CN210986061U - Acoustic surface wave filter with high temperature stability - Google Patents
Acoustic surface wave filter with high temperature stability Download PDFInfo
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- CN210986061U CN210986061U CN201921256970.2U CN201921256970U CN210986061U CN 210986061 U CN210986061 U CN 210986061U CN 201921256970 U CN201921256970 U CN 201921256970U CN 210986061 U CN210986061 U CN 210986061U
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Abstract
The utility model discloses a sound surface wave filter of high temperature stability. The surface acoustic wave filter comprises a piezoelectric substrate and at least one flat surface; an interdigital transducer electrode fixedly disposed on the plane of the piezoelectric substrate; an insulating protective layer having two opposite surfaces, one of which is bonded on the plane of the piezoelectric substrate in a laminated manner and covers the interdigital transducer electrodes; the other surface is provided with a plurality of bulges distributed at intervals. The surface acoustic wave filter has the advantages of low frequency temperature coefficient, low Rayleigh wave spurious response, stable working performance, long service life and the like.
Description
Technical Field
The utility model belongs to the technical field of the microelectronics, concretely relates to sound surface wave filter of high temperature stability.
Background
Surface acoustic wave refers to the propagation of an acoustic wave on the surface of an elastomer, and this wave is called an elastic surface acoustic wave. The propagation velocity of surface acoustic waves is about 10 ten thousand times smaller than the velocity of electromagnetic waves. The surface acoustic wave filter is a special filter device which is made of piezoelectric materials such as quartz crystal, piezoelectric ceramics and the like by utilizing the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. The piezoelectric effect is a phenomenon that when a crystal is subjected to a mechanical action, an electric field proportional to a pressure is generated. When the crystal with piezoelectric effect is acted by electric signal, it will also produce elastic deformation to send out mechanical wave (sound wave), i.e. the electric signal can be converted into sound signal. Since such an acoustic wave propagates only on the crystal surface, it is called a surface acoustic wave.
The surface acoustic wave filter is abbreviated as SAWF in English, and has the advantages of small volume, light weight, reliable performance and no need of complex adjustment. The key device for realizing adjacent frequency transmission in the cable television system. The surface acoustic wave filter has the advantages of flat frequency response, good rectangular coefficient, capability of compensating level loss by using an amplifier and the like. Therefore, the surface acoustic wave filter has been widely applied to the fields of communication and video.
The gulf war at the end of the 20 th century is the starting point of the modern novel war, wherein high-speed information transmission and antagonism play a key role, and the control on the high-speed information transmission is a new control point for competition of enemy and my parties in the modern novel war. Based on the advantages of the SAWF, the SAWF becomes an important frequency component in military information transmission and countermeasure equipment, including civil information transmission equipment. However, due to the influence of the frequency temperature coefficient of the conventional SAWF filter, in consideration of practical application, the pass band width needs to be greatly increased during design, so that a large amount of precious spectrum resources are inevitably occupied. And because the temperature coefficient of the frequency of the conventional SAWF filter is large, in military and civil application environments with large temperature change, the change of the electrical performance of the conventional SAWF filter can deteriorate the performance indexes of military and civil equipment. For example, the SAWF filter is an important component in the T/R channel of the phased array radar, and each T/R channel of the phased array radar has large temperature change due to heating or the influence of the external environment, so that the conventional SAWF has frequency drift and other electrical performance parameter changes due to large frequency temperature coefficient, and the phase change of each channel unit of the phased array radar is caused, and the overall electrical performance of the phased array radar is influenced. In addition, the existing SAWF filter also has a Rayleigh wave parasitic response phenomenon.
Although it is disclosed that a protection layer is also covered on the interdigital in the conventional SAWF filter, the protection layer is only for protection, and thus the rayleigh wave spurious response phenomenon of the SAWF filter cannot be effectively solved, and the problem of large frequency temperature coefficient of the SAWF filter cannot be reduced.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to overcome prior art not enough, provide a sound surface wave filter of high temperature stability to the temperature coefficient who solves current SAWF existence is big and lead to appearing the not enough of electrical property parameter changes such as frequency drift.
In order to realize the utility model discloses the purpose, the utility model discloses an aspect provides a sound table wave filter of high temperature stability. The high temperature stability surface acoustic wave filter includes:
the piezoelectric substrate at least has a plane;
an interdigital transducer electrode fixedly disposed on the plane of the piezoelectric substrate;
an insulating protective layer having two opposite surfaces, one of which is bonded on the plane of the piezoelectric substrate in a laminated manner and covers the interdigital transducer electrodes; the other surface is provided with a plurality of bulges distributed at intervals.
Preferably, the width of the top of a single projection is less than the width of the root, and the side of the single projection is beveled.
Preferably, the ratio of the width of the tip to the width of the root of a single projection is 0.3 to 0.4.
Preferably, the distance between two adjacent protrusions is 0.3-0.8 μm, and the distance between two adjacent protrusions is consistent with the distance between two adjacent metal interdigital bars.
Preferably, the height of the protrusions is 1.0 to 1.1 μm.
Preferably, a single bump is formed at a position corresponding positively to a single electrode of the interdigital transducer electrodes.
Preferably, the total thickness of the insulation protective layer is 0.29-0.31 lambda, and lambda is the wavelength of sound wave.
Preferably, the interdigital transducer electrodes have a thickness of 0.045-0.055 λ.
The utility model discloses another aspect provides the utility model discloses high temperature stability's sound surface wave filter's application. The acoustic surface wave filter with high temperature stability is applied to radars, mobile communication, channelized receivers and remote sensing and telemetry systems.
Compared with the prior art, the utility model discloses high temperature stability's acoustic surface wave filter is through setting up the insulating protective layer that covers the interdigital transducer electrode, and through right the bellied control of insulating protective layer surface distribution can make temperature stability's acoustic surface wave filter's frequency temperature coefficient reduce on the one hand, can make frequency temperature coefficient be superior to-4 ppm/degree C even, even be close to 0; on the other hand, the insulating protective layer can cooperate with the piezoelectric substrate, the interdigital transducer electrode and other components, so that the Rayleigh wave parasitic response of the acoustic surface wave filter with high temperature stability is effectively reduced, and even disappears. Secondly, the insulating protection layer is arranged on the surface of the interdigital transducer electrode, so that the insulating protection layer can effectively play a role in protection, the corrosion resistance performance of the interdigital transducer is improved, and the stability of the working performance of the high-temperature-stability surface acoustic wave filter is improved and the service life of the high-temperature-stability surface acoustic wave filter is prolonged.
Just because the utility model discloses high temperature stability's acoustic surface wave filter has low frequency temperature coefficient and low rayleigh wave spurious response phenomenon, and working property stability and long service life moreover. Therefore, the acoustic surface wave filter with high temperature stability can be effectively applied to the field of communication and video related devices, so that the working performance and the working stability of the corresponding devices are improved.
Drawings
Fig. 1 is a schematic structural diagram of an acoustic surface wave filter with high temperature stability according to an embodiment of the present invention;
fig. 2 is a graph of the relationship between the electromechanical coupling coefficient and the euler angle of the piezoelectric substrate of the acoustic surface wave filter with high temperature stability according to the embodiment of the present invention;
FIG. 3 is a graph of the electromechanical coupling coefficient of an SAW filter with high temperature stability versus the thickness of the interdigital transducer electrodes, hmet/λ, in accordance with an embodiment of the present invention;
FIG. 4 is a graph of the relationship between the admittance of the SAW filter and the topography of the outer surface of the insulating protective layer for high temperature stability of the present invention; wherein, fig. 4a is a topography map when the ratio SR of the protrusion top width a of the outer surface of the insulating protection layer to the root width B is 0.78; FIG. 4B is a graph of the profile of the outer surface of the insulating protective layer with a ratio SR of the protrusion top width A to the root width B of 0.38; FIG. 4c is an admittance diagram of the topography with a protrusion SR of 0.78 on the outer surface of the insulating protection layer; FIG. 4d is an admittance diagram of the topography with a protrusion SR of 0.38 on the outer surface of the insulating protection layer;
fig. 5 is a graph of the relationship between the temperature coefficient of the frequency of the surface acoustic wave filter and the total thickness of the insulating protective layer for high temperature stability according to the embodiment of the present invention;
fig. 6 is a schematic flow chart of a method for manufacturing an acoustic surface wave filter with high temperature stability according to an embodiment of the present invention;
FIG. 7 is a FT-IR spectrum of the acoustic surface wave filter at 400-2000 cm-1 after the insulating protective film layer is formed by deposition.
Detailed Description
In order to make the technical problem, technical scheme and beneficial effect that the utility model will solve more clearly understand, combine the embodiment below, it is right the utility model discloses further detailed description proceeds. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In one aspect, an embodiment of the present invention provides a surface acoustic wave filter (hereinafter, referred to as surface acoustic wave filter for short). The structure of the acoustic surface wave filter with high temperature stability is shown in figure 1, and comprises a piezoelectric substrate 1, interdigital transducer electrodes 2 and an insulating protective layer 3.
The piezoelectric substrate 1 of the surface acoustic wave filter at least has a plane 11, the plane 11 is used for arranging the interdigital transducer electrode 2, in one embodiment, the material of the piezoelectric substrate 1 is L iTaO3At least one of (1). In addition, it was found that the euler angle of the material of the piezoelectric substrate 1 has an influence on the electromechanical coupling system, and in a further embodiment, the euler angle (0, θ, 0) θ of the material of the piezoelectric substrate 1 is 380、410、420Any euler angle of (1). Specifically, as shown in FIG. 2, when the material of the insulating protection layer 3 and the thickness thereof are not changed to SiO2When the thickness of the interdigital transducer is 0.3 lambda (lambda is the acoustic wave length), the material of the interdigital transducer electrode 2 is copper, and the electrode thickness is 0.05 lambda, the material L iTaO of the piezoelectric substrate 1 is controlled3The Euler angle of (c) affects the electromechanical coupling coefficient of the SAW filter, specifically L iTaO3The relationship between the euler angle of (a) and the electromechanical coupling system of the surface acoustic wave filter is shown in fig. 2, it can be seen from fig. 2 that the material of the piezoelectric substrate 1 is L iTaO3And L iTaO3Cut to about 128 degrees, i.e. L iTaO3The euler angle (0, theta, 0) theta of (a) is 38 deg.. In addition, the thickness of the piezoelectric substrate 1 may be a conventional thickness. Therefore, by controlling the material type and characteristics of the piezoelectric substrate 1, such as euler angle, etc., the piezoelectric substrate 1 and other devices, such as the interdigital transducer electrode 2 and the insulating protective layer, have synergistic effect, so that the temperature coefficient of frequency and the rayleigh wave spurious response phenomenon of the surface acoustic wave filter are reduced, and the reduction of the coupling coefficient of the surface acoustic wave filter is improved.
The interdigital transducer electrode 2 contained in the acoustic surface wave filter is fixedly arranged on the plane 11 of the piezoelectric substrate 1; the interdigital transducer electrode 2 can be designed according to the requirement, and is arranged on the plane 11 according to the requirement of a 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 and the devices such as the piezoelectric substrate 1 cooperate to improve the frequency temperature coefficient and the Rayleigh wave parasitic response phenomenon of the surface acoustic wave filter, so as to improve the reduction of the coupling coefficient of the surface acoustic wave filter. In addition, based on the structure of the saw filter, it is found that adjusting the thickness (denoted as hmet) of the interdigital transducer electrode 2 also affects the electromechanical coupling coefficient of the saw filter, and the relationship between the hmet and the electromechanical coupling coefficient is shown in fig. 3. As can be seen from fig. 3, the electromechanical coupling coefficient decreases as the value of hmet increases under the premise that the thickness of the insulating protection layer 3 is constant. Therefore, the thickness hmet of the interdigital transducer electrode 2 is preferably 0.045-0.055 λ, preferably 0.05 λ.
The insulation protective layer 3 contained in the surface acoustic wave filter has two opposite surfaces, one of which is laminated and combined on the plane 11 of the piezoelectric substrate 1 and covers the interdigital transducer electrode 2; the other surface is formed with a plurality of protrusions 31 distributed at intervals. In this way, the insulating protective layer 3 covers the interdigital transducer electrode 2, and on one hand, the insulating protective layer can effectively play a role of a protective layer, so that the interdigital transducer electrode 2 is separated from adverse factors such as water vapor in the outside, and the stability of the working performance of the interdigital transducer electrode 2 is ensured, such as the performances of corrosion resistance and the like are improved; on the other hand, the embodiment of the utility model provides a through the characteristic that changes insulating protective layer 3's surface, specifically be with being formed with a plurality of interval distribution's arch 31 on insulating protective layer 3's the surface, can make acoustic surface wave filter's frequency temperature coefficient reduces, if through adjusting simultaneously and controlling interdigital transducer electrode 2 and piezoelectric substrate 1 performance and material for the three plays synergy, can show to reduce even acoustic surface wave filter frequency temperature coefficient, but also can effectively reduce acoustic surface wave filter's rayleigh wave spurious response.
In addition, further studies have found that the temperature coefficient of the SAW filter frequency can be significantly reduced, such as better than-4 ppm/° C, and even close to 0, by controlling the shape and size of the protrusions 31 on the outer surface of the insulating protective layer 3. thus, in one embodiment, the shape of the individual protrusions 31 is controlled such that the tip width (A) is smaller than the root width (B) and the lateral surface of the individual protrusions 31 is a slope surface. in a further embodiment, the ratio SR of the tip width (A) to the root width (B) of the individual protrusions 31 is 0.3-0.4, preferably 0.38. in another embodiment, the height of the protrusions 31 is 1.0-1.1 μm, which is the vertical distance from the tip to the root of the individual protrusions 31. in a specific embodiment, the SR value is related to the SAW filter admittance as shown in FIG. 4. when the material of the piezoelectric substrate 1 is L TaO iO in FIG. 43The interdigital transducer electrode 2 is made of copper, and the insulating protective layer 3 is made of SiO2When the SR is controlled to be 0.78, as shown in fig. 4a, the rayleigh response phenomenon appears as seen from the acoustic surface wave filter admittance shown in fig. 4 c; when SR is 0.38, as shown in fig. 4b, the rayleigh response phenomenon does not appear and the rayleigh response substantially disappears as seen from the acoustic surface wave filter admittance shown in fig. 4 d.
In yet another embodiment, the distance between adjacent bumps 31 is controlled to be 0.3-0.8 μm (referring to the distance between the roots of adjacent bumps 31), for example, a single bump 31 can be formed at a position corresponding to a single electrode of the interdigital transducer electrode 2, that is, a single bump 31 is disposed directly above a single electrode of the interdigital transducer electrode 2. Thus, the distance between two adjacent bumps 21 is the same as the distance between adjacent metal interdigital strips contained in the interdigital transducer electrode 2. In addition, the overall thickness of the insulating and protective layer 3 (denoted hsio) was found2) Also has an effect on the temperature coefficient of the frequency of the surface acoustic wave filter. The thickness hsio of the insulating protective layer 32Frequency of the acoustic surface wave filterThe relationship of the temperature coefficients is shown in fig. 5. As can be seen from FIG. 5, when the thickness hmet of the interdigital transducer electrode 2 is constant, the temperature coefficient of the acoustic surface wave filter with respect to frequency is determined by hsio2The value increases and decreases. Therefore, in one embodiment, the total thickness hsio of the insulating protection layer 32That is, the vertical thickness from the top A of the protrusion 31 to the surface of the insulating protective layer 3 bonded to the plane of the piezoelectric substrate 1 is 29 to 31% λ, preferably 30% λ.
Therefore, in the above embodiments, the surface acoustic wave filter effectively reduces the frequency temperature coefficient and the rayleigh wave spurious response of the surface acoustic wave filter by arranging the insulating protective layer 3 and arranging the plurality of protrusions distributed at intervals on the outer surface and by cooperating with the insulating protective layer 3, the interdigital transducer electrode 2, the piezoelectric substrate 1, and other components. By controlling and optimizing the size, shape and distribution spacing and position of the bumps 31, the frequency temperature coefficient of the surface acoustic wave filter can be significantly reduced, and the rayleigh wave spurious response of the surface acoustic wave filter can be effectively reduced.
Correspondingly, the embodiment of the utility model provides a preparation method of the high temperature stability's acoustic surface wave filter is still provided above. The preparation method of the surface acoustic wave filter is combined with the figure 1, the process flow of the preparation method of the surface acoustic wave filter is shown in figure 6, and the preparation method comprises the following steps:
s01: preparing an interdigital transducer electrode 2 on a plane 11 of a piezoelectric substrate 1;
s02: depositing an insulating protective film layer on the plane 11 of the piezoelectric substrate 1 such that the insulating protective film layer covers the interdigital transducer electrodes 2;
s03: and etching the outer surface of the insulating protection film layer to form a plurality of bulges 31 distributed at intervals on the surface.
Specifically, in the above step S01, the method of preparing the interdigital transducer electrode 2 on the piezoelectric substrate 1 can be performed according to the existing method of preparing an interdigital transducer electrode. In the embodiment of the utility model, through to preparing interdigital transducer electrode2, the thickness of the interdigital transducer electrode 2 is preferably controlled to be 0.045-0.055 lambda, and preferably 0.05 lambda, wherein the material for preparing the interdigital transducer electrode 2 can be any one of Al, Cu and Ti or Al and Cu alloy as described above, the material and the thickness of the piezoelectric substrate 1 can be L iTaO as described above3In the step S02, the method for depositing the insulating protection film layer may be, but is not limited to, magnetron sputtering. When adopting magnetron sputtering deposition formation during the insulating protection rete, through the research of utility model people discovery, magnetron sputtering's condition change can lead to the change of insulating protection rete elastic constant to influence the sound surface wave filter frequency temperature coefficient of preparation.
In a specific embodiment, the material of the insulating protection film layer is SiO2I.e. deposition of SiO on the piezoelectric substrate 12After the film is formed, the film is aligned to 400-2000 cm-1The wave number of (A) was measured by FT-IR, deposited SiO2The FT-IR spectrum of the film shows three major peaks as shown in fig. 7. The relationship between the peak value and the molecular vibration mode was determined, including the rocking mode (ω 1: 450 cm)-1) Bending mode (ω 3: 800cm-1) And a stretching mode (ω 4: 1070cm-1)。
When different magnetron sputtering technological parameters are used for depositing SiO with the film thickness of 0.3 lambda2The films obtained omega 3 and omega 4 with different peak frequencies, the corresponding peak frequencies are summarized in Table 1, and the peak frequencies omega 3 and omega 4 are respectively 810.9-815.5cm-1And 1065.6-1079.2cm-1The range was varied and the elastic constant was varied by 7%. Through the above studies, when the sputtering process parameters are changed, the temperature coefficient of the elastic constant is changed, thereby causing the change of the TCF.
TABLE 1SiO2FT-IR spectroscopy of deposited films
| Measurement sequence number | ω3(cm-1) | ω4(cm-1) | Spring constant |
| S1 | 810.9 | 1079.2 | 82.0 |
| S2 | 811.1 | 1078.3 | 82.9 |
| S3 | 811.7 | 1076.2 | 83.5 |
| S4 | 812.4 | 1074.4 | 84.2 |
| S5 | 812.9 | 1072.8 | 84.8 |
| S6 | 813.2 | 1070.3 | 85.5 |
| S7 | 813.8 | 1068.7 | 86.1 |
| S8 | 814.4 | 1067.4 | 86.8 |
| S9 | 815.1 | 1066.1 | 87.5 |
| S10 | 815.5 | 1065.6 | 88.0 |
Thus, in one embodiment, magnetron sputtering is used to deposit the insulating protective film layer, in particular SiO2In the case of a thin film, the conditions of magnetron sputtering deposition are as follows: the radio frequency magnetic control discharge is controlled at 10-1～10-2Pa, the magnetic field intensity B of the magnetic control target surface is controlled to be between 30 and 50mT, and the electric field orthogonal to the magnetic field in the vacuum cavity is controlled to be between 500 and 700V. Therefore, the structure of the insulating protective film layer can be controlled and deposited by controlling the input process parameters of magnetron sputtering, and the TCF minimization of the surface acoustic wave filter is realized. For example, the temperature frequency coefficient is controlled to be changed between-20 ppm/DEG C and 0 ppm/DEG C.
In addition, after the insulating protective film layer is formed by deposition, the method also comprises the step of flattening the outer surface of the insulating protective film layer.
In the step S03, the insulating protection film layer formed by deposition is subjected to etching treatment to obtain the insulating protection layer 3 as described above and shown in fig. 1. The surface of the insulating and protecting layer 3 thus exhibits a plurality of projections 31 formed at intervals as shown in fig. 1. The size and distribution position of the protrusions 31 are as described above, and are not described herein for brevity.
In one embodiment, the etching process performed on the outer surface of the insulating protection film layer 3 includes the following steps:
(1) dividing the outer surface of the insulating protective film layer into an etching area and a non-etching area according to the design requirement of the distance between the adjacent protrusions 31, and covering an anti-etching protective film layer on the surface of the non-etching area; then, the product is processed
(2) And carrying out directional etching treatment on the etching area in the outer surface of the insulating protection film layer by adopting an inductive coupling plasma etching process.
In step (1), the protrusion 31 is formed in the non-etching region, that is, the region after the etching process. The protective film is covered to avoid etching the non-etching area during the etching process, so that the etching gas only etches the etching area to form the protrusions 31 with a plurality of profiles.
The process conditions for the directional etching treatment by the Inductively Coupled Plasma (ICP) etching process in step (2) are preferably as follows: the etchant used is SF6The passivating polymer-generating agent is C4F8Said SF6And C4F8Are alternately introduced into the etching chamber. ICP etching using SF6As an etchant, C4F8As a passivating polymer generator. SF6Under the action of inductive glow discharge, a mixture of multiple components such as ionized electrons, charged ions, atoms or atomic groups and the like can be mixed with the material SiO of the insulating protective film layer2If a chemical reaction occurs, introducing C into the reaction chamber during the passivation process4F8Gas, under the action of plasma, performs a plasma polymerization process which is highly isotropic and therefore occurs in SiO2Uniformly covering the surface and the deep groove of the structureA polymer protective film. During the subsequent etching process, the active gas in the reaction chamber is converted into SF6And is decomposed into SF+And SF-The electric field accelerates the positive ions, which increases the energy of the ions in the vertical direction, so that polymer regions parallel to the substrate surface are preferentially removed. With this high directionality, the silicon surface at the bottom of the deep trench is preferentially exposed and F-Reaction to form SiF4And thus etched.
In the aspect of etching depth control, the etching power and the longitudinal bias voltage in the process are increased to realize the control. In the ICP etching process, anisotropy is achieved by a combination of the etching action of reactive ions at the bottom surface of the trench and the inhibition of polymer at the sidewalls. The reactive ions can deflect under the action of a transverse electric field, and the reactive ions in the plasma are difficult to reach the etching surface along with the increase of the etching depth of the groove or the hole under the same power. Therefore, with the increase of the etching depth, the etching power and the longitudinal bias voltage in the process are increased in proportion, and the deflection effect of the transverse electric field is compensated to realize the deep groove etching.
In the aspect of etching angle control, the etching angle control is realized by adjusting the proportion of etching and protective gas. Experiments find that the main factor influencing the etching angle is the flow of the process gas, and SF is alternately introduced by adjusting6、C4F8The flow ratio of the two gases can achieve the purpose of controlling the etching angle. Reduction of SF6Flow and increase C4F8The flow can realize a positive V-shaped groove, and the ratio A/B of the top width A and the root width B of the protrusion 31 can be accurately controlled, so that the requirement on the optimized control of the surface appearance protrusion 31 of the insulating protection layer 3 can be met. Therefore, in an embodiment, the process conditions of the directional etching treatment are as follows:
the SF6The flow rate of the introduced air flow is 30-60 SCCM;
said C is4F8The flow rate of the introduced air flow is 30-60 SCCM;
the etching power is 300-;
the longitudinal bias is 30-35 VDC.
By controlling the directional etching treatment, the directional etching is realized, so that the size and the appearance of the bump 31 formed by etching are accurately controlled.
Therefore, the method for preparing the surface acoustic wave filter performs directional etching treatment on the outer surface of the insulating protective film layer to form the surface with the protrusions 31 distributed at intervals, so that the prepared surface acoustic wave filter has low frequency temperature coefficient and low rayleigh wave parasitic response, and can play a role in protection, so that the prepared surface acoustic wave filter has the advantages of stable working performance, long service life and the like. In addition, the preparation method has controllable process conditions, and can effectively ensure stable performance, high yield and low cost of the prepared acoustic surface wave filter with high temperature stability.
The surface wave filter based on the acoustic surface wave filter and the preparation method thereof has the advantages of low frequency temperature coefficient, low Rayleigh wave spurious response phenomenon, stable working performance, long service life and the like. Therefore, the acoustic surface filter plays a good role in the aspects of suppressing higher harmonics, image information, emission leakage signals, various parasitic clutter interferences and the like of the electronic information equipment, and can realize filtering of amplitude-frequency and phase-frequency characteristics with any required precision. For example, the upper limit frequency of the acoustic surface filter can be increased to 2.5 GHz-3 GHz. Thereby promoting wider application of the acoustic surface filter in the field of EMI resistance. As the Temperature Coefficient of Frequency (TCF) of conventional filters is typically about-45 ppm/deg.C, the acoustic surface filter drops above-4 ppm/deg.C, or even close to 0. And the Rayleigh wave spurious response is low and even disappears. Therefore, the surface acoustic wave filter can be widely applied to radar, mobile communication, channelized receivers and remote sensing and telemetry systems, so that the working performance and the working stability of corresponding devices are improved.
The present invention will now be described in further detail with reference to specific examples. In the following examples, "/" indicates lamination bonding.
1 structural embodiment of surface acoustic wave filter
Example 11
The structure of the surface acoustic wave filter is shown in fig. 1, and the structure of the surface acoustic wave filter is piezoelectric substrate 1/interdigital transducer electrode 2/insulating protective layer 3, wherein the piezoelectric substrate 1 is L iTaO3The euler angle (0, theta, 0) theta is 38 degrees; the interdigital transducer electrode 2 is made of copper, and the thickness of the interdigital transducer electrode is 0.05 lambda; the insulating protective layer 3 is made of SiO2The total thickness of the interdigital transducer electrode is 0.3 lambda, a plurality of protrusions 31 distributed at intervals are formed on the outer surface of the insulating protection layer 3, the positions where the protrusions 31 are formed correspond to the single electrode of the interdigital transducer electrode 2, the distance between every two adjacent protrusions 31 is 0.6 mu m, the width A of the top of each protrusion 31 is smaller than the width B of the root of each protrusion, and the ratio SR of A to B is 0.38.
Example 12
The structure of the surface acoustic wave filter is shown in fig. 1, and the structure of the surface acoustic wave filter is piezoelectric substrate 1/interdigital transducer electrode 2/insulating protective layer 3, wherein the piezoelectric substrate 1 is L iTaO3The Euler angle (0, theta, 0) theta is 42 degrees; the interdigital transducer electrode 2 is made of Al and Cu alloy, and the thickness of the interdigital transducer electrode is 0.045 lambda; the insulating protective layer 3 is made of SiO2The total thickness of the interdigital transducer electrode is 0.31 lambda, a plurality of protrusions 31 distributed at intervals are formed on the outer surface of the insulating protection layer 3, the positions where the protrusions 31 are formed correspond to the single electrode of the interdigital transducer electrode 2, the distance between every two adjacent protrusions 31 is 0.8 mu m, the width A of the top of each protrusion 31 is smaller than the width B of the root of each protrusion, and the ratio SR of A to B is 0.3.
Example 13
The structure of the surface acoustic wave filter is shown in fig. 1, and the structure of the surface acoustic wave filter is piezoelectric substrate 1/interdigital transducer electrode 2/insulating protective layer 3, wherein the piezoelectric substrate 1 is L iTaO3Euler angles (0, theta, 0) theta of 41 DEG; the interdigital transducer electrode 2 is made of Al, and the thickness of the interdigital transducer electrode is 0.055 lambda; the insulating protective layer 3 is made of SiO2The total thickness of the electrode is 0.29 lambda, a plurality of protrusions 31 are formed on the outer surface of the insulating protection layer 3 at intervals, the positions where the protrusions 31 are formed correspond to the single electrodes of the interdigital transducer electrodes 2, the distance between adjacent protrusions 31 is the same as the distance between adjacent electrodes (the electrodes substantially form interdigital electrode metal strips), the width a of the top of each protrusion 31 is smaller than the width B of the root, and the ratio SR of the width a to the width B is 0.4.
2 method for manufacturing surface acoustic wave filter
Example 21
This example provides a method of making the surface acoustic wave filter of example 11. The preparation method comprises the following steps:
s1 at L iTaO3Preparing an interdigital transducer copper electrode 2 on a plane 11 of a piezoelectric substrate 1; controlling the thickness of the interdigital transducer copper electrode 2 to be 0.05% lambda more preferably;
s2: depositing SiO on the plane 11 of the piezoelectric substrate 1 by adopting a magnetron sputtering process2An insulating protective film layer, and enabling the insulating protective film layer to cover the interdigital transducer electrode 2; wherein the total thickness is controlled to be 0.3 lambda, and the process condition of the magnetron sputtering process is that the radio frequency magnetron discharge is controlled to be 10-1～10-2Pa, controlling the magnetic field intensity B of the magnetic control target surface to be 40mT, and controlling the electric field orthogonal to the magnetic field in the vacuum cavity to be 600V;
s03: performing ICP etching treatment on the outer surface of the insulating protection film layer to form a plurality of protrusions 31 distributed at intervals on the surface; wherein the etching agent used for the ICP etching treatment is SF6The passivating polymer-generating agent is C4F8Said SF6And C4F8Alternately introducing into an etching chamber; and the process conditions of the directional etching treatment are as follows:
the SF6The flow rate of the introduced gas flow is 45 SCCM;
said C is4F8The flow rate of the introduced gas flow is 45 SCCM;
the etching power is 350W;
the longitudinal bias is 30 VDC.
Example 22
This example provides a method of making the surface acoustic wave filter of example 12. The preparation method comprises the following steps:
s1 at L iTaO3Preparing an interdigital transducer Al and Cu alloy electrode 2 on a plane 11 of a piezoelectric substrate 1;
s2: depositing SiO on the plane 11 of the piezoelectric substrate 1 by adopting a magnetron sputtering process2An insulating protective film layer, and enabling the insulating protective film layer to cover the interdigital transducer electrode 2; wherein, the technological condition of the magnetron sputtering technology is that the radio frequency magnetron discharge is controlled at 10-1～10-2Pa, controlling the magnetic field intensity B of the magnetic control target surface to be 30mT, and controlling the electric field orthogonal to the magnetic field in the vacuum cavity to be 500V;
s03: performing ICP etching treatment on the outer surface of the insulating protection film layer to form a plurality of protrusions 31 distributed at intervals on the surface; wherein the etching agent used for the ICP etching treatment is SF6The passivating polymer-generating agent is C4F8Said SF6And C4F8Alternately introducing into an etching chamber; and the process conditions of the directional etching treatment are as follows:
the SF6The flow rate of the introduced gas flow is 60 SCCM;
said C is4F8The flow rate of the introduced gas flow is 30 SCCM;
the etching power is 400W;
the longitudinal bias is 30 VDC.
Example 23
This example provides a method of making the surface acoustic wave filter of example 13. The preparation method comprises the following steps:
s1 at L iTaO3Preparing an interdigital transducer Al electrode 2 on a plane 11 of the piezoelectric substrate 1;
s2: depositing SiO on the plane 11 of the piezoelectric substrate 1 by adopting a magnetron sputtering process2An insulating protective film layer, and enabling the insulating protective film layer to cover the interdigital transducer electrode 2; wherein, the process strip of the magnetron sputtering processThe part is controlled at 10 by radio frequency magnetic control discharge-1～10-2Pa, controlling the magnetic field intensity B of the magnetic control target surface at 50mT, and controlling the electric field orthogonal to the magnetic field in the vacuum cavity at 700V;
s03: performing ICP etching treatment on the outer surface of the insulating protection film layer to form a plurality of protrusions 31 distributed at intervals on the surface; wherein the etching agent used for the ICP etching treatment is SF6The passivating polymer-generating agent is C4F8Said SF6And C4F8Alternately introducing into an etching chamber; and the process conditions of the directional etching treatment are as follows:
the SF6The flow rate of the introduced gas flow is 30 SCCM;
said C is4F8The flow rate of the introduced gas flow is 60 SCCM;
the etching power is 300W;
the longitudinal bias is 35 VDC.
Comparative example
Conventional surface acoustic wave filters are commercially available.
3. Acoustic surface wave filter related performance test
The surface acoustic wave filters provided in examples 11 to 13 and the commercially available conventional surface acoustic wave filter provided in the comparative example were subjected to the following correlation performance tests, respectively, and the results were as shown in the following table 1:
TABLE 1
In addition, examples 12 and 13 provide surface acoustic wave filters that are similar to the performance test results in table 1. Therefore, as can be seen from the results of the correlation performance tests in table 1, the surface acoustic wave filter of the present embodiment has a low temperature coefficient of frequency and a low rayleigh wave spurious response, and has stable operation performance and a long service life.
The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, as any modifications, equivalents, improvements and the like made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. A high temperature stable surface acoustic wave filter, comprising: comprises that
The piezoelectric substrate at least has a plane;
an interdigital transducer electrode fixedly disposed on the plane of the piezoelectric substrate;
an insulating protective layer having two opposite surfaces, one of which is bonded on the plane of the piezoelectric substrate in a laminated manner and covers the interdigital transducer electrodes; the other surface is provided with a plurality of bulges distributed at intervals.
2. The surface acoustic wave filter of claim 1, wherein: the width of the top of the single protrusion is smaller than that of the root of the single protrusion, and the side face of the single protrusion is an inclined plane.
3. The surface acoustic wave filter of claim 2, wherein: the ratio of the width of the tip to the width of the root of a single protrusion is 0.3-0.4.
4. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the distance between every two adjacent protrusions is 0.3-0.8 mu m, and the distance between every two adjacent protrusions is consistent with the distance between every two adjacent metal interdigital strips.
5. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the height of the protrusions is 1.0-1.1 μm.
6. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the position where a single bump is formed corresponds positively to a single electrode of the interdigital transducer electrode.
7. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the total thickness of the insulation protective layer is 0.29-0.31 lambda, and lambda is the acoustic wave wavelength.
8. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the thickness of the interdigital transducer electrode is 0.045-0.055 lambda.
9. The acoustic surface wave filter according to any one of claims 1 to 3, wherein: the application in radar, mobile communication, channelized receivers and remote sensing and telemetry systems.
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