Temperature compensation acoustic surface wave filter and preparation method and application thereof
阅读说明:本技术 温度补偿声表波滤波器及其制备方法与应用 (Temperature compensation acoustic surface wave filter and preparation method and application thereof ) 是由 卢翠 刘绍侃 张伟 王玉龙 于 2019-08-05 设计创作,主要内容包括:本发明公开了一种温度补偿声表波滤波器及其制备方法和应用。所述声表波滤波包括叉指换能器电极,所述叉指换能器电极包括第一汇流电极和第二汇流电极,所述第一汇流电极包括间隔设置的若干第一叉指指条电极,所述第二汇流电极包括间隔设置的若干第二叉指指条电极;沿平行于所述第一汇流电极或第二汇流电极方向,由所述第一叉指指条电极的端部末端起向所述第一汇流电极端的一段区域构成为第一边界区域;由所述第二叉指指条电极的端部末端起向所述第二汇流电极端的一段区域构成为第二边界区域;且在所述第一边界区域和第二边界区域内的所述第一叉指指条电极和第二叉指指条电极上沉积绝缘介质层。(The invention discloses a temperature compensation acoustic surface wave filter and a preparation method and application thereof. 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 depositing an insulating medium layer on the first interdigital finger electrode and the second interdigital finger electrode in the first boundary area and the second boundary area.)
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 insulating medium layer is made of Ta2O5(ii) a And/or
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 each single protrusion is smaller than that of the root of each single protrusion, and the side face of each single protrusion is an inclined plane; and/or
The ratio of the top width to the root width of a single projection is 0.3-0.4; and/or
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; and/or
The position where a single bump is formed corresponds to the positive direction of a single electrode of the interdigital transducer electrode; and/or
The insulating protective layer is made of at least one of silicon dioxide and silicon nitride; and/or
The total thickness of the insulation protective layer is 0.29-0.31 lambda, and lambda is the acoustic wave wavelength.
7. The acoustic surface wave filter of any one of claims 1-2, 5 and 6, wherein:
the interdigital transducer electrode is made of any one of Al, Cu and Ti or Al and Cu alloy;
the piezoelectric substrate is made of LiTaO3And has an Euler angle (0, theta, 0) theta of 380、410、420Any value of (1).
8. The method for manufacturing the acoustic surface wave filter according to any one of claims 1 to 7, comprising the steps of:
preparing interdigital transducer electrodes on one plane of a piezoelectric substrate;
and depositing the insulating medium layer in the first boundary area and the second boundary area of the interdigital transducer electrode.
9. The method of claim 8, wherein: the method for depositing the insulating medium layer comprises the following steps:
depositing an insulating medium layer material in the first boundary region and the second boundary region by adopting a plasma enhanced chemical vapor method, and forming the insulating medium layer for inhibiting a mode of acoustic wave transverse propagation loss on the first interdigital finger electrode and the second interdigital finger electrode in at least the first boundary region and the second boundary region;
or/and
after the step of depositing the insulating medium layer, the method further comprises the following steps:
depositing an insulating protective film layer on the plane of the piezoelectric substrate, and enabling the insulating protective film layer to cover the interdigital transducer electrode;
and etching the outer surface of the insulating protection film layer to form a plurality of bulges distributed at intervals on the surface.
10. Use of the surface acoustic wave filter according to any of claims 1-7 in radar, mobile communication, channelized receivers, telemetry systems.
Technical Field
The invention belongs to the technical field of microelectronics, and particularly relates to a temperature compensation surface acoustic wave filter and a 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 generally made of piezoelectric materials such as quartz crystals, piezoelectric ceramics and the like and is manufactured by utilizing the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. The piezoelectric effect is a phenomenon in which an electric field proportional to pressure is generated when a crystal is mechanically acted. When the crystal with piezoelectric effect is under the action of telecommunication signal, it can also produce elastic deformation to produce mechanical wave (sound wave), i.e. can convert the electric signal 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 enemies 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 transmission and diffusion, the acoustic wave can be transmitted to the side surface while being transmitted along the interdigital strip electrode of the interdigital transducer electrode, the acoustic wave transmitted to the side surface causes the loss of the acoustic wave, 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 military and civilian equipment performance indexes. 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.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a temperature compensation surface acoustic wave filter and a preparation method thereof, so as to solve the technical problems that the Q value of the existing SAWF is large or the temperature coefficient is large.
To achieve the object, in one aspect of the present invention, a temperature compensated acoustic surface filter is provided. 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;
interdigital transducer electrodes, which are fixedly arranged 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 which are 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 part tail end of the second interdigital strip electrode to the second bus electrode end forms 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.
In another aspect of the present invention, a method for manufacturing the temperature compensated surface acoustic wave filter of the present invention is provided. The preparation method of the temperature compensation surface acoustic wave filter comprises the following steps:
preparing interdigital transducer electrodes on one plane of a piezoelectric substrate;
and depositing the insulating medium layer in the first boundary area and the second boundary area of the interdigital transducer electrode.
In another aspect of the invention, the invention also provides an application of the temperature compensation surface acoustic wave filter. The temperature compensation acoustic surface wave filter is applied to radar, mobile communication, channelized receivers and remote sensing and telemetry systems.
Compared with the prior art, the temperature compensation surface acoustic wave filter has the advantages that the interdigital transducer electrodes are arranged into the piston structure, and the insulating medium layers are formed on the interdigital finger electrodes in the first boundary area and the second boundary area of the interdigital transducer electrodes of the piston structure. 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 the 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 found to be reduced at the same time.
According to the preparation method of the temperature compensation surface acoustic wave filter, the insulating medium layers are formed in the first boundary area and the second boundary area of the interdigital transducer electrode by adopting a deposition method, so that on one hand, the formed insulating medium layers can be effectively ensured to reduce the speed of acoustic waves propagating to the first boundary area and the second boundary area, the loss of the acoustic waves is effectively reduced, the Q value of the surface acoustic wave filter is effectively reduced, and the parasitic response is reduced at the same time; and on the other hand, the formed insulating medium layer 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. And the preparation method has controllable process conditions, and can effectively ensure stable performance, high yield and low cost of the prepared surface acoustic wave filter.
The temperature compensation surface acoustic wave filter has the characteristics of smaller Q value, low parasitic response and stable working performance. Therefore, the application of the surface acoustic wave filter in the corresponding field is enhanced, so that the working performance and the working stability of the corresponding device are improved.
Drawings
FIG. 1 is a schematic structural diagram of a temperature compensated 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 included in the temperature compensated surface acoustic wave filter of FIG. 1 and a graph of acoustic wave propagation rates in its various regions; wherein, FIG. 2-A is a schematic diagram of the structure 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 preferably including an insulating protective layer according to an embodiment of the present invention;
FIG. 4 is a graph of the electromechanical coupling coefficient of a temperature compensated SAW filter versus the Euler angle of the piezoelectric substrate in accordance with an embodiment of the present invention;
FIG. 5 is a graph of the electromechanical coupling coefficient of a temperature compensated SAW filter versus the thickness hmet/λ of the interdigital transducer electrodes in accordance with an embodiment of the present invention;
FIG. 6 is a graph of the relationship between the admittance of the temperature compensated SAW filter and the topography of the outer surface of the insulating protective layer in accordance with embodiments of the present invention; 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 showing the ratio SR of the protrusion top width A to the root width B on the outer surface of the insulating protective layer being 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 SAW 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 method for manufacturing a temperature compensated 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 problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. 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 a surface acoustic wave filter for short). The structure of the temperature compensation acoustic surface wave filter is shown in figure 1, and comprises a
The
The
In addition to the
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
Based on the structure of the
On the basis of the above embodiments, in an embodiment, as shown in fig. 3, the acoustic surface wave filter further includes an insulating
In a further embodiment, the acoustic surface wave filter comprises an insulating
In addition, further research shows that the temperature coefficient of the frequency of the surface acoustic wave filter can be remarkably reduced, such as better than-4 ppm/DEG C and even close to 0, by controlling the shape and the size of the
In yet another embodiment, the distance between
Therefore, 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 as to effectively reduce the propagation of the acoustic wave to the areas on both sides of the waveguide area, thereby effectively reducing the loss of the acoustic wave, and effectively reducing the Q value and the spurious response of the surface acoustic wave filter. The further insulating
Correspondingly, the embodiment of the invention also provides a preparation method of the temperature compensation surface acoustic wave filter. 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
s02: the insulating dielectric layer 23 is deposited on the first boundary area a1 and the second boundary area a2 of the
Specifically, in the above step S01, the method of preparing the
In the step S02, as an embodiment of the present invention, the method for depositing the insulating dielectric layer 23 includes the following steps:
and respectively depositing insulating dielectric 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 finger electrodes in the first boundary area A1 and the second boundary area A2 to form the insulating dielectric 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 dielectric layer, specifically, a tantalum pentoxide thin film, is deposited on the surfaces in the first boundary area and the second boundary area by utilizing a combined process of 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
s04: and etching the outer surface of the insulating protection film layer to form a plurality of
In the step S03, the method for depositing the insulating protection film layer may be, but is not limited to, magnetron sputtering. When the insulating protective film layer is formed by magnetron sputtering deposition, the inventor researches and developsNow, the change of the magnetron sputtering condition can cause the change of the elastic constant of the insulating protective film layer, thereby influencing the frequency temperature coefficient of the prepared acoustic surface wave filter. In a specific embodiment, the material of the insulating protection film layer is SiO2I.e. deposition of SiO on the
When different magnetron sputtering technological parameters are used for depositing SiO with the film thickness of 0.3 lambda2The films obtained
TABLE 1 SiO2FT-IR spectroscopy of deposited films
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. Such asThe temperature frequency coefficient is controlled to change between-20 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
In one embodiment, the etching process performed on the outer surface of the insulating
(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
(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
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, the mixture of multiple components of ionized electrons, charged ions, atoms or atomic groups and the like can be mixed with the insulating protective film layerMaterial SiO of2If 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 regions of the polymer 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 to 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
the SF6The flow rate of the introduced air flow is 30-60SCCM;
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
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
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 the acoustic surface filter to obtain wider application 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 and channelization
The present invention will now be described in further detail with reference to specific examples. In the following examples, "/" indicates the meaning of lamination bonding.
1 structural embodiment of surface acoustic wave filter
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