Delay line type filter based on optimized single-phase transducer

Abstract

The invention discloses a delay line type filter based on an optimized single-phase transducer, which comprises an electrode layer, a piezoelectric material and a high-sound-velocity substrate, and is characterized in that the electrode layer is a patterned interdigital electrode which is periodically distributed; the graphical periodically-distributed interdigital electrodes are composed of two groups: one group is an input transducer, and the other group is an output transducer; the two groups of transducers are arranged in a mirror image manner, namely, the periodic directions are strictly aligned, and 1-1000 wavelengths are arranged between the two groups of transducers at a certain distance; according to the invention, the delay linear filter formed by the transducer has smaller insertion loss; meanwhile, the structure provided by the invention is suitable for all piezoelectric materials and acoustic modes, and in the LiNbO3-SiC material, the LiNbO3-SiC material has a Loff wave mode with a larger electromechanical coupling coefficient, so that the insertion loss can be reduced.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric transducer technology, and more specifically to a delay linear filter based on an optimized single-phase transducer. Background Technology

[0002] The main performance characteristics of microwave acoustic delay lines (ADLs) depend on the transducer's performance, including the piezoelectric material used, the specific acoustic mode, and the electrode design. The earliest ADLs employed bidirectional interdigital transducers (IDTs) on a quartz substrate to excite Rayleigh-mode surface acoustic waves (SAWs). The single-phase transducer (SPUDT) was proposed in 1982, achieving unidirectional excitation of the acoustic wave by asymmetrically arranging electrodes within a single cycle, resulting in acoustic delay lines with lower losses. Subsequently, a series of SPUDTs with even better unidirectionality were proposed. Representative examples include the DART proposed in 1986 and the EWC-SPUDT proposed in 1989, which have advantages such as simple structure and good unidirectionality, and have been widely used.

[0003] In recent years, the development of advanced piezoelectric thin films such as lithium niobate (LN), aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN) has promoted significant progress in high-performance SPUDTs and ADLs. For example, in 2018, Garcia et al. demonstrated a SPUDT working in SHO mode on LN thin films

[23] . In 2019, Lu et al. realized a Lamb wave SHO mode SPUDT in AlN thin films, and in 2020, the same team developed an A1 type SPUDT on LN thin films. In 2021, a Love-mode SPUDT was successfully realized on an LN-on-sapphire substrate. By 2022, Shao et al. had introduced a SPUDT for the SHO mode in AlScN thin films. However, at present, the unidirectionality of many single-phase transducers still has some room for improvement. This is because, for acoustic modes with large electromechanical coupling coefficients, most current single-phase transducer designs do not take into account the effect of piezoelectric regeneration on piezoelectric acoustic wave reflection. Therefore, for them, the current single-phase transducer settings are not in the optimal position. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to provide a delay line filter based on an optimized single-phase transducer to address the problem that existing single-phase transducers do not specifically consider the relationship between additional electrical reflections caused by piezoelectric regeneration and the distance between the two electrode interfaces, resulting in suboptimal unidirectionality in current single-phase transducer settings. This reduces insertion loss and achieves a higher-performance delay line filter.

[0005] Technical solution: The delay linear filter based on an optimized single-phase transducer of the present invention is characterized by comprising: an electrode layer, a piezoelectric material, and a high-velocity substrate, wherein the electrode layer is a patterned, periodically distributed interdigitated electrode.

[0006] Furthermore, the patterned, periodically distributed interdigitated electrodes consist of two sets: one set is the input transducer, and the other set is the output transducer; the two sets of transducers are mirror images of each other, that is, the periodic directions are strictly aligned, and there is a certain distance between them, ranging from 1 wavelength to 1000 wavelengths.

[0007] Furthermore, each transducer has several cycles, and each transducer is divided into a positive electrode and a negative electrode.

[0008] Furthermore, each cycle has three electrodes, each of which is rectangular; the long side is along the aperture direction and the wide side is along the cycle direction.

[0009] Furthermore, the three electrodes along the periodic direction are a reflective electrode, a signal electrode, and a ground electrode, respectively.

[0010] Furthermore, the width of the signal electrode and the ground electrode is 125nm-12.5um.

[0011] Furthermore, the width of the reflective electrode is 125nm-25um.

[0012] Furthermore, the distance between the center of the reflective electrode and the center of the signal electrode is 437.5 nm-43.75 μm; the electrode length is 10 μm-20 mm.

[0013] Furthermore, the signal electrode is connected to an external signal terminal, and the ground electrode and reflective electrode are connected to an external ground terminal, which are led out to the outside through the first bus electrode and the second bus electrode, respectively. The bus electrode is elongated, with its long side perpendicular to the long side of the interdigital electrode, and its length is 10µm-1mm. The distance between the interdigital electrode and the corresponding bus electrode is generally 0.5µm-2µm.

[0014] This invention presents a novel delay-line filter based on an improved single-phase transducer and an acoustic mode with a large electromechanical coupling coefficient. The single-phase transducer proposed in this invention is a grounded reflective electrode type. By further considering the piezoelectric regeneration effect, particularly the relationship between the additional electrical reflection caused by the piezoelectric regeneration effect and the distance between the two electrode interfaces, a more precise single-phase transducer design structure is obtained. This invention aims to further improve unidirectionality by fixing the signal electrode and the ground electrode and optimizing the reflective electrode.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: Compared with the traditional single-phase transducer, the proposed transducer structure has better unidirectionality; secondly, compared with the traditional transducer, the proposed transducer structure does not require higher process difficulty; moreover, the delay linear filter constructed by the transducer in the present invention has lower insertion loss; at the same time, the structure proposed in the present invention is applicable to all piezoelectric materials and acoustic modes, and in LiNbO3-SiC material, the Love wave mode with a larger electromechanical coupling coefficient is beneficial to reducing insertion loss. Attached Figure Description

[0016] Figure 1 This is a structural diagram of the present invention;

[0017] Figure 2 This is a single-cycle magnified diagram of the present invention;

[0018] Figure 3 The interface reflection of the electrode-non-electrode-electrode region of the present invention; (a) the two electrodes are at floating potentials; (b) the electrodes are grounded, but additional electrical reflection is not considered; (c) the electrodes are grounded, and additional electrical reflection is considered; (d) the relationship between total electrical reflection and electrode spacing β with and without considering additional electrical reflection, and numerical simulation results.

[0019] Figure 4 (a) Relationship between the position of the reflective electrode and the unidirectionality of the transducer when the reflective electrode width is one-eighth of the wavelength (improved design) and three-eighths of the wavelength (traditional design) in a single cycle. (b) Comparison of the unidirectionality of the improved single-phase transducer and the traditional single-phase transducer in 10 cycles. (c) Electrode structure of the traditional single-phase transducer. (d) Electrode structure of the improved single-phase transducer. (f) Energy distribution of the traditional single-phase transducer and the improved single-phase transducer obtained by simulation.

[0020] Figure 5 (a) Improved single-phase delay line filter structure (b) SEM image of filter device (c) Electrode structure of improved single-phase transducer (d) Electrode structure of traditional single-phase transducer (e) Energy distribution diagram of improved (IDART) / traditional (DART) single-phase delay line filter (f) Comparison of improved single-phase delay line filter and traditional single-phase delay line filter S21 at room temperature (g) Comparison of improved single-phase delay line filter and traditional single-phase delay line filter S21 at low temperature (50K).

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] like Figures 1-2As shown, this embodiment of the invention proposes an improved single-phase transducer for the Love mode. Specifically, it has three electrodes in a single cycle: a reflective electrode, a signal electrode, and a ground electrode. The reflective electrode and ground electrode are externally grounded, while the signal electrode is externally connected to a signal.

[0023] like Figure 3 As shown, (a) represents the case where the electrodes in the electrode-non-electrode-electrode structure are at floating potentials, in which case the potential continuity boundary condition can be satisfied without additional electrical reflection; (b) represents the case where the electrodes in the electrode-non-electrode-electrode structure are at ground potentials, in which case the potential continuity boundary condition is not satisfied if additional electrical reflection is not considered; (c) also represents the case where the electrodes in the electrode-non-electrode-electrode structure are at ground potentials, in which case the potential continuity is satisfied by considering additional electrical reflection. In (d), the red curve represents the relationship between the total electrical reflection at interface 1 and 2 and the distance between the two interfaces when considering additional electrical reflection, the black curve represents the relationship between the total electrical reflection at interface 1 and 2 and the distance between the two interfaces when not considering additional electrical reflection, and the blue curve represents the relationship between the total electrical reflection at interface 1 and 2 and the distance between the two interfaces obtained from simulation. It can be seen that the case considering additional electrical reflection is in perfect agreement with the simulation results, proving that the theoretical basis of our design is correct.

[0024] The structure proposed in this invention is applicable to LiNbO3-SiC, where the LiNbO3 thickness can be 100 nm to 2 μm. In this invention, the LiNbO3 is X-cut. The electrodes are periodically arranged interdigitated structures. The electrode materials can be gold, platinum, aluminum, silver, copper, etc. In the structure proposed in this invention, the electrodes are made of 20 nm gold. The electrode period can be 1 μm to 100 μm.

[0025] The three electrodes, from left to right, are a reflective electrode, a signal electrode, and a ground electrode, with their widths maintaining a ratio of approximately 0.9:1:1 to 1.1:1:1 (from left to right for forward transmission). The signal electrode and ground electrode have widths of 125 nm to 12.5 μm. The center-to-center distance between the signal electrode and ground electrode is twice the width of the signal electrode (ground electrode) (250 nm to 25 μm). The center-to-center distance between the reflective electrode and the signal electrode is 3.5 times the width of the signal electrode (ground electrode) (437.5 nm to 43.75 μm).

[0026] The three electrodes, ranging in length from 10µm to 20mm, are arranged in parallel and connected by a bus electrode. The distance between the electrodes and the bus electrode is 1µm to 10µm. The number of electrode pairs ranges from 1 to 100.

[0027] Figure 4As shown, (a) illustrates the relationship between unidirectionality and the position of the reflecting electrode under different reflective electrode widths, where the red curve represents the case where the reflective electrode width is one-eighth of the wavelength, and the blue curve represents the case where the reflective electrode width is three-eighths of the wavelength. (b) shows the difference in unidirectionality between the two transducers over 10 cycles, where the blue curve represents the traditional single-phase transducer and the red curve represents the improved single-phase transducer. (c) shows the electrode structure of the traditional single-phase transducer within a single cycle. (d) shows the electrode structure of the improved single-phase transducer within a single cycle. (f) shows the energy distribution diagrams of the traditional and improved single-phase transducers. The results in the figures show that the improved single-phase transducer design has better unidirectionality and a larger ratio of forward energy to backward energy.

[0028] By placing two identical single-phase transducers opposite each other, a single-line delay line filter can be constructed. The spacing between these two transducers is 10µm-20mm. Changing the spacing can alter the group delay of the delay line filter.

[0029] Figure 5 This paper demonstrates a modified single-phase delay line filter constructed from an improved single-phase transducer. (a) shows a schematic diagram; (b) shows the SEM characterization results of the improved single-phase delay line; (c) shows the single-cycle electrode structure of the improved single-phase transducer; (d) shows the single-cycle electrode structure of the traditional single-phase transducer; (e) shows the energy distribution diagrams of the traditional and improved single-phase transducers; (f) shows a comparison of the S-parameters of the improved and traditional single-phase delay lines at room temperature; and (g) shows a comparison of the S-parameters of the improved and traditional single-phase delay lines at low temperature. It can be seen that the improved single-phase delay line filter exhibits significantly lower insertion loss and more concentrated energy in the transmission region compared to the traditional single-phase delay line filter.

Claims

1. A delay-line filter based on an optimized single-phase transducer, characterized in that, include: The electrode layer (3), the piezoelectric material (2), and the hypersonic substrate (1) are provided, wherein the electrode layer (3) is a patterned, periodically distributed interdigitated electrode.

2. The delay-line filter based on an optimized single-phase transducer according to claim 1, characterized in that, The patterned, periodically distributed interdigitated electrodes consist of two sets: one set is the input transducer, and the other set is the output transducer. The two sets of transducers are mirror images of each other, that is, the periodic direction is strictly aligned, and there is a certain distance between them, ranging from 1 wavelength to 1000 wavelengths.

3. The delay linear filter based on an optimized single-phase transducer according to claim 2, characterized in that, Each transducer has several cycles, and each transducer is divided into a positive electrode (11) and a negative electrode (12).

4. The delay linear filter based on an optimized single-phase transducer according to claim 3, characterized in that, Each cycle has three electrodes, each of which is rectangular; the longer side is along the aperture direction, and the wider side is along the cycle direction.

5. The delay-line filter based on an optimized single-phase transducer according to claim 4, characterized in that, The three electrodes, along the periodic direction, are a reflective electrode (8), a signal electrode (9), and a ground electrode (10).

6. The delay-line filter based on an optimized single-phase transducer according to claim 5, characterized in that, The width of the signal electrode (9) and the ground electrode (10) is 125nm-12.5um.

7. The delay-line filter based on an optimized single-phase transducer according to claim 5, characterized in that, The width of the reflective electrode (8) is 125nm-25um.

8. The delay-line filter based on an optimized single-phase transducer according to claim 5, characterized in that, The distance between the center of the reflective electrode (8) and the center of the signal electrode (9) is 437.5nm-43.75um; the electrode length is 10um-20mm.

9. The delay-line filter based on an optimized single-phase transducer according to claim 8, characterized in that, The signal electrode is connected to the signal terminal, the ground electrode and the reflection electrode are connected to the ground terminal, and are led out to the outside through the first bus electrode (6) and the second bus electrode (7), respectively; wherein, the bus electrode is a strip type, the long side is perpendicular to the long side of the interdigital electrode, and the length is 10um-1mm; the distance between the interdigital electrode and the relative bus electrode is generally 0.5um-2um.

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