阅读说明：本技术 一种低插损高频声表面波滤波器 (Low-insertion-loss high-frequency surface acoustic wave filter ) 是由 王巍 周杨春 黎淼 于 2021-08-13 设计创作，主要内容包括：本发明请求保护一种高频低插损声表面波滤波器,属于声表面波滤波器技术领域,其包括滤波器的结构设计和减小带内波动、减小插入损耗,提高带外抑制性能的优化方法。其中滤波器的结构设计包括4个结构参数相同的并联谐振器P1-P4和4个结构参数不同的串联谐振器S1-S4组成”T+π”型结构以提高带外抑制并优化矩形系数。提高性能的优化方法包括,每个谐振器单元均使用厚金属膜插指电极结构以抑制乐甫波波速并提高瑞利波强度；提高所有串联谐振器的占空比并减小反射栅周期以减少横向模式干扰；通过调整串联谐振器插指对数改变谐振器横向模式频率点的位置使得级联不同谐振器时,由横向模式引入的损耗错位叠加进而在提高带外抑制的同时减小带内波动和插入损耗。(The invention provides a high-frequency low-insertion-loss surface acoustic wave filter, belongs to the technical field of surface acoustic wave filters, and comprises a structural design of the filter and an optimization method for reducing in-band fluctuation, reducing insertion loss and improving out-of-band inhibition performance. The structural design of the filter comprises a T + pi type structure formed by 4 parallel resonators P1-P4 with the same structural parameters and 4 series resonators S1-S4 with different structural parameters so as to improve out-of-band rejection and optimize a rectangular coefficient. The optimization method for improving the performance comprises the steps that each resonator unit uses a thick metal film interdigital electrode structure to inhibit the wave velocity of love waves and improve the Rayleigh wave intensity; increasing the duty cycles of all the series resonators and reducing the period of the reflective grating to reduce the lateral mode interference; the position of the transverse mode frequency point of the resonator is changed by adjusting the number of the inserted fingers of the series resonator, so that when different resonators are cascaded, loss introduced by the transverse mode is superposed in a staggered mode, and in-band fluctuation and insertion loss are reduced while out-of-band rejection is improved.)

1. A low insertion loss high frequency surface acoustic wave filter comprising: four resonators S1, S2, S3 and S4 which are sequentially connected in series, four parallel resonators P1-P4 with the same structural parameters, and grounding end ports of the parallel resonators P1-P4 are connected with each other and then grounded, wherein the other port of the P1 is connected with a port I of the series resonator S1 to serve as a port 1 of the surface acoustic wave filter, and the other port end of the P4 is connected with a port two phase of the series resonator S4 to serve as a port 2 of the surface acoustic wave filter; the other ports of P2 and P3 are both arranged between S2 and S3 in series, the second port of S1 is connected with the first port of S2, and the second port of S3 is connected with the first port of S4. The series resonators S1 and S2 and the parallel resonators P1 and P2 form a pi-type structure, the series resonators S3 and S4 and the parallel resonators P3 and P4 form a pi-type structure, the parallel resonators P2 and P3 and the series resonators S1, S2, S3 and S4 form a T-type structure, and the whole body is combined into a T + pi-type structure in a cascading mode.

2. A low insertion loss high frequency surface acoustic wave filter as set forth in claim 1, wherein all the resonators use a thick metal film interdigital electrode structure.

3. The low-insertion-loss high-frequency surface acoustic wave filter according to claim 2, wherein the electrode material of the thick metal film interdigital electrode structure is metal aluminum, and the relative thickness of the electrode is set to be 33% -36% so as to improve the electromechanical coupling coefficient and the rayleigh wave strength and weaken the love wave velocity.

4. The low-insertion-loss high-frequency surface acoustic wave filter according to claim 2, wherein by increasing the duty ratio of the resonators S1, S2, S3 and S4, η ═ a/b, a is the finger width and b is the finger gap, and decreasing the period of the reflection grating; the duty ratio is the width of the inserted finger divided by the gap of the inserted finger, for the average finger, the duty ratio is 1, the period of the reflection grating is usually half of the period of the inserted finger, and the duty ratio is also adjusted downwards according to 0.5 times of the period lambda of the inserted finger, and the simulation result shows that the interference is reduced along with the reduction of the period of the reflection grating, and the number of inserted fingers of the series resonator is adjusted to change the position of the transverse mode frequency point of the resonator. The transverse modes correspond to different mode SAW modes and have different wave velocities, the transverse modes are only interference modes and are mixed mode signals, and the resonance frequency point of the transverse mode is changed by changing the number of pairs of the inserted fingers.

5. The low-insertion-loss high-frequency surface acoustic wave filter as claimed in claim 4, wherein the duty ratio of the series resonators S1-S4 is increased to 5:1, and the periods of the reflection gratings are each less than 0.5 times the wavelength corresponding to the center frequency.

6. The low insertion loss high frequency surface acoustic wave filter according to claim 3, wherein said thick metal film interdigital electrode structure has a piezoelectric material of 128 ° Y-X LiNbO₃The wavelength lambda of the series resonator is 1.1 μm, the wavelength of the parallel resonator is 1.2 μm, the thicknesses of the fingers of the series resonator and the parallel resonator are both 0.4 μm, and the relative wavelength thicknesses are 36.4% and 33.3%, respectively.

7. The low-insertion-loss high-frequency surface acoustic wave filter according to claim 6, wherein the resonance point of the transverse mode in the pass band is changed by adjusting the pairs of the insertion fingers of the series resonators S1-S4, so that when the resonators are cascaded, the transverse modes can be superposed in a staggered manner to reduce the in-band ripple and insertion loss, and the parallel resonators all adopt a finger-sharing structure.

Technical Field

The invention belongs to the technical field of surface acoustic wave filters, and particularly relates to a design of a high-frequency low-insertion-loss filter above GHz.

Background

At present, the Surface Acoustic Wave (SAW) filter conforms to the development of the mobile communication technology by the characteristics of small volume, high frequency, low insertion loss and the like and is widely applied. Generally, a piezoelectric material having a high acoustic velocity and a high electromechanical coupling coefficient is used to increase the center frequency of a filter, reduce insertion loss, or have a multilayer diamond-containing film structure, and the purpose is to increase the wave velocity of a surface acoustic wave. However, the manufacturing process of the multilayer film structure is relatively complex, and the high electromechanical coupling coefficient tends to enhance the intensity of other modes when enhancing the intensity of the desired surface acoustic wave mode, which undoubtedly enhances the insertion loss of the device.

Compared with a longitudinal coupling structure (LCRF), the SAW filter with the Ladder structure (Ladder) is more flexible in bandwidth design, has lower insertion loss than a dual in-line structure (IIDT), and can improve out-of-band rejection by adjusting a cascade mode, but the same cascade resonator can lead to the superposition of the pass band internal mixed mode intensity and large rectangularity. Therefore, the single-layer film and the trapezoid structure are adopted to be cascaded in a T + pi shape, different series resonators are cascaded to inhibit the mixed mode through cascading different series resonators, the transverse mode is mainly referred to, and the adjustment interpolation means is used for changing the mixed mode superposition of the same frequency point in a logarithmic mode. For the structure, the structural parameters are determined, the wave speed of the corresponding transverse mode can also be determined, the structure is changed, for example, the number of pairs of the insertion fingers is different, the transverse mode also changes, and the simulation structure knows that changing the number of pairs of the insertion fingers changes the resonant frequency point of the transverse mode and suppresses the superposition of the same-frequency points of the intensity of the modes of the stray modes in the pass band.

Disclosure of Invention

The present invention is directed to solving the above problems of the prior art. A low insertion loss high frequency surface acoustic wave filter is provided. The technical scheme of the invention is as follows:

a low insertion loss high frequency surface acoustic wave filter comprising: the resonator comprises four resonators S1, S2, S3 and S4 which are sequentially connected in series, and four parallel resonators P1-P4 with the same structural parameters. Grounding end ports of the parallel resonators P1-P4 are connected with each other and then grounded, wherein the other port of P1 is connected with the first port of the series resonator S1 and is used as a port 1 of the surface acoustic wave filter, and the other port end of P4 is connected with the second port of the series resonator S4 and is used as a port 2 of the surface acoustic wave filter; the other ports of P2 and P3 are both arranged between S2 and S3 in series, the second port of S1 is connected with the first port of S2, and the second port of S3 is connected with the first port of S4. The series resonators S1 and S2 and the parallel resonators P1 and P2 form a pi-type structure, the series resonators S3 and S4 and the parallel resonators P3 and P4 form a pi-type structure, the parallel resonators P2 and P3 and the series resonators S1, S2, S3 and S4 form a T-type structure, and the whole body is combined into a T + pi-type structure in a cascading mode.

Further, the resonator S1, the resonator S2, the resonator S3, the resonator S4 and the four parallel resonators all use thick metal film inter-digitated electrode structures.

Furthermore, the electrode material of the thick metal film interdigital electrode structure is metal aluminum, and the relative thickness of the electrode is set to be 33% -36%, so that the electromechanical coupling coefficient and the Rayleigh wave strength are improved, and the love wave velocity is weakened.

Further, by increasing the duty ratio of the resonator S1, the resonator S2, the resonator S3 and the resonator S4 and reducing the period of the reflecting grating; the number of pairs of fingers of the series resonator is adjusted to change the position of the transverse mode frequency point of the resonator.

Further, the duty ratio (formula 1, a is the width of the finger and b is the gap of the finger) of the series resonators S1-S4 is increased to 5:1, and the periods of the reflection gratings are all less than 0.5 times of the wavelength corresponding to the center frequency. .

Furthermore, the piezoelectric material of the thick metal film finger-inserting electrode structure is 128-degree Y-X LiNbO₃The wavelength lambda of the series resonator is 1.1 μm, the wavelength of the parallel resonator is 1.2 μm, the thicknesses of the fingers of the series resonator and the parallel resonator are both 0.4 μm, and the relative wavelength thicknesses are 36.4% and 33.3%, respectively.

Furthermore, the resonance point of the transverse mode in the pass band is changed by adjusting the number of the inserted finger pairs of the series resonators S1-S4, so that the transverse mode can be superposed in a staggered mode when the resonators are cascaded, the in-band fluctuation and the insertion loss are reduced, and the parallel resonators all adopt a finger-sharing structure.

The invention has the following advantages and beneficial effects:

the invention adopts a single-layer structure, and the process is simpler. The ladder-shaped structure is cascaded in a T + pi type, out-of-band rejection is improved, meanwhile, the rectangularity of the filter is optimized to be closer to 1, and the rectangularity of the filter is closer to 1 through the T + pi type structure. The thinking that the conventional electrode thickness only accounts for 3-10% of the wavelength is broken through, and the electromechanical coupling coefficient is improved by adopting a thick metal membrane electrode structure. The interference of the transverse mode is reduced by improving the duty ratio of the series resonator and reducing the period of the reflecting grating of the series resonator. The superposition of losses introduced by a transverse mode at the same frequency point when the resonators are cascaded is suppressed by changing the number of pairs of the insertion fingers of the series resonators, so that the in-band fluctuation and the insertion loss are reduced while the out-of-band suppression is improved.

Drawings

FIG. 1 is a schematic diagram of the overall (T + π) structure of a filter according to the present invention.

Fig. 2 is a two-dimensional schematic diagram of a series resonator with a high duty cycle, thick film interdigital structure.

Fig. 3 is a simulation diagram of the frequency response of the designed high-frequency low-insertion loss surface acoustic wave filter.

Fig. 4 is a partial enlarged view of fig. 3 at the center frequency.

Detailed Description

The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.

The technical scheme for solving the technical problems is as follows:

a high-frequency low-insertion loss surface acoustic wave filter design comprises a filter structure design and an optimization method for reducing in-band fluctuation, reducing insertion loss and improving out-of-band inhibition performance. The structural design of the filter comprises 4 parallel resonators with the same structural parameters and 4 series resonators with different structural parameters to form a T + pi type structure. The optimization method for improving the performance comprises the following steps that each resonator unit uses a thick metal film interdigital electrode structure; the duty ratio of all series resonators is improved, and the period of the reflecting grating is reduced; the number of pairs of fingers of the series resonator is adjusted to change the position of the transverse mode frequency point of the resonator.

As shown in fig. 1, the two resonators S1 and S2 connected in series with each other on the left and the two resonators S3 and S4 connected in series with each other on the right are respectively connected in parallel with the two parallel resonators P2 and P3 on the left and the right of the series combination structure to form two "pi" type structures, the two parallel resonators P2 and P3 in the middle and the 4 series resonators S1-S4 form a "T" type structure, and the whole is cascaded to form a "T + pi" type structure.

As shown in FIG. 2, the electrode material is aluminum metal, and the piezoelectric material is 128-degree Y-X LiNbO₃The wavelength (λ) of the series resonator is 1.1 μm, and the wavelength of the parallel resonator is 1.2 μm. In order to improve the electromechanical coupling coefficient and the Rayleigh wave intensity and weaken the love wave velocity, a thick metal film insert finger structure is adopted: the thicknesses of the insertion fingers of the series resonators and the parallel resonators are both 0.4 mu m, and the relative wavelength thicknesses are 36.4% and 33.3% respectively. The duty cycle of all series resonators is 5:1 as shown in fig. 2

I.e. the ratio of the finger width (a) to the finger gap (b) is 5:1, and the period of the reflective grating (lambda)_g) High duty cycles of 5:1 are also used, all 0.6 μm, to reduce the effect of the transverse mode on in-band loss.

By adjusting the number of pairs of the fingers of the series resonators S1-S4 to be 61.5 pairs, 59.5 pairs, 63.5 pairs and 57.5 pairs in sequence, the resonance point of the transverse mode in the pass band is changed, so that when the resonators are cascaded, the transverse modes can be overlapped in a staggered mode, and the in-band fluctuation and the insertion loss are reduced.

Fig. 3 shows the result of simulation of the frequency response of a surface acoustic wave filter having an operating frequency of 2.517GHz and using the "T + pi" type. Simulation results show that after the structure and the performance optimization mode are adopted, the-3 dB bandwidth of the filter reaches 3.9% when 99MHz, the central insertion loss and in-band fluctuation are less than 1dB, the squareness degree is 1.3, the out-of-band rejection reaches-32 dB, and the design requirement of high frequency low insertion loss is met.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.