阅读说明：本技术 一种射频声表面波滤波器 (Radio frequency surface acoustic wave filter ) 是由 陈婷婷 杜雪松 谢晓 谢东峰 彭霄 罗璇升 彭雄 张华� 明礼 刘春雪 于 2021-07-22 设计创作，主要内容包括：本发明专利涉及声表面波滤波器,具体涉及本发明提出一种射频声表面波滤波器,包括压电基片以及压电基片上方的结构单元,结构单元为梳状设置的金属指条,每根金属指条的四个端角进行加宽处理,形成活塞式加权,加权的尺寸为：x轴方向的长度为金属指条宽度/20～金属指条宽度/2、y轴方向的长度为金属指条宽度/10～金属指条宽度；本发明对金属指条进行加权设计,提高剥离精确度,使金属指条表面光滑平整,减小表面波能量损耗,使得在中心频率大于2GHz的声表面波滤波器的顶部插损能够减小到1.0以内；该结构也可以补偿曝光显影设备在制作金属指条的失真现象,利用现有设备高精度制作更细的金属指条,实现超高中心频率滤波器的制作。(The invention relates to a surface acoustic wave filter, in particular to a radio frequency surface acoustic wave filter, which comprises a piezoelectric substrate and a structural unit above the piezoelectric substrate, wherein the structural unit is a metal finger strip arranged in a comb shape, four end angles of each metal finger strip are widened to form piston type weighting, and the weighting size is as follows: the length in the x-axis direction is the width of the metal finger/20-2, and the length in the y-axis direction is the width of the metal finger/10-2; according to the invention, the metal finger strip is subjected to weighted design, so that the stripping accuracy is improved, the surface of the metal finger strip is smooth and flat, the surface wave energy loss is reduced, and the insertion loss of the top of the surface acoustic wave filter with the central frequency of more than 2GHz can be reduced to be within 1.0; the structure can also compensate the distortion phenomenon of the exposure and development equipment in the process of manufacturing the metal finger strips, and the existing equipment is utilized to manufacture thinner metal finger strips with high precision, so that the manufacture of the ultrahigh central frequency filter is realized.)

1. The utility model provides a radio frequency surface acoustic wave filter, includes the constitutional unit of piezoelectric substrate and piezoelectric substrate top, the constitutional unit is the metal finger strip that the pectination set up, its characterized in that, four end angles of every metal finger strip widen the processing, form piston weighting, weighted size is: the length in the x-axis direction is the width of the metal finger/20-2, and the length in the y-axis direction is the width of the metal finger/10-2.

2. The rf surface acoustic wave filter of claim 1, wherein the functional layer is disposed over the piezoelectric substrate, and the protective layer is disposed over the metal fingers, and the protective layer has a thickness of between 5nm and 30 nm.

3. The rf surface acoustic wave filter according to claim 2, wherein the functional layer is made of metal titanium, titanium copper gold, or titanium aluminum alloy.

4. The RF surface acoustic wave filter according to claim 2, wherein the protective layer is made of silicon dioxide or silicon nitride, and the thickness of the protective layer is 20-100 nm.

5. The rf surface acoustic wave filter according to claim 1, wherein the structural element is a single-ended interdigital transducer or a longitudinally coupled resonator.

6. The radio frequency surface acoustic wave filter according to claim 1, wherein the piezoelectric substrate is made of lithium tantalate or lithium niobate.

7. The rf surface acoustic wave filter according to claim 1, wherein the metal finger surfaces are covered with a silicon dioxide or silicon nitride material.

8. The RF SAW filter of claim 1, wherein the end of one of the metal fingers is electrically connected to ports, the number of electrical ports being 4-20 and even.

Technical Field

The invention relates to a Surface Acoustic Wave (SAW) filter, in particular to a radio frequency SAW filter.

Background

Since the SAW filter well combines the advantages of high performance, mature technology, small volume, low cost, high consistency and the like, the SAW filter is widely applied to military equipment such as pulse pressure radars, anti-interference receivers, communication radio stations, phased array radars and the like since the seventies of the last century. In the civil market, the television intermediate frequency filter raises the first climax of the large-scale application of the SAW technology; from 2G mobile communication, the miniaturized low-loss SAW rf filter is applied exclusively to a mobile phone, and the second climax of the scale application of the SAW technology is raised.

With the market prospects of global mobile phone filters being viewed consistently, the market size of mobile phone filters is growing rapidly. Among mobile phone filters, the most mature and widely used is the Surface Acoustic Wave (SAW) filter. In recent years, with the development of mobile communication technology, communication data traffic and the number of Long Term Evolution (LTE) frequency bands required by 3GPP have increased significantly, so that frequency band resource allocation of LTE and LTE-advanced (LTE-a) frequency spectrums is more crowded; in addition, Carrier Aggregation (CA) technology for uplink and High Power User Equipment (HPUE) have also begun to find application in various communication systems. In recent years, the filter industry is in a tuyere with high-speed development, and the market demands for a single device or a wafer of a sound surface filter are very urgent, so that for a sound surface production enterprise, how to release the capacity and improve the wafer yield and the finished product rate are problems to be faced and solved at present.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a novel SAW device structure, which weights interdigital transducer metal fingers, reflection grid metal fingers and fake finger metal fingers of a filter, can compensate the exposure precision of the fingers in a photoetching process by utilizing the weighting structure, enables the process to realize the manufacture of thinner metal fingers with higher precision requirement, and greatly improves the manufacture precision and yield of high-frequency and even ultrahigh-frequency radio frequency filters. The length in the x-axis direction is the width of the metal finger/20-2, and the length in the y-axis direction is the width of the metal finger/10-2.

Furthermore, a functional layer is arranged above the piezoelectric substrate, and a protective layer is arranged above the metal finger strips.

Furthermore, the functional layer is made of metal titanium, titanium copper gold or titanium aluminum alloy.

Furthermore, the protective layer is made of silicon dioxide or silicon nitride material.

Further, the structural unit is a single-end interdigital transducer or a longitudinal coupling resonator.

Furthermore, the piezoelectric substrate is made of lithium tantalate or lithium niobate.

Further, the surface of the metal finger strip is covered with silicon dioxide or silicon nitride material.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, the metal finger strip is subjected to weighted design, so that the stripping accuracy is improved, the surface of the metal finger strip is smooth and flat, the surface wave energy loss is reduced, and the insertion loss of the top of the surface acoustic wave filter with the central frequency of more than 2GHz can be reduced to be within 1.0;

(2) according to the invention, the distortion phenomenon of exposure and development equipment in manufacturing metal finger strips is compensated by using the weighting metal block, the influence of process errors on the metal appearance of the filter is reduced, the electrical performance index of the filter is improved, and the purpose of improving the yield is realized;

(3) according to the invention, the distortion phenomenon of exposure and development equipment in manufacturing metal fingers is compensated by using the weighted metal block, and thinner metal fingers are manufactured with high precision by using the existing equipment, so that the manufacture of an ultrahigh central frequency filter is realized;

(4) the finger weighting mode designed by the filter of the invention utilizes the existing equipment to accurately manufacture the high-precision metal finger, reduces clutter loss, realizes high yield of chips and high consistency of process, and meets the increasingly crowded spectrum application requirement in future communication.

Drawings

FIG. 1 is a schematic diagram of a RF SAW filter according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a single-ended interdigital transducer, which is a structural unit of a radio frequency surface acoustic wave filter in an embodiment of the present invention;

FIG. 3 is a diagram of a weighted structure of a metal finger of a single-ended interdigital transducer, which is a structural unit of a radio frequency surface acoustic wave filter in an embodiment of the present invention;

fig. 4 is a schematic diagram of a structural unit of a radio frequency surface acoustic wave filter, namely a structural diagram of a longitudinal coupling resonator in the embodiment of the invention;

FIG. 5 is a diagram of a structure of a metal finger weighting structure of a longitudinally coupled resonator, which is a structural unit of a radio frequency surface acoustic wave filter according to an embodiment of the present invention;

in the figure, 1, a piezoelectric substrate layer, 2, a functional layer, 3, a protective layer, 4, a metal finger, 5, an electric connection port, 6, an acoustic channel, 7 and a weighting layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a radio frequency surface acoustic wave filter, which comprises a piezoelectric substrate and a structural unit above the piezoelectric substrate, wherein the structural unit is a metal finger strip arranged in a comb shape, four end corners of each metal finger strip are widened, the widened metal finger strip is a weighting layer 7 arranged at the end corners in a figure 3 or a figure 5, piston type weighting is formed, and the weighting size, namely the size of the weighting layer 7 is as follows: the length in the x-axis direction is the width of the metal finger/20-2, and the length in the y-axis direction is the width of the metal finger/10-2.

Example 1

As shown in fig. 1, the surface acoustic wave filter of the present invention includes a piezoelectric substrate 1, a functional layer 2 disposed above the piezoelectric substrate 1, a comb-shaped metal finger 4 disposed above the functional layer 2, and a protective layer 3 disposed above the comb-shaped metal finger 4.

In the embodiment of the invention, in order to reduce the difference of the thermal stress of the film layers of the piezoelectric substrate and the metal finger above the piezoelectric substrate, improve the adhesion of the film layer of the metal finger on the piezoelectric substrate and reduce the energy loss of surface acoustic waves during the transmission of the piezoelectric substrate, a functional layer 2 is attached to the upper part of a piezoelectric substrate layer 1 by adopting a physical or chemical method, and the stress mismatching between the piezoelectric substrate and the metal finger film is reduced by utilizing the large yield strength of the functional layer, so that the adhesion of the metal finger on the piezoelectric substrate is improved.

In order to improve the frequency uniformity of the monolithic wafer, particularly the frequency uniformity of the monolithic wafer of 2GHz or higher, a protective layer 4 is covered on the metal finger film layer 3, and the frequency uniformity and reliability of the monolithic wafer are improved by utilizing the temperature characteristic and the frequency characteristic of the protective layer 4.

Specifically, in some embodiments, the piezoelectric substrate 1 is made of lithium tantalate or lithium niobate, and different cut shapes and substrate materials are selected according to different electrical performance index requirements.

Further, the functional layer 2 may be made of metal titanium (Ti), titanium copper (TiCu) alloy or titanium aluminum (TiAl) alloy.

Further, the material of the protective layer 3 can adopt silicon dioxide (SiO)₂) Or silicon nitride (SiN).

As an alternative embodiment, the metal electrode finger 4 may be made of a metal material having excellent conductivity, such as metal aluminum (Al), metal copper (Cu), aluminum copper alloy (AlCu), metal chromium (Cr), metal gold (Au), metal silver (Ag), or metal tungsten (W).

The present invention utilizes the strong yield of the functional layer to reduce the thermal stress mismatch between the piezoelectric substrate and the metal fingers. Since the conductivity of the functional layer is smaller than that of the metal finger layer thin film, the overall energy loss of the filter is affected by the thickness of the functional layer being too thick, and thus the film thickness of the functional layer is usually set to 5nm to 30 nm.

In some embodiments, the protective layer is usually SiO2 material or SiN material, and the heat dissipation property thereof is utilized to improve the quality reliability of the saw filter, but since the protective layer is usually an insulator and the propagation speed of the acoustic wave in the protective layer is obviously different from that in the piezoelectric substrate, the thickness of the protective layer is usually between 20 nm and 100nm, and this thickness does not have a great influence on the electrical performance of the filter.

Example 2

In this embodiment, a single-port interdigital transducer is selected as a structural unit of the acoustic surface filter. As shown in fig. 2, in the present embodiment, one end of the metal finger 4 is connected to an electrical connection port 5; the electrical connection port 5 serves as a main bus bar and can guide an electrical signal to the acoustic channel 6, so that acoustic waves are excited; the acoustic channel 6 is a surface acoustic wave propagation channel formed by interdigital electrodes in a comb-like structure, and is generally located between bus bars (electrical ports 5) on the upper and lower sides (only one bus bar is shown in fig. 2); in this embodiment, the four end corners of all the fingers of the metal finger 4 are weighted to be widened, so that the metal finger has a piston-type structure, the widening dimension is that the length in the x-axis direction is the width of the metal finger/20-2 of the metal finger, the length in the y-axis direction is the width of the metal finger/10-2 of the metal finger, and meanwhile, the adjacent widened fingers are kept unconnected to each other, so as to avoid short circuit.

Example 3

In the present embodiment, longitudinally coupled resonators are selected as structural elements of the acoustic surface filter. As shown in fig. 4, in the present embodiment, one end of the metal finger 4 is connected to an electrical connection port 5; the electrical connection port 5 serves as a main bus bar and can guide an electrical signal to the acoustic channel 6, in the embodiment, the number of the electrical connection ports 5 in fig. 5 is 6, but according to actual design requirements, the number of the electrical connection ports 5 can be 4-20 (note: the number of the electrical connection ports is an even number); the acoustic channel 6 is a surface acoustic wave propagation channel formed by interdigital electrodes in a comb-like structure, and is generally located between bus bars (electrical ports 5) on the upper and lower sides (only one bus bar is shown in fig. 2); in this embodiment, the four end corners of all the metal fingers 4 are weighted by widening, so that the fingers form a piston-type structure, the widening dimension is that the length in the x-axis direction is the metal finger width/20-2, and the length in the y-axis direction is the metal finger width/10-2, and meanwhile, the adjacent widened fingers are kept unconnected to avoid short circuit.

Example 4

This embodiment is further illustrated by widening the end corners of the metal strips to form piston weights, and as shown in fig. 3, in this embodiment, the metal strips 4 are kept in a normal vertical state in the acoustic channel 6, and in view of the characteristics of the acoustic surface filter, the metal strips are divided into an Interdigital Transducer (IDT) having a reflection grating and a comb shape, wherein the IDT is composed of a dummy finger and a real finger electrode finger. In the embodiment of the present invention, all the metal fingers in the acoustic channel, including the four corners of the reflection grating finger, the dummy finger electrode, and the real finger electrode, need to be weighted in a widening manner, as shown in the weighting block 7 in the embodiment.

In the description of the present invention, it is to be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "other end", "upper", "one side", "top", "inner", "outer", "front", "center", "both ends", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "disposed," "connected," "fixed," "rotated," and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; the terms may be directly connected or indirectly connected through an intermediate, and may be communication between two elements or interaction relationship between two elements, unless otherwise specifically limited, and the specific meaning of the terms in the present invention will be understood by those skilled in the art according to specific situations.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.