KR20220162588A - Surface Acoustic Wave device - Google Patents

Abstract

A surface acoustic wave element according to the present invention comprises: a support substrate; an intermediate layer laminated on the support substrate; a piezoelectric layer laminated on the intermediate layer; and an IDT electrode formed on the piezoelectric layer, wherein the Euler angles of the support substrate are (-45°±10°, -54°±10°, 180°±30°), and the Euler angles of the piezoelectric layer are (0°±5°, 112.5°±22.5°, 0°±5°) or (0°±5°, -67.5°±22.5°, 0°±5°). Therefore, the present invention is capable of suppressing a high-frequency spurious component.

Description

Surface acoustic wave device {Surface Acoustic Wave device}

The present invention relates to a surface acoustic wave device.

As the communication industry develops, wireless communication products are gradually becoming smaller, higher quality, and multifunctional. In accordance with this trend, miniaturization and multifunctionalization are required for parts used in wireless communication products, such as filters and duplexers.

As an example of such a component, a surface acoustic wave element includes a piezoelectric substrate, which is a piezoelectric single crystal bare chip, a pair of inter digital transducer (IDT) electrodes formed to face each other in the form of comb teeth on the upper surface thereof, input electrodes and output electrodes connected thereto, and the like. may consist of

When an electrical signal is applied through the input electrode of the surface acoustic wave element, piezoelectric distortion due to the piezoelectric effect is generated as much as the overlapping electrode length between the IDT electrodes facing each other, and the surface acoustic wave transmitted to the piezoelectric substrate is generated by the piezoelectric distortion. and converts it into an electrical signal through the output electrode and outputs it.

Such a surface acoustic wave device has advantages such as being small, easy to process signals, simple circuit, and capable of being mass-produced by using a semiconductor process. In addition, the surface acoustic wave device has a high side rejection within a pass band, and thus has the advantage of being able to transmit and receive high-quality information.

A technical problem to be achieved by the present invention is to provide a surface acoustic wave device capable of suppressing high-frequency spurious components without loss of a main mode.

A surface acoustic wave device according to the present invention for solving the above technical problems includes a support substrate; an intermediate layer laminated on the support substrate; a piezoelectric layer laminated on the intermediate layer; and an IDT electrode formed on the piezoelectric layer, wherein the Euler angles of the support substrate are (-45°±10°, -54°±10°, 180°±30°), and the Euler angles of the piezoelectric layer are (0 ° ± 5 °, 112.5 ° ± 22.5 °, 0 ° ± 5 °) or (0 ° ± 5 °, -67.5 ° ± 22.5 °, 0 ° ± 5 °).

The support substrate may include silicon, and the piezoelectric layer may include lithium tantalate.

The intermediate layer may include a high sound velocity layer laminated on the support substrate; and a low sound speed layer stacked on the high sound speed layer, wherein the sound speed of a bulk wave propagating through the high sound speed layer is higher than the sound speed of an elastic wave propagating through the piezoelectric layer, and the sound speed of a bulk wave propagating through the low sound speed layer is greater than the sound speed of an elastic wave propagating through the piezoelectric layer. It may be less than the speed of sound of an elastic wave propagating through the layer.

The support substrate may be formed of a substrate obtained by rotating a silicon substrate having a plane orientation of <111> by 180°.

The piezoelectric layer may be formed of a 42° YX-cut lithium tantalate substrate.

The Euler angle of the piezoelectric layer may be (0°±5°, 132.7° to 135°, 0°±5°) or (0°±5°, -47.3° to -45°, 0°±5°). have.

According to the present invention described above, it is possible to provide a surface acoustic wave device capable of suppressing high-frequency spurious components without loss of main mode.

1 shows a cross-sectional structure of a surface acoustic wave device according to an embodiment of the present invention.
2 shows a stacked structure of a support substrate and a piezoelectric layer according to a conventional example displayed on a plane.
3 shows a frequency characteristic graph of a surface acoustic wave device according to a conventional example.
4 shows a stacked structure of a support substrate and a piezoelectric layer according to an embodiment of the present invention displayed on a plane.
5 shows a frequency characteristic graph of a surface acoustic wave device according to an embodiment of the present invention.
FIG. 6 shows a graph in which the frequency characteristics of FIG. 3 and the frequency characteristics of FIG. 5 are overlapped.
7 shows wave modes of the thinned piezoelectric layer.
8 shows wave modes resulting from some wave modes being eliminated by the layered structure.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Substantially the same elements in the following description and accompanying drawings are indicated by the same reference numerals, respectively, and redundant description will be omitted. In addition, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

1 shows a cross-sectional structure of a surface acoustic wave device according to an embodiment of the present invention.

Referring to FIG. 1 , the surface acoustic wave device according to the present embodiment includes a support substrate 110, an intermediate layer 120 stacked on the support substrate, a piezoelectric layer 130 stacked on the intermediate layer 120, and a piezoelectric layer. and an IDT electrode 140 formed on (130).

The support substrate 110 may be made of at least one of a silicon (Si) material, a sapphire material, or a diamond material. The plane orientation of the supporting substrate 110 is, for example, <111>, <100>, <110>, or a mixture of these plane orientations. The thickness of the support substrate 110 may be 5 μm or more or twice the wavelength of the surface acoustic wave in consideration of vibration of the surface acoustic wave.

The intermediate layer 120 may include a high sound speed layer 121 stacked on the support substrate 110 and a low sound speed layer 122 stacked on the high sound speed layer 121 . The sound speed of the bulk wave propagating through the high-sonic layer 121 is higher than that of the elastic wave propagating through the piezoelectric layer 130 . The high-sound velocity layer 121 may be made of a material such as aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, polysilicon, sapphire, or diamond. The sound speed of the bulk wave propagating through the low sound velocity layer 122 is lower than the sound speed of an elastic wave propagating through the piezoelectric layer 130 . The low sound velocity layer 122 may be made of a material such as silicon oxide, aluminum nitride, glass, silicon oxynitride, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide. Depending on the embodiment, the middle layer 120 may be composed of only one of a high sound speed layer and a low sound speed layer.

The piezoelectric layer 130 may be made of a material such as lithium tantalate (LiTaO3, LT) or lithium niobate (LiNbO3, LN) and may be a single crystal. The thickness of the piezoelectric layer 130 is not particularly limited and may be appropriately selected depending on the use of the surface acoustic wave element.

The IDT (Interdigital Transducer) electrode 140 is an electrode formed on the upper surface of the piezoelectric layer 130 to generate a surface acoustic wave. The IDT electrode 140 may be a single comb electrode or a double comb electrode. The material forming the IDT electrode 140 is not particularly limited, but may be composed of Al, Al-Cu, Al-Si-Cu, or the like from the viewpoint of workability and cost. The IDT electrode 140 may have any thickness as long as it can exhibit the function of vibrating the surface acoustic wave, but it is preferably about 10 to 500 [nm]. When the thickness of the IDT electrode 140 is less than 10 [nm], the resistivity increases and the loss increases, while when the thickness exceeds 500 [nm], the mass that causes SAW reflection according to the thickness of the electrode This is because there is a possibility that the additional effect becomes remarkable and inhibits the target surface acoustic wave characteristics.

2 shows a stacked structure of a support substrate 110 and a piezoelectric layer 130 according to a conventional example displayed on a plane. In FIG. 2 (similar to FIG. 4 to be described later), the intermediate layer 120 is omitted for convenience. Referring to FIG. 2 , the support substrate 110 is formed of a silicon substrate 110_1 having a plane orientation of <111>, and the piezoelectric layer 130 is formed of a 42° YX-cut lithium tantalate substrate 130_1.

3 shows a frequency characteristic graph of a surface acoustic wave device according to a conventional example. Referring to FIG. 3 , a high frequency spurious component is generated in a frequency domain around 2550 MHz. The high-frequency spurious is generated when the layers under the piezoelectric layer 130 and the high-speed elastic wave expressed in the piezoelectric layer 130 are coupled, and the performance of the relative band may be deteriorated when the duplexer filter is manufactured.

4 shows a stacked structure of a support substrate 110 and a piezoelectric layer 130 according to an embodiment of the present invention displayed on a plane. Referring to FIG. 4 , the support substrate 110 is formed of a substrate 110_2 obtained by rotating a silicon substrate having a plane orientation of <111> by 180°, and a piezoelectric layer 130 is formed of a 42° YX-cut lithium tantalate substrate 130_1 ) is formed.

5 shows a frequency characteristic graph of a surface acoustic wave device according to an embodiment of the present invention. Referring to FIG. 5 , it can be seen that the high frequency spurs near about 2550 MHz shown in FIG. 3 are almost eliminated.

FIG. 6 shows a graph in which the frequency characteristics of FIG. 3 and the frequency characteristics of FIG. 5 are overlapped and displayed. As shown, according to the embodiment of the present invention, compared to the conventional example, it can be seen that only high-frequency spurs can be suppressed without loss of the main mode only by 180 ° rotation of the silicon substrate having a plane orientation <111>. .

The crystal orientation of the support substrate 110 and the piezoelectric layer 130 may also be expressed as Euler angles (λ, μ, θ).

When the support substrate 110 is formed of a substrate 110_2 obtained by rotating a silicon substrate having a plane orientation <111> by 180° as in the embodiment of the present invention, the Euler angle of the support substrate 110 is (-45°±10°). °, -54 ° ± 10 °, 180 ° ± 30 °), for example, (-45 °, -54 °, 180 °).

When the piezoelectric layer 130 is formed of the 42° YX-cut lithium tantalate substrate 130_1 as in the embodiment of the present invention, the Euler angles of the piezoelectric layer 130 are (0°±5°, 112.5°±22.5 It may have a range of °, 0 ° ± 5 °) or (0 ° ± 5 °, -67.5 ° ± 22.5 °, 0 ° ± 5 °), for example (0 °, 132 °, 0 °) or ( 0°, -48°, 0°).

Furthermore, as a result of simulating the frequency characteristics while changing μ of the Euler angles (λ, μ, θ) of the piezoelectric layer 130, it was confirmed that high-frequency spurs were more effectively suppressed when μ was in the range of 132.7° to 135°. . Therefore, more preferably, the Euler angle of the piezoelectric layer 130 is (0°±5°, 132.7° to 135°, 0°±5°) or (0°±5°, -47.3° to -45°, 0°±5°).

7 and 8 are graphs for explaining the principle of the present invention, in which FIG. 7 shows wave modes of a thinned piezoelectric layer, and FIG. indicate modes. A description of each wave mode is as follows.

Referring to FIG. 7 , as a result of Finite Element Method (FEM) simulation in a structure in which a thinned LT piezoelectric layer is suspended in the air, it is confirmed that wave modes as shown exist. Referring to FIG. 8 , in the case of a structure in which an intermediate layer and a support substrate are stacked under a thinned LT piezoelectric layer, coupling occurs between wave modes generated by the stacked layers and the piezoelectric layer, and some wave modes disappear. The combined wave mode has a different speed and amplitude than the conventional (piezoelectric layer alone) due to the mechanical properties of each layer. Therefore, the position and amplitude of the wave mode can be controlled by controlling the mechanical properties of the laminated material. In the case of the L-wave, which is particularly problematic, the mechanical properties of the silicon substrate are an important variable, and the mechanical properties of the silicon substrate are determined by Euler angles.

A method of changing the mechanical properties of silicon substrates of conventional plane orientations <111>, <100>, and <110> is to change the propagation direction, which is the theta(θ) of Euler angles (λ, μ, θ) has the effect of changing That is, changing the propagation direction of the silicon substrate of the plane orientation <111> by 180° means the same as rotating the silicon substrate by 180°, and the Euler angles (-45°, -54°, If the silicon substrate is rotated 180° from 0°), the Euler angles become (-45°, -54°, 180°).

High-frequency spurs are generated by coupling between the piezoelectric layer and elastic waves of the supporting substrate, and these high-frequency spurs move and disappear according to the stiffness of the supporting substrate. Silicon used as a support substrate has different stiffness depending on the Euler angle, and there is an Euler angle under the condition that the L-wave of the piezoelectric layer is eliminated. However, it is difficult to suppress the L-wave of the piezoelectric layer because silicon substrates with normal plane orientations <111>, <100>, and <110> have fixed Euler angles. In an embodiment of the present invention, the L-wave of the piezoelectric layer can be suppressed by changing the theta (θ) of the Euler angle through the rotation (change of propagation direction) of the silicon substrate in the plane orientation <111>. In addition, the embodiment of the present invention has the advantage of suppressing high-frequency spurs without loss of the main mode by using a combination of a conventional silicon substrate and a lithium tantalate substrate.

So far, the present invention has been looked at with respect to its preferred embodiments. Those skilled in the art to which the present invention pertains will be able to understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a limiting point of view. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent scope will be construed as being included in the present invention.

Claims (6)

support substrate;
an intermediate layer laminated on the support substrate;
a piezoelectric layer laminated on the intermediate layer; and
Including an IDT electrode formed on the piezoelectric layer,
The Euler angles of the support substrate are (-45 ° ± 10 °, -54 ° ± 10 °, 180 ° ± 30 °),
The Euler angle of the piezoelectric layer is (0°±5°, 112.5°±22.5°, 0°±5°) or (0°±5°, -67.5°±22.5°, 0°±5°). A surface acoustic wave element to be. According to claim 1,
The support substrate includes silicon,
The surface acoustic wave device according to claim 1, wherein the piezoelectric layer contains lithium tantalate. According to claim 1,
The middle layer,
a high sound velocity layer laminated on the support substrate; and
Including a low sound speed layer laminated on the high sound speed layer,
The sound speed of the bulk wave propagating through the high-sonic layer is higher than the sound speed of the acoustic wave propagating through the piezoelectric layer;
The surface acoustic wave device according to claim 1 , wherein the sound velocity of the bulk wave propagating through the low sound velocity layer is lower than the sound speed of the acoustic wave propagating through the piezoelectric layer. According to any one of claims 1 to 3,
The surface acoustic wave device according to claim 1, wherein the support substrate is formed by rotating a silicon substrate having a plane orientation of <111> by 180°. According to any one of claims 1 to 3,
The surface acoustic wave device according to claim 1, wherein the piezoelectric layer is formed of a 42° YX-cut lithium tantalate substrate. According to any one of claims 1 to 3,
The Euler angle of the piezoelectric layer is (0°±5°, 132.7° to 135°, 0°±5°) or (0°±5°, -47.3° to -45°, 0°±5°). Characterized by a surface acoustic wave device.

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