CN114759896A - Reflection grating design for inhibiting transverse mode interference of surface acoustic wave device - Google Patents

Abstract

The invention discloses a reflection grating design for inhibiting transverse mode interference of a surface acoustic wave device, belongs to the technical field of surface acoustic wave filters, and comprises an IDT type reflection grating structure design and a finite element simulation method of a resonator adopting the reflection grating structure. The invention aims to reduce the propagation loss of a surface acoustic wave filter and the interference of an in-band transverse mode so as to optimize in-band fluctuation and reduce insertion loss. The innovation point is that the reflection grating structure provided by the scheme further effectively reduces the in-band fluctuation and the insertion loss on the basis of the high-performance surface acoustic device with the insertion loss and the in-band fluctuation smaller than 1 dB. The reflective grating structure reduces the maximum peak loss in the band by 8.84% and 35.36% for the resonator and the first-order ladder filter, respectively, relative to the commonly used short-circuited reflective grating structure.

Description

A Reflector Design for Suppressing Transverse Mode Interference of Surface Acoustic Wave Devices

technical field

The invention belongs to the technical field of surface acoustic wave filters, and particularly relates to the reduction of filter propagation loss, the reduction of passband transverse mode interference, the reduction of ripple and the improvement of passband flatness.

Background technique

At present, surface acoustic wave (SAW) filters have been widely used in line with the development of mobile communication technology due to their small size, high frequency and low insertion loss. A surface acoustic wave device is usually composed of a piezoelectric substrate, an interdigital transducer and a reflection grating, and the surface acoustic wave is excited and received on the surface of the piezoelectric material through the piezoelectric effect IDT. In order to avoid the leakage of energy, reflection grid arrays are usually designed on both sides of the IDT and the energy is reflected back into the resonant cavity, but usually, in addition to the surface acoustic wave of the main mode, other acoustic waves such as transverse modes are also reflected, The peak loss caused by it directly increases the ripple of the filter, making the passband uneven, especially in the high frequency band above GHz, the interference of the transverse mode usually makes the in-band fluctuation above 1dB. In order to reduce the ripple and reduce the propagation loss of the device, an IDT-type reflection grating is designed in this paper. Different from the traditional short-circuit reflection grid and open-circuit reflection grid, the structure period of the IDT-type reflection grid is λ and is similar to the IDT structure. The period The inner adjacent reflective electrodes are respectively connected to two different bus bars. Based on COMSOL software, the finite element simulation results of the surface acoustic wave resonator and a ladder filter show that the structure effectively reduces the propagation loss of the device and the interference of the in-band transverse mode.

SUMMARY OF THE INVENTION

The present invention aims to solve the above problems of the prior art. An IDT-type reflector grating design that can reduce propagation loss and lateral mode interference in the passband is proposed, and a finite element model for analyzing the structure is provided. The technical scheme of the present invention is as follows:

A reflection grid design for suppressing lateral mode interference of a surface acoustic wave device, comprising a piezoelectric substrate on which an interdigital transducer is designed; the interdigital transducer is provided with IDT-type reflection grids on both sides ; Also includes a bus bar connecting the interdigital transducer and the IDT-type reflection grating. The reflection grid of the resonator adopts a non-short-circuit reflection grid structure and an open circuit reflection grid structure, but consists of IDT-type interdigitated electrodes; the finite element simulation method of the resonator using the reflection grid structure includes the finite element model modeling of the device, Solving and result analysis.

Further, there is a pair of interdigital electrodes in the structural period (λ) of the reflection grating, similar to the input and output interdigitated electrodes of the transducer, which are staggered and connected to four different bus bars respectively.

Further, the base material of the resonator is 128°YX-LiNbO ₃ , and the material of the IDT and the reflective grid electrode is set to metal Al; a perfect matching layer (PML) and a fixed constraint boundary condition are added at the bottom of the resonator to prevent the bottom surface reflection. Influence, the bus bars connected to the reflection grating are respectively set as different floating potential ports in the electrostatic physics field of the COMSOL finite element analysis software, and the bus bars connected to the interdigital transducer are respectively set as input and output ports.

Further, the input and output ports of the surface acoustic wave resonator are respectively set as "terminating 1W" and "terminating 0W" ports.

The advantages and beneficial effects of the present invention are as follows:

In the IDT type reflective grid structure proposed by the present invention, the reflective grid electrodes are different from the short-circuited reflective grids and the open-circuited reflective grids, but are arranged in a staggered manner similar to the IDT electrodes and are respectively connected to different bus bars. When reflecting the SAW excited by the IDT, due to the piezoelectric effect, the reflective grid bus bar collects the induced charges generated by the reflective grid electrode, and through the inverse piezoelectric effect, the electric field generated by the induced current is fed back to excite the surface acoustic wave, which is the propagation of the SAW. Supplementary energy is provided, thereby reducing propagation losses and in-band fluctuations. Compared with the commonly used short-circuit reflection grid structure, on the basis of high-performance surface acoustic wave devices with insertion loss and in-band fluctuation less than 1dB, for resonators and a ladder filter, the reflection grid structure further reduces the maximum peak in the band. The losses are reduced by 8.84% and 35.36%, respectively.

Description of drawings

FIG. 1 is a schematic diagram of a three-dimensional structure of a resonator using an IDT-type reflection grating.

FIG. 2 is a schematic diagram of the finite element model of the resonator.

FIG. 3 is a comparison diagram of the frequency response of the series resonator provided by the preferred embodiment of the present invention.

FIG. 4 is a comparison diagram of the frequency response of the first-order "T" type bandpass filter provided by the preferred embodiment of the present invention.

Detailed ways

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

The technical scheme that the present invention solves the above-mentioned technical problems is:

Figure 1 is a schematic diagram of a 3-dimensional structure of a resonator using an IDT-type reflection grating. It includes a piezoelectric substrate 10, and an interdigital transducer 8 is designed on the piezoelectric substrate 10; the two sides of the interdigital transducer are IDT-type reflection grids 7 and 9; it also includes a confluence connecting the interdigital transducers Bars 5, 6 and bus bars 1, 2, 3, 4 connecting the IDT-type reflector. The reflection grid of the resonator adopts a non-short-circuit reflection grid structure and an open-circuit reflection grid structure, but consists of IDT-type interdigitated electrodes. There are a pair of electrodes in the structural period (λ) of the reflection gratings 7 and 9, which are similar to the input and output interdigital electrodes of the transducer, and are staggered and connected to 4 different bus bars respectively.

Figure 2 is a schematic diagram of the finite element model of the resonator. The base material of the resonator is 128°YX-LiNbO ₃ , and the material of the IDT and the reflective gate electrode is set to metal Al; a perfect matching layer (PML) and fixed constraints are added at the bottom of the resonator Boundary conditions to prevent the effects of back reflections. The bus bars 1, 2, 3 and 4 connected to the reflection grid are respectively set as 4 different floating potential ports in the electrostatic physics field of the COMSOL finite element analysis software; the bus bars 5 and 6 connected to the interdigital transducer 8 are respectively set It is an input and output port, and is set as the "termination 1W" and "termination 0W" ports respectively.

As shown in Figures 3 and 4, the propagation loss of the resonator and first-order "T" filter using the IDT-type reflection grid is significantly lower than that of the device structure using the short-circuit reflection grid, and the maximum peak loss in the band is respectively decreased by 8.84% and 35.36%.

It should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device comprising a series of elements includes not only those elements, but also Other elements not expressly listed or inherent to such a process, method, article of manufacture or apparatus are also included. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in the process, method, article of manufacture, or device that includes the element.

The above embodiments should be understood as only for illustrating the present invention and not for limiting the protection scope of the present invention. After reading the contents of the description of the present invention, the skilled person can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims (4)

1. A reflection grid design for suppressing lateral mode interference of a surface acoustic wave device, comprising a piezoelectric substrate (10) on which an interdigital transducer (8) is designed; the fork The two sides of the finger transducer are IDT-type reflection gratings (7), (9); it also includes bus bars (5), (6) connecting the interdigital transducers and bus bars connecting the IDT-type reflection gratings (1), (2), (3), (4), it is characterized in that the reflection grid of the resonator adopts a non-short-circuit reflection grid structure and an open-circuit reflection grid structure, but is composed of interdigital electrodes of the transducer IDT type. ; The finite element simulation method of the resonator using the reflection grid structure includes the modeling, solution and result analysis of the finite element model of the device. 2. The design of a reflection grating for suppressing lateral mode interference of a surface acoustic wave device according to claim 1, wherein a pair of electrodes are arranged in the structural period (λ) of the reflection gratings (7) and (9). , and similar to the input and output finger electrodes of the transducer, the reflective grid electrodes are staggered and connected to 4 different bus bars (1), (2), (3), (4). 3. The design of a reflection grid for suppressing lateral mode interference of a surface acoustic wave device according to claim 1, wherein the base material of the resonator is 128° YX-LiNbO ₃ , IDT and reflection grid electrode materials Set to metal Al; add a perfectly matched layer (PML) at the bottom of the resonator and a fixed constraining boundary condition to prevent the effect of bottom reflection, the bus bars (5), (6) connecting the interdigital transducer (8) are set as The input and output ports, the bus bars (1), (2), (3), and (4) connected to the reflection grid are respectively set as four different floating potential ports in the electrostatic physics field of the COMSOL finite element analysis software. 4. a kind of reflection grating design for suppressing lateral mode interference of surface acoustic wave device according to claim 1, it is characterized in that, the input and output ports of surface acoustic wave resonator are respectively set as "termination 1W" and "termination 0W" port.

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