Surface acoustic wave one-way emission structure based on heterogeneous integrated piezoelectric substrate

Abstract

The invention relates to a surface acoustic wave one-way emission structure based on a heterogeneous integrated piezoelectric substrate. The structure is characterized in that a piezoelectric film is provided; the metal electrode and the bus bar are positioned above the piezoelectric film; the supporting substrate is positioned below the piezoelectric film; wherein the phase velocity of the slow shear wave of the support substrate is greater than the phase velocity of the excited surface acoustic wave. Compared with a traditional one-way transmitting device, under the same line width process, the coverage frequency of the one-way transmitting device is twice that of the traditional one-way transmitting device; the larger line width of the interdigital transducer means that under the same working frequency, the device can bear higher power.

Description

Technical Field

[0001] The invention belongs to the technical field of surface acoustic wave devices, and in particular relates to a surface acoustic wave unidirectional emission structure based on a heterogeneous integrated piezoelectric substrate. Background Art

[0002] Surface acoustic wave devices generally require the production of interdigital transducers on the surface of a piezoelectric substrate, applying an AC electrical signal to the interdigital transducers, and generating surface acoustic wave signals through piezoelectric effect resonance. Due to its electromechanical field conversion characteristics and the frequency selectivity of elastic wave resonance, it is widely used in communications, sensing and other fields. Generally, when the interdigital transducer excites the surface acoustic wave, it will emit sound waves symmetrically to both sides, which means that in the use scenario of the elastic wave, a 50% energy loss is naturally introduced. In this context, based on the coupled mode theory, the emission center and the reflection center of the interdigital transducer are staggered by π / 8 through structural design, thereby achieving unidirectional emission of sound waves.

[0003] The current technology has the following main disadvantages:

[0004] ① The line width requirement is large and it is difficult to cover high frequencies: In general unidirectional transmitting forked finger transducers, there are different finger metallization rates (generally the minimum line width is one-eighth of the wavelength) to achieve the purpose of separating the emission center and the reflection center. This means that under the same process conditions, the operating frequency of the current unidirectional surface acoustic wave transmitter can only reach half of that of conventional surface acoustic wave devices. ② The emission direction is not adjustable: In the current unidirectional transmitters, in order to achieve the separation of the emission center and the reflection center, the forked finger transducer structure is not symmetrical, which means that the emission direction of the sound wave cannot be adjusted after the structure is completed. In the past, the natural unidirectional emission tangential direction only excited Rayleigh waves, so there was no adjustability of the unidirectional emission direction.

[0005] ③ The maximum emission ratio is limited: In the current unidirectional transmitter, the maximum forward and reverse emission ratios depend on the reflection capacity of the reflection center. Under the premise of a single metal deposition process, the reflection capacity of the reflection center depends on the metal thickness of the transducer. When the thickness increases, the reflection capacity at the emission center will also increase, which in turn reduces the emission ratio. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a surface acoustic wave unidirectional emission structure based on a heterogeneous integrated piezoelectric substrate, which realizes the unidirectional emission of acoustic waves based on the superposition principle of acoustic wave excitation.

[0007] The present invention provides a surface acoustic wave unidirectional emission structure based on a heterogeneous integrated piezoelectric substrate, the structure comprising:

[0008] Providing a piezoelectric film;

[0009] Metal electrodes and bus bars located above the piezoelectric film;

[0010] a supporting substrate located below the piezoelectric film;

[0011] Wherein, the phase velocity of the slow shear wave of the support substrate is greater than the phase velocity of the excited surface acoustic wave.

[0012] Preferably, the thickness of the metal electrode is 20-2000 nm.

[0013] Preferably, the material of the metal electrode and the bus bar includes one or more of aluminum, copper, gold, titanium, nickel, molybdenum and platinum.

[0014] Preferably, the material cutting type of the piezoelectric film is selected according to the piezoelectric coefficient matrix of the material, specifically: when unidirectionally emitting horizontal shear waves, there are non-zero e16 or e34 and e14 or e36 at the same time; when unidirectionally emitting longitudinal waves, there are non-zero e11 or e35 and e15 or e31 at the same time.

[0015] More preferably, the material of the piezoelectric film is lithium niobate or lithium tantalate with an Euler angle range of (0°, θ°, φ°), θ takes any value, and φ takes -45 to -10 or 10 to 45. All electrodes of the interdigital transducer use the same line width. When the structure transmits sound waves, a radio frequency signal is applied to the interdigital transducer; when the cut of the selected piezoelectric material meets the above requirements, under the same electric field, e16, e34, e15, and e31 will respectively excite opposite deformations on both sides of each electrode, and e14, e36, e11, and e35 will respectively excite the same deformation on both sides of each electrode; in the superimposed frequency bands between the respective piezoelectric resonances, the deformations on one side are superimposed on each other, and the deformations on one side cancel each other out, and the interdigital transducer can realize unidirectional surface acoustic wave emission. The emission direction of the surface acoustic wave unidirectional transmitter of the present invention depends on the positive and negative signs of the parameters of the piezoelectric matrix. By selecting appropriate materials and cut directions, the emission of horizontal shear wave mode and longitudinal wave mode in different directions can be realized.

[0016] Preferably, the piezoelectric film has a thickness of 0.1-1.5 μm.

[0017] Preferably, the material of the support substrate includes one or more of silicon, sapphire, silicon carbide, and diamond. The basic requirement for the selection is that the phase velocity of the slow shear wave needs to be greater than the phase velocity of the excited surface acoustic wave. The increase in the hardness (elastic coefficient) of the support substrate can enhance the mixed wave vector, thereby enhancing the unidirectional emission effect of the same piezoelectric shear.

[0018] Furthermore, a silicon dioxide layer is also included under the piezoelectric film to improve the temperature stability of the structure.

[0019] Preferably, an overly thick silicon dioxide layer will weaken the unidirectional emission effect, so the preferred thickness range of the silicon dioxide layer should be less than 0.8*the period of the surface electrode.

[0020] Beneficial Effects

[0021] ①Compared with the traditional unidirectional transmitting device, the present invention can cover twice the frequency of the traditional unidirectional transmitting device under the same line width process; the larger interdigital transducer line width means that under the same operating frequency, the present invention can withstand higher power. ②Compared with the traditional unidirectional transmitting device, the transmission direction of the sound wave is determined after the transducer is manufactured. By selecting the appropriate piezoelectric material cutting type, the horizontal shear mode and the longitudinal wave mode can be transmitted in different directions.

[0022] ③ The principle of generating unidirectional emission of the present invention is different from that of the traditional unidirectional emission device. The maximum achievable forward and reverse transmission ratios do not depend on the ratio of the reflection capabilities of the electrode reflection center and the emission center. Therefore, the transmission ratio that can be achieved under the thickness of a single metal electrode can be higher than that of the traditional unidirectional emission device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention.

[0024] Figure 2 The figure is a flow chart of the production of the metal electrode of the present invention.

[0025] Figure 3 This is a working schematic diagram of the structure of Example 1.

[0026] Figure 4 This is a test result diagram of Example 2. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0028] like Figure 1 As shown, the present invention provides a unidirectional surface acoustic wave emission structure based on a heterogeneous integrated piezoelectric substrate, the structure comprising: providing a piezoelectric film; a metal electrode and a bus bar located above the piezoelectric film; a supporting substrate located below the piezoelectric film; wherein the phase velocity of the slow shear wave of the supporting substrate is greater than the phase velocity of the excited surface acoustic wave. A silicon dioxide layer is also included below the piezoelectric film.

[0029] The preparation process of the structural heterogeneous integrated piezoelectric substrate includes the following steps:

[0030] ① Ion implantation: He implantation of piezoelectric crystals 2+ Ion implantation, after which the substrate is cleaned and the bonding surface is activated with O2.

[0031] ② Functional layer growth: Grow the silicon dioxide functional layer by magnetron sputtering, plasma enhanced chemical vapor deposition and other methods.

[0032] ③ Bonding: The piezoelectric film and the rigid substrate are bonded together through a bonding machine.

[0033] ④ Peeling off: After bonding, the bonded heterogeneous integrated substrate is annealed within a suitable temperature range. During annealing, the piezoelectric film is split at the ion implantation damage site, completing the peeling off.

[0034] ⑤Polishing: Perform chemical mechanical polishing on the surface of the heterogeneous integrated substrate to obtain a heterogeneous integrated substrate with low surface roughness.

[0035] The metal electrode preparation process of the structure includes the following steps: Figure 2 As shown:

[0036] ① Spin coating: Spin coat a layer of photoresist on the surface of heterogeneous integrated piezoelectric substrate.

[0037] ② Photolithography: Use deep ultraviolet (electron beam) exposure technology to locally expose the photoresist.

[0038] ③ Development: Locally dissolve the photoresist by taking advantage of the difference in solubility of different parts of the photoresist before and after exposure.

[0039] ④Metal deposition: deposit metal of target thickness.

[0040] ⑤ Stripping: removing the residual photoresist on the surface of the heterogeneous integrated piezoelectric substrate and the metal above it, and finally obtaining patterned metal on the surface of the heterogeneous integrated piezoelectric substrate.

[0041] Example 1

[0042] System working diagram is the same as Figure 3, the right side is defined as the "+" direction and the left side as the "-" direction. In this embodiment, the piezoelectric film is selected as 42°Y10°X LiTaO3, the corresponding Euler angle is (0°, -48°, 10°), the piezoelectric film thickness is 400nm, the supporting substrate below is 4H-SiC, the slow shear wave phase velocity is close to 7200m / s, and when the electrode period does not exceed 5 times the thickness of the piezoelectric film, the high sound velocity of 4H-SiC can simultaneously support the transmission of surface longitudinal waves and surface horizontal shear waves; otherwise, it only supports the transmission of surface horizontal shear waves. The electrode structure is a standard interdigital transducer with a metallization rate of 50%, an alternating period of 1.4μm between the port and the ground electrode, and the electrode material is 110nm aluminum; when an AC signal is applied to the port, the structure can unidirectionally emit horizontal shear waves in the "+" direction at around 3.2GHz, and unidirectionally emit longitudinal waves in the "-" direction at around 4.2GHz. The surface acoustic wave unidirectional emission structure based on the heterogeneous integrated piezoelectric substrate of this embodiment achieves an operating frequency twice that of a conventional unidirectional emission electrode under the same line width condition; in addition, acoustic wave emission in different directions at different frequencies can be achieved on the same manufactured device.

[0043] Example 2

[0044] In this embodiment, the piezoelectric film is selected as Y25°X LiNbO3, the corresponding Euler angle is (0°, -90°, 25°), the piezoelectric film thickness is 300nm, the SiO2 layer thickness is 100nm, the lower supporting substrate is 4H-SiC, the electrode structure is a standard interdigital transducer with a metallization rate of 50%, an alternating period of the port and the ground electrode of 1.4μm, and the electrode material is 110nm aluminum; an AC signal is applied to the port, such as Figure 4 As shown, the surface acoustic wave unidirectional emission structure based on the heterogeneous integrated piezoelectric substrate in this embodiment can emit horizontal shear waves in the "+" direction at about 3.6 GHz and emit longitudinal waves in the "-" direction at about 5.4 GHz.

Claims

1. A unidirectional surface acoustic wave emission structure based on a heterogeneous integrated piezoelectric substrate, characterized in that: The structure comprises: Providing a piezoelectric film; Metal electrodes and bus bars located above the piezoelectric film; a supporting substrate located below the piezoelectric film; Wherein, the phase velocity of the slow shear wave of the support substrate is greater than the phase velocity of the excited surface acoustic wave.

2. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: The thickness of the metal electrode is 20-2000nm.

3. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: The materials of the metal electrodes and the busbars include one or more of aluminum, copper, gold, titanium, nickel, molybdenum, and platinum.

4. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: The material cutting type of the piezoelectric film is selected according to the piezoelectric coefficient matrix of the material, specifically: when unidirectionally emitting horizontal shear waves, there are non-zero e16 or e34 and e14 or e36 at the same time; when unidirectionally emitting longitudinal waves, there are non-zero e11 or e35 and e15 or e31 at the same time.

5. The surface acoustic wave unidirectional emission structure according to claim 1 or 4, characterized in that: The material of the piezoelectric film is lithium niobate or lithium tantalate with an Euler angle range of (0°, θ°, φ°), θ taking any value and φ taking -45 to -10 or 10 to 45.

6. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: The thickness of the piezoelectric film is 0.1-1.5 μm.

7. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: The material of the support substrate includes one or more of silicon, sapphire, silicon carbide and diamond.

8. The surface acoustic wave unidirectional emission structure according to claim 1, characterized in that: A silicon dioxide layer may also be included under the piezoelectric film to improve the temperature stability of the device.

9. The surface acoustic wave unidirectional emission structure according to claim 8, characterized in that: The thickness of the silicon dioxide layer is less than 0.8*the period of the surface electrode.

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