CN210986062U - Temperature compensation acoustic surface wave filter - Google Patents
Temperature compensation acoustic surface wave filter Download PDFInfo
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- CN210986062U CN210986062U CN201921257268.8U CN201921257268U CN210986062U CN 210986062 U CN210986062 U CN 210986062U CN 201921257268 U CN201921257268 U CN 201921257268U CN 210986062 U CN210986062 U CN 210986062U
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Abstract
The utility model discloses a temperature compensation sound surface wave filter. The acoustic surface wave filtering device comprises interdigital transducer electrodes, wherein the interdigital transducer electrodes comprise a first bus electrode and a second bus electrode, the first bus electrode comprises a plurality of first interdigital finger electrodes arranged at intervals, and the second bus electrode comprises a plurality of second interdigital finger electrodes arranged at intervals; a first boundary region is formed from a section of the end tip of the first interdigital finger electrode toward the first bus electrode end in a direction parallel to the first bus electrode or the second bus electrode; a section of the second interdigital electrode from the end terminal thereof toward the second bus electrode terminal is configured as a second boundary region; and an insulating medium layer is deposited on the first interdigital finger electrode and the second interdigital finger electrode in the first boundary area and the second boundary area.
Description
Technical Field
The utility model belongs to the technical field of the microelectronics, concretely relates to temperature compensation sound surface wave filter and preparation method and application thereof.
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, in practical application, the existing SAWF has at least the following two problems:
firstly, in the process of transmitting the acoustic wave in the interdigital transducer electrode, due to the characteristics of acoustic wave propagation and diffusion, the acoustic wave is transmitted to the side surface while being transmitted along the interdigital finger electrodes of the interdigital transducer electrode, and the acoustic wave transmitted to the side surface causes the loss of the acoustic wave, so that the attenuation of the acoustic wave is caused, and the Q value of the SAWF is reduced.
Second, due to the large temperature coefficient of frequency of the conventional SAWF filter, in military and civilian application environments with large temperature variations, the variation of the electrical performance of the conventional SAWF filter deteriorates the performance indexes of military and civilian 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. It has also been found that the existing SAWF filter also has a rayleigh wave spurious 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 temperature compensation sound surface wave filter and preparation method thereof to solve the big or further not enough technical problem that has the temperature coefficient big etc. of Q value that current SAWF exists.
In order to realize the utility model discloses the purpose, the utility model discloses an aspect provides a temperature compensation sound surface wave filter. The temperature compensated surface acoustic wave filter includes:
temperature compensation sound table wave filter, its characterized in that: comprises that
The piezoelectric substrate at least has a plane;
an interdigital transducer electrode fixedly disposed on the plane of the piezoelectric substrate;
the interdigital transducer electrodes comprise a first bus electrode and a second bus electrode, and the first bus electrode and the second bus electrode are arranged in a pair mode; the first bus electrode comprises a plurality of first interdigital finger electrodes arranged at intervals, one end of each first interdigital finger electrode is in contact with the first bus electrode, and the other end of each first interdigital finger electrode points to the second bus electrode; the second bus electrode comprises a plurality of second interdigital finger electrodes which are arranged at intervals, one end of each second interdigital finger electrode is in contact with the second bus electrode, and the other end of each second interdigital finger electrode points to the first bus electrode; the first interdigital finger strip electrodes and the first interdigital finger strip electrodes are arranged in a staggered mode;
a first boundary region is formed along a section parallel to the first bus electrode or the second bus electrode from an end tip of the first interdigital finger electrode to the first bus electrode end; and a section of region from the end terminal of the second interdigital strip electrode to the second bus electrode terminal is formed into a second boundary region, and insulating medium layers for inhibiting the transverse propagation loss mode of the acoustic wave are deposited on the first interdigital strip electrode and the second interdigital strip electrode in the first boundary region and the second boundary region.
Preferably, the width of the first boundary region occupies 1-2% of the total length of the first interdigital finger electrode.
Preferably, the width of the second border region is 2-3% of the total length of the second interdigitated finger electrode.
Preferably, the thickness of the insulating dielectric layer is 800-1000 angstroms.
Preferably, the interdigital transducer electrodes have a thickness of 0.045-0.055 λ.
Preferably, the piezoelectric transducer further comprises an insulating protective layer which is laminated and bonded on the plane of the piezoelectric substrate and covers the interdigital transducer electrodes.
Further preferably, the insulating protective layer has 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.
Further 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.
Further 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.
Further preferably, the pitch between adjacent protrusions is 0.3 to 0.8 μm.
Further preferably, the height of the protrusions is 1.0 to 1.1 μm.
Further preferably, a single bump is formed at a position corresponding positively to a single electrode of the interdigital transducer electrodes.
Further preferably, the total thickness of the insulating and protecting layer is 0.29-0.31 lambda, and lambda is the wavelength of sound wave.
Compared with the prior art, the utility model discloses temperature compensation acoustic surface wave filter is through setting interdigital transducer electrode to "piston" structure all form dielectric layer on the interdigital finger electrode in the first border region of interdigital transducer electrode and the second border region. The insulating medium layers are distributed on two sides of the waveguide region for sound wave propagation, so that the sound waves can be effectively reduced from propagating to the regions on two sides of the waveguide region, the loss of the sound waves is effectively reduced, the Q value of the surface acoustic wave filter is effectively reduced, and the parasitic response of the surface acoustic wave filter is also reduced.
Drawings
Fig. 1 is a schematic structural diagram of a temperature compensation surface acoustic wave filter according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the structure of interdigital transducer electrodes and the acoustic wave propagation velocity in each region of the temperature compensated surface acoustic wave filter shown in FIG. 1; wherein, FIG. 2-A is a schematic structural view of an interdigital transducer electrode; FIG. 2-B is a graph of the velocity of sound waves propagating in the various regions of the interdigital transducer electrodes;
FIG. 3 is a schematic structural diagram of a temperature compensated SAW filter according to an embodiment of the present invention, preferably including an insulating protective layer;
fig. 4 is a graph of a relationship between an electromechanical coupling coefficient and a euler angle of a piezoelectric substrate of a temperature compensation surface acoustic wave filter according to an embodiment of the present invention;
FIG. 5 is a graph showing the relationship between the electromechanical coupling coefficient of the temperature compensated SAW filter and the thickness hmet/λ of the interdigital transducer electrodes;
FIG. 6 is a graph showing the relationship between the admittance of the temperature compensated SAW filter and the topography of the outer surface of the insulating protective layer; wherein, fig. 6a 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. 6B 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. 6c is an admittance diagram of the topography with a protrusion SR of 0.78 on the outer surface of the insulating protection layer; FIG. 6d is an admittance diagram of the topography with a protrusion SR of 0.38 on the outer surface of the insulating protection layer;
FIG. 7 is a graph showing the relationship between the temperature coefficient of the frequency of the temperature compensated surface acoustic wave filter and the total thickness of the insulating protective layer according to the embodiment of the present invention;
fig. 8 is a schematic flow chart of a manufacturing method of a temperature compensation surface acoustic wave filter according to an embodiment of the present invention;
FIG. 9 is a FT-IR spectrum of the acoustic surface wave filter at 400-2000 cm-1 after deposition of the insulating protective film layer.
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 temperature compensation surface acoustic wave filter (hereinafter, referred to as surface acoustic wave filter for short). The structure of the temperature compensation acoustic surface wave filter is shown in figure 1, and comprises a piezoelectric substrate 1 and interdigital transducer electrodes 2.
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 is 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 any one of 38 °, 41 °, and 42 °. Specifically, as shown in fig. 4, when the acoustic surface wave filter includes the insulating protective layer 3 shown in fig. 3, the material of the insulating protective layer 3 and the thickness thereof do not change as much as 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. 4, it can be seen from fig. 4 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. In the present embodiment, the interdigital transducer electrode 2 is configured in a "piston" configuration as shown in fig. 2A. Specifically, the interdigital transducer electrode 2 includes a first bus electrode 21 and a second bus electrode 22, the first bus electrode 21 and the second bus electrode 22 being disposed oppositely; the first bus electrode 21 comprises a plurality of first interdigital finger electrodes 211 arranged at intervals, one end of each first interdigital finger electrode 211 is in contact with the first bus electrode 21, and the other end of each first interdigital finger electrode is directed to the second bus electrode 22; the second bus electrode 22 comprises a plurality of second interdigital strip electrodes 221 arranged at intervals, one end of each second interdigital strip electrode 221 is in contact with the second bus electrode 22, and the other end of each second interdigital strip electrode points to the first bus electrode 21; the first interdigital finger electrode 211 and the second interdigital finger electrode 221 are arranged in a staggered manner.
In addition to the interdigital transducer electrode 2 structure shown in fig. 2A, a section from the end of the first interdigital finger electrode 211 to the first bus electrode terminal 21 in a direction parallel to the first bus electrode 21 or the second bus electrode 22 is formed as a first boundary area a1, and since the first boundary area a1 is in a direction parallel to the first bus electrode 21 or the second bus electrode 22, the first boundary area a1 naturally includes a part of the second interdigital electrode 221 distributed in the area. That is, a portion of first interdigital finger electrode 211 and second interdigital finger electrode 221 together form first boundary area a 1. Similarly, a section from the end of the second interdigital electrode 221 to the second bus electrode terminal 22 is configured as a second boundary region a2, and since the second boundary region a2 is also along a direction parallel to the first bus electrode 21 or the second bus electrode 22, the second boundary region a2 naturally includes a portion of the first interdigital electrode 211 distributed in the region. That is, a portion of first interdigital finger electrode 211 and second interdigital finger electrode 221 together form second boundary area a 2. Then the portion of the first interdigital finger electrode 211 and the second interdigital finger electrode 221 which are distributed between the first boundary region a1 and the second boundary region a2 together constitute a waveguide region A3, the first interdigital finger electrode 211 adjacent to the remaining portion of the first bus electrode 21 constitutes a first outer edge source region a4, and the second interdigital finger electrode 221 adjacent to the remaining portion of the second bus electrode 22 constitutes a second outer edge source region a 5.
Further, an insulating medium layer 23 is deposited on the first interdigital finger electrode 211 and the second interdigital finger electrode 221 in the first boundary area a1 and the second boundary area a2 of the interdigital transducer electrode 2 structure depicted in fig. 2A. By providing dielectric layer 23 over the interdigitated finger electrodes in first boundary region a1 and second boundary region a 2. To function as shown in fig. 2B. It was determined that during the propagation of the acoustic wave in the interdigital transducer electrode 2 as shown in fig. 2A, the propagation velocity Vs of the acoustic wave in the first boundary region a1 and the second boundary region a2, the propagation velocity Vf of the acoustic wave in the first outer edge source region a4 and the second outer edge source region a5, and the propagation velocity Vg of the acoustic wave in the waveguide region A3 were measured, wherein Vs is significantly smaller than Vg. Therefore, the existence of the wave-decelerating insulating medium layer 23 can effectively reduce the propagation of the sound wave to the two side regions of the waveguide region a3, thereby effectively reducing the loss of the sound wave, effectively reducing the Q value of the surface acoustic wave filter, and simultaneously playing a role in reducing the parasitic response. In one embodiment, the width of the first boundary region a1 is 1-2% of the total length of the first interdigital finger electrode 211, and the width of the specific first boundary region a1 may be 2-3 μm; or the width of the second boundary area a2 occupies 2-3% of the total length of the second interdigital electrode 221. In another embodiment, the insulating dielectric layer may be made of tantalum pentoxide (Ta)2O5) (ii) a The thickness of the insulating dielectric layer is 800-1000 angstroms. Through the size of the insulating medium layer 23, the propagation of the sound wave to the regions on two sides of the waveguide region a3 is further effectively reduced, so that the Q value of the surface acoustic wave filter is further effectively reduced, and the effect of reducing the parasitic response is achieved.
Based on the structure of the interdigital transducer electrode 2 shown in fig. 2A, in an embodiment, the material of the interdigital transducer electrode 2 can be any one of Al, Cu, and 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. 5. As can be seen from fig. 5, the electromechanical coupling coefficient decreases as the value of hmet increases, under the premise that the insulating protection layer 3 shown in fig. 3 is included and 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.
On the basis of the above embodiments, in an embodiment, as shown in fig. 3, the acoustic surface wave filter further includes an insulating protective layer 3, and the insulating protective layer 3 is laminated on the plane 11 of the piezoelectric substrate 1 and covers the interdigital transducer electrode 2.
In a further embodiment, the acoustic surface wave filter comprises an insulating protective layer 3 having two opposite surfaces, one of which is laminated on the plane 11 of the piezoelectric substrate 1 and covers the interdigital transducer electrodes 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 research shows that the outer surface of the insulating protective layer 3 is protruded31 are controlled to substantially reduce the SAW filter frequency temperature coefficient, e.g., better than-4 ppm/DEG C, and even closer to 0, and also to reduce the SAW filter Rayleigh spurious response, thus, in one embodiment, the shape of a single protrusion 31 is controlled to have a tip width (A) less than a root width (B) and a side of the single protrusion 31 is beveled, in a further embodiment, the ratio SR of the tip width (A) to the root width (B) of the single protrusion 31 is 0.3 to 0.4, preferably the ratio SR is 0.38, in another embodiment, the height of the protrusion 31 is 1.0 to 1.1 mu m, the height being the perpendicular distance from the tip to the root of the single protrusion 31. in a specific embodiment, the SR value is related to the SAW filter admittance as shown in FIG. 6, when the material of the piezoelectric substrate 1 is L iTaO3The 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. 6a, the rayleigh response phenomenon appears as seen from the acoustic surface wave filter admittance shown in fig. 6 c; when SR is 0.38, as shown in fig. 6b, 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. 6 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. 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 32The relationship with the temperature coefficient of frequency of the acoustic surface wave filter is shown in fig. 7. As can be seen from FIG. 7, 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 32I.e. from said projection 31The vertical thickness between the top portion a 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 surface acoustic wave filter in the above embodiments, the interdigital transducer electrodes are arranged in the "piston" structure, and the insulating medium layer 23 is formed on the interdigital electrodes in the first boundary area a1 and the second boundary area a2 of the interdigital transducer electrodes in the "piston" structure, so that the propagation of the acoustic wave to the areas on both sides of the waveguide area is effectively reduced, the loss of the acoustic wave is effectively reduced, and the Q value and the spurious response of the surface acoustic wave filter are effectively reduced. The further insulating protective layer 3 that adds and the setting of 3 surface of insulating protective layer realize to components such as insulating protective layer 3, interdigital transducer electrode 2 and piezoelectric substrate 1 synergism, effectively reduce the frequency temperature coefficient and the spurious response of rayleigh wave of acoustic surface wave filter. In addition, the Q value and the temperature coefficient of the frequency of the surface acoustic wave filter can be obviously reduced by optimizing the control and optimization of the sizes, the shapes, the materials and the like of the interdigital transducer electrode 2, the insulating medium layer 23 and the insulating protection layer 3, and the Rayleigh wave parasitic response of the surface acoustic wave filter can be further reduced.
Correspondingly, the embodiment of the utility model provides a preparation method of temperature compensation sound 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 8, 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: the insulating dielectric layer 23 is deposited on the first boundary area a1 and the second boundary area a2 of the interdigital transducer electrode 2.
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. As long as the "piston" structure shown in fig. 2A can be formed. In one embodiment, the method process conditions for preparing the interdigital transducer electrode 2 are adoptedThe interdigital transducer electrode 2 is preferably controlled to have a thickness of 0.045-0.055 lambda, more preferably 0.05 lambda, wherein the material for preparing the interdigital transducer electrode 2 may be any one of Al, Cu and Ti or an Al, Cu alloy as described above, the piezoelectric substrate 1 may have a material L iTaO as described above with respect to the material and thickness3。
In the step S02, as an embodiment of the present invention, the method for depositing the insulating medium layer 23 includes the following steps:
and respectively depositing insulating medium layer materials in the first boundary area A1 and the second boundary area A2 by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD), and depositing at least the surfaces of the interdigital electrodes in the first boundary area A1 and the second boundary area A2 to form the insulating medium layer 23.
Specifically, a piezoelectric substrate containing an interdigital transducer electrode is placed on an electrode of low-pressure glow discharge, then a proper amount of gas is introduced, and the insulating medium layer, such as a tantalum pentoxide thin film, is deposited on the surfaces in the first boundary area and the second boundary area by utilizing a process of combining chemical reaction and ion bombardment at a certain temperature. In one embodiment, the PECVD working conditions for depositing the insulating dielectric layer are as follows: the working temperature is 250-400 ℃, the radio frequency discharge frequency is 13.56MHz, the radio frequency power is 1-2KW, and the vacuum in the coating cavity is kept at 7 x 10-5Pa or less. The insulating dielectric layer material is tantalum pentoxide as described above.
In one embodiment, the process conditions of the method for preparing the insulating dielectric layer 23 are controlled, and the thickness of the insulating dielectric layer 23 is preferably controlled to be 800-1000 angstroms.
In a further embodiment, after the step S02, as shown in fig. 8, the method further includes the following steps:
s03: 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;
s04: and etching the outer surface of the insulating protection film layer to form a plurality of bulges 31 distributed at intervals on the surface.
In the step S03, 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. 9. 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 1 SiO2FT-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 S04, the insulating protection film layer formed by deposition is etched to obtain the insulating protection film 3 having the protrusions 31 on the outer surface as shown above and in fig. 3. 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 SiO2The surface and the structure deep groove of the substrate are uniformly covered with a 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 preparation method of the acoustic surface wave filter adopts a deposition method to form the insulating medium layer 23 on the first boundary area a1 and the second boundary area a2 of the interdigital transducer electrode 2, so that on one hand, the propagation rate of the acoustic wave to the first boundary area a1 and the second boundary area a2 can be effectively reduced, the loss of the acoustic wave is effectively reduced, the Q value of the acoustic surface wave filter is effectively reduced, and the parasitic response is simultaneously reduced; and on the other hand, the formed insulating medium layer 23 is ensured to have stable performance, so that the Q value and the sound wave quality of the acoustic surface wave filter are ensured to be stable. Further, an insulating protective film layer 3 is formed on the outer surface of the interdigital transducer electrode 2 containing the insulating medium layer 23, and the outer surface of the insulating protective film layer 3 is subjected to directional etching treatment to form a surface with the protrusions 31 distributed at intervals, so that the prepared surface acoustic wave filter has a low frequency temperature coefficient and a low Rayleigh wave parasitic response phenomenon, and can play a role in protection, so that the prepared surface acoustic wave filter has the advantages of working performance stability, 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 temperature compensation surface acoustic wave filter.
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 present embodiment provides an acoustic surface wave filter and a method for manufacturing the same, the structure of the acoustic surface wave filter is shown in fig. 1-2, and the structure of the acoustic surface wave filter is a piezoelectric substrate 1/interdigital transducer electrode 2, 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, the thickness of the interdigital transducer electrode 2 is 0.05 lambda, the interdigital transducer electrode 2 is of a piston structure shown in fig. 2A, the specific structure of the interdigital transducer electrode 2 is as described above, and details are not repeated herein for saving space, wherein the thickness of the insulating medium layer 23 is 800 angstroms, the width of the insulating medium layer accounts for 3% of the total length of the second interdigital strip electrode, and the material of the insulating medium layer is tantalum pentoxide.
Example 12
The present embodiment provides an acoustic surface wave filter and a method for manufacturing the same, the structure of the acoustic surface wave filter is shown in fig. 1-2, and the structure of the acoustic surface wave filter is a piezoelectric substrate 1/interdigital transducer electrode 2, 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, the thickness of the interdigital transducer electrode 2 is 0.05 lambda, the interdigital transducer electrode 2 is of a piston structure shown in fig. 2A, the specific structure of the interdigital transducer electrode 2 is as described above, and details are not repeated herein for saving space, wherein the thickness of the insulating medium layer 23 is 1000 angstroms, the width of the insulating medium layer is 2% of the total length of the second interdigital strip electrode, and the material of the insulating medium layer is tantalum pentoxide.
Example 13
The present embodiment provides an acoustic surface wave filter and a method for manufacturing the same, the structure of the acoustic surface wave filter is shown in fig. 1-3, and the structure of the acoustic surface wave filter is a 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 has a thickness of 0.05 lambdaThe energy device electrode 2 is a "piston" structure as shown in fig. 2A, and the specific structure of the interdigital transducer electrode 2 is as described above, which is not described herein again for saving space, wherein the thickness of the insulating medium layer 23 is 900 angstroms, the width of the insulating medium layer is 3% of the total length of the second interdigital strip electrode, and the material is tantalum pentoxide; 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.
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 shown in FIG. 2A 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 the insulating medium layer 23 on the first boundary area A1 and the second boundary area A2 of the interdigital transducer electrode 2; the method for depositing the insulating medium layer 23 comprises the following steps:
depositing tantalum pentoxide as an insulating medium layer material in the first boundary area A1 and the second boundary area A2 by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, and at least depositing the surfaces of the interdigital finger electrodes in the two areas to form an insulating medium layer 23; the PECVD working conditions for depositing the insulating dielectric layer are as follows: the working temperature is 250-400 ℃, the radio frequency discharge frequency is 13.56MHz, the radio frequency power is 1-2KW, and the vacuum in the coating cavity is kept at 7 x 10-5Pa or less.
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 copper electrode 2 shown in FIG. 2A 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 the insulating medium layer 23 on the first boundary area A1 and the second boundary area A2 of the interdigital transducer electrode 2; the method for depositing the insulating medium layer 23 comprises the following steps:
depositing tantalum pentoxide as an insulating medium layer material in the first boundary area A1 and the second boundary area A2 by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, and at least depositing the surfaces of the interdigital finger electrodes in the two areas to form an insulating medium layer 23; the PECVD working conditions for depositing the insulating dielectric layer are as follows: the working temperature is 250-400 ℃, the radio frequency discharge frequency is 13.56MHz, the radio frequency power is 1-2KW, and the vacuum in the coating cavity is kept at 7 x 10-5Pa or less.
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 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 the insulating medium layer 23 in the first boundary area a1 and the second boundary area a2 of the interdigital transducer electrode 2 with reference to step S2 in example 21;
s3: 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;
s4: carrying out ICP etching treatment on the outer surface of the insulation protection film layer to form a plurality of spaces on the surfaceSpacing the protrusions 31 so that SiO2The insulating protective film layer becomes SiO2An insulating protective layer 3; 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.
Comparative example
Conventional surface acoustic wave filters are commercially available.
3. Acoustic surface wave filter related performance test
The acoustic surface wave filters provided in examples 11 to 13 and the commercially available conventional acoustic surface wave filter provided in comparative example were subjected to the following correlation performance tests, respectively, wherein the results of the acoustic surface wave filters of example 11, example 13 and comparative example 1 are shown in the following table 1:
TABLE 1
In addition, the performance test results of the surface acoustic wave filter provided in example 12 were similar to those of the surface acoustic wave filter of example 11 in table 1. Therefore, as can be seen from the results of the related performance tests in table 1, the surface acoustic wave filter of the present embodiment has a low Q value, 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 (10)
1. A temperature compensated 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;
the interdigital transducer electrode comprises a first bus electrode and a second bus electrode, and the first bus electrode and the second bus electrode are oppositely arranged; the first bus electrode comprises a plurality of first interdigital finger electrodes arranged at intervals, one end of each first interdigital finger electrode is in contact with the first bus electrode, and the other end of each first interdigital finger electrode points to the second bus electrode; the second bus electrode comprises a plurality of second interdigital finger electrodes which are arranged at intervals, one end of each second interdigital finger electrode is in contact with the second bus electrode, and the other end of each second interdigital finger electrode points to the first bus electrode; the first interdigital finger strip electrodes and the second interdigital finger strip electrodes are arranged in a staggered mode;
a first boundary region is formed from a section of the end tip of the first interdigital finger electrode toward the first bus electrode end in a direction parallel to the first bus electrode or the second bus electrode; a section of the second interdigital electrode from the end terminal thereof toward the second bus electrode terminal is configured as a second boundary region; and insulating medium layers for inhibiting the transverse propagation loss mode of the acoustic wave are deposited on the first interdigital finger electrode and the second interdigital finger electrode in the first boundary area and the second boundary area.
2. The surface acoustic wave filter of claim 1, wherein: the width of the first boundary area accounts for 1-2% of the total length of the first interdigital finger electrode; or
The width of the second border region accounts for 2-3% of the total length of the second interdigital finger electrode.
3. The acoustic surface wave filter according to any one of claims 1-2, wherein: the thickness of the insulating dielectric layer is 800-1000 angstroms; and/or
The thickness of the interdigital transducer electrode is 0.045-0.055 lambda.
4. The acoustic surface wave filter according to any one of claims 1-2, wherein: the piezoelectric transducer further comprises an insulating protection layer which is laminated on the plane of the piezoelectric substrate and covers the interdigital transducer electrodes.
5. The surface acoustic wave filter of claim 4, wherein: the insulating protective layer is provided with two opposite surfaces, one surface of the insulating protective layer is laminated and combined on the plane of the piezoelectric substrate and covers the interdigital transducer electrode; the other surface is provided with a plurality of bulges distributed at intervals.
6. The surface acoustic wave filter of claim 5, 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.
7. The surface acoustic wave filter of claim 6, wherein: the ratio of the width of the tip to the width of the root of a single protrusion is 0.3-0.4.
8. The acoustic surface wave filter according to any one of claims 5 to 7, wherein: the distance between the adjacent bulges is 0.3-0.8 mu m; and/or
The height of the protrusions is 1.0-1.1 μm.
9. The acoustic surface wave filter according to any one of claims 5 to 7, wherein: the position where a single bump is formed corresponds positively to a single electrode of the interdigital transducer electrode.
10. The acoustic surface wave filter according to any one of claims 5 to 7, wherein: the total thickness of the insulation protective layer is 0.29-0.31 lambda, and lambda is the acoustic wave wavelength.
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| CN110649908A (en) * | 2019-08-05 | 2020-01-03 | 北京中讯四方科技股份有限公司 | Temperature compensation acoustic surface wave filter and preparation method and application thereof |
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| CN110649908A (en) * | 2019-08-05 | 2020-01-03 | 北京中讯四方科技股份有限公司 | Temperature compensation acoustic surface wave filter and preparation method and application thereof |
| CN115642895A (en) * | 2022-11-10 | 2023-01-24 | 锐石创芯(重庆)科技有限公司 | Surface acoustic wave device, filter, and electronic apparatus |
| CN115642895B (en) * | 2022-11-10 | 2024-05-28 | 锐石创芯(重庆)科技有限公司 | Surface acoustic wave device, filter, and electronic apparatus |
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Address after: 201, 2 / F, block a, 3 Yongjie North Road, Yongfeng Industrial base, Haidian District, Beijing Patentee after: BEIJING ZHONGXUN SIFANG SCIENCE & TECHNOLOGY Co.,Ltd. Patentee after: Zhejiang Huayuan Micro Electronics Technology Co.,Ltd. Address before: 201, 2 / F, block a, 3 Yongjie North Road, Yongfeng Industrial base, Haidian District, Beijing Patentee before: BEIJING ZHONGXUN SIFANG SCIENCE & TECHNOLOGY Co.,Ltd. Patentee before: SHENZHEN HUAYUAN MICRO ELECTRONIC TECHNOLOGY Co.,Ltd. |