Surface acoustic wave ridge waveguide transmission line based on unidirectional transducer

Abstract

The invention discloses a surface acoustic wave ridge waveguide transmission line based on unidirectional transducers. The transmission line at least comprises an input unidirectional transducer, an output unidirectional transducer, a piezoelectric film and a substrate, wherein the input one-way transducer is used for converting an electric signal into a surface acoustic wave; the output one-way transducer converts the surface acoustic wave into an electric signal; the piezoelectric film is arranged on the substrate; the piezoelectric film has a ridge-shaped structure; and the ridge-shaped structure is an independent waveguide or a waveguide comprising a conical structure. According to the surface acoustic wave ridge waveguide transmission line, the unidirectional transducer is used, so that the insertion loss is reduced, the working bandwidth is increased, meanwhile, the conical structure is used, so that the insertion loss is further reduced, the bandwidth is still large, and the in-band fluctuation is small. In addition, the unidirectional transducer is also suitable for a bent waveguide and a Y-shaped beam splitter. The method has important significance in the fields of signal processing, sensing, phonon integrated circuits, quantum acoustics and the like.

Description

Technical Field

[0001] The invention relates to the technical field of surface acoustic wave devices, in particular to an acoustic transmission line based on a surface acoustic wave ridge waveguide, and more particularly to a surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer. Background Art

[0002] Surface acoustic wave is an elastic wave that propagates along the surface of a solid. It was first discovered by British physicist Rayleigh in his research on earthquakes. Later, with the development of electroacoustic transducers and nano-processing technology, a large number of surface acoustic wave devices began to appear, such as filters, resonators, convolvers, duplexers, etc. The speed of surface acoustic waves is 4 to 5 orders of magnitude smaller than that of electromagnetic waves, so the wavelength of surface acoustic waves at the same frequency is also 4 to 5 orders of magnitude smaller. This makes surface acoustic wave devices have advantages such as smaller size and lower loss compared to electromagnetic wave devices. They are widely used in wireless communications, microfluidics, and various sensors. In recent years, people have also found that surface acoustic wave devices can be used in quantum systems, including superconducting quantum bits, color centers, quantum dots, and other fields.

[0003] With the gradual development of new technologies such as the new generation of mobile communications, the Internet of Things, optoacoustic integration, and quantum acoustic technology, the construction of low-loss and high-bandwidth acoustic transmission lines is an important step in the development of surface acoustic wave devices. Among them, acoustic waveguide transmission lines have great advantages due to their low loss and easy control. Electroacoustic transducers are often used in acoustic waveguide transmission lines. They can be used to excite and receive surface acoustic waves, and also affect the device's insertion loss and bandwidth. Improving electroacoustic transducers will help further improve the performance of acoustic waveguide transmission line devices. The electroacoustic transducer is composed of periodic electrodes deposited on a piezoelectric crystal. After applying an electrical signal, the piezoelectric crystal converts the electrical signal into an acoustic signal through the inverse piezoelectric effect, which propagates along both ends of the electroacoustic transducer. The energy excited by this electroacoustic bidirectional transducer propagates evenly to both sides at the same time, resulting in half of the energy loss, which increases the insertion loss of the device. Therefore, although the current acoustic waveguide transmission lines can effectively achieve the restriction, guidance and routing of different modes of surface acoustic waves, their device structures are mostly based on bidirectional transducers or a combination of bidirectional transducers and conical structures or fan-shaped structures. Bidirectional transducers will cause energy loss on one side and are powerless against the reflection of conical and fan-shaped structures. The overall insertion loss of the device is still large and the bandwidth is still small, making it difficult to apply to practical applications, including signal processing, sensing, and phononic integrated circuits. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer to solve the problem that the overall insertion loss of the acoustic waveguide transmission line is still large and the bandwidth is still small.

[0005] Technical solution: The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer described in the present invention is characterized in that the transmission line comprises at least: 1 input unidirectional transducer, 1 output unidirectional transducer, a piezoelectric film and a substrate; wherein the input unidirectional transducer converts an electrical signal into a surface acoustic wave; the output unidirectional transducer converts a surface acoustic wave into an electrical signal; the piezoelectric film is arranged on the substrate; the piezoelectric film has a ridge structure; the ridge structure is a separate waveguide or a waveguide containing a conical structure.

[0006] Furthermore, the constituent material of the piezoelectric film is at least one of piezoelectric materials such as lithium niobate, lithium tantalate, aluminum nitride, gallium nitride, gallium arsenide, zinc oxide, ST-X quartz, etc.; the constituent material of the substrate is at least one of silicon carbide, diamond, sapphire, silicon, and silicon dioxide.

[0007] Furthermore, the cross-section of the ridge structure is an isosceles trapezoid; the width of the top of the isosceles trapezoid is the width of the surface acoustic wave ridge waveguide, which is 0.1-10μm; the base angle of the isosceles trapezoid is 40°-90°; the thickness of the piezoelectric film is greater than or equal to the height of the isosceles trapezoid; the thickness of the piezoelectric film is 0.1-10μm.

[0008] Furthermore, the waveguide has at least one of a straight line, a curved or a Y-shaped beam splitter structure; the bending radius of the curved structure and the Y-shaped beam splitter is 1-100 μm, and the bending angle is 30°-90°; the length of the conical structure is 1-100 μm; the width of the conical structure, that is, the waveguide width in the unidirectional transducer area is 0.2-50 μm.

[0009] Furthermore, the input unidirectional transducer and the output unidirectional transducer both include metal electrodes and a first metal connecting line and a second metal connecting line; wherein the metal electrodes include: a reflection electrode, a signal electrode, and a ground electrode; all metal electrodes are covered on the surface of the piezoelectric film and include at least the upper surface and two side surfaces of the waveguide.

[0010] Furthermore, the applied electrical signal is converted into a surface acoustic wave through the metal electrode and transmitted along the piezoelectric film.

[0011] Furthermore, the metal electrode includes a plurality of finger electrodes, forming at least one complete electrode cycle, wherein each electrode cycle includes a reflection electrode, a signal electrode, and a ground electrode; the reflection electrode is connected to the ground; the signal electrode is connected to the radio frequency signal; and the ground electrode is connected to the ground.

[0012] Furthermore, the constituent materials of the reflective electrode, signal electrode and grounding electrode are at least one of aluminum, gold, chromium, tungsten, platinum and other metals; the length of each finger electrode in the metal electrode is 1-100μm and the thickness is 40-100nm; the width of the reflective electrode is 0.1-3μm; the width of the signal electrode and the grounding electrode are both 0.1-1μm.

[0013] Furthermore, the length of the overlapping portion of the signal electrode and the ground electrode is the aperture, and the length of the aperture is 1-100 μm.

[0014] Furthermore, the first metal connecting line and the second metal connecting line are composed of the same material as the metal electrode, which is at least one of metals such as aluminum, gold, chromium, tungsten, and platinum. The first metal connecting line connects the reflective electrode and the ground electrode, and is connected to the ground pad electrode; the second metal connecting line connects the signal electrode and the signal input pad electrode; the length of the first metal connecting line and the second metal connecting line are both 10-100μm, the width is 5-50μm, and the thickness is 40-100nm.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the surface acoustic wave ridge waveguide in the present invention preferably uses X-cut lithium niobate as the piezoelectric film, which has a large electromechanical coupling coefficient and can effectively convert electrical signals into surface acoustic waves. The substrate preferably uses silicon carbide, which has a high sound velocity. Since the sound velocity of silicon carbide is greater than that of lithium niobate, it can well impose lateral restrictions on the surface acoustic wave, so that the surface acoustic wave propagates along the surface of the lithium niobate piezoelectric film, and a good performance acoustic waveguide transmission line platform can be obtained. Compared with the traditional bidirectional transducer, the unidirectional transducer in the present invention adds a reflection electrode in each electrode period, so that the surface acoustic wave propagating in the forward direction is strengthened, and the surface acoustic wave propagating in the reverse direction is weakened, so that the energy lost in the transmission line is reduced. When the electrode period of the unidirectional transducer is 2μm, the waveguide width is 2μm, and the waveguide length is 50μm, the waveguide transmission line can reach an operating frequency greater than 2.5GHz, the lowest insertion loss is 2.81dB, the operating bandwidth is much larger than the traditional bidirectional transducer waveguide transmission line, and the performance advantage is significant. The present invention adopts a conical structure, so that the effective contact area between the unidirectional transducer and the lithium niobate piezoelectric film is increased, the efficiency of electroacoustic conversion is improved, and the energy loss can be further reduced. When the electrode period of the unidirectional transducer is 2μm, the waveguide width is 2μm, and the waveguide length is 50μm, the insertion loss is reduced to 2.53dB, the working bandwidth is still large, exceeding 150MHz, and the intra-band fluctuation is reduced. The surface acoustic wave mode (quasi-Love mode) of the surface acoustic wave ridge waveguide in the present invention has good anti-bending characteristics, still has good transmission efficiency in curved waveguides and Y-shaped beam splitters, and can also achieve relatively uniform energy splitting in the Y-shaped beam splitter. The unidirectional transducer is also applicable to complex structures such as curved waveguides and Y-shaped beam splitters, which can reduce the insertion loss of the transmission line and increase the working bandwidth. High-performance curved waveguides and Y-shaped beam splitter waveguide transmission lines are conducive to the miniaturization of devices and are of great significance to the development of phononic integrated circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of the present invention; wherein (a) is a top view of a unidirectional transducer surface acoustic wave ridge waveguide transmission line, and (b) is a cross-sectional view of a unidirectional transducer surface acoustic wave ridge waveguide transmission line; Figure 2 A schematic structural diagram of a tapered unidirectional transducer surface acoustic wave ridge straight waveguide transmission line of the present invention; Figure 3 Schematic diagram of the structure of the tapered unidirectional transducer surface acoustic wave ridge waveguide transmission line of the present invention, (a) the bending structure and (b) the Y-shaped beam splitter structure; Figure 4Comparison of simulation and experimental results of the bidirectional transducer and unidirectional transducer surface acoustic wave ridge waveguide transmission lines of the present invention (a) SEM image of the bidirectional transducer transmission line (b) (c) Displacement field and energy field of the bidirectional transducer transmission line (d) SEM image of the unidirectional transducer transmission line (e) (f) Displacement field and energy field of the unidirectional transducer transmission line (g) Transmission spectra of the unidirectional transducer (red line) and bidirectional transducer (blue line) transmission lines (h) Waveguide length L =50μm, the transmission spectrum of the unidirectional transducer transmission line varies with different waveguide widths w 1 Variation of (i) waveguide width w 1 =2μm, the transmission spectrum of the unidirectional transducer transmission line varies with different waveguide lengths L changes; Figure 5 Experimental results of transmission characteristics of the surface acoustic wave ridge waveguide transmission line of the unidirectional transducer of the present invention (a) Experimental measurement and fitting | S 21 The maximum value (red line) and the average value (blue line) of | in the passband vary with the waveguide length. L (b) Experimental measurement and fitting of the delay time with different waveguide lengths L changes; Figure 6 Simulation and experimental results of the tapered unidirectional transducer surface acoustic wave ridge waveguide transmission line of the present invention (a) Schematic diagram of the local model and overall SEM image of the tapered unidirectional transducer surface acoustic wave ridge waveguide transmission line (b) Length of the tapered structure l t =20μm, the transmission spectrum varies with the width of the tapered structure w t (c) Variation of tapered structure width w t =4μm, the transmission spectrum varies with the length of the cone structure l t Variation of (d) tapered structure width w t =4μm, tapered structure length l t =20μm when the displacement field and energy field are simulated (e) waveguide length L =50μm, the transmission spectrum varies with different waveguide widths w 1 Variation of (f) waveguide width w 1 =2μm, the transmission spectrum varies with different waveguide lengths L changes; Figure 7Experimental results of transmission characteristics of the surface acoustic wave ridge waveguide transmission line of the conical structure of the unidirectional transducer of the present invention (a) Experimental measurement and fitting | S 21 The maximum value (red line) and the average value (blue line) of | in the passband vary with the waveguide length. L (b) Experimental measurement and fitting of the delay time with different waveguide lengths L changes; Figure 8 Experimental results of the bent waveguide and Y-shaped beam splitter of the present invention (a) SEM image of the bent waveguide (b) Transmission spectra of the bent waveguide and straight waveguide transmission lines with different waveguide lengths (c) Transmission spectra of the bent waveguide transmission line with unidirectional transducer (red line) and bidirectional transducer (blue line) (d) SEM image of the Y-shaped beam splitter (e) Transmission spectra of the unidirectional transducer (red line) and bidirectional transducer (blue line) | S 21 |(f) Y-shaped beam splitter with unidirectional transducer (red line) and bidirectional transducer (blue line) | S 31 |. DETAILED DESCRIPTION

[0017] The technical scheme of the present invention will be further described in detail below in conjunction with the accompanying drawings. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope of protection that the present invention is intended to protect.

[0018] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0019] Figure 1 The present invention is a surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer, characterized in that the transmission line comprises at least: one input unidirectional transducer, one output unidirectional transducer, a piezoelectric film 1 and a substrate 2; wherein the input unidirectional transducer converts an electrical signal into a surface acoustic wave; the output unidirectional transducer converts a surface acoustic wave into an electrical signal; the piezoelectric film is arranged on the substrate; the piezoelectric film has a ridge structure; the ridge structure is a separate waveguide or a waveguide containing a conical structure.

[0020] The material of the piezoelectric film 1 is selected from lithium niobate, the tangent direction is X-cut, and the horizontal direction of the piezoelectric film 1 is -10°Y, which is perpendicular to the length direction of the metal electrode. The material of the substrate 2 is silicon carbide.

[0021] The surface acoustic wave waveguide formed by the piezoelectric film 1 is a ridge-like structure; the length direction of the ridge-like structure is perpendicular to the length direction of the metal electrode; the cross-section of the ridge-like structure is an isosceles trapezoid; the base angle of the isosceles trapezoid is 55°; the thickness of the piezoelectric film 1 is greater than the height of the isosceles trapezoid; the thickness of the piezoelectric film 1 is 330nm, the height of the isosceles trapezoid is 250nm, and the thickness of the remaining lithium niobate piezoelectric film that has not been etched is 80nm.

[0022] The ridge structure of the surface acoustic wave waveguide is obtained by electron beam lithography and inductively coupled plasma etching; the width of the surface acoustic wave waveguide is the width of the top of the isosceles trapezoid, which is 2μm; the length of the surface acoustic wave waveguide is the distance between the left and right unidirectional transducers, which is 50μm.

[0023] The input and output unidirectional transducers both include metal electrodes and a first metal connecting line 6 and a second metal connecting line 7; the metal electrodes include: a reflection electrode 3, a signal electrode 4, and a grounding electrode 5; the reflection electrode 3, the signal electrode 4, and the grounding electrode 5 are all covered on the surface of the piezoelectric film 1, and include at least the upper surface and two side surfaces of the waveguide. The applied electrical signal is converted into a surface acoustic wave by the metal electrode and transmitted along the piezoelectric film. The metal electrode includes a plurality of finger electrodes, and three finger electrodes form an electrode period, wherein the reflection electrode 3 is connected to the ground, the signal electrode 4 is connected to the RF signal input, and the grounding electrode 5 is connected to the ground, and then the electrode period is repeated, and the distance between two identical finger electrodes is the length of the electrode period.

[0024] The reflection electrode 3, signal electrode 4, and ground electrode 5 are all made of Al; the width of each finger electrode in the metal electrode is 0.25μm, the length is 35μm, and the thickness is 80nm. The length of the overlapping part of the signal electrode 4 and the ground electrode 5 is called the aperture, and the length of the aperture is 30μm. The length of the electrode period is 2μm, the distance between the reflection electrode 3 and the signal electrode 4 is 0.925μm, and the distance between the signal electrode 4 and the ground electrode 5 is 0.25μm.

[0025] The first metal connection line 6 and the second metal connection line 7 are made of the same material as the metal electrodes, both of which are Al; the first metal connection line 6 connects the reflective electrode 3 and the grounding electrode 5, and is also connected to the ground pad electrode; the second metal connection line 7 connects the signal electrode 4 and is also connected to the signal input pad electrode; the first metal connection line 6 and the second metal connection line 7 are both 30 μm long, 10 μm wide, and 80 nm thick.

[0026] like Figure 2As shown, the surface acoustic wave waveguide ridge structure includes a conical structure 9; the conical structure 9 is located between the unidirectional transducer and the waveguide 10, and is used to couple the surface acoustic wave into the waveguide 10; the width of the conical structure 9, that is, the width of the waveguide 11 in the unidirectional transducer area, is 4μm; the length of the conical structure 9 is 20μm.

[0027] The surface acoustic wave ridge waveguide has a curved structure, such as Figure 3 As shown in (a), the bending structure includes two identical bends and forms an S shape. The bending angle of the bend is 90°; the bending radius of the bend is R is 50μm.

[0028] The surface acoustic wave ridge waveguide has a Y-shaped beam splitter structure, such as Figure 3 As shown in (b), the Y-shaped beam splitter structure includes four identical bends and forms two S-shaped branches. The bending angle of the bend is 90°; the bending radius of the bend is R is 50μm.

[0029] The present invention applies a unidirectional transducer to a surface acoustic wave ridge waveguide transmission line. Compared with a traditional bidirectional transducer, the insertion loss of the transmission line is reduced and the working bandwidth of the transmission line is increased. At the same time, by adding a tapered structure, the insertion loss of the transmission line is further reduced, and the bandwidth is still large. The upper and lower vibration amplitudes of the top of the transmission curve are weakened, reducing the intra-band fluctuations.

[0030] Experimental results: Acoustic transmission line is one of the common devices in wireless communication and phononic integrated circuits. It usually contains two electroacoustic transducers and a platform for transmitting acoustic signals, one of which is used as an input transducer to convert electrical signals into acoustic signals, and the other is used as an output transducer to convert the received acoustic signals into electrical signals. In order to further demonstrate the role of unidirectional transducers, we constructed a unidirectional transducer surface acoustic wave ridge waveguide transmission line and compared the bidirectional transducer transmission line with the unidirectional transducer transmission line. Figure 4 (a) and Figure 4 (d) are SEM images of the bidirectional transducer transmission line and the unidirectional transducer transmission line. The bidirectional transducer has the same electrode period as the unidirectional transducer. Each electrode period contains only two electrodes, and the electrode width is 0.5μm. Similarly, in order to better compare the two devices, we also simulate the displacement field and energy field of the two devices. Figure 4 (b) and Figure 4 (e) y The displacement field in the direction, Figure 4 (c) and Figure 4(f) is the energy field. It can be found that the displacement and energy between the two transducers of the unidirectional transducer transmission line are larger, while the two sides are significantly weaker. There is no obvious difference in the displacement and energy on the left and right sides of the input transducer of the bidirectional transducer transmission line, so the bidirectional transducer transmission line loses more energy.

[0031] We further measured the transmission spectra of the two devices and performed impedance matching using the Advanced Design System (ADS). The results are as follows: Figure 4 As shown in (g), the blue line represents the bidirectional transducer transmission line, and the red line represents the unidirectional transducer transmission line. As can be seen from the figure, the unidirectional transducer transmission line has a relatively obvious passband, but there are more wavy shapes at the top of the curve, which is mainly due to the reflection between the two transducers. The minimum loss of the curve is 2.81dB. The bidirectional transducer transmission line does not have a relatively obvious passband area, and the minimum loss is 3.80dB, and the corresponding frequency is lower than the passband frequency of the unidirectional transducer transmission line. Within the passband frequency of the unidirectional transducer transmission line, the loss of the unidirectional transducer transmission line is much smaller than that of the bidirectional transducer transmission line. This shows that the unidirectional transducer can indeed reduce the loss of the device and form a passband area with a larger operating frequency range. Figure 4 (h) is the waveguide length L =50μm unidirectional transducer transmission line transmission spectrum with different waveguide width w 1 As the waveguide width increases, the device loss decreases and the amplitude of the vibration in the passband region also decreases. Figure 4 (i) is the waveguide width w 1 =2μm unidirectional transducer transmission line transmission spectrum with different waveguide lengths L As the waveguide length increases, the loss of the device in the passband region increases significantly, and the number of waves also gradually increases.

[0032] On this basis, Figure 5 The transmission loss and delay time of a unidirectional transducer transmission line are shown. Figure 5 (a) is based on Figure 4 (i) The transmission curve is fitted, which includes two curves. Since the transmission curve has obvious undulations in the passband, the blue line is the one in the passband. S 21 Based on the average value of |, the fitting result is: | S 21 |=−0.01292 L −4.21023 (dB), goodness of fit is R 2 =0.98839, while the red line is |S 21 Based on the maximum value of |, the fitting result is: | S 21 |=−0.00958 L −2.38535 (dB), the goodness of fit is R 2 =0.99254, from the slope of the curve we can get the transmission loss to be 9.58dB / mm. Figure 5 (b) is the delay curve calculated based on the average delay time in the passband. After fitting, we get: delay time = 0.242 L +5.62628 (ns), the goodness of fit is R 2 =0.99939, with good linear variation. According to the inverse of the slope of the fitting delay curve, the propagation speed of sound v = 4132 m / s can be further obtained.

[0033] like Figure 6 As shown, in order to further reduce the loss of the device, we added a tapered structure. By increasing the width of the transducer area, the contact area between the transducer and the piezoelectric material lithium niobate is increased, so that more electrical signals can be converted into acoustic signals. Figure 6 (a) is a local model schematic diagram and overall SEM image of the conical structure unidirectional transducer transmission line, where w t is the width of the tapered structure, i.e. the waveguide width in the unidirectional transducer area, l t is the length of the tapered structure. w t and l t In order to understand the influence of different parameters, we measured the transmission spectra corresponding to different parameters. Figure 6 (b) l t =20μm w t The transmission curves for 2, 4 and 6 μm, the corresponding waveguide width is w 1 = 2μm, the waveguide length is L =50μm. w t = 2μm, that is, when there is no cone structure, the top of the curve fluctuates greatly. w t When the value is 4 and 6 μm, the top of the curve changes more gently, and when w t =4μm, the insertion loss of the device is the smallest. Figure 6 (c) w t =4μml t The corresponding transmission curves when the wavelength is 10, 15 and 20 μm, the corresponding waveguide width is w 1 = 0.5 μm, the waveguide length is L = 200 μm, we can find that the tops of the three curves almost overlap, so we choose l t =20μm. Figure 6 (d) shows the simulated transmission line of a unidirectional transducer with a tapered structure. y From the directional displacement field and energy field, it can be found that the quasi-Love mode excited in the unidirectional transducer area can be well introduced into the waveguide through the tapered structure, with less leakage and better overall propagation effect.

[0034] Similarly, we measured the transmission spectrum of the tapered unidirectional transducer transmission line as a function of the waveguide width. w 1 and waveguide length L changes. Figure 6 (e) L =50μm for different waveguide widths w 1 The transmission spectrum of each curve has a relatively weak fluctuation at the top compared to the unidirectional transducer transmission line without a tapered structure. As the width increases, the insertion loss gradually decreases. w 1 =2μm, the minimum insertion loss is 2.53dB, which is lower than that of the unidirectional transducer transmission line without tapered. Figure 6 (f) w 1 =2μm for different waveguide lengths L The transmission spectrum shows that as the waveguide length increases, the insertion loss gradually increases.

[0035] Figure 7 The transmission loss and delay time of a unidirectional transducer transmission line with a tapered structure are shown. Figure 7 (a) is the transmission loss of the device. Similarly, the blue line is within the passband. S 21 Based on the average value of |, the fitting result is: | S 21 |=−0.01479 L −3.51618 (dB), the goodness of fit is R 2 =0.93388. The red line is | S 21 Based on the maximum value of |, the fitting result is: | S 21 |=−0.01282 L−2.24613 (dB), the goodness of fit is R 2 =0.95393, and the transmission loss obtained from the slope of the curve is 12.82dB / mm. Figure 7 (b) is the delay time of the device. Based on the average delay time of the passband, the fitting result is: delay time = 0.23934 L +5.37512 (ns). The calculated sound velocity of the conical unidirectional transducer transmission line is v t =4178m / s. By comparison, it is found that the transmission loss, delay time and propagation sound velocity of the unidirectional transducer transmission line with a conical structure are not much different from those of the unidirectional transducer transmission line without a conical structure.

[0036] Figure 8 The applicability of unidirectional transducers in curved waveguides and Y-shaped beam splitters is demonstrated. Figure 8 (a) and Figure 8 (d) SEM images of the curved waveguide and Y-shaped beam splitter, respectively. The blue part is the waveguide area, and the green part is the unidirectional transducer area. The distance between the input transducer and the curved part of the curved waveguide is 60 μm, and it still contains a tapered structure. The curved part consists of an S-bend formed by two circles, while the Y-shaped beam splitter consists of two identical branches above and below. The radius of the curved part of the two devices R If both are 50 μm, the distance between the input transducer and the output transducer is 277 μm. Figure 8 (b) shows the transmission spectra of the curved waveguide and the 200μm and 400μm straight waveguides. It can be found that in the curved structure, a good transmission curve can still be obtained, and it is between the transmission curves of the 200μm and 400μm straight waveguides, indicating that the curved structure basically does not affect the propagation of the quasi-Love mode, which is conducive to better control of the quasi-Love mode and its application in more complex structures. At the same time, the overall size of the device can be reduced by the curved structure. Figure 8 (c) is a comparison between the curved waveguide unidirectional transducer transmission line and the bidirectional transducer transmission line. It can be found that the unidirectional transducer transmission line has a larger bandwidth and the insertion loss of the unidirectional transducer transmission line is significantly lower than that of the bidirectional transducer transmission line. Figure 8 (e) and Figure 8 (f) is a comparison between the unidirectional transducer and the bidirectional transducer in the upper and lower branches of the Y-shaped beam splitter. The curves in the two figures are similar to those of the curved waveguide. Both branches of the unidirectional transducer Y-shaped beam splitter show a larger bandwidth and lower insertion loss. Figure 8 (e) and Figure 8(f) shows that the transmission curves of the two branches have a high overlap, indicating that the Y-shaped beam splitter can achieve energy splitting well. This section proves that the unidirectional transducer is also applicable to curved waveguides and Y-shaped beam splitters, which is conducive to applying the unidirectional transducer to more structures and reducing the overall loss of the device.

[0037] This embodiment provides an experimental preparation method for a surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer, but it is not specifically limited in the present invention and can also be prepared by other methods. The preparation of the device starts with a lithium niobate piezoelectric film of about 330nm on silicon carbide. First, 800nm ​​thick silicon is deposited as a hard mask layer by magnetron sputtering, and then a layer of electron beam resist is spin-coated and patterned using high-resolution electron beam lithography, and then transferred to the silicon layer by inductively coupled plasma etching, and then the lithium niobate is etched 250nm by inductively coupled plasma etching. The remaining lithium niobate thickness on the silicon carbide substrate is about 80nm, and the waveguide sidewall maintains an inclination angle of about 55°. After that, we prepare a unidirectional transducer on the waveguide, first spin-coating a layer of electron beam resist and patterning using electron beam lithography, then depositing 5nm chromium and 80nm aluminum by electron beam evaporation, and completing the preparation of the unidirectional transducer through a stripping process. Finally, we patterned the pad electrodes using UV lithography, deposited 10nm chromium and 100nm aluminum by electron beam evaporation, and performed lift-off.

[0038] The above is an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer, characterized in that: The transmission line comprises at least: an input unidirectional transducer, an output unidirectional transducer, a piezoelectric film (1) and a substrate (2); wherein the input unidirectional transducer converts an electrical signal into a surface acoustic wave; the output unidirectional transducer converts a surface acoustic wave into an electrical signal; the piezoelectric film is arranged on the substrate; the piezoelectric film has a ridge structure; the ridge structure is a separate waveguide or a waveguide containing a tapered structure.

2. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 1, characterized in that: The constituent material of the piezoelectric film (1) is at least one of piezoelectric materials such as lithium niobate, lithium tantalate, aluminum nitride, gallium nitride, gallium arsenide, zinc oxide, ST-X quartz, etc.; the constituent material of the substrate is at least one of silicon carbide, diamond, sapphire, silicon, and silicon dioxide.

3. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 1, characterized in that: The cross-section of the ridge structure is an isosceles trapezoid; the width of the top of the isosceles trapezoid is the width of the surface acoustic wave ridge waveguide, which is 0.1-10μm; the base angle of the isosceles trapezoid is 40°-90°; the thickness of the piezoelectric film is greater than or equal to the height of the isosceles trapezoid; the thickness of the piezoelectric film is 0.1-10μm.

4. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 1, characterized in that: The waveguide has at least one of a straight line, a curved or a Y-shaped beam splitter structure; the bending radius of the curved structure and the Y-shaped beam splitter is 1-100 μm, and the bending angle is 30°-90°; the length of the conical structure is 1-100 μm; the width of the conical structure, that is, the waveguide width in the unidirectional transducer area is 0.2-50 μm.

5. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 1, characterized in that: The input unidirectional transducer and the output unidirectional transducer both comprise metal electrodes and a first metal connecting line (6) and a second metal connecting line (7); wherein the metal electrodes comprise: a reflection electrode (3), a signal electrode (4), and a grounding electrode (5); all the metal electrodes are covered on the surface of the piezoelectric film (1) and include at least the upper surface and two side surfaces of the waveguide.

6. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 1, characterized in that: The applied electrical signal is converted into surface acoustic waves by metal electrodes and transmitted along the piezoelectric film.

7. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 5, characterized in that: The metal electrode comprises a plurality of finger electrodes, forming at least one complete electrode cycle, wherein each electrode cycle comprises a reflection electrode (3), a signal electrode (4), and a ground electrode (5); the reflection electrode is connected to the ground; the signal electrode is connected to the radio frequency signal; and the ground electrode is connected to the ground.

8. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 5, characterized in that: The constituent materials of the reflective electrode (3), the signal electrode (4), and the grounding electrode (5) are at least one of metals such as aluminum, gold, chromium, tungsten, and platinum; the length of each finger electrode in the metal electrode is 1-100 μm, and the thickness is 40-100 nm; the width of the reflective electrode is 0.1-3 μm; the width of the signal electrode and the grounding electrode are both 0.1-1 μm.

9. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 5, characterized in that: The length of the overlapping portion of the signal electrode (4) and the ground electrode (5) is the aperture, and the length of the aperture is 1-100 μm.

10. The surface acoustic wave ridge waveguide transmission line based on a unidirectional transducer according to claim 5, characterized in that: The first metal connection line (6) and the second metal connection line (7) are made of the same material as the metal electrode, which is at least one of aluminum, gold, chromium, tungsten, platinum and the like. The first metal connection line is connected to the reflective electrode (3) and the grounding electrode (5), and is also connected to the grounding pad electrode. The second metal connection line is connected to the signal electrode (4) and is also connected to the signal input pad electrode. The first metal connection line and the second metal connection line are both 10-100 μm in length, 5-50 μm in width and 40-100 nm in thickness.

Images