CN109039298B

CN109039298B - Surface acoustic wave device and method for manufacturing the same

Info

Publication number: CN109039298B
Application number: CN201810851088.6A
Authority: CN
Inventors: 彭波华; 李平; 胡念楚; 贾斌
Original assignee: Kaiyuan Communication Technology Xiamen Co ltd
Current assignee: Kaiyuan Communication Technology Xiamen Co ltd
Priority date: 2018-07-27
Filing date: 2018-07-27
Publication date: 2022-06-24
Anticipated expiration: 2038-07-27
Also published as: CN109039298A

Abstract

The present disclosure provides a surface acoustic wave device and a method of manufacturing the same; wherein, this surface acoustic wave device includes: a piezoelectric substrate having a plurality of different euler cut angles; and one or more interdigital transducers (IDTs) formed on a surface of the piezoelectric substrate for exciting a surface acoustic wave formed on the piezoelectric substrate. The invention forms a plurality of different Euler cutting angles on the same substrate, thereby meeting the requirements of filters with different frequency bands and different bandwidths and effectively reducing the cost.

Description

Surface acoustic wave device and method for manufacturing the same

Technical Field

The disclosure belongs to the technical field of wireless communication, and particularly relates to a surface acoustic wave device with piezoelectric substrates with various Euler cut angles and a manufacturing method thereof.

Background

SAW filters may be used in high frequency circuits, such as in bandpass filters. The SAW filter includes a piezoelectric material and an electrode structure. These electrodes can transform high frequency signals into acoustic waves that propagate along the surface of the piezoelectric material. Furthermore, the electrode structure may also be arranged to convert the acoustic wave back into a high frequency signal, thereby selectively extracting a desired frequency band.

However, the existing SAW filter still has the following defects:

(1) the existing saw device substrate is generally obtained directly from a wafer manufacturer, and each wafer corresponds to one euler cut angle.

(2) Although the resonance frequency (fs) and the electromechanical coupling coefficient (k2eff) of the surface acoustic wave device can be adjusted by changing the IDT thickness and the duty ratio of the resonator, the adjustment range is limited.

(3) Some spurious modes can also be suppressed in the same plane by adjusting the orientation of the resonator (i.e., the ψ angle), but without significantly affecting the primary resonant mode (e.g., changing its fs and k2 eff).

Disclosure of Invention

Technical problem to be solved

Based on the above problems, the present disclosure is directed to a surface acoustic wave device having a plurality of euler cut angle piezoelectric substrates and a method for manufacturing the same, so as to solve at least one of the above technical problems.

(II) technical scheme

In order to achieve the above object, as one aspect of the present disclosure, there is provided a surface acoustic wave device including:

a piezoelectric substrate having a plurality of different euler cut angles; and

one or more interdigital transducers (IDTs) formed on a surface of the piezoelectric substrate for exciting a surface acoustic wave formed on the piezoelectric substrate.

In some embodiments, the piezoelectric substrate includes a plurality of regions, and the euler cut angles of adjacent two regions are different.

In some embodiments, the piezoelectric substrate is a lithium tantalate or lithium niobate substrate; the piezoelectric substrate comprises three regions, wherein the second region is positioned between the first region and the third region and is respectively adjacent to the first region and the third region; the first and third regions have euler cut angles of (0, phi, psi) and the second region has euler cut angles of (0, phi-alpha, psi).

In some embodiments, a plurality of different euler cut angles are formed by forming a gully (valley) or ramp shape on the piezoelectric substrate using dry etching or wet etching.

In some embodiments, each interdigital transducer includes a plurality of electrodes, and a dielectric film is formed on the piezoelectric substrate and the electrodes, covering the interdigital transducer to embed it.

In some embodiments, the dielectric film is a temperature compensation layer, and the material of the temperature compensation layer includes silicon oxide, glass, tantalum oxide, fluorine-doped silicon oxide, carbon-doped silicon oxide, and boron-doped silicon oxide.

According to another aspect of the present disclosure, there is provided a method of fabricating a surface acoustic wave device, including:

providing a piezoelectric substrate;

forming a plurality of different euler cut angles on the piezoelectric substrate; and

an interdigital transducer (IDT) layer is formed on the piezoelectric substrate formed with the plurality of different Euler cut angles.

In some embodiments, the method for manufacturing a surface acoustic wave device further includes: forming a dielectric layer on the interdigital transducer (IDT) layer.

In some embodiments, a plurality of different euler kerfs are formed on the piezoelectric substrate by a bulk etch process of the piezoelectric substrate.

In some embodiments, the piezoelectric substrate is a lithium tantalate or lithium niobate substrate; carrying out body etching treatment on the piezoelectric substrate, and forming three regions on the piezoelectric substrate, wherein the second region is positioned between the first region and the third region and is respectively adjacent to the first region and the third region; the first and third regions have euler cut angles of (0, phi, psi) and the second region has euler cut angles of (0, phi-alpha, psi).

(III) advantageous effects

According to the technical scheme, the surface acoustic wave device and the manufacturing method thereof have at least one of the following beneficial effects:

(1) the method has the advantages that the plurality of different Euler cut angles are formed on the same substrate (wafer), so that the requirements of filters with different frequency bands and different bandwidths are met, and the cost is effectively reduced.

(2) The method can be used for manufacturing surface acoustic wave devices such as filters with adjustable bandwidth and switchable frequency bands, and therefore the method can be widely used in high-frequency circuits.

Drawings

Fig. 1 is a schematic diagram of a SAW resonator structure according to the present disclosure.

Fig. 2 is a front cross-sectional view of a SAW resonator in accordance with one embodiment of the present disclosure.

Fig. 3 is a top view of the SAW resonator shown in fig. 2.

Fig. 4 is a front cross-sectional view of a SAW resonator according to another embodiment of the present disclosure.

Fig. 5 is a front cross-sectional view of a SAW resonator according to yet another embodiment of the present disclosure.

Fig. 6 is a front cross-sectional view of a SAW resonator in accordance with yet another embodiment of the present disclosure.

Fig. 7 is a flow chart of a method of fabricating a SAW resonator according to the present disclosure.

Fig. 8 is a graph of the result of IDT simulation by FEM for different euler cut angles LN.

< description of symbols >

A 1-interdigital transducer; 2-a piezoelectric substrate; 3-a dielectric thin film; 4-reflective grating.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure will be described in further detail below with reference to specific embodiments and the accompanying drawings.

SAW devices of the present disclosure use IDTs to convert electrical energy to acoustic energy, or conversely, acoustic energy to electrical energy. The IDT uses a piezoelectric substrate and two opposing bus bars (busbars) at two different potentials and two sets of electrodes connected to the two bus bars. Due to the inverse piezoelectric effect, the electric field between two consecutive electrodes at different potentials provides a sound source. Conversely, if the transducer receives an incident wave, an electrical charge is generated in the electrodes due to the piezoelectric effect. As shown in fig. 1, the resonators are obtained by placing the interdigital transducer 1 between two reflection gratings 4, and the filter or duplexer can be obtained by connecting several resonators or by having one or several transmit IDTs that generate acoustic energy, which is received by one or several IDTs.

SAW devices of the present disclosure comprising rotating y-cut x-propagating lithium niobate (LiNbO)₃LN or lithium tantalate (LiTaO)₃LT) substrate, wherein the definition of the cut angle is defined by the euler angle (θ, Φ, ψ) as follows:

x, y, z are the crystal axes of the substrate. First, a rotation about the z-axis is made across a plane between the x-axis and the y-axis, wherein the x-axis is rotated to the direction of the y-axis. The first euler angle θ is the angle of the rotation. The rotation provides a new set of axes x ', y', z ', where z' is equal to the original axis z.

In the second rotation, the plane between the z ' axis and the y ' axis rotates about the x ' axis. Here, the y 'axis rotates in the direction of the z' axis. The angle of rotation phi represents the second euler angle. This second rotation provides a new set of axes x ", y", z ", where x' is equal to x".

In a third rotation, the x "axis and the y" axis rotate about the z "axis, where the x" axis rotates in the direction of the y "axis.

The angle of rotation psi represents the third euler angle. This third rotation again provides a new set of axes x "', y"', z "', where z" equals z "'.

The transformations described herein provide x and y axis parallel to the surface of the substrate. Further, the z' "axis is orthogonal to the surface of the substrate. The x' "axis is parallel to the propagation direction of the acoustic wave.

The disclosed surface acoustic wave device includes:

a piezoelectric substrate having a plurality of directional euler cut angles; and

Such as resonators, filters, duplexers, etc. Optionally, the piezoelectric substrate includes a plurality of regions, and the euler cut angles of two adjacent regions are different, and at least a part of the regions of the piezoelectric substrate may be etched to form gaps or slopes on the piezoelectric substrate, so as to form a plurality of different euler cut angles.

The piezoelectric substrate material includes but is not limited to LN, LT, quartz, aluminum nitride, sapphire, etc.; the IDT layer material includes, but is not limited to, aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, tungsten, and the like; the temperature compensation layer material includes, but is not limited to, silicon dioxide, glass, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide.

The process for obtaining the piezoelectric substrate with slopes or ravines in the present disclosure includes, but is not limited to, dry etching and wet etching.

In a specific embodiment, as illustrated in fig. 2 and 3, the SAW filter includes: a piezoelectric substrate 2 having euler cut angles in two directions; and an interdigital transducer (IDT)1 formed on the surface of the piezoelectric substrate for exciting a surface acoustic wave formed on the piezoelectric substrate. The piezoelectric substrate is composed of lithium tantalate or lithium niobate, and is subjected to patterning processing to form a slope. There are three regions on the piezoelectric substrate, i.e., the piezoelectric substrate in the I and III regions corresponds to (0, phi, psi), and the region II corresponds to (0, phi-alpha, psi), i.e., the euler angles of the I and III regions are the same in this embodiment, and the euler angles of the region II are different from those of the I and III regions. The SAW resonator manufactured by the embodiment can excite sound waves with different resonant frequencies and electromechanical coupling coefficients, and filters with different frequencies and bandwidths can be constructed by connecting different resonators in series and in parallel.

In addition, by properly adjusting the direction of the IDT, i.e., by adjusting the angle ψ, other modes near the main resonance mode can be suppressed, thereby obtaining a flatter passband and a near out-of-band filter curve.

In another embodiment, as shown in fig. 4, the SAW filter includes: a piezoelectric substrate and an interdigital transducer (IDT). The piezoelectric substrate is patterned to form a plurality of trenches. Unlike the previous embodiment, there are five regions on the piezoelectric substrate, where the piezoelectric substrate for the I, III, V regions corresponds to (0, phi, psi), the II region corresponds to (0, phi-alpha, psi), and the IV region corresponds to (0, phi + alpha, psi). The SAW resonator manufactured by the embodiment can excite a plurality of acoustic waves with different resonant frequencies and electromechanical coupling coefficients.

In addition, resonators may be formed in regions I, II, and IV shown in fig. 4, and devices having different resonance frequencies and different electromechanical coupling coefficients may be obtained in the three regions.

In yet another embodiment, a SAW filter includes: a piezoelectric substrate and a plurality of interdigital transducers (IDTs). There are three regions on the piezoelectric substrate, where the piezoelectric substrate of regions I, III corresponds to (0, φ, ψ) and region II corresponds to (0, φ - α, ψ). As shown in fig. 5, resonators are fabricated in regions II and III, respectively, with different fs and k2eff, thereby constructing filters with different frequency bands and different bandwidths.

In yet another specific embodiment, as shown in fig. 6, a dielectric film 3 is formed on the piezoelectric substrate and the electrodes, covering the interdigital transducer so as to embed it. The dielectric thin film is a temperature compensation layer, and the temperature compensation layer includes, but is not limited to, silicon dioxide, glass, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide.

The present disclosure also provides a method for manufacturing a surface acoustic wave device, as shown in fig. 7, the method for manufacturing a surface acoustic wave device includes:

providing a piezoelectric substrate;

forming Euler cut angles in a plurality of directions on the piezoelectric substrate; and

an interdigital transducer (IDT) layer is formed on the piezoelectric substrate on which the Euler cut angles of the plurality of directions are formed.

Further, the method for manufacturing the surface acoustic wave device further includes forming a dielectric layer on the interdigital transducer (IDT) layer.

Optionally, the piezoelectric substrate is subjected to bulk etching, so that euler cut angles in multiple directions are formed on the piezoelectric substrate.

Optionally, the piezoelectric substrate includes a plurality of regions, and the euler cut angles of two adjacent regions are different.

Further, in one embodiment, LiNbO at (0, 90, 0) and (0, 38, 0)₃In combination (like the SAW device structure shown in fig. 5, phi is 90, alpha is 52, and psi is 0), fig. 8 is a graph showing simulation results of the surface acoustic wave resonators using FEM for the two euler cut angles. As shown in figure 8 of the drawings,

(0, 38, 0) Euler cut angle) has a coupling coefficient of about

(0, 90, 0) euler cut angle) of the filter, thereby making it possible to construct filters having different bandwidths.

To form the SAW filter structure of the present embodiment. First, a bulk etch was performed on a (0, 90, 0) lithium niobate substrate, and the control slope was 52 degrees. Thus, a filter with a large bandwidth can be manufactured by corresponding to the (0, 90, 0) Euler cut angle in the I and III regions. And the region II on the slope corresponds to the Euler cut angle of (0, 38, 0), so that a filter with smaller bandwidth can be manufactured.

Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the disclosure may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, this disclosure should not be construed to reflect the intent: rather, the present disclosure is directed to more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

It is also noted that the illustrations herein may provide examples of parameters that include particular values, but that these parameters need not be exactly equal to the corresponding values, but may be approximated to the corresponding values within acceptable error tolerances or design constraints. Directional phrases used in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., refer only to the direction of the attached drawings and are not intended to limit the scope of the present invention. In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims

1. A surface acoustic wave device comprising:

a piezoelectric substrate having a plurality of different euler cut angles; and

one or more interdigital transducers (IDTs) formed on a surface of the piezoelectric substrate for exciting a surface acoustic wave formed on the piezoelectric substrate;

the piezoelectric substrate comprises a plurality of areas, and Euler cut angles of two adjacent areas are different;

the piezoelectric substrate is a lithium tantalate or lithium niobate substrate; the piezoelectric substrate comprises three regions, wherein the second region is positioned between the first region and the third region and is respectively adjacent to the first region and the third region; the first and third regions have Euler cut angles of (0, phi, psi) and the second region has Euler cut angles of (0, phi-alpha, psi);

the interdigital transducer comprises a first sub-electrode positioned in the first area, a second sub-electrode positioned in the second area and a third sub-electrode positioned in the third area, and the propagation direction of surface acoustic waves formed by excitation of the interdigital transducer is parallel to the boundary line of the first area and the second area on a projection plane facing the piezoelectric substrate.

2. The SAW device of claim 1, wherein a gully or ramp shape is formed on the piezoelectric substrate using dry or wet etching to form a plurality of different Euler cut angles.

3. The surface acoustic wave device as set forth in claim 1, wherein each interdigital transducer includes a plurality of electrodes, and a dielectric film is formed on said piezoelectric substrate and said electrodes, and covers said interdigital transducer so as to be embedded.

4. The SAW device of claim 3, wherein the dielectric thin film is a temperature compensation layer, and the material comprises silicon oxide, glass, tantalum oxide, fluorine-doped silicon oxide, carbon-doped silicon oxide, boron-doped silicon oxide.

5. A method for manufacturing a surface acoustic wave device comprises the following steps:

providing a piezoelectric substrate;

forming an interdigital transducer (IDT) layer on the piezoelectric substrate formed with the plurality of different Euler cut angles;

wherein a plurality of different euler cut angles are formed on the piezoelectric substrate by subjecting the piezoelectric substrate to a bulk etching process;

the piezoelectric substrate is a lithium tantalate or lithium niobate substrate; carrying out body etching treatment on the piezoelectric substrate, and forming three regions on the piezoelectric substrate, wherein the second region is positioned between the first region and the third region and is respectively adjacent to the first region and the third region; the euler cut angles of the first and third regions are (0, phi, psi), and the euler cut angle of the second region is (0, phi-alpha, psi);

6. The method of fabricating a surface acoustic wave device according to claim 5, further comprising: forming a dielectric layer on the interdigital transducer (IDT) layer.