Surface acoustic wave device and method for manufacturing same

Abstract

The present invention relates to: a surface acoustic wave device configured such that IDT electrodes are embedded in a piezoelectric layer and a low-acoustic velocity film layer; and a method for manufacturing same. A surface acoustic wave device according to an embodiment of the present invention comprises: a low-acoustic velocity film layer; a piezoelectric layer formed on the low-acoustic velocity film layer; IDT grooves formed to pass through the piezoelectric layer and the boundary between the piezoelectric layer and the low-acoustic velocity film layer and partially extend by a depth into the low-acoustic velocity film layer; and IDT electrodes formed in the IDT grooves and embedded in the piezoelectric layer and the low-acoustic velocity film layer.

Description

Surface acoustic wave device and method of manufacturing the same

[0001] The present invention relates to a surface acoustic wave device and a method for manufacturing the same, and more specifically, to a surface acoustic wave device configured such that an IDT electrode is embedded in a piezoelectric layer and a low-sonic film layer, and a method for manufacturing the same.

[0002] The present invention is based on the research results of the “Development of High Power Endurance SAW Materials and Devices for 5G Mobile Communications” research project (Executing Organization: SONIX Co., Ltd., Research Period: October 1, 2024 to September 30, 2028), which was carried out with support from the Small and Medium Enterprise Technology Innovation Development Project (Project Unique Number: 2420006593, Project Number: 00508969) organized by the Ministry of SMEs and Startups of the Republic of Korea and managed by the Korea Technology Information Promotion Agency for SMEs.

[0003] Generally, Surface Acoustic Wave (SAW) devices are components that utilize the principle of converting electrical signals into mechanical waves by forming a metal electrode pattern on a piezoelectric substrate. Due to their high-speed operation and low power consumption characteristics, they are applied in various fields such as communication systems, sensors, filters, and signal processing. Surface acoustic wave devices are also referred to as surface elastic wave devices because they propagate along the surface of the piezoelectric substrate.

[0004] Figure 1 is a diagram illustrating a conventional surface acoustic wave device.

[0005] A conventional surface acoustic wave device comprises a support substrate (11), a high-sounding film layer (12) stacked on the support substrate (11), a low-sounding film layer (13) stacked on the high-sounding film layer (12), a piezoelectric layer (14) stacked on the low-sounding film layer (13), and an IDT (Inter Digital Transducer) electrode (15) and a reflector (16) deposited protrudingly on the piezoelectric layer (14).

[0006] The IDT electrode (15) is located at the center of the surface acoustic wave device and is arranged in an interlocking manner with a comb-like electrode pattern made of thin metal. The IDT electrode (15) includes a plurality of electrode fingers, and the thickness and spacing of the electrode fingers can be set to match the frequency of the acoustic wave being propagated. When an electric signal is applied to the input side of the IDT electrode (15), a piezo effect occurs due to the electric field between the electrodes, generating an acoustic wave, and this acoustic wave propagates along the surface of the piezoelectric layer (14), and the acoustic wave propagated to the output side of the IDT electrode (15) is converted into an electric signal and output.

[0007] The reflector (16) is positioned on the piezoelectric layer (14) at both ends of the IDT electrode (15) and is placed within a distance where acoustic waves generated from the IDT electrode (15) can reach, and serves to reflect surface acoustic waves to the IDT electrode (15) to trap energy inside the IDT electrode (15) so that it does not leak out.

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

[0009] Meanwhile, the surface acoustic wave device may cover the IDT electrode (15) and the reflector (16) formed on the piezoelectric layer (14) with a dielectric film to improve temperature characteristics. The dielectric film may be made of a material having a temperature coefficient of frequency (TCF) opposite to the sign of the temperature coefficient of frequency (TCF) of the piezoelectric layer (140). For example, if the piezoelectric layer (140) has a negative TCF, the dielectric film may be made of a silicon oxide film having a positive TCF.

[0010] As shown in FIG. 1, in a conventional surface acoustic wave device, an IDT electrode (15) and a reflector (16) are formed to protrude above the surface of a piezoelectric layer (14). In this structure, when a dielectric film (e.g., a silicon oxide film) is deposited to cover the IDT electrode (15) and the reflector (16), irregularities occur on the upper surface of the dielectric film due to the step difference between the area where the IDT electrode (15) is formed and the area where it is not formed.

[0011] Such irregularities scatter surface acoustic waves, contributing to increased insertion loss. Furthermore, since the size of irregularities in the dielectric film increases with the thickness of the IDT electrode, structural constraints arise when increasing the thickness of the IDT electrode.

[0012] Meanwhile, due to the recent advancement of communication environments such as 5G, there is a demand for excellent power withstand characteristics capable of withstanding high-frequency bands and high-output signals. Generally, the resonance frequency of a surface acoustic wave device is determined by dividing the speed of the acoustic wave by the period (wavelength) of the electrode; therefore, to realize a high-frequency band of 2.0 GHz or higher, the wavelength must be made shorter. This inevitably requires a design that miniaturizes the linewidth and spacing of the IDT electrodes and reflectors.

[0013] However, as the electrode linewidth is miniaturized, resistance increases due to the reduction in cross-sectional area, and vulnerability to thermal and mechanical stress increases. Consequently, electrode miniaturization aimed at securing high-frequency bands can lead to a degradation of high-power withstand characteristics, and a trade-off arises between high-frequency characteristics and withstand characteristics, making it difficult to satisfy both simultaneously.

[0014] The present invention aims to provide a surface acoustic wave device capable of securing high-frequency characteristics by embedding IDT electrodes inside a piezoelectric layer and a low-sonic film layer, while simultaneously maintaining excellent power withstand characteristics even in a high-power environment.

[0015] Furthermore, the present invention aims to provide a surface acoustic wave device capable of improving acoustic velocity and electromechanical coupling coefficients and realizing excellent resonance characteristics by embedding an IDT electrode within a piezoelectric layer and a low-sonic film layer, and securing an optimal embedding depth ratio relative to the thickness of the low-sonic film layer.

[0016] Furthermore, the present invention aims to provide a surface acoustic wave device capable of reducing insertion loss degradation caused by surface irregularities by embedding an IDT electrode within a piezoelectric layer and a low-sonic film layer to uniformly form the surfaces of the IDT electrode and the piezoelectric layer, thereby flattening the upper surface of a dielectric film formed thereon.

[0017] In addition, the present invention aims to provide a surface acoustic wave device having excellent temperature stability by depositing a dielectric film having a frequency temperature coefficient with a sign opposite to that of the piezoelectric layer on the piezoelectric layer to compensate the total frequency temperature coefficient to be close to zero.

[0018] In addition, the present invention aims to provide a method for manufacturing a surface acoustic wave device that precisely forms a fine etching groove extending to a low-sonic film layer by penetrating the piezoelectric layer without damaging the photoresist by applying a composite material mask composed of a metal mask and a photoresist mask.

[0019] A surface acoustic wave device according to an embodiment of the present invention for achieving the above-mentioned purpose comprises a low-sonic film layer, a piezoelectric layer formed on the low-sonic film layer, an IDT groove formed by penetrating the piezoelectric layer and extending to a certain depth into the low-sonic film layer through the boundary surface between the piezoelectric layer and the low-sonic film layer, and an IDT electrode formed in the IDT groove and embedded in the piezoelectric layer and the low-sonic film layer.

[0020] The ratio of the total thickness of the low-sonic film layer to the burial depth of the IDT electrode is 30 to 100%.

[0021] The ratio of the total thickness of the low-sonic film layer to the burial depth of the IDT electrode is 80~100%.

[0022] The IDT electrode is made of one of aluminum, copper, tungsten, or an alloy thereof.

[0023] The piezoelectric layer is lithium tantalate or lithium niobate.

[0024] The IDT electrodes are positioned at a certain angle relative to the direction of acoustic wave propagation.

[0025] It further includes an embedded reflector that is embedded inside the piezoelectric layer on the outer side of the IDT electrode and is formed symmetrically around the IDT electrode.

[0026] The buried reflector is formed by extending into the low-sonic film layer.

[0027] It further includes a dielectric film layer coated on the piezoelectric layer and the IDT electrode, having a frequency temperature coefficient of opposite sign to that of the piezoelectric layer.

[0028] A method for manufacturing a surface acoustic wave device according to an embodiment of the present invention comprises: a first step of preparing a composite piezoelectric substrate configured by stacking a low-sonic film layer and a piezoelectric layer; a second step of forming a metal layer on the composite piezoelectric substrate; a third step of coating a photoresist on the metal layer; a fourth step of creating a photoresist mask by exposing and developing the photoresist along an IDT pattern; a fifth step of creating a composite material mask by etching the metal layer based on the photoresist mask to create a metal mask; a sixth step of creating an IDT groove by etching the entire piezoelectric layer and a portion of the low-sonic film layer to a depth using the composite material mask; and a seventh step of removing the composite material mask and filling the IDT groove with an IDT electrode material to form an IDT electrode.

[0029] The ratio of the total thickness of the low-sonic film layer to the burial depth of the IDT electrode is 30 to 100%.

[0030] The ratio of the total thickness of the low-sonic film layer to the burial depth of the IDT electrode is 80~100%.

[0031] The metal layer uses at least one material among Al, Cr, and Ni.

[0032] The IDT electrode material is made of one of aluminum, copper, tungsten, or an alloy thereof.

[0033] The IDT electrodes are positioned at a certain angle relative to the direction of acoustic wave propagation.

[0034] The composite material mask further includes an embedded reflector pattern symmetrically outward from the IDT electrode with the IDT electrode as the center, and step 6 further includes the step of forming an embedded reflector using the composite material mask.

[0035] After Step 7, the method further includes the step of forming a dielectric film layer having a frequency temperature coefficient of opposite sign to that of the piezoelectric layer on the piezoelectric layer and the IDT electrode.

[0036] According to the present invention, by embedding the IDT electrode within the piezoelectric layer and the low-sonic film layer, an embedded structure can be realized in which the electrode does not protrude above the surface of the piezoelectric layer. Accordingly, the step difference and surface irregularities that occurred during the process of the dielectric film covering the electrode are effectively eliminated, thereby suppressing the increase in insertion loss and improving the electrical characteristics of the device.

[0037] In addition, according to the present invention, by securing an optimal burial depth ratio relative to the thickness of the low-sonic film layer, the acoustic velocity can be increased and the electromechanical coupling coefficient improved, thereby securing more stable resonance characteristics and obtaining excellent frequency response characteristics even in the high-frequency band of 2 GHz or higher.

[0038] In addition, according to the present invention, since the IDT electrode is embedded within the piezoelectric layer and the low-sonic film layer and is protected from thermal and mechanical stress, the risk of electrode failure is significantly reduced, and even if the line width of the electrode is miniaturized, the effective thickness of the electrode is secured, thereby preventing thermal failure and degradation of characteristics of the electrode, which can greatly improve the power withstand characteristics.

[0039] In addition, the present invention applies a dielectric film having a frequency temperature coefficient with the opposite sign to the piezoelectric layer, thereby compensating the effective frequency temperature coefficient to be close to zero, which minimizes the resonance frequency deviation due to temperature changes and ensures high temperature stability.

[0040] Finally, by using a composite material mask including a metal mask, fine etching grooves that penetrate the piezoelectric layer and extend to the low-sonic film layer can be precisely formed without damaging the photoresist.

[0041] 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.

[0042] Figure 1 is a diagram showing the configuration of a typical surface acoustic wave device.

[0043] FIG. 2 is a side cross-sectional view of a surface acoustic wave device according to a first embodiment of the present invention.

[0044] Figure 3 is a graph comparing the frequency-admittance characteristics of different IDT electrode materials of a surface acoustic wave device according to the first embodiment of the present invention.

[0045] FIG. 4 is a side cross-sectional view of a surface acoustic wave device according to a second embodiment of the present invention.

[0046] Figure 5 is a graph comparing the frequency-admittance characteristics of IDT electrode materials of a surface acoustic wave device according to a second embodiment of the present invention.

[0047] FIG. 6 is a side cross-sectional view of a surface acoustic wave device according to a third embodiment of the present invention.

[0048] FIG. 7 is a graph comparing the frequency-admittance characteristics of IDT electrode materials of a surface acoustic wave device according to the third embodiment of the present invention.

[0049] FIG. 8 is a side cross-sectional view of a surface acoustic wave device according to the first comparative example.

[0050] FIG. 9 is a side cross-sectional view of a surface acoustic wave device according to the second comparative example.

[0051] FIGS. 10 and FIGS. 11 are drawings illustrating the manufacturing process of a surface acoustic wave device according to the present invention.

[0052] [Explanation of the symbol]

[0053] 21: Support substrate 22: High-frequency film layer

[0054] 23: Low-sonic film layer 24: Piezoelectric layer

[0055] 25: IDT electrode 26: Embedded reflector

[0056] 27: Silicon oxide film layer

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] [Surface Acoustic Wave Device]

[0062] FIG. 2 is a side cross-sectional view of a surface acoustic wave device according to a first embodiment of the present invention.

[0063] A surface acoustic wave device according to a first embodiment of the present invention comprises a support substrate (21), a high-sounding film layer (22) disposed on the support substrate (21), a low-sounding film layer (23) disposed on the high-sounding film layer (22), a piezoelectric layer (24) disposed on the low-sounding film layer (23), an IDT groove formed by penetrating the piezoelectric layer (24) and extending to a certain depth into the low-sounding film layer (23) through the boundary surface between the piezoelectric layer (24) and the low-sounding film layer (23), and an IDT electrode (25) filled in the IDT groove and embedded in the piezoelectric layer (24) and the low-sounding film layer (23).

[0064] The surface acoustic wave device of the present invention may further include a buried reflector (26) that is embedded inside the piezoelectric layer (24) outside the IDT electrode (25) and formed symmetrically around the IDT electrode (25). The buried reflector (26) may be a groove, and the buried reflector (26) may be formed extending from the piezoelectric layer (24) to the low-sonic film layer (23). This buried reflector (26) can function to suppress the leakage of acoustic waves to the outside by reflecting acoustic waves propagating in a direction different from the acoustic wave propagation direction and trapping them inside the IDT electrode.

[0065] The surface acoustic wave device according to the present invention may further include a silicon oxide film layer (27) deposited to cover the piezoelectric layer (24), IDT electrode (25), and reflector (26) to improve temperature characteristics.

[0066] The support substrate (21) may be a silicon (Si) support substrate. Additionally, the support substrate (21) may be used as other substrates having a high acoustic wave propagation speed of 4500 m / s or more, such as a quartz substrate, a glass substrate, diamond, sapphire, silicon carbide (SiC), silicon nitride (Si3N4), or aluminum nitride (AlN). It is preferable that the thickness of the support substrate (21) be thicker than the thickness of the piezoelectric layer (24). The acoustic impedance of the support substrate (21) is approximately the same as the acoustic impedance of the piezoelectric layer (24), preferably within a plus / minus 25% range, and more preferably within a plus / minus 15% range.

[0067] The high-sonic film layer (22) is a thin film layer of a material in which the bulk wave sound speed propagating through the piezoelectric layer (24) is faster than the sound speed of the acoustic wave propagating through the piezoelectric layer (24). The material of the high-sonic film layer (22) may be any one of the following: a piezoelectric material such as polysilicon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, or quartz; various ceramics such as alumina, zirconia, cordierite, mullite, stearite, or forsterite; magnesia diamond; 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.

[0068] The low-sonic film layer (23) is a thin film layer of a material in which the bulk wave sound speed propagating through the piezoelectric layer (24) is lower than the sound speed of the acoustic wave propagating through the piezoelectric layer (24). The material of the low-sonic film layer (23) may be silicon oxide, glass, silicon oxynitride, tantalum oxide, a compound of silicon oxide with added fluorine, carbon, or boron, or any one of the materials having each of the above materials as a main component. Since the IDT electrode (25) is embedded in a part of the low-sonic film layer (23), the thickness of the low-sonic film layer (23) can be formed to be less than 0.2λ.

[0069] The piezoelectric layer (24) may be composed of lithium tantalate (LiTaO3), or other piezoelectric single crystals or piezoelectric ceramics such as lithium niobate (LiNbO3). The piezoelectric layer (24) may be attached to the low-sonic film layer (23) by direct bonding, for example, using SmartCut™ layer transfer technology.

[0070] The IDT electrodes (25) are arranged in pairs facing each other and include a plurality of electrode fingers, which extend from the electrode busbar and are configured to interlock with each other. The IDT electrodes (25) may be suitable metals or alloys such as aluminum (Al), copper (Cu), nickel (Ni), nickel-chromium (Ni-Cr) alloy, aluminum-copper (Al-Cu) alloy, titanium (Ti), tungsten (W), platinum (Pt), etc., which have an acoustic impedance lower than the impedance of the piezoelectric layer (24). Generally, it is suitable to use lighter electrode materials for the IDT electrodes, starting with chromium, which are lighter than manganese.

[0071] The IDT electrodes (25) can be provided on the same plane. These IDT electrodes (25) can be formed in an IDT groove that penetrates the piezoelectric layer (24), passes the boundary between the piezoelectric layer (24) and the low-sonic film layer (23), and extends to a certain depth into the interior of the low-sonic film layer (23). That is, the IDT electrodes (25) can be formed by being embedded in a portion of the piezoelectric layer (24) and the low-sonic film layer (23), and the IDT electrodes (25) can be formed with a thickness of 0.2 to 0.7λ.

[0072] When the IDT electrode (25) is embedded in the piezoelectric layer (24) and the low-sonic film layer (23) in this way, the surface of the IDT electrode (25) and the surface of the piezoelectric layer (24) form the same plane, and no irregularities are formed on the silicon oxide film layer (27) formed on the upper part of the IDT electrode (25) and the piezoelectric layer (24). The IDT electrode (25) can be positioned at a certain angle of inclination with respect to the direction of acoustic wave propagation.

[0073] In FIG. 2, the total height (thickness) of the low-sonic film layer (23) is 'A', and the depth at which the IDT electrode (25) is embedded within the low-sonic film layer (23), i.e., the electrode embedding depth, may be 'a1'. The electrode embedding ratio may be defined as the ratio (a1 / A) of the total thickness (A) of the low-sonic film layer (23) and the electrode embedding depth (a1). The electrode embedding ratio may be 30 to 100%. More preferably, the electrode embedding ratio may be 80 to 100%.

[0074] In the first embodiment of FIG. 2, the thickness of the piezoelectric layer (24) may be 600 nm, the total thickness (A) of the low-sonic film layer (23) may be 500 nm, and the etching depth of the IDT electrode may be 800 nm. That is, the depth (a1) in which the IDT electrode (24) is embedded into the interior of the low-sonic film layer (23) is 200 nm, and thus the ratio of the electrode embedding depth (a1) to the total thickness (A) of the low-sonic film layer may be 40%.

[0075] In other words, in the first embodiment illustrated in FIG. 2, the depth to which the IDT electrode (25) penetrates the piezoelectric layer (24) and is embedded into the low-sonic film layer (23) is a depth corresponding to approximately 40% of the total thickness of the low-sonic film layer (23). That is, it refers to a structure in which the lower end of the IDT electrode (25) that has penetrated the piezoelectric layer (24) is embedded up to a position of approximately 40% of the thickness of the low-sonic film layer (23).

[0076] Figure 3 is a graph comparing the frequency-admittance characteristics of different IDT electrode materials of a surface acoustic wave device according to the first embodiment of the present invention.

[0077] The horizontal axis (X-axis) of the graph represents the frequency (unit: GHz), and the vertical axis (Y-axis) represents the admittance (unit: dB). This graph shows the results of changing the electrode material while keeping the period of the IDT electrode fixed at 4.0 μm.

[0078] Referring to Figure 3, it can be seen that the resonance frequency and the resonance / anti-resonance ratio (Y-ratio) change depending on the physical properties (density and elastic modulus) of the electrode material.

[0079] When the electrode material is aluminum (Al), the resonant frequency is located in the 2.4–2.5 GHz band, and the resonance-to-valley ratio (Y-ratio), which is the difference between the peak and valley points, is the highest at 94.84 dB. This indicates that the low electrode resistance and high energy confinement efficiency provide the best insertion loss characteristics and steepness when designing filters. When the electrode material is copper (Cu), the resonant frequency is lowest at approximately the 2.2 GHz band, and the resonance-to-valley ratio (Y-ratio) is 69.37 dB. When the electrode material is tungsten (W), the resonant frequency is highest around the 2.7 GHz band, and the Y-ratio is the lowest at 52.68 dB.

[0080] Table 1 is a table summarizing the performance indicators by electrode material in the structure of the first embodiment (electrode embedding ratio 40%).

[0081] Fs[MHz]Fp[MHz]K eff 2 [%]Velocity(m / s)Bode-QY-ratio[dB]Al2412.222489.067.3996496415.1094.84C u2161.782227.007.0286479321.8069.37W2668.282697.812.67106733899.2052.68

[0082] In Table 1, the resonant frequency (Fs) is the series resonant frequency at which impedance is minimized, and the anti-resonant frequency (Fp) is the parallel anti-resonant frequency at which impedance is maximized. The resonant frequency is lowest for copper and highest for tungsten. This means that the resonant frequency shifts depending on the electrode material, even with the same electrode period. Therefore, it is advantageous to use copper as the electrode material in the low-frequency band and tungsten in the high-frequency band. Resonant frequency tuning is possible simply by changing the electrode material. Electromechanical coupling coefficient (K eff 2 ) represents the efficiency of converting electrical energy into mechanical vibration energy and is a key indicator for determining the bandwidth of a surface acoustic device. Aluminum has an efficiency of 7.39% and copper has 7.02%, enabling the implementation of a broadband filter, while tungsten has 2.67%, enabling the implementation of a narrowband filter. Therefore, design flexibility can be improved by selecting electrode materials according to the application (broadband communication or narrowband communication).

[0083] The velocity of surface acoustic waves (m / s) is an indicator that determines the resonance frequency. That is, at the same wavelength (λ), the velocity and the resonance frequency are proportional. When aluminum is applied as the IDT electrode, the velocity of the surface acoustic waves is 9,649 m / s, exhibiting the most typical and balanced velocity characteristics.

[0084] The quality factor (Bode-Q) is an indicator of how little energy loss there is. Based on aluminum, the Bode-Q is approximately 6415, indicating very high performance. In addition, the Y-ratio is the ratio of the signal magnitude at the resonant frequency to the signal magnitude at the anti-resonant frequency, and it can be confirmed that the Y-ratio of the aluminum electrode is 94.84 dB, which is a very high value.

[0085] FIG. 4 is a side cross-sectional view of a surface acoustic wave device according to a second embodiment of the present invention.

[0086] A surface acoustic wave device according to the second embodiment is configured such that, in a structure in which a support substrate (21), a high-sounding film layer (22), a low-sounding film layer (42), and a piezoelectric layer (24) are stacked, an IDT electrode (41) penetrates the piezoelectric layer (24) and is deeply embedded within the low-sounding film layer (42).

[0087] In the second embodiment, when the thickness of the piezoelectric layer (24) is 600 nm and the thickness (A) of the low-sonic film layer (42) is 500 nm, the etching depth of the IDT electrode is 1000 nm, and the depth (a2) in which the IDT electrode (41) is embedded into the low-sonic film layer (42) is 400 nm. Therefore, the ratio of the embedded depth (a2) to the total thickness (A) of the low-sonic film layer is 80%.

[0088] FIG. 5 is a graph comparing the frequency-admittance characteristics of IDT electrode materials of a surface acoustic wave device according to a second embodiment of the present invention. The horizontal axis (X-axis) of the graph represents the frequency (unit: GHz), and the vertical axis (Y-axis) represents the magnitude of admittance (unit: dB). This graph illustrates the results of changing the electrode material in the structure of the second embodiment (electrode embedding ratio 80%) while fixing the period of the IDT electrode at 4.0 μm.

[0089] The resonant frequency of the copper electrode is approximately 2.15 GHz, the resonant frequency of the aluminum electrode is approximately 2.41 GHz, and the resonant frequency of the tungsten electrode is approximately 2.65 GHz. The Y-ratio is 95.26 dB for aluminum, confirming that it has the best filter characteristics.

[0090] Table 2 is a table summarizing the performance indicators by electrode material in the structure of the second embodiment (electrode embedding ratio 80%).

[0091] Fs[MHz]Fp[MHz]K eff 2[%]Velocity(m / s)Bode-QY-ratio[dB]Al2413.392492.237.5796546219.2095.26C u2151.452217.257.1186069746.4068.83W2652.852681.182.58106112844.7064.01

[0092] Based on the aluminum (Al) electrode, the Y-ratio is the highest at 95.26 dB, and the electromechanical coupling coefficient (K eff 2 It can be confirmed that ) is a high value of 7.57%. By applying aluminum electrodes, a high-performance broadband filter can be implemented. Fig. 6 is a side cross-sectional view of a surface acoustic wave device according to the third embodiment of the present invention.

[0093] The surface acoustic wave device according to the second embodiment is a structure in which a support substrate (21), a high-sounding film layer (22), a low-sounding film layer (42), and a piezoelectric layer (24) are stacked, and an IDT electrode (61) penetrates both the piezoelectric layer (24) and the low-sounding film layer (62).

[0094] In the third embodiment, when the thickness of the piezoelectric layer (24) is 600 nm and the thickness (A) of the low-sonic film layer (62) is 500 nm, the etching depth of the IDT electrode is 1100 nm, so that the IDT electrode (61) penetrates both the piezoelectric layer (24) and the low-sonic film layer (62), and the depth (a3) ​​embedded inside the low-sonic film layer (62) is 500 nm, which is the same as the thickness of the low-sonic film layer (62). Therefore, the ratio of the depth (a3) ​​in which the electrode is embedded to the total thickness (A) of the low-sonic film layer is 100%.

[0095] FIG. 7 is a graph comparing the frequency-admittance characteristics of IDT electrode materials of a surface acoustic wave device according to the third embodiment of the present invention. The horizontal axis (X-axis) of the graph represents the frequency (unit: GHz), and the vertical axis (Y-axis) represents the magnitude of admittance (unit: dB). This graph illustrates the results of changing the electrode material in the structure of the third embodiment (electrode embedding ratio 100%) while fixing the period of the IDT electrode at 4.0 μm.

[0096] The resonant frequency of the copper electrode is approximately 2.18 GHz, the resonant frequency of the aluminum electrode is approximately 2.43 GHz, and the resonant frequency of the tungsten electrode is approximately 2.69 GHz. The Y-ratio is 95.55 dB for aluminum, confirming that it has the best filter characteristics.

[0097] Table 3 is a table summarizing the performance indicators by electrode material in the structure of the third embodiment (electrode embedding ratio 100%).

[0098] Fs[MHz]Fp[MHz]K eff 2 [%]Velocity(m / s)Bode-QY-ratio[dB]Al2431.482511.427.6197266357.9095.55C u2183.632248.646.9387359607.2075.79W2692.862725.942.96107716262.7046.40

[0099] Based on the aluminum (Al) electrode, the Y-ratio is the highest at 95.55 dB, and the electromechanical coupling coefficient (K eff 2 It can be confirmed that the value is high at 7.61%. By applying aluminum electrodes, a high-performance broadband filter can be implemented. Fig. 8 is a side cross-sectional view of a surface acoustic wave device according to the first comparative example.

[0100] The surface acoustic wave device according to the first comparative example is a structure in which a support substrate (21), a high-sonic film layer (22), a low-sonic film layer (82), and a piezoelectric layer (24) are stacked, and an IDT electrode (81) penetrates the piezoelectric layer (24). That is, the IDT electrode (81) is embedded only to the extent of the thickness of the piezoelectric layer (24), and its bottom surface is located at the boundary surface between the piezoelectric layer (24) and the low-sonic film layer (82). As a result, the IDT electrode (81) is a structure in which it does not extend into the low-sonic film layer (82) at all (electrode embedding ratio 0%).

[0101] FIG. 9 is a side cross-sectional view of a surface acoustic wave device according to the second comparative example.

[0102] A surface acoustic wave device according to the second comparative example is configured such that, in a structure in which a support substrate (21), a high-sounding film layer (93), a low-sounding film layer (92), and a piezoelectric layer (24) are stacked, an IDT electrode (91) penetrates the piezoelectric layer (24) and the low-sounding film layer (92) and extends to the high-sounding film layer (93).

[0103] Specifically, when the thickness of the piezoelectric layer (24) is 600 nm and the thickness (A) of the low-sonic film layer (92) is 500 nm, the etching depth of the IDT electrode is 1400 nm, and the IDT electrode (91) is configured to penetrate both the piezoelectric layer (24) and the low-sonic film layer (92) and extend into the high-sonic film layer (93).

[0104] Table 4 is the result of a comprehensive comparison of the performance indicators of surface acoustic wave devices according to the first to third embodiments and the first to second comparative examples. In this case, aluminum was used as the electrode material.

[0105] Fs[MHz]Fp[MHz]K eff 2 [%] Velocity(m / s) Y-ratio[dB] Example 1 241 2.22248 9.06 7.3996 499 4.84 Example 2 241 3.39249 2.237.5796 549 5.26 Example 3 243 1.4825 11.42 7.6 1972 695.55 Comparative Example 1 243 9.0925 11.66 6.93975 692.93 Comparative Example 2 242 4.2225 04.16 7.6396 979 0.10

[0106] The first comparative example (electrode embedding ratio 0%) is a structure in which the IDT electrode is embedded only in the piezoelectric layer and does not extend into the low-sonic film layer, and the electromechanical coupling coefficient (K eff 2 ) is the lowest at 6.93%. On the other hand, in the case of the first to third embodiments where the IDT electrode is embedded to a predetermined depth (40%~100%) in a low-sonic film layer, the electromechanical coupling coefficient (K eff 2The value was significantly improved to 7.39%–7.61%. This means that when the electrode is embedded within the low-sonic film layer, a wider bandwidth can be secured compared to the first comparative example. In addition, the Y-ratio of the first to third embodiments was 94.84–95.55 dB compared to the first comparative example (92.93 dB), confirming that the quality of resonance is superior. Comparing the first to third embodiments, as the electrode embedding ratio increases (40%, 80%, 100%), the electromechanical coupling coefficient (K eff 2 ) and Y-ratio gradually increase, showing maximum performance in the third embodiment (electrode embedding ratio 100%).

[0107] However, in the case of the second comparative example where the IDT electrode penetrates the low-sonic film layer and extends to the high-sonic film layer, the electromechanical coupling coefficient (K eff 2 ) is 7.63%, which is slightly higher than that of the first to third embodiments, but the Y-ratio dropped sharply to 90.10 dB. This means that if the IDT electrode is extended to the high-sonic film layer, the insertion loss may increase and the characteristics may deteriorate even if the bandwidth is maintained.

[0108] As described above, when an IDT electrode is formed by embedding the piezoelectric layer and the low-sonic film layer to a certain depth, harmonics can be utilized, making it usable in the high-frequency band; furthermore, the Y-ratio increases, improving the IL (inserting loss) characteristics and enabling the implementation of a SAW filter with a wider bandwidth.

[0109] In addition, forming the IDT electrode as an embedded structure can improve power handling characteristics. Frequency (f) is the value obtained by dividing the velocity (v) by the wavelength (λ).

[0110] In a typical IDT electrode protruding structure, if the IDT electrode period is designed to be 4.0 μm, the resonant frequency achieved is only in the band of approximately 0.9 to 1.0 GHz, and the power withstand capability of such a band filter is approximately 33 dBm. On the other hand, to achieve 2.3 to 2.5 GHz with an IDT electrode protruding structure, the IDT electrode period must be reduced to less than 4.0 μm, and as a result, the power withstand capability is reduced to 29 dBm.

[0111] On the other hand, when implementing the embedded structure of the first to third embodiments of the present invention, it can be confirmed that the resonant frequency shifts significantly upward to the approximately 2.3 to 2.5 GHz band even if the IDT electrode period is designed to be 4.0 μm. That is, since the wide and thick electrode pattern (4.0 μm period) used in the approximately 0.9 to 1.0 GHz band can be applied directly to the 2.5 GHz band filter, it can have a power withstand characteristic of approximately 33 dBm, which is equivalent to that of the 0.9 GHz band filter.

[0112] [Manufacturing Method]

[0113] FIGS. 10 and FIGS. 11 are drawings illustrating the manufacturing process of a surface acoustic wave device according to the present invention.

[0114] First, a composite piezoelectric substrate is prepared by stacking a support substrate (101), a high-sonic film layer (102), a low-sonic film layer (103), and a piezoelectric layer (104), as shown in FIG. 10 (a). The composite piezoelectric substrate may be a piezoelectric-on-insulator (POI) substrate.

[0115] Next, as shown in Fig. 10 (b), a metal layer (105) for forming a metal mask is deposited on the composite piezoelectric substrate. The metal layer (105) may be made of a metal material such as aluminum (Al), chromium (Cr), or nickel (Ni), and may be deposited using an evaporator deposition method that uses metal vapor, a sputtering deposition method that applies physical impact to the material, etc.

[0116] Next, as shown in (c) of FIG. 10, a photoresist (106) is coated on the metal layer (105).

[0117] Next, as illustrated in FIG. 11 (a), a photoresist (106) is exposed and developed along an IDT electrode pattern to create a photoresist mask (107). Here, the exposure equipment may use an I-LINE stepper using near UV or a KrF stepper using deep UV. The developer may use a developer containing 0.38% tetramethylammonium hydroxide (TMAH). Additionally, a metal layer (105) is etched based on the photoresist mask (107) to create a metal mask (108). Chlorine (Cl-based) gas may be used for the etching of the metal mask (108). Through this, a composite material mask consisting of the metal mask (108) and the photoresist mask (107) can be obtained.

[0118] Next, as shown in FIG. 11 (b), the entire piezoelectric layer (104) and a portion of the depth of the low-sonic film layer (103) are etched based on a composite material mask composed of a metal mask (108) and a photoresist mask (107) to create an IDT groove (109).

[0119] The reason for forming an IDT electrode using a composite material mask composed of a metal mask (108) and a photoresist mask (107) is explained. In order to form a fine pattern of the IDT electrode, a photoresist mask of 8,000 angstroms (Å) must be used. However, if the entire piezoelectric layer (104) and a portion of the low-sonic film layer (103) are etched using a photoresist mask of this thickness, the photoresist mask may be damaged during the etching process, and pattern etching may not be possible. In contrast, the present invention enables etching to a portion of the piezoelectric layer (104) and the low-sonic film layer (103) using a photoresist mask (107) and a metal mask (108). The IDT groove (109) may have a pyramid shape, a trapezoidal shape, a V-shape, a U-shape cross-section, and / or convex, concave, or scallop-shaped side walls and / or a bottom.

[0120] In the composite material mask, an embedded reflector pattern may be further formed symmetrically on the outer side of the IDT electrode, centered on the IDT electrode. In the process of etching the entire piezoelectric layer (104) and a portion of the depth of the low-sonic film layer (103) based on the composite material mask, an embedded reflector may be further generated.

[0121] Next, as shown in Fig. 11 (c), the photoresist mask and metal mask are removed using a wet etching method, and the IDT electrode material is filled into the IDT groove to form an IDT electrode (110).

[0122] After step (c) of FIG. 11, a dielectric layer having a frequency temperature coefficient opposite to that of the piezoelectric layer can be further deposited on the piezoelectric layer (104) and the IDT electrode (110). For example, a silicon oxide film layer having a positive frequency temperature coefficient can be further deposited to improve the temperature characteristics of the surface acoustic wave device.

[0123] 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.

[0124] 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. The low-sonic membrane layer and, A piezoelectric layer formed on the above-mentioned low-sonic film layer, An IDT groove formed by penetrating the piezoelectric layer and extending to a certain depth into the interior of the low-sonic film layer, passing through the interface between the piezoelectric layer and the low-sonic film layer, and Including an IDT electrode formed in the above IDT groove and embedded in the above piezoelectric layer and the above low-sonic film layer, Surface acoustic wave device.

2. In Paragraph 1, The ratio of the total thickness of the above-mentioned low-sonic film layer to the burial depth of the above-mentioned IDT electrode is 30 to 100%, Surface acoustic wave device.

3. In Paragraph 2, The ratio of the total thickness of the above-mentioned low-sonic film layer to the burial depth of the above-mentioned IDT electrode is 80~100%, Surface acoustic wave device.

4. In Paragraph 2, The above IDT electrode is made of one of aluminum, copper, tungsten, or an alloy thereof, Surface acoustic wave device.

5. In Paragraph 2, The above piezoelectric layer is lithium tantalate or lithium niobate, Surface acoustic wave device.

6. In Paragraph 2, The above IDT electrode is positioned at a certain angle with respect to the direction of acoustic wave propagation, Surface acoustic wave device.

7. In Paragraph 2, A further comprising an embedded reflector formed symmetrically around the IDT electrode and embedded within the piezoelectric layer on the outer side of the IDT electrode. Surface acoustic wave device.

8. In Paragraph 7, The above-mentioned embedded reflector is formed by extending into the above-mentioned low-sonic film layer, Surface acoustic wave device.

9. In Paragraph 2, A dielectric film layer further comprising a dielectric film layer coated on the piezoelectric layer and the IDT electrode and having a frequency temperature coefficient of opposite sign to that of the piezoelectric layer. Surface acoustic wave device.

10. A first step of preparing a composite piezoelectric substrate composed of a stacked low-sonic film layer and a piezoelectric layer, and A second step of forming a metal layer on the above composite piezoelectric plate, A third step of coating a photoresist on the metal layer above, A fourth step of creating a photoresist mask by exposing and developing the above photoresist along an IDT pattern, Step 5, forming a composite material mask by etching the metal layer based on the photoresist mask to create a metal mask, Step 6, creating an IDT groove by etching the entire piezoelectric layer and a portion of the low-sonic film layer to a depth using the composite material mask, and A seventh step comprising removing the composite material mask and filling the IDT groove with an IDT electrode material to form an IDT electrode. Method for manufacturing a surface acoustic wave device.

11. In Paragraph 10, The ratio of the total thickness of the above-mentioned low-sonic film layer to the burial depth of the above-mentioned IDT electrode is 30 to 100%, Method for manufacturing a surface acoustic wave device.

12. In Paragraph 11, The ratio of the total thickness of the above-mentioned low-sonic film layer to the burial depth of the above-mentioned IDT electrode is 80~100%, Method for manufacturing a surface acoustic wave device.

13. In Paragraph 11, The above metal layer uses at least one material among Al, Cr, and Ni, Method for manufacturing a surface acoustic wave device.

14. In Paragraph 11, The above IDT electrode material is composed of one of aluminum, copper, tungsten, or an alloy thereof, Method for manufacturing a surface acoustic wave device.

15. In Paragraph 11, The above IDT electrode is positioned at a certain angle with respect to the direction of acoustic wave propagation, Method for manufacturing a surface acoustic wave device.

16. In Paragraph 11, The above composite material mask further includes an embedded reflector pattern symmetrically positioned outward from the IDT electrode with the IDT electrode as the center, and The above sixth step further includes the step of forming a buried reflector using the composite material mask, Method for manufacturing a surface acoustic wave device.

17. In Paragraph 11, The method further comprises the step of forming a dielectric film layer having a frequency temperature coefficient opposite in sign to the piezoelectric layer on the piezoelectric layer and the IDT electrode after the above 7th step. Method for manufacturing a surface acoustic wave device.

Images