Single-phase one-way interdigital transducer with fundamental frequency and frequency doubling double-frequency working characteristics

Abstract

The invention belongs to the technical field of surface acoustic wave devices, and discloses a single-phase unidirectional interdigital transducer with fundamental frequency and frequency doubling double-frequency working characteristics. Each single-phase one-way interdigital transducer is composed of three electrodes in a periodic unit, and the three electrodes comprise a pair of rotating conductive electrodes with the width being lambda / 8 and a reflecting electrode with the width being lambda / 4. The pair of rotating conductive electrodes is marked as a first rotating conductive electrode and a second rotating conductive electrode; the first transduction electrode is located between the reflection electrode and the second transduction electrode. The distance between the center of the reflecting electrode and the center of the first transduction electrode adjacent to the reflecting electrode is 3 lambda / 8; the distance between the center of the first transconductance electrode and the center of the second transconductance electrode is lambda / 4. The single-phase one-way interdigital transducer has fundamental frequency and frequency doubling double-frequency working characteristics, the insertion loss (smaller than 6dB) of a device is reduced, in-band ripples are reduced, and out-of-band rejection is increased.

Description

Technical Field

[0001] This invention belongs to the field of surface acoustic wave device technology, specifically relating to a single-phase unidirectional interdigital transducer with dual-frequency operating characteristics. Background Technology

[0002] Surface acoustic wave (SAW) devices are widely used in fields such as radio frequency communication, sensors, and signal processing due to their advantages such as small size, high frequency selectivity, and low power consumption. These characteristics make SAW devices play an important role in modern technology.

[0003] With the development of mobile communication technology, high-performance surface acoustic wave (SAW) devices with characteristics such as low insertion loss and high operating frequency are currently a research hotspot. Traditional bidirectional interdigital transducer structures suffer from high insertion loss (>6dB) due to bidirectional energy radiation and limited device efficiency, making it difficult to meet the stringent requirements of 5G communication for high-frequency, low-loss devices.

[0004] To address the high loss problem of bidirectional interdigital transducers, single-phase unidirectional interdigital transducers introduce an asymmetric electrode structure. By using a reflective electrode to reflect the back-propagating surface acoustic wave (SAW), and by leveraging the coherent and constructive properties of the wave, unidirectional propagation of acoustic energy is achieved. This results in an insertion loss of less than 6 dB and improved directivity, making it one of the important research directions for the optimization of SAW devices in recent years.

[0005] Due to the presence of reflective electrodes in a single-phase unidirectional interdigital transducer, its period is twice that of a bidirectional interdigital transducer, even with the same characteristic dimensions, resulting in a center frequency that is half that of the bidirectional interdigital transducer.

[0006] The single-phase unidirectional interdigital transducer of this invention consists of three electrodes within a single periodic unit, including a pair of transducing electrodes with a width of λ / 8 and a reflecting electrode with a width of λ / 4. The single-phase unidirectional interdigital transducer of this invention can achieve both fundamental and harmonic frequency dual-frequency responses. Summary of the Invention

[0007] To overcome the shortcomings and deficiencies of existing technologies, this invention provides a single-phase unidirectional interdigital transducer with dual-frequency operation characteristics of both fundamental and harmonic frequencies. This invention achieves both fundamental and harmonic frequency responses within a single-phase unidirectional interdigital transducer structure, enabling the same operating frequency response with the same characteristic dimensions as a traditional bidirectional interdigital transducer (i.e., twice the period). Furthermore, the device exhibits advantages of low insertion loss and high out-of-band rejection in both fundamental and harmonic response conditions, which is beneficial for the application of surface acoustic wave (SAW) devices at high frequencies.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency is disclosed. The single-phase unidirectional interdigital transducer comprises three electrodes within a single cycle unit, including a pair of transducing electrodes, each with a width of λ / 8, and a reflecting electrode with a width of λ / 4. The pair of transducing electrodes is designated as transducing electrode number one and transducing electrode number two. Transducing electrode number one is located between the reflecting electrode and transducing electrode number two, and the three electrodes are arranged side-by-side. The reflecting electrode and transducing electrode number two are connected to a busbar on one side, and transducing electrode number one is connected to a busbar on the other side. The distance between the center of the reflecting electrode and the center of the adjacent transducing electrode number one is 3λ / 8, and the distance between the center of transducing electrode number one and the center of transducing electrode number two is λ / 4.

[0010] The transconducting electrode pair is an interdigital electrode pair.

[0011] The three electrodes are distributed in parallel along the direction perpendicular to the propagation direction of surface acoustic waves.

[0012] The period of the single-phase unidirectional interdigital transducer is λ.

[0013] The number of periodic units in the single-phase unidirectional interdigitated transducer is ≥2. When the number of periodic units in the single-phase unidirectional interdigitated transducer is ≥2, the distance between the center of the second transducer in the previous periodic unit and the center of the reflector in the next periodic unit is 3λ / 8.

[0014] Both the transducer and reflector electrodes are made of aluminum, and titanium is used to increase the adhesion between the interdigital transducer and the substrate.

[0015] The single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency is used for surface acoustic wave devices, which can achieve dual-frequency response and is suitable for scenarios such as 5G communication and high-frequency signal processing.

[0016] A delay line comprising an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer includes an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer. Both the input and output single-phase unidirectional interdigital transducers are composed of the aforementioned periodic unit structure with 25 cycles. The delay distance between the input and output single-phase unidirectional interdigital transducers is 40λ, and the acoustic aperture in both transducers is 40λ. In the input single-phase unidirectional interdigital transducer, the reflective electrode is located to the left of the first transducer; in the output single-phase unidirectional interdigital transducer, the reflective electrode is located to the right of the first transducer.

[0017] The advantages of this invention are:

[0018] (1) The single-phase unidirectional interdigital transducer of the present invention reduces the insertion loss of the device (less than 6dB), reduces in-band ripple and increases out-of-band rejection.

[0019] (2) This invention utilizes the dual-frequency response characteristics of a single-phase unidirectional interdigital transducer to achieve dual-frequency response at both the fundamental frequency and the harmonic frequency, thus solving the problem of the operating frequency of a single-phase unidirectional interdigital transducer being halved. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the single-phase unidirectional interdigitated transducer of the present invention;

[0021] Figure 2 This is a schematic diagram of the delay line structure of the present invention;

[0022] Figure 3 This is a schematic diagram of the finite element simulation model of Example 1; where the red transconducting electrode represents the signal receiving electrode, and the blue reflecting electrode and transconducting electrode represent the grounding electrode;

[0023] Figure 4 This is the S21 curve of the simulation model of Example 1 performing frequency domain scanning;

[0024] Figure 5 This is a diagram of the surface acoustic wave device under test in Example 2; where 1-input single-phase unidirectional interdigital transducer; 2-output single-phase unidirectional interdigital transducer; 3-128° Y-cut single-crystal lithium niobate substrate; 4-PCB backplane; 5-SMA interface; 6-lead wire; 7-conductive silver paste; 8-transductive electrodes (transductive electrode 1 and transductive electrode 2); 9-reflecting electrode; the left figure is the actual diagram of the surface acoustic wave device under test, and the right figure is the optical micrograph of the single-phase unidirectional interdigital transducer in the surface acoustic wave device under test;

[0025] Figure 6 This is the S21 curve diagram of Example 2;

[0026] Figure 7 This is the response test curve of a traditional bidirectional interdigital transducer. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments all adopt a surface acoustic wave delay line structure, but the implementation of the present invention is not limited thereto.

[0028] Example 1

[0029] A single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency is shown in the schematic diagram below. Figure 1As shown. The single-phase unidirectional interdigitated transducer consists of three electrodes within one cycle unit, including a pair of transducing electrodes with a width of λ / 8 and a reflecting electrode with a width of λ / 4; the pair of transducing electrodes is designated as transducing electrode number one and transducing electrode number two; the transducing electrode number one is located between the reflecting electrode and the transducing electrode number two, and the three electrodes are arranged side by side; the transducing electrodes are a pair of interdigitated electrodes; the reflecting electrode and the transducing electrode number two are connected to a busbar on one side, and the transducing electrode number one is connected to a busbar on the other side; the distance between the center of the reflecting electrode and the center of the adjacent transducing electrode number one is 3λ / 8; the distance between the center of the transducing electrode number one and the center of the transducing electrode number two is λ / 4.

[0030] The three electrodes are distributed in parallel along the direction perpendicular to the propagation direction of surface acoustic waves.

[0031] The period of the single-phase unidirectional interdigital transducer is λ.

[0032] A schematic diagram of a delay line structure containing an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer is shown below. Figure 2 As shown. The delay line includes an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer. Both the input and output single-phase unidirectional interdigital transducers are composed of periodic unit structures of the aforementioned single-phase unidirectional interdigital transducers with fundamental and harmonic dual-band operating characteristics, each with 25 cycles. The delay distance and acoustic aperture are both 40λ. In the input single-phase unidirectional interdigital transducer, the reflective electrode is located to the left of the first transducer electrode; in the output single-phase unidirectional interdigital transducer, the reflective electrode is located to the right of the first transducer electrode.

[0033] In the input single-phase unidirectional interdigitated transducer, the distance between the center of the second transducer in the previous cycle unit and the center of the reflector in the next cycle unit is 3λ / 8.

[0034] In the single-phase unidirectional interdigital transducer, the distance between the center of the reflective electrode in the previous cycle unit and the center of the second transducer in the next cycle unit is 3λ / 8.

[0035] Constructing using finite element simulation software (such as COMSOL Multiphysics) Figure 3 The simulation model shown is an example. The piezoelectric substrate is a 128° Y-cut lithium niobate substrate with a period λ of 1.6 μm.

[0036] The simulation model uses Figure 2 The delay line structure is shown, and the transconducting electrode adjacent to the reflecting electrode is set as the terminal boundary condition, and the reflecting electrode and another transconducting electrode are set as the ground boundary condition. At the same time, in order to simulate a substrate of semi-infinite thickness, perfect matching layer boundary conditions are set on the bottom and sides of the model.

[0037] Figure 4 Yes Figure 3 The S21 curve was obtained by frequency domain scanning of the simulation model. As can be seen from the figure, the single-phase unidirectional interdigital transducer delay line structure with dual-frequency operation in this embodiment achieves frequency response at both the fundamental frequency and the second harmonic.

[0038] Example 2

[0039] A schematic diagram of the surface acoustic wave device under test in this embodiment is shown below. Figure 5 As shown. The surface acoustic wave device includes a 128°Y-cut lithium niobate substrate and a surface acoustic wave device fabricated on the 128°Y-cut lithium niobate substrate using photolithography and DC sputtering processes. Figure 2 The surface acoustic wave delay line shown has a period λ of 64 μm. Both the input and output unidirectional single-phase interdigital transducers are made of aluminum, and titanium is used to increase the adhesion between the aluminum electrodes and the lithium niobate substrate.

[0040] The total thickness of the metal electrode is 200 nm.

[0041] In this embodiment, a substrate with a surface acoustic wave delay line of a single-phase unidirectional interdigital transducer is fixed to a PCB backplane. Two SMA connectors are soldered to both ends of the PCB using a soldering method.

[0042] The busbar connected to the first transducer electrode and the output signal section of the PCB are connected by a silver paste soldering process using wires (i.e., leads); the busbar connected to the reflector electrode and the second transducer electrode is connected to the ground section of the PCB in the same way.

[0043] Figure 6 It was obtained using a network analyzer. Figure 5 The S21 curve of the surface acoustic wave device shows that the single-phase unidirectional interdigital transducer delay line structure with dual-frequency operation in this embodiment achieves frequency response at both the fundamental frequency and the second harmonic.

[0044] analyze Figure 6 The center frequency at the fundamental frequency is 57.6MHz, the insertion loss is 8.0dB, the out-of-band rejection is 24.3dB, and the 3dB bandwidth is 1.3MHz; the center frequency at the harmonics is 114.8MHz, the insertion loss is 7.2dB, the out-of-band rejection is 26.8dB, and the 3dB bandwidth is 1.7MHz. Both the fundamental frequency and harmonics have the same excellent frequency response performance.

[0045] The response test results of a traditional bidirectional interdigital transducer are as follows: Figure 7 As shown, traditional bidirectional interdigital transducers (IDTs) do not have dual-frequency response characteristics and have higher losses and larger in-band ripples than single-phase unidirectional IDTs.

Claims

1. A single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency, characterized in that: Each periodic unit consists of three electrodes: a pair of transconducting electrodes, each with a width of λ / 8, and a reflecting electrode with a width of λ / 4. The pair of transconducting electrodes is designated as transconducting electrode number one and transconducting electrode number two. Transconducting electrode number one is located between the reflecting electrode and transconducting electrode number two, and the three electrodes are arranged side by side. The reflecting electrode and transconducting electrode number two are connected to a busbar on one side, and transconducting electrode number one is connected to a busbar on the other side. The distance between the center of the reflecting electrode and the center of the adjacent transconducting electrode number one is 3λ / 8, and the distance between the center of the transconducting electrode number one and the center of transconducting electrode number two is λ / 4.

2. The single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency as described in claim 1, characterized in that: The three electrodes are distributed in parallel along the direction perpendicular to the propagation direction of surface acoustic waves; The period of the single-phase unidirectional interdigital transducer is λ.

3. The single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency as described in claim 1, characterized in that: The number of periodic units in the single-phase unidirectional interdigitated transducer is ≥2; When the number of periodic units in a single-phase unidirectional interdigitated transducer is ≥2, the distance between the center of the second transducer in the previous periodic unit and the center of the reflector in the next periodic unit is 3λ / 8.

4. The single-phase unidirectional interdigital transducer with dual-band operation of fundamental frequency and harmonic frequency as described in claim 1, characterized in that: Both the transducer and reflector electrodes are made of aluminum, and titanium is used to increase the adhesion between the interdigital transducer and the substrate.

5. A delay line comprising an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer, characterized in that: This includes input single-phase unidirectional interdigital transducers and output single-phase unidirectional interdigital transducers; Both the input single-phase unidirectional interdigital transducer and the output single-phase unidirectional interdigital transducer are composed of a single-phase unidirectional interdigital transducer periodic unit structure with fundamental frequency and harmonic frequency dual-band operating characteristics as defined in any one of claims 1 to 4. The delay distance between the input single-phase unidirectional interdigital transducer and the output single-phase unidirectional interdigital transducer is 40λ. The acoustic aperture in both the input and output single-phase unidirectional interdigital transducers is 40λ. In the input single-phase unidirectional interdigital transducer, the reflective electrode is located to the left of the first transducer electrode. In the output single-phase unidirectional interdigital transducer, the reflective electrode is located to the right of the first transducer electrode.

6. The delay line comprising an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer according to claim 5, characterized in that: The number of cycles for both the input single-phase unidirectional interdigital transducer and the output single-phase unidirectional interdigital transducer is 25.

7. The delay line comprising an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer according to claim 5, characterized in that: The delay line containing an input single-phase unidirectional interdigital transducer and an output single-phase unidirectional interdigital transducer is used in surface acoustic wave devices to achieve dual-frequency response.

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