Surface acoustic wave device

Abstract

The present invention relates to a surface acoustic wave device in which buried reflectors and protruding reflectors are alternately arranged. The surface acoustic wave device according to the present invention comprises: a piezoelectric layer and an IDT electrode formed on the piezoelectric layer; and a plurality of reflector units periodically and repeatedly formed, along an acoustic wave propagation direction, outside the IDT electrode in the acoustic wave propagation direction. The reflector units include: protruding reflectors formed on the piezoelectric layer and extending in a direction perpendicular to the acoustic wave propagation direction; and buried reflectors buried in the piezoelectric layer and formed parallel to the protruding reflectors in the direction perpendicular to the acoustic wave propagation direction.

Description

Surface acoustic wave device

[0001] The present invention relates to a surface acoustic wave device, and more specifically, to a surface acoustic wave device in which a buried reflector and a protruding reflector are alternately arranged.

[0002] The present invention is based on the research results of the “Development of 6-inch Thin-film SAW Foundry Technology for Next-Generation Filters” research project (Executing Organization: SONIX Co., Ltd., Research Period: April 1, 2023 to December 31, 2026), which was carried out with support from the Broadcasting and Telecommunications Industry Technology Development Project (Project Unique Number: 2710008066, Project Number: 00222621) organized by the Ministry of Science and ICT of the Republic of Korea and managed by the Institute of Information and Communications Technology Planning and Evaluation.

[0003] Generally, a Surface Acoustic Wave (SAW) device is a component that converts electrical signals into mechanical waves using a metal electrode pattern formed on a piezoelectric substrate. Based on its advantages of high-speed operation and low power consumption, it is utilized in various fields such as communication systems, sensors, filters, and signal processing. Due to the characteristic that surface acoustic waves propagate along the surface of the piezoelectric substrate, it is also referred to as a 'surface acoustic wave device'.

[0004] FIG. 1 is a drawing showing a surface acoustic wave device according to the prior art.

[0005] The surface acoustic wave device is composed of a support substrate (11), a piezoelectric layer (13) located on the support substrate (11), an intermediate layer (12) provided between the support substrate (11) and the piezoelectric layer (13), and an IDT (Inter Digital Transducer) electrode (14) and a reflector (15, 16) deposited on the piezoelectric layer (13).

[0006] The IDT electrode (14) is located at the center of the surface acoustic wave device and is formed of a comb-like electrode pattern made of thin metal that is interlocked with one another. The IDT electrode (14) is composed of multiple electrode fingers, and the thickness and spacing of the fingers are designed to match the target frequency of the acoustic wave to be propagated. When an electric signal is applied to the input side of the IDT electrode (14), a piezo effect occurs due to the electric field between the electrodes, generating an acoustic wave, and the generated acoustic wave propagates along the surface of the piezoelectric layer (13). Subsequently, the propagated acoustic wave is converted back into an electric signal at the output side of the IDT electrode (14) and output.

[0007] Reflectors (15, 16) are located on both sides of the IDT electrode (14) on the piezoelectric layer (13) and are positioned within a reachable range for acoustic waves generated from the IDT electrode (14). The reflectors (15, 16) reflect surface acoustic waves toward the IDT electrode (14) to prevent energy from leaking out and to keep it inside the IDT electrode (14).

[0008] The surface acoustic wave device is arranged in the order of reflector (15) - IDT electrode (14) - reflector (16) on the piezoelectric layer (13), so that acoustic waves generated from the IDT electrode (14) are reflected from both reflectors (15, 16) and return to the IDT electrode (14). This creates a resonance phenomenon, and improves the quality factor (Q-factor) and frequency response characteristics of the device. The reflectors (15, 16) can be formed by depositing a metal layer on the piezoelectric layer (13).

[0009] FIG. 2 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of FIG. 1. The horizontal axis (X-axis) of the graph represents frequency (unit: MHz), and the vertical axis (Y-axis) represents the magnitude of admittance (unit: dB). For a structure including three pairs of protruding reflector units on each side of the IDT electrode (14), the frequency-admittance characteristics were measured, and a resonance point of magnitude 8.75022 dB was observed around 1590 MHz, and an anti-resonance point of magnitude -69.9905 dB was observed around 1675 MHz. Accordingly, the resonance / anti-resonance ratio (Y-ratio) of the conventional surface acoustic wave device according to FIG. 1 is calculated to be approximately 78.74 dB.

[0010] However, as described above, there are several problems when configuring the reflector solely with a protruding structure by depositing a metal layer. Although the protruding reflector can effectively reflect acoustic waves propagating along the surface of the piezoelectric layer, it cannot reflect acoustic waves propagating into the piezoelectric layer, which can lead to energy leakage and, as a result, an increase in insertion loss. Furthermore, the metal layer of the reflector is sensitive to heat, so if it is subjected to significant stress due to thermal expansion in a high-temperature environment, delamination or deformation may occur with respect to the piezoelectric layer, and there is also a problem of degradation when high power is applied.

[0011] The present invention aims to provide a surface acoustic wave device capable of minimizing energy leakage, reducing insertion loss, and improving resonance characteristics by effectively reflecting not only acoustic waves propagating along the surface of the piezoelectric layer but also acoustic waves transmitted into the piezoelectric layer, by alternately arranging an embedded reflector embedded within the piezoelectric layer and a protruding reflector protruding above the piezoelectric layer.

[0012] In addition, the present invention aims to provide a surface acoustic wave device capable of stable operation even in high-temperature or high-power environments by improving thermal stability in high-temperature environments through a composite reflector structure including a buried reflector, and improving reliability issues such as peeling, deformation, and degradation caused by thermal expansion.

[0013] In addition, the present invention aims to provide a miniaturized surface acoustic wave device that can reduce the overall size by maximizing the reflection efficiency of acoustic waves through a composite reflector structure in which a buried reflector and a protruding reflector are combined, thereby securing performance equivalent to or better than that of conventional technology with only a smaller number of reflector units.

[0014] The technical problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0015] A surface acoustic wave device according to the present invention for achieving the above-mentioned purpose comprises a piezoelectric layer and an IDT electrode formed on the piezoelectric layer, wherein the device includes a plurality of reflector units that are periodically and repeatedly formed along the acoustic wave propagation direction outward from the acoustic wave propagation direction of the IDT electrode, and the reflector units include a protruding reflector formed on the piezoelectric layer extending in a direction orthogonal to the acoustic wave propagation direction and a buried reflector formed embedded in the piezoelectric layer parallel to the protruding reflector in a direction orthogonal to the acoustic wave propagation direction.

[0016] The width of the reflector unit is λ.

[0017] The embedded reflector is a groove formed inside the piezoelectric layer.

[0018] The groove is formed without a step in the downward direction of the piezoelectric layer.

[0019] The groove has a shape that narrows in width towards the lower side of the piezoelectric layer.

[0020] The depth of the groove is greater than half the thickness of the piezoelectric layer.

[0021] The depth of the groove is the same as the thickness of the piezoelectric layer.

[0022] The reflector unit adjacent to the IDT electrode at the starting point of the acoustic wave propagation direction and the reflector unit adjacent to the IDT electrode at the ending point of the acoustic wave propagation direction are arranged symmetrically with respect to the IDT electrode.

[0023] The reflector unit consists of a protruding reflector, a first piezoelectric layer exposed area adjacent to the protruding reflector, a buried reflector adjacent to the first piezoelectric layer exposed area, and a second piezoelectric layer exposed area adjacent to the buried reflector, and the widths of the protruding reflector, the first piezoelectric layer exposed area, the buried reflector, and the second piezoelectric layer exposed area are each λ / 4.

[0024] All protruding reflectors constituting multiple reflector units are connected to the reflector busbar, and the embedded reflectors extend to the reflector busbar, and the embedded reflectors formed below the reflector busbar are filled with the same material as the reflector busbar.

[0025] The protruding reflector and the buried reflector constituting the reflector unit are formed on the same line in the vertical direction, and the buried reflector is filled with the same material as the protruding reflector.

[0026] The reflector unit includes a protruding reflector, a buried reflector adjacent to the protruding reflector, and a piezoelectric layer exposed area adjacent to the buried reflector.

[0027] The recessed reflector is filled with the same material as the protruding reflector, and the protruding reflector extends to the top of the recessed reflector. The protruding reflector and the recessed reflector are connected by the same material, forming an L-shaped reflector.

[0028] According to the present invention, by alternately arranging buried reflectors and protruding reflectors, not only surface acoustic waves but also internal acoustic waves can be reflected, thereby significantly reducing energy leakage, and consequently, insertion loss is reduced and electrical characteristics can be improved.

[0029] According to the present invention, since the energy confinement efficiency is dramatically improved by reflecting both the surface of the piezoelectric plate and the acoustic waves inside, the reflectivity per unit is increased, and accordingly, sufficient reflection performance can be obtained even with fewer reflector units than in the prior art, making it possible to achieve a miniaturized design that reduces the chip size.

[0030] According to the present invention, since the embedded reflector is not exposed to the external environment, thermal expansion stress due to temperature changes can be significantly reduced, and accordingly, problems such as peeling, deformation, and deterioration of the metal layer in high-temperature environments can be mitigated, thereby improving the reliability of the device.

[0031] According to the present invention, the composite reflector structure reduces local stress concentration caused by heat, so that the reflector structure is not deformed or damaged even when high power is applied, and thus stability can be ensured in communication and sensor systems that require high power and high temperature operation.

[0032] The effects that the present invention aims to achieve are not limited to those mentioned above, and other unmentioned effects can be clearly understood by those skilled in the art from the description below.

[0033] FIG. 1 is a drawing for explaining a surface acoustic wave device of the prior art.

[0034] Figure 2 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of Figure 1.

[0035] FIG. 3 is a plan view of a surface acoustic wave device according to a first embodiment of the present invention.

[0036] Figure 4 is a cross-sectional view of the AA line of the surface acoustic wave device of Figure 3.

[0037] Figure 5 is a cross-sectional view of the BB line of the surface acoustic wave device of Figure 3.

[0038] Figure 6 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of Figure 3.

[0039] FIG. 7 is a plan view of a surface acoustic wave device according to a second embodiment of the present invention.

[0040] Figure 8 is a cross-sectional view of the AA line of the surface acoustic wave device of Figure 7.

[0041] Figure 9 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of Figure 7.

[0042] FIG. 10 is a plan view of a surface acoustic wave device according to a third embodiment of the present invention.

[0043] Figure 11 is a cross-sectional view of the AA line of the surface acoustic wave device of Figure 10.

[0044] Figure 12 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of Figure 10.

[0045] FIG. 13 is a graph comparing the resonance / anti-resonance ratio (Y-ratio) of a surface acoustic wave device according to the prior art and the first to third embodiments of the present invention.

[0046] [Explanation of the symbol]

[0047] 21: Support substrate 22: Intermediate layer

[0048] 23: Piezoelectric layer 24: IDT electrode

[0049] 25, 26: Reflector unit 27: Projecting reflector

[0050] 29: Embedded reflector 71: Support substrate

[0051] 72: Intermediate layer 73: Piezoelectric layer

[0052] 74: IDT electrode 75, 76: Reflector unit

[0053] 77: Projecting reflector 78: Recessed reflector

[0054] 101: Support substrate 102: Intermediate layer

[0055] 103: Piezoelectric layer 104: IDT electrode

[0056] 105, 106: Reflector unit 107: Projection reflector

[0057] 108: Recessed reflector

[0058] Hereinafter, embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. It should be noted that the drawings are schematic and not drawn to scale. Relative dimensions and proportions of parts in the drawings are exaggerated or reduced in size for clarity and convenience in the drawings, and any dimensions are merely illustrative and not limiting. Also, the same reference numerals are used to denote similar features for identical structures, elements, or parts appearing in two or more drawings.

[0059] The embodiments of the present invention specifically illustrate ideal embodiments of the present invention. As a result, various variations of the illustrations are expected. Accordingly, the embodiments are not limited to specific forms of the illustrated areas and include, for example, variations in form resulting from manufacturing. All technical and scientific terms used herein, unless otherwise defined, have the meaning generally understood by those skilled in the art to which the present invention pertains. All terms used herein are selected for the purpose of further clarifying the present invention and are not selected to limit the scope of rights according to the present invention.

[0060] Expressions used in this specification, such as "comprising," "comprising," and "having," should be understood as open-ended terms implying the possibility of including other embodiments, unless otherwise stated in the phrase or sentence containing such expressions. Singular expressions described in this specification may include a plural meaning unless otherwise stated, and this applies likewise to singular expressions described in the claims. Expressions used in this specification, such as "first," "second," etc., are used to distinguish multiple components from one another and do not limit the order or importance of said components.

[0061] As used in this specification, 'module' and 'part' refer to a unit that processes at least one function or operation, and may refer to hardware components such as software, an FPGA, or one or more processors. In describing embodiments of the present invention, if it is determined that a detailed description of related known functions or known configurations may unnecessarily obscure the essence of the present invention, such detailed description may be omitted.

[0062] [1st Example]

[0063] FIG. 3 is a plan view of a surface acoustic wave device according to a first embodiment of the present invention, FIG. 4 is a cross-sectional view along line AA of the surface acoustic wave device of FIG. 3, and FIG. 5 is a cross-sectional view along line BB of the surface acoustic wave device of FIG. 3.

[0064] A surface acoustic wave device according to a first embodiment of the present invention is described with reference to FIGS. 3 to 5. The surface acoustic wave device according to the first embodiment of the present invention includes a support substrate (21), a piezoelectric layer (23) located on the support substrate (21), an intermediate layer (22) provided between the support substrate (21) and the piezoelectric layer (23), an IDT electrode (24) deposited on the piezoelectric layer (23), and a plurality of reflector units (25, 26) that are periodically and repeatedly formed along the acoustic wave propagation direction on both outer sides of the acoustic wave propagation direction of the IDT electrode (24).

[0065] The reflector unit (25, 26) can prevent acoustic waves from leaking out by reflecting acoustic waves that propagate in a direction different from the direction of acoustic wave propagation and trapping them inside the IDT electrode (24).

[0066] Each reflector unit (25, 26) includes a protruding reflector (27) formed by extending in a direction orthogonal to the acoustic wave propagation direction on the piezoelectric layer (23), and a buried reflector (29) formed by being embedded inside the piezoelectric layer (23) parallel to the protruding reflector (27) in a direction orthogonal to the acoustic wave propagation direction. The width of each reflector unit (25, 26) may be λ. Here, λ represents the wavelength of the acoustic wave determined by the electrode period of the IDT electrode (24).

[0067] The reflector unit (25) adjacent to the IDT electrode (24) at the starting point of the acoustic wave propagation direction and the reflector unit (26) adjacent to the IDT electrode (24) at the ending point of the acoustic wave propagation direction are arranged symmetrically with respect to the IDT electrode (24).

[0068] The reflector unit (25) is composed of a protruding reflector (27), a first piezoelectric layer exposed area (28) adjacent to the protruding reflector (27), a buried reflector (29) adjacent to the first piezoelectric layer exposed area (28), and a second piezoelectric layer exposed area (30) adjacent to the buried reflector (29), and the widths of the protruding reflector (27), the first piezoelectric layer exposed area (28), the buried reflector (29), and the second piezoelectric layer exposed area (30) are each λ / 4.

[0069] The IDT electrode (24) has an electrode busbar (24a) extending in the direction of acoustic wave propagation and a plurality of electrode fingers (24b) connected to the electrode busbar (24a) and extending in a direction orthogonal to the direction of acoustic wave propagation.

[0070] The support substrate (21) may be a silicon support substrate.

[0071] The intermediate layer (22) may include a polysilicon layer disposed on a support substrate (21) and a silicon oxide layer disposed on the polysilicon layer. A piezoelectric layer (23) may be disposed on the silicon oxide layer, and an IDT electrode (24) may be formed on the piezoelectric layer (23). The polysilicon layer is a layer in which the bulk wave speed propagating through the piezoelectric layer (23) is faster than the acoustic wave speed propagating through the piezoelectric layer (23), and the silicon oxide layer may be a layer in which the bulk wave speed propagating through the piezoelectric layer (23) is slower than the acoustic wave speed propagating through the piezoelectric layer (23).

[0072] The polysilicon layer may be modified into any one of the following: aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, various ceramics such as alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, diamond, or a material having each of the above materials as a main component, or a material having a mixture of each of the above materials as a main component.

[0073] The silicon oxide layer may be modified into any one of silicon oxide, glass, silicon nitride, tantalum oxide, a compound of silicon oxide with added fluorine, carbon, or boron, or a material having each of the above materials as a main component.

[0074] The piezoelectric layer (23) may be composed of lithium tantalate (LiTaO3) or other piezoelectric single crystals, piezoelectric ceramics, such as lithium niobate (LiNbO3).

[0075] The material of the IDT electrode (24) may be a suitable metal or alloy such as copper (Cu), nickel (Ni), nickel-chromium (Ni-Cr) alloy, aluminum-copper (Al-Cu) alloy, titanium (Ti), aluminum (Al), platinum (Pt).

[0076] The intermediate layer (22) can be formed by sequentially stacking a polysilicon layer and a silicon oxide layer. When a piezoelectric layer (23) is stacked on the intermediate layer (22), acoustic waves propagated from the piezoelectric layer (23) can be reflected at the interface between the silicon oxide layer and the polysilicon layer and returned to the piezoelectric layer (23), thereby allowing acoustic wave energy to be efficiently trapped within the piezoelectric layer (23).

[0077] Reflector units (25, 26) can be periodically and repeatedly formed on both outer sides of the IDT electrode (24). At this time, the width of each reflector unit (25, 26) may be λ.

[0078] In the first embodiment, the reflector units (25, 26) are illustrated such that a protruding reflector (27) is formed at a position adjacent to the IDT electrode (24) and a buried reflector (29) is positioned at a position relatively far from the IDT electrode (24), but are not limited thereto; they may also be positioned such that a buried reflector is formed at a position adjacent to the IDT electrode (24) and a protruding reflector is formed at a position relatively far from the IDT electrode (24). The widths of the protruding reflector (27), the first piezoelectric layer exposed area (28), the buried reflector (29), and the second piezoelectric layer exposed area (30) constituting the reflector units (25, 26) are each λ / 4, so that the total width of the reflector unit may be λ. Although a surface acoustic wave device with two reflector units connected is illustrated in FIGS. 3 to 5, the present invention is not limited thereto and a larger number of reflector units may be connected.

[0079] The protruding reflector (27) may be formed from a metal material. The metal material of the protruding reflector (27) may be a suitable metal or alloy such as copper (Cu), nickel (Ni), nickel-chromium (Ni-Cr) alloy, aluminum-copper (Al-Cu) alloy, titanium (Ti), aluminum (Al), platinum (Pt).

[0080] The embedded reflector (29) may be a groove formed inside the piezoelectric layer (23).

[0081] As shown in FIG. 4, the groove may be formed without a step in the downward direction of the piezoelectric layer (23), or it may be formed with a step in the downward direction of the piezoelectric layer (23). Also, the groove may have a shape in which the width narrows as it goes downward towards the piezoelectric layer (23).

[0082] The depth of the groove may be greater than half the thickness of the piezoelectric layer (23). The depth of the groove may be equal to the thickness of the piezoelectric layer (23) as shown in FIG. 4, or it may be greater than the thickness of the piezoelectric layer (23) so that the groove extends to the intermediate layer (22). Alternatively, the depth of the groove may be smaller than the thickness of the piezoelectric layer (23) so that the groove is formed only up to a part of the piezoelectric layer (23).

[0083] All protruding reflectors (27) constituting a plurality of reflector units (25, 26) are each connected to a reflector busbar (25a), and the embedded reflectors can be extended to the lower part of the reflector busbar (25a), and the embedded reflectors extended to the lower part of the reflector busbar (25a) can be referred to as the busbar lower embedded reflectors (29a). The busbar lower embedded reflectors (29a) can be filled with the same material as the reflector busbar (25a).

[0084] The filling material of the reflector busbar (25a) and the busbar lower embedded reflector (29a) may be a suitable metal or alloy such as copper (Cu), nickel (Ni), nickel-chromium (Ni-Cr) alloy, aluminum-copper (Al-Cu) alloy, titanium (Ti), aluminum (Al), platinum (Pt).

[0085] Accordingly, looking at the AA cross-section of FIG. 3, the embedded reflector (29) is a groove formed in the piezoelectric layer (23), but looking at the BB cross-section of FIG. 4, the reflector bus bar (25a) extends along the acoustic wave propagation direction on both sides of the electrode bus bar (24a), and the protruding reflector is connected to the reflector bus bar (25a), and the bus bar lower embedded reflector (29a) is also extended and formed below the reflector bus bar (25a), and the bus bar lower embedded reflector (29a) can be filled with reflector material.

[0086] These reflector units are formed such that protruding reflectors (27) and embedded reflectors (29) are formed alternately, thereby reducing the number of protruding reflectors (27) formed of metal layers.

[0087] FIG. 6 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of FIG. 3. The horizontal axis (X-axis) of the graph represents the frequency (unit: MHz), and the vertical axis (Y-axis) represents the magnitude of the admittance (unit: dB). This measurement was performed on a surface acoustic wave device configured to include three reflector units on each side of the IDT electrode (24).

[0088] Referring to the graph, the resonance point occurs at a frequency of approximately 1590 MHz with a magnitude of 13.2750 dB, and the anti-resonance point occurs at a frequency of approximately 1678 MHz with a magnitude of -77.0804 dB. Accordingly, the resonance / anti-resonance ratio (Y-ratio) of the surface acoustic wave device according to the first embodiment of the present invention illustrated in FIGS. 3 to 5 is calculated to be approximately 90.36 dB.

[0089] The resonance-to-anti-resonance ratio (Y-ratio) refers to the difference between the maximum (dB) admittance peak at the resonance point and the minimum (dB) admittance peak at the anti-resonance point, and is closely related to the electro-acoustic conversion efficiency and reflection intensity of surface acoustic devices. Since the Y-ratio significantly affects filter performance, particularly bandwidth, insertion loss, stopband rejection rate, and in-band ripple, it is a very important parameter for evaluating the characteristics of surface acoustic devices.

[0090] According to the present invention, by alternately arranging a protruding reflector (27) and a buried reflector (29), the protruding reflector (27) reflects acoustic wave components propagating to the surface of the piezoelectric layer (23), and the buried reflector (29) reflects acoustic wave components propagating into the interior of the piezoelectric layer (23). Since three-dimensional reflection occurs simultaneously on the surface and inside of the piezoelectric layer (23), energy leakage outside the reflector area is fundamentally blocked, thereby minimizing loss and maximizing energy confinement efficiency. As a result, the present invention can realize a high-performance surface acoustic wave device having a high Y-ratio of 90 dB or more.

[0091] [2nd Example]

[0092] FIG. 7 is a plan view of a surface acoustic wave device according to a second embodiment of the present invention, and FIG. 8 is a cross-sectional view along line AA of the surface acoustic wave device of FIG. 7.

[0093] A surface acoustic wave device according to a second embodiment of the present invention is described with reference to FIGS. 7 and 8. The surface acoustic wave device according to the second embodiment of the present invention includes a support substrate (71), a piezoelectric layer (73) located on the support substrate (71), an intermediate layer (72) provided between the support substrate (71) and the piezoelectric layer (73), an IDT electrode (74) deposited on the piezoelectric layer (73), and a plurality of reflector units (75, 76) that are periodically and repeatedly formed along the acoustic wave propagation direction on both outer sides of the acoustic wave propagation direction of the IDT electrode (74).

[0094] The reflector unit (75, 76) can prevent acoustic waves from leaking out by reflecting acoustic waves that propagate in a direction different from the direction of acoustic wave propagation and trapping them inside the IDT electrode (74).

[0095] Each reflector unit (75, 76) consists of a protruding reflector (77) formed by extending in a direction orthogonal to the direction of acoustic wave propagation on the piezoelectric layer (73), and a buried reflector (78) formed in a vertical line with the protruding reflector (77) and filled with the same material as the protruding reflector (77).

[0096] A surface acoustic wave device according to the second embodiment of the present invention can form a groove by etching a piezoelectric layer (73) according to the pattern of a protruding reflector (77), and form a buried reflector (78) by filling the groove with reflector material, and can form a protruding reflector (77) on the buried reflector (78).

[0097] The depth of the groove forming the embedded reflector (78) may be greater than half the thickness of the piezoelectric layer (73). For example, the depth of the groove forming the embedded reflector (78) may be equal to the thickness of the piezoelectric layer (73) as shown in FIG. 8. The depth of the groove may be greater than the thickness of the piezoelectric layer (73) so that the groove extends to a part of the intermediate layer (72), or it may be smaller than the thickness of the piezoelectric layer (73) so that the groove is formed only to a part of the piezoelectric layer (73).

[0098] The reflector material may be a suitable metal or alloy such as copper (Cu), nickel (Ni), nickel-chromium (Ni-Cr) alloy, aluminum-copper (Al-Cu) alloy, titanium (Ti), aluminum (Al), platinum (Pt).

[0099] According to this second embodiment, since the buried reflector (78) and the protruding reflector (77) are located on the same vertical line, both the buried reflector (78) and the protruding reflector (77) can be formed as a fine pattern, so the process can be simplified.

[0100] FIG. 9 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of FIG. 7. The horizontal axis (X-axis) of the graph represents the frequency (unit: MHz), and the vertical axis (Y-axis) represents the magnitude of the admittance (unit: dB). This measurement was performed on a surface acoustic wave device configured to include three reflector units on each side of the IDT electrode (74).

[0101] Referring to the graph, the resonance point occurs at a frequency of approximately 1590 MHz with a magnitude of 12.2378 dB, and the anti-resonance point occurs at a frequency of approximately 1675 MHz with a magnitude of -78.5744 dB. Accordingly, the resonance / anti-resonance ratio (Y-ratio) of the surface acoustic wave device according to the second embodiment of the present invention illustrated in FIGS. 7 and 8 is calculated to be approximately 90.8117 dB.

[0102] According to the present invention, by arranging a protruding reflector (77) and a buried reflector (78) in a straight line, the protruding reflector (77) reflects acoustic wave components propagating to the surface of the piezoelectric layer (73), and the buried reflector (78) reflects acoustic wave components propagating into the interior of the piezoelectric layer (73). Since three-dimensional reflection occurs simultaneously on the surface and inside of the piezoelectric layer (73), energy leakage outside the reflector area is fundamentally blocked, thereby minimizing loss and maximizing energy confinement efficiency. As a result, the present invention can realize a high-performance surface acoustic wave device having a high Y-ratio of 90 dB or more.

[0103] [3rd Example]

[0104] FIG. 10 is a plan view of a surface acoustic wave device according to a third embodiment of the present invention, and FIG. 11 is a cross-sectional view along line AA of the surface acoustic wave device of FIG. 10.

[0105] A surface acoustic wave device according to a third embodiment of the present invention is described with reference to FIGS. 10 and 11. The surface acoustic wave device according to the third embodiment of the present invention includes a support substrate (101), a piezoelectric layer (103) located on the support substrate (101), an intermediate layer (102) provided between the support substrate (101) and the piezoelectric layer (103), an IDT electrode (104) deposited on the piezoelectric layer (103), and a plurality of reflector units (105, 106) that are periodically and repeatedly formed along the acoustic wave propagation direction on both outer sides of the acoustic wave propagation direction of the IDT electrode (104).

[0106] The reflector unit (105, 106) can suppress the leakage of acoustic waves to the outside by reflecting acoustic waves propagating in a direction different from the direction of acoustic wave propagation and trapping them inside the IDT electrode (104).

[0107] Each reflector unit (105, 106) is composed of a protruding reflector (107) and a buried reflector (108) that is positioned adjacent to the protruding reflector (107) and filled with the same material as the protruding reflector (107), and the protruding reflector (107) extends to the top of the buried reflector (108) so that the protruding reflector (107) and the buried reflector (108) are connected by the same material.

[0108] That is, in the first embodiment, there is an exposed piezoelectric layer area between the protruding reflector and the buried reflector, whereas in the third embodiment, there is no exposed piezoelectric layer area between the protruding reflector and the buried reflector, and the protruding reflector extends to the top of the buried reflector to form a reflector in an L-shape.

[0109] FIG. 12 is a graph showing the frequency-admittance characteristics of the surface acoustic wave device of FIG. 10. The horizontal axis (X-axis) of the graph represents the frequency (unit: MHz), and the vertical axis (Y-axis) represents the magnitude of the admittance (unit: dB). This measurement was performed on a surface acoustic wave device configured to include three reflector units on each side of the IDT electrode (104).

[0110] Referring to the graph, the resonance point occurs at a frequency of approximately 1590 MHz with a magnitude of 13.9289 dB, and the anti-resonance point occurs at a frequency of approximately 1675 MHz with a magnitude of -77.1345 dB. Accordingly, the resonance / anti-resonance ratio (Y-ratio) of the surface acoustic wave device according to the third embodiment of the present invention illustrated in FIGS. 10 and 11 is calculated to be approximately 91.06 dB.

[0111] The surface acoustic wave device of the third embodiment was measured to have the highest admittance magnitude at the resonance point at 13.9289 dB. A high admittance at the resonance point means that the impedance is low at the corresponding frequency, that is, the impedance is low at the resonance frequency. Therefore, it can be seen that the insertion loss in the filter's passband is reduced.

[0112] FIG. 13 is a graph showing a comparison of the resonance / anti-resonance ratio (Y-ratio) of a surface acoustic wave device according to the prior art and the first to third embodiments of the present invention.

[0113] In the case of conventional technology, the structure consists only of protruding reflectors on the upper part of the piezoelectric layer, and the Y-ratio remains at approximately 78.74 dB. This is analyzed to be due to energy leakage occurring because the protruding reflectors fail to reflect acoustic waves that have penetrated into the piezoelectric layer.

[0114] On the other hand, the first to third embodiments of the present invention adopt a composite reflector structure in which a protruding reflector and a buried reflector are combined, thereby exhibiting a high Y-ratio of 90 dB or higher. This is interpreted as a result of minimizing energy leakage by effectively reflecting not only acoustic waves propagating along the surface of the piezoelectric layer but also acoustic waves transmitted into the piezoelectric layer.

[0115] In summary, the Y-ratio of the surface acoustic wave device according to the present invention is improved by about 15% compared to the prior art, which reduces energy leakage and thus reduces insertion loss, and at the same time allows the same performance to be implemented in a smaller structure, which is advantageous for miniaturization of the device.

[0116] That is, according to the present invention, since the energy confinement efficiency is dramatically improved by reflecting both the surface of the piezoelectric plate and the acoustic waves inside, the reflectivity per unit is increased, and accordingly, sufficient reflection performance can be obtained even with fewer reflector units than in the prior art, making it possible to achieve a miniaturized design that reduces the chip size.

[0117] The foregoing description is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented by dividing it into multiple elements, and likewise, components described as multiple elements may also be implemented as a single unit.

[0118] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. A surface acoustic wave device comprising a piezoelectric layer and an IDT electrode formed on the piezoelectric layer, It includes a plurality of reflector units that are periodically and repeatedly formed along the acoustic wave propagation direction on the outer side of the acoustic wave propagation direction of the IDT electrode, and The above reflector unit includes a protruding reflector formed on the piezoelectric layer extending in a direction orthogonal to the direction of acoustic wave propagation and a buried reflector formed embedded in the piezoelectric layer parallel to the protruding reflector in a direction orthogonal to the direction of acoustic wave propagation. Surface acoustic wave device.

2. In Paragraph 1, The width of the above reflector unit is λ, Surface acoustic wave device.

3. In Paragraph 1, The above-mentioned embedded reflector is a groove formed inside the piezoelectric layer, Surface acoustic wave device.

4. In Paragraph 3, The above groove is formed without a step in the downward direction of the piezoelectric layer, Surface acoustic wave device.

5. In Paragraph 3, The above groove has a shape in which the width narrows as it moves toward the lower side of the piezoelectric layer. Surface acoustic wave device.

6. In Paragraph 3, The depth of the groove is greater than half the thickness of the piezoelectric layer, Surface acoustic wave device.

7. In Paragraph 6, The depth of the above groove is the same as the thickness of the above piezoelectric layer, Surface acoustic wave device.

8. In Paragraph 1, The reflector unit adjacent to the IDT electrode at the starting point of the acoustic wave propagation direction and the reflector unit adjacent to the IDT electrode at the ending point of the acoustic wave propagation direction are arranged symmetrically with respect to the IDT electrode. Surface acoustic wave device.

9. In Paragraph 1, The above reflector unit is composed of the protruding reflector, a first piezoelectric layer exposed area adjacent to the protruding reflector, the buried reflector adjacent to the first piezoelectric layer exposed area, and a second piezoelectric layer exposed area adjacent to the buried reflector. The widths of the above protruding reflector and the first piezoelectric layer exposed area, the above buried reflector and the second piezoelectric layer exposed area are each λ / 4, Surface acoustic wave device.

10. In Paragraph 9, All protruding reflectors constituting the above plurality of reflector units are connected to the reflector busbar, and The above-mentioned embedded reflector extends to the above-mentioned reflector busbar, and The embedded reflector formed on the lower side of the above reflector busbar is filled with the same material as the above reflector busbar, Surface acoustic wave device.

11. In Paragraph 1, The protruding reflector and the embedded reflector constituting the above reflector unit are formed on the same line in the vertical direction, and The above-mentioned buried reflector is filled with the same material as the above-mentioned protruding reflector, Surface acoustic wave device.

12. In Paragraph 1, The above reflector unit includes the protruding reflector, the buried reflector adjacent to the protruding reflector, and a piezoelectric layer exposed area adjacent to the buried reflector. Surface acoustic wave device.

13. In Paragraph 12, The above-mentioned buried reflector is filled with the same material as the above-mentioned protruding reflector, and The above protruding reflector extends to the upper part of the above-mentioned recessed reflector, and the protruding reflector and the above-mentioned recessed reflector are connected by the same material, so that the protruding reflector and the above-mentioned recessed reflector form an L-shaped reflector. Surface acoustic wave device.

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