusions distributed at intervals.

[0011] In another aspect, the present invention provides a method for preparing a surface acoustic wave filter with high temperature stability. The method for preparing a surface acoustic wave filter with high temperature stability comprises the following steps:

[0012] An interdigital transducer electrode is prepared on a plane of a piezoelectric substrate;

[0013] Depositing an insulating protective film layer on the plane of the piezoelectric substrate, and making the insulating protective film layer cover the interdigital transducer electrodes;

[0014] The outer surface of the insulating protection film layer is etched so that a plurality of protrusions distributed at intervals are formed on the surface.

[0015] In another aspect, the present invention also provides the application of the surface acoustic wave filter with high temperature stability of the present invention, which is applied in radar, mobile communication, channelized receiver, and remote sensing and telemetry system.

[0016] Compared with the prior art, the surface acoustic wave filter with high temperature stability of the present invention is provided with an insulating protective layer covering the electrodes of the interdigital transducer, and by controlling the protrusions distributed on the outer surface of the insulating protective layer, on the one hand, the frequency temperature coefficient of the surface acoustic wave filter with temperature stability can be reduced, and the frequency temperature coefficient can even be better than -4ppm / ℃, or even close to 0; on the other hand, the insulating protective layer can cooperate with components such as the piezoelectric substrate and the interdigital transducer electrodes to effectively reduce the Rayleigh wave parasitic response of the surface acoustic wave filter with high temperature stability, or even eliminate it. Secondly, since the insulating protective layer is provided on the surface of the interdigital transducer electrodes, it can effectively play a protective role, thereby improving the corrosion resistance of the interdigital transducer, thereby improving the stability and service life of the working performance of the surface acoustic wave filter with high temperature stability.

[0017] The method for preparing a surface acoustic wave filter with high temperature stability of the present invention adopts the method of first depositing an insulating protective film layer, and then directional etching the outer surface of the insulating protective film layer to form a surface with spaced protrusions, thereby giving the prepared surface acoustic wave filter with high temperature stability a low frequency temperature coefficient and a low Rayleigh wave parasitic response phenomenon, and can play a protective role, so as to give the prepared surface acoustic wave filter with high temperature stability the advantages of stable working performance and long service life. In addition, the process conditions of the preparation method are controllable, which can effectively ensure that the prepared surface acoustic wave filter with high temperature stability has stable performance, high yield and low cost.

[0018] Because the surface acoustic wave filter with high temperature stability of the present invention has low frequency temperature coefficient and low Rayleigh wave parasitic response phenomenon, and has stable working performance and long service life, the surface acoustic wave filter with high temperature stability can be effectively applied to the field of communication and video related devices, thereby improving the working performance and working stability of the corresponding devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of a surface acoustic wave filter with high temperature stability according to an embodiment of the present invention;

[0020] Figure 2 is a curve diagram showing the relationship between the electromechanical coupling coefficient and the Euler angle of the piezoelectric substrate of the surface acoustic wave filter with high temperature stability according to an embodiment of the present invention;

[0021] Figure 3 is a relationship diagram between the electromechanical coupling coefficient of the surface acoustic wave filter with high temperature stability and the thickness hmet / λ of the interdigital transducer electrode in an embodiment of the present invention;

[0022] Figure 4: is a relationship diagram between the admittance of the surface acoustic wave filter with high temperature stability and the outer surface morphology of the insulating protective layer according to an embodiment of the present invention; wherein, Figure 4 a is a morphology diagram when the ratio SR of the top width A of the protrusion on the outer surface of the insulating protective layer to the root width B is 0.78; Figure 4 b is a morphology diagram when the ratio SR of the top width A of the protrusion on the outer surface of the insulating protective layer to the root width B is 0.38; Figure 4 c is the admittance diagram of the morphology when the SR of the outer surface of the insulating protective layer is 0.78; Figure 4 d is the admittance diagram of the morphology when the SR of the outer surface of the insulating protective layer is 0.38;

[0023] Figure 5 is a curve diagram showing the relationship between the frequency temperature coefficient of the surface acoustic wave filter with high temperature stability and the total thickness of the insulating protection layer in an embodiment of the present invention;

[0024] Figure 6 It is a schematic flow chart of a method for preparing a surface acoustic wave filter with high temperature stability according to an embodiment of the present invention;

[0025] Figure 7 This is the FT-IR spectrum of the surface acoustic wave filter at 400-2000cm-1 after the insulating protective film layer is deposited. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] On the one hand, an embodiment of the present invention provides a surface acoustic wave filter with high temperature stability (hereinafter referred to as a surface acoustic wave filter). The structure of the surface acoustic wave filter with high temperature stability is as follows: Figure 1 As shown, it includes a piezoelectric substrate 1 , an interdigital transducer electrode 2 and an insulating protection layer 3 .

[0028] The piezoelectric substrate 1 contained in the surface acoustic wave filter has at least one plane 11, and the plane 11 is used to set the interdigital transducer electrode 2. In one embodiment, the material of the piezoelectric substrate 1 is at least one of LiTaO3. In addition, it is found that the Euler angle of the material of the piezoelectric substrate 1 has an influence on the electromechanical coupling system. In a further embodiment, the Euler angle (0, θ, 0) θ of the material of the piezoelectric substrate 1 is any one of 38°, 41°, and 42°. Specifically, Figure 2As shown in FIG. 1 , when the material and thickness of the insulating protective layer 3 remain unchanged, such as SiO2, and its thickness is 0.3λ (λ is the wavelength of the acoustic wave), and the material of the IDT electrode 2 is copper and the electrode thickness is 0.05λ, controlling the Euler angle of the piezoelectric substrate 1 material LiTaO3 will affect the electromechanical coupling coefficient of the SAW filter. Specifically, the relationship between the Euler angle of LiTaO3 and the electromechanical coupling coefficient of the SAW filter is as follows: Figure 2 As shown. Figure 2 It can be known that when the material of the piezoelectric substrate 1 is LiTaO3, and the cut shape of LiTaO3 is about 128°, that is, the Euler angle (0, θ, 0)θ of LiTaO3 is 38°. In addition, the thickness of the piezoelectric substrate 1 can be a conventional thickness. Therefore, by controlling the material type and characteristics of the piezoelectric substrate 1 such as the Euler angle and other factors, the piezoelectric substrate 1 and other devices such as the interdigital transducer electrode 2 and the insulating protective layer play a synergistic role, thereby reducing the frequency temperature coefficient of the surface acoustic wave filter and the Rayleigh wave parasitic response phenomenon, so as to improve the coupling coefficient of the surface acoustic wave filter.

[0029] The interdigital transducer electrode 2 contained in the surface acoustic wave filter is fixedly arranged on the plane 11 of the piezoelectric substrate 1; the interdigital transducer electrode 2 can be designed as needed and laid out on the plane 11 according to the requirements of the surface acoustic wave filter. In one embodiment, the material of the interdigital transducer electrode 2 can be any one of Al, Cu, Ti or an alloy of Al and Cu. The selection of the material of the interdigital transducer electrode 2 works in synergy with the piezoelectric substrate 1 and other devices to improve the frequency temperature coefficient and Rayleigh wave parasitic response phenomenon of the surface acoustic wave filter, so as to reduce the coupling coefficient of the surface acoustic wave filter. In addition, the study found that based on the structure of the surface acoustic wave filter, adjusting the thickness of the interdigital transducer electrode 2 (denoted as hmet) will also affect the electromechanical coupling coefficient of the surface acoustic wave filter. The relationship between the hmet and the electromechanical coupling coefficient is as shown in FIG. Figure 3 As shown. Figure 3 It can be seen that, under the premise of a certain thickness of the insulating protective layer 3, the electromechanical coupling coefficient decreases as the value of hmet increases. Therefore, the preferred thickness hmet of the IDT electrode 2 is 0.045-0.055λ, preferably 0.05λ.

[0030] The insulating protective layer 3 included in the surface acoustic wave filter has two opposite surfaces, one of which is laminated and bonded on the plane 11 of the piezoelectric substrate 1 and covers the IDT electrode 2; and the other surface is formed with a plurality of protrusions 31 distributed at intervals. In this way, since the insulating protective layer 3 covers the IDT electrode 2, it can effectively play the role of a protective layer on the one hand, isolating the IDT electrode 2 from adverse factors such as water vapor in the outside world, and ensuring the stability of the working performance of the IDT electrode 2, such as improving its corrosion resistance and other properties; on the other hand, the embodiment of the present invention can reduce the frequency temperature coefficient of the surface acoustic wave filter by changing the characteristics of the outer surface of the insulating protective layer 3, specifically forming a plurality of protrusions 31 distributed at intervals on the outer surface of the insulating protective layer 3, such as by simultaneously adjusting and controlling the performance and materials of the IDT electrode 2 and the piezoelectric substrate 1, so that the three play a synergistic role, and can even significantly reduce the frequency temperature coefficient of the surface acoustic wave filter, and can also effectively reduce the Rayleigh wave parasitic response of the surface acoustic wave filter.

[0031] In addition, further studies have found that by controlling the shape and size of the protrusions 31 on the outer surface of the insulating protective layer 3, the frequency temperature coefficient of the surface acoustic wave filter can be significantly reduced, such as better than -4ppm / °C, or even close to 0. It is also possible to reduce the Rayleigh wave parasitic response of the surface acoustic wave filter. Therefore, in one embodiment, the shape of a single protrusion 31 is controlled as follows: the top width (A) is smaller than the root width (B), and the side surface of a single protrusion 31 is a slope. In a further embodiment, the ratio SR of the top width (A) to the root width (B) of a single protrusion 31 is 0.3-0.4, and the preferred ratio SR is 0.38. In another embodiment, the height of the protrusion 31 is 1.0-1.1μm, and the height is the vertical distance from the top to the root of a single protrusion 31. As in a specific embodiment, the relationship between the SR value and the admittance of the surface acoustic wave filter is as follows: Figure 4 As shown. Figure 4 When the material of the piezoelectric substrate 1 is LiTaO3, the material of the IDT electrode 2 is copper, and the material of the insulating protective layer 3 is SiO2, the SR is controlled to be 0.78. Figure 4 a, by the SAW filter admittance Figure 4 c shows that the Rayleigh response phenomenon occurs; when SR is 0.38, Figure 4 b, the admittance of the SAW filter Figure 4 d, it can be seen that there is no Rayleigh response phenomenon, and the Rayleigh response basically disappears.

[0032] In another embodiment, the spacing between adjacent protrusions 31 is controlled to be 0.3-0.8 μm (referring to the spacing between the roots of adjacent protrusions 31). For example, the position where a single protrusion 31 is formed can correspond to a single electrode of the interdigital transducer electrode 2, that is, the single protrusion 31 is set directly above the single electrode of the interdigital transducer electrode 2. In this way, the spacing between the two adjacent protrusions 21 is consistent with the spacing between adjacent metal interdigital strips contained in the interdigital transducer electrode 2. In addition, studies have found that the total thickness of the insulating protective layer 3 (denoted as hsio2) will also affect the frequency temperature coefficient of the surface acoustic wave filter. The relationship between the thickness hsio2 of the insulating protective layer 3 and the frequency temperature coefficient of the surface acoustic wave filter is as follows: Figure 5 As shown. Figure 5 It can be seen that when the thickness hmet of the IDT electrode 2 is constant, the frequency temperature coefficient of the SAW filter decreases with the increase of the hsio2 value. Therefore, in one embodiment, the total thickness hsio2 of the insulating protection layer 3, that is, the vertical thickness from the top A of the protrusion 31 to the surface of the insulating protection layer 3 combined with the plane of the piezoelectric substrate 1 is 29-31%λ, preferably 30%λ.

[0033] Therefore, the surface acoustic wave filter in the above embodiments effectively reduces the frequency temperature coefficient and Rayleigh wave parasitic response of the surface acoustic wave filter by setting the insulating protective layer 3 and setting a plurality of protrusions distributed at intervals on the outer surface, and by the synergistic effect of the insulating protective layer 3, the interdigital transducer electrode 2 and the piezoelectric substrate 1. By controlling and optimizing the size, shape, distribution spacing and position of the protrusions 31, the frequency temperature coefficient of the surface acoustic wave filter can be significantly reduced, and the Rayleigh wave parasitic response of the surface acoustic wave filter can also be effectively reduced.

[0034] Accordingly, the embodiment of the present invention also provides a method for preparing the surface acoustic wave filter with high temperature stability as described above. The surface acoustic wave filter preparation method is combined with Figure 1 The process flow of the preparation method of the surface acoustic wave filter is as follows: Figure 6 As shown, it includes the following steps:

[0035] S01: preparing an interdigital transducer electrode 2 on a plane 11 of a piezoelectric substrate 1;

[0036] S02: depositing an insulating protective film layer on the plane 11 of the piezoelectric substrate 1, and making the insulating protective film layer cover the interdigital transducer electrode 2;

[0037] S03: etching the outer surface of the insulating protection film layer so that a plurality of protrusions 31 distributed at intervals are formed on the surface.

[0038] Specifically, in the above step S01, the method for preparing the IDT electrode 2 on the piezoelectric substrate 1 can be prepared according to the existing method for preparing the IDT electrode. In an embodiment of the present invention, by controlling the process conditions of the method for preparing the IDT electrode 2, the thickness of the IDT electrode 2 is preferably controlled to be 0.045-0.055λ, preferably 0.05λ. Among them, the material used to prepare the IDT electrode 2 can be any one of Al, Cu, Ti or Al, Cu alloy as described above. The material and thickness of the piezoelectric substrate 1 can be LiTaO3 as described above. In the step S02, the method for depositing the insulating protective film layer can be but not only formed by magnetron sputtering. When the insulating protective film layer is formed by magnetron sputtering deposition, the inventors have found that changes in the conditions of magnetron sputtering will lead to changes in the elastic constant of the insulating protective film layer, thereby affecting the frequency temperature coefficient of the prepared surface acoustic wave filter.

[0039] In a specific embodiment, the material of the insulating protective film layer is SiO2, that is, after depositing the SiO2 film on the piezoelectric substrate 1, the 400-2000 cm -1 The FT-IR spectrum of the deposited SiO2 film showed three main peaks, such as Figure 7 The relationship between the measured peaks and the molecular vibration modes, including the rocking mode (ω1: 450cm -1 ), bending mode (ω3: 800cm -1 ) and stretching mode (ω4: 1070cm -1 ).

[0040] When different magnetron sputtering process parameters are used to deposit SiO2 films with a film thickness of 0.3λ, different peak frequencies of ω3 and ω4 are obtained. The corresponding peak frequencies are summarized in Table 1. The peak frequencies ω3 and ω4 are 810.9-815.5cm -1 and 1065.6-1079.2cm -1 The elastic constant changes by 7% when the sputtering process parameters change. Through the above research, when the sputtering process parameters change, the temperature coefficient of the elastic constant will change accordingly, thus causing the change of TCF.

[0041] Table 1 FT-IR spectrum of SiO2 deposited films

[0042]

[0043]

[0044] Therefore, in one embodiment, when the insulating protective film layer is deposited by magnetron sputtering, for example, when a SiO2 film is deposited, the conditions for magnetron sputtering deposition are: the RF magnetron discharge is controlled at 10 -1 ~10 -2 Pa, the magnetic field strength B of the magnetron target surface is controlled between 30 and 50 mT, and the electric field orthogonal to the magnetic field in the vacuum chamber is controlled between 500 and 700 V. Thus, the structure of the insulating protective film layer deposited can be controlled by controlling the input process parameters of magnetron sputtering, thereby minimizing the TCF of the surface acoustic wave filter. For example, the temperature frequency coefficient is controlled to vary between -20 and 0 ppm / °C.

[0045] In addition, after the insulating protective film layer is deposited and formed, the method further includes a step of flattening the outer surface of the insulating protective film layer.

[0046] In the step S03, the insulating protective film layer formed by deposition is etched to obtain the above and attached Figure 1 The insulating protective layer 3 shown in FIG. Figure 1 As shown in , there are formed a plurality of protrusions 31 distributed at intervals. The size and distribution position of the protrusions 31 are as described above, and will not be repeated here for the sake of space saving.

[0047] In one embodiment, etching the outer surface of the insulating protective film layer 3 comprises the following steps:

[0048] (1) according to the design requirements of the spacing between adjacent protrusions 31, the outer surface of the insulating protective film layer is divided into an etching area and a non-etching area, and an anti-etching protective film layer is covered on the surface of the non-etching area; and

[0049] (2) Directional etching is performed on the etching area on the outer surface of the insulating protective film layer using an inductively coupled plasma etching process.

[0050] In step (1), the non-etched area is the area where the protrusions 31 are formed after etching. The protective film layer is used to prevent the non-etched area from being etched during the etching process, so that the etching gas only etches the etched area, thereby forming a plurality of protrusions 31 that are distributed in a simple manner.

[0051] The process conditions for the directional etching treatment in the inductively coupled plasma (ICP) etching process in step (2) are preferably as follows: the etchant used is SF6, the passivating polymer generator is C4F8, and the SF6 and C4F8 are alternately introduced into the etching chamber. ICP etching uses SF6 as the etchant and C4F8 as the passivating polymer generator. Under the action of inductive glow discharge, SF6 ionizes into a mixture of multiple components such as electrons, charged ions, atoms or atomic groups. These particles will chemically react with the material SiO2 of the insulating protective film layer. During the passivation process, C4F8 gas is introduced into the reaction chamber, and the plasma polymerization process is completed under the action of plasma. This process is highly isotropic, so a layer of polymer protective film will be evenly covered on the surface of SiO2 and in the deep grooves of the structure. In the subsequent etching process, the active gas in the reaction chamber is converted into SF6 and decomposed into SF + and SF - The electric field accelerates the positive ions, thus increasing the ion energy in the vertical direction, causing the polymer area parallel to the substrate surface to be removed preferentially. With this high orientation, the silicon surface at the bottom of the deep trench is preferentially exposed to the F - The reaction generates SiF4 which is then etched.

[0052] In terms of etching depth control, it is achieved by increasing the etching power and longitudinal bias during the process. In the ICP etching process, anisotropy is achieved by combining the etching effect of reactive ions on the bottom surface of the groove and the inhibition effect of polymer on the side wall. Reactive ions will be deflected under the action of the lateral electric field. At the same power, as the etching depth of the groove or hole increases, it is difficult for reactive ions in the plasma to reach the etching surface. Therefore, as the etching depth increases, the etching power and longitudinal bias during the process are increased proportionally to compensate for the lateral electric field deflection effect to achieve deep groove etching.

[0053] In terms of etching angle control, it is achieved by adjusting the ratio of etching and protective gas. Experiments have found that the main factor affecting the etching angle is the flow rate of the process gas. The purpose of controlling the etching angle can be achieved by adjusting the flow ratio of the two gases SF6 and C4F8 that are alternately introduced. Reducing the SF6 flow rate and increasing the C4F8 flow rate can achieve a positive V-shaped groove and achieve precise control of the ratio A / B of the top width A of the protrusion 31 and the root width B, so as to meet the requirements for optimizing the control of the surface morphology of the protrusion 31 of the insulating protective layer 3. Therefore, in one embodiment, the process conditions of the directional etching treatment are as follows:

[0054] The flow rate of the SF6 gas flow is 30-60 SCCM;

[0055] The air flow rate of the C4F8 is 30-60 SCCM;

[0056] Etching power is 300-400W;

[0057] The longitudinal bias voltage is 30-35VDC.

[0058] By controlling the directional etching process, directional etching is achieved, thereby achieving precise control over the size and shape of the protrusion 31 formed by etching.

[0059] Therefore, the surface acoustic wave filter preparation method described above performs a directional etching process on the outer surface of the insulating protective film layer to form a surface with spaced protrusions 31, thereby giving the prepared surface acoustic wave filter a low frequency temperature coefficient and a low Rayleigh wave parasitic response phenomenon, and can play a protective role, so as to give the prepared surface acoustic wave filter the advantages of stable working performance and long service life. In addition, the process conditions of the preparation method are controllable, which can effectively ensure that the prepared surface acoustic wave filter with high temperature stability has stable performance, high yield and low cost.

[0060] Based on the surface acoustic wave filter and its preparation method described above, the surface acoustic wave filter has the advantages of low frequency temperature coefficient and low Rayleigh wave parasitic response phenomenon, as well as stable working performance and long service life. Therefore, the surface acoustic wave filter plays a good role in suppressing high-order harmonics, image information, transmission leakage signals and various parasitic interferences of electronic information equipment, and can achieve filtering of amplitude-frequency and phase-frequency characteristics of any required accuracy. For example, the upper limit frequency of use on the surface acoustic wave filter can be increased to 2.5GHz~3GHz. Thereby promoting the surface acoustic wave filter to be more widely used in the field of anti-EMI. For example, the frequency temperature coefficient (TCF) of conventional filters is usually about -45ppm / ℃, while the surface acoustic wave filter is reduced to above -4ppm / ℃, even close to 0. Moreover, the Rayleigh wave parasitic response is low or even disappears. Therefore, the surface acoustic wave filter can be widely used in radar, mobile communications, channelized receivers, remote sensing and telemetry systems, thereby improving the working performance and stable working performance of the corresponding devices.

[0061] The present invention is now further described in detail with reference to specific examples. In the following embodiments, " / " means stacking combination.

[0062] 1. SAW filter structure embodiment

[0063] Embodiment 11

[0064] This embodiment provides a surface acoustic wave filter and a method for manufacturing the same. The structure of the surface acoustic wave filter is as follows: Figure 1As shown, the structure of the surface acoustic wave filter is: piezoelectric substrate 1 / interdigital transducer electrode 2 / insulating protection layer 3. The piezoelectric substrate 1 is LiTaO3, and its Euler angle (0, θ, 0) θ is 38°; the material of the interdigital transducer electrode 2 is copper, and its thickness is 0.05λ; the material of the insulating protection layer 3 is SiO2, and its total thickness is 0.3λ, and a plurality of spaced protrusions 31 are formed on the outer surface of the insulating protection layer 3, and the positions where the protrusions 31 are formed correspond to the single electrodes of the interdigital transducer electrode 2, the spacing between adjacent protrusions 31 is 0.6μm, the top width A of the protrusion 31 is smaller than the root width B, and the ratio SR of A to B is 0.38.

[0065] Example 12

[0066] This embodiment provides a surface acoustic wave filter and a method for manufacturing the same. The structure of the surface acoustic wave filter is as follows: Figure 1 As shown, the structure of the surface acoustic wave filter is: piezoelectric substrate 1 / interdigital transducer electrode 2 / insulating protection layer 3. The piezoelectric substrate 1 is LiTaO3, and its Euler angle (0, θ, 0) θ is 42°; the material of the interdigital transducer electrode 2 is Al and Cu alloy, and its thickness is 0.045λ; the material of the insulating protection layer 3 is SiO2, and its total thickness is 0.31λ, and a plurality of spaced protrusions 31 are formed on the outer surface of the insulating protection layer 3, and the positions where the protrusions 31 are formed correspond to the single electrodes of the interdigital transducer electrode 2, the spacing between adjacent protrusions 31 is 0.8μm, the top width A of the protrusion 31 is smaller than the root width B, and the ratio of A to B SR=0.3.

[0067] Embodiment 13

[0068] This embodiment provides a surface acoustic wave filter and a method for manufacturing the same. The structure of the surface acoustic wave filter is as follows: Figure 1 As shown, the structure of the surface acoustic wave filter is: piezoelectric substrate 1 / interdigital transducer electrode 2 / insulating protection layer 3. The piezoelectric substrate 1 is LiTaO3, and its Euler angle (0, θ, 0) θ is 41°; the material of the interdigital transducer electrode 2 is Al, and its thickness is 0.055λ; the material of the insulating protection layer 3 is SiO2, and its total thickness is 0.29λ, and a plurality of spaced protrusions 31 are formed on the outer surface of the insulating protection layer 3, and the positions where the protrusions 31 are formed correspond to the single electrodes of the interdigital transducer electrode 2, the spacing between adjacent protrusions 31 is consistent with the spacing between adjacent electrodes (the electrodes are actually interdigital electrode metal strips), the top width A of the protrusion 31 is smaller than the root width B, and the ratio SR of A to B is 0.4.

[0069] 2. Example of preparation method of surface acoustic wave filter

[0070] Embodiment 21

[0071] This embodiment provides a method for preparing the surface acoustic wave filter in Embodiment 11. The preparation method comprises the following steps:

[0072] S1: preparing an IDT copper electrode 2 on a plane 11 of a LiTaO3 piezoelectric substrate 1; controlling the thickness of the IDT copper electrode 2 to be more preferably 0.05%λ;

[0073] S2: depositing a SiO2 insulating protective film layer on the plane 11 of the piezoelectric substrate 1 by a magnetron sputtering process, and making the insulating protective film layer cover the interdigital transducer electrode 2; wherein the total thickness is controlled to be 0.3λ, and the process conditions of the magnetron sputtering process are that the RF magnetron discharge is controlled at 10 -1 ~10 -2 Pa, the magnetic field strength B of the magnetron target surface is controlled at 40mT, and the electric field orthogonal to the magnetic field in the vacuum chamber is controlled at 600V;

[0074] S03: performing ICP etching on the outer surface of the insulating protective film layer, so that a plurality of spaced protrusions 31 are formed on the surface; wherein the etchant used in the ICP etching is SF6, and the passivation polymer generator is C4F8, and the SF6 and C4F8 are alternately introduced into the etching chamber; and the process conditions of the directional etching treatment are as follows:

[0075] The SF6 gas flow rate is 45 SCCM;

[0076] The air flow rate of the C4F8 is 45 SCCM;

[0077] The etching power is 350W;

[0078] The longitudinal bias voltage is 30 VDC.

[0079] Embodiment 22

[0080] This embodiment provides a method for preparing the surface acoustic wave filter in Embodiment 12. The preparation method comprises the following steps:

[0081] S1: preparing an Al and Cu alloy electrode 2 of an interdigital transducer on a plane 11 of a LiTaO3 piezoelectric substrate 1;

[0082] S2: depositing a SiO2 insulating protective film layer on the plane 11 of the piezoelectric substrate 1 by a magnetron sputtering process, and making the insulating protective film layer cover the interdigital transducer electrode 2; wherein the process conditions of the magnetron sputtering process are that the radio frequency magnetron discharge is controlled at 10 -1 ~10 -2Pa, the magnetic field strength B of the magnetron target surface is controlled at 30mT, and the electric field orthogonal to the magnetic field in the vacuum chamber is controlled at 500V;

[0083] S03: performing ICP etching on the outer surface of the insulating protective film layer, so that a plurality of spaced protrusions 31 are formed on the surface; wherein the etchant used in the ICP etching is SF6, and the passivation polymer generator is C4F8, and the SF6 and C4F8 are alternately introduced into the etching chamber; and the process conditions of the directional etching treatment are as follows:

[0084] The flow rate of the SF6 gas flow is 60 SCCM;

[0085] The air flow rate of the C4F8 is 30 SCCM;

[0086] The etching power is 400W;

[0087] The longitudinal bias voltage is 30 VDC.

[0088] Embodiment 23

[0089] This embodiment provides a method for preparing the surface acoustic wave filter in Embodiment 13. The preparation method comprises the following steps:

[0090] S1: preparing an interdigital transducer Al electrode 2 on a plane 11 of a LiTaO3 piezoelectric substrate 1;

[0091] S2: depositing a SiO2 insulating protective film layer on the plane 11 of the piezoelectric substrate 1 by a magnetron sputtering process, and making the insulating protective film layer cover the interdigital transducer electrode 2; wherein the process conditions of the magnetron sputtering process are that the radio frequency magnetron discharge is controlled at 10 -1 ~10 -2 Pa, the magnetic field strength B of the magnetron target surface is controlled at 50mT, and the electric field orthogonal to the magnetic field in the vacuum chamber is controlled at 700V;

[0092] S03: performing ICP etching on the outer surface of the insulating protective film layer, so that a plurality of spaced protrusions 31 are formed on the surface; wherein the etchant used in the ICP etching is SF6, and the passivation polymer generator is C4F8, and the SF6 and C4F8 are alternately introduced into the etching chamber; and the process conditions of the directional etching treatment are as follows:

[0093] The flow rate of the SF6 gas flow is 30 SCCM;

[0094] The air flow rate of the C4F8 is 60 SCCM;

[0095] The etching power is 300W;

[0096] The longitudinal bias voltage is 35VDC.

[0097] Comparative Example

[0098] Conventional surface acoustic wave filters are commercially available.

[0099] 3. SAW filter related performance test

[0100] The surface acoustic wave filters provided in Examples 11-13 and the commercially available conventional surface acoustic wave filters provided in the comparative example were subjected to the following relevant performance tests, and the test results are shown in the following Table 1:

[0101] Table 1

[0102]

[0103] In addition, the surface acoustic wave filters provided in Examples 12 and 13 have similar performance test results as shown in Table 1. Therefore, it can be seen from the relevant performance test results in Table 1 that the surface acoustic wave filter of this embodiment has a low frequency temperature coefficient and a low Rayleigh wave parasitic response phenomenon, and has stable working performance and a long service life.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave filter with high temperature stability, characterized in that: include: A piezoelectric substrate having at least one plane; An IDT electrode, wherein the IDT electrode is fixedly disposed on the plane of the piezoelectric substrate; An insulating protective layer, the insulating protective layer having two opposite surfaces, one of which is laminated and bonded on the plane of the piezoelectric substrate and covers the interdigital transducer electrode; and the other surface is formed with a plurality of protrusions distributed at intervals; The total thickness of the insulating protective layer is 0.29-0.31λ, where λ is the wavelength of the acoustic wave; the thickness of the interdigital transducer electrode is 0.045-0.055λ, where λ is the wavelength of the acoustic wave; the Euler angle (0, θ, 0) θ of the material of the piezoelectric substrate is 38 0 , 41 0 , 42 0 Any value in ; The ratio of the top width to the root width of a single protrusion is 0.3-0.4; the height of the protrusion is 1.0-1.1 μm; The height is the vertical distance from the top to the root of a single protrusion.

2. The surface acoustic wave filter according to claim 1, characterized in that: The top width of a single protrusion is smaller than the root width, and the side surface of a single protrusion is an inclined surface.

3. The surface acoustic wave filter according to any one of claims 1 to 2, characterized in that: The spacing between adjacent protrusions is 0.3-0.8 μm, and the spacing between two adjacent protrusions is consistent with the spacing between adjacent metal interdigitated strips; and / or The position where a single protrusion is formed corresponds to a single electrode of the interdigital transducer electrode.

4. The surface acoustic wave filter according to any one of claims 1 to 2, characterized in that: The material of the insulating protective layer is at least one of silicon dioxide and silicon nitride; The material of the IDT electrodes is any one of Al, Cu, Ti, or an alloy of Al and Cu; The material of the piezoelectric substrate is LiTaO3.

5. The method for preparing the surface acoustic wave filter according to any one of claims 1 to 4, comprising the following steps: An interdigital transducer electrode is prepared on a plane of a piezoelectric substrate; Depositing an insulating protective film layer on the plane of the piezoelectric substrate, and making the insulating protective film layer cover the interdigital transducer electrodes; Etching the outer surface of the insulating protective film layer so that a plurality of protrusions distributed at intervals are formed on the surface; in, Etching the outer surface of the insulating protective film layer comprises the following steps: dividing the outer surface of the insulating protective film layer into an etching area and a non-etching area according to the design requirements of the spacing between adjacent protrusions, and covering the surface of the non-etching area with an anti-etching protective film layer; Then, an inductively coupled plasma etching process is used to perform directionally etching treatment on the etching area on the outer surface of the insulating protective film layer; The etchant used in the directional etching process is SF6, the passivation polymer generator is C4F8, and the SF6 and C4F8 are alternately introduced into the etching chamber; and the process conditions of the directional etching process are as follows: The SF6 gas flow rate is 30-60 SCCM; The air flow rate of the C4F8 is 30-60 SCCM; Etching power is 300-400 W; The longitudinal bias voltage is 30-35 VDC.

6. Application of the surface acoustic wave filter according to any one of claims 1 to 4 in radar, mobile communication, channelized receiver, and remote sensing and telemetry system.

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