Broadband surface acoustic wave device

Abstract

A broadband surface acoustic wave (SAW) device is provided. The broadband SAW device includes: a piezoelectric substrate; and a plurality of interdigital transducer (IDT) electrodes formed on the piezoelectric substrate, wherein the piezoelectric substrate comprises magnesium oxide (MgO)-doped lithium tantalate (LiTaO3) as a piezoelectric material.

Description

Technical Field

[0001] This invention relates to a broadband surface acoustic wave device, and more specifically, to a device with an improved electromechanical coupling coefficient (k... 2 ) and surface acoustic wave devices with wide bandwidth and low insertion loss. Background Technology

[0002] Surface acoustic waves (SAWs) are waves that propagate along the surface of an elastic solid. Their energy is concentrated near the surface during propagation, and they belong to the category of mechanical waves. A surface acoustic wave device is an electromechanical device that utilizes the interaction between surface acoustic waves and conduction electrons, taking advantage of surface acoustic waves propagating on the surface of a piezoelectric crystal. These surface acoustic wave devices have wide applications in industrial fields such as sensors, oscillators, and filters, and offer numerous advantages including miniaturization, lightweight design, robustness, stability, high sensitivity, low cost, and real-time performance.

[0003] The bandwidth of a surface acoustic wave (SAW) filter is determined by the electromechanical coupling coefficient of the device. The electromechanical coupling coefficient mainly depends on the type of piezoelectric substrate material, the crystal cutting angle, and the SAW propagation mode used.

[0004] Lithium niobate (LiNbO3, LN) and lithium tantalate (LiTaO3, LT) are typically used as piezoelectric materials. LT is primarily used in narrowband surface acoustic wave (SAW) filters, while LN is mainly used in broadband filters. SAW devices using LN achieve k at 0° YX-cut. 2 The maximum improvement can reach approximately 25%, but the temperature coefficient of sound velocity (TCV) of SAW is -50 ppm / K, indicating poor performance. To compensate for this deficiency, silicon oxide (SiO2) with a positive (+) TCV is typically deposited as a compensating film. However, depositing SiO2 requires additional process steps and increases manufacturing costs.

[0005] On the other hand, when using LT, due to its good performance (TCV of -20 ppm / K), SiO2 is often unnecessary. However, k 2 The bandwidth is as low as about 9%, which essentially limits the relative bandwidth of the filter, making it difficult to achieve a broadband filter using only an LT substrate. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method that improves the electromechanical coupling coefficient (k) 2 ) and surface acoustic wave devices with wide bandwidth and low insertion loss.

[0007] The technical issues of this invention are not limited to those described above, and other technical issues not mentioned herein can be clearly understood by those skilled in the art from the following description.

[0008] To address the aforementioned technical challenges, a broadband surface acoustic wave device according to an embodiment of the present invention includes: a piezoelectric substrate; and a plurality of interdigital transducer (IDT) electrodes formed on the piezoelectric substrate, wherein the piezoelectric substrate comprises magnesium oxide (MgO)-doped lithium tantalate (LiTaO3) as a piezoelectric material.

[0009] In some embodiments of the present invention, the MgO may be doped at a ratio of 3 mol% to 10 mol% of the total mass of the piezoelectric substrate.

[0010] In some embodiments of the present invention, an insulating film covering the piezoelectric substrate and the plurality of IDT electrodes may also be included.

[0011] In some embodiments of the present invention, the insulating film may contain at least one material selected from silicon nitride (Si3N4), silicon oxide (SiO2), aluminum oxide (Al2O3), and aluminum nitride (AlN).

[0012] In some embodiments of the present invention, the plurality of IDT electrodes may contain aluminum (Al) or copper (Cu) as the main component.

[0013] In some embodiments of the present invention, the thickness of the insulating film may be from 3 nm to 150 nm.

[0014] In some embodiments of the present invention, a support substrate may also be included below the piezoelectric substrate on which the plurality of IDT electrodes are formed.

[0015] In some embodiments of the present invention, an intermediate layer disposed between the support substrate and the piezoelectric substrate may also be included.

[0016] In some embodiments of the present invention, the intermediate layer may include at least one of a high-velocity layer that transmits elastic waves with a higher velocity than those propagated by the piezoelectric substrate, and a low-velocity layer that transmits lower velocity.

[0017] Specific details of other embodiments are included in the detailed description and accompanying drawings.

[0018] The broadband surface acoustic wave device according to embodiments of the present invention achieves a higher k-value compared to the case where the substrate is composed solely of an LT substrate by including MgO-doped LT in the piezoelectric layer of the piezoelectric substrate. 2 This increases the value, thus achieving a larger filter bandwidth. Furthermore, it improves the k-value. 2 This value helps achieve impedance matching and reduces insertion loss.

[0019] The effects of the present invention are not limited to those described above, and other effects not mentioned can be clearly understood by those skilled in the art from the content of the claims. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of a broadband surface acoustic wave device according to an embodiment of the present invention.

[0021] Figures 2 to 5 These are graphs used to illustrate the effects of a broadband surface acoustic wave device according to embodiments of the present invention.

[0022] Figure 6a and Figure 6b This is a cross-sectional view illustrating a temperature-compensated surface acoustic wave device according to another embodiment of the present invention. In the following description, identical parts are omitted, and the differences are emphasized.

[0023] Label Explanation 1, 2, 3: Broadband surface acoustic wave devices 110: Piezoelectric substrate; 120: Insulating film; 130: Supporting substrate; 140: Intermediate layer; 150: IDT electrode. Detailed Implementation

[0024] The advantages, features, and implementation methods of the present invention will become clear from the accompanying drawings and the embodiments described in the following detailed description. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in many different forms. These embodiments are only used to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art. The scope of protection of the present invention is defined only by the claims. Throughout the specification, the same reference numerals denote the same constituent elements.

[0025] When a component is described as "connected to" or "coupled to" another component, it means that it is directly connected or coupled to the other component, or that other components are involved in the connection. Conversely, if a component is described as "directly connected to" or "directly coupled to" another component, it means that no other components are involved. "And / or" includes each of the items mentioned individually, as well as all combinations thereof.

[0026] The terminology used in this specification is for descriptive purposes only and is not intended to limit the invention. Unless otherwise stated, the singular form includes the plural form in this specification. The use of "comprises" and / or "comprising" in this specification to refer to constituent elements, steps, operations, and / or components does not exclude the presence or addition of one or more other constituent elements, steps, operations, and / or components.

[0027] Although terms such as "first," "second," etc., are used to describe various constituent elements, these constituent elements are not limited by these terms. These terms are only used to distinguish one constituent element from another. Therefore, the "first constituent element" mentioned below can also be a "second constituent element" within the scope of the technical concept of this invention.

[0028] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) shall have the meanings commonly understood by one of ordinary skill in the art. Furthermore, terms defined in general dictionaries should not be idealized or over-interpreted unless explicitly defined.

[0029] Figure 1 This is a cross-sectional view of a broadband surface acoustic wave device according to an embodiment of the present invention.

[0030] Reference Figure 1 According to an embodiment of the present invention, the broadband surface acoustic wave device 1 may include a piezoelectric substrate 110, a plurality of IDT electrodes 150, an insulating film 120, etc.

[0031] The piezoelectric substrate 110 can generate elastic waves through the piezoelectric material based on the signal applied to the IDT electrode 150. In particular, the piezoelectric substrate 110 of the broadband surface acoustic wave device 1 according to an embodiment of the present invention may contain MgO-doped lithium tantalate (LiTaO3, LT).

[0032] Besides surface acoustic wave devices, LT materials are also used in electro-optics, optical integrated circuits, and nonlinear optics. In particular, materials in which MgO is doped into LT to reduce photorefractive damage are known to be suitable for high-power lasers and frequency conversion devices.

[0033] The inventors of this invention have discovered that by using MgO-doped LT as the piezoelectric material of the piezoelectric substrate 110, it is possible to achieve improved k... 2 The value of surface acoustic wave devices. The following is combined with... Figures 2 to 5 This invention explains the effect of using MgO-doped LT as a piezoelectric material in the broadband surface acoustic wave device 1 of the present invention.

[0034] Figures 2 to 5These are graphs used to illustrate the effects of a broadband surface acoustic wave device according to embodiments of the present invention.

[0035] All figures are based on measurements taken from the following sample: a 46.3° Y-cut LT wafer was used as the piezoelectric substrate 110, on which MgO was doped at a ratio of 5 mol% to form an IDT electrode, which was then covered with an insulating film. The IDT electrode was made of an aluminum-based material, and the insulating film was a 25 nm thick silicon nitride (Si3N4). Furthermore, the horizontal axis of each figure represents the ratio of the surface acoustic wave wavelength defined by the spacing between multiple IDT electrodes to the film thickness of the IDT electrode 150, i.e., the wavelength-normalized film thickness (Hmet%), which varies from 5.6% to 8.8%.

[0036] First refer to Figure 2 When using only LT wafers, k 2 The value changed from approximately 8% (Hmet% = 5.6%) to 8.7% (Hmet% = 8.8%), and as Hmet% increased, k... 2 The value is trending upward.

[0037] However, when using MgO-doped LT, it can be observed that k 2 The value changed from approximately 8.5% (Hmet% = 5.6%) to 9.4% (Hmet% = 8.8%), compared to the case where only LT wafers were used, k 2 The value increase rate is approximately 6.25% to 8%.

[0038] In addition, refer to Figure 3 When using only LT wafers, the velocity of sound (vsaw) changed from approximately 3,180 m / s (Hmet% = 5.6%) to 4,790 m / s (Hmet% = 8.8%), showing an increasing trend with increasing Hmet%. When using MgO-doped LT wafers, the velocity of sound changed from approximately 3,210 m / s (Hmet% = 5.6%) to 4,840 m / s (Hmet% = 8.8%), representing an average increase of 0.8% to 0.9% compared to using only LT wafers.

[0039] In summary, the broadband surface acoustic wave device 1 according to the embodiments of the present invention, by employing MgO-doped LT in the piezoelectric layer of the piezoelectric substrate 110, achieves a higher k-value compared to the case where the substrate is composed solely of LT. 2 This increases the value, thus achieving a larger filter bandwidth. Furthermore, it improves the k-value. 2 This value helps achieve impedance matching and reduces insertion loss.

[0040] In addition, the increase in sound velocity brought about by MgO doping LT is also beneficial to the realization of high frequency and filter characteristics.

[0041] Reference Figure 4 The graph illustrates the change in electrostatic capacitance of the piezoelectric layer of the piezoelectric substrate 110 as the wavelength-normalized film thickness (Hmet%) varies. In both cases, the electrostatic capacitance (C0) decreases with increasing Hmet%. When using only LT wafers, the electrostatic capacitance changes from approximately 3.82 pF (Hmet% = 5.6%) to 2.35 pF (Hmet% = 8.8%); when using MgO-doped LT wafers, the electrostatic capacitance changes from approximately 3.75 pF (Hmet% = 5.6%) to 2.25 pF (Hmet% = 8.8%).

[0042] In other words, using MgO-doped LT can reduce the electrostatic capacitance of the piezoelectric substrate by approximately 0.4% to 4.25%. This change in electrostatic capacitance is small and will not affect the size of the surface acoustic wave device.

[0043] In addition, such as Figure 5 As shown, it can be observed that the ratio of anti-resonant impedance to resonant impedance Zratio between MgO-doped LT wafers and pure LT wafers has only a slight difference of less than 0.5%, indicating that it has no significant impact on resonator characteristics, filter characteristics, etc.

[0044] Refer again Figure 1 The piezoelectric substrate 110 containing MgO-doped LT can be prepared, for example, by mixing MgO powder with LiTaO3 raw material and sintering at high temperature, followed by crystal growth using the Czochralski method or similar methods to obtain a MgO-doped LT single crystal. This forms the piezoelectric substrate 110 containing MgO-doped LT, wherein the doping ratio of MgO relative to the total mass is 3 mol% to 10 mol%.

[0045] Multiple IDT electrodes 150 can be arranged on the surface of the piezoelectric substrate 110.

[0046] Multiple IDT electrodes 150 may comprise metallic materials, such as at least one material selected from aluminum (Al), titanium (Ti), magnesium (Mg), zinc (Zn), scandium (Sc), ruthenium (Ru), copper (Cu), silver (Ag), gold (Au), platinum (Pt), tungsten (W), chromium (Cr), and molybdenum (Mo). In some embodiments, the multiple IDT electrodes 150 may also have a structure with two or more metal layers stacked together.

[0047] Multiple IDT electrodes 150 can be formed by lift-off or etching processes. Specifically, the lift-off process involves forming a photoresist pattern on the piezoelectric substrate 110, depositing a metal film on the photoresist pattern, and then removing the photoresist pattern to form the IDT electrode 150. The etching process involves forming a metal film on the piezoelectric substrate 110, forming a mask pattern such as photoresist on the metal film, and using the mask pattern as an etching mask to pattern the metal film to form the IDT electrode 150.

[0048] In addition, an insulating film 120 may be formed to cover the piezoelectric substrate 110 and the plurality of IDT electrodes 150. The insulating film 120 may contain at least one material selected from insulating materials such as silicon nitride (Si3N4), silicon oxide (SiO2), and aluminum oxide (Al2O3). The thickness of the insulating film 120 covering the piezoelectric substrate 110 may be formed, for example, from 3 nm to 150 nm.

[0049] Figure 6a and Figure 6b This is a cross-sectional view illustrating a temperature-compensated surface acoustic wave device according to another embodiment of the present invention. In the following description, identical parts are omitted, and the differences are emphasized.

[0050] Reference Figure 6a According to another embodiment of the present invention, the broadband surface acoustic wave device 2 may further include a support substrate 130 for supporting the piezoelectric substrate 110.

[0051] The support substrate 130 may be made of, for example, a semiconductor substrate such as silicon, a ceramic substrate, or an insulating substrate. The support substrate 130 and the piezoelectric substrate 110 may be surface-treated and then joined together by wafer bonding technology.

[0052] Reference Figure 6b According to another embodiment of the present invention, the broadband surface acoustic wave device 3 may further include an intermediate layer 140 disposed between the piezoelectric substrate 110 and the support substrate 130.

[0053] The sound velocity of the intermediate layer 140 may be lower or higher than the sound velocity of the elastic wave propagating through the piezoelectric substrate 110. The high-velocity layer may contain at least one of aluminum nitride, aluminum oxide, silicon nitride, silicon oxynitride, silicon, etc.; the low-velocity layer may contain at least one of a variety of known materials such as silicon oxide, glass, silicon oxynitride, etc. In some embodiments, the intermediate layer 140 may include a low-velocity layer stacked on the high-velocity layer.

[0054] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, those skilled in the art should understand that the present invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the above embodiments should be considered exemplary rather than restrictive in all respects.

Claims

1. A broadband surface acoustic wave device, characterized in that, include: Piezoelectric substrate; as well as Multiple interdigitated transducer (IDT) electrodes formed on the piezoelectric substrate, The piezoelectric substrate contains magnesium oxide (MgO) doped lithium tantalate (LiTaO3) as the piezoelectric material.

2. The broadband surface acoustic wave device according to claim 1, characterized in that, The MgO is doped at a ratio of 3 mol% to 10 mol% of the total mass of the piezoelectric substrate.

3. The broadband surface acoustic wave device according to claim 1, characterized in that, It also includes an insulating film covering the piezoelectric substrate and multiple IDT electrodes.

4. The broadband surface acoustic wave device according to claim 3, characterized in that, The insulating film contains at least one material selected from silicon nitride (Si3N4), silicon oxide (SiO2), aluminum oxide (Al2O3), and aluminum nitride (AlN).

5. The broadband surface acoustic wave device according to claim 3, characterized in that, The thickness of the insulating film is 50 nm to 150 nm.

6. The broadband surface acoustic wave device according to claim 1, characterized in that, It also includes a support substrate disposed below the piezoelectric substrate on which the plurality of IDT electrodes are formed.

7. The broadband surface acoustic wave device according to claim 6, characterized in that, It also includes an intermediate layer disposed between the support substrate and the piezoelectric substrate.

8. The broadband surface acoustic wave device according to claim 7, characterized in that, The intermediate layer includes at least one of a high-velocity layer that transmits elastic waves with a higher velocity than those propagated by the piezoelectric substrate, and a low-velocity layer that transmits lower velocity.

9. The broadband surface acoustic wave device according to claim 1, characterized in that, The plurality of IDT electrodes contain aluminum (Al) or copper (Cu) as the main component.

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