A heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices

Abstract

The present invention discloses a heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices. The substrate utilizes horizontal shear leaky surface acoustic waves and includes an interdigital transducer, a piezoelectric film layer, at least one Bragg reflector layer, and a substrate layer arranged in sequence. The Bragg reflector layer is formed by covering a high acoustic impedance layer with a low acoustic impedance layer. The piezoelectric film layer is a scandium-doped aluminum nitride film. When the Euler angles of the scandium-doped aluminum nitride film are set to (0°±5°, θ, ψ), θ and ψ respectively satisfy the following conditions: 50°≤θ≤90°, 40°≤ψ≤80°. The heterogeneous layered piezoelectric substrate of the present invention can suppress energy leakage to the substrate, concentrate energy within the effective piezoelectric layer, and improve piezoelectric conversion efficiency. By rotating the Euler angles to optimize the orientation of the piezoelectric film, the acoustic field distribution can be adjusted to obtain a leaky surface acoustic wave with excellent surface acoustic wave performance. The substrate is particularly suitable for high-frequency, broadband surface acoustic wave devices and has great application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of surface acoustic waves and relates to a heterogeneous layered piezoelectric substrate suitable for high-frequency and broadband surface acoustic wave devices. Background Art

[0002] Surface Acoustics Wave (SAW) devices have the advantages of high performance, low loss, miniaturization and low cost. Duplexers and filters based on SAW resonators are mass-produced and applied in mobile communication systems. With the rapid development of modern mobile wireless communications, the frequency range of the emerging Long Term Evolution (LTE) standard has increased from several hundred MHz to 3 GHz, and the bandwidth has increased from 10 MHz to 90 MHz, making the radio communication band a limited and precious natural resource. In particular, with the advent of the 5G era, higher requirements are placed on the high electromechanical coupling coefficient of SAW devices. There is an urgent need for high-frequency, large-bandwidth and high-quality (Q) surface acoustic wave filters. The frequency and bandwidth of surface acoustic wave devices mainly depend on the acoustic velocity (V) and electromechanical coupling coefficient (K) of their piezoelectric substrates. 2 ).

[0003] Currently, piezoelectric single crystal materials (such as lithium niobate (LN) and lithium tantalate (LT)) are the most commonly used piezoelectric materials in commercial SAW devices, but their acoustic velocities are low, all below 4000 m / s, which limits their applications in high-frequency applications. In recent years, aluminum nitride (AlN) films have a high phase velocity and can significantly enhance their piezoelectricity by doping with scandium (Sc), making them a research hotspot in the field of SAW / BAW devices. The results show that the layered structure composed of scandium-doped aluminum nitride (ScAlN) piezoelectric films combined with high acoustic velocity substrates (such as diamond, silicon carbide, etc.) can not only provide a larger phase velocity, but also a higher electromechanical coupling coefficient, which is very beneficial for high-frequency and broadband applications, and is expected to become an alternative to piezoelectric substrates that can meet the needs of mobile communications. However, due to the high preparation cost and difficulty in large-scale manufacturing of such structures, their mass production in industrial applications is limited.

[0004] Silicon (Si) offers advantages such as high cost-effectiveness and mature micromachining technology. Sputtering ScAlN thin films onto Si substrates to fabricate SAW devices based on a ScAlN / Si layered structure is a viable solution for mass production. However, the SAW mode (SAW wave) with a high electromechanical coupling coefficient in the ScAlN / Si structure can only be excited within a certain ScAlN film thickness, and the electromechanical coupling coefficient is not as high as that obtained using a high-acoustic-velocity substrate. This is due to the leakage of SAW energy into the low-acoustic-velocity Si substrate.

[0005] Therefore, how to solve the energy leakage problem of surface acoustic waves on scandium-doped aluminum nitride layered structures and optimize the device structure and material configuration to obtain high V and K 2 The SAW mode of this type of layered surface acoustic wave devices is urgently needed to prepare high-frequency, broadband surface acoustic wave devices. Summary of the Invention

[0006] The purpose of the present invention is to provide a heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices. In order to overcome the defects of surface acoustic wave energy leakage and low electromechanical coupling coefficient of the SAW wave mode on the existing scandium-doped aluminum nitride layered structure, high and low acoustic impedance layers are alternately stacked between the scandium-doped aluminum nitride piezoelectric film layer and the substrate layer to form a heterogeneous layered piezoelectric substrate structure, and the Euler angle of the scandium-doped aluminum nitride piezoelectric film is rotated. This can not only effectively suppress energy leakage while ensuring a higher frequency, but also adjust the acoustic field distribution, improve the electromechanical coupling coefficient, and obtain a SAW mode with excellent characteristics. It is particularly suitable for high-frequency, broadband surface acoustic wave devices and has great application prospects.

[0007] To achieve the above objectives, the present invention specifically provides the following technical solutions:

[0008] A heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices, utilizing horizontal shear leaky surface acoustic waves (SH-type LSAW), comprising sequentially arranged interdigital transducers (IDTs), a piezoelectric film layer, a Bragg reflector layer, and a substrate layer;

[0009] The piezoelectric film layer is a scandium-doped aluminum nitride film. When the Euler angle of the scandium-doped aluminum nitride film is set to (0°±5°, θ, ψ), θ and ψ respectively meet the following conditions:

[0010] 50°≤θ≤90°, 40°≤ψ≤80°.

[0011] When θ and ψ satisfy the above conditions, the scandium-doped aluminum nitride film can be guaranteed to have leaky acoustic surface waves with excellent SAW characteristics.

[0012] As the preferred technical solution:

[0013] A heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices as described above, wherein the scandium-doped aluminum nitride (ScAlN) film has a doping molar percentage of scandium of 0 to 40%, which ensures that the ScAlN film has good c-axis orientation and piezoelectric properties;

[0014] The thickness of the scandium-doped aluminum nitride (ScAlN) film ranges from 0.1λ to λ, where λ is the wavelength of the surface acoustic wave. The thickness of the scandium-doped aluminum nitride film is preferably from 0.1λ to 0.4λ.

[0015] A heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices as described above, wherein n Bragg reflection layers are stacked between the piezoelectric film layer and the substrate layer, where n≥1;

[0016] The Bragg reflector layer is formed by covering a high acoustic impedance layer with a low acoustic impedance layer. The acoustic velocity of the low acoustic impedance layer is lower than that of the high acoustic impedance layer. In the same Bragg reflector layer, the low acoustic impedance layer is closer to the piezoelectric thin film layer than the high acoustic impedance layer. The Bragg reflector layer (high and low acoustic impedance layer) provided in the present invention mainly solves the technical problem of energy leakage and can improve the electromechanical coupling coefficient. At the same time, compared with the case without a Bragg reflector layer (n=0), the addition of a Bragg reflector layer can gradually concentrate the energy near the surface of the piezoelectric thin film layer, limit the energy of the surface acoustic wave from leaking to the substrate, obtain a higher quality factor Q, improve the SAW characteristics, and reduce losses. Due to the depth-directed waveguide effect of the high acoustic impedance layer and the adjacent low acoustic impedance layer, the results of adding multiple layers and one Bragg reflector layer are not much different, so the present invention uses at least one Bragg reflector layer as an embodiment.

[0017] The heterogeneous layered piezoelectric substrate described above is suitable for high-frequency, broadband surface acoustic wave devices. The low acoustic impedance layer comprises materials such as SiO2, SiON, and Ta2O5, while the high acoustic impedance layer comprises materials such as AlN, Sapphire, SiN, Mo, and Pt. The scope of protection of the present invention is not limited to these examples. These examples only represent some feasible technical solutions. Those skilled in the art may select appropriate materials based on their actual needs.

[0018] In the heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices, the material of the low acoustic impedance layer is SiO2 film. According to the propagation characteristics of SH-type LSAW used in the present invention, the thickness of the SiO2 film is set in the range of 0.1λ to λ (λ is the wavelength of the surface acoustic wave) to ensure that the obtained K 2 If the thickness of SiO2 film is too thick or too thin, K 2 The preferred thickness of the SiO2 film is 0.1λ~0.5λ, and the SAW propagation characteristics are better within this thickness range.

[0019] In the aforementioned heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices, the high acoustic impedance layer is made of an AlN film, and the thickness of the AlN film is between 0.1λ and λ, where λ is the surface acoustic wave wavelength. Because the AlN layer has a slight tuning effect on SAW energy propagation, the thickness of the AlN film can be adjusted within a certain range based on actual needs, but the adjustment range should not be too large.

[0020] The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices described above, wherein the substrate layer is specifically a silicon (Si) substrate. This invention merely provides a feasible technical solution, and the scope of protection of the invention is not limited thereto. Persons skilled in the art may select appropriate materials based on actual needs.

[0021] The electromechanical coupling coefficient K of the horizontal shear leaky acoustic surface wave of the heterogeneous layered piezoelectric substrate suitable for high-frequency and broadband surface acoustic wave devices of the present invention 2 It is 10-14%.

[0022] Beneficial effects:

[0023] (1) The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices of the present invention uses a silicon substrate as a substrate layer, which is low in cost and easy to process, greatly reducing production costs and improving product yield;

[0024] (2) The heterogeneous layered piezoelectric substrate of the present invention, which is suitable for high-frequency, broadband surface acoustic wave devices, can suppress energy leakage to the substrate, concentrate the energy in the effective piezoelectric layer, and improve the piezoelectric conversion efficiency;

[0025] (3) The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices of the present invention can optimize the orientation of the piezoelectric film by rotating the Euler angle, can adjust the sound field distribution, and obtain a leaky surface acoustic wave with excellent surface acoustic wave performance, preferably a horizontal shear leaky surface acoustic wave with a high electromechanical coupling coefficient and high frequency, which is very suitable for high-frequency, broadband surface acoustic wave devices and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a 3D structural model of a heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices according to the present invention;

[0027] Figure 2 is a cross-sectional view of a heterogeneous layered piezoelectric substrate according to the present invention;

[0028] Figure 3 1 is a curve showing a typical change in input admittance of a SAW resonator on a heterogeneous layered piezoelectric substrate of the present invention at a characteristic frequency as a function of frequency when the Euler angles are set to (0°, 0°, 0°) and (0°, 90°, 60°) respectively;

[0029] Figure 4 is a graph showing the electromechanical coupling coefficient of leaky acoustic surface waves (LSAW) propagating on the heterogeneous layered piezoelectric substrate of the present invention as a function of the thickness of the scandium-doped aluminum nitride film when the Euler angle is set to (0°, 90°, 50°);

[0030] Figure 5The electromechanical coupling coefficient K of the horizontal shear leaky surface wave (SH-type LSAW) propagating on the heterogeneous layered piezoelectric substrate of the present invention when the Euler angle is set to (0°, 90°, 50°) is: 2 Curve graph showing changes with silicon dioxide film thickness;

[0031] Figure 6 The electromechanical coupling coefficient K of the horizontal shear leaky surface wave (SH-type LSAW) propagating on the heterogeneous layered piezoelectric substrate of the present invention when the Euler angle is set to (0°, 90°, 50°) is: 2 Curve graph showing changes with aluminum nitride film thickness;

[0032] Figure 7 The electromechanical coupling coefficient K of the leaky acoustic surface wave on the heterogeneous layered piezoelectric substrate when the Euler angle is set to (0°, 90°, ψ) 2 Graph of the variation with ψ;

[0033] Figure 8 The electromechanical coupling coefficient K of Rayleigh-type leaky acoustic surface waves on heterogeneous layered piezoelectric substrates when the Euler angles are set to (0°, θ, 90°) is 2 The curve of the change with the change of θ;

[0034] Figure 9 When the Euler angles are set to (0°, θ, ψ), the horizontal shear leaky surface wave (SH-type LSAW) K on the heterogeneous layered piezoelectric substrate 2 The change curve diagram of

[0035] Among them, 1 is an interdigital transducer, 2 is a piezoelectric film layer, 3 is a Bragg reflection layer, 31 is a low acoustic impedance layer, 32 is a high acoustic impedance layer, and 4 is a substrate layer. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0037] A heterogeneous layered piezoelectric substrate for high-frequency, broadband surface acoustic wave devices, using horizontal shear leaky acoustic surface waves, such as Figure 1 and Figure 2 As shown, it includes an interdigital transducer 1, a piezoelectric film layer 2, a Bragg reflection layer 3 and a substrate layer 4 arranged in sequence.

[0038] The metallization ratio of the electrodes of the IDT 1 is 0.5, and the thickness of the metal electrodes is set to 0.

[0039] The piezoelectric film layer 2 is a scandium-doped aluminum nitride film, in which the molar percentage of scandium doping is 40%, and its thickness is 0.1λ~λ. When the Euler angle of the scandium-doped aluminum nitride film is (0°±5°, θ, ψ), θ and ψ respectively meet the following conditions: 50°≤θ≤90°, 40°≤ψ≤80°.

[0040] The Bragg reflector 3 is a single layer (the number of layers can be adjusted by those skilled in the art according to actual needs, and this is only an example). It is formed by a low acoustic impedance layer 31 covering a high acoustic impedance layer 32. The low acoustic impedance layer is a SiO2 film with a thickness of 0.1λ~λ, and the high acoustic impedance layer is an AlN film with a thickness of 0.1λ~λ.

[0041] The substrate layer 4 is specifically a silicon substrate.

[0042] like Figure 3 As shown in FIG, when the Euler angles are set to (0°, 0°, 0°) and (0°, 90°, 60°), the typical input admittance of the SAW resonator on the heterogeneous layered piezoelectric substrate varies with frequency at the characteristic frequency; Figure 3 As can be seen in the figure, when the Euler angles of the scandium-doped aluminum nitride film are (0°, 0°, 0°), a variety of SAW modes, including Rayleigh waves and their higher-order SiSava waves, are excited on the heterogeneous layered structure based on the scandium-doped aluminum nitride film. In addition, by rotating the Euler angles of the scandium-doped aluminum nitride film (0°, θ, ψ), the high-order SiSava waves in the heterogeneous layered piezoelectric substrate are suppressed, and at the same time, the horizontal shear-type leaky acoustic surface wave (SH-type LSAW) is excited, which can concentrate the leaked surface acoustic wave energy and obtain a higher electromechanical coupling coefficient. Compared with the scandium-doped aluminum nitride film with Euler angles of (0°, 0°, 0°), the horizontal shear-type leaky acoustic surface wave exhibits relatively excellent SAW characteristics.

[0043] like Figure 4 As shown in Figure 2, the Euler angle of the scandium-doped aluminum nitride film is set to (0°, 90°, 50°), and the film thicknesses of the silicon dioxide film and the aluminum nitride film are set to 0.2λ and λ, respectively. The electromechanical coupling coefficient K of the leaky acoustic surface wave (LSAW) propagating on the heterogeneous layered piezoelectric substrate is 2 Curve of the change of thickness of scandium-doped aluminum nitride film; Figure 4 It can be seen that when the Euler angle is rotated, Rayleigh-type LSAW and horizontal shear-type LSAW are excited on the heterogeneous layered piezoelectric substrate, and the horizontal shear-type LSAW exhibits relatively good SAW characteristics. Figure 4 It can be seen that the electromechanical coupling coefficient K of the horizontal shear type leaky acoustic surface wave (SH-type LSAW) in the range of 0.1λ to 0.4λ of the scandium-doped aluminum nitride film thickness is 2Relatively high (> 6%), when the scandium-doped aluminum nitride film thickness is 0.2λ, K 2 Reaching a maximum value of 10%.

[0044] like Figure 5 As shown in the figure, the electromechanical coupling coefficient K of the horizontal shear leaky surface wave (SH-type LSAW) propagating on the heterogeneous layered piezoelectric substrate is set to 0.2λ and λ when the film thickness of the scandium-doped aluminum nitride film and the aluminum nitride film are set to 0.2λ and λ respectively. 2 With the change of silicon dioxide film thickness curve; Figure 5 It can be seen that when the Euler angle is set to (0°, 90°, 50°), as the thickness of the silicon dioxide film increases, the electromechanical coupling coefficient K of the horizontal shear type leaky acoustic surface wave (SH-type LSAW) increases. 2 It shows a change situation of first increasing and then decreasing. Figure 5 It can be seen that the electromechanical coupling coefficient K of the horizontal shear type leaky surface wave (SH-type LSAW) is within the range of 0.1λ to 0.5λ in the silicon dioxide film thickness. 2 Relatively high (>7%), when the silicon dioxide film thickness is 0.2λ, K 2 Reaching a maximum of 10.3%.

[0045] like Figure 6 As shown, the electromechanical coupling coefficient K of the horizontal shear-type leaky acoustic surface wave (SH-type LSAW) propagating on a heterogeneous layered piezoelectric substrate is 2 With the change of aluminum nitride film thickness curve; Figure 6 It can be seen that when the Euler angle is set to (0°, 90°, 50°), and the film thickness of the scandium-doped aluminum nitride film and the silicon dioxide film is set to 0.2λ and 0.2λ respectively, when the aluminum nitride film thickness changes in the range of 0.1λ to λ, the electromechanical coupling coefficient K of the horizontal shear type leaky acoustic surface wave (SH-type LSAW) is 2 It shows a significant change. When the aluminum nitride film thickness is greater than λ, K 2 It remains basically unchanged and has a slight tuning effect on SAW energy propagation. Figure 6 In the figure, the thickness of the aluminum nitride film is equal to λ.

[0046] Next, in order to confirm the relationship between the Euler angle and the horizontal shear type leaky acoustic surface wave, the thickness of the scandium-doped aluminum nitride film, the thickness of the silicon dioxide film, and the thickness of the aluminum nitride film were set to 0.2λ, 0.2λ, and λ respectively. Figure 7 It can be seen that when the Euler angle (0°, 90°, ψ) changes, the electromechanical coupling coefficient K of the two types of leaky acoustic surface waves on the heterogeneous layered piezoelectric substrate is 2The changes in the φ are significant. Furthermore, it is found that both types of leaky surface waves increase in the Euler angle ψ range of 40° to 80°. In particular, the horizontal shear leaky surface wave increases significantly around 55° to 65°.

[0047] Figure 8 is the electromechanical coupling coefficient K of the Rayleigh-type leaky acoustic surface wave on the heterogeneous layered piezoelectric substrate when the Euler angle θ changes in the embodiment of the present invention. 2 The change curve of Figure 8 It can be seen that when the Euler angle ψ is 90°, the horizontal shear-type acoustic leakage surface wave is not excited when the Euler angle θ is changed.

[0048] like Figure 9 As shown, the electromechanical coupling coefficient K between the Euler angles (0°, θ, ψ) of the scandium-doped aluminum nitride film and the horizontal shear leaky surface wave (SH-type LSAW) 2 The relationship change diagram of Figure 9 It can be seen that the electromechanical coupling coefficient K of the horizontal shear leakage acoustic surface wave is 2 The Euler angle θ is 50° to 90° and the Euler angle ψ is 40° to 80°. + 3°) Electromechanical coupling coefficient K of horizontal shear leakage surface waves 2 The maximum value is about 10-14%, and the frequency is kept in the high frequency range of 2-3 GHz. In addition, when the Euler angle is (0°, 0°, 0°), the horizontal shear leakage surface wave is not excited.

[0049] That is, by tuning the thickness of the heterogeneous layer structure and controlling the Euler angle of the scandium-doped aluminum nitride film, the range of the electromechanical coupling coefficient can be expanded, thereby effectively improving the bandwidth of the filter.

[0050] It has been verified that the heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices of the present invention can inhibit the leakage of energy to the substrate, concentrate the energy in the effective piezoelectric layer, and improve the piezoelectric conversion efficiency; by optimizing the orientation of the piezoelectric film by rotating the Euler angle, the sound field distribution can be adjusted to obtain a leaky surface acoustic wave with excellent surface acoustic wave performance, preferably a horizontal shear leaky surface acoustic wave with a high electromechanical coupling coefficient and high frequency, which is very suitable for high-frequency, broadband surface acoustic wave devices and has great application prospects.

[0051] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention.

Claims

1. A heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices, characterized in that: Utilizing a horizontal shear type leaky acoustic surface wave, the method comprises an interdigital transducer, a piezoelectric film layer, a Bragg reflection layer and a substrate layer arranged in sequence; The piezoelectric film layer is a scandium-doped aluminum nitride film, and the molar percentage of scandium doping in the scandium-doped aluminum nitride film is 0-40%. The thickness of the scandium-doped aluminum nitride film is 0.1λ-0.4λ, where λ is the wavelength of the surface acoustic wave. The Euler angle of the scandium-doped aluminum nitride piezoelectric film is rotated. When the Euler angle of the scandium-doped aluminum nitride film is set to (0°±5°, θ, ψ), θ and ψ respectively meet the following conditions: 50°≤θ≤90°, 40°≤ψ≤80°; n Bragg reflection layers are stacked between the piezoelectric film layer and the substrate layer, where n≥1; The Bragg reflection layer is formed by covering a high acoustic impedance layer with a low acoustic impedance layer. The sound velocity of the low acoustic impedance layer is lower than that of the high acoustic impedance layer. In the same Bragg reflection layer, the low acoustic impedance layer is closer to the piezoelectric thin film layer than the high acoustic impedance layer. The low acoustic impedance layer is a SiO2 film with a thickness of 0.1λ~λ.

2. The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices according to claim 1, characterized in that: The high acoustic impedance layer is an AlN film, a Sapphire film, a SiN film, a Mo film or a Pt film.

3. The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices according to claim 1, characterized in that: The thickness of the SiO2 film is 0.1λ to 0.5λ.

4. The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices according to claim 2, characterized in that: The high acoustic impedance layer is an AlN film, and the thickness of the AlN film ranges from 0.1λ to λ, where λ is the wavelength of the surface acoustic wave.

5. The heterogeneous layered piezoelectric substrate suitable for high-frequency, broadband surface acoustic wave devices according to claim 1, characterized in that: The substrate layer is a silicon substrate.

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